Flight: 2-18-34

Launch: 1440

Land: 1449

B-52 Pilots Maj. Allavie and Sq. Ldr. Archer

Launch Panel Jack Russell

Chase I Major White

Chase II Cdr. Petersen

Chase III Major Daniel

Chase IV Major Rushworth

NASA 2 (Beatty) Jack McKay

NASA 1 (Edwards) Stan Butchart

I. DISCREPANCIES

The normal preparation procedures for this flight were accomplished, in fact were amplified. For instance, three operations were required to get a satisfactory engine ground run, resulting in that much more engine start procedural practice. Landing practice utilizing F-104 aircraft and flight plan practice utilizing the ground simulation were also doubled because of two flight postponements and change of ground controllers.

In addition we devoted more than average attention to trying emergency operations - part thrust operation, partial loss of pilot presentation, partial losses of stability augmentation and premature engine shutdown. So the actual requirement to throttle the engine which developed after launch did not leave us unprepared. We knew that we could get better than 5000 ft/sec even at 50% thrust, provided we followed the climb path and got to altitude. However the exact situation could not be anticipated, so some last minute improvisation was required. Our presentation tells us where we are, not where we ought to be. This information is at the ground station.

I did not have any doubt about reaching either Edwards or an intermediate landing site.

III. FLIGHT OPERATIONS
 

During powered flight panel scan included attitude, heading, angle of attack, fuel inlet pressure, pressure altitude, inertial altitude, inertial total velocity, inertial vertical velocity, hydraulic pressure, cabin pressure, stopwatch.

The inertial attitude and velocity and altitude system functioned in a superior manner. Speed brake extension was initiated at 5200 ft/sec during pushover. Maximum inertial altitude was just over 110,000 feet. Vertical velocity was still responding and sensing correctly during glide.

Although it was disappointing not to accomplish the prime objective we still obtained valuable information. It developed that the aircraft was fairly difficult to maintain steady wings level and zero yawing when attempting to reach 15° angle of attack after shutdown. This problem was proportional to angle of attack. After getting the motions subdued, a rudder pulse caused the same motions to resume. The lateral control had to be used in a manner much as we had anticipated for speed brakes out - roll and yaw dampers off.

The penetration of heating into the aircraft could be observed in a qualitative manner by observing start, increase, and decrease of smoke tendrils curling up between top of instrument panel and canopy. At this same time creaks, pops, and bangs occurred, followed by a quiet period, and then more creaks and bangs. This transpired after speed decreased from maximum and gives the pilot some concept of lag time.

Just after the end of the cool down, two, possibly three instances of stall buffet were encountered when attempting to pull up to fifteen degrees angle of attack. This resembled that which occurs to an F-104 at Mi 0.9 in a mild stall.

At this time no further lateral- directional control problem was observed and the rest of flight directed toward letting down and landing. After a rather precipitous descent from above 80,000 feet, speed brakes extended fully, combined with a left turn to downwind leg, I retracted speed brakes by visual reference to ground position and altitude. Small amounts of speed brakes were used twice in the pattern to adjust altitude. Touchdown was 200 feet short of intended point. The ground slide was shortened by raising flaps, extending speed brakes, and using full back stick.

IV. CONCLUSIONS
 

It is my belief that a reevaluation of our preflight and preparational procedures would be in order so as to verify that we're obtaining full value from the operations that we are presently going through. For instance, on this particular operation, contrary to the desired and standard routine relative to stable platform, we departed on the flight without entire inertial system within desired accuracy. We did have the attitude system working before we left and while on the outbound cruise to Mud Lake launch the inertial system became accurate to the extent that at launch we had the launch altitude on inertial altitude, we had the proper total velocity on inertial velocity and we had zero vertical velocity on that indicator and had been this way for several minutes prior to launch. During the flight the whole system worked as well or better than any best previous operation. I was able, during the climb, to rely upon velocity and altitude and check that we peaked out at just over 110,000 by the inertial indicator. Radar altitude readout was 115,000. I think possibly that there may be several other systems which we could fruitfully shorten some of the checkout procedures. It may even be that we are wearing these things out by constantly running them to make sure they are working on the ground.

