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{{Short description|British twin-engine heavy fighter}}
<!-- This article is a part of [[Wikipedia:WikiProject Aircraft]]. Please see [[Wikipedia:WikiProject Aircraft/page content]] for recommended layout. -->
{{Use dmy dates|date=March 2018}}
{{Use British English|date=March 2018}}
{{Infobox aircraft
 |name = Welkin
 |image = Westland Welkin.jpg
 |image_caption = Welkin Mk I
 |aircraft_type = High altitude fighter
 |national_origin= United Kingdom
 |manufacturer = [[Westland Aircraft]]
 |designer = [[W.E.W. Petter]]
 |first_flight = 1 November 1942
 |introduction = May [[1944 in aviation|1944]]
 |retired = November 1944
 |status = <!--in most cases, this field is redundant; use it sparingly-->
 |primary_user = [[Royal Air Force]]
 |more_users = <!--up to three more. please separate with <br />.-->
 |produced = 1940-1945
 |number_built = 77
 |unit cost =
 |developed_from = <!-- the aircraft which formed the basis for the topic type -->
 |variants = <!-- variants OF the topic type -->
}}

The '''Westland Welkin''' was a British twin-engine [[heavy fighter]] from the [[Westland Aircraft|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.<ref>{{cite web |title=welkin, n. |url=http://www.oed.com/view/Entry/226977?redirectedFrom=welkin |work=OED Online |date=September 2013 |publisher=Oxford University Press |access-date=13 September 2013 |url-access=subscription}}</ref> First conceived in 1940, the plane was built in response to the arrival of modified [[Junkers Ju 86]]P bombers flying [[reconnaissance]] missions,{{sfn|Velek|Ovčáčík|Susa |2005|p=1}} which suggested the [[Luftwaffe]] might attempt to re-open the bombing of Britain from high altitude. Construction was from 1942 to 1943. 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 [[Westland Whirlwind (fighter)|Whirlwind]] fighter layout (and a more experimental twin, the P.13) to meet [[Air Ministry]] [[List of Air Ministry specifications|Specification F.4 of 1940]] for a high altitude fighter.<ref>{{Harvnb|Buttler|2004|p=47.}}</ref> The most obvious feature was the enormous [[aspect ratio|high aspect ratio]] wing, with a span on the production aircraft of {{convert|70|ft|m}}.{{efn|For comparison, the [[Avro Lancaster]] four-engined heavy bomber had a span of {{convert|102|ft|m}} and the [[de Havilland Mosquito]] twin-engined light bomber and fighter had a {{convert|54|ft|m|adj=on}} span.{{cn|date=April 2021}}}} 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. The most significant feature was a pressurised cockpit, which took the majority of effort in the design. 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 {{convert|3.5|psi|kPa|abbr=on}} over the exterior pressure. This resulted in an apparent [[cabin pressurization#Cabin altitude|cabin altitude]] of {{convert|24000|ft|m}} when the aircraft was operating at its design altitude of {{convert|45000|ft|m|abbr=on}}. 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 [[flap (aircraft)|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 (physics)|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.{{sfn|Boot|1990 |p=12}} Compressibility caused the [[flight envelope]] (flyable speed range) between high-incidence [[Stall (flight)|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 aircraft|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%,{{sfn|Gunston|1973|p=16}} a t/c ratio which delays compressibility effects to an aircraft speed of about Mach 0.85.{{sfn|Gunston|1962|p=26}}

Information on the Welkin was only released at the end of the war.<ref>{{citation |url=http://www.flightglobal.com/pdfarchive/view/1945/1945%20-%201216.html |work=Flight |date=21 June 1945 |title=New Aircraft Types |page=664 }}</ref>

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.<ref>{{Harvnb|Buttler|2004|p=48.}}</ref>{{sfn|Velek|Ovčáčík|Susa|2005|pp=13–14}}

==Operational history==
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 [[Supermarine Spitfire (early Merlin powered variants)#Mk VI (Type 350)|specially modified Supermarine Spitfires]]. Only 77 complete Welkins were produced, plus a further 26 as engine-less airframes.{{sfn|Velek|Ovčáčík|Susa|2005|p=3}} 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.{{sfn|Thetford|1962|p=552}}

==Variants==
* '''P.14''': Two prototypes built to meet Air Ministry Specification F.7/41.
* '''Welkin Mk.I''': Single-seat twin-engine high altitude fighter aircraft, 75 built, further 26 aircraft were completed without engines.
* '''Welkin NF.Mk.II''': Two-seat night fighter prototype, one converted from Mark I.

==Operators==
;{{UK}}
* [[Royal Air Force]]
** [[Fighter Interception Unit]] – [[RAF Wittering]] (two aircraft for evaluation)

