September 5, 1968

MEMORANDUM for Assistant Chief, Research Projects

Flight 1-79-139 was flown on August 21, 1968, by William H. Dana for the purpose of:

Extension of the WTR experiment was normal and the retraction sequence began in a normal manner, however, the automatic timer activated during the retract sequence removing power to the equipment and completed the retract sequence. Data obtained from the radiometer indicate the threshold settings were too high. Steps to reset the threshold were initiated.

Satisfactory data were obtained from the fluidic probe, fixed-sphere and MIT horizon scanner experiments.

Flight Track and Profile

The radar track and profile for this flight are shown in figure 1.

Because the X-15 angle of attack indicated 5.5 degrees rather than the nominal 2 to 3 degrees reported during most previous prelaunch checks with the X-15, a ten minute delay and turn were initiated at three minutes to launch. This discrepancy appeared to result because the B-52 had not achieved the normal airspeed of 0.8 Mach number. Once this airspeed had been achieved, the nominal indication of angle of attack was observed.

The launch was at Railroad Valley #2 on a magnetic heading of 183 degrees. The planned rotation angle of attack of 11 degrees was held until the aircraft reached the planned pitch attitude of 40 degrees, which occurred two seconds later than planned.

The pilot initiated engine shutdown at an indicated velocity of 4950 feet per second. Five seconds later, at a velocity of 4910 fps there was a jump in the indicated velocity to 5080 fps. The velocity indicator does not appear to have been functioning properly at shutdown. An indicated velocity of 5100 fps would produce the 12,000 feet overshoot in altitude that was experienced on this flight.

There was a thrust misalinement at engine shutdown which caused the aircraft to sideslip 2 degrees nose left against the corrective rudder applied by the pilot.

Stability and Control

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

As mentioned previously, the X-15 angle of attack appeared to be indicating significantly high during the prelaunch activities. Data from four previous X-15 flights are shown in figure 3. Although insufficient data have been previously recorded, a trend is apparent. The data reported during the prelaunch tend to be of slightly higher magnitude, however, the 4.5 degrees angle of attack reported at 0.78 Mach number does not appear to be abnormal.

The ball nose ceased to be accurate about 250,000 feet. The angle of sideslip data from the ball nose indicated an 11 degree nose left drift during a period in which the heading change was to a nose right attitude. The angle of sideslip began to drift back following peak altitude and was functional at about 250,000 feet.

The pilot elected not to disengage the pitch axis reaction augmentation system at 210,000 feet as planned because he considered the aircraft to be "loose" with pitch and yaw RAS engaged.

The angle of attack during entry began at the planned 22 degrees but dropped to 17°-18° during the "g" buildup. Dynamic pressure reached a maximum near 1500 psf and was held higher than planned by the pilot in order to get rid of the excess energy resulting from the overshoot in altitude.

Air Force Western Test Range Launch Monitor

The experiment was extended 129 seconds after launch and began the search mode 8 seconds later. Shortly after the search mode was begun, both elevation and azimuth torquers saturated. Mirror position indicated the system had been driven against the stops. This apparently results when the experiment is extended prior to achieving the pitch attitude requirements of 0 ±2 degrees. Future flights will plan to extend the experiment after the aircraft has achieved a pitch attitude of 2 degrees or less. This will be expected to occur as the aircraft reaches apogee.

At about 208 seconds after launch NASA-l requested the pilot to retract the experiment. The experiment began a normal retract sequence without experiencing the delays noted during previous flights. However, due to the overshoot in altitude, the call came too close to the automatic timer sequencing. As a result the automatic timer interrupted the normal action and retracted the experiment with the emergency sequence. A normal retraction was not successfully accomplished and is required. This sequence will be rescheduled for checks during the next flight.

Checks of the equipment following the flight revealed a blown fuse in the video-recorder. This results from electrical transients during cycling of the experiment switch and possibly occurred while the aircraft was in the service area.

Data from the radiometer show the system saturated and indicate lower threshold levels will be required. These threshold levels are being changed and will be evaluated during the next flight.

MIT/Apollo Simultaneous Photographic Horizon Scanner

Star recognition was not achieved from the experiment. The equipment is being checked to verify proper operation. Satisfactory data were obtained from all data channels except star magnitude. The Barnes edgetracker portion of the experiment functioned normally and data were obtained. The experiment is scheduled to be flown during the next flight.

Fixed-Sphere Flow Direction Sensor

Data were obtained and are being analyzed.

Fluidic Probe

Data were obtained and are being analyzed.

Sky Brightness

Analysis of the data from the previous flight indicated a sensitivity change occurred during the flight. The experiment was removed from the aircraft and returned to the experimenter for study. The experiment was not flown during flight 1-79-139.

Operational Discrepancies

A thrust misalinement at shutdown caused the aircraft to sideslip 2 degrees nose left against the corrective rudder applied by the pilot. Following the flight, checks of the engine revealed ammonia contamination of the lube oil. A seal is suspected and the engine will be replaced and an engine run made prior to the next flight.

Because of the high angle of attack values reported prior to launch, an investigation of the ball nose was conducted following the flight. The ball nose was functioning properly but the response was not considered satisfactory and the ball nose was replaced.

The cockpit film indicates a jump in indicated velocity from 4910 feet per second to 5080 feet per second occurred five seconds after shutdown. Postflight checks of the inertial system disclosed broken insulation exposing conductors of the system electrical harness may have caused this discrepancy. The electrical harness has been repaired.

Data System Discrepancies

Acceptable data were not obtained from the forward-looking wing pod camera except during a period of about 100 seconds near apogee. However, this was the prime data period and data are usable. Efforts to improve film quality are being made. One internal data discrepancy was noted; the MIT Star magnitude signal data channel did not function.

James R. Welsh

Head, X-15 Research Project Office