Summary

Flight 2-44-79 was flown essentially as planned by Lt. Col. Rushworth on May 18, 1966, to obtain data and handling quality evaluation of ventral-on stability and control of X-15-2, to evaluate ablative material on the port horizontal stabilizer, jettisonable ventral and the lower vertical, and to measure local flow field parameters at a location on the ventral stabilizer.

Handling qualities of the X-15-2 with ventral on were approximately the same as previously obtained at the requested flight conditions. Data from telemetry were as expected. The controllability boundary, with ventral on, was not encountered during angle of attack pull-up to about six degrees with SAS off.

Results of the ablative tests appeared to be about as expected. Visual evaluation of ablative condition will be required due to loss of thermocouple data. Some cracking was observed on the horizontal stabilizer and ventral stub. In general, the ablative results appear to have been very successful.

Flight Profile

The data indicate the flight was flown essentially as planned. The maximum altitude was approximately 99,000 feet. A significant discrepancy in maximum velocity exists between radar data and cockpit film. The maximum velocity from radar was 5,550 feet per second, while cockpit film indicated shutdown at 5,250 feet per second and trail- off to 5,350 feet per second. Burn time for the flight was not as originally planned during simulator studies. A malfunction of the ammonia jettison valve, resulting in a small continuous loss of ammonia, limited the burn time to approximately 81 seconds. The cockpit velocity is higher than would be anticipated for this burn time based on the simulation of the planned flight. After final velocity and engine performance are determined, the flight will be "matched" on the simulator in determining where the discrepancy exists.

After launch, the pilot increased the angle of attack to about 13 degrees and then allowed angle of attack to settle on the planned 10 degrees for rotation. The maximum normal acceleration during rotation was approximately 2.3 "g."

The pitch attitude for climbout was attained at 25.1 which was about 6 seconds earlier than planned. Pushover to zero "g" occurred at 36.6 seconds which was 5.4 seconds early. Cockpit film indicated the aircraft had achieved the pushover altitude of 58,000 feet at this time.

As a result of pilot cross-checks. velocity and altitude and the "steep" call from NASA l, the pilot held slightly less than zero "g" after pushover. The correction was compensating and peak altitude was about 99,000 feet as planned.

At 4,000 to 4,500 feet per second, during boost, the pilot reported a "grumble" in the aircraft which remains unexplained.

About 40 seconds into boost, angle of sideslip drifted out to 2 degrees nose left and remained offset throughout the flight.

The profile after burnout was essentially as planned and all stability maneuvers were performed. The aircraft appeared to be out of trim in the roll axis during the flight. Shortly after performing the final maneuver for ventral-on evaluation, the pilot trimmed the aircraft and released the stick. At about 2,000 feet per second on velocity, the aircraft rolled to the right at about 7 degrees per second. The ablative coating on only one stabilizer may be the reason for the out-of-trim condition.

Ventral On Stability and Control

Maneuvers requested for study of ventral-on stability and control of X-15-2 were accomplished as planned and all objectives were met.

At about 5,000 feet per second (using cockpit film) the yaw and yar damper-off point, with angle of attack of 4 degrees, damping appeared neutral to the pilot and telemetry indicated a slight convergence. The pilot disengaged the roll damper and gradually increased angle of attack to 8 degrees. Angle of sideslip appears slightly divergent, however, the pilot indicated he may have forced the oscillation attempting to stop the aircraft tendency to roll off to the right. Pilot ratings for this data point were q - 2.5, f - 4.5, y - 4, and the pilot indicated the aircraft could be flown under these conditions.

The second data point was a repeat of the first series at about 4,200 feet per second. With the yaw and yar damper off at 4 degrees angle of attack, slight convergence was noted. At 4,000 feet per second with roll damper off and increasing angle of attack to 6 degrees, angle of sideslip was slightly divergent. The pilot rated this point as q - 2.5, f - 5, y - 3.5.

At about 3,100 feet per second, with the yaw and yar damper disengaged, the oscillations at 4 degrees angle of attack were convergent. At 2,800 feet per second, the roll damper was disengaged and at 4 degrees angle of attack the pilot rated this point as q - 2, f - 2, y - 2.

At about 2,000 feet per second, the pilot disengaged the yaw and yar damper and performed a rudder pulse, which appeared to be convergent. The pilot engaged the yaw damper, but elected not to re-engage the yar.

The above results were about as expected from earlier flight and analytical data. The pilot ratings were essentially the same as have been obtained during previous flights with ventral off or on. The pilot indicated the aircraft could be flown to at least 6 degrees angle of attack with the dampers disengaged. The pilot did not pull up on angle of attack sufficiently high to actually determine the controllability boundary.

Ablatives

Precast ablative materials were tested on the nose gear door, panels near the nose ballistic control system, and leading edges of the lower vertical stabilizer, and port horizontal stabilizer. Ablative coats were sprayed on top and lower surfaces of the horizontal stabilizer and lower vertical. Sections of ceramic ablative material (Avcot II) were placed on the leading edge of the lower vertical and jettisonable ventral.

Visual examination of the ablative coatings revealed surface cracking in the ablative material sprayed on the horizontal stabilizer. This may require modification of the spray-on process. Antenna and leading edge results were considered excellent. Leading edge test samples of Avcot II were completely consumed, as had been expected. This material was being considered for possible use on the antenna, but is not considered unacceptable.

Landing Loads

The pilot indicated the aircraft landing was the hardest he had felt. The landing appeared normal from measured data. Internal recordings did not function and no correlation is presently available to estimate the landing loads on X-15-2. Slide-out after touchdown was 7,349 feet. The pilot indicated he did not recall pushing forward on the stick after touchdown.

Ventral Local Flow

Data were obtained for the required conditions on the two probes located on the jettisonable ventral. The probes and transducers were destroyed by aerodynamic heating subsequent to the time when data were requested. These data will be analyzed to determine the local flow conditions and their affect on the proposed Ramjet installation.

Instrumentation and Operational Discrepancies

The film processor malfunctioned during the processing of 0-9-36C, 0-19-36C, and P-1-4E data from the flight. These rolls were cut and damaged in varying degrees. Approximately 40 seconds of data were lost from P-1-4E shortly after launch. Sections of 0-19-36C are not reproducible.

Data were not obtained from the thermocouple recordings on 0-9-36C. This apparently resulted from a freeze-up of the commutators of the T/C package located adjacent to the LOX tank in the center of gravity compartment of X-15-2.

The thermocouple identifier on 0-19-36C was inoperative after 185 seconds.

Satisfactory postflight calibrations could not be obtained for yaw BCS, inertial velocity, nose gear hook load, left and right-hand up-lock hook loads, and right-hand main gear drag snubber as recorded on 0-18-36C and the V-Port and Statham longitudinal acceleration records on 0-26-36C.

The channel 2 and 6 thermocouple sequences were not totally functional on 0-l9-36C.

Inertial vertical velocity was inoperative on 0-18-36C.

During the fueling sequence, the ammonia jettison valve failed to seat properly following ground jettison checks. The resulting ammonia leak was measured at 20 gallons per hour. In order to assure adequate fuel on board, the tanks were reserviced at 0850 hours and B-52 takeoff was at 0934 hours. It was estimated the leak would result in 3 seconds less burn time than planned for the flight. This estimate proved to be accurate.
 
 

Elmor J. Adkins, Head

X-15 Research Project Office