Word got around about the picture. Later in the day, the center director happened to casually stop by the pilot’s office. He had obviously heard about the picture since he did not normally visit our office. He was a very quiet, reserved individual who seldom showed any real emotion. He rather nonchalantly glanced at the picture as he walked by John’s desk. A big smile came over his face as he walked back out of the office. We had scored a double coup, and in addition, had saved John from a tongue lashing.
But, back to the X-15. We also lost cabin pressure due to aerodynamic heating. The heating would cause the canopy to distort enough to allow outside air to reach the canopy seal. The outside air would burn through the seal in milli-seconds. A small metal lip was installed ahead of the canopy leading edge to shield the gap from the airstream and solve this problem.
One of the things that I always worried about in the X-15 was the canopy coming off at high speed. The canopy opened from the front and hinged in the rear just like the suicide door on some cars that were built in the early 1930s. During flight, cabin pressure and aerodynamic heating caused the canopy to distort and open up a gap at the front or leading edge of the canopy. I could envision the air getting under the edge of the canopy, causing the canopy hooks to fail and the canopy to depart the airplane. If that had happened at high speed, the pilot would have been cooked to a charred mass in a matter of seconds. A complete window failure would have been just as catastrophic.
The auxiliary power units or APUs in the X-15 were, in reality, improperly named. They were not really auxiliary power units, but were the primary power units for electrical and hydraulic power, since there were no conventional engine driven pumps or generators. The X-15 had two APUs for redundancy. If these two units failed, we lost the airplane. As described earlier, these units were small steam turbines powered by steam created by the decomposition of hydrogen peroxide. These units each drove a generator and a hydraulic pump to provide electrical and hydraulic power. APU failures occurred on several flights early in the program. Joe Walker lost one APU during an altitude flight and then lost the second one just after landing. These early APU failures were finally determined to be caused by the vaporization of the lubricating oil in the APU gear case at high altitude and low atmospheric pressure. The gear box would quickly fail without lubrication. The solution to this problem was to pressurize the APU gear case.
The most startling APU failure occurred on the 184th flight. Pete Knight was scheduled to make a flight to 250,000 feet with two piggyback experiments. The prelaunch checklist procedure progressed without incident. After launch, Chase confirmed a good engine light. NASA-1 also verified this and then told Pete to “Check your alpha and watch your heading.” NASA-1 then indicated that Pete’s track was looking good and he was coming up on profile. At about 28 seconds after launch, NASA-1 informed Pete that they had him on theta (climb angle) and that his track and profile were good. In fact, NASA-1 said, “Beautiful track, Pete.” NASA-1 called out an altitude check at 80,000 feet and then, a few seconds later, told Pete he was coming up on 104,000 feet. Almost simultaneously Pete called out, “Shutdown.”
NASA-1: “Understand shutdown, Pete.”
NASA-1: “We’ve got a Grapevine time here.” [The premature shutdown time dictated an emergency landing at Grapevine Lake.]
NASA-1: “Chase, we will confirm Grapevine landing.”
NASA-1: “How do you read, Pete?”
Chase-3: “NASA-1, did you say Grapevine?”
NASA-1: “That’s affirm. How do you read me, Pete?”
NASA-1: “Is anybody reading the X-15?”
NASA-1: “Chase-1, NASA-1, do you read anybody?”
Chase-1: “I don’t read Pete.”
Chase-3: “Do you have a position here?”
NASA-1: “No, we have lost TM.”
When Pete called “shutdown,” it was as though the X-15 had literally disappeared. The control room lost radar track, telemetry, and radio communications. All the marker pens on the plotting boards just stopped. The radar slewed around some, attempting to reacquire a lockon, but then it too stopped. Some control room personnel thought that the airplane blew up. It was as if Pete and the X-15 had flown into the Bermuda Triangle and disappeared.
In the X-15, just before engine shutdown, Pete saw a ripple of red and yellow warning lights: an inertial system gross malfunction light, all three stability augmentation system (SAS) lights, the engine vibration malfunction light, and the number two APU light. Numerous other warning lights were about to come on, but Pete was spared from further warning lights by a complete electrical failure.
