Power Jets WU
| WU | |
|---|---|
| Type | Turbojet |
| Manufacturer | Power Jets |
| First run | 12 April 1937 |
| Major applications | none |
| Number built | 3 |
| Developed into | Power Jets W.1 |
The Power Jets WU (Whittle Unit) was a series of three very different experimental jet engines produced and tested by Frank Whittle and his small team in the late 1930s.
The WU "First Model", also known by Whittle as the first "experimental" engine, and the "1st edition", was the first turbojet engine to be built and run in the world. Although an experimental engine and not intended for flight it was designed to be very light by normal engineering standards. The engine had four basic components: a single stage centrifugal compressor with double-sided impeller, a single straight-through combustion chamber, a single stage, axial flow turbine and a convergent propelling nozzle attached to a jet pipe. The shaft connecting the turbine to the compressor was made as short as possible to avoid whirling. The combustion chamber was connected to the compressor outlet by a very large single spiral duct giving the engine a very asymmetric appearance.
Whittle designed the centrifugal compressor to develop about 4:1 pressure ratio when, as far as he was aware, the best previously demonstrated performance in a single stage was about 2.5:1. He specified a double sided impeller to give his required air flow from a smaller diameter impeller than could be obtained from a single-sided one. The smaller impeller allowed a higher turbine speed which reduced the loading on the single stage turbine and improved its efficiency. The 16.5 in (419 mm) diameter turbine had to develop 3,000 horsepower (2,237 kW) to drive the compressor. One disadvantage of a double-sided impeller is the requirement, in an aircraft installation, for an intake with a plenum with its higher pressure losses. A disadvantage for the design of the rotor thrust bearing is no axial load from the impeller to balance that from the turbine.
Whittle sought help in designing the combustion system and had visited the British Industries Fair. When he discussed the requirements for his combustion chamber with various exhibitors he had been "practically laughed off every stand" until he discovered Laidlaw, Drew and Company, a firm prepared to tackle the difficult problem of combustion at intensities 20x those in refractory-lined industrial applications. By the end of 1936 total expenditure on design and manufacture of the engine amounted to £2,000.
Testing of the first model started on 12 April 1937 at Rugby. During the testing the British Thomson-Houston (BTH) Chief Engineer considered it unwise to exceed 12,000 r.p.m. in the open factory for safety reasons after a run on 23 August up to 13,600 r.p.m. The 31st and final run was on 24 August 1937.
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