NASA's program on icing research and technology

NASA Technical Memorandum 10 1989

I ’

NASA’s Program on Icing

Research and Technology

- (IsASB-TB- 10 lS89) BASA‘s PPCGEALLJ Obl X C I I G N89-2 2569 B E S E A X H A113 TECBbCLCGY ( N A S A . L e w i s fiesearcb C e n t e r ) 5 5 F CSCL 01B U n c l a s G3/01 02043S6 John J. Reinmann, Robert J. Shaw,

and Richard J . Ranaudo

Lewis Research Center

Clevelund, Ohio

Prepared for the

Symposium on Flight in Adverse Environmental Conditions

sponsored by the Flight Mechanics Panel (FMP) of AGARD

Gol, Norway, May 8-12, 1989

NASA's PROGRAM ON I C I N G RESEARCH AND TECHNOLOGY John J . Reinmann, R o b e r t J . Shaw and R i c h a r d J . Ranaudo N a t i o n a l A e r o n a u t i c s and Space A d m i n i s t r a t i o n L e w i s Research C e n t e r C l e v e l a n d , O h i o 44135 U . S . A .

SUMMARY T h i s p a p e r r e v i e w s N A S A ' s p r o g r a m i n a i r c r a f t i c i n g r e s e a r c h and t e c h - n o l o g y . The p r o g r a m r e l i e s h e a v i l y o n computer codes and modern a p p l i e d phys- i c s t e c h n o l o g y i n s e e k i n g i c i n g s o l u t i o n s o n a f i n e r s c a l e t h a n t h o s e o f f e r e d i n e a r l i e r p r o g r a m s . T h r e e m a j o r g o a l s of t h i s p r o g r a m a r e ( 1 ) t o o f f e r new a p p r o a c h e s t o i c e p r o t e c t i o n , (2) t o i m p r o v e o u r a b i l i t y t o model t h e r e s p o n s e o f a n a i r c r a f t t o an i c i n g e n c o u n t e r , and (3) t o p r o v i d e i m p r o v e d t e c h n i q u e s and f a c i l i t i e s f o r g r o u n d and f l i g h t t e s t i n g . T h i s p a p e r r e v i e w s t h e f o l l o w i n g p r o g r a m e l e m e n t s : ( 1 ) new a p p r o a c h e s t o i c e p r o t e c t i o n ; (2) n u m e r i c a l codes for d e i c e r a n a l y s i s ; ( 3 ) measurement and p r e d i c t i o n of i c e a c c r e t i o n and i t s e f f e c t o n a i r c r a f t and a i r c r a f t components; ( 4 ) s p e c i a l w i n d t u n n e l t e s t t e c h - n i q u e s f o r r o t o r c r a f t i c i n g ; ( 5 ) improvements o f i c i n g w i n d t u n n e l s and r e s e a r c h a i r c r a f t ; ( 6 ) g r o u n d d e i c i n g f l u i d s used i n w i n t e r o p e r a t i o n ; ( 7 ) fun- d a m e n t a l s t u d i e s i n i c i n g ; and ( 8 ) d r o p l e t s i z i n g i n s t r u m e n t s f o r i c i n g c l o u d s .

INTRODUCTION The i c i n g p r o b l e m i s r e c e i v i n g more a t t e n t i o n t o d a y t h a n i t has i n a n y o t h e r p e r i o d o f t h e l a s t 2 5 y e a r s . For example, a t t h e NASA L e w i s R e s e a r c h C e n t e r , t e s t i n g a c t i v i t y i n t h e I c i n g R e s e a r c h Tunnel ( I R T ) has i n c r e a s e d s t e a d i l y o v e r t h e p a s t 10 y e a r s , and i n 1988 t h e I R T l o g g e d 1330 h r of t e s t t i m e , w h i c h i s t h e h i g h e s t a n n u a l usage o n r e c o r d s i n c e 1950.

T h e r e a r e many r e a s o n s f o r t h e c u r r e n t i n t e r e s t i n i c i n g : ( 1 ) t h e more e f f i c i e n t , h i g h by-pass r a t i o e n g i n e s of t o d a y and t h e advanced t u r b o p r o p e n g i n e s o f tomorrow have l i m i t e d b l e e d a i r f o r i c e p r o t e c t i o n , so t h e a i r - f r a m e r s a r e s e e k i n g more e f f i c i e n t systems; (2) a i r f o i l d e s i g n e r s d o n o t want t h e i r modern, h i g h - p e r f o r m a n c e s u r f a c e s c o n t a m i n a t e d w i t h i c e , so t h e y a r e i n t e n s i - f y i n g p r e s s u r e t o d e v e l o p i c e p r o t e c t i o n systems t h a t m i n i m i z e r e s i d u a l i c e and t h e r e b y a l l o w t h e a i r f r a m e r t o k e e p a i r f o i l s u r f a c e a r e a t o t h e minimum; (3) new m i l i t a r y a i r c r a f t r e q u i r i n g a l l - w e a t h e r c a p a b i l i t y a r e c u r r e n t l y u n d e r d e v e l o p m e n t ; ( 4 ) some e x i s t i n g m i l i t a r y a i r c r a f t , b e i n g used p r i m a r i l y f o r t r a i n i n g m i s s i o n s , a r e e x p e r i e n c i n g f o r e i g n o b j e c t damage ( F O D ) due t o i c i n g c o n d i t i o n s t h e y w o u l d n o t n o r m a l l y e n c o u n t e r i n combat; ( 5 ) d e s i g n e r s o f h i g h p e r f o r m a n c e m i l i t a r y a i r c r a f t want t o a v o i d b u r d e n i n g t h e a i r c r a f t w i t h i c e p r o t e c t i o n , so t h e y want t o know where and how much i c e w i l l b u i l d o n t h e a i r - c r a f t and w h e t h e r t h e a e r o p e r f o r m a n c e p e n a l t i e s a r e a c c e p t a b l e ; ( 6 ) d e s i g n e r s c o f f u t u r e h i g h p e r f o r m a n c e a i r c r a f t w i t h r e l a x e d s t a t i c s t a b i l i t y need t o know how t h e i r a i r c r a f t w i l l p e r f o r m w i t h c o n t a m i n a t e d a e r o d y n a m i c s u r f a c e s ; ( 7 ) l i t t l e i s known a b o u t t h e e f f e c t s of i c e a c c r e t i o n o n t h e o p e r a t i o n and p e r f o r m a n c e o f advanced t u r b o p r o p s , and w h e t h e r or n o t i c e p r o t e c t i o n w i l l be r e q u i r e d ; and ( 8 ) t h e FAA has c e r t i f i e d o n l y one c i v i l i a n h e l i c o p t e r f o r f l i g h t i n t o f o r e c a s t e d i c i n g , w h i c h i m p l i e s a s t r o n g need f o r s u p p o r t o f h e l i c o p t e r i c i n g .

N A S A ' s i c i n g p r o g r a m was first r e v i e w e d i n 1983 ( R e f . 1 ) . Many e l e m e n t s s t i l l i n p r o g r e s s , and t h e y a r e b r o u g h t up t o d a t e i n of t h e e a r l y p r o g r a m a r e t h i s p a p e r . Some new e l e m e n t s have been added, t h e most n o t a b l e ones b e i n g t h e f o l l o w i n g : i c e p r o t e c t i o n systems based o n e l e c t r o - m e c h a n i c a l i m p u l s e s ; e f f e c t s of g r o u n d d e i c i n g f l u i d s o n w i n g a e r o d y n a m i c p e r f o r m a n c e d u r i n g t a k e o f f ; u p g r a d e s and enhancements t o t h e L E W I C E i c e a c c r e t i o n p r e d i c t i o n code; a p p l i - c a t i o n s of v i s c o u s flow codes t o t h e i c i n g p r o b l e m ; e x p e r i m e n t a l o b s e r v a t i o n s of t h e i c e a c c r e t i o n p r o c e s s ; and s t r u c t u r a l and a d h e s i v e p r o p e r t i e s of i m p a c t i c e .

O t h e r r e v i e w a r t i c l e s have been p u b l i s h e d o n p a r t s o f t h e NASA a i r c r a f t 2 , p u b l i s h e d i n 1984, gave an a c c o u n t o f o u r a i r - i c i n g program. R e f e r e n c e c r a f t i c i n g a n a l y s i s a c t i v i t i e s ( a n a l y t i c a l and e x p e r i m e n t a l ) . S e v e r a l r e v i e w ( R e f s . 3 t o 5 ) were p u b l i s h e d i n 1988. R e f e r e n c e 3 gave an u p d a t e of p a p e r s o u r i c i n g a n a l y s i s a c t i v i t i e s f o r i c e a c c r e t i o n o n u n p r o t e c t e d a i r f o i l s . Ref- e r e n c e 4 r e v i e w e d our a n a l y t i c a l m o d e l i n g , w i n d t u n n e l e x p e r i m e n t s , and f l i g h t o f m o d e l i n g t h e e f f e c t of i c i n g t e s t i n g and showed how t h e y s u p p o r t o u r g o a l o n t h e w h o l e a i r c r a f t . R e f e r e n c e 5 r e v i e w e d t h e n u m e r i c a l codes t h a t model t h e t r a n s i e n t p e r f o r m a n c e o f e l e c t r o t h e r m a l d e i c i n g s y s t e m s .

T h i s p a p e r a t t e m p t s t o p r e s e n t t h e f u l l scope o f N A S A ' s e x t e n s i v e p r o g r a m i n a i r c r a f t i c i n g r e s e a r c h and t e c h n o l o g y . T h r e e m a j o r g o a l s of t h i s p r o g r a m a r e ( 1 ) t o o f f e r new a p p r o a c h e s t o i c e p r o t e c t i o n , ( 2 ) t o i m p r o v e o u r a b i l i t y t o model t h e r e s p o n s e o f an a i r c r a f t t o an i c i n g e n c o u n t e r , and ( 3 ) t o p r o v i d e i m p r o v e d t e c h n i q u e s and f a c i l i t i e s f o r g r o u n d and f l i g h t t e s t i n g .

For s e v e r a l y e a r s , t h e F e d e r a l A v i a t i o n A d m i n i s t r a t i o n ( F A A ) has c o n t r i - b u t e d f i n a n c i a l s u p p o r t t o t h e NASA i c i n g p r o g r a m , e s p e c i a l l y i n t h e a r e a s of i c e a c c r e t i o n m o d e l i n g , c l o u d d r o p l e t i n s t r u m e n t a t i o n e v a l u a t i o n and c a l i b r a - t i o n , and i c i n g s c a l i n g .

ICE PROTECTION SYSTEMS S i n c e t h e m i d 1 9 5 0 ' s , j e t t r a n s p o r t s have k e p t t h e i r c r i t i c a l l i f t i n g s u r - o f i c e b y e m p l o y i n g h o t a i r a n t i - i c i n g f a c e s and e n g i n e i n l e t s c o m p l e t e l y c l e a r s y s t e m s . B u t more r e c e n t l y , as j e t e n g i n e m a n u f a c t u r e r s have begun i n c r e a s i n g e n g i n e b y - p a s s - r a t i o s t o a c h i e v e h i g h e r e f f i c i e n c i e s , t h e e n g i n e c o r e s have become s m a l l e r and t h e amount o f h o t b l e e d a i r a v a i l a b l e f o r a n t i - i c i n g has s h r u n k s i g n i f i c a n t l y ( F i g . 1 ) . To cope w i t h t h i s loss o f b l e e d a i r , a i r f r a m e r s a r e ( 1 ) e l i m i n a t i n g i c e p r o t e c t i o n from s e l e c t e d components, or ( 2 ) d e v e l o p i n g t h e more e n e r g y - e f f i c i e n t d e i c i n g systems t h a t r e q u i r e some b u i l d u p of i c e b e f o r e a c t i v a t i o n . H e l i c o p t e r s , g e n e r a l a v i a t i o n , and l i g h t t r a n s p o r t a i r - c r a f t , a l l w i t h r e l a t i v e l y s m a l l p a y l o a d f r a c t i o n s and low power m a r g i n s , have a l w a y s r e l i e d h e a v i l y o n t h e more e f f i c i e n t d e i c i n g s y s t e m s .

I Always i n demand a r e new i c e p r o t e c t i o n systems t h a t can o f f e r a n y of t h e f o l l o w i n g i m p r o v e m e n t s : l o w e r w e i g h t , l o w e r power c o n s u m p t i o n , more e f f e c t i v e i c e r e m o v a l , more r e l i a b l e o p e r a t i o n , more e a s i l y r e t r o f i t t e d t o e x i s t i n g com- p o n e n t s , s m a l l e r a e r o p e n a l t i e s , lower m a i n t e n a n c e costs or l o w e r m a n u f a c t u r - i n g c o s t s . NASA has s e l e c t i v e l y s u p p o r t e d t h e d e v e l o p m e n t o f i c e p r o t e c t i o n systems, w i t h emphasis o n t h e more e f f i c i e n t d e i c i n g s y s t e m s .

N e x t t o p n e u m a t i c d e i c e r b o o t s , t h e most e f f i c i e n t m e c h a n i c a l d e i c i n g sys- tems a r e t h o s e t h a t employ e l e c t r o - m e c h a n i c a l i m p u l s e s . T y p i c a l l y , t h e power r e q u i r e d f o r e l e c t r o - m e c h a n i c a l d e i c i n g i s a b o u t one p e r c e n t o f t h a t used for e v a p o r a t i v e a n t i - i c i n g . E l e c t r o - m e c h a n i c a l d e i c e r s use a b o u t as much power as t h e a i r c r a f t ' s l a n d i n g l i g h t s .

T h r e e d e i c i n g systems e m p l o y i n g e l e c t r o - m e c h a n i c a l i m p u l s e s have been sup- These a r e ( 1 ) t h e E l e c t r o - E x p u l s i v e S e p a r a t i o n System ( E E S S ) , p o r t e d b y NASA.

( 2 ) E l e c t r o m a g n e t i c I m p u l s e D e i c e r s ( E I D I ) , and (3) Eddy C u r r e n t R e p u l s i o n D e i c e r Boots (ECRDIB). A l l t h r e e o f t h e s e systems a r e e n e r g i z e d b y r a p i d l y d i s c h a r g i n g a c a p a c i t o r t h r o u g h e l e c t r i c a l c o n d u c t o r s whose c u r r e n t s s e t up o p p o s i n g m a g n e t i c f i e l d s t h a t f o r c e t h e c o n d u c t o r s r a p i d l y a p a r t . The s h o r t d i s c h a r g e p u l s e , a f r a c t i o n o f a m i l l i s e c o n d i n d u r a t i o n , i m p a r t s an i m p u l s i v e force t o t h e i c e t h a t s h a t t e r s , debonds, and e x p e l s i t from t h e s u r f a c e . The r e q u i r e d power s u p p l i e s and s w i t c h i n g c i r c u i t r y a r e n e a r l y i d e n t i c a l for t h e t h r e e s y s t e m s .

S y s t e m E l e c t r o - E x p u l s i v e S e p a r a t i o n The EESS s y s t e m was i n v e n t e d and p a t e n t e d b y M r . L . A . H a s l i m of t h e NASA Ames R e s e a r c h C e n t e r , M o f f e t t F i e l d , CA ( U . S . P a t e n t No. 4,690,353; September 1 , 1 9 8 7 ) . Though i t has undergone o n l y l i m i t e d i c i n g t e s t i n g t o d a t e , i t a p p e a r s t o be an e f f e c t i v e d e i c e r . I t seems t o be e s p e c i a l l y e f f e c - t i v e for r e m o v i n g t h i n l a y e r s o f i c e . Thus t h e E E S S can be a c t i v a t e d a f t e r v e r y t h i n l a y e r s o f i c e have b u i l t up, w h i c h s h o u l d m i n i m i z e t h e a e r o p e r f o r - mance p e n a l t i e s caused b y i c e a c c u m u l a t e d between a c t i v a t i o n s or b y r e s i d u a l i c e l e f t a f t e r a c t i v a t i o n . Because i t can be e a s i l y m a n u f a c t u r e d as a t h i n b o o t and e a s i l y r e t r o f i t t e d b y b o n d i n g t o t h e o u t s i d e o f any component, sev- e r a l i t t o b o t h c i v i l i a n and m i l i t a r y companies a r e i n t e r e s t e d i n a p p l y i n g a i r c r a f t .

A s shown i n F i g . 2 t h e EESS c o n d u c t o r s a r e a r r a n g e d as a s e r i e s of U-shaped flows r i b b o n s such t h a t t h e c u r r e n t i n t o one l e g o f t h e U and o u t t h e o t h e r .

When t h e c a p a c i t o r d i s c h a r g e s i n t o t h e r i b b o n , t h e o p p o s i n g c u r r e n t s i n t h e two l e g s c r e a t e o p p o s i n g m a g n e t i c f i e l d s t h a t f o r c e a d j a c e n t r i b b o n s r a p i d l y a p a r t . The c o n d u c t o r s a r e embedded i n t h e e l a s t o m e r i c b o o t as shown i n F i g . 3 .

S l i t s i n t h e d e i c e r b o o t a l l o w t h e r i b b o n c o n d u c t o r s t o move r a p i d l y a p a r t and t h e n t h e y q u i c k l y c o l l a p s e b a c k t o a t h i n l a y e r .

The B . F . G o o d r i c h Company t e s t e d t h e EESS s y s t e m o n b o a r d t h e NASA T w i n O t t e r i c i n g r e s e a r c h a i r c r a f t , and D a t a P r o d u c t s o f N e w E n g l a n d t e s t e d i t i n t h e NASA I R T . and o n t h e T w i n O t t e r .

Through a c o m p e t i t i v e b i d d i n g p r o c e s s , NASA has g r a n t e d 1 i m i t e d p a t e n t R e f e r - r i g h t s f o r t h e EESS t o D a t a P r o d u c t s of N e w E n g l a n d , W a l l i n g f o r d , C T .

ence 6 p r o v i d e s a d i s c u s s i o n o f t h e improvements t h a t D a t a P r o d u c t s of New E n g l a n d i s c u r r e n t l y c a r r y i n g o u t o n t h e E E S S .

