A summary of rotor-hub bending moments encountered by a high performance hingeless- rotor helicopter during nap-of-the-earth maneuvers

APPENDIX A FACTORS RELATING TO ASYMMETRICAL BEHAVIOR O F TEST HELICOPTER AND LACK O F COORDINATION DURING SLALOM l"EUVERS The flight data and pilot comment have revealed that rapid negotiation of the slalom course in the test helicopter results in asymmetrical behavior and difficulties in coordi- nation. Some of the factors relating t o these findings are as follows: 1. Longitudinal inflow variation and coning in forward flight which results in lateral (This factor is inherent t o some extent in all types aircraft moments (lateral t r i m shift).

of rotors .)

2. Fuselage and rotor-pylon interference may be occurring in the azimuth positions (This factor could be inherent to some extent in all helicopters but aft of the rotor pylon.

may be larger in a helicopter where the rotor is mounted close t o the fuselage.)

3. Excessive collective-pitch sensitivity which leads to poor power coordination and high fluctuations in normal acceleration (0.4g to 0.6g per in. (0.15g to 0.23g per cm) of collective stick).

4. Control inputs couple with vertical motion of the spring-mounted cabin (0.83 in.

(2.11 cm) of longitudinal control per g and 0.50 in. (1.27 cm) of lateral control per g).

5. Asymmetric adverse yaw which leads to poor directional control.

6. Crosswinds which cause alternating upwind and downwind turns.

7. Cross-coupling of rotor pitch and roll control inputs which results from gyro- control springs acting through bellcrank motions which become nonlinear for large pilot control inputs.

The combination of all or some of these factors results in an erratic and poorly coordinated maneuver and subsequently in high blade stresses.

The NASA research pilot who performed the flights reported in this paper has sub- sequently flown an uninstrumented production-prototype version of the test helicopter through the slalom course. This prototype, which had several modifications including rigid mounting of the cabin, appeared t o perform the maneuvers in a smoother and more coordinated manner.

APPENDIX B INSTRUMENTATION Main Rotor: Strain gages: Hub flapwise bending at a station 6 in. (15.2 cm) from center line of main rotor Hub chordwise bending at a station 6 in. (15.2 cm) from center line of main rotor Mast bending 90° from instrumented hub a r m Mast bending 00 from instrumented hub a r m Axial-load pitch link Position transmitters: Blade angle Control Svstem: Strain gages: Axial load of boost-idler linkages, longitudinal and lateral Axial load of swash-plate linkages, longitudinal and lateral Control-stick force, longitudinal and lateral Position transmitters : Swash plate, longitudinal and lateral positions Control stick, longitudinal and lateral positions Accelerations and Angular Velocities: Rate gyros: Pitch rate in transmission compartment Roll rate in cabin Accelerometers: Longitudinal, lateral, and vertical cabin accelerations

APPENDIX B Vibrations: Vibration pickups: Longitudinal, lateral, and vertical cabin vibrations Longitudinal, lateral, and vertical transmission vibrations Horizontal Tail:

Vertical bending at a station 9 in. (22.8 cm) from center line of fuselage

Tail Rotor: Strain gages: Flapwise bending at a station 19.5 in. (49.5 cm) from center line of tail rotor Chordwise bending at a station 19.5 in. (49.5 cm) from center line of tail rotor Axial loads in pitch link Perf o r mance : Airspeed Altitude Engine and fuel-control parameters . . - REFERENCES 1. Huston, Robert J. (with appendix A by Robert J. Huston and William J. Snyder): An Exploratory Investigation of Factors Affecting the Handling Qualities of a Rudimen- t a r y Hingeless Rotor Helicopter. NASA TN D-3418, 1966.

2. Huston, Robert J.; and Ward, John F.: Handling Qualities and Structural Characteris- tics of the Hingeless-Rotor Helicopter. Conference on V/STOL and STOL Aircraft, NASA SP-116, 1966, pp. 1-16.

3. Ward, John F.: Exploratory Flight Investigation and Analysis of Structural Loads Encountered by a Helicopter Hingeless Rotor System. NASA TN D-3676, 1966.

4. Wyrick, D. R.; and Buzzetti, C. J.: Final Flight Test Report and Pre-Military Research Evaluation Conference Report - XH-51A Rigid Rotor Helicopter.

Rept. No. 16933 Suppl. I (Contract No. NOW 62-0665-d), Lockheed-California Co., Sept. 10, 1963.

5. Lockheed-California Co.: Investigation of Elastic Coupling Phenomena of High Speed Rigid Rotor Systems. TRECOM Tech. Rept. 63-75 (Lockheed Rept. No. 17013), U.S. Army Transportation Res. Command (Fort Eustis, Va.), June 1964.

6. Burpo, Frank B.: Maneuverability Data From an Army Helicopter Flying a Simulated Armament Mission. Rept. No. 831-099-003, Bell Helicopter Co., Apr. 1965.

