During this phase we were expanding the flight envelope to higher dynamic pressures and to higher heating regions. We were intentionally flying fast at lower and lower altitudes to load and heat the aircraft up to its design limits.
This phase began with Flight 53 and continued through Flight 100. The time span for this phase was roughly from April 1962 through January 1964. The primary pilots participating in this phase were Walker, White, McKay, and Rushworth. All three aircraft were utilized during this phase. The maximum speed and altitude achieved during this phase was Mach 6.06 and 354,200 feet. The maximum dynamic pressure recorded was 2,027 pounds per square foot and the maximum temperature measured on the aircraft was 1,323° F.
All of these flights were made from remote launch lakes. One accident occurred during this phase—a landing accident in the number two aircraft. We began carrying some generic research and scientific experiments in the latter half of this phase.
PHASE VIII
This phase was the generic research and scientific experiment phase. Generic research involved aerodynamic experiments that were independent of the aircraft. The X-15 was simply used as a testbed to get the experiment to a desired flight condition. As an example of one of these generic research experiments, we installed a sharp leading edge on the upper vertical stabilizer. We measured the skin friction and heating rates behind this leading edge and then compared that data to theory and to data obtained behind the original blunt leading edge. Another generic experiment involved measurement of the standoff distance of the bow shock in front of a blunt conical nose shape. There were a number of generic experiments flown during this phase.
Other experiments flown during this phase were scientific experiments that were completely unrelated to aircraft. These were nonaerodynamic experiments that again utilized the X-15 as a testbed. Examples of these experiments were experiments to collect micrometeorites; measure the ultraviolet stellar radiation; measure sky brightness; measure the high-altitude infrared background of the earth, horizon, and sky; and measure optical degradation at hypersonic speeds by using standard and infrared cameras to photograph targets on the ground.
The X-15 carried more than thirty experiments at various times, some aerodynamic, some space-related. The X-15 was an excellent testbed since an experiment could be carried into space and then returned to be adjusted if necessary and flown again. Many potential satellite payloads and experiments were developed using the X-15 as a testbed.
This phase began on the seventy-fifth flight and continued on through the duration of the program. This phase overlapped the latter half of Phase VII, the basic aircraft research phase. It began in December 1962 and ended in December 1968 at the conclusion of the program. The primary pilots involved in this phase were Rushworth, McKay, Engle, Thompson, Knight, Dana, and Adams.
The major portion of the generic research experiments were flown on the number three aircraft, although all three aircraft carried scientific experiments. In general, the generic research experiments involved flights at the lower altitudes while most of the scientific experiments involved high-altitude flights up to 300,000 feet. There were a number of problems encountered during this phase as well as the loss of Mike Adams and the number three aircraft.
PHASE IX
This phase was the X-15A-2 envelope expansion phase. This phase was intended to demonstrate the capability of the X-15A-2 aircraft to carry a scramjet experiment to a speed in excess of Mach 7.0. It involved the expansion of the flight envelope of the modified airplane in incremental steps up to Mach 6.7. This phase began on the 109th flight, the first flight of the modified X-15A-2, and concluded on the 188th flight after a total of twenty-one flights on the X-15A-2 airplane. This phase started on June 25, 1964, and ended on October 3, 1967.
Bob Rushworth, Jack McKay, and Pete Knight flew all the flights in this phase. During Phase IX, a maximum speed of Mach 6.7 was achieved. There were a number of problems encountered during the envelope expansion flight culminating with major damage to the aircraft on its last maximum-speed flight. Bob Rushworth encountered landing gear extension problems while Pete Knight experienced unanticipated heating problems. The aircraft was repaired, but it never flew again. The program officials decided to terminate the X-15 program before the repairs were completed.