D a t a P r o d u c t s o f New E n g l a n d o f f e r s b l a n k e t s from 0.040 t o 0.080 i n . t h i c k , smooth o n b o t h s i d e s , and c a p a b l e of b e i n g f e a t h e r e d i n t o t h e s u r f a c e o n w h i c h t h e y a r e i n s t a l l e d . T h i c k n e s s adds d u r a b i l i t y , b u t r e d u c e s b l a n k e t e f f i c i e n c y and may a f f e c t a i r f l o w . B l a n k e t s w e i g h between 0 . 7 and 1 . 1 l b / f t 2 . Each r e c - t a n g u l a r a r e a o f a p p r o x i m a t e l y 70 i n . 2 maximum i s c o n n e c t e d t o one B l a n k e t F i v e sep- D r i v e r Assembly ( i . e . , a c a p a c i t o r and r e l a t e d s w i t c h i n g c i r c u i t r y ) .

a r a t e b l a n k e t s w e r e p u l s e d f o r a t o t a l o f 50 000 c y c l e s , w i t h g r e a t e r t h a n 10 000 c y c l e s b e i n g t h e h i g h e s t o n one b l a n k e t , w i t h n o d i s c e r n i b l e d e g r a d a t i o n .

E l e c t r o m a g n e t i c I m p u l s e D e i c e r NASA r e c e n t l y c o m p l e t e d a d e v e l o p m e n t p r o g r a m o n t h e E I D I s y s t e m t h a t began i n 1982. R e f e r e n c e 7 i s t h e f i n a l E I D I r e p o r t t h a t summarizes t h e p r o - gram h i s t o r y , t e s t r e s u l t s , t e c h n i c a l a c c o m p l i s h m e n t s , and a n a l y s i s and d e s i g n p r o c e d u r e s f o r t h e i m p l e m e n t a t i o n o f an E I D I s y s t e m .

The p h y s i c a l form o f t h e E I D I method i s shown i n F i g . 4 . F l a t - w o u n d c o i l s made of c o p p e r r i b b o n w i r e a r e p l a c e d j u s t i n s i d e t h e l e a d i n g edge of a w i n g ' s s k i n w i t h a s m a l l gap s e p a r a t i n g s k i n and c o i l . E i t h e r one or two c o i l s a r e p l a c e d a t a g i v e n span w i s e s t a t i o n , d e p e n d i n g on t h e s i z e and shape of t h e l e a d i n g edge. Two methods o f s u p p o r t i n g c o i l s a r e shown: s u p p o r t b y a f r o n t s p a r or from a beam a t t a c h e d t o r i b s i s g e n e r a l l y u s e d , b u t m o u n t i n g t o t h e s k i n i t s e l f i s sometimes u s e d .

Energy i s d i s c h a r g e d from a c a p a c i t o r t h r o u g h t h e E I D I c o i l . The r a p i d d i s c h a r g e c r e a t e s a r a p i d l y f o r m i n g and c o l l a p s i n g e l e c t r o m a g n e t i c f i e l d w h i c h i n d u c e s eddy c u r r e n t s i n t h e m e t a l s k i n . The m a g n e t i c f i e l d s r e s u l t i n g from c u r r e n t flow i n t h e c o i l and s k i n c r e a t e a r e o u l s i v e f o r c e o f s e v e r a l h u n d r e d A s m a l l pounds m a g n i t u d e , b u t a d u r a t i o n o n l y a f r a c t i o n o f a m i l l i s e c o n d .

a m p l i t u d e , h i g h a c c e l e r a t i o n movement o f t h e s k i n a c t s t o s h a t t e r debond and e x p e l t h e i c e . Two or t h r e e such " h i t s " a r e p e r f o r m e d s e q u e n t i a l y, s e p a r a t e d b y t h e t i m e r e q u i r e d t o r e c h a r g e t h e c a p a c i t o r s , t h e n i c e i s perm t t e d t o accu- m u l a t e u n t i l i t a g a i n a p p r o a c h e s an u n d e s i r a b l e t h i c k n e s s .

D e i c i n g has been s u c c e s s f u l l y a c c o m p l i s h e d i n t h e i c i n g w i n d u n n e l and i n f l i g h t f o r - t y p i n a c e l l e s c a l g e n e r a l a v i a t j o n and. t r a n s p o r t w i n g s and i n l e t u n d e r a w i d e r a nge o f v e l o c i t i e s , a n g l e s o f a t t a c k , i c i n g r a t e s and tempera- t u r e s . T e s t i n g c o n s i s t e d o f e l e v e n s e t s o f i c i n g t u n n e l t e s t s and two f l i g h t t e s t p r o g r a m s . F a t i g u e t e s t s w e r e c o n d u c t e d f o r t h e w i n g s k i n and t h e E I D I components. T e s t s o n e l e c t r o m a g n e t i c i n t e r f e r e n c e ( E M I ) w i t h o t h e r a i r c r a f t s y s t e m s was a l s o c o n d u c t e d . B o t h f a t i g u e l i f e and EM1 e m i s s i o n s can be made a c c e p t a b l e .

E I D I ' s m a j o r a d v a n t a g e i s t h a t i t does n o t a l t e r t h e e x t e r n a l s u r f a c e s of t h e a i r c r a f t , and t h e r e f o r e does n o t impose an a e r o d y n a m i c p e r f o r m a n c e p e n a l t y .

I t s l i m i t a t i o n i s t h a t i t does n o t a d a p t r e a d i l y t o r e t r o f i t t i n g , s i n c e i n most cases i t m u s t be c o n s i d e r e d a p a r t o f t h e o r i g i n a l d e s i g n of t h e compo- n e n t . The f u n d a m e n t a l t e c h n o l o g y f o r E I D I i s now e s t a b l i s h e d , and i t i s up t o t h e v a r i o u s a i r f r a m e r s and e n g i n e n a c e l l e f a b r i c a t o r s t o a d o p t i t . Those who have worked o n t h e E I D I p r o g r a m a r e c o n v i n c e d t h a t i t i s j u s t a m a t t e r of t i m e u n t i l i t makes i t s way o n t o a n e x t g e n e r a t i o n a i r c r a f t .

Eddy C u r r e n t R e p u l s i o n D e i c i n g Boot The E C R D I B c o n t a i n s e l e c t r i c a l c o n d u c t o r s i n an e l a s t o m e r i c b o o t t h a t i s bonded t o t h e l e a d i n g edge o f a w i n g . When a c a p a c i t o r i s d i s c h a r g e d t h r o u g h t h e c o n d u c t o r s , eddy c u r r e n t s a r e i n d u c e d i n t h e s k i n o f t h e w i n g , j u s t as i n E I D I . O p p o s i n g m a g n e t i c f i e l d s r e p e l t h e b o o t r a p i d l y away from t h e w i n g . W e say t h a t E C R D I B i s E I D I a p p l i e d o n t h e o u t s i d e r a t h e r t h a n t h e i n s i d e of t h e w i n g . ( E C R D I B d i f f e r s from EESP i n t h a t EESP does n o t i n d u c e eddy c u r r e n t s . ) NASA has a s m a l l c o n t r a c t w i t h E l e c t r o i m p a c t , I n c . , S e a t t l e , WA, t o f a b r i c a t e s e v e r a l E C R D I B u n i t s and t e s t them o n a l a r g e - c h o r d and a s m a l l - c h o r d w i n g sec t i o n i n t h e NASA I R T .

The E C R D I B c o n d u c t o r s w i l l be f a b r i c a t e d from s t a c k s o f t h i n , f l e x i b l e c i r c u i t b o a r d s , w i t h a c o i l c o n d u c t o r p a t t e r n t h a t a l l o w s c u r r e n t t o e n t e r and e x i t t h e edge, r a t h e r t h a n t h e c e n t e r , o f t h e c i r c u i t b o a r d . A s h e e t o f e l a s - t o m e r i c m a t e r i a l w i l l c o v e r t h e c i r c u i t b o a r d s t o form t h e b o o t . The i n v e n t o r (Ref. 8 ) has c a l c u l a t e d t h a t f o r t h e same p u l s e o f e n e r g y , t h e E C R D I B s h o u l d d e i c e a b o u t two t o f o u r t i m e s t h e a r e a an EESS w o u l d d e i c e .

The EESS and t h e ECRDIB systems a r e embedded i n e l a s t o m e r i c b o o t s t h a t a r e a p p l i e d o v e r t h e o u t s i d e o f t h e a i r f o i l . A s w i t h t h e p n e u m a t i c b o o t , t h e s e e l a s t o m e r i c o u t e r s u r f a c e s w i l l t e n d t o g e t p u l l e d away from t h e a i r f o i l s k i n i n t h e r e g i o n o f n e g a t i v e p r e s s u r e s or s u c t i o n p r e s s u r e s , i . e . , o n t h e u p p e r l e a d i n g edge o f t h e a i r f o i l . T h i s w o u l d cause u p p e r s u r f a c e d i s t o r t i o n and an a t t e n d a n t a e r o d y n a m i c p e r f o r m a n c e p e n a l t y . D e s i g n e r s o f p n e u m a t i c b o o t s p u l l a vacuum o n t h e i n s i d e o f t h e b o o t t o p r e v e n t t h e b o o t from s t a y i n g i n f l a t e d a f t e r t h e b o o t s a r e a c t i v a t e d . P u l l i n g a vacuum o n an E E S S or E C R D I B seems i m p r a c t i c a l , and some o t h e r means must be f o u n d t o overcome t h i s p r o b l e m .

D a t a P r o d u c t s a p p e a r s t o have s o l v e d t h i s p r o b l e m f o r E E S S .

The o t h e r i s s u e w i t h e l a s t o m e r i c m a t e r i a l s i s t h e i r a b i l i t y t o w i t h s t a n d r a i n and sand e r o s i o n . E r o s i o n w o u l d be most s e r i o u s n e a r t h e o u t b o a r d sec- t i o n s o f h e l i c o p t e r r o t o r s . Perhaps an a c c e p t a b l e s o l u t i o n f o r rotors w o u l d be a h y b r i d s y s t e m c o n s i s t i n g o f EESS o n t h e i n b o a r d s e c t i o n s and e l e c t r o t h e r - mal o n t h e o u t b o a r d s e c t i o n s .

PREDICTIONS OF AIRFOIL AERODYNAMIC PERFORMANCE DEGRADATION DUE TO I C I N G A m a j o r g o a l of t h e NASA a i r c r a f t i c i n g p r o g r a m i s t o d e v e l o p and e x p e r - i m e n t a l l y v a l i d a t e a g r o u p c o m p u t e r codes t h a t w i l l p r e d i c t t h e d e t a i l s of an a i r c r a f t i c i n g e n c o u n t e r . The f l o w c h a r t i n F i g . 5 shows t h e many codes r e q u i r e d t o form such an o v e r a l l i c i n g a n a l y s i s m e t h o d o l o g y and i n d i c a t e s t h e codes c u r r e n t l y u n d e r d e v e l o p m e n t b y N A S A . Once v a l i d a t e d , t h e s e codes can be used for ( 1 ) p r e l i m i n a r y d e s i g n s t u d i e s t o a s c e r t a i n component s e n s i t i v i t y t o i c i n g , ( 2 ) p e r f o r m a n c e p r e d i c t i o n s o f p r o p o s e d i c e p r o t e c t i o n s y s t e m s , ( 3 ) computer-based c e r t i f i c a t i o n or q u a l i f i c a t i o n s t u d i e s t o r e d u c e t h e amount of r e q u i r e d i c i n g f l i g h t t e s t i n g , and ( 4 ) more r e a l i s t i c i c i n g e f f e c t s i n p u t s for use i n f l i g h t t r a i n i n g s i m u l a t o r s .

T h i s s e c t i o n w i l l r e v i e w t h e p r o g r e s s o n one g o a l o f t h e o v e r a l l a c t i v i t y , namely, t o p r o d u c e codes t h a t p r e d i c t t h e i c e b u i l d u p o n an u n p r o t e c t e d a i r f o i l and t h e r e s u l t i n g a e r o d y n a m i c d e g r a d a t i o n . NASA has g i v e n t h e name LEWICE t o i t s o v e r a l l i c e a c c r e t i o n code. ( T h i s s e c t i o n i s a c o n d e n s a t i o n o f t h e mate- r i a l i n Ref. 3 and a l s o i n c l u d e s some more r e c e n t m a t e r i a l ) .

F i g u r e 6 i 1 1 u s t r a t e s t h e aerodynami c p e r f o r m a n c e p e n a l t i e s caused b y l e a d - i n g edge i c e : ( 1 ) i n c r e a s e d d r a g e v e n a t low a n g l e s - o f - a t t a c k ; ( 2 ) a i r f o i l d e c a m b e r i n g due t o a t h i c k e n e d u p p e r s u r f a c e b o u n d a r y l a y e r ; and ( 3 ) r e d u c e d Clmax and p r e m a t u r e s t a l l due t o s e p a r a t i o n o f t h e a i r f o i l u p p e r s u r f a c e bound- a r y l a y e r .

O v e r a l l A p p r o a c h F i g u r e 7 shows t h e k e y p h y s i c a l p r o c e s s e s t h a t m u s t be a d e q u a t e l y modeled i n a n y a i r f o i l i c i n g a n a l y s i s m e t h o d o l o g y . I n t h e LEWICE a p p r o a c h , i c e i s grown l a y e r b y l a y e r , where e a c h l a y e r r e p r e s e n t s t h e i c e a c c r e t i o n f o r o n e u s e r - s p e c i f i e d t i m e i n c r e m e n t . The o v e r a l l a p p r o a c h f o r LEWICE i s as f o l l o w s : ( 1 ) a p o t e n t i a l flow code c a l c u l a t e s t h e flow f i e l d a r o u n d t h e a i r f o i l ; ( 2 ) a d r o p l e t t r a j e c t o r y c o d e , u s i n g t h e i n v i s c i d flow v e l o c i t i e s , computes t h e l o c a l w a t e r f l u x a r o u n d t h e a i r f o i l ; and ( 3 ) an i c e a c c r e t i o n code, u s i n g t h e l o c a l w a t e r f l u x e s and i n v i s c i d v e l o c i t i e s , c a l c u l a t e s t h e l o c a l i c e g r o w t h a r o u n d t h e a i r f o i l . A t t h i s p o i n t t h e code can l o o p b a c k and r e - r u n t h e p o t e n t i a l f l o w a n a l y s i s t o d e t e r m i n e t h e new i n v i s c i d flow f i e l d a r o u n d t h e i c e d a i r - f o i l . Then a new d r o p l e t t r a j e c t o r y c a l c u l a t i o n and a new i c e a c c r e t i o n c a l c u - l a t i o n can be c o m p l e t e d f o r t h e second t i m e s t e p , and so o n . The l o o p i n g p r o c e s s i s r e p e a t e d f o r as many t i m e i n c r e m e n t s as r e q u i r e d t o r e a c h t h e o v e r - a l l i c i n g e n c o u n t e r t i m e . I f a e r o d y n a m i c p e r f o r m a n c e l o s s e s a r e r e q u i r e d for t h e i c e d a i r f o i l , t h e n a v i s c o u s f l o w f i e l d c a l c u l a t i o n i s p e r f o r m e d f o r t h e p r e d i c t e d i c e shape.

I t i s h i g h l y d e s i r a b l e t o r e p l a c e t h e s e p a r a t e i n v i s c i d and v i s c o u s flow c a l c u l a t i o n s w i t h a s i n g l e v i s c o u s f l o w c a l c u l a t i o n . However, we have n o t y e t made t h e r e p l a c e m e n t because a v i s c o u s flow c a l c u l a t i o n r e q u i r e s f a r more com- p u t e r t i m e t h a n does an i n v i s c i d c a l c u l a t i o n , so t h e t o t a l CPU t i m e t o c a l c u - l a t e an i c e shape w o u l d be i m p r a c t i c a l f o r r o u t i n e c a l c u l a t i o n s . O b v i o u s l y as t h e i c e shape grows and d o m i n a t e s t h e a i r f o i l l e a d i n g edge f l o w f i e l d , v i s c o u s e f f e c t s ( b o u n d a r y l a y e r s e p a r a t i o n and r e a t t a c h m e n t ) w i l l become so i m p o r t a n t t h a t t h e s i m p l i f i e d i n v i s c i d a n a l y s i s w i l l n o l o n g e r be a p p r o p r i a t e .

The f o l l o w i n g s e c t i o n s w i l l look a t t h e modules i n more d e t a i l .

I n v i s c i d F l o w f i e l d / D r o p l e t T r a j e c t o r i e s The i n v i s c i d f l o w f i e l d code i s a second o r d e r p a n e l c o d e . D r o p l e t t r a j e c - t o r i e s a r e o b t a i n e d b y i n t e g r a t i n g N e w t o n ' s second l a w o f m o t i o n u s i n g a p r e d i c t o r - c o r r e c t o r scheme o p t i m i z e d for s t i f f systems of e q u a t i o n s .

An e x p e r i m e n t a l d r o p l e t i m p i n g e m e n t d a t a base i s b e i n g o b t a i n e d f o r u s e i n v a l i d a t i n g t h e d r o p l e t t r a j e c t o r y p r e d i c t i o n codes ( R e f . 3 ) . Comparisons between a n a l y s i s and e x p e r i m e n t a r e shown i n F i g . 8. The c o m p a r i s o n s show t h a t t h e p r e d i c t i o n , when u s i n g e i t h e r i n v i s c i d or v i s c o u s f l o w f i e l d v e l o c i - t i e s , i s q u i t e a c c u r a t e f o r cases o f s m a l l i c e a c c r e t i o n , b u t n o t as a c c u r a t e for l a r g e i c e a c c r e t i o n s t h a t have m a s s i v e f l o w s e p a r a t i o n w i t h u n s t e a d y flow.

