Power Jets WU
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The Power Jets WU (Whittle Unit) was a series of three very different experimental
jet engine A jet engine is a type of reaction engine discharging a fast-moving jet of heated gas (usually air) that generates thrust by jet propulsion. While this broad definition can include rocket, Pump-jet, water jet, and hybrid propulsion, the term ...
s produced and tested by
Frank Whittle Air Commodore Sir Frank Whittle, (1 June 1907 – 8 August 1996) was an English engineer, inventor and Royal Air Force (RAF) air officer. He is credited with inventing the turbojet engine. A patent was submitted by Maxime Guillaume in 1921 for ...
and his small team in the late 1930s.


Design and development

The WU "First Model", also known by Whittle as the first "experimental" engine, and the "1st edition","The Early History of the Whittle Jet Propulsion Gas Turbine" The First James Clayton Lecture 1945, Air Commodore Frank Whittle, Institution of Mechanical Engineers, London 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 Centrifugal compressors, sometimes called impeller compressors or radial compressors, are a sub-class of dynamic axisymmetric work-absorbing turbomachinery. They achieve pressure rise by adding energy to the continuous flow of fluid through th ...
with double-sided impeller, a single straight-through
combustion chamber A combustion chamber is part of an internal combustion engine in which the fuel/air mix is burned. For steam engines, the term has also been used for an extension of the firebox which is used to allow a more complete combustion process. Intern ...
, a single stage, axial flow
turbine A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating ...
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 an asymmetrical 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 An impeller or impellor is a rotor used to increase the pressure and flow of a fluid. It is the opposite of a turbine, which extracts energy from, and reduces the pressure of, a flowing fluid. In pumps An impeller is a rotating componen ...
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 diameter turbine had to develop 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
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. 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. A significantly different, symmetrical design was adopted for the second model. Ten spiral ducts connected the compressor outlet to a single, large, reverse-flow combustion chamber, the outlet of which discharged forward through the turbine before turning rearwards to exhaust through ten jet pipes. Some heat exchange was expected from the exhaust pipes to the ten ducts delivering air to the combustion chamber as they were all enclosed by the outer casing. Testing began with a reconstructed engine at the premises of the BTH's redundant Ladywood foundry at nearby
Lutterworth Lutterworth is a market town and civil parish in the Harborough district of Leicestershire, England. The town is located in southern Leicestershire, close to the borders with Warwickshire and Northamptonshire. It is located north of Rugby, ...
in
Leicestershire Leicestershire ( ; postal abbreviation Leics.) is a ceremonial and non-metropolitan county in the East Midlands, England. The county borders Nottinghamshire to the north, Lincolnshire to the north-east, Rutland to the east, Northamptonshire t ...
on 16 April 1938 and continued until the turbine was damaged on 6 May 1938. A third reconstructed engine was ready for testing on 26 October 1938. Significant changes were also introduced in the third model. It had ten reverse-flow combustion chambers giving 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 The Rolls-Royce RB.23 Welland was Britain's first production jet engine.Janes 1989, p.268. It entered production in 1943 for the Gloster Meteor. The name Welland is taken from the River Welland, in keeping with the Rolls-Royce policy of naming ...
and
General Electric J31 The General Electric J31 was the first jet engine to be mass-produced in the United States. Design and development After a visit to England mid-1941, General Henry H. Arnold was so impressed by flight demonstrations of the Gloster E.28/39 je ...
jet engines. One advantage of using 10 combustion chambers, smaller by a factor of (1/sqrt10), was they could be more easily be tested on a combustion rig. Owing to a shortage of funds, many of the components would be modified or repaired for testing on later engines. Whittle and his team experienced many problems developing the three models. Compressor and turbine efficiencies and durability were improved. Poor fuel system and combustion performance no longer limited the testing of other parts of the engine. The general design of the follow-on W1 engine was very similar to the third model of the experimental engine. The team demonstrated that the turbojet had the potential to compete with the large reciprocating aero-engines then being mass-produced for the UK Re-armament Programme. The initial rounded "bulb" de Laval-type root fixing was later replaced with a new triangular "fir-tree" design after repeated stress/fatigue failures of the earlier type. The "fir-tree" design would be used on all Whittle's subsequent engines. After severe initial combustion problems, in late 1940 a new design of combustion chamber designed by Isaac Lubbock of the Shell Fulham Laboratory was incorporated. This 'Lubbock' chamber/burner proved the answer to many of the combustion problems. The reverse-flow type of combustion chamber, as implemented on the third engine, was necessary to allow the continued use of the more expensive components, eg rotor assembly, which had been designed for the completely different straight-through combustion chamber used on the first engine. The reverse-flow arrangement had no thermal expansion problems, it allowed the continued use of a very short shaft between the impeller and turbine, the end covers at the rear of the chambers could be easily removed for inspection and modifications to the combustor components. Whittle had assumed the use of vortex flow in the turbine blades however BTH engineers had not incorporated this and had manufactured the blades with insufficient twist. Whittle's subsequent insistence on this subsequently led to deteriorating relations with BTH engineers. The WU was effectively destroyed by turbine disc failure on 22 February 1941. Work continued with the Power Jets W.1.


Variants

;WU First Model Experimental Engine :Initial design with asymmetric spiral duct connecting compressor outlet to single straight-through combustion chamber. First run 12 April 1937 Design Data *Airflow: ~25.7 lb/s (~11.66 kg/s) *Shaft Speed: 17750rpm (296rev/s) *Turbine Power Output: ~2950 hp (~2200 kW) *Compressor Impeller Diameter: ~19.69in (~500mm) *Compressor Impeller Tip Speed: ~1525 ft/s (~465 m/s) *Turbine Tip Diameter:~15.75in (~400mm) *Turbine Tip Speed: ~1220 ft/s (~372 m/s) ;WU Second Model Experimental Engine :single reverse-flow combustion chamber. First run 16 April 1938 ;WU Third Model Experimental Engine :Ten reverse-flow combustion chambers. First run 26 October 1938


Applications

None.


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


See also

*
Heinkel HeS 1 The Heinkel HeS 1 ''(HeS - Heinkel Strahltriebwerke)'' was Germany's first jet engine, which was a stationary test item that ran on hydrogen. History In 1933, Hans von Ohain wrote his PhD thesis at the University of Göttingen on the topic of an ...
* Power Jets W.1 * Power Jets W.2 *
Rolls-Royce Welland The Rolls-Royce RB.23 Welland was Britain's first production jet engine.Janes 1989, p.268. It entered production in 1943 for the Gloster Meteor. The name Welland is taken from the River Welland, in keeping with the Rolls-Royce policy of naming ...


References


Notes


Bibliography


External links


"A Tribute to a Cambridge engineering student"
a 1951 ''Flight'' article.
"The early history of the Whittle jet propulsion gas turbine"
a 1945 I Mech E paper by
Frank Whittle Air Commodore Sir Frank Whittle, (1 June 1907 – 8 August 1996) was an English engineer, inventor and Royal Air Force (RAF) air officer. He is credited with inventing the turbojet engine. A patent was submitted by Maxime Guillaume in 1921 for ...
.
"The Whittle Jet Propulsion Gas Turbine"
a 1945 article in ''The Engineer'' {{Power Jets aeroengines 1930s turbojet engines Centrifugal-flow turbojet engines WU