MEMORANDUM for Acting Chief, Research Division
Subject: Flight Research Report on flight 3-38-61
I. Purpose of flight
1. Skin friction - Flight requirements were V = 5,000 fps 0 < a < 3°, q constant at approximately 1200 PSF, for approximately 20 seconds.
2. Ablative tests - no specific flight requirements were made.
3. Flow field experiment - no specific flight requirements were made.
4. Nose Gear Modification Checkout - no specific flight requirements were made.
5. Boundary-layer noise - No specific flight requirements were made.
The flight plan was based on the skin friction experiment flight requirements. The primary data point was obtained as planned prior to burnout.A maximum Mach number of 5.55 was reached due to a longer burn time on the engine. However, this velocity was satisfactory for the ablative tests and did not adversely affect the other experiments.
The flight was flown as planned except for small deviations which were acceptable.
III. Instrumentation by Experiments
Skin friction; 23 channels on osc. 0-23, man. P-27 and P-8.
Ablative; 12 channels on T.C. osc. 0-25.
Local flow; 35 channels on osc. 0-7, 0-23, man. P-2 and P-8.
Nose Gear Modification Checkout; 5 channels on osc. 0-7.
Boundary-layer noise; 4 tracks on tape recorder number 38.
Results
A. Skin friction
The skin friction gage recording on osc. 0-23 operated satisfactorily. Pressures recorded on man. P-11 and P-27 appear satisfactory. Therefore, all the desired data for this experiment have been obtained satisfactorily.
B. Ablative tests
The following test panels were installed:
F-3 Langley Purple Blend Ablative
F-4 General Electric Ablative
On osc. 0-25, some T.C. traces appeared as smudges on channels 17 and 20. Channel 20 is not used for ablative or heating tests. However, ten T.C.'s are read on channel 17 and these were lost. No corrective action was taken. This osc. is overdue servicing. Same thing existed on flight 3-37.
C. Flow Field
No instrumentation malfunctions occurred and usable data were obtained.
D. Nose Gear Modification Checkout
No instrumentation malfunctions were noted. All the desired data were obtained satisfactorily.
E. Boundary Layer Noise
No instrumentation malfunctions were noted, and all desired data were obtained satisfactorily.
12-16-64 Delayed due to lack of C-l3O's
12-17-64 Delayed due to weather
12-18-64 Delayed due to turbo pump lube oil leak. Engine # 106 exchanged for #103
12-22-64 Flight 3-38-61 flown.
B. Ball Nose Total Pressure Leaks
The ball nose was replaced due to internal leakage in the total pressure sensing system. The o-ring which leaked on the previous flight was replaced by hard line fittings. No leakage was noticed on this flight.
C. Objectionable Roll Oscillations
The pilot reported that an objectionable roll oscillation occurred after launch and persisted for 86 seconds. Internal recordings indicate a roll oscillation which varied from approximately 1 cps to 2 cps with variations of roll to 10°. During the preflight check of the flight control system, a one-half degree rudder offset was observed. The roll oscillations reported by the pilot and observed on internal recording followed rudder servo and rudder displacement.
During the aircraft postflight, the rudder control cable was observed to be off one of the pulleys immediately forward of the yaw tension regulator in the engine compartment and to be outside the control cable pulley guide. This produced an increase in hysteresis and a decrease in performance in the yaw axis of the flight control system. The roll oscillation observed by the pilot resulted from the rolling moment due to rudder with lower ventral removed, and the degradation of performance in the yaw damper. These roll oscillations were duplicated on the X-15 simulator with the rudder cable displaced from the pulley.
The flight was flown satisfactorily. A rudder cable was found to be off one of the pulleys causing an objectionable roll oscillation. However, the oscillations were small enough to not affect the data at the desired data point. Normal periodic instrumentation servicing has been extended. Servicing shall be performed at the first opportunity. Review of on-board recordings indicate that the desired data were obtained for the experiments.
J. A. LaPierre
Aerospace Engineer