The rocket engine startup procedure sounds quite complex but it really is not. In the X-15, we first had to pressurize the propellant tanks (the liquid oxygen and liquid ammonia tanks) with gaseous helium. This pressure was used to force the propellant out of the tanks into the main feed lines to the turbopump and the engine.
The next sequence was a precool sequence to cool down the oxygen system to ensure that the liquid oxygen would not be heated up and vaporized before it got to the turbopump. Vaporized LOX would cause the turbopump to cavitate and go into an overspeed condition which could cause an automatic shutdown or pump failure. It required 10 minutes to chill the oxygen system down to operating temperature. Once it was chilled down, we went to the engine prime sequence which allowed a low flow of liquid oxygen and ammonia to circulate through the propellant lines and into the turbopump. The igniter-ready light came on when the prime sequence commenced and we then selected the precool cycle to increase the flow of LOX to the engine turbopump. Once this flow was established we turned the igniter switch on to prepare the engine for the ignition cycle.
The ignition cycle was initiated by pressing the pump-idle button to start the turbopump. The turbopump came up to idle speed quickly and forced propellants into the first-stage igniter. These propellants were ignited by the spark plug in the first-stage igniter. Propellant was next forced into the second-stage igniter chamber where it was ignited by the flame of the first stage. The second-stage igniter itself produced 1,500 pounds of thrust. That is a pretty impressive pilot light.
The main chamber was lit by advancing the throttle. This action forced propellant at a rate of 30 gallons a second into the main chamber where it was ignited by the second-stage igniter. Main chamber ignition produced a real kick in the pants, 60,000 pounds of thrust in one big bang.
During ground runs, we would light the main chamber at 100 percent thrust and stabilize for 8 seconds. We would retard the throttle to idle for 5 seconds and then shut the engine down. Next we would go through an emergency restart sequence and relight the main chamber at 75 percent thrust. We would stabilize at 75 percent thrust for 5 seconds, reduce throttle to idle for a second or 2 and then, shut the engine down. This completed the engine run.
Each pilot normally made his own engine run prior to a flight, however, on occasion, another pilot made the engine run. I made an engine run for Bob Rushworth one time when he had a scheduling conflict. His upcoming flight called for the engine to be throttled back to obtain some stabilized speed data. During the engine run we attempted to duplicate the proposed thrust reduction, but when the throttle was retarded, the engine quit. We tried it again with the same results. Since it was essential to reduce thrust to get the desired flight data, a decision was made to delay the flight and fix the engine. Rocket engines are very temperamental. They seem to either work properly or they do not work at all. There does not seem to be any middle ground.
The X-15 engine was one of the few rocket engines that had a throttling capability. The throttling capability was designed to allow the pilot to achieve stabilized test points, but it complicated the reliability of the engine. It required the engine to run at a nonoptimum condition. The engine did not like to run at a nonoptimum condition and occasionally, it would refuse to cooperate and just quit. Many adjustments and fine tuning were required to make it operate satisfactorily at reduced power settings.
Before the next engine run, a number of adjustments were made and some components were changed. We attempted another engine run a couple of days after the first run. The results were the same. When the throttle was retarded, the engine quit.
Following that engine run, the engine was removed from the aircraft and checked thoroughly. A number of components were replaced and some more adjustments were made before the engine was reinstalled and prepared for another run. The results of that run were the same. We tried two more times to fix the engine and get a successful run, but no luck. Every time we pulled the throttle back, the engine quit. By this time, the entire maintenance crew was really frustrated. I finally suggested that we give up trying to fix the engine and just not bother to tell Rushworth that the engine would quit when he throttled back. After all, if a pilot cannot make his own engine run, he should not be too picky about the results.
During the X-15 program I was asked to serve as a technical advisor to the producers of the movie “X-15.” On one occasion, I escorted a number of the film crew to the X-15 engine run-up and test area to observe an engine run. We watched the operation from a vantage point about 100 yards in front of the aircraft. I was explaining the engine run process as it progressed from one sequence to another. I described the aircraft crew actions as they entered and exited their pillboxes during the various stages of the engine firing sequence, making a special point of the danger involved and the need to be in the pillbox during the actual engine run. The engine run sequence proceeded smoothly and finally the command was issued to fire the engine. The main chamber lit off with its characteristic explosive boom and then all of a sudden the hatch on one of the pillboxes flew open and the two occupants came out in a dead run.
Their pillbox was almost directly behind the X-15 and within 50 feet of it. It was almost within the flame pattern of the engine. That did not seem to deter the two occupants one bit as they ran directly across the exhaust of the engine. They ran like terrorized wild African antelope fleeing from an attacking lion. They would run three or four strides and then leap into the air as though they were looking for the pursuing lion. It was an amazing sight to behold.
One of the occupants, Wayne Ottinger, had failed to remove his radio headphones. As he reached the end of the headphone extension cord, the cord snapped taut and stopped his head in midflight. His legs and body continued on until he was stretched out flat in midair. We could hear the thump as he hit the ground over the deafening banshee wail of the rocket engine. He seemed to bounce immediately back into the air on his feet and he continued running without missing a stride. It was the most hilarious scene that I had ever witnessed. It was as humorous as any Charlie Chaplin or Marx Brothers routine that I had ever seen.
