May 16, 1967

MEMORANDUM for Chief, Research Projects Office

Flight 1-71-121 was flown on April 28, 1967, by Major Michael J. Adams for the purpose of:

The maximum velocity was 5400 fps (3682 MPH and a true Mach number of 5.32) at an altitude of 116,000 feet. The maximum altitude reached during the flight was 167,000 feet.

The major malfunction which occurred during the flight was a failure of the pilot's pitch attitude display system during the powered portion of the flight.

Flight Track and Profile

The radar track and profile for this flight are shown in figure 1. The ground track was about 2° east of the planned track during the powered portion of the flight. A heading correction initiated just prior to engine shutdown resulted in the ground track being about 2° west of the planned track after peak altitude. This small heading discrepancy resulted in the airplane ground track passing about four nautical miles west of the sonic boom site.

The flight profile shown in figure 1 was lower than planned from the time the planned pitch attitude was obtained until the re-entry maneuver. This discrepancy was caused by an erratic presentation of pitch attitude to the pilot. Because of the erratic presentation, the pilot was unable to maintain the planned attitude during the climbout portion of the flight. Because of this discrepancy the profile eventually went about 13,000 feet lower than planned.

Stability and Control

A time history of the significant stability and control parameters telemetered during the flight is shown in figure 2. The launch was at Delamar Lake from 45,000 feet altitude. Launch was normal with 8° of right roll and 3° of sideslip. Engine light occurred 0.9 seconds after launch and reached 100 percent thrust in 0.7 second. Rotation after launch initially peaked at approximately 13° angle of attack then lowered to a 8.5° average, as compared to the planned 11°, until a pitch attitude of 24° was attained in 24 seconds. The maximum normal acceleration during rotation was 1.9 g.

The planned pitch attitude of 28° was attained in approximately 36 seconds, 14 seconds later than planned. A pitch attitude of 28° was maintained for only five seconds, due to the erratic presentation the pilot was receiving on his display. Pitch attitude and angle of attack drifted down to minimums of 22° and 2°, respectively, during the powered portion of the flight and were increased to approximately 26° and 9°, respectively, just prior to engine shutdown.

Engine shutdown was initiated by the pilot at 5200 fps, as planned, after 82.0 seconds of powered time with final shutdown being accomplished at 5400 fps. This additional velocity, resulting from the 2.0 seconds longer burn time than planned, did not offset the altitude lost due to a low pitch attitude. The peak altitude of 167,000 feet was 13,000 feet lower than was planned. The angle of attack was maintained at approximately zero degrees until the pilot initiated a pullup maneuver in preparation for re-entry. The maximum angle of attack and normal acceleration during re-entry was 20.5° and 2.2 g, respectively. The approach, landing, and rollout were normal.

A time history of the total airplane weight is shown in figure 3. and of the longitudinal center of gravity position is shown in figure 4. The calculated landing weight was 16,260 pounds with a longitudinal center of gravity position of 11.15 percent of the mean aerodynamic chord.

Air Force Western Test Range Launch Monitoring

This was the first flight of the experiment and was to provide an operational checkout of the systems operation. Failure to obtain sufficient altitude, required for low dynamic pressure forces, resulted in deletion of a portion of the planned checkout. The portion of the checkout deleted was the opening of the flip-top elevator bay doors and the extending and retracting of the scanning device.

Postflight examination of the experiment produced several discrepancies which had developed during the flight. These discrepancies were:

MIT/Apollo Simultaneous Photographic Horizon Scanner

This was the first flight of the experiment with the improved tracker system and provided an operational checkout for the unit. Preliminary analysis of the data indicated that all systems functioned satisfactorily.

The experiment will be flown on the next flight, planned for May 18.

Horizontal Stabilizer Local Flow Direction

Although this was only a moderate altitude flight, data were obtained on this experiment. Preliminary analysis of the data showed no apparent problems.

Sonic Boom Study

Instruments were setup near Cuddeback Lake to record the sonic boom generated during this flight. No data were recorded because the recording team failed to receive radio transmissions to turn on instrumentation. This radio problem is being investigated and will be corrected prior to next flight.

Third Skid

This flight provided an additional checkout for the third skid operation. Investigation of the system after landing indicated the system functioned as expected.

Electrical Loads

Data for the survey of the electrical loads on the APU's were recorded on this flight. Analysis of the data is in progress.

IRIG Timer

A new timing system was installed for this flight. This is a digital time code system with the primary purposes of improving the overall accuracy of airborne timing systems, of simplifying visual and automatic data reduction, and of providing versatility and interchangeability of all airborne timing systems.

Analysis of data showed one discrepancy occurred during flight. When the generators were reset after APU start the time reset to zero. Preliminary investigation of this discrepancy indicates it resulted because of the difference in voltage levels between the battery and the ship's power at power transfer.

Precision Attitude Indicator

A precision attitude indicator was installed on the pilot's cockpit display for this flight. During the flight the pilot was to observe the indicator, when possible, to determine if it was functioning properly. The pilot indicated that both the heading and roll looked noisy and erratic.

This discrepancy is being investigated and will be corrected prior to the next flight.

Operational Discrepancies

Prior to flight the orifice in the motor generator cooling system was replaced with a smaller size because excessive cooling had occurred on the previous flight.

During the prelaunch portion of the flight the motor generator began to overheat and was shutdown. This was because the new orifice was too small and provided inadequate cooling to the motor generator. Because of this overheat condition the motor generator remained off for the remainder of the flight operation.

A slightly larger cooling orifice will be installed for the next flight to correct this problem.

Data Systems Discrepancies

During the boost portion of the flight, the pilot was required to attain a planned pitch attitude of 28° and maintain it until shutdown. As the pilot approached the 28° null-point on the pitch attitude vernier he noted the instrument seemed to be extremely sensitive. He commented that a null position could not be maintained and that the indicator oscillated through a +6 to -4 degrees range.

The precision attitude indicator, which the pilot indicated was noisy and erratic, is being investigated simultaneously with the pitch attitude discrepancy.

Initial postflight checkout of these systems indicated they functioned properly, as the discrepancies could not be duplicated. Investigation of the discrepancies continued during a scheduled APU run on May 15. The run was performed with Major Adams in the cockpit. Both the pitch attitude display and the precision attitude indicator discrepancies were duplicated.

It was noted that these discrepancies existed only with both APUs and both generators "on the line". With either generator off the discrepancies did not exist, which tends to indicate a phase problem within the system. Further investigation of this problem area is being continued.

The pilot also indicated a problem may exist in the inertial velocity readout in the cockpit. His comment was that the presentation seemed to stick and then jump forward instead of showing a constant increasing trend during the boost phase of the flight. This discrepancy is being investigated concurrently with that of the pitch attitude.

These discrepancies will be corrected prior to the next flight.

Inspection of the internally recorded flight records showed the angle of sideslip and angle of attack record (SV-2-3N) had no timing lines. This discrepancy is being investigated and will be repaired prior to next flight.

The airspeed-altitude record (P-3-4E) and oscillograph O-42-36C ran at different speeds than the other records. This discrepancy was a result of the recording instruments being set to record at an incorrect speed while the instrument was in the laboratory for repair. These recorders will be set for the correct operating speed for the next flight.

Analysis of data showed that when the generators were reset after APU start the IRIG timing system reset time to zero. Preliminary investigation of this discrepancy indicates it resulted because of the difference in voltage levels between the battery and the ship's power at power transfer. To correct this discrepancy the battery will be fully charged prior to flight.

(James R. Welsh for)

E. James Adkins, Head

X-15 Project Office