|Welkin Mk I|
|Role||high altitude fighter|
|National origin||United Kingdom|
|First flight||1 November 1942|
|Primary user||Royal Air Force|
|Number built||75 + 2 prototypes + 26 engine-less airframes|
The Westland Welkin was a British twin-engine heavy fighter from the Westland Aircraft Company, designed to fight at extremely high altitudes, in the stratosphere; the word welkin meaning "the vault of heaven" or the upper atmosphere. First conceived in 1940, the plane was built in response to the arrival of modified Junkers Ju 86P bombers flying reconnaissance missions that suggested the Luftwaffe might attempt to re-open the bombing of England from high altitude. Construction was from 1942–43. The threat never materialised; consequently, Westland produced only a small number of Welkins and few of these flew.
Design and development
Westland put forward their P.14, essentially an adaptation of Westland's Whirlwind fighter layout (and a more experimental twin, the P.13) to meet Air Ministry Specification F.4 of 1940 for a high altitude fighter. The most obvious feature was the enormous high aspect ratio wing, with a span on the production aircraft of 70 feet (21 m). The compact but troublesome Rolls-Royce Peregrine engines of the Whirlwind were replaced by the more powerful two-stage Rolls Royce Merlin Mk.76/77. However, the most significant feature was a pressurised cockpit. The last item required the majority of the effort in designing what would become the Welkin. After extensive development a new cockpit was developed that was built out of heavy-gauge duraluminium bolted directly to the front of the main spar. The cockpit hood used an internal layer of thick perspex to hold the pressure, and an outer thin layer to form a smooth line. Heated air was blown between the two to keep the canopy clear of frost.
In January 1941, the Ministry of Aircraft Production authorised the building of two P.14 prototypes DG558 & DG562. The F.4/40 specification was revised into F.7/41 that year. The Welkin design was now in competition with the Vickers Type 432 with Merlin 61 engines.
The pressurisation system was driven by a Rotol supercharger attached to the left-hand engine (this was the difference between the Merlin 76 and 77), providing a constant pressure of 3.5 psi (24 kPa) over the exterior pressure. This resulted in an apparent cabin altitude of 24,000 feet (7,300 m) when the aircraft was operating at its design altitude of 45,000 ft (14,000 m). This cabin altitude was still too high for normal breathing, so the pilot had to wear an oxygen mask during flight. A rubber gasket filled with the pressurized air sealed the canopy when the system was turned on, and a valve ensured the pressure was controlled automatically. Moreover, the pilot also had to wear a high altitude suit as he might have been required to bail out at altitude.
The Welkin required a sophisticated electrical system. This was to minimise the number of seals and points of entry in the cockpit for the controls and instrumentation. It took an electrician experienced in the features of the Welkin four hours to undertake a pre-flight check of this system. The wings were so large that the high lift Fowler flaps of the Whirlwind were not needed, and were replaced by a simple split flap. The extra wing area also required more stability, so the tail was lengthened to provide a longer moment arm. The armament − four Hispano 20 mm cannon − was the same as the Whirlwind's, but the Welkin carried the guns in a tray in its belly, which facilitated loading. In that position, muzzle flash was also less likely to dazzle the pilot.
The Welkin was seriously handicapped by compressibility problems caused by its long, high aspect-ratio wing which needed to be thick at the root (thickness-to-chord ratio of about 19%) for strength reasons. Compressibility caused the flight envelope (flyable speed range) between high-incidence stall and shock-stall to become very small at high altitudes – any decrease in airspeed causing a "normal" stall, any increase causing a shock-stall due to the aircraft's limiting critical Mach number. This reduction of the speed envelope is a problem common to all subsonic, high altitude designs and also occurred with the later Lockheed U-2. When W.E.W. Petter came to design his next high-altitude aircraft, the English Electric Canberra jet bomber, the required wing area was distinguished by noticeably short wings, with thickness-to-chord ratio (t/c) at the root of 12%, a t/c ratio which delays compressibility effects to an aircraft speed of about Mach 0.85.
Information on the Welkin was only released at the end of the war.
A two-seat, radar-equipped night fighter version known as the Welkin NF.Mk.II for specification F.9/43 was developed but only one was eventually produced as the variant was not ordered into production.
