Summary

Flight 2-52-96 was flown on August 21, 1967, by Major William J. Knight for the purpose of obtaining data for:

The primary flight objectives were attained. The pilot indicated there were no major differences in aircraft handling qualities which might be attributed to the ablative material. Acceptable data were obtained on all experiments.

The inertial altitude indicator malfunctioned at 10,000 feet during the descent. A possible mechanical malfunction in either the computer or altitude indicator is suspected and the investigation is continuing. The ramjet shape separated properly when ejected, however, insufficient altitude remained after main chute deployment and the dummy ramjet was damaged upon impact. A structural member of the induced turbulence experiment mount failed during landing. The mount is being repaired.

Flight Track and Profile

The radar track and profile are shown in figure 1. The launch was from Hidden Hills Lake number 1 at an altitude of 45,500 ft. on a heading of 223°.

Stability and Control

A time history of stability and control parameters telemetered during the flight is shown in figure 2.

The launch was normal with an average angle of attack of 10° during rotation. A maximum normal acceleration of 2.2 "g" and dynamic pressure of 800 psf occurred during the rotation.

The average pitch attitude of 27° maintained during the climb was 2° higher than planned. The pushover to zero "g" was initiated at an indicated rate of climb of 900 feet per second.

After peak altitude, the pilot began the stability and control maneuvers. The maneuvers were performed under the following conditions:
 

Maneuver	Damper Setting	Initial a	Velocity	Speed Brakes
Pitch Pulse	Pitch - Low	7.3°	4460	Out
Pitch Pulse	Pitch - Low	7.0	4360	Out
Yaw Pulse	Yaw - Low	7.8	4170	Out
Pitch Pulse	Pitch - Low	7.5	4100	Out
Yaw Pulse	Yaw - Low	6.8	3910	Out
Trim Run	---	10.5-1-10.5	3550-3360	In
Yaw Pulse	Yaw - High	6.3	3180	In
Yaw Pulse	Yaw - Off	10.0	3010	In
Yaw Pulse	Yaw - Off	6.3	2750	In
Pitch Pulse	Pitch - Off	5.4	2500	In

The pilot reported he could not detect any major differences in aircraft handling qualities that might be attributed to the presence of the ablative material. The pilot indicated the aircraft response to the pitch pulses closely approached that predicted by the simulator. The pilot reported the rudder pulse at Mach 3 and 10° angle of attack with the yaw damper off resulted in a neutrally damped oscillation. After a few cycles, the pilot damped the b oscillations with a rudder input. No major difference in handling qualities was reported during the pattern with the exception that the pilot noted the change in aircraft trim while decelerating between Mach 2 and Mach 1. A pilot rating of 3 was assigned to the task of controlling pitch in this area.

A time history of airplane weight and longitudinal center of gravity are shown in figures 3 and 4, respectively. After landing, the aircraft was weighed at 16,390 pounds. Compensating for the weight of pilot, equipment, and propellant boil-off, the projected landing weight was 16,600 pounds.

Ablative Evaluation

The total heat load was about one-third the level expected for a maximum velocity flight. The overall performance of the coating was very good and over half the ablative coating returned without any change in appearance.

One failure due to spray application occurred on the upper left side of the vertical stabilizer. Delamination occurred between the 50 mil base layer and the 100 mil plus outer layer which was applied after the base layer cured. The result was a large number of blisters, twelve of which popped open during the flight. The delamination was caused by spraying too dry an outer layer. This prevented good adhesion to the base coat. The failure occurred at the interface of the two spray layers. A tension test of that area during application showed a tensile strength of 19.5 psi. Although 20 psi had been set as the minimum value for quality assurance, the coating was accepted without further qualification since the load was only 0.5 psi below the qualification level. During future applications, areas which show this kind of failure will be given a careful inspection and recoated if necessary. The blistered material was removed and a new coating has been applied for the next flight.

With the exception of the canopy, ventral pylon, and forward dog leg T/M antenna leading edges, the leading edges and speed brakes experienced about 50 mils of char during the flight. The canopy leading edge did not char due to masking of the flow by the forward fuselage. It is believed that shock waves originating from the dummy ramjet shape and the impact pressure rake caused severe erosion on the ventral pylon leading edge. This leading edge piece has been replaced for the next flight. Shock impingement from the ram air door on the antenna leading edge is believed to have caused localized heating. The material covering the ram air door protruded 0.8-inch above the surrounding material and is believed to have produced the shock. The door material will be sanded flush for the next flight. Material on the speed brakes has been removed and a new coating applied. The char on the remaining leading edges has been sanded off to provide a smooth layer for the outer wear layer of silicone paint. Part of the tape used to mask the pitot tube in front of the canopy was not removed prior to flight, possibly producing some fogging of the right canopy window.

Refurbishment has been completed and reduction of temperature data is now in progress.

Induced Turbulence

Data were obtained during the flight and are being analyzed. System operation during the flight appears to have been normal. The outer mount frame failed during landing. Stress analysis and vibrational studies have been conducted. New parts are being fabricated and repair of the equipment is scheduled to begin the week of September 11. The experiment is expected to be ready for flight 2-54.

Dummy Ramjet

Pressure measurements were obtained on the engine inlet spike, afterbody and base, as well as on the pylon leading edge and sidewall. Temperatures were measured on the spike and afterbody. Vibration accelerations were measured at three locations in the dummy shape and at one location in the pylon. Qualitative analysis indicates the data are not significantly different from that obtained previously when the airplane was not covered with ablative material. A detailed analysis of data is in progress.

The dummy ramjet shape was ejected at Mach 0.48 (velocity of 545 fps) at an altitude of 2900 feet and a dynamic pressure of 352 PSF. Initial viewing of ground camera coverage indicates the separation was similar to the last flight. The ejection caused a slight pitching oscillation of ±l angle of attack which was not observed by the pilot. The ramjet separated properly, however, insufficient altitude remained after main chute deployment for a clean recovery, and the dummy ramjet was damaged on impact. The ramjet shape is repairable.

Canopy Eyelid

The left window protected by the canopy eyelid remained clear during the flight. The unprotected right window became fogged on the forward quarter of the glass. This fogging may have resulted from burning of some masking tape used and left on the pitot tube in front of the canopy. The pilot reported that the landing was made using the left window and resulted in the left skid touching down first.
 
 

Alternate Attitude Indicator

Analysis of the cockpit film indicates the alternate attitude indicator installed prior to this flight performed satisfactorily until a roll angle greater than 70° was exceeded during the 3 "g" turn to high key. The pitch attitude began to diverge rapidly, however, the roll attitude was within 15° of the standard at the end of the flight.

Alternate Pitot-Static System

During the pattern the pilot compared the standard and alternate airspeed systems with the chase aircraft and concluded the alternate source was the better and, therefore, used it to complete the landing. The following comparisons were reported:

Chase StandardAlternate

400 300 375

- 280-290 350

- 270 350

Data Systems Discrepancies

The inertial altitude indicator ceased to respond after the X-15 descended to an altitude of 10,000 feet. A possible mechanical malfunction is suspected in either the computer or the altitude indicator. The system has been removed to the laboratory for checkout.

The following discrepancies in data instrumentation were reported:

There were no major operational discrepancies reported.

E. J. Adkins, Chief

X-15 Research Projects Office