One might wonder why all the fuss about 8 extra seconds of burn time. It was very significant because I was accumulating too much energy (speed) approaching Edwards. With too much energy, I could not slow down to land at Edwards and could go whizzing on by with no place to land.
When I reversed the turn, I put in a relatively large roll command and at the same time pushed the nose down to prevent the aircraft from climbing as I rolled over the top. Then, as I approached 60 degrees right bank, I put in a healthy roll command to stop the roll at 60 degrees bank. My speed at this time was close to 5,500 feet per second (approximately 3,700 MPH) and my altitude was just under 100,000 feet.
Just as I completed this maneuver, the aircraft started rolling violently back and forth. At the same time, it was pitching up and down. I was being thrown against the straps with tremendous force. I was flying at almost 4,000 MPH and the airplane was totally out of control. I happened to glance out the window during one oscillation and everything was black. At the time, I could not figure that out. It was, of course, the sky as seen from high altitudes. I had never been that high before. This wild oscillation continued for what seemed like an eternity, but was actually only 8 to 10 seconds and then the aircraft motions stopped just as quickly as they had started. That was some ride—just like being on a wild bull. I tentatively moved the control stick and the aircraft responded normally, so I rolled back to the 60 degree right bank that I was supposed to be in and pulled up to 10 degrees angle of attack which gave me about a 2.5 g turn to the right.
Thinking about the last few seconds, I realized that NASA-1 was unusually silent during that violent maneuver. Usually when something unplanned occurred on a flight, the experts in the flight control room were clamoring to tell you what the problem was and what action to take to correct it. In this case, nothing.
NASA-1 finally called and said, “Watch your H dot” (rate of descent) and then said, “Ninety-eight thousand, bring her down a little bit.” I said, “OK.” As I decelerated through 4,300 feet per second velocity, I pulled on up to 17 degrees angle of attack and rolled to 90 degrees bank angle just as NASA-1 called to say, “Bring brakes out now and come on up to 17 degrees.” A few seconds later NASA-1 advised me that I was passing over Three Sisters. They were only about 40 miles northeast of Edwards.
As I discussed earlier, I was now in a real high-energy situation. I was still traveling about Mach 4 (close to 3,000 MPH) and I was only 40 miles out. I was hotter than a pistol and I really had to slow it down. I was supposed to reverse my turn at 3,800 feet per second, but I had turned too far on the first turn and I was way high on energy, so I called NASA-1 and asked what to do about the turn.
NASA-1 responded, “Hold it there in the right turn and we will want you about two-two-five degrees” (heading). The next call, a couple of seconds later, was, “Bring it around to two-four-five.” A few seconds later, NASA-1 said, “You’re coming up abeam Cuddeback now. Have you down to 70,000 and 3.5. Full speed brakes now.”
Cuddeback, another of our emergency dry lakebeds, was only 30 miles from Edwards and I was still traveling over 2,300 MPH at 70,000 foot altitude. I said, “OK, full out.” NASA-1 called again to say, “OK, keep her coming on downhill, looks real good. Field is off to about your ten o’clock, do you have it in sight?” I said, “Yep.” A few more seconds and NASA-1 said, “You’re about 15 (miles) out now, coming through Mach two now, real nice. Keep your brakes out.” The next call from NASA-1, about 15 seconds later was, “You can bring the brakes in now, have you about 10 (miles) out. One point five Mach.” My energy was now in good shape.
The next call came from Bob Rushworth, Chase-4, who was flying in the Edwards area waiting to pick me up during the landing approach. “OK, Milt, you can go to jettison anytime.” We usually waited to jettison any remaining propellant until the landing chase called, since it provided the chase pilot a good visual cue to locate you. The jettisoned propellants normally came out like a white vapor trail. I responded, “OK.” Chase-4 then asked, “What’s your altitude?” I said, “I got 40.”
