During an early 1941 visit to England, then-Maj. Gen. Harold H. Arnold, acting deputy chief of staff for the Army Air Corps, became interested in the jet propulsion engine under development by the British. At the time, the British were ahead of the United States in this technology. The engine was developed by Air Commodore Frank Whittle of the Royal Air Force and was known as the Whittle Engine.
In August 1941, then-Maj. D.J. Keirn, head of the Power Plant Laboratory at Wright Field, visited the Power Jets plant in Lutterworth, England, where the Whittle Engine was being constructed and tested. By October 1941, a Whittle Engine arrived at Wright Field, Ohio.
A conference was held in Arnold’s office on Dec. 4 and 5, 1941. Attendees decided to build the Whittle engine in the United States, leading to a contract between HQ Army Air Corps and General Electric on Dec. 8, 1941. General Electric agreed to manufacture 15 Whittle-type engines for a total cost of $730,000. By early 1942, this number was increased to 46.
On Oct. 7, 1942, then-Col. B.W. Chidlaw, AC/S(E) of Materiel Command in Washington, D.C., directed the Materiel Center at Wright Field to plan and develop jet propulsion engines and jet-propelled aircraft. By Dec. 11, 1942, an organization was established at Wright Field to handle the research and development of jet propulsion engines and aircraft. This group, part of the Technical Staff at the Power Plant Laboratory, also collaborated with units in the Aircraft Laboratories of the Engineering Division at Wright Field.
Now a brigadier general, Chidlaw, chief of the Materiel Division in Washington, D.C., announced on Oct. 25, 1943, a tentative program for developing jet propulsion aircraft based on two types of engines: pure jet and gas turbine. This program was designed to be flexible, adapting to new tactical requirements or engineering changes.
On Jan. 8, 1944, at Muroc Army Airfield (later Edwards Air Force Base), Lockheed’s chief engineering test pilot, Milo Garrett Burcham, conducted the maiden flight of the prototype Model L-140, the Army Air Forces XP-80 (serial number 44-83020). This aircraft used a General Electric variant of the Whittle Engine.
In February 1944, at Arnold’s request, Maj. Gen. O.P. Echols, AC/AS, MM&D in Washington, D.C., submitted estimated performance data on the P-59A and XP-80A airplanes, along with information on the I-40 engine. The first I-40/J-33 engine underwent static testing on Jan. 11, 1944, at the General Electric plant. Although preliminary runs were not conducted at rated speed and thrust, the engine operation was deemed satisfactory. Five months later, an I-40 engine flew in the XP-80A. Development of the I-40 began in June 1943, with the first run achieved in an impressive six months. By Aug. 21, 1944, J-33 engines built to specifications had a probable life of 50 hours before major parts required repair or replacement.
On April 8, 1944, the Resources Control Section at Wright Field recommended licensing Allison Division of General Motors Corporation in Indianapolis, Indiana, to build I-40 engines and tooling Plant No. 5 at Allison to produce 1,000 units per month. This recommendation was made due to General Electric’s poor production rates.
From Muroc Army Airfield, Lockheed Aircraft reported that the prototype XP-80A airplane (using the new I-40 engine) made its initial flight on June 10, 1944. Due to difficulties with the flap mechanism, the airplane landed after 35 minutes of flight. The engine functioned satisfactorily and cooled well.
A few days later, on June 14, 1944, Brig. Gen. O.R. Cook, chief of the Production Division at Materiel Command, sent a memorandum to AAF leaders in Washington. The memo stated that provisions were made for installing I-40 engines in the XP-81 and XP-83 under the contract with General Electric. Additionally, General Motors’ Allison Division and General Electric continued to produce engines for the XP-80A.
As the war was nearing its end, a meeting was held at Wright Field on Jan. 30, 1945, by the Army Air Forces’ Air Technical Service Command, Materiel Command, Engineering Division. The meeting addressed the I-40 engine's operation in connection with the XP-80A and YP-80A airplanes. Discussion focused on Lockheed Aircraft Corporation’s development problems with the YP-80A, operational and maintenance difficulties with General Electric’s I-40-3, and a summary from Lockheed on additional flight test experience with the I-40 engine in the Lockheed XP-80 aircraft.
After the war ended on Sept. 18, 1945, leaders from Wright Field and HQ Army Air Forces decided to terminate General Electric’s I-40 contract and transition to Allison Division. Allison Division expressed willingness to take full responsibility for engineering design and further development of the I-40. Allison also had a better production record with the I-40 compared to General Electric. It was believed that assigning Allison as the sole manufacturer “would do a great deal toward ensuring continuation of Allison in the development and production of both liquid-cooled and gas turbine engines.”
J-33 engines of various variants continued to be used in F-80s during the Korean War and later around the world.
Specifications for the I-40:
- Type: Turbojet
- Compressor: Single-stage centrifugal
- Turbine: Single axial
- Weight: 1,875 lbs
- Thrust: 4,600 lbs max (AAF originally requested between 3,000 to 4,000 lbs of thrust)
- RPM: 11,750 max
- Altitude: 47,000 ft
- Combustor: 14 interconnected straight-through chambers
Weight, thrust, and other specifications varied with different engine variants.
The J-33/I-40 was General Electric’s first turbojet engine of its own design, its last all-centrifugal-flow engine, and the last used in U.S. military combat aircraft. The Allison J-33 was the first mass-produced jet engine used by the U.S. military, powering first-generation jet aircraft including the Martin XB-51, Lockheed XP-81, F-80A/B/C, RF-80A, QF-80F, XF-14/A, TF-80C, T-33A/B, AT-33A, DT-33A/B/C, RT-33A, QT-33A, WT-33A, T-1A, North American F-86C, Northrop F-89J, and Bell XP-83.
Full text: https://media.defense.gov/2024/Sep/06/2003538838/-1/-1/1/FLASHBACK_I-40%20-%20J-33%20ENGINE.PDF/FLASHBACK_I-40%20-%20J-33%20ENGINE.PDF