==Specifications (Welkin Mk I)==
{{Aircraft specs
|ref=British Aircraft of world War Two : Westland Welkin,<ref name="Welkin"/> RAF Fighters, Part 3<ref name="GreenSwanboroughp60">{{Harvnb|Green|Swanborough|1981|p=60.}}</ref>
|prime units?=imp
<!--
        General characteristics
-->
|crew=1
|length ft=41
|length in=6
|length note=
|span ft=70
|span in=0
|span note=
|height ft=15
|height in=9
|height note=
|wing area sqft=250
|wing area note=
|aspect ratio=<!-- sailplanes -->
|airfoil='''root:''' [[NACA airfoil|NACA]] 23021; '''tip:''' NACA 23015<ref name="Selig">{{cite web |last1=Lednicer |first1=David |title=The Incomplete Guide to Airfoil Usage |url=https://m-selig.ae.illinois.edu/ads/aircraft.html |website=UIUC Applied Aerodynamics Group  |access-date=16 April 2019}}</ref>
|empty weight lb=8310
|empty weight note=
|gross weight lb=10356
|gross weight note=
|max takeoff weight lb=
|max takeoff weight note=11410
|fuel capacity=
|more general=
<!--
        Powerplant
-->
|eng1 number=2
|eng1 name=[[Rolls-Royce Merlin 76]]
|eng1 type=V-12 liquid-cooled piston engine
|eng1 hp=1233
|prop blade number=4
|prop name=constant-speed propellers
|prop dia ft=<!-- propeller aircraft -->
|prop dia in=<!-- propeller aircraft -->
|prop dia note=
<!--
        Performance
-->
|max speed mph=385
|max speed note=at 26000 ft (7900 m)
|cruise speed mph=
|cruise speed note=
|stall speed mph=
|stall speed note=
|never exceed speed mph=
|never exceed speed note=
|minimum control speed mph=
|minimum control speed note=
|range miles=1480
|range note=
|combat range miles=
|combat range note=
|ferry range miles=
|ferry range note=
|endurance=<!-- if range unknown -->
|ceiling ft=44000
|ceiling note=<ref name="Welkin">{{cite web |title=Westland Welkin |url=http://www.jaapteeuwen.com/ww2aircraft/html%20pages/WESTLAND%20WELKIN.htm |website=British Aircraft of World War Two |access-date=2 May 2019 |archive-url=https://web.archive.org/web/20090107195639/http://www.jaapteeuwen.com/ww2aircraft/html%20pages/WESTLAND%20WELKIN.htm |archive-date=7 January 2009}}</ref><ref name="GreenSwanboroughp60"/>
|g limits=<!-- aerobatic -->
|roll rate=<!-- aerobatic -->
|climb rate ftmin=3850
|climb rate note=
|time to altitude=
|wing loading lb/sqft=41
|wing loading note=
|fuel consumption lb/mi=
|power/mass={{convert|0.11|hp/lb|kW/kg|abbr=on}}
|thrust/weight=

|more performance=
<!--
        Armament
-->
|guns= 4 × [[Hispano HS.404|20 mm Hispano cannon]]
}}

==See also==
{{aircontent|
|related=
* [[Westland Whirlwind (fighter)|Westland Whirlwind]]
|similar aircraft=
* [[Vickers Type 432]]
* [[Hütter Hü 211]]
|sequence=
|lists=
* [[List of aircraft of World War II]]
* [[List of aircraft of the Royal Air Force]]
|see also=<!-- other relevant information -->
}}

==References==

===Notes===
{{notelist}}
{{reflist}}

===Bibliography===
{{refbegin}}
* {{cite book |last=Boot |first=Roy |year=1990 |title=From Spitfire To Eurofighter 45 Years of Combat Aircraft Design |publisher=Airlife Publishing |isbn=1-85310093-5}}
* {{cite book |last=Buttler |first=T. |title=British Secret Projects: Fighters and Bombers 1935–1950 |location=Hinckley, UK |publisher=Midland |date=2004 |isbn=1-85780-179-2}}
* {{cite book |last1=Goulding |first1=James |last2=Jones |first2=Robert |chapter=Meteor, Whirlwind and Welkin |title=Camouflage and Markings: RAF Fighter Command Northern Europe, 1936–45 |place=London |publisher=Ducimus Books |year=1971 |isbn=0-903234-00-9}}
* {{cite book |last1=Green |first=W. |last2=Swanborough |first2=G. |title=RAF Fighters, Part 3 (WW2 Aircraft Fact Files) |location=London |publisher=Jane's Publishing |date=1981 |isbn=0-7106-0119-0}}
* {{cite book |last=Gunston |first=Bill |year=1973 |title=Bombers of the West |place=New York |publisher=Charles Scribner's Sons |isbn=0-684-13623-6}}
* {{cite book |editor-last=Gunston |editor-first=W. T. |year=1962 |title=Flight Handbook The Theory and Practice of Powered Flight |publisher=Iliffe Books |edition=6th |lccn=39-30641}}
* {{cite book |last=James |first=Derek N. |title=Westland: A History |place=Gloucestershire UK |publisher=Tempus Publishing |year=2002 |isbn=0-7524-2772-5}}
* {{cite book |last=Mondey |first=David |title=Westland |series=Planemakers |volume=2 |place=London |publisher=Jane's Publishing Company |year=1982 |isbn=0-7106-0134-4}}
* {{cite book |last=Thetford |first=Owen |year=1962 |title=Aircraft Of The Royal Air Force Since 1918 |publisher=Putnam& Co. |edition=3rd}}
* {{cite book |last1=Velek|first1=M. |last2=Ovčáčík|first2=M. |last3=Susa|first3=K |title=Westland Welkin F Mk.1, NF Mk.II |location=Prague, Czech Republic |publisher=Mark I Ltd |date=2005 |isbn=80-86637-01-8}}
* {{cite magazine |last=Webb |first=D. Collier |title=Tested & Failed, Flight Test Accidents of the 1940s–1960s: Westland Welkin |magazine=Aeroplane Monthly |date=February 1996}}
{{refend}}

==External links==
{{Commons category}}
* [https://web.archive.org/web/20070930180511/http://www.britishaircraft.co.uk/aircraftpage.php?ID=589 Westland Welkin] – British Aircraft Directory

{{Westland aircraft}}

[[Category:1940s British fighter aircraft]]
[[Category:Westland aircraft|Welkin]]
[[Category:Twin piston-engined tractor aircraft]]
[[Category:Mid-wing aircraft]]
[[Category:Aircraft first flown in 1942]]
[[Category:Aircraft with retractable conventional landing gear]]