In 1942 Jack Northrop proposed to the Army Air Force a super high-performance, flying wing, rocket-powered manned interceptor. Development was authorised in January 1943 under extreme secrecy, the official XP-79 designation being assigned but the work being simply known as 'Project X'. GALCIT at the California Institute of Technology, the only organization in the United States capable of such work, began parallel design of two liquid propellant rocket engine variants for the XP-79. One, the XLR-7, used what would become the later standard gas turbine pump feeding a combustion chamber. The other, using an ancient Greek concept, was dubbed the Aerotojet. The Aerojet company was formed to handle the Project X and JATO government contracts coming GALCIT's way.
The Aerotojet consisted of a pair of 130 kgf thrust chambers mounted longitudinally on a drive shaft. The thrust chambers were preset at a small angle and attached to the shaft by lever arms. The side component of thrust created a torque, in effect like the ancient Greek aeolipile, a steam rocket designed by Hero. This drove the shaft, which, in turn, entered a gearbox driving the aniline fuel and red fuming nitric acid oxidizer pumps. This rotating rocket concept was developed in parallel with the (later) more conventional high pressure gas turbine pump feeding a fixed chamber. However in 1942 no work on combustion of gases at turbine compatible temperatures had ever been attempted, and it was not clear which of the two approaches was technically feasible. The ancient aeolipile approach seemed simpler at first glance.
The two 130 kgf thrust chambers provided cruise thrust for the rocket interceptor. For boost, they served as the propellant feed system to two 330 kgf thrust regeneratively cooled chambers fixed to the airframe
Test work was accomplished under Project No. 1 at GALCIT. Paul Meeks built a test fixture with rotating components that successfully simulated the critical torque producing elements of the system. The test rig immediately showed that leakage from the rotating bearing and oxidizer pump seals was a major issue. This could never be solved, so the final solution was to cut the leakage to a minimum and dump the unburned propellants overboard. But the corrosive nitric acid fumes would short out electrical components.
Erik Petau, an experienced mechanical aircraft engineer, was Project X Chief Designer. His successful design of the high speed gear box, with many advanced and unproven components, was especially noteworthy.
Project X was plagued with development delays through 1943 and 1944. One four month delay alone was attributed to an unqualified designer who was given the task of removing weight from the prototype to flight-weight standards. His drawings were beautiful, but it turned out he was just a draftsman, and the parts being cast to his drawings could not endure the forces they would be subjected to.
Chandler Ross, later one of Aerojet's senior engineers, was supervising the pump design, which had been subcontracted to the Byron Jackson Pump Company. The chief engineer there, Aladar Hollander, had been a student of von Karman back in Germany. The resulting pumps were multistage, barrel type, centrifugal pumps, operating at 12,000 and 8,000 rpm - unheard-of at the time. They passed the acceptance tests, pumping water in place of the actual propellants, without any discrepancy.
In 1944 the first flight engine had completed assembly and was installed in a GALCIT test pit. The entire staff of GALCIT Project No. 1 and Aerojet gathered to watch the first test, the result of two years of hard work. The limited instrumentation consisted of a fuel gauges being filmed by a camera. The firing button was pressed, and the engine promptly exploded into tiny pieces. No data was recovered that would allow the cause of the failure to be diagnosed. It was believed that the engine had not been properly bled before start or that the sequencing of propellants into the injector was miscalculated. But this ended development of the Aerotojet for the XP-79. Development of the XLR7 continued for the P-79, and this engine was successfully tested in August 1945. The aircraft itself was then cancelled at the end of 1945 when the prototype crashed on its first flight, killing the pilot.
However the Aerotojet was proven in the following year by successful build and reliable running of the 2/3-scale Centrojet, using the same concept. But the tests also provided that the aeolipile scheme could not dynamically be scaled up to larger thrust engines, so the unique technology was abandoned.
Application: XP-79 Northrop Flying Wing.
Thrust (sl): 9.120 kN (2,050 lbf). Thrust (sl): 930 kgf. Propellant Formulation: RFNA/Aniline+Furfural Alcohol.
AKA: Aerotojet; XCALR-2000A-1.
Thrust: 9.12 kN (2,050 lbf).
First Launch: January 1943.