PILOTS FLIGHT NOTES

Plane: X-15 No. 670 Date: August 4, 1960

Flt. No.: 1/9/17 Launch: 0859

Pilot: Joseph A. Walker Land: 0909

Total: :10

Subject: Maximum Speed Flight - Stability and Control and Aerodynamic Heating The outstanding remark which can be made about this flight is that we attained our objectives. Maximum indicated Mach number reached was above 3.5. The aircraft handled without any difficulty at all and absolutely no problem was encountered in flying the flight plan from shackle release to touchdown. Considering that we have had a long layoff this is gratifying.

I had been wondering how well I would be able to fly the airplane even though having the best of intentions, after the layoff from actual flight experience in the X-15 on the order of 3 months, and was pleasantly surprised to discover that practice on the flight plan and working out flight plan details using the electronic ground simulator plus flight practice with the F-104 for glide and landing approach is a good substitute for a flight in the X-15 itself. I believe that this contributed in great measure to the ability to fly the profile schedule as desired and in accordance with the flight plan. Since a copy of the flight plan is attached, I will only comment on the various phases as to accomplishment and observation.

Very minute roll errors were encountered at the launch. Once again I had about 1 1/2 inches of lateral stick deflection to the left at shackle release. After about 3 lateral jiggles while arriving at lateral trim after leaving the flow field of the B-52 there were no lateral oscillation problems except those induced later on by intentional maneuvers. During the engine start, the angle of attack built up to about 10° and was checked there at onset of buffeting. Since the airplane seemed to be handling fairly well the round out angle of attack was maintained at 9° to 10° and then reduced to 8° after starting back up in the climb. No difficulty at all was encountered in flying the climb schedule.

The pitch SAS off pulses were accomplished at 1.6 and 2.0. In response to the pitch pulse, at 1.6 the airplane was moderately damped and lightly damped at Mach 2. There was no indication of disturbance about the directional axis as a result of the pitching oscillation.

At 75,000 ft. pushover to Zero "g" was initiated and it was observed that as the angle of attack approached Zero there was a tendency for the aircraft to wobble laterally. This seemed to be associated somewhat with the rate of the pitchdown motion in that the tendency to wallow reduced as the pitching velocity was reduced to Zero upon reaching Zero angle of attack although all the way over while at Zero "g", it felt weak laterally.

As soon as level pitch attitude was obtained the aircraft was held at 1/2 "g" for the remainder of the powered flight and a gradual increasing dive angle was obtained during the course of acceleration to maximum speed. During this phase the airplane felt very good about all axes with a very small tendency toward minute lateral residual oscillation. However, this was so small as to be of no consequence as far as control of the airplane was concerned. Burnout occurred at slightly over indicated Mach 3.5. The 5 second coast at 1/2 "g" was carried out, then pullup to 4 "g" was initiated. The airplane responded with good control as the load factor increased. At about 3.8 "g" a noticeable tendency to small oscillation directionally was observed and in response to this indication, 3.8 "g" was the maximum pullup load factor. Then the nose was lowered and 1 "g" flight maintained from that point on as we were about level.

A SAS on pitch pulse was obtained at 1 "g" and the airplane was essentially dead beat. The SAS 4-0-0 directional pulse was then accomplished and it was observed that, although lateral oscillation ensued, it was damped.

Because of the geographical position of the aircraft, the pitch pulse was omitted and the left turn to 10° angle of attack was accomplished. Upon establishing this condition a SAS 4-00 rudder pulse was accomplished. Once again the aircraft responded with a lateral oscillation which appeared to be undamped. Neither of these two directional maneuvers would be considered as being stable enough that the airplane could be used without stability augmentation on these axes. Although the one at low angle of attack did indicate that some damping existed, the amount was not sufficient to be adequate.

Subsequent to this second directional pulse, the aircraft was returned to level flight, the pitch SAS turned off, and several pitch pulses accomplished during the remainder of the letdown from altitude and positioning for the landing approach.

As the speed came down it was noted that for the second pulse which should be in the neighborhood of Mach 1.7 to 1.5, the aircraft was almost neutral longitudinally. At about 33,000 ft. still with the pitch SAS off, the speed was reduced to 220 knots at 10° angle of attack followed by a pushdown to nearly Zero "g". This particular maneuver was done in order to check several static orifices as to their relative merit for use in connection with the alternate air speed system. With pitch SAS back on the remainder of the glide and approach to landing was accomplished without incident; the flight pattern was flown at 310 kts. and the landing had the appearance in the cockpit of being probably the lightest touchdown and following nose impact with the ground of any of the four flights I have flown.

General Comments: The stability augmentation system appeared to be functioning much better than on any flight previously. The residual lateral oscillation which had been prevalent was not observed, either being non-existent, or extremely minute quantity. For instance, in the climb, the only lateral corrections required were essentially one shot in order to pick up a low wing or to correct the heading. The stable platform driven three axis attitude ball worked extremely well and the whole flight profile was flown using that as the heading and attitude reference. The computed altitude and velocity indications appeared to not be accurate. In fact, the altitude was 10,000 ft. behind the pressure altitude indicator during the climb. However, it is conceded that the total erection time allowed for the stable platform was not of sufficient duration to guarantee the best performance output. The altitude was, however, the same as the pressure altitude at launch. No difficulties were encountered with any of the airplane's systems. Engine start, operation and shutdown were smooth and, according to past experience, at about optimum level. I would say that with the stability augmentation system functioning, the overall handling characteristics in the speed range covered on this flight are very satisfactory.

Joseph A. Walker