A rotor-mounted digital instrumentation system for helicopter blade flight research measurements

APPENDIX A METHOD O F APPLYING A T H I N AERODYNAMIC INSTRUMENTATION FAIRING ON HELICOPTER BLADES A f l i g h t - q u a l i f i e d and flight-tested method of a t t a c h i n g instrumentation t o the e x t e r n a l surface of a r o t o r blade has been developed. This method is The advantageous when measurements are needed on e x i s t i n g h e l i c o p t e r b l a d e s .

method permits attachment of the instrumentation t o an a i r f o i l s u r f a c e so t h a t no s t r u c t u r a l a l t e r a t i o n is r e q u i r e d , s t r u c t u r a l i n t e g r i t y is preserved, and aerodynamic p r o p e r t i e s of the a i r f o i l remain e s s e n t i a l l y unaltered. Figure 11 is a photograph of a t y p i c a l instrument i n s t a l l a t i o n on an a i r f o i l s e c t i o n .

Figure 12 is a c r o s s - s e c t i o n a l drawing of the e x t e r n a l l y applied instrumenta t i o n on a r o t o r c r a f t a i r f o i l .

The instrumentation is i n s t a l l e d as follows. F i r s t , t h e a i r f o i l p a i n t is removed from t h e areas where t h e instrumentation is t o be attached. The areas are cleaned, and glass fiber c l o t h is bonded t o t h e a i r f o i l by means of a f u e l - r e s i s t a n t adhesive. The adhesive resists degradation by petroleum f u e l s a s t r i p p a b l e base t o facilitate u l t i m a t e removal w i t h a solvent y e t provides without damaging t h e h e l i c o p t e r b l a d e s or instrumentation. Next, c e l l u l o s e a c e t a t e foam f i l l e r material is bonded by epoxy t o t h e a i r f o i l and trimmed t o form a t a p e r towards t h e edges. Areas are c u t out of t h e foam t o allow f o r the instrumentation. The instrumentation c o n s i s t s of a microelectronic p r i n t e d c i r c u i t board, s e n s o r s , and i n t e r c o n n e c t i n g wiring. The foam is faired t o t h e contours of the a i r f o i l and thinned t o t h e thickness of the instrumentation.

The p r i n t e d c i r c u i t board is attached w i t h epoxy along its edges. It is h e l d i n place during curing by a nonadhering l a y e r of scrim c l o t h and a vacuum bag.

The bag is placed and evacuated so t h a t a f o r c e is maintained between t h e s u r face of the blade and t h e bag.

The sensors are placed i n t h e i r recesses i n t h e foam and secured by self- vulcanizing s i l i c o n e rubber. I n t h e case of p r e s s u r e s e n s o r s , t h e sensing d i a phragms are i n s t a l l e d l e v e l and f l u s h w i t h t h e foam p r o f i l e . The instrumenta t i o n wiring is connected i n recessed wireways and h e l d i n place w i t h epoxy.

After the wiring and instrumentation checkout is completed, t h e remaining voids are f i l l e d w i t h an epoxy silica f i l l e r and worked t o a smooth s u r f a c e .

F i n a l l y , three layers of epoxy-resin-saturated g l a s s f i b e r c l o t h , 25.4 p m t h i c k , are a p p l i e d , w i t h c u t o u t s f o r t h e instrumentation. A f o u r t h layer is t h e sensors. Each l a y e r a p p l i e d which covers t h e p r i n t e d c i r c u i t board but not is c u t t o overlap t h e preceding layer t o provide a smooth t r a n s i t i o n of lami n a t e . The e n t i r e assembly is sanded w i t h f i n e a b r a s i v e s t o provide a smooth aerodynamic s u r f a c e . A n epoxy p a i n t is a p p l i e d over t h e glass fiber f o r weather p r o t e c t i o n .

The instrumentation can be removed from the blade by s t r i p p i n g t h e glass fiber c l o t h after s o f t e n i n g t h e epoxy bond w i t h a s o l v e n t . After t h e i n s t r u mentation is removed, t h e c i r c u i t board, s e n s o r s , and h e l i c o p t e r blades are reusable.

APPENDIX B SENSORS AND INSTRUMENTATION SUBASSEMBLIES Sensors An example of each type o f AH-1G r o t o r sensor is shown i n figure 13.

Blade p i t c h and teeter angles are measured w i t h c o n t r o l p o s i t i o n transducers (CPT) which are mechanically coupled t o the h e l i c o p t e r blade. The CPT sensing element is a p r e c i s i o n r o t a r y potentiometer t h a t provides approximately 3600 of electrical r o t a t i o n . The potentiometers are e x c i t e d by a 2 6 V dc r e g u l a t o r and have a combined h y s t e r e s i s and n o n l i n e a r i t y of 0.2 percent of the f u l l - s c a l e range of t h e potentiometer r e s i s t a n c e .

Rotor azimuth angle is measured by a d i g i t a l shaft encoder which is mounted i n s i d e t h e c a n i s t e r assembly. The encoder is an electromechanical device t h a t converts t h e s h a f t angle using c o n t a c t c l o s u r e s . The c o n t a c t clo s u r e s are provided by brushes which ride on m u l t i p l e t r a c k s of a coded drum.

Each t r a c k o p e r a t e s as a more familiar generator commutator with conducting and nonconducting segments arranged i n a Gray code d i g i t a l format. The encoder generates an e i g h t - b i t d i g i t a l word by providing c o n t a c t c l o s u r e s which s i n k c u r r e n t from +5-V l o g i c d e t e c t o r c i r c u i t s located i n t h e c a n i s t e r . The encoder h a s a f u l l - s c a l e range of 3600. The e i g h t - b i t code d i v i d e s t h e 3600 range i n t o 256 segments which provide r o t o r l o c a t i o n i n 1.40 increments. The measurement accuracy of t h e s h a f t encoder commutator is 0.3O. The encoder o p e r a t e s i n - f l i g h t a t 5.4 r p s and is sampled approximately 185 times p e r 3600 r e v o l u t i o n .

