Summary

Flight 2-48-85 was flown on August 12, 1966, by Major William J. Knight for the purpose of obtaining data for a) ultraviolet stellar photography (exp. #1), b) alternate pitot-static systems, c) base drag, and d) thermal protection systems development.

The maximum velocity attained was 5050 feet per second (3443 mph and a Mach number of 4.7) at an altitude of 138,000 feet. The maximum altitude during the flight was 230,000 feet.

The flight was accomplished essentially as planned with one exception. About 23 seconds prior to shutdown, the pilot elected not to control the planned pitch attitude precisely because the simulator had shown the flight path would be insensitive to small pitch attitude changes near shutdown. Pitch attitude was gradually reduced from the planned 37 degrees to 34 degrees at two seconds prior to shutdown. The planned peak altitude was achieved with the reduced pitch attitude.

There were no significant malfunctions during the flight. Preliminary information indicates acceptable data were obtained on all experiments.

Flight Track and Profile

The X-15 was launched at Delamar #l (east). The radar ground track and profile are shown in figure 1. The planned launch time was dictated by the ultraviolet stellar photography experiment. The X 15 heading at launch was 214.9 degrees.

A maximum altitude of 230,000 feet was reached during the flight as planned. A discrepancy in the performance of X-15-2 between simulation and flight data has been suspected on prior flights. The planned peak altitude was achieved even though the planned pitch attitude of 37 degrees was not maintained prior to shutdown.

Stability and Control

A time history of the flight is shown in figure 2, The altitude and velocity shown are adjusted radar data, while the other parameters are uncorrected telemetered data.

Engine light occurred one second after a normal launch. An average angle of attack of 11.5 degrees was maintained during rotation. The pilot reported he ran out of trim at a Mach number of 1.6. The internal data indicate the maximum horizontal stabilizer during rotation was 22 degrees. Similar trim discrepancies have been noted on previous flights of X-15-2.

The planned pitch attitude of 37 degrees was maintained during the early portion of the climbout. The pilot reported that the engine misalignment experienced on previous flights was present to a lesser degree during this flight. Throughout the boost phase, the pilot was concerned with controlling the lateral direction motion of the aircraft which was associated with the engine misalignment (3 degrees of sideslip and 3 degrees of roll attitude at shutdown).

The pilot allowed the pitch attitude to reduce during the final 23 seconds of powered flight. The pilot was concerned with controlling the lateral directional motion of the aircraft and indicated he did not feel the pitch error at this time would affect the peak altitude, since the simulator had shown the flight path was not significantly affected by attitude changes near shutdown.

The ballistic control system was actuated about 0.8 seconds after engine shutdown. Four control rockets were not primed at the time the system was engaged. The left roll rocket of number 1 BCS system did not respond to pilot commands during the first 20 seconds after engagement. Similarly, the number 2 right roll rocket did not fire for 30 seconds and no thrust was detected from the number 1 and number 2 pitch down rockets for 40 seconds. Once the rockets were primed, operation of the ballistic control system was satisfactory. The check valves which maintain hydrogen peroxide pressure in the rocket feed lines will be inspected prior to the next altitude flight to verify proper operation.

The reaction augmentation system was engaged 27 seconds after shutdown and functioned satisfactorily with the exception of the pitch rocket malfunctions mentioned in the preceding paragraph and two periods of roll limit cycle operation. The roll limit cycle occurred in two 8.5 seconds bursts during the initial portion of the entry. The limit cycle frequency was 1.3 cycles per second (qp-p » 0.2 degrees; Pp-p » 2 deg/sec). The roll limit cycle oscillation occurred 30 seconds after completion of the Star Tracker mission and did not materially affect the flight. The limit cycle was not reported by the pilot and is not considered objectionable,

An average angle of attack of 15 degrees was maintained during the entry. The maximum angle of attack during the entry was 19.2 degrees. Full trim command produced -22 of horizontal stabilizer deflection,

Ultraviolet Stellar Photography (exp. #l)

The target star for August 12, 1966, was Alpha Gemini. The star Beta Aurigea was initially selected, however, because of delays caused by M2 flight operations and preflight difficulties, the launch time was changed to permit acquisition of the star Alpha Gemini.

In order to accomplish the mission on August 12, a short turn of the B-52 was conducted to gain the time necessary to place the X-15 at the launch point at the required time. The pitch and roll attitude requirements for the Star Tracker coordinates were established by the 25 minutes to launch point. The coordinates established at that time were 91.2 (+1.2 degrees in pitch attitude) and 83.5 (-6.5 degrees of roll attitude). At the time the experiment was activated the aircraft attitude was -1 degree in pitch and 6 degrees in roll. The aircraft attitude was maintained at O ±0.5 degrees in pitch and 6 ±1 degree in roll during the data acquisition period.

Data obtained from the flight were not analyzed at NASA FRC, however, the experimenter has indicated that data were obtained on the photometer which measures background radiation. The experimenter has not analyzed film obtained from the flight but has indicated that star data are anticipated on the basis of photometer data.

The experimenter has indicated that further flights of the Star Tracker will be requested from NASA Headquarters. Until such time as this request receives approval, flight 2-48 completes the flights requested for this experiment.

Alternate Pitot-Static System

Data were obtained and are being processed for analysis.

Base Drag Study

Data were obtained. Analysis of these data are being conducted on a continuing basis.

Ablative Materials

Ablative material was installed as thermal protection on the fixed lower vertical of X-15-2 for flight 2-46 and has remained on the lower vertical for three flights.

The ablative material located on the lower ventral has shown no significant deterioration during the successive flights. The material will remain on the lower ventral for flight 2-49.

Instrumentation Discrepancies

The following discrepancies were reported in instrumentation:

The film in 0-26-36C indicates erratic drum speed during the flight. Steps in travel occur at 3 to 4 second intervals. A gear on the oscillograph was determined the cause of the malfunction and has been replaced.

The thermocouple identifiers on oscillograph 0-9-36C, channels 4, 10, and 16 were fuzzy with the first 135 seconds missing on the lower identifier marks.

The angle of attack channel on recorder SV-1-3N was oscillatory during prelaunch data.

Data were not obtained from 24 of the 120 thermocouples recorded on oscillograph 0-19-36C.

Satisfactory calibrates were not obtained on Star Tracker free air temperature and postflight of the statham longitudinal accelerometer.

Operations Discrepancies

The engine misalignment noted on previous flights was present to a lesser degree following realignment of the engine for this flight.

Full nose-up trim setting continues to produce less than specified horizontal stabilizer deflection during rotation and entry.

Check valves of the left roll and pitch down rockets of the number 1 BCS and the right roll and pitch down rockets of the number 2 BCS did not maintain a prime condition in the hydrogen peroxide lines between the prelaunch checks and the activation of BCS at altitudes. The operation of these valves will be checked prior to the next altitude flight of X-15-2.

E. J. Adkins, Chief

X-15 Research Planning Office