(de Havilland) DH 108 Swallow @·AIRCRAFTUBE

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de Havilland DH 108 "Swallow"

The de Havilland DH 108 was a British experimental aircraft designed by John Carver Meadows Frost in October 1945. The DH 108 featured a tailless, swept wing with a vertical tail, closely resembling the layout of the wartime German Messerschmitt Me 163 Komet rocket powered point-defense interceptor. Initially designed to evaluate swept-wing handling characteristics at low and high subsonic speeds for the proposed early tailless design of the Comet airliner, three examples of the DH 108 were built to the Air Ministry specifications E.1/45 and E.11/45. With the adoption of a conventional tail for the Comet, the aircraft were used instead to investigate swept wing handling up to supersonic speeds. All three prototypes were lost in fatal crashes.

Employing the main fuselage section and engine of the de Havilland Vampire mated to a longer fuselage with a single tail fin and swept wings, the de Havilland DH 108 was proposed in 1944 as a test "mule" for the DH 106 Comet which had initially considered a tailless, swept-wing concept. Despite the Comet design taking on more conventional features, the value of testing the unique configuration to provide basic data for the de Havilland DH.110 spurred de Havilland to continue development of the DH 108. Selecting two airframes from the English Electric Vampire F 1 production line, the new aircraft had unmistakable similarities to its fighter origins, especially in the original forward fuselage which retained the nose, cockpit and other components of the Vampire. The Ministry of Supply named the DH 108 the "Swallow," a name that was never officially adopted by the company.

The new metal wing incorporating a 43˚ sweepback was approximately 15% greater in area than the standard Vampire wing. Control was based on the conventional rudder in combination with elevons that were part elevator and ailerons, fitted outboard of the split trailing edge flaps. Although the Vampire fuselage was retained, as development continued, a revised nose and streamlined, reinforced canopy was incorporated.

Testing

The first DH108 prototype, TG283, utilizing the de Havilland Vampire fuselage and a 43° swept wing flew on 15 May 1946. Designed to investigate low-speed handling, it was capable of only 280 mph (or 451 km/h). During the 1946 Society of British Aircraft Constructors (SBAC) air show at Radlett, de Havilland Chief Test Pilot Geoffrey de Havilland Jr put on an impressive display in the DH 108. In later, low-speed testing, in order to clear the rear fuselage at high angles of attack, the first prototype was fitted with longer Sea Vampire landing gear.

The second, high-speed prototype, TG306, with a 45° swept wing with automatic leading-edge Handley Page slats and powered by a de Havilland Goblin 3 turbojet, flew soon after in June 1946. Modifications to the design included a more streamlined, longer nose and a smaller canopy (framed by a strengthened metal fairing) facilitated by lowering the pilot's seat. Unfortunately, on 27 September 1946, the TG306 suffered a catastrophic structural failure that occurred in a dive from 10,000 ft (or 3,050 m) at Mach 0.9 and crashed in the Thames Estuary. The pilot, Geoffrey de Havilland Jr., the chief test pilot and son of de Havilland company owner-designer Geoffrey de Havilland, was killed in the accident. Early wind tunnel testing had pointed to potentially dangerous flight behaviours, however, pitch oscillation at high-speed had been unexpected. The subsequent accident investigation centred on a structural failure that occurred as air built up at Mach 0.9, pitching the aircraft into a shock stall that placed tremendous loads on the fuselage and wings. The main spar cracked at the roots with the wings immediately folding backwards.

After the loss of the second prototype, VW120 became the third and final prototype based on the newer Vampire F.5 fighter built at Hatfield. It differed from the first test aircraft in that it featured an even more streamlined pointed nose and smaller reinforced canopy (lowering the pilot's seat allowed for a more aerodynamic canopy shape to be employed). Power-boosted elevators had been specified as a means to control the pitch oscillations at the root of the earlier disaster. A more powerful Goblin 4 of 3,738 lb (16.67 kN) thrust had the potential to push the DH 108 into the supersonic range. Considered an important testbed for high-speed flight, VW120 was readied for an attempt at the World Speed Record held by a Gloster Meteor at 616 mph (991 km/h). The second prototype, TG306 was a "back up" for the attempt and was being used to evaluate handling characteristics at high-speed when it fatally crashed.