I should also point out that I was aware as we started out on the flight, since it was 1345 Pacific Daylight Time at takeoff, that our return course was going to bring about the problem of strong sun glare during the climb portion of the flight and this did, in fact, occur to the extent that part of the climb I was forced to hold my left hand up over the visor to shield my eyes so I could see the instrument panel. A tinted or dark visor which could have pulled down .......... strong that it had to be completely cut off in order to be able to see.

As culmination of thoughts concerning the X-15, I would conclude that we have an unsolved problem facing us; one that has not been considered to be a problem. This airplane handled after power shutdown and in attempting to pull up to angle of attack to do the rudder kick, as though it had little or no damping. Especially noticeable was the fact that in spite of an 8 setting on the pitch damper gain still the nose bobbed up and down when attempting to adjust angle of attack, almost as bad as it had on my previous flight when I did not have a pitch damper functioning. Subsequent attempts to steady the wings and stop a yawing motion brought forth an in-flight comment that I was having to use the lateral control system the same as I had expected to have to use it for our intended flight plan speed brakes out and roll and yaw dampers off. I had the feeling that I ought to do something about the motion of the aircraft. It was a fairly long period and subsequent check of the records indicate that the period was in excess of four seconds but it also felt if I did not do something about it, it would continue to oscillate and increase in amplitude.

The morning following the flight a series of runs on the ground simulator were made attempting to establish conditions which would more or less duplicate what we had experienced during the flight. The only way which this could be done with any amount of satisfaction was by cutting way down on the damper gains but the period wouldn't come out right at the velocity and altitude which we had had during the flight. If we increased angle of attack the simulated airplane would climb as it had not done on the flight, however, all in all, the best combination of experimentation was where the gains were down to at least 3 on all augmentation axes, the angle of attack was above 15° and the q was low. What I am attempting to say is we have one of two things facing us; either we are not experiencing the stability in flight which has been indicated for the airplane from wind tunnel tests because it isn't there, or this q is too low, or we're flying at a lot higher angle of attack than indicated to the pilot and recorded on instrumentation. The apparent stall buffet encountered tends to indicate that we are at a higher angle of attack than we think. While reading essentially 10° to 12° angle of attack it is apparent that in this speed range that an actual angle of attack of better than 20° would be required to approach this type of a situation. Further if it can be shown that the angle of attack is correct and that the dampers were functioning as they should have for the particular gains being used on this flight, I would think that we would be led to conclude that our stability is low. As a result of this type thinking and having observed during flight that the problem of damping oscillations was increased as the angle of attack was increased, consideration of attempting maximum speed flight with this aircraft by eliminating the jettisonable portion of the lower ventral should be gone into very carefully inasmuch as this would seem to be in the direction of further decreasing directional stability.

We have been utilizing Mud Lake launch site for these higher speed flights with a good approach in mind, namely that by judicious use of speed brake we can handle the energy involved in that distance without danger of overshooting Rogers Dry Lake. However, this is at the same time rather penalizing us from an investigatory standpoint if only on the basis of flight duration. There is only so much one can do in a given length of time, if it is a pulse and we have a long period, in order to get stabilized for the pulse, do the pulse, and allow time for the pulse to continue to a worthwhile extent, time passes. Consideration of utilizing a longer flight range would be advisable, thereby allowing us to possibly accomplish more per flight. For instance on this flight even though we did miss intended initial part of the flight program, I was aware of a very short interval between power cutoff and when the necessity for extending the speed brakes in order to make the approach for Rogers occurred. In fact to have been a little better off we should have extended the brakes sooner. Admittedly if we had had the brakes out at the beginning then the problem would have been reduced on the end of the flight. However, this is a case in point to illustrate our extreme dependence on the added drag.

The head bumper which we have installed in the aircraft for use in connection with deceleration showed itself to be a very useful device when I was letting down at the end of this flight. We added a heater in the pressure suit vent supply system which proved to be the answer we had been looking for in connection with reduction or elimination of a cold vent gas problem.

I would say if we were to plan a flight to higher speed, even to the maximum possible, that the problems that I observed on this flight would not be particularly detrimental in as much as they were problems only at angles of attack above those required to achieve such a flight. Further that this particular type flight would probably be worthwhile whether we attempted to study higher angles of attack with the dampers on or whether we again attempted to investigate an emergency condition with the speed brakes out, roll and yaw dampers off. However our rate of accomplishment has not been too good for dampers off at low q and perhaps better results could be obtained on this score on a different flight plan.
 

Joseph A. Walker

Aeronautical Research Pilot