NASA-1 called to tell me, “Engine Master off.” I said, “OK. Am I coming across the highway?” As I mentioned earlier, the windows in the X-15 were very limiting in downward vision. NASA-1 said, “Coming across the highway now.” This was the highway just north of the Edwards lakebed running between Mojave and Boron. I said, “OK.” NASA-1 said, “And if you got time, give us a calibrate.” I said, “OK, damper disengaging.” NASA-1 then said, “OK, coming subsonic, watch your angle of attack.”
Chase-4 then chimed in with a “Tallyho.” He had finally spotted me. NASA-1 then called and said, “Check your flap and squat circuit breakers.” I said, “They’re in.” NASA-1 said, “Experiment off,” and I said, “Rog.” NASA-1 said, “You can set in your nose down trim now if you want,” and I responded, “OK. I’m using some brakes in here.” Chase-4 then said, “You can go to pressurize anytime now. I don’t see any jettison at all.” We always repressurized the fuel tanks after we jettisoned fuel to gain extra fuselage rigidity during the landing, to minimize the chance of the fuselage breaking as the nose slammed down.
My next call was, “Flaps,” and Chase-4 called, “Flaps coming down.” I then called, “Gear,” and Chase-4 said, “Looks good” and finally, when I touched down, he said, “Good.” I slid for about 2 miles on the lakebed before I stopped. The flight from launch to landing lasted just under 7 minutes.
During that flight, I had zipped on up to 3,750 MPH, performed a number of test maneuvers, lost control of the aircraft momentarily, traveled over 150 miles of desert and landed back home at Edwards in a 2-mile-long cloud of dust, all in less time than it it takes to smoke a king-sized cigarette. As I said before, it is a poor way to build up flight time and it is really tough to get your 4 hours minimum flight time a month.
While I was sitting in the suit van, getting out of the pressure suit, I reflected back on the flight. For 10 seconds during that flight, the airplane had been doing its own thing. That reinforced my previous thought that the X-15 was like a bull. When it decided to do something on its own, it did it. There was nothing you could do to stop it. I had momentarily lost control of the bull.
It only took a couple of days after the flight to determine why the engine burned an extra 8 seconds. Normally, in level flight, the engine burned out when the propellant level in the tank dropped below the level of the top of the propellant line leading out of the tank. At that time, pressurizing gas also began escaping and the fuel pump cavitated. In that condition we normally ended up with about 150 gallons of residual propellant left in the tanks at burnout. In my 4 g turn, the propellant was forced to the rear wall of the tank in such a manner that no pressurizing gas escaped until all the propellant went out the line. I managed to use up all the propellant and got 8 more seconds of burn time. Chase-4 confirmed this theory when he mentioned during the flight that he saw no jettison at all.
The other problem—loss of control—took about a month to solve. At first, Bob Rushworth facetiously said it was just a result of my ham-fisted flying. (Rushworth, at that time, was the senior X-15 pilot.) He implied that I had caused the aircraft to go unstable with my large control inputs just before burnout. We were all aware of the need to treat the system gently. To counter that, I dug up some of the records from one or two of Rushworth’s flights and showed him where he had made similar control inputs. I really liked Bob and had tremendous respect for him, but I knew this was a unique problem that I had encountered.
After many hours on the simulator and some necessary improvements to the simulator, our control system experts were finally able to duplicate the problem. In essence, that smart control system had fooled itself into thinking that it was at a more benign flight condition. When I applied control it gave me much more control deflection than I should have gotten. The airplane then responded more than the control system thought it should, and the control system in turn fought that excessive response. A limit cycle, oscillation de
veloped wherein the system was periodically calling for full control, first one way and then the other. The airplane was forced into a sustained violent oscillation in both pitch and roll. It was a wild ride.
After about 10 seconds of this nonsense, the system finally stabilized itself and the aircraft recovered. It did not cause any damage during this flight, but at a more severe flight condition, it could have torn the aircraft apart. We learned something new about the airplane.