All the lights went out, including the cockpit lights. Pete was now in a darkened cockpit climbing out of the atmosphere at over 2,000 feet a second. The majority of his instruments were no longer working and he quickly noted that his aerodynamic controls were not responding to his attempted inputs. Indeed, his controls were essentially locked. He tried his ballistic controls, but they provided little noticeable response. The airplane began to wallow around as it continued up to the peak of its trajectory.
Postflight simulation indicated that the X-15 peaked out at approximately 173,000 feet altitude. In one sense, Pete was lucky. Even though he had little or no aerodynamic control, there was enough aerodynamic pressure at this altitude to keep the aircraft from swapping ends immediately. It was oscillating in roll through large bank angles. At one point, Pete noted that it was a beautiful day as he looked down on the desert. He decided about that time that he would have to eject. Then he noticed Mud Lake below him and made a decision to try to land there if he got the airplane back under control.
Pete realized that he had lost both APUs since he had neither hydraulic or electrical power. He attempted to start his number one APU with no success. He then remembered that he had to turn on his emergency battery to provide power to start his APUs. With the emergency battery on, he managed to get the number one APU started. He tried the number two APU again, but could not get it going. Then he tried resetting his number one generator to regain electrical power. The generator would not reset. During this critical period, Pete had no help from the control room or his chase aircraft because he had lost his radios. This was another example of the fallacy of assuming that ground control could always help the pilot in an emergency. If the pilot lost his radios, he was on his own. Radio failure or momentary loss of radio reception was very common during X-15 flight operations. It was hard to believe that in this age of rockets and space travel we could still have total loss of communications, but we had numerous instances of this occurring.
Pete had to give up on resetting the generator because he had to position the aircraft for the reentry. He had no indication of his angle of attack and yet he knew he had to maintain a fairly high one to successfully reenter. He resorted to flying by the seat of his pants. He pulled the nose up until it started to diverge sideways and then lowered the nose slightly. This little maneuver gave Pete a rough indication that he was at an acceptable angle of attack for the entry. He held this attitude until the g forces started building up and then, when he felt that he had made the pullout, he rolled into a steep bank to start the turn back to Mud Lake. Pete had managed to make a successful reentry without instruments and without any stability augmentation—quite a feat.
On the ground, NASA-1 was still trying to determine what happened. Chase-3 reported, “I’ve looked all over Grapevine.” Based on energy management calculations, Pete should have headed for Grapevine, but Grapevine was one of the smaller lakes. Pete elected to try to get back to Mud Lake, a much bigger and better lake for an emergency landing.
NASA-1: “Chase-3, you can be looking for jettison down around Grapevine.”
Chase-3: “Roger One, I’m looking.”
NASA-1: “OK. Pete, do you read?”
Chase-3: “Over Grapevine at 30,000 feet.”
NASA-1: “I kind of think he will be coming in from the southeast if he comes in there.”
Chase-1: “OK
.”
NASA-1: “Chase-1 & -2, keep an eye around Mud.”
Chase-2: “Rog, Mike. I’m over Mud and keeping an eye peeled.”
NASA-1: “Rog.”
Chase-2: “Pete, do you read?”
Chase-3: “Seen or heard anything?”
At this point, over 8 minutes had elapsed since Pete and the X-15 had disappeared. Again, 8 minutes does not sound like a lot of time, but it can be an eternity to those waiting to hear some word, any word. An airplane does not just disappear. Someone has to see or hear something—a Mayday call, a parachute, a dust cloud from a landing or a crash, or at least pieces of the airplane lying on the ground. Then, all of a sudden, Chase-2 called, “He is going into Mud. I think he is landing east to west.” Several seconds later Chase-2 said, “He’s in the center of Mud and in good shape right now.” NASA-1 said, “Roger, understand.” That message was almost drowned out by the noise of a couple hundred hearts beginning to beat again. “Gentlemen, start your hearts.”