We subsequently learned that the hatch on that pillbox would not seal properly that day. During the engine start-up sequence, some ammonia vapors had drifted over the pillbox and had seeped in. Those vapors were so pungent that you had to run to escape them. The pillbox occupants were so panicked by the ammonia vapors that they ran directly through the exhaust of the rocket engine. Their graceful leaps into the air were desperate attempts to get above the ammonia cloud and get a breath of fresh air. That ammonia vapor was a real Olympic-class athletic stimulant. It could make a world-class runner out of any poor slob who got a whiff of it.
PART 2
THE PROGRAM
Chapter 3
Program Phases
The X-15 program was a joint effort of NASA, the USAF, and the U.S. Navy. NASA had technical control of the program and did the conceptual design of the aircraft. The USAF and the Navy funded the design and construction and managed those phases of the program. The program involved the design and construction of the aircraft and its rocket engine. Three aircraft were constructed. The program also included the modification of two B-52 aircraft to carry the X-15 aircraft.
The flight program was under NASA management with NASA and the air force both providing people and support. NASA maintained and operated the X-15 aircraft, the Hi-Range, the X-15 simulator, and half of the chase aircraft. NASA also maintained the APUs, the inertial platform, the ball nose, and the instrumentation system. The USAF operated and maintained the B-52 motherships, the C-130 support aircraft, the rescue helicopters, half of the chase aircraft, the X-15 servicing area, and the rocket engine test stand. The USAF also maintained the rocket engines, the pilot’s pressure suits, the ejection seats, and provided the standard base support such as fire trucks, crash and rescue vehicles, and ambulances. Both organizations provided X-15 pilots, chase pilots, and engineering support.
The
primary objective of the flight program was to explore the hypersonic-flight region by using the X-15 as the means to get to that region of flight. The X-15 aircraft configuration was only of passing interest. We could have used any of a number of different aircraft configurations to probe the hypersonic-speed region as evidenced by the different configurations proposed by the various contractors. The real interest was in the reaction of the air to a large-scale winged object traveling at hypersonic speeds. Did the air react as theory would predict or as the wind tunnel indicated that it would? This is where the X-15 configuration became important. The configuration had been analyzed and tested at small scale in the wind tunnel. By flying the X-15 airplane, we would obtain flight data to compare to these predictions. In this manner we would determine, for example, what the real boundary layer characteristics were, what the actual stagnation temperatures were, and what the true heating rates were. We could then update our analytical tools and our wind tunnels to improve our predictive capability for future aircraft.
The flight program consisted of a number of phases, some distinct and some not so distinct. Several of these phases were not foreseen in the original program plan. They evolved during the program as a result of unanticipated problems or developments. As an example, the airplane initially flew with an interim engine, the LR-11, due to development problems with the LR-99 engine. This resulted in the addition of an LR-11 checkout and demonstration phase.
The number three aircraft blew up during a ground run of the new LR-99 engine. During the rebuilding of the aircraft, a new flight control system (the MH-96 system) was installed, which then required a separate flight demonstration phase.
The number two aircraft was seriously damaged in a landing accident on its thirty-first flight. The program planners decided to modify the aircraft during rebuilding to carry an experimental scramjet engine to test at hypersonic speeds. This dictated another new demonstration phase. The flight program ultimately involved nine identifiable phases rather than the four or five originally envisioned. These nine phases are not officially designated in the records of the flight program, but are instead my own postflight definitions.
PHASE I
The first phase was the contractor demonstration phase using the LR-11 engine. The purpose of this phase was to check out and demonstrate the proper operation of all of the various systems in the aircraft and to demonstrate the structural integrity of the aircraft. During this phase, the number one and two aircraft were tested and demonstrated. The number three aircraft was also scheduled to be demonstrated in this phase, but as mentioned previously, it blew up during a ground run and its checkout and demonstration was delayed and eventually completed by the government. The low level of thrust developed by the LR-11 engines severely limited the performance of the X-15, but their use did allow the flight program to begin on schedule.
This phase consisted of eleven flights—one through eight, ten, eleven, and seventeen. This phase began on June 8, 1959, and concluded on May 26, 1960. Scott Crossfield made all of these flights. The airplanes involved were the number one and two aircraft. The maximum speed and altitude achieved during these flights were Mach 2.53 and 88,116 feet, respectively. These flights were all made in the immediate vicinity of the Rogers lakebed at Edwards Air Force Base. A number of significant problems were encountered during this phase. These included a severe PIO problem during a landing approach, a failure of the fuselage structure following an emergency landing, and several rocket engine fires.
PHASE II
The second phase of the program was the government envelope expansion phase using the LR-11 engine. During this phase, the aircraft flight envelope was expanded incrementally to the maximum attainable Mach and altitude to demonstrate the airworthiness of the aircraft. This phase consisted of ten flights—numbers nine, twelve through sixteen, and eighteen through twenty-one. These flights began on March 25, 1960, and ended on September 10, 1960. This phase commenced before the conclusion of Phase I.
