Westland Welkin
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| Westland Welkin | |
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| Welkin Mk.I DX282 | |
| Type | high altitude fighter |
| Manufacturer | Westland Aircraft |
| Designed by | W. E. W. Petter |
| Maiden flight | November 1 1942 |
| Introduced | May 1944 |
| Retired | November 1944 |
| Primary user | Royal Air Force |
| Number built | 75 + 26 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". It was created in 1942-43 in response to the arrival of modified Junkers Ju 86 bombers flying reconnaissance missions which suggested the Luftwaffe might attempt to re-open bombing of England at high altitudes. In the end this threat never materialised, and the Welkin was produced only in small numbers.
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[edit] Design and development
The Welkin was essentially an evolution of the Whirlwind built to Air Ministry Specification F.4/40. The most obvious feature was the enormous high aspect ratio wing, with a span of 70 feet (21.3 metres). For comparison, the Avro Lancaster four-engined heavy bomber spanned 102 feet (31.1 metres) or the Supermarine Spitfire Mk.VB single-engined fighter had 36.8 feet (11.2 metres). The Whirlwind's troublesome Rolls-Royce Peregrine engines were replaced by the Rolls Royce Merlin Mk.76 / 77. However, the most important feature was a pressurised cockpit. The last item required the majority of the effort in designing the Welkin. After extensive development a new cockpit was developed that was built out of heavy-gauge duraluminum 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.
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 lb/in² (24 kPa) over the exterior pressure. This resulted in an apparent altitude of 24,000 ft (7,300 m) when the plane was operating at its design altitude of 45,000 ft (13,700 m). This apparent altitude is still too high for normal breathing, so the pilot still 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. The pilot still had to wear a high-altitude suit, however, as he may have 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 weren't 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 was the same as the Whirlwind - four Hispano 20 mm cannon - but these were relocated to a tray in the belly, which facilitated loading and was less likely to dazzle the pilot from barrel flash.
[edit] Operational history
By the time the plane was complete and rolling off the line, it was apparent that the Germans had lost interest in the high-altitude mission, due largely to successful interceptions by specially modified Supermarine Spitfires. In the end, only 75 complete Welkins were produced, plus a further 26 as engine-less airframes. 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. A two-seat night fighter version known as the Welkin NF Mk. II for specification F.9/43 was developed but only two produced as the design was not ordered into production.
The Welkin was seriously handicapped by compressibility problems exacerbated by its long but thick wings, causing the 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 aircraft, the English Electric Canberra, it was distinguished by noticeably short wings.
[edit] Variants
- Welkin Mk I : Single-seat twin-engine high-altitude fighter aircraft.
- Welkin NF.Mk II : Two-seat night fighter prototype.
[edit] Operators
[edit] Specifications (Welkin)
General characteristics
- Crew: One pilot
- Length: 41 ft 6 in (12.67 m)
- Wingspan: 70 ft 0 in (21.30 m)
- Height: 15 ft 9 in (4.80 m)
- Wing area: 250 ft² (23 m²)
- Empty weight: 8,310 lb (3,768 kg)
- Loaded weight: 10,356 lb (4,697 kg)
- Max takeoff weight: 11,410 lb (5,175 kg)
- Powerplant: 2× Rolls-Royce Merlin 76 liquid-cooled piston engine, 1,233 hp (920 kW) each
Performance
- Maximum speed: 385 mph (625 km/h)
- Range: 1,043 nm (1,931 km)
- Service ceiling: 44,000 ft [1] ()
- Rate of climb: ft/min (m/s)
- Wing loading: 41 lb/ft² (204 kg/m²)
- Power/mass: 0.11 hp/lb (0.18 kW/kg)
Armament
- 4x 20 mm Hispano cannon in nose
[edit] References
- Tested & Failed; Flight Test Accidents of the 19402 - 1960s, D. Collier Webb, Aeroplane Monthly, February 1996
[edit] External links
[edit] Related content
Related development
Comparable aircraft
Designation sequence
Westland Lysander - Westland Whirlwind - Westland Welkin - Westland Wyvern
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