June 2, 1964

MEMORANDUM for Chief, Research Division

Subject: Preliminary Report of X-15 Flight 3-28-47

A. General information - Flight 3-28-47 was flown May 12, 1964. The stated purpose of the flight was: "Heat transfer and skin friction experiments with the sharp upper vertical fin, and boundary-layer noise experiment."

The launch configuration for this flight was MH-96 adaptive, Roll Hold "ON," R.C. "OFF," BCS "OFF," heading vernier to "standby," and ventral fin "OFF."

The launch point was Hidden Hills. The magnetic heading was 207° at an altitude of 45,000 feet, and a velocity of 800 ft per second.

B. Mission Objectives - The maximum altitude attained was approximately 73,000 feet; (planned Hmax = 69,000 ft). Maximum velocity was 4,540 feet per second; (planned Vmax = 4070 feet per second).

The pilot was asked to attain and hold a dynamic pressure of 1150 psf for twenty seconds. The records show that a steady state dynamic pressure equal to 1300 psf was maintained for approximately 40 seconds.

The performance described here differs from that of the flight plan, however, it is remarkable in light of the fact that both inertial velocity, and altitude were unusable throughout the entire flight. The performance of the X-15 during this flight was such that the major mission objectives were essentially attained.

C. Stability and Control - Approximately 0.6 seconds after launch the pitch and roll dampers disengaged. Oscillations in all modes were observed, and the following values for the rates and attitudes were recorded:
 

Parameter	Value
q	+9.0 deg/sec
	-6.0
p	+30.0 deg/sec
	-45.0
f	+13 degrees
	-49
b	+3.5 degrees
	-5.5

 

Five seconds after the dampers disengaged they were reset by the pilot. However, they again disengaged 7.6 seconds later. Again oscillations were observed subsequent to damper disengagement. The rate and angular values were: fpp » 25.4, fmax » 16.5°, Pmax » -25°/sec. These oscillations were damped 3.3 seconds after the disengage, coincident with the pilot's action to reengage the pitch and roll dampers for the final time.

During the rotation an amax = 16° was reached 3.7 seconds after launch. An indicated angle of attack of -2° was attained during the powered pushover, however, no adverse control problems were noted by the pilot.

D. Handling Qualities - At no time, during the flight, was the pilot confronted with an "adverse" control task. However, the portion of flight during which the dampers malfunctioned was considered, by the pilot as the most difficult. His ratings for this phase are:

q 4 , f 4 , y 3 .

With dampers engaged, and the control system functioning normally, the pilot rated the airplane as:

q 2 , f 2 , y 2 .

The pilot was flying without the aid of his inertial velocity and altitude indicators. This situation should be considered when evaluating the damper "ON" ratings.

E. Systems Operation - Several system failures occurred during this flight, the results of which have been discussed previously. An itemized account of the failures appear in Table I.

The adaptive control system functioned normally for the remainder of the flight.

At the time of damper reengagement the pilot noted that the inertial velocity and altitude continued to show the launch values. However, the 3-axis ball was giving accurate pitch and roll information. The pilot continued the flight using the pitch schedule and q as profile checks.

A postflight examination of the inertial platform showed a failure in a power supply circuit as the probably cause of the failure.

F. Conclusions - Although several failures in the damper system occurred, and the pilot suffered the loss of two vital profile parameters the flight was amazingly successful.

Because of the long steady state q condition the primary objectives of the flight were fulfilled, and the damper failure presented some unexpected controllability information.

An important by-product was an example of the adaptability of the pilot in unusual flight conditions.

Donald J. O'Mara

Aerospace Engineer