Walker and White, the prime government pilots, split these flights, each making five flights. These flights were all made in the number one aircraft. The maximum speed and altitude achieved during this phase were Mach 3.31 and 136,500 feet respectively. These maximums were achieved on separate flights. Four of these flights were made in the immediate vicinity of Edwards, while the other six were made starting from Silver Lake. This was the first use of a remote launch lake by a rocket aircraft.
One additional LR-11 envelope expansion flight (Flight 33) was made following the completion of the pilot checkout phase (Phase III). This flight was made by Bob White to a maximum speed of Mach 3.50. This was the last flight using the LR-11 engine. No significant problems were encountered during this phase.
PHASE III
This phase was the pilot checkout phase using the LR-11 engine. The purpose of this phase was to check out the four backup government pilots. Each of the four pilots received two flights for a total of eight flights in this phase—flights twenty-two through twenty-five, twenty-seven, twenty-nine, thirty-one and thirty-two.
This phase began on September 23, 1960, and ended on February 1, 1961. The pilots involved were Forrest Petersen, Jack McKay, Bob Rushworth, and Neil Armstrong. The number one aircraft was used for all of these flights. The flights were all made in the immediate vicinity of Edwards. The planned nominal maximum speed and altitude for these flights were Mach 2.0 and 50,000 feet. No significant problems were encountered during this phase.
PHASE IV
This phase was the contractor demonstration phase using the LR-99 engine. During this phase, the contractor demonstrated the various capabilities of the LR-99 engine including normal airstart and operation, throttling from 50 to 100 percent power and restart capability. This phase consisted of only three flights, numbers twenty-six, twenty-eight, and thirty. These flights began on November 15, 1960, and ended on December 6, 1960. This phase was accomplished within the same time frame as Phase III.
Scott Crossfield made these three flights using the number two aircraft, which was the first aircraft to fly using the LR-99 engine. The maximum speed and altitude achieved were Mach 2.97 and 81,200 feet. These flights were made in the immediate vicinity of Edwards. No significant problems occurred during these flights.
PHASE V
This phase was the government envelope expansion phase using the LR-99 engine. The purpose of this phase was to demonstrate the airworthiness of the X-15 up to its design speed and altitude—the primary objective of the flight program. The flight envelope was expanded in incremental steps to the design speed of Mach 6 and the design altitude of 250,000 feet. This was accomplished in ten flights–numbers thirty-four through thirty-eight, forty, forty-three through forty-five, and fifty-two. These flights began on March 7, 1961, and concluded on April 30, 1962.
Walker and White alternated flights, each making five. White achieved the design Mach number of 6 with an actual Mach number of 6.04 and Walker achieved the design altitude of 250,000 feet with an actual altitude of 247,000 feet. Eight of these flights were made using the number two aircraft and two using the number one aircraft. These flights were all made using remote launch lakes.
We were to fly faster and much higher on subsequent flights, but these flights concluded the basic design envelope expansion phase. Surprisingly, there were no major problems encountered on these flights.
PHASE VI
This phase was the Minneapolis-Honeywell (MH-96) flight control system checkout and demonstration phase. The purpose of this phase was to demonstrate the capabilities of the MH-96 system, an advanced command augmentation type control system. This system offered a number of potential advantages over the original X-15 flight control system, particularly during exoatmospheric flights.
This phase consisted of four flights—numbers forty-six, forty-eight, forty-nine, and fifty-one. These flights were the first four flights in the number three aircraft and they were all made by Neil Armstrong. The flights began on December 20, 1961, an
d ended on April 20, 1962. The flights were accomplished within the same time period as Phase V. The maximum speed and altitude achieved during these flights were Mach 5.51 and 207,500 feet. All of these flights were made from remote launch lakes. No major problems were encountered during this phase, however an operational hazard was highlighted, namely, bouncing back out of the atmosphere during a pullout fom high altitude. This created major energy management problems
This flight control system was later flown to higher speeds and much higher altitudes. The system was subsequently utilized for all planned altitude flights above 270,000 feet.
PHASE VII
This phase was the basic aircraft research phase. During this phase we were attempting to determine the flight characteristics of the basic airplane. We were measuring its performance characteristics, its stability and control characteristics, its handling qualities, or flying qualities, and the loads acting on the structure of the aircraft. We were measuring the aerodynamic pressures acting on various parts of the airplane, the temperatures of the structure at points of interest, and calculating the aerodynamic heating rates at various flight conditions. At the completion of this phase, we would know the characteristics of the aircraft thoroughly and would be able to compare its actual characteristics with those predicted by wind tunnel tests or theory. This comparison would reveal any errors in the predictive techniques and ultimately allow the engineers to revise and improve these techniques for use on future aircraft. This is a primary reason for building and flying research aircraft, to investigate a new configuration or probe a new flight region and bring back data that will help to design the next aircraft better.
At the Edge of Space Page 11