The encoder is approximately 2.5 c m i n diameter and 3 c m high. A d e s c r i p t i o n of t h e mechanical i n s t a l l a t i o n of t h e shaft encoder is covered i n t h e s e c t i o n "Canister Mechanical Design Features" i n t h i s appendix.

Absolute p r e s s u r e measurements are made with semiconductor s t r a i n gages as t h e sensing elements which are connected i n a four-active-arm Wheatstone bridge c o n f i g u r a t i o n , having approximately a 500-R bridge r e s i s t a n c e . Each bridge is compensated t o minimize thermal z e r o s h i f t and s e n s i t i v i t y e r r o r s .

The semiconductor gages measure s t r a i n i n a beryllium-copper diaphragm which is 6.3 mm i n diameter and 0.76 mm t h i c k . The pressure sensor is bonded t o a s t a i n l e s s steel mounting p a l l e t 1.9 c m i n diameter. The t o t a l thickness of a sensor and pallet is about 1.9 1 1 1 1 1 1 . The pressure sensors are e x c i t e d by +4 V dc and have t h e following characteristics: s e n s i t i v i t y of 1.0 mV/kPa, temperature effect on zero of 0.06 percent f u l l s c a l e per OC, temperature e f f e c t on s e n s i t i v i t y of 0.06 percent f u l l scale p e r OC, combined h y s t e r e s i s and l i n e a r i t y e r r o r o f 0.3 percent f u l l scale, and a n a t u r a l frequency of 30 kHz. The volume of t h e p r e s s u r e sensor i n s t a l l a t i o n c a v i t i e s is very s m a l l and has n e g l i g i b l e effect on t h e desired dynamic response. The t y p i c a l fre quency response of t h e sensor is f l a t w i t h i n 0.6 percent of the a p p l i e d pres s u r e l e v e l from dc t o 200 Hz, and t& n a t u r a l frequency o f t h e combined sensor and i n s t a l l a t i o n c a v i t y is about 800 Hz. The f i l t e r c h a r a c t e r i s t i c s of t h e c a v i t y combined w i t h t h e resistance-capacitance ( R C ) f i l t e r characteristic of each measurement channel provide ample a t t e n u a t i o n of unwanted a c o u s t i c a l n o i s e pressure. The sensors are held i n s i d e t h e r o t o r blade c a v i t i e s by dowel p i n s and rubber i n s e r t s t o provide n e g l i g i b l e sensor output due t o s t r a i n produced

APPENDIX B by the r o t o r blade bending. The sensors are also unaffected by t h e o p e r a t i o n a l a c c e l e r a t i o n l e v e l s near t h e blade t i p . E x c i t a t i o n and s i g n a l wires f o r t h e pressure sensors i n t e r f a c e d i r e c t l y w i t h t h e remote m i c r o e l e c t r o n i c blade s t a t i o n .

Moment and f o r c e measurements are made w i t h approximately 0.08-mm-thick metal-foil s t r a i n gages (see ref. 2) connected i n a four-active-arm Wheatstone bridge arrangement. S t r a i n gages are i n s t a l l e d on t h e h e l i c o p t e r blade a t var i o u s l o c a t i o n s t o measure bending moments. Three a d d i t i o n a l s t r u c t u r a l members are instrumented with s t r a i n gages. The first is the r o t o r mast f o r measuring mast torque, t h e second is the r o t o r blade p i t c h l i n k f o r measuring a p p l i e d f o r c e , and the t h i r d is t h e r o t o r drag brace f o r measuring applied f o r c e . The i n d i v i d u a l s t r a i n gages within each four-active-arm bridge are matched f o r equal r e s i s t a n c e t o provide n e g l i g i b l e thermal z e r o s h i f t and s e n s i t i v i t y s h i f t . The gages are e x c i t e d by a 26 V dc r e g u l a t o r and have the following c h a r a c t e r i s t i c s : bridge r e s i s t a n c e of 350 fi 2 1 p e r c e n t , gage f a c t o r of 2.0, 20.1-percent n o n l i n e a r i t y , and 20.15-percent hysteresis. Leads from t h e moment gages are run down t h e top o f the blade t o a connector l o c a t e d on t h e blade c l o s e t o t h e hub. Power and s i g n a l leads f o r the moment and f o r c e sensors i n t e r f a c e w i t h t h e c a n i s t e r e l e c t r o n i c s . Offset r e s i s t o r s are added t o each Wheatstone b r i d g e measuring c i r c u i t as required t o o b t a i n t h e d e s i r e d quiescent s i g n a l operating p o i n t .

Temperatures are measured w i t h a s i n g l e a c t i v e temperature-sensitive ele ment and t h r e e f i x e d r e s i s t o r s mounted together t o form a Wheatstone b r i d g e sensor. Two of t h e s e n s o r s measure temperature near the blade t i p and use a n i c k e l r e s i s t i v e sensing element. The first, which measures blade temperature near t h e p r e s s u r e transducers, is mounted on a metal p a l l e t 1.9 c m i n diameter.

The t o t a l thickness of sensor and p a l l e t is 1.9 mm. The second sensor is bonded t o t h e remote m u l t i p l e x e r - d i g i t i z e r p r i n t e d c i r c u i t board and measures e l e c t r o n i c s temperature. Both sensors i n t e r f a c e w i t h t h e remote e l e c t r o n i c sta t i o n and o p e r a t e from +4 V dc. A t h i r d sensor which u s e s a s i l i c o n t h e r m i s t o r a c t i v e element is mounted on a c a n i s t e r p r i n t e d c i r c u i t board and measures c a n i s t e r i n t e r n a l temperature. It i n t e r f a c e s w i t h t h e c a n i s t e r e l e c t r o n i c s and is excited by 26 V dc. The s e n s i t i v i t y of the s e n s o r s is set a t approxi mately 0.8 mV/OC, and there is no d i s c e r n i b l e hysteresis. The sensors are capable of measuring temperature a t their mounting l o c a t i o n within 21.00 C.