Chapter 4
Demonstration Phase
(1959–1962)
Scott Crossfield had a couple of exciting flights during the initial contractor demonstration phase. Scott launched on the first flight with an inoperable pitch damper even though mission rules dictated an abort. He elected to launch since it was a very benign glide flight to a landing on the extra long lakebed runway three-five. The flight went well until Scott began the landing flare. As he attempted to decrease the steep glide path, he unintentionally initiated a longitudinal oscillation which quickly became divergent as he attempted to dampen the oscillation. It was a classic PIO (pilot-induced oscillation) maneuver, which was potentially catastrophic because he was rapidly approaching the ground. Scott’s plane was losing airspeed and the oscillation was increasing in amplitude.
Scott somehow managed to touchdown safely on the bottom of an oscillation. It was a terrifying sight, but he was able to salvage the airplane. The landing was firm enough, however, to damage the landing gear. The aircraft had to be returned to Los Angeles for repairs. Increasing the horizontal stabilizer actuator rate later resolved the PIO problem.
Shortly after launch on Scott’s fourth flight, one of the rocket chambers exploded causing an engine bay fire. Scott shut down the engine and began jettisoning propellants while setting up for an emergency landing on Rosamond Lake. Due to the steep nose-down attitude during the landing approach, Scott was unable to jettison all of the propellants. He touched down at a low speed in a nose-high attitude with a considerable amount of propellant in the tanks. When the nose slammed down the fuselage buckled just behind the cockpit. The airplane slid out on its nose gear, belly, and main gear skids. Scott’s only injury was to his pride. It definitely was not his best landing.
Scott still tells the story about his tug-of-war with the flight surgeon after the aircraft came to a stop. The flight surgeon aboard the rescue helicopter overheard someone say something about a broken back. The comment actually referred to the aircraft, but he assumed that Scott’s back was broken as a result of the landing accident. When the rescue helicopter landed next to the X-15, the flight surgeon jumped out with a backboard and ran up to the X-15 cockpit to rescue Scott from the burning plane. Scott had partially opened the canopy in preparation for an evacuation of the aircraft. The flight surgeon decided that he had to get the canopy out of the way to get the backboard on Scott before moving him from the cockpit. The flight surgeon pushed the canopy up to open it further. When Scott realized what the flight surgeon was doing, he grabbed onto the canopy in a desperate attempt to hold it down since he knew that excessive canopy motion would arm the ejection seat. He did not want to be ejected accidentally after surviving an explosion, a fire, and an emergency landing. Scott could not talk to the flight surgeon since his faceplate was still closed. The two highly motivated individuals struggled mightily—one pushing, the other pulling on the canopy, both attempting to save Scott’s life. After a minute or two of this Herculean effort, the flight surgeon finally gave up. He rationalized that Scott could not be seriously injured if he could pull that hard on the canopy.
The remainder of Scott’s flights were uneventful, although he did have a couple more minor fires with the LR-11 engine. He completed the checkout and demonstration of the various aircraft systems using the LR-11 engine and then concluded his participation in the flight program by making three flights with the LR-99 engine. On these flights he demonstrated all of the unique features of the LR-99 engine, such as the restart and throttling capabilities.
At one point in the X-15 program, North American Aviation made a proposal to modify the X-15 to enable it to fly into orbit and then reenter and fly back to a land
ing. North American Aviation made the proposal during the early days of the space program as an alternative to Mercury and/or Dyna-Soar. The government did not take the proposal too seriously although it was a major topic of discussion for awhile among some of the X-15 program personnel.
Scott Crossfield touted the proposal on several occasions, thus prompting Jack Allavie, one of the B-52 pilots, to come up with his own proposal for putting the X-15 into orbit. He said, “I’m going to get Scott up to the launch point and then I’m going to count down to the drop. (In that early phase of the program, the B-52 crew launched the X-15.) I’ll say, ‘Five, four, three, two, one, drop,’ but I won’t drop him. Crossfield will think that I launched him and he will light his big rocket engine. That rocket engine of his will start the B-52 spinning like a top and as a result, the B-52 will climb on up to 100,000 feet, and then I’ll drop him and Crossfield will go into orbit hollering, ‘Bonus, bonus, bonus!’ ”
Jack Allavie was a real colorful character and an excellent B-52 pilot even if he did taxi the B-52 at 90 MPH. The gaggle of ground vehicles that were following the B-52 and X-15 out to the takeoff runway would be strung out for a mile, really straining to keep up. Allavie was a B-52 mothership pilot during the first 3 years of the program. He was the B-52 pilot on Bob White’s record altitude flight to 314,750 feet. That was Jack’s last B-52 drop flight.