I was always impressed with the philosophy used in the early days of flying in World War I. Any mechanic who worked on an aircraft could be ordered to fly with the pilot on the first flight after the repair work was done. Any parachute rigger could be ordered to jump in any of the chutes that he had packed. That really created an incentive for quality work. It also weeded out the incompetents since they did not make it back to work after a failure. I wish the control system designer had been along on this ride.
I strongly recommended that the control system be modified to prevent this from ever happening again, but modification of the control system would have been very expensive and time consuming. Program officials decided against any modification. They believed we now understood the problem and could take preventative steps to ensure that this problem would not cause the loss of the aircraft. This decision came back to haunt us.
MY ALTITUDE FLIGHTS
I flew my first altitude flight in the number one X-15. This aircraft had separate controllers for aerodynamic and reaction controls. Aerodynamic controls were on the right sidestick controller and reaction controls were on the left sidestick controller. On an altitude flight in this aircraft, the pilot was flying with both hands. The flight was planned to an altitude of 180,000 feet. The purpose of the flight was to provide an altitude buildup flight for me to obtain data with the MIT horizon photometer, and to check out the Dyna-Soar Honeywell Inertial System. (Even though I did not have the opportunity to fly Dyna-Soar, I did get to fly some of its parts.) Altitude buildup flights were normally done in 40,000- to 50,000-foot increments. In my case, my highest previous altitude was 100,000 feet, so I was taking an 80,000-foot step in maximum altitude. That is a pretty big step.
The flight was to be launched at Mud Lake on May 25, 1965. The prelaunch activities proceeded without a hitch and I was launched at 10:12:07.5. I got a good light and pulled up to 11 degrees angle of attack. I held 11 degrees alpha for approximately 24 seconds until I reached my climb attitude of 30 degrees. My speed had increased to 1,700 feet per second as I stabilized on my climb angle. When I reached a speed of 2,000 feet per second, I opened my speed brakes to slow down my rate of climb. This procedure was used during altitude buildup flights to give the pilot more opportunity to observe the transition from aerodynamic to space flight and enable him to better feel out the airplane during this transition. At 82 seconds of burn time, I shut the engine down as I passed through a speed of 4,900 feet per second. I then retracted the speed brakes and sat back for the long coast to peak altitude.
As I continued to coast up to peak altitude, I was surprised at how easy it was to fly an altitude flight compared to the exacting heating flights that I had been flying. On these altitude flights, I simply pointed the airplane uphill at the proper climb altitude and then shut the engine off at the specified velocity. There was none of this business of pushing over to 0 g opening speed brakes, adjusting the throttle and pulling into turns while maintaining the precise altitude and velocity that was required on heating flights. Altitude flights were easy, and fun.
Admittedly, flying two-handed was not the most simple task, but so far I was doing a pretty good job of it. I was able to hold pitch and roll attitude and compass heading within a couple degrees of the desired values. I tended to work each axis individually with the left-hand reaction controller, rather than make combined inputs. I was primarily concentrating on maintaining heading and a wings level attitude while slowly adjusting pitch attitude to correlate with flight path angle. The control technique utilized by most of the pilots with the left-hand controller was to make pulse type control inputs in one axis at a time.
These inputs were used in pitch to change the pitch attitude as required and in yaw and roll to maintain heading and a wings level attitude. The one thing the pilot did not want to do was get the airplane moving in more than one axis at a time. He wanted to keep the aircraft motions simple and slow. At these lower peak altitudes, below 200,000 feet, he was assisted in his task by small aerodynamic forces that tended to keep the airplane pointed in the right direction. Do not misunderstand. A pilot could still get in trouble and lose control at these lower peak altitudes, but he had some help from the inherent aerodynamic stability of the airplane.
Above 200,000 feet, the pilot was on his own. If something caused the aircraft to start rotating in any axis, it would continue to rotate until he put in a control pulse to stop it. The airplane could turn completely around if he did not stop it. That is why he really did not want to get the airplane moving in more than one axis at a time. If it ever did get moving in more than one axis at a time, the best control technique was to stabilize the motion in one axis before working on the other axis.