F i g u r e 8 shows t h a t w h i l e t h e p r e d i c t e d c o l l e c t i o n e f f i c i e n c i e s were lower when t h e v i s c o u s f l o w v e l o c i t i e s were u s e d i n t h e t r a j e c t o r y c a l c u l a t i o n s , t h e y were n o t as low as t h o s e o b s e r v e d i n t h e e x p e r i m e n t . S i n c e t h e N a v i e r - S t o k e s codes o v e r p r e d i c t s t h e v e l o c i t i e s n e a r t h e s e p a r a t i o n p o i n t s , t h e n e x t l o g i c a l s t e p seems t o be t o r e p l a c e t h e a c t u a l model g e o m e t r y w i t h a g e o m e t r y t h a t f o l - T h i s lows t h e o u t e r b o u n d a r y o f t h e s e p a r a t e d flow r e g i o n b e h i n d t h e h o r n s .

g e o m e t r y s h o u l d n o t p r o d u c e t h e h i g h e r v e l o c i t i e s n e a r t h e b e g i n n i n g of s e p a r a - t i o n , and s h o u l d b e g i n t u r n i n g t h e f l o w f u r t h e r u p s t r e a m , t h e r e b y r e d u c i n g t h e d r o p l e t c o l l e c t i o n e f f i c i e n c y . W e p l a n t o t r y t h i s i n t h e n e a r f u t u r e .

I c e A c c r e t i o n The i c e shape module p r e d i c t s i c e shapes b y s o l v i n g t h e c o n t i n u i t y and c o n t r o l volumes o n t h e s u r f a c e o f t h e a i r - e n e r g y e q u a t i o n s f o r d i f f e r e n t i a l f o i l as d e p i c t e d i n F i g . 9 . The code d e t e r m i n e s t h e f r a c t i o n o f i n c o m i n g w a t e r t h a t f r e e z e s i n e a c h c o n t r o l volume. Any w a t e r t h a t does n o t f r e e z e i n a con- t r o l volume i s assumed t o flow b a c k t o t h e i m m e d i a t e l y a f t c o n t r o l volume.

F i g u r e 10 shows r e p r e s e n t a t i v e c o m p a r i s o n s o f p r e d i c t e d shapes v e r s u s a c t u a l i c e shapes grown o n a NACA 0012 a i r f o i l i n t h e NASA I R T . The agreement i n p r e d i c t e d v e r s u s measured i c e shape f o r b o t h t h e r i m e and g l a z e i c e was j u d g e d t o be a c c e p t a b l e . T y p i c a l l y , LEWICE p r e d i c t s r i m e i c e shapes v e r y w e l l , b u t i t can have d i f f i c u l t y w i t h g l a z e i c e p r e d i c t i o n s . O t h e r c o m p a r i s o n s w i t h i n - f l i g h t i c i n g a r e g i v e n i n R e f . 9 .

The dependence o f a i r f o i l d r a g o n i c e f o r m a t i o n t e m p e r a t u r e i s shown i n F i g . 1 1 ( R e f . 10). Notice t h a t a t t h e warmer t e m p e r a t u r e s t h e d r a g i s e x t r e m e l y s e n s i t i v e t o i c e f o r m a t i o n t e m p e r a t u r e . Also n o t e t h a t t h e mass of a c c r e t e d i c e s t a y s r e l a t i v e l y c o n s t a n t u n t i l t h e t e m p e r a t u r e a p p r o a c h e s t h e f r e e z i n g p o i n t o f w a t e r , and t h e n t h e mass d r o p s o f f , p r e s u m a b l y because t h e r u n b a c k w a t e r b l o w s o f f t h e a i r f o i l . The c u r r e n t NASA i c e a c c r e t i o n module does n o t a c c o u n t f o r w a t e r b l o w o f f .

A key p a r t o f t h e i c e a c c r e t i o n module i s t h e method used t o p r e d i c t h e a t and mass t r a n s f e r c o n v e c t i o n c o e f f i c i e n t s . The c o n v e c t i o n c o e f f i c i e n t s a r e c a l c u l a t e d b y t h e i n t e g r a l b o u n d a r y l a y e r method ( R e f . 3 ) . The a b i l i t y t o model s u r f a c e r o u g h n e s s as an e q u i v a l e n t sand g r a i n r o u g h n e s s i s a n i m p o r t a n t f e a t u r e o f t h e i n t e g r a l b o u n d a r y l a y e r method. The p r e d i c t i o n s were compared w i t h r e s u l t s from a h e a t t r a n s f e r e x p e r i m e n t i n w h i c h i c e shapes grown o n a c y l i n d e r i n t h e I R T were r e p l i c a t e d i n a wood model t h a t was i n s t r u m e n t e d w i t h s u r f a c e h e a t f l u x gauges ( R e f . 1 1 ) . The p r e d i c t e d h e a t t r a n s f e r c o e f f i c i e n t s shown i n F i g . 12 d o n o t a g r e e f a v o r a b l y w i t h t h e e x p e r i m e n t a l d a t a .

F i g u r e 13 compares t h e e x p e r i m e n t a l d a t a w i t h p r e d i c t i o n s made w i t h a N a v i e r - S t o k e s code t h a t s o l v e s t h e e n e r g y e q u a t i o n and u s e s a d i s t r i b u t e d r o u g h n e s s model ( R e f . 1 2 ) . The agreement between a n a l y s i s and e x p e r i m e n t i s good.

i c i n g p r o c e s s modeled i n LEWICE follows c l o s e l y t h e model g i v e n b y The M e s s i n g e r ( R e f . 1 3 ) . The M e s s i n g e r m o d e l , as d e p i c t e d b y O l s e n ( R e f . 1 4 ) , i s shown i n F i g . 1 4 . O l s e n took c l o s e u p m o v i e s o f t h e a c t u a l i c e a c c r e t i o n i n t h e I R T , and h i s o b s e r - p r o c e s s u n d e r a v a r i e t y o f i c e f o r m a t i o n c o n d i t i o n s v a t i o n s l e a d h i m t o propose t h e new model shown i n F i g . 1 5 . I n t h i s m o d e l , w a t e r flows a l o n g t h e s u r f a c e o n l y d u r i n g t h e i n i t i a l moments o f e x p o s u r e t o t h e i c i n g c l o u d . A f t e r t h a t , t h e w a t e r b e g i n s t o form beads o n t h e s u r f a c e as shown i n F i g . 1 6 . I c e forms i n t h e base o f t h e beads and i m p i n g i n g w a t e r accu- m u l a t e s a t t h e t o p o f t h e beads.

Hansman ( R e f s . 15 and 1 6 ) l a t e r f o l l o w e d up o n O l s e n ' s work and b a s i c a l l y c o n f i r m e d O l s e n ' s o b s e r v a t i o n s . Hansman o b s e r v e d s e v e r a l d i s t i n c t zones of s u r - f a c e w a t e r b e h a v i o r : a smooth w e t zone i n t h e s t a g n a t i o n r e g i o n w i t h a u n i f o r m w a t e r f i l m ; a r o u g h zone where s u r f a c e t e n s i o n e f f e c t s caused c o a l e s c e n c e of s u r f a c e w a t e r i n t o s t a t i o n a r y beads; a h o r n zone where r o u g h n e s s e l e m e n t s grew i n t o h o r n shapes; a r u n b a c k zone where s u r f a c e w a t e r r a n b a c k as r i v u l e t s ; and a d r y zone where r i m e f e a t h e r s f o r m e d . The l o c a t i o n o f t h e t r a n s i t i o n from t h e smooth t o t h e r o u g h zone was f o u n d t o m i g r a t e w i t h t i m e t o w a r d s t h e s t a g n a - t i o n p o i n t . The b e h a v i o r o f t h e t r a n s i t i o n a p p e a r e d t o be c o n t r o l l e d b y bound- a r y l a y e r t r a n s i t i o n and bead f o r m a t i o n mechanisms a t t h e i n t e r f a c e b e t w e e n t h e smooth and r o u g h z o n e s . R e g i o n s o f wet i c e g r o w t h and enhanced h e a t t r a n s f e r were c l e a r l y o b s e r v e d w i t h i n f r a r e d v i d e o r e c o r d i n g s o f g l a z e i c e s u r f a c e s .

Hansman f o r m u l a t e d a t h r e e zone model and t e s t e d i t b y f o r c i n g t h e LEWICE i c e a c c r e t i o n module t o have t h r e e z o n e s . A zone n e a r t h e s t a g n a t i o n r e g i o n was modeled b y t h e o r i g i n a l c o n t r o l volume a p p r o a c h . A second zone was modeled as f r e e z i n g a l l t h e w a t e r t h a t i m p i n g e d o n i t . A t h i r d zone was modeled a s a t r a n s i t i o n zone s e p a r a t i n g t h e o t h e r two zones. I n t h e t r a n s i t i o n zone t h e c o n t r o l volumes had f r e e z i n g f r a c t i o n s t h a t v a r i e d l i n e a r l y from t h e v a l u e a t t h e edge o f t h e f i r s t zone t o a v a l u e o f u n i t y a t t h e edge o f t h e second z o n e .

F i g u r e 17 shows how an e x p e r i m e n t a l i c e shape f o r m e d o n a c y l i n d e r compared w i t h t h e p r e d i c t i o n s made b y t h e u n m o d i f i e d a p p r o a c h and b y t h e Hansman a p p r o a c h .

Hansman's model gave r e s u l t s f a r s u p e r i o r t o t h e u n m o d i f i e d a p p r o a c h .

Because t h i s new m u l t i - z o n e model h o l d s p r o m i s e o f b e i n g more r e p r e s e n t a - t i v e , NASA w i l l c o n t i n u e t o c o n d u c t f u n d a m e n t a l e x p e r i m e n t s o n t h e d e t a i l s of t h e i c e a c c r e t i o n p r o c e s s , such a s , c l o s e u p m o v i e s i n n a t u r a l i c i n g c l o u d s and i n f r a r e d s t u d i e s o f t h e s u r f a c e o f t h e i c e ( R e f . 1 6 ) Aerodynamic Performance A s n o t e d e a r l i e r , i t i s h i g h l y d e s i r a b l e t o r e p l a c e t h e p o t e n t i a l f l o w code i n LEWICE w i t h a v i s c o u s flow code t h a t more a c c u r a t e l y m o d e l s t h e flow- f i e l d and a l s o a l l o w s a d i r e c t c a l c u l a t i o n o f l i f t , d r a g , and p i t c h i n g moment.

To t h i s end, NASA i s d e v e l o p i n g two v i s c o u s f l o w c o d e s : ( 1 ) a R e y n o l d s a v e r - aged t h i n l a y e r N a v i e r - S t o k e s code (ARC2D) ( R e f . 1 7 ) , and ( 2 ) an i n t e r a c t i v e b o u n d a r y l a y e r code ( I B L ) ( R e f . 1 8 ) . B o t h o f t h e s e codes were d e s i g n e d t o han- d l e c l e a n a i r f o i l s and a r e b e i n g e x t e n d e d t o h a n d l e i c e d a i r f o i l s f o r w h i c h flow s e p a r a t i o n and r e a t t a c h m e n t a t l o w e r a n g l e s - o f - a t t a c k i s n o t uncommon.

The I B L code i s a t t r a c t i v e f o r i n c l u s i o n i n LEWICE because i t u t i l i z e s a p o t e n - t i a l flow code w h i c h r e q u i r e s f a r l e s s c o m p u t e r power t h a n t h e N a v i e r - S t o k e s code.

A c o m p r e h e n s i v e e x p e r i m e n t a l d a t a base f o r v a l i d a t i n g t h e v i s c o u s flow codes i s b e i n g d e v e l o p e d as F i g . 18 i l l u s t r a t e s . A NACA 0012 a i r f o i l model was m o d i f i e d t o have a l e a d i n g edge i c e shape t h a t had t h e g r o s s c r o s s s e c t i o n a l f e a t u r e s o f an i c e shape grown i n t h e I R T , b u t a l s o had a g e o m e t r y t h a t c o u l d be a c c u r a t e l y d i g i t i z e d t o a l l o w i n p u t t i n g t o flow a n a l y s i s c o d e s .

F i g u r e 19 compares t h e p r e d i c t i o n s - ' o f t h e ARC2D and I B L codes w i t h t h e e x p e r i m e n t a l d a t a base d e s c r i b e d b y F i g . 18. A t l o w e r a n g l e s - o f - a t t a c k , b o t h codes compared w e l l w i t h e x p e r i m e n t . A t t h e h i g h e r a n g l e s - o f - a t t a c k t h e IBL code u n d e r p r e d i c t e d t h e measured d r a g l e v e l s . A t t h e s e h i g h e r a n g l e s t h e ARC2D code p r e d i c t e d u n s t e a d y f l o w . A l t h o u g h t h e I B L code a p p e a r e d i n a d e q u a t e a t t h e h i g h a l p h a s f o r t h i s c a s e , Cebeci ( R e f . 1 9 ) showed t h a t t h e I B L code can do a good j o b o n c l e a n a i r f o i l s beyond s t a l l .

NASA i s s u p p o r t i n g g r i d d e f i n i t i o n s t u d i e s ( R e f . 4 ) and a l s o d e v e l o p i n g an a d a p t i v e g r i d g e n e r a t i o n code t h a t s h o u l d p r o v e u s e f u l f o r g e n e r a t i n g a new g r i d f o r each new t i m e s t e p i n t h e LEWICE i c e a c c r e t i o n c a l c u l a t i o n . A n o t h e r s u p p o r t i n g e f f o r t f o r t h e ARC2D code i s t h e t e s t i n g o f v a r i o u s t u r b u l e n c e models such as t h e Baldwin-Lomax model and t h e J o h n s o n - K i n g m o d e l , as w e l l as a model d e v e l o p e d i n - h o u s e ( R e f . 20).

Work i s c o n t i n u i n g o n i m p r o v i n g t h e t w o - d i m e n s i o n a l v i s c o u s flow codes and o n c o n d u c t i n g e x p e r i m e n t s to v a l i d a t e them. The n e x t s t e p i s t o b e g i n work o n t h r e e - d i m e n s i o n a l codes f o r a p p l i c a t i o n t o modern s w e p t - w i n g a i r c r a f t . To t h i s end, NASA i s c o n d u c t i n g w i n d t u n n e l t e s t i n g a t t h e O h i o S t a t e U n i v e r s i t y ( R e f . 21) o n t h r e e - d i m e n s i o n a l r e c t a n g u l a r and swept semi-span w i n g s w i t h and w i t h o u t a t t a c h e d i c e shapes. A d a t a base s i m i l a r t o t h e t w o - d i m e n s i o n a l d a t a base ( s e e F i g . 18) w i l l be a c q u i r e d . NASA i s a l s o s u p p o r t i n g d e v e l o p m e n t of a t h r e e d i m e n s i o n a l N a v i e r - S t o k e s code ( R e f . 22) t h a t w i l l be v a l i d a t e d a g a i n s t t h e e x p e r i m e n t a l d a t a .

A l t h o u g h a g r e a t d e a l o f r e s e a r c h s t i l l needs t o be done o n i c e a c c r e t i o n m o d e l i n g and a e r o p e r f o r m a n c e p e n a l t i e s , t h e codes p r e s e n t e d i n t h i s s e c t i o n a r e r e p r e s e n t a t i v e o f t h e b e s t a v a i l a b l e a t t h i s t i m e . Many o r g a n i z a t i o n s i n t h e U . S . A . a r e u s i n g t h e s e codes as r e s e a r c h codes and a r e r e l a y i n g t h e i r e x p e r i e n c e s w i t h them t o NASA and i t s g r a n t e e s and c o n t r a c t o r s .

AIRPLANE PERFORMANCE AND S T A B I L I T Y AND CONTROL CHANGES DUE TO I C I N G S i n c e i c e w i l l a c c u m u l a t e o n s e l e c t e d s u r f a c e s of modern a i r c r a f t , and s i n c e f a i l u r e o f any i c e p r o t e c t i o n s y s t e m w i l l r e s u l t i n i c e a c c u m u l a t i o n s , NASA has a m a j o r p r o g r a m e l e m e n t t o s t u d y t h e e f f e c t s o f i c i n g o n a i r c r a f t p e r - formance and s t a b i 1 i t y and c o n t r o l . The a p p r o a c h employs t h r e e i n t e r r e l a t e d e l e m e n t s : a n a l y s i s , w i n d t u n n e l e x p e r i m e n t s , and c o n s i d e r a b l e f l i g h t t e s t i n g i n n a t u r a l i c i n g c l o u d s .

I n t h e p r e v i o u s s e c t i o n , we r e v i e w e d NASA's r e s e a r c h o n t h e e f f e c t s of i c i n g o n a i r f o i l a e r o d y n a m i c s . I n t h i s s e c t i o n we w i l l c o n c e n t r a t e o n f l i g h t t e s t i n g i n n a t u r a l i c i n g c l o u d s .

Research A i r c r a f t The NASA L e w i s i c i n g r e s e a r c h a i r c r a f t shown i n F i g . 20 i s a m o d i f i e d D e H a v i l l a n d DH-6 T w i n O t t e r ( R e f s . 23 t o 2 5 ) . The a i r c r a f t i s e q u i p p e d w i t h e l e c t r o t h e r m a l a n t i - i c e r s o n t h e p r o p e l l e r s , e n g i n e i n l e t s , and w i n d s h i e l d .

P n e u m a t i c d e i c e r b o o t s a r e l o c a t e d o n t h e w i n g o u t b o a r d o f t h e e n g i n e n a c e l l e s , o n b o t h t h e h o r i z o n t a l and v e r t i c a l s t a b i l i z e r s , o n t h e w i n g s t r u t s , and o n t h e r e a r l a n d i n g g e a r s t r u t s . The p n e u m a t i c d e i c e r s l o c a t e d o n t h e v e r t i c a l s t a b i l i z e r , w i n g s t r u t s , and l a n d i n g g e a r s t r u t s a r e n o n s t a n d a r d i t e m s t h a t p r o v i d e a d d i t i o n a l r e s e a r c h c a p a b i l i t y for m e a s u r i n g component d r a g t h r o u g h s e l e c t i v e d e i c i n g . The a i r c r a f t i s e q u i p p e d w i t h s e v e r a l s t a n d a r d i n s t r u m e n t s for m e a s u r i n g i c i n g c l o u d p r o p e r t i e s ( R e f . 2 6 ) .

