MEMORANDUM for Chief, Research Division
Subject: Preliminary evaluation of X-15 Flight No. 3-13-23

1. Flight 3-13-23 was flown on December 20, 1962, by Joseph Walker for the purposes of:

2. Small pitch and roll mistrim conditions from AFCS null, caused by stick position drift, resulted in several indications of temporary malfunctions in the AFCS. The stick position drift has been attributed to the side-stick boost servo and will require corrective action prior to the next flight. This condition had no apparent affect on the flight or on the AFCS in-flight operation.

3. The launch was made in the vicinity of Mud Lake at an altitude of 45,000 feet and the flight was completed as planned. The maximum altitude for the flight was approximately 160,000 feet. During the rotation after launch, a maximum dynamic pressure of approximately 1500 psf was attained. The control system limit cycle in roll at this maximum dynamic pressure was slightly more severe than previously noted but still did not have sufficient amplitude to feed back to the pilot's stick. The pilot, however, did notice the existence of the limit cycle. The limit cycle characteristics were as follows:

peak-to-peak amplitude in p-dot = 65°/sec2

p = 7°/sec

f = 1°

da = 1.5°

Ay = .07 g

frequency approximately = 1.74 cps

There were periodic occasional bursts of two or three cycles of about twice the above amplitude as the adaptive gain went super-critical. Small periodic bursts were also evidenced in pitch and yaw. The adaptive roll gain was at the minimum value for about 15 seconds during the period of maximum dynamic pressure. The adaptive pitch and yaw gain were never at the minimum value. Based on this flight data, it is felt that the roll limit cycle amplitude would still be acceptable for entry conditions where angle of attack was approximately 26° and dynamic pressure was less than 1500 psf.

Lateral pulses were accomplished after shutdown at an angle of attack of about 20° with partially extended speed brakes. Properly phased lateral control by the pilot precipitated a slightly divergent sideslip oscillation that had a maximum amplitude of -2.5° to +3.0°. This oscillation subsided when lateral control was quiescent. Additional lateral pulses were obtained at angles of attack between 15° and 23° which were accompanied by sideslip excursions of less than 2°. The pilot's impressions of the aircraft's handling qualities throughout this flight were highly favorable. It is suggested that the next ventral-off flight is an altitude flight to about 250,000 feet with a speed brake closed entry and an initial angle of attack of 10° to 12° increasing to 15°-18° at 1 g.

4. Automatic reaction controls were used on this flight and functioned satisfactorily. Approximately 25 pounds of hydrogen peroxide were used by the AFCS.

5. The automatic AFCS disengage switch was again used during the landing for this flight. A maximum stabilizer deflection of -12° occurred 0.6 seconds before nose gear touch down, at which time the stabilizer was at -4° with the AFCS off. Landing gear loads were lower than any previously experienced except on flight 3-12-22 when the pilot pushed forward on the control stick. It is recommended that the procedure used during this landing, be continued as standard practice.
 
 
 
 

Elmor J. Adkins

Aerospace Engineer