Remote Multiplexer-Digitizer S t a t i o n Under c o n t r o l o f the hub-mounted c a n i s t e r , t h e remote blade-mounted elec t r o n i c s shown i n f i g u r e 4 provides e x c i t a t i o n , a m p l i f i c a t i o n , sampling, and analog-to-digital (A-to-D) conversion of 15 AH-1G sensors. The data are returned t o t h e c a n i s t e r as a s e r i a l ’ n o n r e t u r n t o z e r o l e v e l (NRZ-L) PCM t r a i n and become channels 1 t o 15 of t h e master PCM frame. Figure 14 is a block diagram of t h e remote m u l t i p l e x e r - d i g i t i z e r .

Capability is provided t o accommodate m i l l i v o l t - l e v e l s i g n a l s from up t o 25 sensors. Each channel has its own s i g n a l conditioning a m p l i f i e r which con t a i n s a single-pole RC filter. Gain, o f f s e t , and frequency response of each

APPENDIX B channel are i n d i v i d u a l l y adjusted t o maintain t h e analog s i g n a l w i t h i n the desired o p e r a t i n g range. Each a m p l i f i e r output is a p p l i e d t o a separate v o l t age l e v e l comparator with sampling accomplished by d i g i t a l multiplexers which s e q u e n t i a l l y select the a p p r o p r i a t e comparator. An e i g h t - b i t A-to-D conversion is made with a successive approximation r e g i s t e r ( S A R ) . The SAR c o n t r o l s a r e s i s t i v e ladder network whose output is buffered and applied as a r e f e r e n c e f o r a l l the i n d i v i d u a l channel comparators. The conversion is implemented by successively comparing the r e f e r e n c e feedback voltage with the amplified sensor voltage one b i t a t a time beginning with t h e most s i g n i f i c a n t b i t . The output of t h e A-to-D converter is a serial NRZ-L PCM t r a i n of e i g h t - b i t binary-coded data words representing t h e analog data sampled by t h e blade s t a t i o n e l e c t r o n i c s .

The remote s t a t i o n accepts regulated 215 V dc and unregulated +5 V dc from t h e c a n i s t e r f o r the analog and d i g i t a l c i r c u i t r y and g e n e r a t e s regulated +4 V dc f o r sensor e x c i t a t i o n and reference voltage f o r t h e A-to-D converter.

It a l s o a c c e p t s clock and synchronization s i g n a l s from t h e c a n i s t e r and gener ates timing and c o n t r o l s i g n a l s f o r channel sampling and A-to-D conversion.

The remote s t a t i o n is 17.8 c m by 25.4 c m . It is 2.5 mm t h i c k and weighs 0.156 kg.

Canister Multiplexer-Digitizer S t a t i o n The canister-mounted m u l t i p l e x e r - d i g i t i z e r s t a t i o n provides a m p l i f i c a t i o n , sampling, and analog-to-digital conversion of 14 AH-1G transducers connected . d i r e c t l y t o t h e c a n i s t e r . The data are converted t o a serial NRZ-L PCM t r a i n and become channels 16 t o 29 of t h e master PCM frame. Figure 15 is a block diagram of t h e c a n i s t e r m u l t i p l e x e r - d i g i t i z e r ; t h e e l e c t r o n i c s is contained on two p r i n t e d c i r c u i t boards shown i n f i g u r e 7.

The c a n i s t e r s t a t i o n can accept m i l l i v o l t - l e v e l s i g n a l s from a maximum of 16 sensors. Each s i g n a l is amplified by a gain-adjustable instrumentation a m p l i f i e r and applied t o t h e i n p u t of a 16-channel analog multiplexer. Each a m p l i f i e r channel a l s o c o n t a i n s an a d j u s t a b l e single-pole RC f i l t e r . A-to-D conversion is accomplished on each of t h e s i g n a l s by first b u f f e r i n g t h e multi plexer output and then applying t h e multiplexed s i g n a l s t o an A-to-D converter.

The A-to-D converter c o n t a i n s an i n t e r n a l voltage comparator and ladder network and o p e r a t e s on t h e successive approximation p r i n c i p l e . The output of t h e A-to-D converter is a serial NRZ-L PCM t r a i n of eight-bit binary-coded data words representing t h e analog data sampled by t h e c a n i s t e r e l e c t r o n i c s . The analog multiplexer sampling sequence and t h e A-to-D conversion are under c o n t r o l of t h e c a n i s t e r master timing and c o n t r o l e l e c t r o n i c s .

The c a n i s t e r m u l t i p l e x e r - d i g i t i z e r s t a t i o n r e q u i r e s regulated 115 V dc f o r t h e analog c i r c u i t r y , regulated +6 V dc f o r sensor e x c i t a t i o n and r e f e r e n c e voltage f o r t h e c a n i s t e r A-to-D c o n v e r t e r , and unregulated +5 V dc f o r t h e d i g i t a l c i r c u i t r y .

APPENDIX B Master T i m i n g and Control The system master t i m i n g and c o n t r o l e l e c t r o n i c s is contained on one of the c a n i s t e r p r i n t e d c i r c u i t boards shown i n f i g u r e 7. Figure 16 is a master timing and c o n t r o l diagram. ' A c r y s t a l - c o n t r o l l e d o s c i l l a t o r g e n e r a t e s a 1024-kHz clock s i g n a l which is divided by 4 t o produce a 256-kHz b i t rate clock.

