The Allison J35 was a turbojet engine which was the power plant of some military aircraft, such as the Republic F-84 Thunderjet, the Northrop F-89 Scorpion, and the North American FJ-1 Fury. Originally developed by General Electric, it was an axial-flow type, from which several versions was developed, producing between 5,000 and 7,500 pounds of thrust. Engine speed was 8,000 rpm.
The Allison J35 turbojet engine was an axial-flow design, which was composed of an annular 11-stage compressor, eight can-type combustion chambers, a single-stage turbine wheel with 95 cups, and an afterburner. It also had a fuel nozzle and an accessory gear drive. This turbojet engine produced 7,200 pounds of thrust. The induction air entered the engine intake and was progressively compressed through the eleven stages of the compressor section.
The main flow of the compressed air was forced into the eight combustion chambers where fuel was sprayed under pressure as ignition plugs provided the spark to ignite the fuel. Then the hot combustion gases rotated the single-stage turbine, which also drove the compressor as the turbine wheel and compressor were mounted on the same shaft.
The Allison J35 was designed to be broken down into major sections to facilitate engine assembly and overhaul. These section consisted of the air inlet, the accessory gear case assembly, the compressor assembly, the combustor section, the turbine assembly, and the afterburner assembly. The latter was equipped with two-position eyelid assemblies for exhaust nozzle control.
The Allison J35-A-21 was the initial engine installation of the first two version of the Scorpion aircraft; the F-89A and the F-89B. A power-operated hoist system was developed to allow the engine to be rotated 18 inches inboard from the aircraft fuselage keel in order to expose the entire power plant for maintenance. The difference between the J35-A-21 and the -21A version was that the latter featured a full-scavenging oil system; oil was re-circulated through the engine instead of continuously dumping it overboard while the engine was running.
The next variant of the engine for the F-89C was the J35-A-33A. This version featured 'hot nose' anti-icing. Hot air from the compressor eleventh stage was used for anti-icing the bullet nose fairing, inlet guide vanes, forward frame struts, and engine islands. It also had retractable air inlet screens as added protection against icing.
The J35-A-35 was the next development to power the F-89D variant of aircraft. This engine was fitted with a high-altitude flame holder and a dual element fuel pump with a centrifugal booster to provide the necessary fuel inlet pressure in the event of a fuel system boost pump failure. It also had a modification to the 'open eyelid' operation to decrease the engine rpm acceleration time to approximately seven seconds, as well as a high-altitude bleed valve to prevent engine overspeeding during high-altitude afterburning operations.
Below, a schematic drawing of the Allison J35, with the parts that compose it.
A photo of the J35-A-21 version. Notice the can-type combustion chambers.