Wing l e a d i n g edge i c e shapes a r e measured i n f l i g h t w i t h a s t e r e o p h o t o g - r a p h y s y s t e m . Wing s e c t i o n d r a g i s measured w i t h a wake s u r v e y p r o b e mounted o n t h e w i n g b e h i n d t h e r e g i o n where t h e s t e r e o p h o t o s a r e t a k e n . A noseboom i s u s e d t o measure a i r s p e e d , a n g l e - o f - a t t a c k , and s i d e s l i p .

A c o m p l e t e f l i g h t t e s t s y s t e m i s b e i n g b u i l t up t o measure f l i g h t d y n a m i c s a l o n g a f l i g h t p a t h . The s y s t e m w i l l i n c l u d e a d a t a a c q u i s i t i o n s y s t e m and an i n e r t i a l package t h a t c o n t a i n s r a t e g y r o s , d i r e c t i o n a l g y r o s , and s e r v o a c c e l e r o m e t e r s .

Wing I c e Shapes and D r a g One p u r p o s e o f t h e i c i n g f l i g h t r e s e a r c h p r o g r a m i s t o o b t a i n i n f l i g h t d a t a t h a t can be used t o v a l i d a t e c o m p u t e r codes and t o c o n f i r m t h a t t h e NASA L e w i s I c i n g Research Tunnel a d e q u a t e l y s i m u l a t e s n a t u r a l i c i n g . W e have f l o w n numerous f l i g h t s t h r o u g h n a t u r a l i c i n g c l o u d s , i n w h i c h i c e was a l l o w e d t o b u i l d up o n t h e w i n g l e a d i n g edge. The a i r c r a f t was t h e n f l o w n o u t of t h e c l o u d i n t o c l e a r a i r , where stereo p h o t o g r a p h s were t a k e n o f t h e i c e shape and a d r a g wake s u r v e y p r o b e was moved a c r o s s t h e t r a i l i n g edge o f t h e w i n g b e h i n d t h e i c e shape ( R e f . 2 4 ) . F i g u r e 21 shows t h e i c e shape d e r i v e d from t h e s t e r e o p h o t o s and F i g . 22 shows t h e i n c r e a s e i n d r a g v e r s u s a n g l e - o - a t t a c k .

L a t e r t h i s y e a r , a s e c t i o n o f a T w i n O t t e r w i n g w i l l be mounted i n t h e I R T ( F i g . 2 3 ) , and i c e shape and d r a g w i l l be measured u n d e r t h e same c o n d i t i o n s as i n f l i g h t so t h a t a d i r e c t c o m p a r i s o n can be made between fl g h t and t h e I R T .

A i r c r a f t P e r f o r m a n c e l i f t and i n c r e a s - A i r f r a m e i c i n g d e g r a d e s a i r c r a f t p e r f o r m a n c e b y r e d u c i n g i n g d r a g . T h i s r e s u l t s i n h i g h e r s t a l l speeds, lower a n g l e s - o f - a t t a c k for s t a l l , l o w e r c l i m b , lower c r u i s e , and l o w e r power m a r g i n s f o r e n g i n e o u t p e r - formance. These p e r f o r m a n c e d e g r a d a t i o n s were measured o n t h e i c i n g r e s e a r c h a i r c r a f t f o r a w i d e r a n g e of i c i n g c o n d i t i o n s . By d e i c i n g one a i r f r a m e compo- n e n t a t a t i m e and t a k i n g a s e t o f p e r f o r m a n c e measurements a f t e r each d e i c i n g e v e n t , we o b t a i n e d l i f t loss o n t h e w i n g and r e l a t i v e v a l u e s o f d r a g i n c r e a s e for e a c h a i r f r a m e component. For some cases power r e q u i r e d v e r s u s power a v a i l - a b l e was measured t o a s s e s s t h e e f f e c t s o n e n g i n e - o u t p e r f o r m a n c e ( R e f . 2 7 ) .

from a f l i g h t i n g l a z e i c i n g c o n d i t i o n s ( R e f . 2 7 ) a r e shown i n R e s u l t s F i g . 24. The most n o t i c e a b l e changes i n t h e l i f t c u r v e s due t o i c e a r e l o w e r s l o p e s and r e d u c e d Clmax. The t e s t a i r c r a f t has a Clmax o f a p p r o x i m a t e l y 1 . 4 n o f l a p c o n f i g u r a t i o n . W i t h i c e , Clmax i s r e d u c e d t o s o m e t h i n g i n t h e c l e a n , l e s s t h a n 1.0. The loss i n l i f t t h a t r e m a i n s a f t e r d e i c i n g a l l components i s l a r g e l y because t h e p o r t i o n o f t h e w i n g between t h e e n g i n e n a c e l l e s and f u s e - l a g e has n o i c e p r o t e c t i o n . A n o t h e r f a c t o r , more d i f f i c u l t t o e v a l u a t e , i s t h e c o n t r i b u t i o n t o l i f t loss made b y r e s i d u a l i c e l e f t o n t h e w i n g s a f t e r c y c l i n g t h e d e i c e r b o o t s .

t o a i r f r a m e i c i n g . To a F i g u r e 24 a l s o shows t h e d r a g i n c r e a s e due p i l o t , t h i s t r a n s l a t e s i n t o d e g r a d e d a i r c r a f t p e r f o r m a n c e , e s p e c i a l l y i n t h e e v e n t o f an e n g i n e - o u t c o n d i t i o n . F i g u r e 2 5 shows t h e r e l a t i o n s h i p between power r e q u i r e d and power a v a i l a b l e u n d e r t h e g l a z e i c i n g c o n d i t i o n s . The i n c r e a s e i n power r e q u i r e d means l o w e r c l i m b r a t e s , a l t i t u d e p o t e n t i a l , and c r u i s e speeds. These f a c t o r s become e s s e n t i a l f o r t h e p i l o t t o c o n s i d e r when p l a n n i n g h i s o p t i o n s u n d e r an e n g i n e - o u t c o n d i t i o n .

S t a b i l i t y and C o n t r o l NASA i s f o r m u l a t i n g a m e t h o d o l o g y t h a t w i l l p r e d i c t t h e e f f e c t of i c e a c c r e t i o n s o n t h e s t a b i l i t y and c o n t r o l c h a r a c t e r i s t i c s o f a i r c r a f t . T h i s m e t h o d o l o g y w i l l be u s e f u l i n a i r c r a f t d e s i g n , s a f e t y and a i r w o r t h i n e s s a n a l y - ses, f l i g h t c o n t r o l s y s t e m d e s i g n for r e l a x e d s t a t i c s t a b i l i t y a i r c r a f t , and p o s s i b l y i n p r o v i d i n g s i m u l a t o r s o f t w a r e f o r p i l o t t r a i n i n g .

R a t h e r l i m i t e d f l i g h t t e s t s have been c o n d u c t e d so f a r . These t e s t s were s t r u c t u r e d t o d e t e r m i n e w h e t h e r t h e i c i n g e f f e c t s were m e a s u r a b l e , and if so, what t h e i r v a l u e s w e r e . The s t a b i l i t y and c o n t r o l f l i g h t t e s t s i n v e s t i g a t e d o n l y t h e l o n g i t u d i n a l c h a r a c t e r i s t i c s ( R e f . 25 and 2 8 ) . F o r t h e s e t e s t s t h e i c i n g r e s e a r c h a i r c r a f t was c o n f i g u r e d w i t h a S t y r o f o a m l a y e r o f s i m u l a t e d i c e bonded t o t h e l e a d i n g edge o f t h e h o r i z o n t a l t a i l as shown i n F i g . 2 6 .

The f l i g h t t e s t maneuvers and d a t a a c q u i s i t i o n were d e s i g n e d t o p r o v i d e a s t a t i s t i c a l l y s i g n i f i c a n t ensemble o f d a t a p o i n t s t h a t c o u l d be a n a l y z e d b y a M o d i f i e d S t e p w i s e R e g r e s s i o n ( M S R ) t e c h n i q u e t o y i e l d e s t i m a t e s o f t h e s t a b i l i - t y and c o n t r o l d e r i v a t i v e s . The a i r c r a f t was f l o w n i n t h e c l e a n ( b a s e l i n e ) c o n f i g u r a t i o n and t h e n l a t e r w i t h t h e " S t y r o f o a m i c e " o n t h e h o r i z o n t a l t a i l .

Forty f i v e r e p e a t maneuvers were f l o w n a t i d e n t i c a l c o n d i t i o n s for each c o n f i g u r a t i o n .

The MSR t e c h n i q u e ( R e f s . 28 and 2 9 ) a c c u r a t e l y e s t i m a t e d t h e l o n g i - t u d i n a l s t a b i l i t y and c o n t r o l d e r i v a t i v e s t h r o u g h o u t t h e f l i g h t e n v e l o p e o f t h e a i r c r a f t . F i g u r e 27 shows how e l e v a t o r c o n t r o l power was d e g r a d e d o v e r t h e r a n g e of a t t a i n a b l e f l i g h t speeds a t a c o n s t a n t power s e t t i n g . Note t h a t t h e e s t i m a t e d v a r i a t i o n s , o r p r e d i c t e d bands o f u n c e r t a i n t y , were l e s s t h a n t h e measured changes.

I n a s u p p o r t i n g a n a l y t i c a l e f f o r t , t h e i c i n g r e s e a r c h a i r c r a f t g e o m e t r y was p a n e l e d up f o r i n p u t t o a t h r e e d i m e n s i o n a l a i r f l o w code ( V S A E R O ) . The d i g i t a l d e s c r i p t i o n i n c l u d e d p r o p e l l e r s and b o t h t h e b a s e l i n e and i c e d - t a i l g e o m e t r y . The ARC2D ( R e f . 1 7 ) code was a l s o r u n t o o b t a i n a m o d i f i e d g e o m e t r i c d e f i n i t i o n o f t h e i c e d t a i l f o r i n p u t t o VSAERO. The i n i t i a l VSAERO c a l c u l a - t i o n s p r e d i c t e d n e a r l y t h e same d e c r e a s e i n s t a b i l i t y due t o i c e as t h e f l i g h t t e s t d i d . However, t h e c a l c u l a t e d r e s u l t s a l s o i n d i c a t e d t h a t t h e n o n l i n e a r downwash due t o t h e p r o p e l l e r must be b e t t e r modeled i n VSAERO t o o b t a i n t h e c o r r e c t power e f f e c t s .

ROTORCRAFT I C I N G RESEARCH H e l i c o p t e r companies use t h e NASA I R T and o t h e r i c i n g t u n n e l s f o r t e s t i n g e n g i n e i n l e t s , r o t o r i c e p r o t e c t i o n systems o n a s t a t i o n a r y r o t o r b l a d e ( i . e . , no c e n t r i f u g a l f o r c e ) , s t a b i l a t o r s , e x t e r n a l s t o r e s , weapons s y s t e m s , o p t i c a l s y s t e m s , v e l o c i t y s e n s o r s , and o t h e r v u l n e r a b l e p a r t s o f a h e l i c o p t e r . How- e v e r , a f u l l - s c a l e , r o t a t i n g m a i n r o t o r w i l l n o t f i t i n t o any known i c i n g w i n d t u n n e l . T h e r e f o r e , t o p r o v e t h a t t h e m a i n rotor and t a i l r o t o r can o p e r a t e s u c c e s s f u l l y i n i c i n g , m a n u f a c t u r e r s have n o c h o i c e b u t t o f l y t h e i r h e l i c o p t - e r s i n i c i n g c l o u d s .

Because h e l i c o p t e r s a r e slow and have a s h o r t r a n g e , t h e y must w a i t for t h e w e a t h e r t o come t o t h e i r home base o f o p e r a t i o n s . T h i s dependence o n l o c a l w e a t h e r f u r t h e r a g g r a v a t e s t h e most d i f f i c u l t i c i n g c e r t i f i c a t i o n p r o b - l e m : f i n d i n g c l o u d s t h a t c o v e r t h e w i d e r a n g e o f n a t u r a l i c i n g c o n d i t i o n s r e q u i r e d for c e r t i f i c a t i o n -- a r a n g e t h a t o f t e n s e e m s u n a t t a i n a b l e due t o t h e low p r o b a b i l i t y o f some o f t h e c o n d i t i o n s . Thus i t r e q u i r e s y e a r s t o a c q u i r e enough i c i n g d a t a f o r e i t h e r FAA c e r t i f i c a t i o n or m i l i t a r y q u a l i f i c a t i o n .

S i n c e U . S . h e l i c o p t e r m a n u f a c t u r e r s want a l l - w e a t h e r o p e r a t i o n a l c a p a b i l i t y and want t o overcome t h i s h e a v y dependence o n f l i g h t t e s t i n g , NASA has been w o r k i n g w i t h them t o d e v e l o p a n i c i n g t e s t c a p a b i l i t y f o r s u b - s c a l e h e l i c o p t e r r o t o r s i n t h e NASA I R T .

1 1 Model Rotor T e s t i n g i n t h e NASA I c i n g Research Tunnel W e have r e c e n t l y c o m p l e t e d an i c i n g t e s t o f a r o t a t i n g OH-58 t a i l r o t o r i n t h e I R T . The OH-58 t a i l r o t o r has a 1 3 . 3 cm c h o r d and a 1.57 m d i a m e t e r .

The p r i m a r y p u r p o s e o f t h i s t e s t was t o d e v e l o p t h e t e c h n i q u e s for o p e r a t i n g a model r o t o r i n an i c i n g w i n d t u n n e l . The s e c o n d a r y p u r p o s e was t o a c q u i r e d a t a f o r use i n d e v e l o p i n g v a r i o u s c o m p u t e r codes t h a t p r e d i c t i c e a c c r e t i o n , i c e s h e d d i n g , and r o t o r p e r f o r m a n c e d e g r a d a t i o n due t o i c e o n r o t o r s .

O p e r a t i o n a l c o n c e r n s a d d r e s s e d i n t h e t e s t p r o g r a m were as f o l l o w s : model and t u n n e l s t a r t u p ; c o o r d i n a t i o n o f model and t u n n e l o p e r a t i o n ; model and t u n n e l shutdown; o b s e r v a t i o n and d o c u m e n t a t i o n o f t h e r o t o r i c e a c c r e t i o n and s h e d d i n g ; s a f e t y and emergency p r o c e d u r e s ; r e a c t i o n o f t h e r o t o r t o t h e a c c r e t i o n and s h e d d i n g o f i c e , and t h e c o n t r o l o f t h e model under t h e s e c i r c u m s t a n c e s .

V i d e o cameras r e c o r d e d o v e r a l l and c l o s e u p v i e w s o f t h e r o t o r i c e b u i l d u p and s h e d d i n g p r o c e s s e s . A r e m o t e l y c o n t r o l l e d 35-mm camera was a l s o used for d e t a i l e d p h o t o g r a p h s o f t h e i c e f o r m a t i o n s d u r i n g t h e r u n s . A f t e r each r u n , p h o t o g r a p h s and t r a c i n g s o f t h e i c e shapes were t a k e n for each b l a d e . For some s e l e c t e d i c e shapes, m o l d s were made from w h i c h c a s t i n g s o f t h e i c e w i l l e v e n t u a l l y be made.

A s u b s t a n t i a l and u n i q u e r o t o r i c e a c c r e t i o n and p e r f o r m a n c e d a t a base was a c q u i r e d i n t h i s t e s t . The r o t o r b l a d e i c e shapes were found t o be q u i t e r e p e a t a b l e f o r a g i v e n s e t o f c o n d i t i o n s , and c o r r e s p o n d i n g i c e d r o t o r t o r q u e v a l u e s were a l s o r e p e a t a b l e up t o t h e o n s e t o f s h e d d i n g . When i c e d i d shed, t h e i n b o a r d r a d i a l e x t e n t from w h i c h i c e n e v e r shed was r e l a t i v e l y r e p e a t a b l e , b u t t h e shed t i m e s , l o c a t i o n s , and q u a n t i t i e s o f i c e shed v a r i e d s u b s t a n t i a l l y from r u n t o r u n . A l t h o u g h c o n s i d e r e d p r e l i m i n a r y , t h i s d a t a w i l l be u s e f u l f o r c o m p a r i s o n s w i t h t h e p r e d i c t i o n s of i c e a c c r e t i o n codes, rotor p e r f o r m a n c e codes, and i c e s h e d d i n g m o d e l s .

F i g u r e s 28 and 2 9 show p h o t o s of t h e OH-58 t a i l r o t o r r i g and of i c e a c c r e t i o n s o n t h e r o t o r , and F i g . 30 shows r o t o r t o r q u e v e r s u s t i m e d u r i n g a t y p i c a l i c i n g e n c o u n t e r . A d e t a i l e d r e p o r t o f t h e s e t e s t s i s i n p r e p a r a t i o n and w i l l be p u b l i s h e d as R e f . 30.

The s u c c e s s f u l t e s t o f t h e OH-58 t a i l r o t o r has p r e p a r e d t h e way f o r a more s o p h i s t i c a t e d model r o t o r t e s t t h a t w i l l be r u n i n t h e I R T l a t e r t h i s y e a r . I n t h i s t e s t , a s c a l e model o f t h e UH-60 B l a c k h a w k ( F i g . 28) w i l l be t e s t e d w i t h f o u r NACA 0012 rotor b l a d e s , and d a t a w i l l be a c q u i r e d w i t h a s i x - c o m p o n e n t f o r c e b a l a n c e . A l l f o u r m a j o r U . S . h e l i c o p t e r companies w i l l p a r t i c i p a t e i n t h e t e s t .

