Back to Flying

In its own way, the X-15 program was "politically correct," even if the term did not yet exist. Paul Bikle had decided that a NASA pilot should make the first government X-15 flight, but he would later give the honor of performing the first government XLR99 flight to an Air Force pilot. The initial piloting duties were split evenly between one NASA pilot and one Air Force pilot. It seemed only fitting, therefore, that the third government pilot to qualify in the X-15 should be from the Navy.

Forrest Petersen checked out in the airplane while Joe Walker and Bob White conducted the envelope-expansion phase with the XLR11 engine. Like all of the early pilot familiarization flights, Petersen’s first flight would be low and slow, if that describes Mach 2 and 50,000 feet. The flight plan showed Petersen launching over Palmdale, heading toward Boron, turning left to fly back toward Mojave, and making another left turn toward Edwards. The launch went well, but as the airplane approached Boron the upper engine began to fail; soon it stopped altogether. Petersen reported that he "believed erroneously that the lower engine was still running, but the inability to hold altitude, and airspeed variations from values expected for single engine operation forced the pilot to the inevitable conclusion that both engines were shut down." Milt Thompson, who was NASA-1 for the flight, advised Petersen to head directly for Rogers Dry Lake. Petersen arrived at high key with only 25,000 feet altitude, much lower than desired, and Joe Walker tucked a chase plane into formation and coached Petersen through a tight turn onto final. The landing was almost perfect, and Petersen handled the entire incident with his usual aplomb. Petersen’s final report was understated: "Nothing during the flight surprised the pilot with the exception of early engine shutdown." The only Navy pilot was an excellent addition to the team.-1106

It was time for Crossfield to go back to work with the ultimate engine. The first flight attempt of X-15-2 with the XLR99 was on 13 October 1960, but a peroxide leak in the no. 2 APU ended the day prior to launch. Just to show how many things can go wrong on a single flight, there was also liquid-oxygen impingement on the aft fuselage during the prime cycle, manifold pressure fluctuations during engine turbopump operation, and fuel-tank pressure fluctuations during the jettison cycle. Two weeks later, Crossfield again entered the cockpit with the goal of making the first XLR99 flight. More problems with the no. 2 APU forced an abort.

On 15 November 1960, everything went right and Crossfield made the first flight (2-10-21) of X – 15-2 powered by the XLR99. The primary flight objective was to demonstrate engine operation at 50% thrust. The launch was at Mach 0.83 and 46,000 feet, and the X-15 managed to climb to 81,200 feet and Mach 2.97 using somewhat less than half the available power. The second XLR99 flight (2-11-22) tested the engine’s restart and throttling capability. Crossfield made the flight on 22 November, again using the second X-15. During the post-flight inspection of the aircraft and its engine, engineers found that, like most of the ground-test engines, the XLR99 was beginning to shed some of the Rokide coating on the exhaust nozzle.[107]

Despite being fast-paced, the X-15 program was never reckless. As North American prepared X – 15-2 for its next flight during December 1960, AFFTC commander Brigadier General John Carpenter heard rumors about the Rokide coating and called a meeting to discuss the matter. Representatives from the Air Force, NASA, North American, and Reaction Motors were present.

Each gave his opinion, which was that it appeared safe to continue. Carpenter dismissed the meeting but asked Scott Crossfield and Harrison Storms to stay. During this session he questioned Crossfield on his feelings about making the flight given the condition of the engine. Scott did not show any concern and indicated he was willing to go ahead with the flight. Carpenter excused Crossfield but asked Storms to stay.-1108

Storms recalled, "When we were alone, General Carpenter asked my opinion. I told him that earlier this day on my arrival at Edwards that I had inspected the thrust chamber in question and did not have any great concerns. Yes, some of the insulation was gone, but not to any great extent and the individual areas were small. It had not all been lost in one area, but the loss was fairly evenly well distributed over the entire area. Further, it certainly had not caused any negative comments from the manufacturer or their test engineers. The General’s comment was, ‘Very well, we will make it a joint decision to proceed with the flight.’ … Seriously, there is a point to be made here. That is, there is a very fine line between stopping progress and being reckless. That the necessary ingredient in this situation of solving a sticky problem is attitude and approach. The answer, in my opinion, is what I refer to as ‘thoughtful courage.’ If you don’t have that, you will very easily fall into the habit of ‘fearful safety’ and end up with a very long and tedious-type solution at the hands of some committee. This can very well end up giving a test program a disease commonly referred to as ‘cancelitis,’ which results in little or no progress." It was an excellent observation, and is as applicable today as it was in 1960.[109]