As I approached peak altitude, I concentrated on changing pitch attitude to be in the proper attitude for entry. The flight path changes quite rapidly on these high-altitude flights as we go over the top, since we come down as steeply as we go up. In just a matter of seconds, the flight path changes from +30 degrees to -30 degrees. It was very desirable to have our entry pitch attitude established as we peaked out in altitude. We actually began pushing the nose over before we reached peak altitude and ended up going over the top with the aircraft in a 10- to 20-degree nose-down attitude. As I reached a nose-level attitude before going over the top, I had my first look at the earth from high altitude. It was impressive. As Bob White replied when asked how far he could see on his maximum altitude flight, “You could see as far as you looked.”
The earth was very bright below me. I could see the earth curve away in all directions and the atmosphere appeared as a band of blue haze sitting below me and just above the horizon. The sky was quite black above and to the sides. But something seemed strange. The bright earth was under the nose of the airplane. Out ahead, the earth was a darker color, a bluish grey color. All of a sudden I realized I was looking down on the Pacific Ocean. The California coastline was down under my nose at what appeared to be a 45-degree angle. I was going to reenter over the Pacific Ocean!
I could not believe it. Someone had made a horrible mistake. I was either launched too far down range or I was higher and farther down the track than my instruments and ground radar indicated. I was going to end up in the Pacific Ocean and I did not even have a life raft in my emergency bailout kit. For that matter, I did not have a life vest. I was in deep crap. There was no way I could get the airplane back down in the atmosphere and turned around before crossing the coastline.
As I sat there dumbfounded, NASA-1 continued to babble on about how nice my track and profile were. Little did they realize what was happening. I was tempted to tell NASA-1 that they did not know what the hell they were talking about. I was in real trouble. But, as I sat there subconsciously flying the airplane and wondering about the ditching characteristics of the X-15, the blue band of the atmosphere began to get thicker and thicker and all of a sudden it enveloped me. The g forces started to build up and the ocean seemed to recede from my view.
I began to see the desert and the mountains in a more familiar perspective. I could now look out ahead and see land, not water. In fact, there ahead was good old Rogers Lakebed at Edwards. It was still down below my nose, but now I could convince myself that I could get the airplane down to a landing on the lakebed. Somehow things had worked out. But I was still upset and I was going to raise hell with the guy who had planned that flight. He had scared the hell out of me and I had survived only through my own skill and cunning. I was going to kick his butt. He could have at least warned me about this.
; I learned later that each of the pilots had been similarly surprised on their first high-altitude flight. The geometry of the flight profile was highly unusual. At peak altitude, the pilot was within 100 miles of his destination but he was close to 40 miles high on a 200,000-foot flight and almost 60 miles high on a 300,000-foot flight. Experience with normal airplanes would indicate that you could not possibly descend fast enough to remain over land from that position. But the X-15 was not a normal airplane. It was a super airplane—a cross between an airplane and a spacecraft. It was something else.
The remainder of the flight was routine and I made an uneventful landing at 10:21:09.5. Total free flight time—9 minutes, 2.5 seconds. Not quite enough to qualify for flight pay, but then we did not get flight pay anyway.
My second altitude flight was even more uneventful than the first. I went to a higher altitude, 214,000 feet, but I had no problems and again felt that altitude flights were a piece of cake. I might qualify that statement somewhat. Altitude flights were extremely easy to fly if the flight control system was working properly. If it was not, the pilot could very easily get into trouble real fast, especially during reentry. During entry he had to hold a fairly high angle of attack to accomplish the pullout. At these high angles of attack, the X-15 was not exceptionally stable and would oscillate if disturbed, particularly in the roll and yaw axes. It required stability augmentation, or artificial damping, to cope with these high-frequency aircraft oscillations. Without damping, these airplane oscillations could result in loss of control. We really did not want to lose stability augmentation during entry.
At the Edge of Space Page 26