The b i t rate clock is f u r t h e r divided t o produce word rate, frame rate, b i t count, and word address. For t h e AH-1G system, t h e r e are 32 words per frame and 1000 frames p e r second. A n o p t i o n a l b i t rate o f 512 kHz can be selected i n the countdown timing generator. Lower b i t rates can a l s o be obtained by u t i l i z a t i o n of a lower master clock frequency.

A programmable read only memory (PROM) is used t o program t h e combination of data channels and c o n t r o l t h e system timing. The PROM is sequenced by t h e word addresses from the clock countdown timing generator. The PROM a l s o con t r o l s the generation of two frame synchronization words. The system provides a m u l t i p l e x e r - d i g i t i z e r c a p a b i l i t y f o r 30 channels - any combination of up t o 25 remote channels and up t o 16 c a n i s t e r channels. The AH-1G system is pro grammed f o r a combination of 15 remote channels, 15 c a n i s t e r channels, and 2 frame synchronization words.

Output c o n t r o l s i g n a l s are s e n t t o both the c a n i s t e r and t h e remote m u l t i p l e x e r - d i g i t i z e r s t a t i o n s . The c a n i s t e r s t a t i o n r e c e i v e s b i t and word rate clocks f o r c o n t r o l l i n g t h e A-to-D converter and four d i s c r e t e binary b i t s for cycling the analog multiplexer switch. The remote s t a t i o n r e c e i v e s a b i t rate clock and a master frame rate reset pulse t o c o n t r o l the remote channel sampling and A-to-D conversions.

Serial NRZ-L d i g i t a l data from both t h e c a n i s t e r and t h e remote m u l t i p l e x e r - d i g i t i z e r s t a t i o n s and p a r a l l e l data from the azimuth angle shaft encoder are accepted by the master timing and c o n t r o l e l e c t r o n i c s t o form a master serial PCM frame. Under PROM c o n t r o l , a complete 32-word frame is generated as follows : ( 1 ) F i f t e e n remote s t a t i o n analog channels are synchronized, sampled, and converted t o serial d i g i t a l words d u r i n g time s l o t s 1 t o 15 of t h e main frame .

(2) Fourteen c a n i s t e r s t a t i o n analog channels are synchronized, sampled, and converted t o serial d i g i t a l words during time s l o t s 16 t o 29.

( 3 ) The azimuth angle d i g i t a l sensor is converted from p a r a l l e l Gray code t o o f f s e t binary and is output s e r i a l l y during time s l o t 30.

( 4 ) Data combiner gates select, a t t h e proper t i m e , serial words 16 t o 29 from t h e c a n i s t e r A-to-D converter, word 30 from t h e d i g i t a l shaft encoder, and words 31 and 32 from t h e PCM frame synchronization generator.

(5) The r e s u l t i n g words 16 t o 32 a r e merged by t h e master data combiner gates w i t h words 1 t o 15 from the remote blade s t a t i o n t o form t h e complete

APPENDIX B PCM main frame. The combined 256-kilobit NRZ-L data are converted t o biphase l e v e l (Si$-L) code and s e n t t o t h e t r a n s m i t t e r located i n t h e c a n i s t e r .

The master timing and c o n t r o l l o g i c c i r c u i t s r e q u i r e unregulated +5 V dc i n a d d i t i o n t o regulated -9 V dc f o r the PROM.

Airborne Telemetry and Data Recording PCM data are telemetered from t h e r o t o r t o t h e ground and t o t h e h e l i c o p t e r fuselage where they are received and recorded on t h e magnetic t a p e recorder.

Figure 8 is a photo Figure 7 shows the t r a n s m i t t e r and its a s s o c i a t e d antenna.

graph of the r e c e i v e r and tape recorder. Figure 17 is a photograph of the fuselage-mounted r e c e i v i n g antenna.

The t r a n s m i t t e r is 8.3 c m by 3.4 c m by 5.7 c m and has an output power of 1 W. It o p e r a t e s d i r e c t l y from t h e 28-V b a t t e r y and r e q u i r e s 16 W. The t r a n s mitter is an L-band frequency-modulation type w i t h t h e following character istics: rf power output of 1 W, carrier deviation of +600 kHz, frequency response from 10 Hz t o 1 MHz, and deviation s e n s i t i v i t y of i200 kHz/V peak t o peak. The t r a n s m i t t i n g antenna, mounted on t h e top of t h e c a n i s t e r , is a quarter-wave monopole s p i k e which provides an omnidirectional r a d i a t i o n p a t t e r n i n t h e azimuthal plane. The antenna is approximately 1.3 cm i n diameter and 5.1 c m high.

The fuselage-mounted L-band r e c e i v e r has an i n p u t s e n s i t i v i t y of -85 deci b e l s below a I-mV l e v e l and an output s e n s i t i v i t y of 0.01-V peak p e r kHz devia t i o n . The unit is 4.4 c m by 17.8 cm by 8.3 c m . The r e c e i v e r o p e r a t e s from 28 V d c and r e q u i r e s 3.5 W. The receiving antenna is a low-profile type which is mounted on t h e top of t h e cockpit canopy and conforms t o t h e e x t e r i o r s u r face. The antenna c o n s i s t s of a m i c r o s t r i p d i s k which is constructed on a 0.16-cm-thick laminate material. The rf c h a r a c t e r i s t i c s of t h e antenna are equivalent t o a quarter-wave monopole spike which provides an omnidirectional receiving p a t t e r n i n t h e azimuthal plane.

The fuselage-mounted magnetic tape recorder is a 14-channel analog u n i t which meets t h e Inter-Range Instrumentation Group ( I R I G ) Telemetry Standards (ref. 3) f o r Wideband I1 direct recording. The recorder is operated a t 76.2 cm/sec f o r a maximum o f 30 minutes and provides a bandwidth from 400 H z t o 500 kHz. The recorder can operate a t s i x speeds between 4.76 cm/sec and.

152.4 cm/sec. The recorder is approximately 40.6 c m by 30.5 c m by 12.7 c m .