ADVANCED TURBOPROP ICING STUDIES NASA Lewis R e s e a r c h C e n t e r has been t h e U . S . l e a d e r i n managing t h e d e v e l o p m e n t o f t h e new h i g h speed, h i g h e f f i c i e n c y a i r c r a f t p r o p u l s i o n system, The A T P can o p e r a t e e f f i c i e n t l y up t o c a l l e d t h e advanced t u r b o p r o p ( A T P ) .

i s s u e s t h a t r e q u i r e s a b o u t 0 . 8 5 Mach numbers. One o f t h e ATP t e c h n o l o g y r e s e a r c h i s i c e p r o t e c t i o n ( R e f . 3 1 ) . A l t h o u g h a i r c r a f t e q u i p p e d w i t h advanced above t h e FAR P a r t 25 A p p e n d i x C i c i n g t u r b o p r o p s w i l l c r u i s e a t a l t i t u d e s e n v e l o p e s , t h e y a r e e x p e c t e d t o e n c o u n t e r i c i n g c o n d i t i o n s d u r i n g g r o u n d o p e r a - t i o n , t a k e - o f f , c l i m b , d e s c e n t , low a l t i t u d e h o l d , and t h e y may c r u i s e w i t h a c c r e t e d i c e o b t a i n e d a t t h e lower a l t i t u d e s . O f p r i m a r y c o n c e r n i s t h e p o t e n - t i a l p e r f o r m a n c e d e g r a d a t i o n o f A T P ' s i n i c i n g e n v i r o n m e n t s . Advanced t u r b o - p r o p s a r e b u i l t so r u g g e d l y t h a t i t i s u n l i k e l y t h a t a s y m m e t r i c a l i c e sheds w i l l pose a s e r i o u s v i b r a t i o n p r o b l e m , i f any a t a l l .

Whether t h e A T P w i l l r e q u i r e i c e p r o t e c t i o n i s n o t known y e t . A t warmer i c i n g t e m p e r a t u r e s , i t i s l i k e l y t h a t t h e i c e can be shed from t h e t u r b o p r o p b l a d e s b y s i m p l y i n c r e a s i n g e n g i n e rpm. B u t t h e i c e may n o t shed a t t h e c o l d - e s t i c i n g t e m p e r a t u r e s where i c e a d h e s i o n i s known t o be s t r o n g e r . Even if t h e i c e can be shed a t t h e c o l d e s t t e m p e r a t u r e s , some r e s i d u a l i c e may c l i n g t o t h e b l a d e s and cause a loss i n l i f t and an i n c r e a s e i n d r a g .

To s t u d y t h e e f f e c t o f i c e a c c r e t i o n o n A T P p e r f o r m a n c e , N A S A , H a m i l t o n S t a n d a r d , and P r a t t & W h i t n e y j o i n t l y c o n d u c t e d an i c i n g t e s t p r o g r a m a t t h e F l u i d y n e I c i n g Tunnel ( R e f . 3 1 ) . The t e s t i n g c o n s i s t e d o f e v a l u a t i n g t h e i c e a c c r e t i o n c h a r a c t e r i s t i c s and r e s u l t i n g a e r o d y n a m i c d e g r a d a t i o n f o r two t h i n , t w o - d i m e n s i o n a l a i r f o i l s e c t i o n s t h a t were r e p r e s e n t a t i v e o f advanced t u r b o - p r o p a i r f o i l s . The t e s t s were c o n d u c t e d o v e r a w i d e r a n g e o f i c i n g c o n d i t i o n s , a n g l e s - o f - a t t a c k , and Mach numbers ( 0 . 3 t o 0 . 8 ) . A t each t e s t p o i n t , t h e a c c r e t e d i c e shape and w e i g h t were r e c o r d e d . A i r f o i l d r a g and s u r f a c e p r e s - s u r e s were measured f o r each r u n .

T h i s d a t a can be used f o r s e v e r a l p u r p o s e s : ( 1 ) t o compare w i t h LEWICE p r e d i c t i o n s o f i c e shape; ( 2 ) t o compare w i t h l i f t and d r a g p r e d i c t i o n s i n t h e l i t e r a t u r e ; ( 3 ) f o r p r e d i c t i n g A T P p e r f o r m a n c e i n i c i n g ; and (4) f o r c o n s t r u c t - i n g a c o m p o s i t e i c e shape t h a t c o u l d be bonded t o t h e l e a d i n g edge of A T P b l a d e s for m e a s u r i n g p e r f o r m a n c e l o s s e s d u r i n g f l i g h t .

O t h e r p r o p o s e d e f f o r t s u n d e r c o n s i d e r a t i o n f o r t h e l o n g e r t e r m i n c l u d e The g o a l s o f t h e s e t e s t s w o u l d be t e s t i n g of a s c a l e - m o d e l A T P i n t h e I R T .

( 1 ) t o measure p e r f o r m a n c e changes due t o i c i n g , ( 2 ) r e c o r d a c t u a l i c e a c c r e - t i o n shapes, ( 3 ) o b s e r v e s h e d d i n g c h a r a c t e r i s t i c s , and ( 4 ) u s e t h e r e s u l t i n g I t i s d a t a t o v a l i d a t e p r o p e l l e r p e r f o r m a n c e codes and i c e s h e d d i n g c o d e s .

u n l i k e l y t h a t s a t i s f a c t o r y i c i n g s c a l i n g l a w s w i l l be f o u n d f o r r e l a t i n g s u b - s c a l e model t e s t i n g t o f u l l - s c a l e . B u t i f t h e s u b - s c a l e d a t a c a n be used t o d e v e l o p f u n d a m e n t a l c o m p u t e r models f o r p r e d i c t i n g changes i n p e r f o r m a n c e and i c e s h e d d i n g c h a r a c t e r i s t i c s , we may be a b l e t o bypass t h e s c a l i n g q u e s - t i o n and u s e t h e s e models t o p r e d i c t f u l l - s c a l e r e s u l t s .

GROUND DEICING FLUIDS FOR WINTER OPERATION The B o e i n g Commercial A i r p l a n e s Company and NASA c o n d u c t e d a j o i n t t e s t p r o g r a m i n t h e I R T t o e v a l u a t e t h e Type I and Type I 1 g r o u n d d e i c i n g f l u i d s t h a t a r e used b y t h e A s s o c i a t i o n o f European A i r l i n e s ( A E A ) d u r i n g w i n t e r o p e r - a t i o n s ( R e f . 3.2). S e v e r a l e x p e r i m e n t a l f l u i d s were a l s o t e s t e d as p o s s i b l e c a n d i d a t e s t o r e p l a c e t h e t h e n - c u r r e n t Type I 1 f l u i d s . The o b j e c t of t h e t e s t s t o a s s e s s t h e a e r o d y n a m i c p e r f o r m a n c e p e n a l t i e s t h a t r e s u l t when an a i r - was p l a n e t a k e s o f f w i t h g r o u n d d e i c i n g f l u i d s o n i t s w i n g s .

Type I f l u i d s a r e p r o p y l e n e g l y c o l , w h i c h have h o l d t i m e s s i m i l a r t o t h o s e o f t h e e t h y l e n e g l y c o l f l u i d s u s e d i n t h e U.S.A. f o r r e m o v i n g i c e and snow from a i r c r a f t p r i o r t o t a k e o f f . Type I 1 f l u i d s a r e non-Newtonian ( t h i x o - t r o p i c ) f l u i d s whose v i s c o s i t y v a r i e s i n v e r s e l y w i t h t h e r a t e o f s h e a r a p p l i e d t o t h e f l u i d . The Type I 1 f l u i d i s a l s o c a l l e d a t h i c k e n e d f l u i d , because i t has t h e v i s c o s i t y o f a g e l when s i t t i n g o n t h e w i n g s o f a g r o u n d e d a i r p l a n e .

B u t d u r i n g t a k e o f f , t h e a i r r u s h i n g o v e r t h e w i n g s e x e r t s a shear s t r e s s o n t h e f l u i d , t h u s r e d u c i n g i t s v i s c o s i t y and a l l o w i n g t h e f l u i d t o flow o f f t h e w i n g .

P r i o r t o t h e I R T t e s t s , t h e A E A and B o e i n g had c o n d u c t e d a j o i n t f l i g h t t e s t p r o g r a m on a B o e i n g 737 a i r c r a f t t o e v a l u a t e t h e Type I and Type I 1 f l u i d s d u r i n g t a k e o f f . The r e s u l t s o f t h o s e t e s t s were as follows: D u r i n g t a k e o f f , as t h e a i r s p e e d o v e r t h e w i n g i n c r e a s e d , t h e f l u i d s u r f a c e became wavy and t h e f l u i d began t o r u n o f f t h e w i n g , b u t i t a l s o a c c u m u l a t e d n e a r t h e t r a i l i n g edge. The w a v i n e s s r o u g h e n e d t h e u p p e r a i r f o i l s u r f a c e , and t h e f l u i d accumu- l a t i o n near t h e t r a i l i n g edge decambered t h e a i r f o i l . B o t h o f t h e s e e f f e c t s caused a loss i n l i f t , an i n c r e a s e i n d r a g , and a r e d u c e d s t a l l a n g l e - o f - a t t a c k . The l a s t e f f e c t was o b s e r v e d l a t e r i n t h e w i n d t u n n e l t e s t s , b u t n o t i n t h e f l i g h t t e s t s because t h e a i r c r a f t was n o t f l o w n i n t o s t a l l w h i l e so c l o s e t o t h e g r o u n d .

T e s t s were c o n d u c t e d o n two models i n t h e I R T : ( 1 ) a 0.091 s c a l e 3D h a l f model o f t h e B o e i n g 737-200 ADV a i r c r a f t , and ( 2 ) a 0 . 1 8 s c a l e 20 a i r f o i l sec- t i o n a t t h e 65 p e r c e n t span o f t h e 737-200 ADV a i r c r a f t ( F i g . 31 and 32 r e s p e c t i v e l y ) . Wind t u n n e l t e s t o b j e c t i v e s were as f o l l o w s : ( 1 ) c o r r e l a t e w i n d t u n n e l and f l i g h t t e s t measurements o f a e r o d y n a m i c e f f e c t s o f d e - / a n t i - i c i n g f l u i d s ; ( 2 ) e v a l u a t e f l u i d e f f e c t s t h a t c o u l d n o t be s a f e l y p e r f o r m e d d u r i n g f l i g h t t e s t s ; (3) expand f l i g h t t e s t r e s u l t s f o r p a r a m e t r i c v a r i a t i o n s o f tem- p e r a t u r e , a i r f o i l c o n f i g u r a t i o n , and f l u i d f o r m u l a t i o n ; ( 4 ) c o n t r i b u t e t o t h e d a t a base f o r e s t a b l i s h i n g a e r o d y n a m i c a c c e p t a n c e s t a n d a r d s for g r o u n d d e - / a n t i - i c i n g f l u i d s ; and ( 5 ) o b t a i n d a t a t h a t c o n t r i b u t e s t o a p h y s i c a l u n d e r s t a n d i n g o f t h e l i f t loss mechanism.

The d a t a o b t a i n e d from t h e w i n d t u n n e l t e s t s i n c l u d e d ( 1 ) model f o r c e d a t a from i n t e r n a l b a l a n c e s ; ( 2 ) s u r f a c e s t a t i c p r e s s u r e s ; ( 3 ) i n i t i a l f l u i d f i l m d e p t h from a gap gauge, ( 4 ) f l u i d f i l m d e p t h from a r e l a t i o n s h i p b e t w e e n d e p t h and p h o t o g r a p h e d f l u o r e s c e n t i n t e n s i t y ( a f l u o r e s c e n t dye added t o t h e f l u i d and i l l u m i n a t e d w i t h u l t r a - v i o l e t l i g h t ) ; ( 5 ) v i d e o r e c o r d i n g s of f l u i d flow-off c h a r a c t e r i s t i c s ; and ( 6 ) b o u n d a r y l a y e r v e l o c i t y p r o f i l e s .

T y p i c a l r e s u l t s a r e shown i n b a r c h a r t form i n F i g . 33 where t h e p e r c e n t loss i n l i f t a t 8" a n g l e - o f - a t t a c k and a l s o a t s t a l l a r e p r e s e n t e d f o r t h e Type I ( l a b e l e d 1 ) and Type I 1 ( l a b e l e d 3) f l u i d s and e i g h t e x p e r i m e n t a l Type I 1 f l u i d s . A l l o f t h e e x p e r i m e n t a l f l u i d s showed l o w e r l i f t l o s s t h a n t h e t h e n - c u r r e n t Type I 1 f l u i d , and t h e l o s s e s f o r t h e e x p e r i m e n t a l f l u i d s were c o m p a r a b l e t o t h e l o s s e s f o r t h e Type I f l u i d .

An i m p o r t a n t outcome o f t h i s t e s t p r o g r a m was t h a t t h e e x p e r i m e n t a l Type I 1 f l u i d s t e s t e d i n t h e I R T i n A p r i l 1988 have now become t h e c u r r e n t o p e r a - t i o n a l f l u i d s i n Europe. A n o t h e r s i g n i f i c a n t outcome i s t h a t t h e s e q u a n t i f i a - b l e t e s t r e s u l t s showed t h a t t h e s e new Type I 1 f l u i d s d o n o t d e g r a d e t a k e o f f a e r o d y n a m i c p e r f o r m a n c e anymore t h a n do t h e Type I f l u i d s . The Type I 1 f l u i d s t h a n t h e AEA have been shown b y t h e AEA t o have f a r g r e a t e r h o l d o v e r t i m e s Type I f l u i d s .

NASA also is funding research by Dr. C.S. Yih at the University of Florida t o derive an analytical model of the surface instability that causes the fluid waves o n the airfoil. Dr. Yih has identified the instability as being driven by the large fluid-to-air viscosity ratio. He has also derived dimensionless parameters that should be preserved during scale model testing to assure that model test results will represent full-scale results. A paper o n the analyti- cal formulation and mathematical solution will be published later.

DROPLET S I Z I N G INSTRUMENTATION FOR I C I N G CLOUDS Very accurate droplet size data is needed to validate droplet trajectory codes, such as the one used in LEWICE. And automated droplet sizing systems are needed to calibrate the IRT in a shorter time and with far fewer personnel than were employed in the earlier calibration program of the 1 9 5 0 ' s . NASA's droplet sizing effort i s divided into two parts: ( 1 ) research to devise meth- ods of calibrating and checking the accuracy of existing droplet sizing instru- ments; and ( 2 ) development of a new instrument that promises t o overcome some of the known problems of the existing instruments.

Calibration Devices for Existing Wind Tunnel and Flight Instruments Reference 33 presents a detailed review of the droplet sizing research conducted to understand the calibration and operation of two instruments manu- factured by Particle Measuring Systems, Inc. (PMS): the FSSP (forward scatter- ing spectrometer probe) and OAP (optical array probe).

A rotating pinhole device (Fig. 34) was developed (Refs. 33 and 34) t o

check the calibration of the FSSP. A calibration curve o f the FSSP using

rotating pinholes is given i n Fig. 35. The value of this device is that it

can be inserted into the FSSP probe volume at anytime to check whether the instrument is scattering light into the correct droplet size bin. This device can uncover misalignment of the laser o r its optical system, it can measure optical parameters such as depth-of-field and optical collection angles, it

can detect dirt o r other contamination o n the laser optics, and it can detect

problems with the electronics systems. The device has proved invaluable in the recent calibration of the I R T , where it was demonstrated that s u c h a calibra- tion device i s absolutely essential to the proper field operation of the F S S P .

NASA has checked the sizing accuracy of the FSSP by three methods: ( 1 ) pinholes, ( 2 ) glass beads, and ( 3 ) a water droplet generator. The results of these checks are shown in Fig. 36 where it can be seen that at the mid to upper range of the FSSP, the measured droplet size begins to depart signifi- cantly from the actual size. Thus i n clouds with large droplets, the FSSP would undersize the median volume diameter 5 to 1 0 pm.

The ODtical Array Probe (OAP) is used to measure droplets from 1 0 t o 620 pm. NASA has developed a rotating reticle calibration disk for the OAP that provides absolute calibration over the entire size range of the OAP (Refs. 33 and 3 5 ) . Figure 37 shows the calibration curve for the OAP using the rotating eticle.

When cal brating the icing cloud i n the IRT, both the FSSP and the OAP were required

the range of the

because the droplet size range extended beyond i c e d t o g e t h e r FSSP a l o n e . Thus r e s u l t s from t h e OAP and FSSP had t o be sp t h e s p l i c i n g p r o c - to o b t a i n a c o n t i n u o u s d r o p l e t d i s t r i b u t i o n . U n f o r t u n a t e l y , o f t h e c l o u d i s ess i s n o t e x a c t , and s i n c e t h e m e d i a n volume d i a m e t e r ( M V D ) e x t r e m e l y s e n s i t i v e t o t h e number o f l a r g e r d r o p l e t s , t h e me surement o f t h e l a r g e r M V D ' s has an i n d e t e r m i n a t e u n c e r t a i n t y .

Development o f a Wind Tunnel and F l i q h t I n s t r u m e n t A newer i n s t r u m e n t d e v e l o p e d b y A e r o m e t r i c s , I n c . , named t h e Phase D o p p l e r shows p r o m i s e o f e l i m i n a t i n g some o f t h e l i m i t a t i o n s P a r t i c l e A n a l y z e r ( P D P A ) , we have i n c a l i b r a t i n g t h e I R T w i t h t h e FSSP and OAP ( R e f . 3 6 ) . NASA has worked v e r y c l o s e l y w i t h A e r o m e t r i c s t o u p g r a d e t h e l a b o r a t o r y PDPA i n s t r u - ment. These u p g r a d e s , w h i c h c e n t e r o n t h e s i g n a l p r o c e s s o r , w i l l r e s u l t i n t h e f o l l o w i n g improvements: ( 1 ) measurement o f p a r t i c l e s w i t h v e l o c i t i e s r e p r e s e n - t a t i v e of f l i g h t speeds; ( 2 ) i n c r e a s e i n dynamic s i z e r a n g e from 35 t o 50 (dynamic s i z e r a n g e i s t h e r a t i o o f l a r g e s t p a r t i c l e s i z e t o s m a l l e s t p a r t i c l e s i z e ) ; and ( 3 ) g r e a t e r s i z e a c c u r a c y a t h i g h speeds and dense s p r a y s . These u p g r a d e s , when c o m p l e t e d , s h o u l d a l l o w us t o use a s i n g l e i n s t r u m e n t for meas- u r i n g t h e e n t i r e o p e r a t i n g e n v e l o p e o f t h e I R T c l o u d .

