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The Northrop Turbodyne (XT37)
Jack Northrop's Reply to
Threatened Turbodyne Project Cancellation
13 Oct 1947
1) Northrop Aircraft representatives were to be at Wright Field on Monday 27 Oct 1947 to review the then-current plan for completing the contract.
2) Since the decision to discontinue using Northrop Aircraft facilities for engine development and production were presumably based upon project evaluation, Northrop Aircraft wanted to identify pertinent facts that may not have been considered.
3) On 10 Nov 1944, a CPFF contract for $748,076.00 was issued to design, construct, test and report upon a multi-stage compressor, combustion chamber system, and a turbine. This contract was increased by $42,104.07 on 1 Oct 1945 for special test equipment. Not until 3 Jan 1946 was the contract expanded to assemble the components into a gas turbine, build three additional laboratory gas turbines, and to test these. Provisions were also made on 1 Oct for spare parts, a propeller reduction gear, and a fuel control system; this increased the contract by $1,429,078.81. An additional $38,973.91 was allocated for laboratory test equipment on 17 Oct 1946. Since the program scope proved larger than initially envisioned, a $1,474945.25 overrun was applied for in November 1946 and granted on 24 Apr 1947. In summary, the contract then totaled $3,555,229.88 for design, construction and development testing of four gas turbins, spares and accessories; of this, $1,000,000.00 was then unspent. Special test equipment then totaled $81,077.98. The fixed fee was $83,527.18.
4) Design started in November 1944 and actual work began on the originally specified component parts at the Northrop-Hendy Sunnyvale Division in June 1945. The first unit, a compressor, was delivered to Northrop Aircraft, Hawthorne in September 1946, and the first laboratory model gas turbine was delivered in December 1946, 12 months after contract signing. A San Francisco Bay Area machinists strike delayed completion of these and subsequent units by about 6 months. Elapsed time from start of design to compressor completion was 22 months and 25 months for the first complete turbine. Actual manufacturing time (eliminating lost time due to the strike) was 9 months for the compressor and 12 months for the first engine.
The power-absorbing compressor was calibrated and mechanically shaken down during January 1947. The first complete turbine was shaken down, fired hot and ran self-supported on 14 Feb 1947 (27 months from design inception, 13 months from contract signing). Attempts to load the engine during March resulted in failure of the Allison V-1710-63 starting engine, and it was decided to remove stages from the power-absorbing compressor to reduce starting load. Several no-load runs were made in April. During a run on 16 Apr 1947 and aluminum compressor blade failure seriously damaged the unit. Forged steel compressor blades were procured and used to build a second laboratory engine, which was delivered in August.
During August, the second engine was checked out mechanically and run up to 4,400 rpm with no load. On 4 Sep 1947, a no-load run up to 6,250 rpm was made, and on 18 Sep 1947 a no-load cruise speed run at 6,750 rpm was made. On 26 Sep 1947 a load run at 6,750 rpm produced 4,050 equivalent hp (shaft hp plus jet thrust) at the 7,088 military speed with only a 1,310°F nozzle temperature. The tripping of a fuel pump circuit breaker inadvertently terminated this run. If the run had been completed to 1,500°F nozzle temperature, the unit would have produced 5,800 equivalent hp. Load testing was to soon continue on this unit.
Work on the third laboratory engine had been delayed because the only difference between it and Units 1 and 2 was the full annular combustion chamber. The fourth engine was scheduled for completion in February 1948; it was to incorporate changes to reduce weight and increase power about 20% over the Unit 1.
5) The funds then allocated would allow additional testing of the first two turbines and complete testing of the fourth, all before June 1948. Testing indicated that the fourth engine would exceed contract performance specifications by 10%. On the date the letter was written only about $2,450,000 had been expended and a gas turbine had developed 4,460 equivalent hp on the test stand. Northrop Aircraft opined that such performance during the first military power run represented an achievement usually reached after a protracted developmental test period.
6) The Joshua Hendy Torrance, California plant had adequate facilities had adequate facilities to produce two XT37s per month. The company was financed and organized to expand that facility to its full 27 acres when necessary, and expansion that could be accomplished at no cost to the government.
7) On 30 Sep 1947, Mr. H.M. Horner, President of United Aircraft Corporation stated before the President's Air Policy Commission, "For a present day high-powered engine, either a reciprocating or turbine, this phase (i.e., design and development of a power plant through type test) takes roughly three years or more and cost some ten to fifteen millions of dollars." By comparison, Northrop-Hendy will have designed and completely tested a 7,000 shp gas turbine in 3.5 years at a cost of 3.5 million dollars, a schedule that was in line with Horner's prediction but at a price that was 0.30 – 0.25 of his estimate. This makes the completion of a high-power gas turbine such as the XT37 an outstanding accomplishment.
8) The turboprop engine was by far the best type available to meet medium and long-range bomber requirements. Northrop Aircraft had been reliably informed that the XT37 and Curtiss-Wright XT35 were the only turboprops then beyond the paper stage. Northrop Aircraft thought the axial-flow XT37 smaller, lighter and more powerful than the XT35, which used a centrifugal compressor. Northrop Aircraft also believed the axial-flow design would result in lower SFC.
9) Northrop-Hendy maintained that it could provide adequate facilities for reasonable production quantities without government aid. Northrop-Hendy believed that with its competitive development schedule and low cost, as compared to other organizations developing high-powered engine, the "chosen instrument" policy, which was the only possible justification for discontinuing Northrop-Hendy's turbine engine operations, was highly dangerous and restrictive to free competition, new and important ideas, and youthful organizations. U.S. technical superiority was founded on free enterprise and free competition in all fields. Northrop Aircraft maintained it was unwise to and unjust to terminate a vitally important development to protect a "chosen instrument."
10) In light of the foregoing, Northrop-Hendy requested that the government reconsider its decision and continue using Northrop-Hendy as a development and production resource.
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