May 15, 1964

MEMORANDUM for Chief, Research Division

Subject: Preliminary results of X-15 flight 1-47-74

Flight 1-47-74 was flown April 29, 1964, by Major Robert Rushworth. The stated purpose of the flight was a "Phase II Optical Degradation Experiment, and checkout of Optical Attitude Indicator." The launch point was Delamar Lake #1 and the launch heading was 214° magnetic.

General results - The powered portion of flight lasted 80 sec. as opposed to a planned engine burning time of 84 sec. The maximum velocity was 5725 ft/sec - the planned Vmax was 5700 ft/sec. The maximum altitude was 102,000 feet which corresponds to the planned Hmax exactly.

The total flight time amounted to 574.31 seconds (9.57 min.). Touchdown occurred approximately 280 feet North of the two-mile marker. At touchdown dh » 0, Hdot = -1 ft/sec, and a » 3°. The maximum landing gear load was 7900 pounds.

Systems operation - The SAS system functioned properly throughout the flight. The SAS gains were "hi-lo-hi" (8-4-8), ASAS was "armed," and RAS and the BCS were "off." The heading vernier was on "standby," and the flight was made with the jettisonable ventral fin "off."

A postflight review of the internal data showed phased oscillations in the pitch and roll modes throughout the flight. The rate of these oscillations were q = ±5°/sec and f = ±2°/sec, the period was about one cycle/sec. A postflight check showed that the SAS system was not at fault. Further investigation revealed that the oscillations were probably caused by actuator drift, and abnormally high actuator valve breakout forces, (0.5 to 4.5 pounds » normal is 0.2 pounds), on the port hydraulic surface actuator.

After landing the landing disengage switch was utilized and the servos were centered and locked 0.28 seconds after main gear touchdown.

Stability and Control - Major Rushworth reported that no problem was experienced in positioning the airplane to overfly the targets.

A bank angle change of f = -25° was used to reposition the airplane for the pass over the Pahrump target.

A +56° bank angle was used to reposition for the Cuddeback target run.

During the passes over each target the pitch and roll angles (i.e. q and f) were held within the prescribed limits of ±8°.

The airplane was rotated to a maximum angle of attack (indicated) of 15.3° approximately 5 sec after launch. During this period the pilot experienced buffet, a fact which has been verified by the internal records.

Handling Qualities - Evidence of buffet after launch was noted by the pilot. The pilot felt that the first 40 sec of flight, during which a rotation to climb q, and a pushover to zero "g" occurred was the most difficult to fly.

The most adverse pilot ratings were for the climb portion of the flight. They are:

q = 3.5

f = 1.5

y = 2.0

Flight Objective Results - The radar data reveals that the X-15 had the following attitudes and positions over the targets:

Target q f Position

Nellis 2° 0° No observed position error

Pahrump 2° -2° 1/2 mile right

Pilot Knob 2° 1.5° 1 mile left

Cuddeback 0° 1° 1 mile left

These attitudes and positions are well within the prescribed limits for this flight.

The results of the optical attitude indicator experiment were deemed unsatisfactory by the pilot.
 
 

Donald J. O'Mara

Aerospace Engineer

X-15 Research Planning Office