C u r r e n t l y , t h e PDPA i s a l a b o r a t o r y i n s t r u m e n t t h a t can p r o b e c l o u d s up t o a b o u t 2 f t i n d e p t h . B u t i n i t s p r e s e n t form, i t c a n n o t be used i n t h e I R T , whose t e s t s e c t i o n i s 1.82 b y 2 . 7 4 m (6 b y 9 ft). Nor can i t be used i n an a i r c r a f t t o sample c l o u d s . To c o n v e r t t h e l a b o r a t o r y PDPA f o r use o n a i r c r a f t o r t h e I R T , A e r o m e t r i c s was awarded Phase I and Phase I1 S m a l l B u s i n e s s I n n o v a - t i v e Research c o n t r a c t s . For t h e f l i g h t v e r s i o n , a s m a l l t r a n s m i t t e r and r e c e i v e r u n i t w i l l be p l a c e d i n t h e c l o u d and t h e l a s e r l i g h t w i l l be s e n t t o and from t h e u n i t b y f i b e r o p t i c c a b l e s . The Phase I 1 c o n t r a c t i s f o r 2 y e a r s i s j u s t g e t t i n g u n d e r way.

and EXPERIMENTAL I C I N G F A C I L I T I E S The NASA I c i n g Research Tunnel has f o r s e v e r a l y e a r s been one of N A S A ' s most h e a v i l y s c h e d u l e d w i n d t u n n e l s , w i t h t e s t s s c h e d u l e d up t o two y e a r s i n advance. I n 1988, t h e t u n n e l l o g g e d 1330 t e s t h o u r s , w h i c h i s t h e h i g h e s t a n n u a l usage o n r e c o r d s i n c e 1950. The I R T i s t h e l a r g e s t r e f r i g e r a t e d t u n n e l i n t h e w o r l d . The t e s t s e c t i o n i s 1 . 8 2 m h i g h b y 2 . 7 4 m w i d e b y 6 . 0 9 m l o n g ( 6 ft h i g h b y 9 f t w i d e b y 2 0 f t l o n g ) . I t s maximum a i r s p e e d empty i s 134 m / sec ( 3 0 0 mph), and i t s maximum a i r s p e e d w i t h a model i n s t a l l e d depends o n t h e model b l o c k a g e . The I R T can p r o v i d e t u n n e l t o t a l t e m p e r a t u r e s from 0 t o -35 " C ( + 3 2 t o -30 O F ) . Two d i f f e r e n t s e t s o f n o z z l e s a r e a v a i l a b l e f o r p r o d u c i n g s u p e r c o o l e d i c i n g c l o u d s t h a t c o v e r most, b u t n o t a l l , o f t h e FAA P a r t 2 5 Appendix C i c i n g e n v e l o p e s .

Recent R e h a b i l i t a t i o n o f t h e NASA I c i n q R e s e a r c h Tunnel Two y e a r s ago, t h e I R T u n d e r w e n t e x t e n s i v e r e n o v a t i o n s aimed a t i m p r o v i n g i t s r e l i a b i l i t y and p r o d u c t i v i t y . The m a j o r i m p r o v e m e n t s a r e as f o l l o w s : ( 1 ) a new s p r a y b a r s y s t e m , w h i c h has e i g h t b a r s t o p r o v i d e a more u n i f o r m c l o u d t h a n d i d t h e o r i g i n a l s i x b a r s ; ( 2 ) a new 3 . 7 3 MW (5000 h p ) d r i v e motor; ( 3 ) new s o l i d s t a t e c o n t r o l s f o r t h e d r i v e motor; ( 4 ) a new d i s t r i b u t e d p r o c - ess c o n t r o l system, w h i c h p r o v i d e s programmable, d i g i t a l c o n t r o l o f t h e d r i v e motor, t h e r e f r i g e r a t i o n s y s t e m , t h e s p r a y b a r system, and o t h e r s u p p o r t sys- tems; ( 5 ) a t h r e e - t i m e s - a r g e r c o n t r o l room w i t h v a s t l y i m p r o v e d a c o u s t i c s ; ( 6 ) new e l e c t r i c a l Dower s u m l i e s f o r o D e r a t i o n o f a i r c r a f t t e s t models w h i l e i n t h e I R T ; and ( 7 ) ' r e p l a c e m e n t o f a l l wooden floors w i t h c o n c r e t e f l o o r s .

F i g u r e 38 shows a s c h e m a t i c o f t h e I R T f l o w c i r c u i t and i d e n t i f i e s t h e components t h a t were r e h a b i l i t a t e d . These improvements n o t o n l y have i n c r e a s e d p r o d u c t i v i t y , b u t a l s o have p r o v i d e d new t e s t c a p a b i l i t i e s . For example, t h e BoeingjNASA g r o u n d d e i c i n g f l u i d s t e s t p r o g r a m , w h i c h r e q u i r e d r a m p i n g t h e I R T a i r s p e e d t o s i m u l a t e t a k e o f f , c o u l d n o t have been done w i t h t h e o l d d r i v e motor and c o n t r o l s .

R e c a l i b r a t i o n o f t h e NASA I c i n g Research Tunnel The p u r p o s e o f t h e I R T i s t o s i m u l a t e a f l i g h t t h r o u g h n a t u r a l i c i n g c l o u d s . The q u a l i t y o f t h a t s i m u l a t i o n depends o n i t s c a l i b r a t i o n f o r t h e f o l - l o w i n g p a r a m e t e r s : t h e a e r o t h e r m o d y n a m i c v a r i a b l e s o f a i r s p e e d , t e m p e r a t u r e , and t u r b u l e n c e l e v e l ; and t h e i c i n g c l o u d v a r i a b l e s o f l i q u i d w a t e r c o n t e n t and d r o p l e t s i z e . O t h e r s i m u l a t i o n i s s u e s , such as s c a l i n g , a r e r e s o l v e d b y a n a l y s e s and e x p e r i m e n t a l t e c h n i q u e .

The r e c e n t c a l i b r a t i o n i n c l u d e d a l l o f t h e above p a r a m e t e r s . F i g u r e 39 shows a p r e l i m i n a r y d r o p l e t s i z e c a l i b r a t i o n f o r t h e I R T " s t a n d a r d " n o z z l e s .

F i g u r e 40 shows t h e I R T o p e r a t i n g e n v e l o p e f o r b o t h t h e " s t a n d a r d " and "mod 1 " n o z z l e s a t a t u n n e l a i r s p e e d o f ( 1 1 2 m / s e c > 250 mph. T h i s was t h e f i r s t r e c a l - i b r a t i o n o f t h e s p r a y n o z z l e s s i n c e 1956. One improvement o v e r t h e o l d C a l i - b r a t i o n i s t h a t t h e u p p e r l i m i t o n c a l i b r a t e d MVD d r o p l e t s i z e has been i n c r e a s e d from 2 0 t o 40 pm.

Tunnel S i m u l a t i o n V e r s u s N a t u r a l I n - F l i g h t T e s t s Flow t u r b u l e n c e l e v e l i s a l w a y s an e l e m e n t o f c o n c e r n i n a n i c i n g t u n n e l because b o t h t h e p h y s i c a l b l o c k a g e o f s p r a y b a r s and t h e w a t e r and a i r t h a t come o u t of t h e s p r a y b a r s s h o u l d a f f e c t t u r b u l e n c e . S i n c e t u r b u l e n c e l e v e l i n t h e I R T w o u l d a f f e c t b o t h t h e i c e a c c r e t i o n p r o c e s s and t h e e v a l u a t i o n of t h e r m a l i c e p r o t e c t i o n s y s t e m s , u s e r s o f t e n want t o know about t h e I R T ' s t u r b u - l e n c e l e v e l and i f i t a d e q u a t e l y s i m u l a t e s i n f l i g h t c o n d i t i o n s .

The t u r b u l e n c e l e v e l i n t h e I R T t e s t s e c t i o n , as measured b y VanFossen ( R e f . 37) w i t h h o t w i r e s , i s a b o u t 0.5 p e r c e n t when t h e w a t e r and a i r t o t h e s p r a y b a r s a r e t u r n e d o f f . O b v i o u s l y , t h e t u r b u l e n c e l e v e l c a n n o t be measured w i t h t h e c l o u d o n because t h e w a t e r d r o p l e t s s t r i k i n g t h e h o t w i r e s w o u l d i n v a l i d a t e t h e i r r e a d i n g s . B u t we have t r i e d t o measure t h e t u r b u l e n c e l e v e l A t f i r s t i t a p p e a r e d t h a t a w i t h t h e h o t ( 1 8 0 O F ) s p r a y b a r a i r t u r n e d o n .

v a l i d h o t w i r e r e a d i n g was p o s s i b l e , b u t a f t e r c a r e f u l s t u d y , VanFossen d e c i d e d t h a t f i l a m e n t s o f t h e h o t s p r a y b a r a i r may have been h i t t i n g t h e h o t w i r e s and g i v i n g i n c o r r e c t r e a d i n g s .

To a d d r e s s t h e h e a t t r a n s f e r q u e s t i o n f o r t h e I R T , NASA measured h e a t t r a n s f e r p e r f o r m a n c e o n a NACA 0012 a i r f o i l ( 5 3 . 3 c m ( 2 1 i n . ) c h o r d ) i n t h e I R T ( w i t h h o t s p r a y b a r a i r t u r n e d o n ) and compared i t w i t h h e a t t r a n s f e r p e r - formance o n t h e same model i n f l i g h t ( R e f . 3 8 ) . The model was e x t e n d e d o u t t h e o v e r h e a d h a t c h o f t h e T w i n O t t e r as shown i n F i g . 41. F i g u r e 42 shows a p l o t o f F r o s s l i n g number v e r s u s l o c a t i o n o n t h e a i r f o i l f o r d a t a t a k e n i n f l i g h t and i n t h e I R T ( R e f . 3 9 ) . The f i g u r e shows t h a t t h e r e i s n o d i s t i n - g u i s h a b l e d i f f e r e n c e between h e a t t r a n s f e r i n f l i g h t and i n t h e I R T .

FUNDAMENTAL STUDIES I N ICING NASA m a i n t a i n s a s t r o n g e f f o r t i n i c i n g f u n d a m e n t a l s , w h i c h i s t h e back- bone of a n y p r o g r a m t h a t i s d e v e l o p i n g new c o m p u t e r codes and new t e s t t e c h - n i q u e s . W e have a l r e a d y d e s c r i b e d s e v e r a l f u n d a m e n t a l s t u d i e s , for example, i n f o r m u l a t i n g a new d e s c r i p t i o n o f t h e i c e a c c r e t i o n p r o c e s s , and i n o b t a i n i n g fundamental f l o w f i e l d d a t a f o r f l o w o v e r i c e shapes t h a t cause f l o w s e p a r a t i o n and r e a t t a c h m e n t . I n t h i s s e c t i o n we r e v i e w work o n two i m p o r t a n t p r o b l e m s : i c i n g s c a l i n g l a w s , and s t r u c t u r a l and a d h e s i v e p r o p e r t i e s o f i n - f l i g h t i c e .

I c i n s S c a l i n g Laws The p r o p o s e d or d e s i r e d t e s t m a t r i x f o r an i c i n g t e s t u s u a l l y i n v o l v e s t h e f o l l o w i n g v a r i a b l e s : a i r s p e e d , o u t s i d e a i r t e m p e r a t u r e , a l t i t u d e , c l o u d l i q u i d w a t e r c o n t e n t , c l o u d d r o p l e t s i z e d i s t r i b u t i o n or median volume d i a m e t e r , and model s i z e o r s c a l e . I n a f l i g h t t e s t i n n a t u r a l i c i n g , or i n an a r t i f i c i a l c l o u d b e h i n d an i n - f l i g h t s p r a y t a n k e r , chances a r e t h a t t h e e x a c t s e t of v a r - i a b l e s d e s i r e d w i l l be u n a t t a i n a b l e . I n a w i n d t u n n e l t e s t , c e r t a i n combina- tions o f variables also will be unattainable. For example, m o s t i c i n g wind t u n n e l s have maximum a i r s p e e d s f a r b e l o w t h e speeds o f modern t r a n s p o r t or m i l i t a r y a i r c r a f t . And due t o t h e p r a c t i c a l l i m i t s o n n o z z l e t u r n - d o w n r a t i o s and n o z z l e d r o p l e t s i z e r a n g e s n o w i n d t u n n e l can a c h i e v e t h e f u l l FAA P a r t 2 5 A p p e n d i x C o p e r a t i n g e n v e l o p e s o v e r t h e f u l l speed r a n g e o f t h e t u n n e l .

I f t h e d e s i r e d t e s t v a r i a b l e s c a n n o t be met, t h e e x p e r i m e n t e r m u s t r e s o r t t o some form o f s c a l i n g . V a r i o u s o b j e c t i v e s can be i m a g i n e d f o r any p a r t i c u l a r s c a l e d t e s t : ( 1 ) a g e o m e t r i c a l l y s i m i l a r i c e shape; ( 2 ) an e q u i v a l e n t d r a g c o e f f i c i e n t f o r t h e i c e shape/model c o m b i n a t i o n ; ( 3 ) t h e same w a t e r f l u x a r o u n d t h e a i r f o i l l e a d i n g edge; ( 4 ) t h e same h e a t t r a n s f e r r e s u l t s for a t h e r m a l i c e p r o t e c t i o n system; ( 5 ) r i m e i c i n g c o n d i t i o n s ( i . e . , a l l w a t e r must f r e e z e imme- d i a t e l y upon i m p a c t ) ; and so o n . S c a l i n g l a w s have a l w a y s been u s e d , b u t n e v e r r i g o r o u s l y v a l i d a t e d ( R e f . 4 0 ) . T h i s does n o t mean t h e t e s t s were done i n c o r - r e c t l y , f o r i c i n g has been and a l w a y s w i l l be p a r t s c i e n c e and p a r t a r t . T h i s i s why i n f l i g h t t e s t i n g i n n a t u r a l i c i n g c l o u d s a l w a y s w i l l be a r e q u i r e d p a r t of t h e certification/qualification p r o c e s s .

R e f e r e n c e 40 g i v e s a good b i b l i o g r a p h y o f t h e work done p r e v i o u s l y o n s c a l i n g . Most o f t h e s e works o n s c a l i n g r e l y o n an a n a l y s i s o f t h e i c e a c c r e - t i o n p r o c e s s d e s c r i b e d b y M e s s i n g e r ( R e f . 13) o v e r 30 y e a r s ago. New i n s i g h t s i n t o t h e i c e a c c r e t i o n p r o c e s s b y O l s e n ( R e f . 14) and Hansman ( R e f s . 15 and 1 6 ) have l e d B i l a n i n ( R e f . 41) t o a p p l y t h e Buckingham p i t h e o r y t o t h e i c e a c c r e - t i o n p r o b l e m . B i l a n i n showed t h a t t h e n o r m a l i z e d t h i c k n e s s o f t h e i c e a c c r e t e d o n t h e a i r f o i l i s a f u n c t i o n o f 18 n o n d i m e n s i o n a l g r o u p s . A l t h o u g h many o f t h e g r o u p s a r e s a t i s f i e d i n a n y s c a l i n g t e s t , t h e r e e x i s t s a p r o b l e m h o l d i n g Mach, R e y n o l d s and Weber numbers c o n s t a n t between t e s t s . He c o n c l u d e d t h a t t h e o l d M e s s i n g e r f o r m u l a t i o n may be i n a d e q u a t e , and t h a t i m p r o v e d i c e a c c r e t i o n seal- i n g may r e q u i r e a b e t t e r m a t c h i n R e y n o l d s number and c o n s i d e r a t i o n o f t h e s u r f a c e .

p h y s i c s o f w a t e r f i l m and d r o p l e t s p l a s h dynamics o n t h e a i r f o i l I n R e f . 41 B i l a n i n c o n c l u d e d t h a t c o m p e t i n g p h y s i c a l e f f e c t s d o n o t i n g e n e r a l a l l o w a r i g o r o u s s c a l i n g m e t h o d o l o g y , b u t an a c c e p t a b l e a p p r o x i m a t e s c a l i n g scheme may be p o s s i b l e .

He has s u g g e s t e d a s e r i e s o f t e s t s o n r o t a t i n g and n o n r o t a t i n g c y l i n d e r s t o v a l i d a t e t h e a p p r o x i m a t e schemes. NASA p l a n s t o p a r t i c i p a t e i n a j o i n t A i r Force/FAA/NASA p r o g r a m t o c a r r y o u t t h e s e s u g g e s t e d t e s t s l a t e r t h i s y e a r .

S t r u c t u r a l and A d h e s i v e P r o p e r t i e s o f I n - F l i g h t I c e Over t h e p a s t 5 y e a r s , NASA has s u p p o r t e d a c o n t i n u o u s , b u t l o w - l e v e l e f f o r t t o s t u d y t h e s t r u c t u r a l p r o p e r t i e s o f i c e f o r m e d i n f l i g h t . T h i s work i s d e s c r i b e d i n R e f s . 42 t o 4 7 . I c e f o r m e d i n f l i g h t or i n an i c i n g r e s e a r c h t u n n e l r e s u l t s from s u p e r c o o l e d w a t e r d r o p l e t s i m p a c t i n g a s u r f a c e a t f l i g h t speed or w i n d t u n n e l a i r s p e e d . W e r e f e r t o i c e so f o r m e d as ' i m p a c t ' i c e .