I n order t o avoid e r r o r s caused by b i t j i t t e r due t o v a r i a t i o n s i n tape speed during recording and playback, t h e Bi4-L code w a s s e l e c t e d f o r t h e PCM output data. The Bi4-L code has a t r a n s i t i o n d e n s i t y of a t least one t r a n s i t i o n per b i t t i m e which enables the data processing s t a t i o n t o lock on t h e reproduced PCM data during playback of the f l i g h t tape and maintain frame synchronization i n t h e presence o f b i t jitter caus6d by v a r i a t i o n s up t o 3 percent. The power s p e c t r a l d e n s i t y of t h e Bi4-L code has no dc frequency component; t h u s , t h e need f o r a tape recorder having dc frequency response is eliminated. The band width normally a l l o c a t e d for Bi4-L data is twice the PCM b i t rate. Thus, a tape recorder covering t h e bandwidth o f 400 Hz t o 500 kHz w a s compatible with t h e b i t rate of 256 k i l o b i t s / s e c .

APPENDIX B Power D i s t r i b u t i o n F l i g h t power f o r t h e instrumentation is provided by a nickel-cadmium bat t e r y power supply located i n the bottom of t h e c a n i s t e r . The b a t t e r y c o n t a i n s 18 cells rated a t 1.5-A-hr capacity and 11 cells rated a t 3.5-A-hr capacity.

The batteries are connected i n series t o produce +5 V , +12 V , +28 V , and -6 V.

The batteries are packaged i n a balsa wood c o n t a i n e r which is shown i n f i g u r e 7.

Figure 18 is a s i m p l i f i e d diagram of t h e power d i s t r i b u t i o n system. During ground checkout o p e r a t i o n s , power can be supplied t o t h e e l e c t r o n i c s from either the i n t e r n a l batteries or through an umbilical cable from e x t e r n a l power sup p l i e d under c o n t r o l of t h e ground support equipment ( G S E ) . The system is turned on by a c e n t r i f u g a l switch mounted i n the c a n i s t e r when t h e r o t o r speed exceeds 114 rpm. System voltage r e g u l a t i o n and dc-to-dc conversion are performed i n the c a n i s t e r with t h e exception of +4 V dc which is regulated i n t h e remote e l e c t r o n i c s f o r the b l a d e s t a t i o n sensors and A-to-D converter r e f e r e n c e . The regulated voltages generated i n t h e c a n i s t e r are k6 V dc f o r c a n i s t e r sensor e x c i t a t i o n and A-to-D converter r e f e r e n c e , 215 V dc f o r a l l system analog c i r c u i t r y , and -9 V dc required by the PROM. The system l o g i c c i r c u i t s and t h e t r a n s m i t t e r are powered by unregulated b a t t e r y v o l t a g e of +5 V and +28 V , r e s p e c t i v e l y . The b a t t e r y outputs are protected from overload by f u s e s .

Canister Mechanical Design Features The c a n i s t e r and its instrumentation are shown i n f i g u r e 7. The c a n i s t e r c o n t a i n s three p r i n t e d c i r c u i t boards, t h e b a t t e r y power supply, t h e t r a n s mitter, and t h e antenna. The batteries are packaged i n the bottom of t h e c a n i s t e r t o provide a low c e n t e r of g r a v i t y . The p r i n t e d c i r c u i t boards and are assembled on a metal b a s e p l a t e and mounted over the top of t h e t r a n s m i t t e r b a t t e r y . The c a n i s t e r design permits easy i n s t a l l a t i o n and removal of elec t r o n i c s and batteries through t h e t o p cover f o r s e t u p , maintenance, and bat t e r y charging. Electrical connectors provide quick connection or s e p a r a t i o n of the c a n i s t e r electrical-mechanical i n t e r f a c e . The c a n i s t e r a l s o c o n t a i n s the umbilical i n t e r f a c e connector f o r e x t e r n a l power operation and i n t e r n a l / e x t e r n a l c o n t r o l .

A s i m p l i f i e d drawing of t h e c a n i s t e r mechanical assembly excluding t h e e l e c t r o n i c s and batteries is shown i n f i g u r e 19. Figure 20 is a photograph of the c a n i s t e r mounted on t h e AH-1G r o t o r . The c a n i s t e r , approximately 26.7 c m i n diameter and 18.4 c m high, is attached t o a support assembly which is approximately 7.6 c m i n diameter and 14.8 c m high. The c a n i s t e r and support assembly are attached t o t h e r o t o r by a s p e c i a l nut which r e p l a c e s t h e standard AH-1G r o t o r mast nut and is screwed onto t h e r o t o r mast. The base of t h e attachment nut is approximately 10.4 c m i n diameter and 5.7 c m high. The com p l e t e c a n i s t e r assembly including e l e c t r o n i c s and batteries weighs 13.4 kg.

The d i g i t a l shaft encoder housing is mounted i n s i d e t h e c a n i s t e r support assembly. The c a n i s t e r , support assembly, and encoder housing t u r n w i t h t h e r o t o r . The shaft of t h e encoder is held s t a t i o n a r y by a spacer shaft which is

APPENDIX B connected t o a nonrotating standpipe. The standpipe is a hollow t u b e attached t o the bottom of the h e l i c o p t e r transmission and extends through the hollow r o t o r mast. The standpipe has a v e r t i c a l s l o t which couples with a shear p i n i n t h e spacer.

P r e f 1 i gh t Calibrat i on A n abbreviated c a l i b r a t i o n procedure is performed on t h e instrumentation p r i o r t o each flight. The procedure c o n s i s t s of recording on the aircraft t a p e recorder the system d i g i t a l values corresponding t o ( 1 ) an llambientlf reading of a l l sensor channels, (2) t w o l e v e l s of a p p l i e d pressure f o r each p r e s s u r e sensor, and ( 3 ) a shunt resistor c a l i b r a t i o n of the moment and f o r c e sensors.