With the blessing of Carpenter and Storms, North American conducted the third and final XLR99 demonstration flight (2-12-23) using X-15-2 on 6 December 1960. Crossfield successfully accomplished the engine-throttling, shutdown, and restart objectives. This marked the last X-15 flight for North American Aviation and Scott Crossfield. The job of flying the X-15 was now totally in the hands of the government test pilots. Crossfield, the engineer, transferred to testing the Hound Dog cruise missile and then to the Apollo program.-1110

After this flight, the program established a work schedule that would allow an early XLR99 flight with a government pilot using North American maintenance personnel. Bob White would make the flight as early as 21 December 1960, assuming North American could accomplish the necessary maintenance work in time. This included replacing the engine, which had suffered excessive chamber coating loss; installing redesigned canopy hooks and a reinforced vertical stabilizer; rearranging the alternate airspeed system; and relocating the ammonia tank helium pressure regulator into the fixed portion of the upper vertical. The company made good progress until engineers found a pinhole leak in the chamber throat of the replacement engine during a ground run. Although Reaction Motors considered the leak acceptable, it became increasingly worse during a subsequent test. Since a spare XLR99 was not available, the program canceled the flight and established a schedule to deliver the aircraft to the government prior to another flight. As a result, North American formally delivered X-15-2 to the Air Force and turned the airplane over to NASA on 7 February 1961. On the same day, X-15-1 was returned to the North American plant for conversion to the XLR99, having completed the last XLR11 flight (1-21-36) of the program the day before with Bob White at the controls.-111

The first two years of the flight program showed five major reasons for flight cancellations: problems with the APUs and their fuel system, XLR11 problems, propellant system (less engine) difficulties, weather, and heating and ventilation troubles. When the ultimate engine came on line, the top five reasons changed slightly to XLR99 problems, propulsion system (less engine) difficulties, miscellaneous, problems with the APU and its fuel system, and stable platform failures. It was not surprising that the engine became a major source of delays, since the XLR99 was a major leap forward in rocket engine technology and growing pains were to be expected. Many of the propulsion-system problems were a direct result of the XLR99, such as some plastic seal materials being incompatible with anhydrous ammonia. Although the XLR99 was performing satisfactorily in flight, by the end of December 1960, maintenance personnel had discovered ammonia leaks in the thrust chambers of three engines. Reaction Motors dispatched technicians to Edwards to correct the problems while the Air Force, NASA, North American, and Reaction Motors all looked for a cause.112

Back to Flying

Major Robert M. White flew the last XLR11 flight of the program (1-21-36) on 7 February 1961. This was the fastest XLR11 flight, reaching 2,275 mph and Mach 3.50. Six months earlier White had gone to 136,500 feet using the XLR11s. Bob White holds the distinction of being the first man to fly Mach 3, Mach 4, Mach 5, and Mach 6, and the first pilot to fly to 200,000 feet and 300,000 feet, all in the X-15. (NASA)

From the beginning of the X-15 flight program in 1959 until the end of 1960, seven pilots had made 31 flights with the first two airplanes. The NB-52s had carried the two X-15s 55 times, including two scheduled captive flights and 22 aborted launch attempts. However, X-15-1 was experiencing an odd problem. When the pilot started the APU, the hydraulic pressure was either slow in coming up or dropped off out of limits when he moved the control surfaces. The solution to the problem was found after researchers placed additional instrumentation on the hydraulic system. The bootstrap line that pressurized the hydraulic reservoir was freezing, causing a flow restriction or stoppage. Under these conditions the hydraulic pump would cavitate, resulting in little or no pressure rise. The apparent cause of this problem was the addition of a liquid-nitrogen line to cool the stable platform. Since North American had installed the nitrogen line adjacent to the hydraulic lines, it caused the Orinite hydraulic oil to freeze. The solution was to add electric heaters to the affected hydraulic lines, since there was not enough room in the side tunnel to separate the lines sufficiently to prevent the problem.

Some problems defied all efforts to fix them. For example, North American tested the APU and its fuel system for many hours on an exact replica of the airplane installation. Yet, over the course of the program, the APUs caused more schedule delays and cancellations than any other system. One of the major problems was a critical pressure switch. Although the switch had been thoroughly (and correctly) qualified by the vendor, the program had to replace it by the dozen. Even with improvements, the switch continued to be a problem.-113

Paul Bikle closed the year by saying that he was generally pleased with the progress made: "The data coverage within this envelope has been fairly complete in the areas of performance, flight dynamics, control, and structural loads, but somewhat limited in structural heating due to the low heating rates encountered." Bikle cautioned, however, that the short duration and transient nature of each flight had generally precluded the acquisition of extensive or systematic measurements under selected flight conditions, as was possible with conventionally powered aircraft.-114-