Forrest Petersen was the first pilot to check out in the X-15 after Joe Walker and Bob White completed the envelope expansion phase with the LR-11 engine. Pete’s first checkout flight called for a launch in the Palmdale area on a heading toward Boron. At Boron Pete was to make a left turn and fly toward Mojave. At Mojave he would make another left turn and head back toward the Edwards lakebed, for a landing on runway one-eight. These checkout flights were made at a nominal speed and altitude of Mach 2 at 50,000 feet.
Pete got both engines going after launch and headed out for Boron. On reaching Boron he started his left turn and immediately noticed a change in longitudinal acceleration. He was decelerating. Pete glanced down at his engine instruments and noted that both chamber and manifold pressures were dropping on the upper engine. Within seconds he also noted a pump overspeed light. The upper engine had shut down.
Pete immediately attempted to restart the chambers of the upper engine, but with no luck. He tried again with the same results. He then realized the lower engine had also shut down. This was confirmed by NASA-1, who advised Pete to continue the turnaround to head for a high-key position on runway one-eight. Pete did as he was advised and arrived at high key with 25,000 feet of altitude. This was lower than desired for a comfortable approach and Pete was not sure that he could make it around the pattern. Joe Walker, who was flying chase on Pete, quickly advised him that he had enough altitude and that he should continue on with the approach. With Joe flying a tight-wing position and coaching him along, Pete rolled into a tight turn and pulled it on around. He actually ended up slightly high on energy on final approach and had to use some speed brakes to get the airplane on the runway at the desired touchdown location. Joe was right, as usual. Pete had had ample energy for the approach. Pete’s first flight resulted in an emergency landing, but he handled the incident with his usual aplomb.
There had been a lot of chomping at the bit to get to the LR-99 envelope expansion phase. Joe Walker and Bob White were the primary pilots conducting this phase. Forrest Petersen made two flights and attempted a third, but had engine problems and had to abort. During the envelope expansion phase the aircraft was to be flown to its maximum design limits—the ultimate demonstration of the airplane. The flight envelope would be expanded to the design altitude of 250,000 feet and to the design speed of Mach 6.
Logic tells us that we would encounter our major problems during envelope expansion to the design speed and altitude. During expansion, we were probing the effects of higher speeds and higher altitudes on the airplane. The principal concerns were the maximum temperatures to be applied to the airplane and the effects of these temperatures on the structure of the aircraft. There was also a major concern about the stresses that would be introduced into the structure by the extreme temperature gradients that would be established between the hot external skin and the cool internal structure during the initial heating of the aircraft.
Would we have a structural failure or burn through or would a control surface bind up due to thermal expansion? These were new, unique concerns for the hypersonic speed regime. The standard concerns that accompany a new airplane were also not forgotten. Will the airplane be controllable? Will it be stable, or will it swap ends? Will the structure withstand the aerodynamic forces imposed on it by ramming through the air at over 4,000 MPH? Will the wings stay on during a 6 g pullout from 250,000 feet altitude after they have been heated to 1,200° F? Will the ballistic controls work properly outside the atmosphere or will we lose control and come back into the atmosphere backwards or sideways or upside down? These were just a few of our many concerns.
The X-15 Joint Operating Committee designated Joe Walker and Bob White to bring back the answers to these and many more questions. The pilots would probe higher and faster on each successive flight to address these concerns individually. They would prove the designers right and get a medal for doing so, or they would prove them wrong and get a street named after them on the base at Edwards. (Streets at Edwards are named after pilots killed during test missions.)