The p r e f l i g h t c a l i b r a t i o n s are used during data reduction t o c o r r e c t the sensors f o r any long-term d r i f t and t o c o r r e c t the p r e s s u r e sensors f o r any temperature e r r o r s which occur i n f l i g h t .

.. .

APPENDIX C DERIVATION O F EQUATIONS AND PROCEDURE F O R PRESSURE SENSOR DATA REDUCTION Symbols . The following list includes symbols which are used i n t h i s appendix. Some of them were defined i n the main t e x t and are redefined h e r e f o r completeness.

D PCM d i g i t a l output value (range 0 t o 255 counts) s l o p e r e p r e s e n t i n g sensor response at p r e f l i g h t c a l i b r a t i o n m l temperature, Pa/mV s l o p e r e p r e s e n t i n g sensor response a t any temperature, Pa/mV m i ( T I h l change i n m l per change i n temperature f o r p r e s s u r e sensor m 2 s l o p e r e p r e s e n t i n g PCM e l e c t r o n i c response, mV/digital increment P p r e s s u r e , Pa i n p u t p r e s s u r e , Pa P i pressure which produces zero output from sensor a t p r e f l i g h t C a l i P O b r a t i o n temperature, Pa pressure which produces zero output from sensor a t any PJT) temperature, Pa A P O change i n po per change i n temperature f o r pressure s e n s o r , Pa p(T) corrected p r e s s u r e a t any temperature, Pa uncorrected p r e s s u r e , Pa P U T temperature of sensing element f o r which temperature c o e f f i c i e n t s are a v a i l a b l e , OC AT d i f f e r e n c e i n temperature between p r e f l i g h t c a l i b r a t i o n condition and a c t u a l temperature a t t i m e of measurement f o r sensor, OC temperature d i f f e r e n t i a l between two data sets u t i l i z e d t o o b t a i n *Tr a c o r r e c t i o n c o e f f i c i e n t , O C V i n p u t t o PCM e l e c t r o n i c s required t o produce p a r t i c u l a r output count, mV i n p u t t o PCM e l e c t r o n i c s which produces z e r o d i g i t a l output value, mV VO '1 8

APPENDIX C Equations and Procedure The general equation f o r t h e p r e s s u r e sensor is p = mlV + p0 where ml is t h e s l o p e and po is t h e z e r o i n t e r c e p t as depicted i n f i g u r e 21.

The equation for: t h e PCM e l e c t r o n i c s is V = m 2 D + Vo (C2) The equation f o r t h e pressure sensor a t any temperature is Assume a l i n e a r v a r i a t i o n i n s l o p e and zero i n t e r c e p t with temperature. L e t Obtain p ( T ) by s u b s t i t u t i n g equations (C2), ( C 4 ) , and (C5) i n equation ( C 3 ) and expanding : p ( T ) = ( m l + Ami AT)(m2D + Vo) + po + Apo AT = (ml + Am1 AT)m2D + po + Apo AT + (ml + Am1 AT)Vo = (mlm2 + m 2 A m 1 A T ) D + (po + mlVo) + Apo AT + A m i AT Vo ( C 6 ) The p r e f l i g h t c a l i b r a t i o n procedure f o r t h e p r e s s u r e s e n s o r s r e s u l t e d i n t h e d i r e c t determination of t h e product (mlm2) and t h e sum (po + mlVo).

The values o f m 2 and Vo are determined from l a b o r a t o r y c a l i b r a t i o n of t h e PCM e l e c t r o n i c s . Two sets of v a l u e s of A m 1 and Apo were obtained from t h e b e s t s t r a i g h t - l i n e sensor c a l i b r a t i o n s . One set w a s computed f o r t h e temperature range from -lo C t o 24O C as follows: (c7) . 1.9

APPENDIX C A second set was obtained f o r t h e range from 240 C t o 49O C.

The uncorrected p r e s s u r e s are obtained by setting AT equal t o z e r o i n equation (C6). The c o r r e c t i o n procedure r e q u i r e s t h a t AT be computed first and then s u b s t i t u t e d i n equation ((26) w i t h the a p p r o p r i a t e Am1 and Apo t o o b t a i n the corrected p r e s s u r e s . The data shown i n f i g u r e 10(b) were obtained from t h e following equations :

P i - Pu

Uncorrected e r r o r i n % FS = )loo (c9) FS pressure

P i - p(T)

Corrected e r r o r i n % FS = )loo FS p r e s s u r e REFERENCES 1. Dean, Mills, 111; and Douglas, Richard D., eds.: Semiconductor and Conven tional Strain Gages. Academic Press, Inc., 1962.

2. Kottkamp, E.; Wilhelm, H.; and Kohl, D.: Strain Gauge Measurements on Volume 7 of AGARD Flight Test Instrumentation Series, .K. C.

Aircraft.

Sanderson and A. Pool, eds., AGARD-AG-160, Vol. 7, Apr. 1976.

3. Telemetry Working Group: Telemetry Standards - Revised January 1971.

[IRIG] Doc. 106-7 1 , Range Commanders Counc .