The cause of the APU shutdown was never proven. There was speculation that the first APU to shutdown was momentarily overloaded due to a large electrical power demand. That transient load probably stalled the APU, which in turn activated a safety circuit that shut it down. When that APU shut down, it transferred its essential electrical power demands to the other APU, as it was designed to do. The other APU was, however, already heavily loaded down with a high power demand and was unable to accept the additional power load and maintain speed. It, too, stalled and shutdown.
The APUs were generally reliable, but they required a lot of tender care and feeding. They were usually completely disassembled after each flight, refurbished, reassembled, and then test run before being reinstalled in the aircraft. We were very conscious of the fact that APU problems could be catastrophic.
Pete was extremely lucky. The circumstances of the APU failures were such that he was able to control the aircraft using reaction controls until he was able to restart an APU. If he had been flying a low-altitude speed type flight, the airplane would probably have swapped ends and either failed structurally or crashed due to the loss of stability and control.
Paul Bikle has said on numerous occasions that Pete’s recovery of the airplane on this flight was one of the most impressive events of the whole program. Pete should have been mentally prepared for this emergency. He told me about a complete electrical failure he had early in his flying career in a T-33 over Detroit, Michigan, at night in severe weather conditions. It was a hairy story—almost as hairy as this one. Pete also managed to recover that airplane.
Landing gear problems persisted throughout the flight program. The most serious problems involved the main landing gear, the two struts at the rear of the aircraft with skids instead of wheels. Landing gear failures of a minor nature occurred on a number of flights. Most of these failures were attributed to the larger than anticipated aerodynamic loads imposed by the horizontal stabilizer after the aircraft was on the ground. Aerodynamic loads caused a catastrophic landing gear failure on one of Jack McKay’s flights out of Mud Lake. In that incident, the main gear failed completely and the aircraft ended up on its back after flipping over during slideout.
In an attempt to solve this problem, a squat switch was added to disable the stability augmentation system at landing and thus prevent the horizontal stabilizer from deflecting full leading edge down as the nose of the aircraft slammed down. This fix helped to relieve the aerodynamic loads, but it was not enough.
The next fix required the pilots to push forward sharply on the stick when the nose began to fall through after main gear touchdown. This procedure resulted in a leading edge up horizontal stabilizer deflection at nose gear touchdown which significantly reduced the main gear loads. On a number of occasions, the pilots actually lifted the rear end of the aircraft off the ground during the landing slideout. This procedure worked well as long as the pilot remembered to do it. Every now and then the pilot forgot to perform the maneuver and loads reached design limits.
The obvious answer to the design engineer was to design and install an automatic system to push the stick forward as the aircraft touched down. The pilots rebelled at this proposal, fearing a premature actuation of this system before landing. The engineers, however, persisted and after adding a few safe-guards to prevent premature actuation, the system was implemented on the aircraft. This system worked as advertised, but the engineers finally decided to add a third skid on the lower ventral to substantially reduce the original main gear loads. This was the final mod to the landing gear, not necessarily because it was the ultimate fix, but because the program came to an end. We are now assured that the landing gear will not collapse as the aircraft sits in the museum.
The LR-99 engine was amazingly reliable if we got it lit, and if we did not move the throttle while it was running. Joe Vensel, our director of flight operations, used to say, “If you get the engine lit, leave it alone, don’t screw with it.” He was right.
The LR-99 had a poor starting record initially. It quite often took two attempts to start the engine and occasionally, it would not start at all or would hang up at low thrust. The starting problem appeared to be due to the instability of the engine at low thrust settings. Initially, we were trying to start the engine at minimum throttle which was about 30 percent thrust. The engine just did not want to start or run at that thrust level. We then began to start the engine with the throttle at the 100 percent thrust level. This greatly improved the start reliability. We very seldom had to make a restart attempt using that procedure.
