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CL-400 SUNTAN Engine Tests

The testing of the 304 engines was carried out at Pratt & Whitney's new center west of West Palm Beach, Florida. The test center, still under construction in the fall of 1957, was the result of several years of planning by United Aircraft officials to overcome the limited space for testing at their Connecticut plant. Problems of safety and noise made a more remote site desirable, and there were considerations of dispersal of facilities for defense reasons. These had led to the choice of West Palm Beach County as a desirable test site. United Aircraft acquired a large tract of land, swapped part of it for adjacent land owned by the state, and ended up with 27 square kilometers of sand, scrub pine, swamp, and alligators - well suited for remote testing of new engines. In the negotiations for the hydrogen engine contract, United Aircraft officials indicated a willingness to invest $20 million in permanent facilities at the new center if the Air Force would pay for all movable equipment, also estimated to be about $20 million. The cost sharing was agreed upon in principal, if not in the exact amounts, and construction proceeded. During initial operations, the test crew often had to call for a bulldozer to clear the unpaved roads of deep ruts to allow passage; alligators were a common sight.

The first 304 engine tests began on 11 September 1957 using three fluids: nitrogen, gaseous hydrogen, and liquid hydrogen. The inert nitrogen was used to check the fuel system and rotating machinery, especially bearings and seals. The first series of runs lasted through October; 4 1/2 hours were logged, including 38 minutes with liquid hydrogen. The engine was removed for inspection and overhaul when turbine oil consumption became excessive. When reinstalled for a second series of runs on 20 December 1957, no significant failures occurred, but the engine was periodically removed, inspected, overhauled and reinstalled.

Six series of runs were made through the first part of July 1958 and 5 1/2 hours of operation with hydrogen were accumulated. Only minor problems were encountered until the last run, when there was a major failure of bearings, turbine, and heat exchanger. Meanwhile, a second engine of the same type had been installed on a twin test stand; its first run was made on 16 January 1958. Tests continued on the second engine into the first part of April, with a little over 10 hours of operation with hydrogen. The engine was removed when the low pressure section of the turbine failed.

During the testing period, Coar and Mulready designed and built a second model of the 304 engine, which had an additional (fifth) compressor stage and lower specific fuel consumption. The first 304-2 was assembled at East Hartford on 20 June 1958 and four days later was operated at the Florida test center. Tests continued for a month, with 3 1/3 hours of accumulated running time with hydrogen before the engine experienced a complete turbine failure. It was removed for repair and strengthening of the turbine disks. While this engine was in the shop, another 304 engine (presumably of the first design) was installed and operations began in mid-August. This engine operated satisfactorily through September and accumulated over 6 hours time using hydrogen. By the end of September 1958, the repaired 304-2 engine was back on the stand and made a short run, and another 304 engine was nearing assembly at East Hartford.

Characteristics of Pratt & Whitney's Model 304 Engines 

Model 304-1

Test Performance

Model 304-2

Test peformance


Spec A6600



Spec A-6600A

Sea level static thrust


55 600

55 422

53 429

60 048

35 028


(12 500)

(12 460)

(12 012)

(13 500)

(7 875)

Thrust specific fuel consumption, kg/N . hr






Compressor speed, rpm

3 600

3 630

3 300

3 600

2 503

Pump discharge pressure, atm






Overall turbine efficiency







Note: Model 304-1 had 4 compressor stages.
Model 304-2 had 5 compressor stages.

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