TABLE I.- AH-1G INSTRUMENTATION SYSTEM MEASUREMENTS Channel Maximum Measurement Range number error 1 8.7 t o 144.8 kPa 2.04 kPa pus 16.5 t o 136.0 kPa 1.79 kPa Pls 11.8 t o 127.2 kPa 1.73 kPa Pus 26.1 t o 132.2 kPa 1.59 kPa Pls 23.0 t o 118.5 kPa 5 1.43 kPa pus 6 22.2 t o 130.8 kPa 1.63 kPa Pls 7 00 t o 800 C

10 c

Tre 16.9 t o 115.5 kPa 1.48 kPa pus 38.1 t o 116.4 kPa 9 1.17 kPa Pls 00 t o 800 C

10 c

Tb 33.8 t o 114.0 kPa 1.2 kPa pus 46.1 to 121.4 kPa 1.13 kPa Pls 48.8 to 119.9 kPa 1.07 kPa pus 44.7 to 118.6 kPa 1.11 kPa Pls 15 47.6 t o 126.8 kPa 1.19 kPa Pls TABLE I.- Concluded ~ Maximum Channel Range Measurement e r r o r number ~ 400 t o -120 0.780 83/4 120 t o -120 0.3O 17 B 18 16.9 t o -12.5 kN 0.44 kN Fdb 30.5 t o -9.3 kN-m 0.60 kN-m 19 Q 20 14.2 t o -16.9 kN 0.47 kN FPl 21 27.1 t o -9.9 kN-m 0.55 kN-m MC 22 45.2 t o -26.0 kN-m 1.07 kN-m MC 0.28 kN-m 23 9.0 t o -9.9 kN-m Mb 3.6 t o -2.8 kN-m 0.10 kN-m Mb 25 3.2 t o -3.4 kN-m 0.10 kN-m Mb 0.4 t o -4.5 kN-m 0.07 kN-m M b 27 3.2 t o -1.4 kN-m 0.07 kN-m Mb 0.06 kN-m 28 2.8 t o -1.0 kN-m M t 00 t o 800 C 10 c Tce 00 t o 360° 0.3O J, - __ TABLE 11.- AH-1G DATA SYSTEM STATIC PERFORMANCE FOR BLADE PITCH ANGLE CHANNEL Error ~ Input , output, Absolute, Percent of deg deg f u l l scale deg 0.18 39.22 39.40 0.35 33.25 .06 .12 33.19 28.40 28.47 .07 .a3 24.48 -.07 24.55 .13 20.50 20.35 .15 .29 16.82 . l l 16.93 .21

-. 14

13.45 13.31 .27 9.68 . l l .21 9.57 6.23 6.15 .08 .15 2.75 2.78 .03 .06

-. 04

-.63 -. 67 .08

-4.12 -4.05 -.07 .13 -7.48 -.09 -7.57 .17 -1 1.86 -1 1.94 -.08 .15 Figure 1.- Helicopter rotor-mounted instrumentation system concept.

L-76-52 13.1 Figure 2.- AH-1G research h e l i c o p t e r .

HUB-MOUNTED Blade Moments CANISTER (8) REMOTE INSTRUMENTATION BLADE ----

- 1 STATION

Blade Pitch Angle r.

?

I

Blade Station Timing ~ Multiplexer,.

I w Multiplexer, -

I Temperature & Pitch-Link Force L-Band Pressure

I

Canister Station Temperature Temperature

I

- - - -

FUSELAGE MOUNTED

v L-BAND

r - - - - - 1 I I Separate I Airborne I Aerodynamic I Receiver & I I Inertial I Recorder I Measurements I Figure 3.- Block diagram of AH-1G airborne instrumentation system.

. " - L-75-5397 1 Figure 4 .- Microelectronic multiplexer-digitizer blade station.

L-75-7755.1 Figure 5.- Location of remote e l e c t r o n i c s and pressure sensors on AH-1G blade.

_ _ w PRESSURE or TEMPERATURE SENSOR SENSOR COVER MULTIPLEXER -DIGITIZER ELECTRONICS PRESSURE SENSOR PRESSURE PORT COVERS Figure 6.- Cross section of AH-IC helicopter blade with tip instrumentation in cavities.

4 L-77-2648.1 Figure 7.- Hub-mounted canister and instrumentation.

W i lu L-77-2645-1 Figure 8. - Fuselage-mounted instrumentation.

t n Fr 0 40 80 120 160 200 240 Digital output, counts Figure 9.- Performance of a typical PCM measurement channel.

t n Fr Y E Q) k Q) a k"

z

k

w

0 20 40 60 80 100 120 140 Absolute pressure, kPa ( a ) During l a b o r a t o r y c a l i b r a t i o n .

Figure 10.- Performance of a t y p i c a l p r e s s u r e sensor with f u l l - s c a l e range of 124.1 kPa (13.78 t o 137.88 kPa).

0 Uncorrecte m 2

\

Fr

2 1 al

Constant k P r e s s u r e of al EIC a 0 106.9 kPa k" 0 -1 k k

w

-2 -3 - 4 Constant P r e s s u r e of 44.8 kPa 0 10 20 30 40 50 60 Temperature,, OC (b) Before and after c o r r e c t i o n for temperature e r r o r .

Figure 10.- Concluded.

w OI L-77-2646. I Figure 11.- Rotor blade s e c t i o n w i t h instrument Pairing attached.

Pressure transducer Undercoat of .101.6-pm glass cloth bonded with rubber-base contact adhesive Bond with flexible two-part epoxy

4 layers of 25.4-pm

Electronics glass cloth bonded with rubber-base contact adhesive Plastic foam Figure 12.- Cross section of externally applied instrumentation on rotorcraft blade.

Figure 13 .- AH-1G r o t o r sensors.

I Sensor Sensor Level A-to-D

Interface I Amplifiers Comparators

Conversion

I I

4 J plexer

Ladder ri!

Canister I I Network.

I 1

I Buffer Amplifier

I I

L - _ _ _ _ _ - - _ _ - _ _ - --A

Multiplexer Control SAR Control I

Ladder Bit Rate Reference Clock Voltage Rate Reset

A

Sensor J

Excitation Unregulated +5 V to Logic Regulator 215 V for Analog Circuits +5V +15V Figure 1 4 . - Block diagram of blade s t a t i o n m u l t i p l e x e r - d i g i t i z e r .

J= Buffer Sensor Sensor Amplifier Amplifiers Interface NRZ-L 8-Bit A-to-D Analog Serial PCM Multiplexer Converter

1 Bit &Word

I

Canister Rate Clocks Master

I

Timing

I

&

I

Control Analog Multiplexer to

-

\ .

