Power Jets WU

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.

Design and development

WU First Model was the very first jet engine to be built and run in the UK and possibly the world. Purely an experimental engine, the WU was not intended for flight so little attempt was made to save on weight. The straight through engine had four basic components: a single stage, double-sided, centrifugal compressor, a combustor with a single straight through 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. Whittle had previously visited the British Industries Fair and on discussing his combustion chamber requirements with various exhibitors had been "practically laughed off every stand" until he discovered the firm of Laidlaw, Drew and Company, a firm prepared to tackle the difficult problem of combustion.^[1]

Consequently, the engine had 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 of such a unit was about 2.5:1. He specified a double sided impeller, not only to minimise the engine diameter, but also to increase the shaft speed. This reduced the loading on the single stage turbine, thereby improving its efficiency. The turbine, of 16.5 in (419 mm) outside diameter, was designed to develop 3,000 horsepower (2,237 kW), all absorbed by the compressor. By this time total expenditure on the engine amounted to £3,000.^[2]

Testing continued with the W.U. Edition 1. The 31st and final run was on 24 August 1937. The British Thomson-Houston (BTH) Chief Engineer placed a maximum speed of 12,000 r.p.m. on testing at the Rugby factory for safety reasons after a run on 23 August at up to 13,600 r.p.m..^[3] Testing was to recommence with the same, but greatly modified unit (W.U. Edition 2) at the premises of the BTH's redundant Ladywood foundry at nearby Lutterworth in Leicestershire in March, 1938 until this the turbine of this unit was damaged on 6 May 1938.

A significantly different symmetric trombone-style design was adopted for the second model. Ten spiral ducts connecting the compressor outlet to a large reverse-flow combustor, the outlet of which discharged forward through the turbine before turning rearwards to exhaust through multiple jet pipes.

Significant changes were also introduced in the third model, which featured multiple reverse-flow combustors and had a similar configuration to that of the later Power Jets W.1 and Power Jets W.2 turbojet engines. This configuration was also adopted for the Rolls-Royce Welland and General Electric J31 jet engines. One advantage of the multiple combustors was that a single unit could easily be tested in isolation.

Owing to a shortage of funds, many of the components would have been recycled through the later models.

Whittle and his team experienced many problems developing these units, including poor compressor performance, combustion instability and turbine blade failures. The team did, however, demonstrate that the turbojet had the potential to compete with the large reciprocating aero-engines then being mass-produced for the UK Re-armament Programme.

Variants

WU First Model Experimental Engine

Initial straight through design with asymmetric spiral duct connecting compressor outlet to annular combustor. First run 12 April 1937

WU Second Model Experimental Engine

Trombone-style configuration with single reverse-flow combustor. First run 16 April 1938

WU Third Model Experimental Engine

Trombone-style configuration with multiple reverse-flow combustors. First run 26 October 1938

Applications

None.

Specifications (WU First Model Design Assumptions, performance not actually achieved)

General characteristics

• Type: Centrifugal flow turbojet
• Length: ~67.2 in (~1707 mm) excluding jet pipe
• Diameter: ~45 in (~1143 mm) across compressor
• Dry weight:

Components

• Compressor: 19-inch diameter, single stage double sided centrifugal flow, with no diffuser vanes, material: Hiduminium RR 56
• Combustors: single straight through design, located immediately downstream of elbow in spiral pipe
• Turbine: 14-inch diameter with 66 blades, single stage axial flow, with no nozzle guide vanes, material of disc and blades: Vickers-Firth Stayblade
• Fuel type: Kerosene

Performance

• Maximum thrust: ~1,389 lbf (~6.18 kN)
• Overall pressure ratio: ~4.4:1
• Air mass flow: ~26l lb/s (~11.79 kg/s)
• Turbine inlet temperature: ~1434 F (~779 C)
• Specific fuel consumption: 0.942 lb/hr/lbf (~26.69 g/s/kN)
• Power-to-weight ratio:

See also

• Power Jets W.1
• Power Jets W.2
• Rolls-Royce Welland

References

1. ↑ "World Encyclopedia of Aero Engines - 5th edition" by Bill Gunston, Sutton Publishing, 2006, p.160
2. ↑ "World Encyclopedia of Aero Engines - 5th edition" by Bill Gunston, Sutton Publishing, 2006. p.160
3. ↑ The National Archive, AIR62/15

Bibliography

External links

Wikimedia Commons has media related to Power Jets WU.

• "A Tribute to a Cambridge engineering student"
• "The Secret Years" a 1951 Flight article.
• "The early history of the Whittle jet propulsion gas turbine", a 1945 I Mech E paper by Frank Whittle.
• "The Whittle Jet Propulsion Gas Turbine" a 1945 article in The Engineer