I m p a c t i c e can v a r y i n t y p e o v e r a w i d e r a n g e , d e p e n d i n g o n t h e l i q u i d w a t e r c o n t e n t and d r o p l e t s i z e d i s t r i b u t i o n i n t h e c l o u d , o n t h e o u t s i d e a i r tempera- t u r e , and o n t h e d r o p l e t v e l o c i t i e s . The a d h e s i o n o f i c e t o a s u r f a c e depends n o t o n l y o n t h e t y p e o f i c e f o r m e d , b u t a l s o o n t h e r o u g h n e s s , p o r o s i t y , and o t h e r f u n d a m e n t a l p r o p e r t i e s o f t h e s u r f a c e . The s t a t i s t i c a l v a r i a t i o n of i c e from one t e s t t o t h e n e x t i s a r e a l phenomenon, and i t m u s t be p r o p e r t i e s a c c o u n t e d f o r i n t h e d e s i g n o f systems t h a t depend o n i c e s h e d d i n g for t h e i r o p e r a t i o n .

The o v e r a l l o b j e c t i v e s o f t h e p r o j e c t a r e ( 1 ) t o measure t h e s t r u c t u r a l p r o p e r t i e s of i m p a c t i c e , such a s , b a s i c t e n s i l e p r o p e r t i e s , a d h e s i v e c h a r a c t - e r i s t i c s , and p e e l p r o p e r t i e s and ( 2 ) t o d e v e l o p f i n i t e e l e m e n t a n a l y t i c a l methods for use i n t h e a n a l y s i s and d e s i g n o f d e i c i n g systems and i c i n g t e s t i n g a p p a r a t u s .

T e s t a p p a r a t u s e s have been d e s i g n e d t o measure each o f t h e t h r e e b a s i c m e c h a n i c a l p r o p e r t i e s : ( 1 ) t e n s i l e ( Y o u n g ' s modulus ( E ) , and u l t i m a t e t e n s i l e s t r e n g t h o f i m p a c t i c e i n a d i r e c t i o n t r a n s v e r s e t o t h e d i r e c t i o n of i c e g r o w t h ) ; ( 2 ) s h e a r ( a d h e s i o n ) ; and ( 3 ) p e e l i n g . D a t a has been o b t a i n e d o n b o t h a d h e s i v e s h e a r s t r e n g t h o f i m p a c t i c e s and p e e l i n g f o r c e s for v a r i o u s i c i n g c o n d i t i o n s . B e i n g s t u d i e d a r e t h e i n f l u e n c e s o f k e y p a r a m e t e r s , such a s , t u n - n e l t e m p e r a t u r e , w i n d v e l o c i t,y, w a t e r d r o p s i z e , s u b s t r a t e m a t e r i a l , s u b s t r a t e s u r f a c e t e m p e r a t u r e , and i c e t h i c k n e s s . A f i n i t e e l e m e n t a n a l y s i s o f t h e s h e a r t e s t a p p a r a t u s was d e v e l o p e d i n o r d e r t o g a i n more i n s i g h t i n t o t h e e v a l u a t i o n of t h e t e s t d a t a .

Measurements i n d i c a t e t h a t s u r f a c e r o u g h n e s s has a m a j o r e f f e c t o n t h e a d h e s i v e s h e a r s t r e n g t h . A d d i t i o n a l a d h e s i v e s h e a r s t r e n g t h t e s t s a r e p l a n n e d i n w h i c h t h e s u r f a c e r o u g h n e s s w i l l be s y s t e m a t i c a l l y v a r i e d .

I n t h e s e F i x e d a i r f o i l s , r o t o r b l a d e s , and p r o p e l l e r s a r e b e i n g s t u d i e d .

s t u d i e s , t h e a d h e s i v e s h e a r s t r e n g t h o f t h e i m p a c t i c e i s an i m p o r t a n t parame- t e r . S u r f a c e r o u g h n e s s and t h e s t a t i s t i c a l n a t u r e o f t h e d a t a m u s t be c o n s i d - e r e d . For r o t a t i n g s u r f a c e s , n o t o n l y i s t h e a d h e s i v e s t r e n g t h i m p o r t a n t b u t a l s o t h e t e n s i l e s t r e n g t h o f t h e i c e p e r p e n d i c u l a r t o t h e d i r e c t i o n o f g r o w t h .

A t t h e p r e s e n t t i m e , t h e f i n i t e e l e m e n t a n a l y s i s o f r o t a t i n g a i r f o i l s i s b e i n g emphasized. A n a l y t i c a l r e s u l t s w i l l be compared t o r e c e n t d a t a from t h e OH-58 t a i l r o t o r t e s t s i n t h e I R T . The s t a t i s t i c a l n a t u r e o f t h e f r a c t u r e o f i m p a c t i c e w i l l be c o n s i d e r e d i n t h e a n a l y s i s .

J ~ ~ The NASTRAN f i n i t e e l e m e n t code was a l s o used t o p r e d i c t d e i c i n g of an E I D I i c e p r o t e c t i o n s y s t e m , f o r w h i c h e x p e r i m e n t a l d a t a was a v a i l a b l e ( R e f . 4 6 ) . Even t h o u g h a d d i t i o n a l c o r r e l a t i o n s w i t h o t h e r d a t a a r e needed, r e s u l t s from t h i s i n i t i a l s t u d y were e n c o u r a g i n g .

T h e r e i s a p o s s i b i l i t y t h a t a f r a c t u r e m e c h a n i c s a p p r o a c h c o u l d be u s e d t o p r e d i c t t h e p e a l i n g o f i c e from d e i c i n g systems such as a p n e u m a t i c b o o t .

D a t a o b t a i n e d from p e a l i n g measurements i s b e i n g r e d u c e d t o o b t a i n t h e c r i t i c a l s t r e s s i n t e n s i t y c o n s t a n t o f f r a c t u r e m e c h a n i c s .

REFERENCES 1 . Reinmann, J . J . , Shaw, R.J., and O l s e n . W . A . ; " A i r c r a f t I c i n g Research a t NASA," June 1982, NASA TM-82919.

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Shaw, R J ; " P r o g r e s s Toward t h e Development o f an A i c r a f t I c i n g A n a l y s i s C a p a b i l i t y , " Jan. 1984, A I A A Paper 0 1 0 5 .

3 . Shaw, R.J., P o t a p c z u k , M . G . , and B i d w e l l , C . S . ; " P r e d i c t i o n s o f A i r f o i l Aerodynamic P e r f o r m a n c e D e g r a d a t i o n Due t o I c i n g , " F o u r t h Symposium o n N u m e r i c a l and P h y s i c a l A s p e c t s o f Aerodynamic Flows, J a n . 1989.

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5 . K e i t h , T . G . , D e W i t t , K.J., W r i g h t , W.B., and M a s i u l a n i e c , K.C., " O v e r v i e w o f N u m e r i c a l Codes D e v e l o p e d f o r P r e d i c t e d E l e c t r o t h e r m a l D e - I c i n g of A i c r a f t B l a d e s , " J a n . 1988, A I A A Paper 88-0288.

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O l s e n , W . A . , Shaw, R.J., and Newton, J . , " I c e Shapes and t h e R e s u l t i n g D r a g I n c r e a s e f o r a NACA 0012 A i r f o i l , " J a n . 1984, NASA TM-83556.

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Van Fossen, G . J . , Semonian, R . J . , O l s e n , W . A . , and Shaw, R . J . , " H e a t T r a n s f e r D i s t r i b u t i o n s A r o u n d Nominal I c e A c c r e t i o n Shapes Formed o n a C y l i n d e r i n t h e NASA L e w i s I c i n g R e s e a r c h T u n n e l , " J a n . 1984, A I A A Paper 84-001 7 .

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S c o t t , J.N., G i e l d a , T . P . , and Hankey, W.L., " N a v i e r - S t o k e s S o l u t i o n s of F l o w f i e l d C h a r a c t e r i s t i c s P r o d u c e d b y I c e A c c r e t i o n , " Jan. 1988, A I A A Paper 88-0290.

2 0 13. M e s s i n g e r , B . L . ; " E q u i l i b r i u m T e m p e r a t u r e o f an U n h e a t e d I c i n g S u r f a c e as a F u n c t i o n o f A i r s p e e d , " J o u r n a l o f A e r o n a u t i c s S c i e n c e s , J a n . 1958.

14. O l s e n , W . , and W a l k e r , E . , " E x p e r i m e n t a l E v i d e n c e f o r M o d i f y i n g t h e C u r r e n t P h y s i c a l Model f o r I c e A c c r e t i o n o n A i r c r a f t S u r f a c e s , " May 1986, NASA TM-87 1 84, 15. Hansman, R.J., and T u r n o c k , S . R . , " I n v e s t i g a t i o n o f M i c r o p h y s i c a l Fac- tors Which I n f l u e n c e S u r f a c e Roughness D u r i n g G l a z e I c e A c c r e t i o n , " F o u r t h I n t e r n a t i o n a l C o n f e r e n c e o n A t m o s p h e r i c I c i n g o f S t r u c t u r e s , S e p t .

1988.

16. Hansman, R . I . , Yamaguchi, K . , B e r k o w i t z , B . , and P o t a p c z u k , M . , "Model- i n g o f S u r f a c e Roughness E f f e c t s o n G l a z e I c e A c c r e t i o n , " J a n . 1989, A I A A Paper 89-0734.

17. P u l l i a m , T . H . , " E u l e r and T h i n - L a y e r N a v i e r - S t o k e s Codes: ARC3D, ARC3D," N o t e s f o r C o m p u t a t i o n a l F l u i d Dynamics U s e r ' s Workshop, The U n i v e r s i t y o f Tennessee Space I n s t i t u t e , T u l l a h o m a , TN, 1984.

18. C e b e i , T . , " E f f e c t s o f E n v i r o n m e n t a l l y Imposed Roughness o n A i r f o i l P e r f o r m a n c e , " June 1987, NASA CR-179639.

19. C e b e c i , T . , Jau, J . , V i t i e l l o , D . , and Chang, K.C., " P r e d i c t i o n o f P o s t - S t a l l Flows o n A i r f o i l s , " F o u r t h Symposium o n N u m e r i c a l and P h y s i c a l A s p e c t s o f Aerodynamic Flows, J a n . 1989.

20. P o t a p c z u k , M . G . , " P e r s o n a l Communication o n D o c t o r a l D i s s e r t a t i o n . NASA L e w i s R e s e a r c h C e n t e r , C l e v e l a n d , OH.

21. B r a g g , M . B . , and K h o d a d o u s t , A . , " E f f e c t o f S i m u l a t e d G l a z e I c e o n a R e c t a n g u l a r Wing," J a n . 1989, A I A A Paper 89-0750.

2 2 . S a n k a r , L . , Chiwu, J . , and H u f f , D . , " E v a l u a t i o n o f T h r e e T u r b u l e n c e Models f o r t h e P r e d i c t i o n o f S t e a d y and U n s t e a d y A i r f l o w s , " J a n . 1989, A I A A Paper 89-0609.

2 3 . M i k k e l s e n , K . L . , M c K n i g h t , R . C . , Ranaudo, R . J . , and P e r k i n s , P . J . , J r . , " I c i n g F l i g h t R e s e a r c h : Aerodynamic E f f e c t s o f I c e and I c e Shape Documen- t a t i o n W i t h S t e r o P h o t o g r a p h y , " J a n . 1985, A I A A Paper 85-0468 24. M i k k e l s e n , K . , J u h a s z , N . , Ranaudo, R . , and M c K n i g h t , R . , " I n - F l i g h t Measurements o f Wing I c e Shapes and Wing S e c t i o n D r a g I n c r e a s e s Caused by N a t u r a l I c i n g C o n d i t i o n s , " A p r . 1986, N A S A TM-87307.

25. Ranaudo, R . J . , M i k k e l s e n , K . L . , M c K n i g h t , R . C . , I d e , R . F . , and R e e h o r s t , A . L . , "The Measurement o f A i r c r a f t P e r f o r m a n c e and S t a b i l i t y and C o n t r o l A f t e r F l i g h t Through N a t u r a l I c i n g C o n d i t i o n s , " A p r . 1986, A I A A Paper 86-9758.

2 6 . I d e , R.F., and R i c h t e r , G . P . , " C o m p a r i s o n o f I c i n g C l o u d I n s t r u m e n t s for 1982-1983 I c i n g Season F l i g h t Program," J a n . 1984, NASA TM-83569.

27. Ranaudo, R.J., M i k k e l s e n , K . L . , M c K n i g h t , R . C . , and P e r k i n s , P.J., J r . , " P e r f o r m a n c e D e g r a d a t i o n o f a T y p i c a l Twin Engine Commuter Type A i r c r a f t i n Measured N a t u r a l I c i n g C o n d i t i o n s , " 1984, NASA TM-83564.

28. Ranaudo, R . J . , B a t t e r s o n , J.G., R e e h o r s t , A.L., Bond, T . H . , and Omara, T . M . , " D e t e r m i n a t i o n o f L o n g i t u d i n a l Aerodynamic D e r i v a t i v e s U s i n g F l i g h t Data From an I c i n g Research A i r c r a f t , " J a n . 1989, A I A A Paper 89-0754.

29. B a t t e r s o n , J.G., and O ' M a r a , T.M. " E s t i m a t i o n o f L o n g i t u d i n a l S t a b i l i t y and C o n t r o l D e r i v a t i v e s f o r an I c i n g Research A i r c r a f t From F l i g h t D a t a , " Mar. 1989, NASA TM-4099.

30. M i l l e r , T . L . , and Bond, T . H . , "An I c i n g R e s e a r c h Tunnel T e s t of a Model H e l i c o p t e r . To be p r e s e n t e d a t t h e A m e r i c a n H e l i c o p t e r S o c i e t y 4 5 t h Annual Forum and T e c h n o l o q y D i s p l a y , B o s t o n , MA, May 22-24, 1989.

31. P i k e , J.A., W a i n a u s k i , H . S . , and Boyd, L . S . , "Prop-Fan A i r f o i l I c i n g C h a r a c t e r i s t i c s , " J a n . 1989, A I A A Paper 89-0753.

32. H i l l , E . G . , Z i e r t o n , T . A . , and Runyan, J . J . , " R e s u l t s o f a F l i g h t and Wind Tunnel I n v e s t i g a t i o n o f Aerodynamic E f f e c t s o f A i r c r a f t Ground D e - / a n t i - I c i n g F l u i d s , " E f f e c t o f an A d v e r s e E n v i r o n m e n t o n F 1 i g h t , (AGARD F l i g h t M e c h a n i c s Panel Symposium), Gol, Norway, May 1989.

33. Hovanec, E . A . ; " D r o p l e t S i z i n g I n s t r u m e n t a t i o n Used f o r I c i n g R e s e a r c h : O p e r a t i o n , C a l i b r a t i o n , and A c c u r a c y ; Phase I F i n a l R e p o r t , " NASA CR- ( t o be p u b l i s h e d j o i n t l y b y NASA and FAA).

34. Hovenac, E . A . , and I d e , R . F . , " P e r f o r m a n c e o f t h e F o r w a r d S c a t t e r i n g S p e c t r o m e t e r Probe i n N A S A ' s I c i n g Research T u n n e l , " J a n . 1989, A I A A Paper 89-0769.

35. Hovenac, E . A . , H i r l e m a n , E . D . , and I d e , R . F . , " C a l i b r a t i o n and Sample Volume C h a r a c t e r i z a t i o n o f PMS O p t i c a l A r r a y P r o b e s , " I n t e r n a t i o n a l Con- f e r e n c e o n L i q u i d A t o m i z a t i o n and S p r a y Systems, J u l y 1985.

36. B a c h a l o , W.D., and Houser, J . J . , "Phase D o p p l e r S p r a y A n a l y z e r for t h e S i m u l t a n e o u s Measurements o f D r o p l e t S i z e and V e l o c i t y D i s t r i b u t i o n s , " 1984, O p t i c a l E n g i n e e r i n g , Vol. 23, no. 5 , p p . 583-590.

37. VanFossen, G . J . , " P r i v a t e C o m m u n i c a t i o n . NASA Lewis R e s e a r c h C e n t e r , C l e v e l a n d , OH.

38. Newton, J . E . , VanFossen, G . J . , P o i n s a t t e , P . E . , and d e W i t t , K . J . , "Measurement o f L o c a l C o n v e c t i v e Heat T r a n s f e r C o e f f i c i e n t s From a Smooth and Roughened NACA-0012 A i r f o i l F l i g h t T e s t D a t a , " Jan. 1988, A I A A Paper 88-0287.

39. Van Fossen, G.J.: P r i v a t e C o m m u n i c a t i o n . NASA Lewis R e s e a r c h C e n t e r , C l e v e l a n d , OH.

40. B i l a n i n , A.J., " P r o p o s e d M o d i f i c a t i o n s t o I c e A c c r e t i o n / I c i n g S c a l i n g Theory," Jan. 1988, A I A A Paper 88-0203.

41. B i l a n i n , A . J . , " P r o b l e m s i n U n d e r s t a n d i n g A i r c r a f t I c i n g Dynamics," Jan. 1988, A I A A Paper 89-0735.

M . , Scavuzzo, R.J., and O l s e n , W . , "Measurement o f A d h e s i v e Shear 42. Chu, S t r e n g t h o f I m p a c t I c e i n an I c i n g Wind T u n n e l , " P r o c e e d i n g s o f 3 r d I n t e r - n a t i o n a l Workshop o n t h e A t m o s p h e r i c I c i n g o f S t r u c t u r e s , May 1986.

R.J., Chu, J . L . , and Lam, P . D . , "Development o f a C o m p o s i t e 43. Scavuzzo, Technique i n t h e D e t e r m i n a t i o n o f t h e T e n s i l e S t r e n g t h o f I m p a c t I c e s .

P r o c e e d i n g s o f 3 r d I n t e r n a t i o n a l Workshop o n t h e A t m o s p h e r i c I c i n g o f S t r u c t u r e s , May 1986.