TABLE I . - PHYSICAL PARAMETERS OF XH-51N Main rotor (hingeless): Number of main-rotor blades . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Main-rotor diameter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35 f t (10.7 m) Main-rotor blade chord . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.5 in. (34.3 cm) Main-rotor disk area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 962 f t 2 (89.4 m2) Solidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.0614 Airfoil section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . NACA 0012 Blade twist (linear washout) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 5 O Fixed coning angle, hub . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.8' from horizontal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 . 8 ' from horizontal Fixed coning angle, blade Normal rotor speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355 rpm Blade weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 lbf/blade (382 N/blade) Rotor m a s s moment of inertia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 760 slug-ft2 (1030 kg-ma) Blade sweepforward a t 75 percent radius . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.25 in. (5.7 cm) Flapwise natural frequency of rotating blade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40.9 rad/sec Chordwise natural frequency of rotating blade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.3 rad/sec Control gyro: D i a m e t e r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 in. (196 cm) Gyro m a s s moment of inertia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5 slug-ft2 (10.2 kg-ma) Tail rotor (teetering): Number of blades . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Rotor diameter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 ft (1.83 m) area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28.27 f t 2 (2.63 m2) Disk Blade chord . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5 in. (21.6 cm) Solidity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .0.149 Airfoil section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . NACA 0012 Blade t w i s t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -4.40° Fixed coning angle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oo Normal rotor speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2085 rpm Rotor m a s s moment of inertia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.302 slug-ft2 (0.41 kg-ma) Effective cant angle of flapping hinge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15O Horizontal tail: Span . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 in. (2.13 m) Chord . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 in. (33 cm) Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.55 ft2 (0.7 m2) Aspect ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.45 Fixed incidence angle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -5.5' Airfoil section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . NACA 0015 (18 238 N) Gross weight for this investigation (right seat, pilot; left seat, lead ballast). . . . . . . . . . . . . 4100 lbf Longitudinal center of gravity for this investigation, from center line of main rotor . . . . . . . 0.3 in. (0.8 cm) aft 0 in. (0 cm) Lateral center of gravity for this investigation, from center line of main rotor . . . . . . . . . . . . . .

TABLE 11.- SUMMARY OF TASKS AND RESULTS ~~

Approximate Percent of I

m

time to time spent Predominant Comments Task above assigned maneuvers complete task,

s e c endurance rimit 1

I 1 Slalom course 1 Rapid roll reversals 1 30 I 40 1 Stresses occur far in excess of assigned 1 I I I endurance limit 20 50 Moderately high stresses

Teardrop turns ' Rolling and pitching

S-turn Rolling 16 30 Moderately high stresses I I

~ Hit-the-deck Pitching I 8 I 18 Moderate stresses

1 Scramble Pitching I 10 i 40 I Moderate stresses

~ ~ ~~ ~~

1 Whoa-boy ' Pitch, yaw, and roll 30 Moderate stresses

Figure 1.- Experimental hingeless-rotor helicopter XH-51N. L-68-839 Figure 2.- Photograph of XH-51N h u b and mast showing locations of s t r a i n gages.

L-68-840

Pitch positive ---T P i t c h negative

Figure 3.- Control-system details of XH-SIN helicopter.

Ild -

(a) Slalom course (top view).

\

* -

(b) Teardrop t u r n (top view).

(c) S - t u r n (top view).

Figure 4.- Maneuver tasks.

(d) Hit-the-deck (side view).

(e) Scramble (side view).

(f) Whoa-boy (side view).

Figure 4.- Concluded.

hl

500x10 3 N-m

0 100 200 300 400

30x lo3

40x Id N-m

Main-rotor h u b flapwise bending moment, station 6, i n - l b 20 c)

0 100 200 300 400 x loJ

M a i n - r o t o r h u b chordwise bending moment, station 6, i n - l b Figure 5.- Conversion diagram for determining maximum stresses from chordwise and flapwise bending moments.

L

Normal acceleration, 9 units I - ~t 160 x103 I I - *a cyclic bladeroot angle 54 I amplitude, el, de9 0 - I 30 I I I I I 25 15 20 5 10 Time, sec Normal acceleration, g u n i t s f 120 f 80 Main-rotor h u b chordwise cyclic bending moment amplitude, station 6 , in-lb *do A.

Coupled flapwise and chordwise ? 30 . \ endurance l i m i t

Main-rotor h u b flapwise *

cyclic bending moment * 10

amplitude, station 6, in-lb 0 U R 1 Rolling velocity, p, radlsec 0 L -1 up . 5 Pitching velocity, q, radhec 0 Dn -.5 f 8 Cyclic blade-root angle ? 4 amplitude, el' deg 25 30 0 10 15 20 Time, sec Figure 7.- Slalom-course maneuver performed at 45 to 50 knots t h r o u g h 200-foot (61-m) spaced markers.