By the time the Welkin Mk.I was complete and in production, it was apparent that the Luftwaffe was no longer conducting high altitude missions, due largely to successful interceptions by specially modified Supermarine Spitfires. Only 77 complete Welkins were produced, plus a further 26 as engine-less airframes. Although two Welkins served with the Fighter Interception Unit based at RAF Wittering from May to November 1944, where they were used to gain experience and formulate tactics for high altitude fighter operations, the Welkin was never used operationally by the RAF.
- Welkin Mk.I : Single-seat twin-engine high altitude fighter aircraft.
- Welkin NF.Mk.II : Two-seat night fighter prototype.
Specifications (Welkin F.Mk.I)
- Crew: 1
- Length: 41 ft 6 in (12.65 m)
- Wingspan: 70 ft 0 in (21.34 m)
- Height: 15 ft 9 in (4.80 m)
- Wing area: 250 sq ft (23 m2)
- Airfoil: root: NACA 23021; tip: NACA 23015
- Empty weight: 8,310 lb (3,769 kg)
- Gross weight: 10,356 lb (4,697 kg)
- Powerplant: 2 × Rolls-Royce Merlin 76 V-12 liquid-cooled piston engine, 1,233 hp (919 kW) each
- Propellers: 4-bladed constant-speed propellers
- Maximum speed: 385 mph (620 km/h, 335 kn)
- Range: 1,480 mi (2,380 km, 1,290 nmi)
- Service ceiling: 44,000 ft (13,000 m) 
- Rate of climb: 3,850 ft/min (19.6 m/s)
- Wing loading: 41 lb/sq ft (200 kg/m2)
- Power/mass: 0.11 hp/lb (0.18 kW/kg)
- Guns: 4 x 20 mm Hispano cannon
Aircraft of comparable role, configuration and era
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- Velek, Ovčáčík & Susa 2005, p. 1.
- Buttler 2004, p. 47.
- For comparison, the Avro Lancaster four-engined heavy bomber had a span of 102 feet (31 m) and the de Havilland Mosquito twin-engined light bomber and fighter had a 54-foot (16 m) span.
- From Spitfire To Eurofighter 45 Years of Combat Aircraft Design, Roy Boot 1990, Airlife Publishing Ltd., ISBN 1 85310093 5, p.12
- Bombers of the West, Bill Gunston 1973, Charles Scribner's Sons, New York, SBN 684-13623-6, p.16
- Flight Handbook The Theory and Practice of Powered Flight,edited by W.T.Gunston, Sixth Edition 1962, Iliffe Books Ltd., U.S. Library of Congress Catalog Card Number 39-30641, p.26
- "New Aircraft Types", Flight, p. 664, 21 June 1945
- Buttler 2004, p. 48.
- Velek, Ovčáčík & Susa 2005, pp. 13–14.
- Velek, Ovčáčík & Susa 2005, p. 3.
- Aircraft Of The Royal Air Force Since 1918, Owen Thetford, Third Edition 1962, Putnam& Co. Ltd, p.552
- "Westland Welkin". British Aircraft of World War Two. Archived from the original on 7 January 2009. Retrieved 2 May 2019.
- Green & Swanborough 1981, p. 60.
- Lednicer, David. "The Incomplete Guide to Airfoil Usage". UIUC Applied Aerodynamics Group. Retrieved 16 April 2019.
- Buttler, T. (2004). British Secret Projects: Fighters and Bombers 1935–1950. Hinckley, UK: Midland. ISBN 1-85780-179-2.
- Goulding, James and Robert Jones. "Meteor, Whirlwind and Welkin". Camouflage and Markings: RAF Fighter Command Northern Europe, 1936–45. London: Ducimus Books, 1971. ISBN 0-903234-00-9.
- Green, W.; Swanborough, G. (1981). RAF Fighters, Part 3 (WW2 Aircraft Fact Files). London: Jane's Publishing. ISBN 0-7106-0119-0.
- James, Derek N. Westland: A History. Gloucestershire UK: Tempus Publishing Ltd., 2002. ISBN 0-7524-2772-5.
- Mondey, David. Westland (Planemakers 2). London: Jane's Publishing Company, 1982. ISBN 0-7106-0134-4.
- Velek, M.; Ovčáčík, M.; Susa, K (2005). Westland Welkin F Mk.1, NF Mk.II. Prague, Czech Republic: Mark I Ltd. ISBN 80-86637-01-8.
- Webb, D. Collier. "Tested & Failed, Flight Test Accidents of the 1940s–1960s: Westland Welkin." Aeroplane Monthly, February 1996.
|Wikimedia Commons has media related to Westland Welkin.|
- Westland Welkin – British Aircraft Directory