4 4 . Scavuzzo, R.J., Chu, M.L., and O l s e n , W.A., " S t r u c t u r a l P r o p e r t i e s o f I m p a c t I c e s A c c r e t e d a t A i r c r a f t S t r u c t u r e s , " Jan. 1987, NASA CR 179580.

45. K h a t k h a t e , A . A . , Scavuzzo, R . J . , and Chu, M . , " A F i n i t e E l e m e n t S t u d y of t h e E I D I S y s t e m , " J a n . 1988, A I A A Paper 88-0022.

4 6 . Chu, M., Scavuzzo, R . J . , and Z i a n , X . T . , " H y b r i a F i n i t e E l e m e n t - E x p e r i m e n t a l T e c h n i q u e f o r D e t e r m i n a t i o n o f I c e / I m p a c t I c e T e n s i l e S t r e n g t h , " P r o c e e d i n g s o f t h e 4 t h I n t e r n a t i o n a l C o n f e r e n c e o n A t m o s p h e r i c I c i n g o f S t r u c t u r e s , 1988.

4 7 . Scavuzzo, R.J., Chu, M.L., and B r i k m a n i s , C.K., " A d h e s i v e P e e l S t r e n g t h o f A r t i f i c i a l I c e , " P r o c e e d i n g s o f t h e 4 t h I n t e r n a t i o n a l C o n f e r e n c e o n A t m o s p h e r i c I c i n g o f S t r u c t u r e s , 1988.

ADVANCED -TURBOFANS GEARED TURBOFANS ULTRA BYPASS NG I NES 10%

f

\ FIGURE 2. - EESS CONDUCTOR GEOMETRY.

FIGURE 3. - EESS CONDUCTORS EMBEDDED IN ELASTOMERIC BOOT.

A I RCRAFT SURFACE 7, \ DOUBLERS TO CAPACITOR COIL-/' FIGURE 4. - EIDI COILS I N LEADING EDGE.

c c ..

W I -

x

A > CL I -

{ -

W > E n o o w m w

- CLEAN

I-- ICED DECAMBER I N G FIGURE 6. - AERODYNAMIC PERFORMANCE DEGRADATION DUE TO ICING.

THICK, DISTORTED BOUNDARY LAYER I FLOW RE-ATTACHMENT 7 ? 'WEPARATED FLOW ZONE Lc1 <SURFACE ROUGHNESS FIGURE 7 . - KEY ASPECTS O F AIRFOIL ICING.

a EXPERIMENTAL

e - . . . .

NAVIER-STOKES 1 FLOWFIELD

-

POTENTIAL FLOW PREDICTION

-

.go -

bl .60 Q > u

-

.48 : t !

LL

-

Y .36 I - L W

-

5 .24

Is E Q E .I2

- n

a

u

n

d o ( A ) CLEAN CYLINDER, (B) "ICED" CYLINDER.

8. - DROPLET COLLECTION EFFICIENCY COMPARISONS.

FIGURE CONVECT I ON WATER FLOW EVAPORATION IMP1 NGING WATER /

WATER FLOW I .u /

INTO CV FIGURE 9. - CONTROL VOLUME ANALYSIS OF ICE ACCRETION PROCESS.

COMPARISON EXPERIMENTAL MVD = 12 p M V , = 52 M/SEC T , = -26 OC CALCULATED COMPARISON EXPERIMENTAL = 1.20 g M / M 3 MVD = 20 p~ Lwc V , = 89 M/SEC T , = -11 OC FIGURE 10. - COMPARISON OF I C E SHAPE PREDICTIONS WITH AIRFOIL ICING DATA.

0 AIRSPEED. 209 KM/HR: LWC, 1.3 g/M3: TIME, 8 M I N TOTAL TEMPERATURE -26 OC -20 OC -18 OC -15 OC -12 OC -8 OC -5 OC -2 OC -1 OC 0 OC AIRSPEED, 338 KM/HR; LWC, 1.05 g/M3: TIME, 6.2 M I N TEMPERATURE -26 OC -17 OC -12 OC -8 OC -2 OC 0 OC (A) ICE SHAPE.

0 V = 338 KM/HR. LWC = 1 . 0 5 - g / ~ ~ , T = 6.2 MIN . 0 8 k L : -06 .04 L .02 I - u W v, -30 -20 -10 0 TOTAL TEMPERATURE, OC (B) SECTION DRAG COEFFICIENT FIGURE 11. - EFFECT OF TOTAL TEMPERATURE ON ICE SHAPE AND DRAG.

0 I I I I I I I I

-10 0 10 20 30 40 50 60 70

CYLINDER ANGLE, e

FIGURE 12. - NUSSELT NUMBER PREDICTION BASED ON INTEGRAL BOUNDARY LAYER METHOD.

Tu, ROUGH

-

x EXACT SOLUTION FOR CYLINDER 0 0.5 NO

----

0 3.5 NO -.I-- RANGE OF UNSTEADY

FLUCTUATIONS a .5 YES

0 3.5 YES

---

NUMERICAL SOLUTION FOR 15 M I N GLAZE ICE SHAPE

E

RE = 136 000 L + 1000 -I w v) v) =I L 17 15 13 11 9 8 5 3 1 GAGE NUMBER 0 20 40 60 80 ANGLE FROM STAGNATION POINT, DEG FIGURE 13. - NUSSELT NUMBER PREDICTION BASED ON NAVIER-STOKES SOLUTION OF ENERGY EQUATION.

I DROPLETS I (STREAKS 1

I- -

n -

I t ,->- AIRFOIL

I STREAM LINES I

I --

I -i---.- I FLOWING I I I WATER . 0 I \ I FILM

'I' I t ' I '

I I I I , I FIGURE 14. - EXISTING PHYSICAL MODEL FOR ICE ACCRETION.

- : \ \ , . .

AIRFOIL ( A > NO FREEZING OCCURRING (ABOVE 0 O C O R BEFORE FREEZING STOPS SURFACE DROPS).

FREEZING AT $

0 OC ALONG \\ NARY WATER DROPS ON CATCH AND ALSO INCREASE AIRSIDE HEAT TRANSFER COEFFICIENT (B) FREEZING OCCURRING.

FIGURE 15. - PROPOSED NEW PHYSICAL MODEL FOR ICING PROCESS, T = 50 SEC FIGURE 16. - CLOSE-UP PHOTO OF I C E FORMED AT -2 'C.

( A ) NORMAL LEWICE AT 45, 105, AND 150 S E C .

(B) EXPERIMENTAL RESULT AT 30, 90, AND 150 SEC.

( C ) MODIFIED LEWICE AT 45, 105, AND 150 S E C .

FIGURE 1 7 . - EXPERIMENTAL ICE SHAPE COMPARED TO MODIFIED LEWICE PRE- , D I CT LONS NACA 0012 MODEL - 2 C V -'.? 0 .2 . I ( .6 .8 1.0 X/C FLOW VISUALIZATION DETAILED SURFACE BOUNDARY LAYER PROFILES PRESSURES FIGURE 18. - CODE VALIDATION DATA BASE FOR ICED AIRFOIL PERFORMANCE.

A INTERACT I VE BOUNDARY LAYER ( I BL 1 0 NAVIER-STOKES (NS) 0 EXPERIMENT .16 U u

'20F L B

k Y t !

LL LL w u a w n 0 2 4 6 8 10 ANGLE OF ATTACK DEG a, DEG FIGURE 19. - COMPARISON OF CODE PREDICTIONS WITH EXPERIMENT FOR AN ICED AIRFOIL.

D E W PO I NT ICE DETECTOR r FORWARD STEREO / CAMERA PORT ROSEMOUNT TOTAL A I R TEMPERATURE PROBE I

k

,-AFT STEREO CAMERA PORT ROSEMOUNT ICE DETECTOR -- STEREO CAMERA PORT

ROSEMOUNT ICE DETECTOR ---L

# , - r A

c L I I m..

'- OVERHEAD EXPERIMENT '- OVERHEAD EXPERIMENT

\ I HATCH

\ i.4s-c-I

I r 858 ROSEMOUNT PROBE - V -

PNEUMATIC DE-ICER BOOTS FIGURE 20. - NASA TWIN OTTER ICING RESEARCH AIRCRAFT.

REGION 5 0 RAGGED. DIS-

0 I

i, -2 -4 - l t -6 -8 X, I N .

#

-2 0 2 4 6 x. cn FIGURE 21. - ICE SHAPE PROFILE MEASURED BY STEREO PHOTO- GRAPHY: FLIGHT 85-24B.

AIRCRAFT ANGLE OF ATTACK (REFERENCED TO AIRCRAFT WATERLINE). a. DEG FIGURE 22. - INCREASE I N WING SECTION DRAG DUE TO I C E ACCRETION; F L I G H T 85-24B.

NASA I C I N G RESEARCH AIRCRAFT FULL SCALE WING SECTION I N I R T FIGURE 23. - F L I G H T VERSUS TUNNEL COMPARISON OF A I R F O I L I C E ACCRETION AND DRAG INCREASE.

1.2 1 .o -J V .2 0 2 4 6 8 10 ANGLE O F ATTACK (REFERENCED TO AIRCRAFT FLOOR LINE), a, DEG ( A ) VARIATION OF AIRCRAFT CL VERSUS a.

.12 a .10 I - L k ! !

E .08 LL W V LI -0- ALL ICED

2 .06

-+-- WINGS DEICED

-*- WINGS AND

EMPENNAGE D E ICED .04 BASEL I N E

no2 1 1 1 1 1 1

0 .2 .4 .6 . 8 1 .o LIFT COEFFICIENT SQUARED, Cf (B) SHIFT I N AIRCRAFT DRAG POLAR.

FIGURE 24. - EFFECT O F GLAZE ICE ON AIRCRAFT LIFT CURVE A N D DRAG POLAR: FLIGHT 83-10.

!i 200 r

( A ) FLIGHT TEST DATA CORRECTED TO STANDARD oi W DAY. SEAL LEVEL, AND STANDARD WEIGHT CON- n DITIONS.

w 8 1000 I F cn 5E 900 I - , O N E ENGINE POWER AVAILABLE -0- ALL ICED --El--- WINGS DEICED --&- WINGS AND - /*- EMPENNAGE DEICED BASEL I NE 60 80 100 120 140 160 180 TRUE AIRSPEED, KNOTS ( B > TEST CONDITIONS AT 6000 FT FLIGHT TEST TO STANDARD WEIGHT ONLY.

DATA CORRECTED FIGURE 25. - EFFECT OF GLAZE ICE ON POWER REQUIRED COMPARED TO ONE ENGINE POWER AVAILABLE: FLIGHT 83-10.

FIGURE 26. - 'STYROFOAM I C E ' BONDED T O LEADING EDGE OF HORIZONTAL TAIL.

-1.4

- FLAPS: 0 DEG

-1.6

- Q15,$@P 0

Q Q 0

a l

G o o w

-

r -1.8 V

Q

0 C n b e -2.0 0 C M b e ICE

- 9 Po

20 ERRORS I I I I Q 9 , -2.2 END VIEW OF TYPICAL OH-58 ICED OH-58 T A I L ROTOR R I G I N IRT ROTOR BLADE ICE SHAPE NEXT ROTOR TEST I N I R T : OH-58 T A I L ROTOR R I G DRIVE SIKORSKY POWERED FORCE SYSTEM MODEL WITH 6-COMPONENT INTERNAL FORCE BALANCE FIGURE 28. - ROTORCRAFT ICING TESTS I N NASA IRT.

- FIGURE 29. I C E ACCRETION ALONG SPAN OF OH-58 T A I L ROTOR.

44 ORIGINAL PAGE BLACK AND WHITE P H O W ~ m -I I I- L L W x

x

I- o z I-

s

10 { ( O( ICING TEST IN THE NASA IRT.

P FIGURE 31. - BOEING 737-200 ADV HALF MODEL WITH GROUND PLANE, INSTALLED I N NASA I R T .

ORIGINAL PAGE

m m ANI, WHITE PWTOGRAPH

L ._ ORIGINAL PA%F BLACK AND WHITE PHOTOGRAPH FIGURE 32. - FRONT VIEW OF 2 D AIRFOIL MODEL (BOEING 737-200 ADV) INSTALLED BETWEEN SPLITTER WALLS I N NASA IRT.

0 NASA LEWIS IRT AT a = 8 DEG 0 2D MODEL

FLAPS 5, SEALED SLAT AT c

%A*

n

. --_- FIGURE 33. - LIFT LOSS OF EXPERIMENTAL TYPE I1 GROUND DEICING FLUIDS COMPARED WITH ORIGINAL TYPE I (1) AND TYPE I 1 (3) FLUIDS.

~ ~ ~ _ _ _ ~ ( A > COMPONENTS O F THE CALIBRATOR, (B> CALIBRATOR ATTACHED TO FSSP.

FIGURE 34. - ROTATING PINHOLE CALIBRATOR.

I- 30 W

-

a W 0 10 20 30 40 50 60 70 80 90 100 PINHOLD DIAMETER. UM FIGURE 35. - CALIBRATION OF FSSP USING ROTATING PINHOLES .

0 PINHOLES 10 0 GLASS BEADS (NASA) 0 GLASS BEADS (MANUAL) W A DROPLET GENERATOR =I CT + v) =I E x 0 = E 1 C T -

O 0 0 .\- CALIBRATION TREND

W C T + w w I- -5

-'. 0

z g -\

n -

\ o O A

n n -10 W @ = '\ D v) '.

W E -15 O A -20 0 10 20 30 40 50 60 70 80 90 100 DIAMETER, pM FIGURE 36. - CALIBRATION ACCURACY O F THE EXTENDED- RANGE FSSP.

650 -

600 -

MORE THAN 50% O F THE COUNTS 5 TO 50% OF THE COUNTS

550 -

LESS THAN 5% OF THE COUNTS

- L I N E OF PERFECT CALIBRATION

500 -

5 450 -

=

-

w 400 I - W E

2 350 -

n n

2 300 -

m

2 250 -

E CL

-

a 200

150 -

-

0 50 100 150 200 250 300 350 400 450 500 550 600 650 RECICLE DISK DIAMETER, P M FIGURE 37. - CALIBRATION CURVE FOR THE OAP USING THE ROTATING RETICLE.

"5000-HP FAN SYSTEM"

\

"VAR ICHRON SYSTEM"

(I> 0-0.4

"SPRAY BAR \ CONTROLS BUILDING"

/ \

/

"6- BY ~ - F T 20 FT LONG" "CONTROL ROOM" "SPRAY BAR SYSTEM" FIGURE 38. - SCHEMATIC OF NASA I C I N G RESEARCH TUNNEL FLOW CIRCUIT.

10 20 30 40 50

5 28

n > 24 PRESSURE, E 20 PSIG I - 16 w

8L- 4

0 20 40 60 80 100 WATER - A I R PRESSURE, P S I D FIGURE 39. - DROPLET S I Z E CALIBRATION FOR STANDARD NOZZLES I N NASA I R T .

2.5 2.0 m r \

7 1.5

V 1 .o .5 0 10 20 30 40 50 DROPLET S I Z E (MVD), U M FIGURE 40. - OPERATING ENVELOPE FOR THE NASA I R T CLOUD AT 250 MPH.

OR tG 1 NAC PAGE

BLACK AND WHJTE PHOTOGRAPH FIGURE 41. - A I R F O I L WITH HEAT TRANSFER GAUGES SHOWN MOUNTED ON THE TWIN OTTER.

DENSE ROUGHNESS PATTERN REYNOLDS NUMBER = 1 200 000 0 F L I G H T DATA -.04 -.02 0 .02 .04 .06 .08 .IO DIMENSIONLESS DISTANCE FROM STAGNATION FIGURE 42. - COMPARISON OF HEAT TRANSFER BETWEEN F L I G H T AND NASA I R T .

N/\sA

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National Aeronautics and %ace Administration 1. Report No.

2. Government Accession No. 3. Recipient’s Catalog No.

NASA TM-101989 4. Title and Subtitle 5. Report Date NASA’s Program on Icing Research and Technology 6. Performing Organization Code 7. Author@) 8. Performing Organization Report No.

John J. Reinmann, Robert J. Shaw, and Richard J. Ranaudo E-4692 10. Work Unit No.

9. Performing Organization Name and Address 11. Contract or Grant No.

National Aeronautics and Space Administration Lewis Research Center Cleveland, Ohio 44135-3191 13. Type of Report and Period Covered Technical Memorandum 2. Sponsoring Agency Name and Address ~~ National Aeronautics and Space Administration 114. Sponsoring Agency Code Washington, D.C. 20546-0001 5 . Supplementary Notes Prepared for the Symposium on Flight in Adverse Environmental Conditions sponsored by the Flight Mechanics Panel (FMP) of AGARD, Gol, Norway, May 8-12, 1989.

6. Abstract This paper reviews NASA’s program in aircraft icing research and technology. The program relies heavily on computer codes and modern applied physics technology in seeking icing solutions on a finer scale than those offered in earlier programs. Three major goals of this program are (1) to offer new approaches to ice protection, (2) to improve our ability to model the response of an aircraft to an icing encounter, and (3) to provide improved techniques and facilities for ground and flight testing. This paper reviews the following program elements: (1) new approaches to ice protection; (2) numerical codes for deicer analysis; (3) measurement and prediction of ice accretion and its effect on aircraft and aircraft components; (4) special wind tunnel test techniques for rotorcraft icing; (5) improvements of icing wind tunnels and research aircraft; (6) ground de-icing fluids used in winter operation; (7) fundamental studies in icing; and (8) droplet sizing instruments for icing clouds.

7. Key Words (Suggested by Author@)) 18. Distribution Statement Aircraft icing Unclassified - Unlimited Subject Category 01 9. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No of pages 22. Price’ Unclassified Unclassified 54 A04 S A FORM 1626 OCT 86 *For sale by the National Technical Information Service, Springfield, Virginia 221 61 b