Main- rotor h u b f lapwise bending moment, station 6, in-lb M a i n -rotor h u b chordwise bending moment, station 6, in-lb Rolling velocity, p, rad/sec L -.5

-

-

- - - - Blade-root collective . ~ . . I - . .

pitch angle, eo, deg _ _ _ _ Pitching velocity, q, radsec

D n -.5 L

+1.I 1.LLLl.l.I.J -1. 11. I 1 . 1 I. I }..l.l-.LLJ~U-i (LLLLLhLLy I IO 20 30 40 M a i n rotor revolutions, 9 = Oo Figure 8.- Roll reversal performed at 45 to 50 knots d u r i n g negotiation of early slalom course with 200-foot (61-m) markers in t h e XH-51N.

Ma i n- roto r h u b f la pw i se

bending moment, station 6,

i n - l b

I O

M a i n-rotor hub chordwise

bending moment, station 6,

i n - l b

Blade root a n g u l a r motion,

2Ot__,,, J\

v u -

0, de9 0

Rolling velocity p, radhec 0

-

L - . 5

. Awn e\. v fc

Normal acceleration, I

g u n i t s

\ ' I ! I 1 I I I I ! I I ! I I I I I I / I I 1 ! I I I I I i l l I I 1 I I I I ! '

0 I O 20 30 40

Main-rotor revolutions, = Oo

Figure 9.- Roll reversal performed at 45 knots during negotiation of last slalom course with 200-foot (61-m) markers in the XH-51N.

IO ~ 0 3

Main-rotor blade flapwise bending moment, N- m station 41, in-lb 0 -5 Main-rotor blade chordwise bending moment, station 41, in-lb 0 Bladeroot angular motion, e , deg

Rolling velocity, p, radlsec

-

Normal acceleration, g units O L

I ' I I I t I t l f I ' I ' I I I I I I ' I I I I t I ' 1 1 I ' I I

i '

1 10 20 30 40

Main-rotor revolutions, q~ = 0 '

Figure 10.- Roll reversal performed at 70 knots in XH-DN.

k m Normal acceleration, g units 1 bending moment amplitude, station 6, i n - l b Coupled flapwise - 0 ' a n d chordwise *30 xl$

*20 y x 10 ,d e n d u r a n c e l i m i t 7

M a i n - r o t o r h u b flapwise cyclic b e n d i n g moment amplitude, station 6, i n - l b R o l l i n g velocity, p, radlsec P i t c h i n g velocity, 9, radlsec Cyclic blade-root angle amplitude, el, deg 0 ' Figure 11.- Teardrop t u r n performed at an entry speed of 70 knots.

Normal acceleration, g units Main-rotor h u b chordwise

cyclic bending moment * 40

amplitude, station 6 , in-lb

I ' - 0

Coupled flapwise - 3 3 0 xIO3

*a

and chordwise ', Main-rotor h u b flaDwise cyclic endurance l i m i t - . , bending moment amplitude,

* 10

station 6 , in-lb Rolling velocity, p, radlsec n

-

-. - /

----------l----- / - - _ - - - . . /---\ A -

P -

Pitching velocity, q, radlsec 0 Cyclic blade-root angle * 4

- ,/----- : a \ / / \

0 2 4 6 8 10 12 14 16 Time, sec Figure 12.- S - t u r n performed at a n entry speed of 65 knots.

Normal acceleration, g u n i t s

* 80

f 40

c

Main-rotor h u b chordwise cyclic bending moment amplitude, station 6, in-lb - and chordwise

* 20

Main-rotor h u b flapwise cyclic bending moment amplitude, station 6, in-lb up .5 Pitching velocity, q, rad/sec

Dn -. 5

B lade-root collective p i t c h angle, e , deg f 6

r

Cyclic blade-root i4 angle amplitude, i2 el, deg I I I I I I I 1 I 1 2 3 4 5 6 7 a Time, sec Figure 13.- Hit-the-deck maneuver from 200-foot (61-m) altitude with entry speed of 70 knots.

2 - /- 1 Normal acceleration

-

g u n i t s

0 L

M a i n - r o t o r h u b chordwise cyclic bending moment amplitude, station 6 , i n - l b Main- r o t o r h u b f lapwise cyclic bending moment amplitude, station 6, i n - l b P i t c h i n g velocity, q, rad/sec Blade-root collective p i t c h angle, eo, deg Cyclic blade-root angle amplitude, el’ deg Figure 14.- Scramble maneuver from ground to 80 knots.

w -

- -

Normal acceleration, 1 g u n i t s - +PO ~ 1 0 3 *80 x 10 - - - - - - M a i n - r o t o r h u b chordwise +40 N- m c y c l i c b e n d i n g moment amplitude, station 6, i n - l b Coupled flapwise

i

0 a n d chordwise

+ 20

e n d u r a n c e l i m i t M a i n - r o t o r h u b f lapwise c y c l i c b e n d i n g moment + l o N- m amplitude, station 6, i n - l b R . 5 R o l l i n g velocity, p, rad/sec L -.5 u p . 5 P i t c h i n g velocity, q, rad/sec

O n -. 5

Blade- root collective p i t c h angle, e 0 , deg

4 r- L

+ 8

r

C y c l i c blade-root a n g l e + 4 amplitude, e , deg c (0 a m

I

w N IY cn m Figure 15.- Whoa-boy maneuver with entry speed of about 80 knots.

CL W