I w Control

I I

f6 V A-to-D Reference

*

515 V to Analog Circuits

-

dc Sensor Excitation I 4 f6 V Power Unregulated c5 V to Logic Figure 15.- Block diagram of canister multiplexer-digitizer.

-

Master Clock Countdown Timing (2) (2) Word Rate 1024 kHz Generator To Canister

-

Word Address Analog Bit Count Multiplexer Control

--- --- &

Frame Rate (1) Bit Rate Clock Programmable To Remote < Frame Read only

- Synchronization Multiplexer-

(3) Master Frame I

Memory (PROM) Digitizer Station

-

Generator (3) i Words 31 &32 Serial Data Master NRZ-L NRZ-L

I

Words 16 to 32 Combiner Combiner To b to word$ Logic Gates Logic Gates Transmitter Bi$-L Converter

-

Words

I

1 to 15

S e r i a l ~ ~ z - ~ I

< from Remote Blade 1

Parallel Station A-to-D Gray Code

Converter I

to Serial Binary Converter A Words 16 to 29 I < Serial NRZ-L from Canister A-to-D Converter

I

Azimuth Angle Shaft Figure 16.- Diagram of master timing and control.

L-76-602.1 Figure 17.- Fuselage-mounted receiving antenna.

UNREGULATED SYSTEM dc-to-dc VOLTAGES VOLTAGE CONVERSION & REGULATION Battery +28 V Transmitter

d I

+12 v -

External

Near-Hub -

Sensors Power from GSE Canister 215 V 26 V dc Umbilical e A-to-D Regulated Regulated Reference Cable c.

+15 V dc Internal In Regulator

} Canister

t - i External

To All 215 V dc

I

Analog Internal Cillcuit s Command dc- t0-dc from GSE Converters & Regulators 1 I

1 Centrifugal Flight

- Power Switch - -15 V -9 V dc ,ToPROM Regulator Regulate;

- ) On R e m Regulator L g i Blade

Station Reference Figure 18.- Simplified block diagram of power distribution system.

J= w Cover &

- - - = - - - - = &.Eht B I

I I I & Canister Support Assembly ter Attachment Rotor Rotor Mast

Nonrotating 1

-pipe Figure 1 9 . - S i m p l i f i e d drawing of c a n i s t e r mechanical assembly.

P

- 0 t

V

Figure 21.- Typical slope and intercept characteristics of a linear pressure sensor.

- .~ - . .

2. Government Accession No.

1. Report No. 3. Recipient's Catalog No.

NASA TP-1146

-- - _ I ~. i

4. Title and Subtitle 5. Report Date A ROTOR-MOUNTED DIGITAL INSTRUMENTATION SYSTEM FOR HELICOPTER BLADE FLIGHT RESEARCH MEASUREMENTS . _ 8. Performing Organization Report No.

7. Author(s)

Vernie H. Knight, Jr., William S. Haywood, Jr., I L-119 5 6

and Milton L. Williams _ _ _ _ _ - . 1 10. Work Unit No.

-~ 9 Performing Organization Name and Address

I 505-10-23-07

NASA Langley Research Center 1 1 . Contract or Grant No.

Hampton, VA 23665 I 13. Type of Report and Period Covered ~. ~~. . . - .~ - . . - . . _. . - - . . .

12. Sponsoring Agency Name and Address National Aeronautics and Space Administration Washington, DC 20546 .. . _ _ . .. ~ ~ ~ 15. Supplementary Notes ~ _ _ .. - - - _ 16 Abstract A rotor-mounted flight instrumentation system developed by the NASA Langley Research Center for helicopter rotor blade research is described. The system utilizes high-speed digital techniques to acquire research data from miniature pressure transducers on advanced rotor airfoils which are flight tested on an AH-1G helicopter. The system employs microelectronic pulse code modulation (PCM) multiplexer-digitizer stations located remotely on the blade and in a hub-mounted metal canister. As many as 25 sensors can be remotely digitized by a 2.5-mm thick electronics package mounted on the blade near the tip to reduce blade wiring. The electronics contained in the canister digitizes up to 16 sensors, formats these data with serial PCM data from the remote stations, and transmits the data from the canister which is above the plane of the rotor. Data are transmitted over an rf link to the ground for real-time monitoring and to the helicopter fuselage for tape recording. The complete system is powered by batteries located in the canister and requires no slip rings on the rotor shaft.

The instrumentation described provides flight measurements of blade param eters such as pressures, bending moments, temperatures, rotor angles, and rotor control forces. These experimental measurements are of value to an improved understanding of rotor performance and for advancement of helicopter blade design techniques.

- - . . .

7. Key Words (Suggested by Author(s)) 18. Distribution Statement Flight instrumentation of helicopter rotors Unclassified - Unlimited Pulse code modulation rf telemetry Battery-powered rotating instrumentation On-blade remote electronics Miniature pressure transducers ~ - - _ - _ 9. Security Classif. (of this report) 20. Security Classif. (of this page) Unclassified Unclassified * For sale by the National Technical Information Service, SprinRfield, VirEinla 22161 - NASA-Langley, 1978 - THIRD-CLASS B U L K R A T E Postage and Fees Paid National Aeronautics and National Aeronautics and Space Administration Space Administration- N A S A 4 5 1 Washington, D.C.

20546 , Official Business Penalty for Private Use, $300 2 1 10,A. 032178 ~ 0 0 9 0 3 ~ ~ .

DEFT O F TEE AIR F O R C E . .

, - AF WEAPONS L A E O B B T O R P E.TTN: TECHR'ICBL ' Z T E R A B Y (SOX) H I R T L A l D B F B %Fl 87117 . \ . , I I If Undeliverable (Section 158 Postal Manual) Do Not Return

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