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The Gloster E.28/39 was an experimental aircraft designed to flight test the jet engine designs of Frank Whittle.


Design and Construction[]

Development of the E.28/39 began when Whittle's Power Jets company received a contract for a flight engine.[N 2] Thus, ten years after he had first tried to get someone interested and more than three years after the first test run, Whittle’s invention was suddenly (and for the first time) recognised as important. Moreover, as the Power Jets team was quite literally having to count pennies, the Air Ministry bought the original engine, and for the first time Whittle had no financial worries. This allowed thoughts to turn to the question of flight-testing the new engine. Whittle had thought about this for years. The simplest answer was to mount it under or in the tail of an existing aircraft, and he sketched arrangements based on the Wellington. Later it would become common practice for new types of jet engine to begin flight testing attached to such aircraft as the Lancaster, B-29, Tu-16 and A340, but Whittle could see that to make any kind of impact on ignorant politicians, his engine had to actually power the testbed aircraft.

Accordingly, in early 1939 he roughed out a preliminary design, with the hope that Power Jets might be awarded the flight-test contract, subcontracting the aircraft to an established aircraft constructor. Back in 1931 he had filed a patent jointly with Flt Lt "Mac" Reynolds. Now, in 1939, Reynolds was Air Ministry Overseer at the Gloster Aircraft Company. This firm was busy making Hurricanes (and later almost all the Typhoons), but it had spare design capacity. In April 1939 Whittle telephoned Reynolds, as a result of which, on the 28th of that month, he drove to the design office at Brockworth. Soon he was in the office of George Carter, the chief designer. Whittle drew from his briefcase the three-view of his proposed jet aeroplane. Carter was instantly enthusiastic. In fact, predictably, the Ministry of Aircraft Production (MAP) awarded Gloster the whole contract, which called for two aircraft to be built to Experimental Specification E.28/39. The requirement was well framed, and among other things it was decreed that provision should be made for four fuselage-mounted 0-303in Browning guns. This was not, as has often been reported, so that the aircraft might form the basis of a fighter, which was a ridiculous notion, but so that interaction between the guns and the jet intake might be studied. In the event, they were never fitted.

The aircraft received the unofficial names Pioneer and Weaver. After studying various tail-first schemes, Carter stuck to the conventional layout Whittle had suggested, with straight-through nose-to-tail flow. Like the Heinkel designers, Carter placed the cockpit well forward, ahead of the engine, between left and right air ducts. [N 3] Power Jets began testing its second engine, the W.1X, on December 14, 1940. lt then managed to run the W.1 flight engine on April 12, 1941, four years to the day alter the WU.

Though this is hard to believe, throughout this time Britain is supposed to have been completely ignorant of Germany's jets. Turbojets were not mentioned in the “Oslo parcel" (a package of information on secret German projects left at the British Embassy in Oslo in November 1939 by “a well-wisher"), but how could we possibly have known nothing of the work by so many engineers in a dozen companies? But then we did not know of the existence of the Focke-Wulf Fw 190, which like the He 178 was repeatedly flown from a public aerodrome before the war. - Bill Gunston

In 1940 the need was for Hurricanes and Spitfires, and all priority was removed from Whittle’s work. Indeed, his drawings had been handed to BTH and the Rover Car Co, and on May 20, 1940, all work on jet engines was halted, as having no immediate relevance! Priority was eventually restored on June 11, but Whittle considered that the loss of momentum equated to a real delay of several months. Even a year later, the total of Whittle engines able to run was still just two, but one of these, the W.1, was flying in the first E.28/39. The aircraft bore the serial number W4041/G. [N 4]


Gloster chief test pilot P.E.G. “Gerry” Sayer had made the first taxying tests on April 7, 1941, at Brockworth. Then Whittle himself had a go. Following various modifications, the aircraft was trucked to Cranwell. Here, at dusk on the bitterly cold May 15, Sayer made the first flight.


  • Airframe: This was made almost entirely of traditional 24ST light alloy, exterior skin being flush-riveted, except for the elevators and rudder which were fabric-covered. The contrast in empty weight with the He 178 is astonishing. The original wing, of NACA 23012 profile, had a single spar running straight from tip rib to tip rib, with the main attachments to the fuselage at Frame 7 and the trunnions for the main undercarriage. An auxiliary spar carried the ailerons and split flaps. The “high speed" wing fitted later, and to W4046, had elliptic-cubic EC1240 profile. The fuselage was of circular section and incorporated an air duct from the open nose, passing on each side of the cockpit to discharge into the engine compartment at Frame 7. Between Frames 7 and 9 was the engine bay, the upper part of which was removable in one piece to give immediate access to the engine and to permit the engine to be changed. The jetpipe, of refractory welded sheet, was usually aligned with the longitudinal axis.
  • Undercarriage: All three units were designed and made by Dowty Equipment. The nose unit was steered via the pedals and retracted backwards. The main units were of the levered-suspension type, folding inwards into bays covered by twin doors, with small blisters above and below the wing.
  • Systems: The fuel system was fed with JP-1 kerosene from an 81gal tank occupying the bay between the inlet ducts between Frames 6 and 7. It was filled by gravity. The hydraulic system was filled with DTD.585 mineral fluid and operated at 1,500lb/in’. It incorporated an accumulator, charged before each flight. This enabled the undercarriage to be retracted quickly on take-off. Subsequently the pilot maintained pressure by a hand pump, and this had to be used for the flaps and gear extension the nose-leg coming down against air drag. The engine incorporated a self-contained oil system, circulation being by a gear pump. The W.1X incorporated a water cooling system, circulated past the rear face of the turbine disc. Flight controls were actuated by rods, with grease lubrication. The cockpit could be cooled by fresh air from a ram inlet under the port wing root, and was supplied with gaseous oxygen from a single bottle under the cockpit floor, but had neither pressurization nor heating. initial taxiing tests were done with W4046 unpainted, with a strip of temperature-sensitive paint along each side of the rear fuselage. Subsequently dark green and dark earth above and training yellow below, with prototype P in a circle in yellow. In 1943 upper surfaces repainted with dark earth replaced by medium sea grey.[2]



  1. For taxying tests, Power Jets W.1X, 620lb static thrust; for initial flight trials, W1, 860lb-thrust; Subsequently W.1A, 1,160lb-thrust; Rover W.2B, 1,200lb-thrust; Rolls-Royce W.2B/23, 1,400lb-thrust; Power Jets W.2/500, 1,700lb-thrust.[2]
  2. Basically, this means an engine designed to power an aeroplane
  3. When, in 1955, Bill Gunston argued the advantages of using twin engines, Caravelle style. Whittle replied: “Yes, but we didn’t have two enginesl"
  4. The suffix /G meant that the aircraft should have an armed guard when on the ground.


  1. 456 FIS
  2. 2.0 2.1 2.2 2.3 Aeroplane Magazine Database: May 2001 (Early Jet Aircraft)