We still had problems, though. The engine would often quit when we attempted to move it back to minimum throttle. If the pilot throttled the engine back before he gained enough energy to get home, he risked making an emergency landing at one of the intermediate lakebeds. To correct this problem, we increased the minimum throttle setting to 40 percent thrust. We also moved the throttle gently and said a quick prayer before we moved it. This procedure further improved the engine reliability, but I still had to hitchhike one time.
In all, there were eight emergency landings as a result of propulsion system problems with the LR-99 engine—one due to no light, one due to a hangup at low thrust, one due to premature shutdown at throttle reduction, two due to low fuel line pressures, one due to a turbopump case failure, one due to a fuel tank rupture, and one due to lack of fuel flow from an external tank.
On Jack McKay’s twenty-fifth flight, he was scheduled to carry three experiments to high altitude. These experiments were an atmospheric density measurement, a micrometeorite collector, and a horizon scanner. The flight was the 157th flight of the program and it was launched at Delamar Lake. Jack got the engine lit right after launch and pulled up to begin the climb. He had just reached his planned climb angle when the engine quit. The engine turbo-pump that supplied the propellants to the thrust chamber failed due to a rupture of the case and propellants began spewing at high pressure into the engine compartment. Luckily, there was no fire, but Jack had a problem getting the airplane turned around and headed back toward the launch lake.
The engine had burned 35 seconds and during that time the airplane had accelerated to Mach 2.2 in the climb. Jack peaked out at 78,400 feet altitude during the wingover turn back to Delamar. He made a nice approach pattern, but he was high on energy. Jack was an old navy pilot like me, and we both carried an extra 5 knots of airspeed in the approach for each kid, to ensure that we did not stall the aircraft. Trouble was, Jack had eight kids. He landed long and ran off the edge of the lake about 500 feet in the sagebrush before stopping. It did not hurt the airplane and Jack did not let it effect his ego. After the postflight debriefing, someone asked Jack how long the lakebed runway was. Jack’s answer was, “Three miles with a 500-foot over-run.”
Jack made his third emergency landing on his twenty-ninth flight, which was his last X-15 flight. He launched at Smith Ranch Lake on September 8, 1966. Shortly after he began his climb, he noticed that his fuel line pressure
was low. He throttled the engine back to 50 percent thrust on the recommendation of NASA-1 to see if the fuel line pressure would recover. When it failed to recover, he shut the engine down, turned the airplane around and made an uneventful landing at Smith Ranch. With this landing, Jack established an all time record for emergency landings. He had three. No other pilot had more than one.
For its time, the LR-99 was a very impressive engine. It was unique in its throttling capability and its restart feature. It produced almost as much thrust as the Redstone missile booster and it was reusable—another unique feature.
The X-15 made 199 flights with only eight flight engines. There were no catastrophic engine failures and no serious design deficiencies. The engine was temperamental, but so were all the other rocket engines. Twenty-five years later, rocket engines are still temperamental. They still occasionally fail to light properly and they still quit unexpectedly and they still blow up once in a while. So what’s new?
As the program progressed, the airplane became somewhat safer and more reliable in some respects since most of the major problems were fixed as they were encountered. Thus, at least the variety of problems was reduced. In some cases, however, the fixes were not complete fixes and we had recurring problems after the fixes were incorporated. To some extent, this was due to a lack of money. We could not afford the luxury of a complete redesign whenever we encountered a problem. Some problems were not fixed at all. We lived with them and modified our procedures or our flight operations. As a result of these actions and inactions, we continued to have problems throughout the entire program. We also continued to have emergencies.
We encountered some new problems after 150 flights. Some of these new problems appeared to be aging or fatigue problems. An engine turbopump case failed, a bulkhead in the fuel tank failed, and yet the airplanes did not have a lot of flight time on them. In fact, they averaged 10 hours of free flight time apiece at the end of the program. They were only 10 years old at the end of the program, but they did not have a lot of miles on them. In the classified pages of the newspapers, they could have been advertised as low mileage airplanes, flown by little old ladies only on Sundays.
At the Edge of Space Page 29