THE 1956 INDUSTRY CONFERENCE

The XLR99 presented several unique challenges to Reaction Motors. Perhaps the major one was that the engine was being developed for a manned vehicle, which entailed more safety and reliability requirements than unmanned missiles. However, perhaps even more challenging were the requirements to be able to throttle and restart the engine in flight-something that had not yet been attempted with a large rocket engine. The Reaction Motor representative at the 1956 industry conference concluded his presentation with the observation that developing the XLR99 was going to be challenging. Subsequent events proved this correct.-138

Подпись: TURBINE THRUSTПодпись:

THE 1956 INDUSTRY CONFERENCE Подпись: MA N LOX

Robert W. Seaman from Reaction Motors presented preliminary specifications for the XLR99-RM-1 at the conference. The oxygen-ammonia engine could vary its thrust from 19,200 lbf (34%) to 57,200 lbf at 40,000 feet, and had a specific impulse between 256 seconds and 276 seconds depending on the altitude and throttle setting. The engine fit into a space 71.7 inches long and 43.2 inches in diameter. At this point, Reaction Motors was predicting a 618-pound dry weight and a 748-pound gross weight. A two-stage impulse turbine drove the single-inlet oxidizer pump and two-inlet fuel pump. The hydrogen-peroxide-driven turbopump exhausted into the thrust chamber. Regulating the amount of hydrogen peroxide that was decomposed to drive the turbopump provided the throttle control.-139

LOX

i—cm

lOX ‘

ACCUMULATOR

Подпись: POWER CONSOL Подпись: IGNITER MART THE 1956 INDUSTRY CONFERENCE THE 1956 INDUSTRY CONFERENCE

Подпись:

THE 1956 INDUSTRY CONFERENCE
Подпись: POOPEUAHT VALVE

GENERATOR

THE 1956 INDUSTRY CONFERENCEBASIC ENGINE SCHEMATIC

Although not the most powerful rocket engine of its era, the XLR99 was the most advanced and used a sophisticated turbopump to supply liquid oxygen and anhydrous ammonia propellants to the combustion chamber. The engine was capable of being restarted in flight, an unusual feature for the time (or even today) and numerous safety systems automatically shut down the engine in the event of a problem. (NASA)

Engineers decided to control thrust by regulating the speed of the turbopump because the other possibilities resulted in the turbopump speeding up as pressure decreased, resulting in cavitation. Controlling the propellant to the turbopump also required fewer controls and less instrumentation. However, varying the fuel flow led to other issues, such as how to provide adequate coolant (fuel) to the thrust chamber.[40]

The engineers also had to give engine compartment temperatures more consideration than they did for previous engines due to the high heat transfer expected from the X-15 hot-structure. This was one of the first instances in which the surrounding airframe structure would be hotter than the engine. Since North American was designing the hot structure of the X-15 to withstand temperatures well in excess of those the engine produced, the engineers were not planning to insulate the engine compartment.-41

Another paper discussed engine controls and instruments, accessory installation, and various propellant system components. The 1,000-gallon liquid-oxygen tank was located just ahead of the aircraft center of gravity, and the 1,400-gallon anhydrous-ammonia tank was just behind it. A 3,600-psi helium supply tube within the liquid-oxygen tank supplied the gas to pressurize both tanks. A 75-gallon hydrogen-peroxide tank behind the ammonia tank provided the monopropellant for the turbopump, using a small, additional supply of helium.-421

The liquid-oxygen and ammonia tanks had triple compartments arranged to force the propellants toward the center of gravity during normal operations and during jettisoning. The design needed to compensate for the acceleration of the X-15, which tended to force propellants toward one end of the tanks or the other. Further complicating the design of the tanks was the necessity for efficient loading and minimizing the remaining propellant after burnout or jettisoning.

Fortunately, the tanks did not present any insurmountable problems during early tests.-431

Because the engineers did not yet fully understand the vibration characteristics of the XLR99, they designed a rigid engine mount without any special vibration attenuation. The engine-mount truss attached to the fuselage at three fittings, and by adjusting the lower two fittings the engineers could tailor the thrust vector of the engine. Three large removable doors in the aft fuselage provided access to the engine and allowed closed-circuit television cameras to observe the engine during ground testing. Ultimately, this mounting technique would also make it much easier to use the interim XLR11 engines.-441