VW120 first flew on 24 July 1947 flown by John Cunningham, the wartime nightfighter ace. The following year, on 12 April 1948, it established a new World Air Speed Record of 974.02 km/h (604.98 mph) on a 100 km (62 mi) circuit. Then, on 9 September 1948, it exceeded the speed of sound in a shallow dive from 12,195 m (40,000) ft to 9,145 m (30,000) ft.

In 1949, VW120 put on a stunning aerial display at Farnborough and scored a third place in the Society of British Aircraft Constructors Challenge Trophy Air Race before being turned over to the Ministry of Supply and Test flown at RAE Farnborough.

The third DH 108 was destroyed on 15 February 1950, in a fatal crash near Brickhill, Buckinghamshire, killing its test pilot, Squadron Leader Stuart Muller-Rowland. Accident investigation pointed to a faulty oxygen system that incapacitated the pilot.

Finally, on 1 May 1950, during stall tests, the first prototype was lost in a crash at Hartley Wintney, killing the pilot, George Genders. In all, 480 flights had been made by the three Swallows.

Legacy

The DH108 established a number of "firsts" for British aircraft: it was the first British swept-winged jet aircraft and the first British tailless jet aircraft (the German Horten Ho 229, a twin-engined, tailless jet designed by the Horten brothers, often incorrectly called the Gotha Go 229 because the Gotha company was selected to put it into production, flew under power for the first time in early 1945); it was the first British aircraft to exceed Mach 1, one of the first jet-powered aircraft in the world to achieve this landmark speed. Two of the aircraft which earlier had exceeded the speed of sound, the Bell X-1 and the Douglas Skyrocket, were both rocket-powered. The XP-86 (the prototype for the F-86 Sabre) had also broken the sound barrier in a test flight on 26 April 1948.

The de Havilland H-1 Goblin engine

The Goblin engine consisted of a single sided centrifugal compressor feeding sixteen straight-flow combustion chambers, a single stage turbine, exhaust case and propelling nozzle.

The combination of a single sided impeller and straight-through combustion eliminated the third bearing normally present. The larger impeller had a slower rotational speed and thus generated less centrifugal stress, while the ducting of air to the single-sided impeller was less complicated than a double-sided impeller.

The Goblin I engine was the first British jet to pass the official type-test in the new Gas Turbine category and held Approval Certificate No. 1.

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This text is available under the Creative Commons Attribution-ShareAlike License
Source : Article de Havilland DH 108 of Wikipedia ( authors )

Specifications (DH 108 "VW120": third prototype)

  • Length: 26 ft 10 in (8.17 m).
  • Height: 14 ft (4.27 m).
  • Wingspan: 39 ft (11.89 m).
  • Wing area: 327.86 ft² (30.47 m²).
  • Wing loading: 27 lb/ft² (133 kg/m²).
  • Loaded weight: 8,940 lb (4,064 kg).
  • Maximum speed: 580 kn (677 mph, 1,090 km/h).
  • Range: 634 NM (730 mi, 1,175 km).
  • Service ceiling 35,425 ft (10,800 m).
  • Powerplant: One de Havilland Goblin-4 turbojet.
  • Thrust: 3,738 lbf (16.67 kN).
  • Thrust/weight: 0.42.

The de Havilland H-1 Goblin engine

  • Weight: 681 kg (1,500 lb).
  • Static Thrust: 1,362 kg (3,000 lb) in it's production form
  • Rated RPM: 10,200.
  • Length 2,553 mm (100.5 in).
  • Maximum diameter 1,270 mm (50 in).
  • Used in: D.H. 108, Meteor Mk.II, Saab 21R, & Vampire.

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This text is available under the Creative Commons Attribution-ShareAlike License
Source : Article de Havilland DH 108 of Wikipedia ( authors )
de Havilland DH 108 Swallow : Your comments on this subject
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