The flight program was laid out to expand speed and altitude concurrently. Normally speed was increased first to ensure that the aircraft was controllable at the speed needed to make the next higher-altitude flight. During the speed flights, the flight plan called for the pilot to pull up in angle of attack to simulate a pullout from high altitude. This allowed a relatively safe evaluation of the effects of a pullout. Expansion of the flight envelope to the maximum design conditions of Mach 6 and 250,000 feet altitude involved only ten flights. These flights began at the maximum flight conditions achieved with the LR-11 engine, Mach 3.50 and 136,500 feet altitude.
This phase began with Flight 34, a flight to Mach 4.43 by Bob White. Bob had previously flown to Mach 3.50 on Flight 33 with the LR-11 engine. Thus the envelope expansion with the LR-99 engine began with an increase of almost one Mach number on the first flight.
Joe Walker made the next flight, Flight 35, to an altitude of 169,600 feet, which was 30,000 feet higher than the previous maximum altitude. The planned altitude was only 150,000 feet. This flight also went off without any real problem. Joe made a couple of interesting observations on this flight. A fixed base simulator was adequate to prepare for this flight as long as the pilot had been exposed to centrifuge simulation training. Unfortunately, this centrifuge training procedure was not followed for the second group of pilots and it caused some surprises and problems due to the many unusual forces and accelerations involved in an altitude flight. The second observation was that 0 g flight was not a problem from the piloting standpoint. Joe commented, “One consciously appreciates the sensation of resting after the great physical effort while power is on.” In other words, 0 g was quite pleasant.
Bob made the next flight, Flight 36, to a speed of Mach 4.62. The planned Mach number was 4.60. This was his first flight at 100 percent thrust. He commented, “That’s quite a push,” after lighting the engine. During the flight he noticed a few bangs and thumps after engine shutdown as well as wisping smoke in the cockpit.
Joe made the next flight, Flight 37, another speed flight to Mach 4.95. The planned Mach number was 5.00. Joe had several problems on this flight. He lost his stability augmentation at launch and was unable to reengage it. As a result, the airplane was very loose in pitch with the nose continually bobbing up and down. During engine burn, Joe initially held his head forward off the headrest. As the g force increased, he could no longer hold his head forward and he allowed it to move back onto the headrest. When he did so, he got the immediate sensation that the airplane had just gone over on its back. He had to have total faith in his
instruments to convince himself otherwise. During a later pullup to higher angle of attack, he noted that the airplane wallowed in roll without stability augmentation.
Bob made Flight 38, another speed flight to Mach 5.27, just under the planned Mach 5.30. He had a couple of minor problems on this flight. Bob noted smoke in the cockpit and his pressure suit inflated due to a partial loss of cabin pressure. He had some minor controllability problems due to the loss of mobility with the inflated pressure suit. There was some wing skin buckling and a couple of popped rivets due to thermal expansion of the wing skin.
The next envelope expansion flight was Flight 40. Joe was scheduled to fly to Mach 5.60 on that flight, but only reached 5.21 due to a propulsion system problem. Joe also saw smoke curling up into the cockpit and heard creaks, pops, and bangs after engine shutdown. Joe again commented on the poor handling qualities of the aircraft at higher angles of attack without stability augmentation. He indicated that the aircraft was neutrally damped or even divergent at these conditions. Joe also complained about the big loss in pilot proficiency as a result of flying one flight every 4 to 6 months. Joe’s last flight had been almost 4 months earlier. This was indeed a real problem for all the X-15 pilots. A pilot obviously could not stay proficient in the aircraft while only flying 10 to 12 minutes at a time once every few months. Each flight seemed like a first flight under those circumstances. He felt reasonably proficient if he could fly at least once a month. Throughout the program, however, the average time between flights for each pilot was twice that long.
At the Edge of Space Page 12
