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== Design and development == === Origins === During development of the earlier [[Hawker Typhoon]], the design team, under the leadership of [[Sydney Camm]], had already planned out a series of design improvements; these improvements culminated in the ''Hawker P. 1012'', otherwise known as the ''Typhoon II'' or "Thin-Wing Typhoon".<ref>Thomas and Shores 1988, pp. 18, 105.</ref><ref name=Mason67_3_4/> Although the Typhoon was generally considered to be a good design, Camm and his design team were disappointed with the performance of its [[wing]], which had proved to be too thick in its [[Cross section (geometry)|cross section]], and thus created airflow problems which inhibited flight performance, especially at higher altitudes and speeds where it was affected by [[compressibility]]. The Typhoon's wing, which used a [[NACA airfoil|NACA 4 digit series wing section]], had a maximum [[thickness-to-chord ratio]] of 19.5 per cent (root) to 12 per cent (tip),<ref name=Thomas105/> in comparison to the [[Supermarine Spitfire]]'s 13.2 per cent tapering to 6 per cent at the tip, the thinner design being deliberately chosen to reduce drag.<ref>J. A. D. Ackroyd. [http://aerosociety.com/Assets/Docs/Publications/The%20Journal%20of%20Aeronautical%20History/2013-02_SpitfireWing-Ackroyd.pdf "The Spitfire Wing Planform: A Suggestion."] ''Journal of Aeronautical History'', Paper No. 2013/02.</ref><ref group=nb>Both the Spitfire and the Typhoon were designed when little was known about the behaviour of air at high subsonic [[Mach number]]s, and of what would later become known as the [[Critical Mach number]]. The importance of this to high speed, high altitude flight would be discovered during combat in the [[Battle of Britain]], where the Spitfire's thinner wing gave it an advantage at higher altitudes over the thicker wing-sectioned Hurricane, which was affected to a greater extent by compressibility. Fortuitously, the Spitfire had been designed with a thin wing that was subsequently discovered by the RAE to possess a high Critical Mach No.</ref> In addition, there had been other issues experienced with the Typhoon, such as engine unreliability, insufficient structural integrity, and the inability to perform high altitude interception duties.<ref name=Mason67_3>Mason 1967, p. 3.</ref> [[File:Hawker Tempest I HM599.jpg|thumb|left|Tempest I prototype ''HM599'' with later bubble canopy; when first flown, it had the "car-door" canopy and small tail unit.]] In March 1940, engineers were assigned to investigate the new [[Drag (physics)|low–drag]] laminar flow wing developed by [[NACA]] in the United States, which was later used in the [[North American Aviation|North American]] [[P-51 Mustang]]. A laminar flow wing adopted for the Tempest series had a maximum thickness-to-chord ratio of 14.5 per cent at the root, tapering to 10 per cent at the tip.<ref name=Thomas105>Thomas and Shores 1988, p. 105.</ref><ref name=Mason67_3/> The maximum thickness of the Tempest wing was set further back at 37.5 per cent of the chord versus 30 per cent for the Typhoon's wing, reducing the thickness of the wing root by five inches on the new design.<ref name=Thomas105/><ref name=Mason67_3/> The wingspan was originally greater than that of the Typhoon at {{convert|43|ft|m|abbr=on}}, but the wingtips were later "clipped" and the wing became shorter; {{convert|41|ft|m|abbr=on}} versus {{convert|41|ft|7|in|m|abbr=on}}.<ref name=Thomas105/> The wing [[planform (aeronautics)|planform]] was changed to a near-[[elliptical wing|elliptical]] shape to accommodate the 800 rounds of [[ammunition]] for the four 20 mm [[Hispano-Suiza HS.404|Hispano cannon]]s, which were moved back further into the wing. The new wing had greater area than the Typhoon's,{{#tag:ref|Camm later remarked: "The [[Chief of the Air Staff (United Kingdom)|Air Staff]] wouldn't buy anything that didn't look like a [[Supermarine Spitfire|Spitfire]]."{{citation needed|date=September 2023}}|group=nb}} but the new wing design sacrificed the [[leading edge]] fuel tanks of the Typhoon. To make up for this loss in capacity, Hawker engineers added a new {{convert|21|in|cm|abbr=on}} fuel bay in front of the [[cockpit (aviation)|cockpit]], with a 76 I[[gallon|gal]] (345 L) fuel tank.<ref name=Mason67_3_4>Mason 1967, pp. 3–4.</ref><ref name=Thomas105/> In addition, two inter-spar wing tanks, each of 28 Igal (127 L), were fitted on either side of the centre section and, starting with late model Tempest Vs, a 30 Igal (136 L) tank was carried in the leading edge of the port wingroot, giving the Tempest a total internal fuel capacity of 162 Igal (736 L).<ref>Tempest V Pilot's Notes 1944, pp. 6–7, 31.</ref> Another important feature of the new wing was Camm's proposal that the [[radiator (engine cooling)|radiator]]s for cooling the engine be fitted into the [[leading edge]] of the wing inboard of the [[Landing gear|undercarriage]]. This eliminated the distinctive "[[beard|chin]]" radiator of the Typhoon and improved [[aerodynamics]].<ref name=Thomas105/><ref name=Mason67_3/> A further improvement of the Tempest wing over that of the Typhoon was the exceptional, flush-riveted surface finish, essential on a high-performance laminar flow [[airfoil]].<ref>Bentley 1973, p. 95.</ref> The new wing and airfoil, and the use of a four-bladed propeller, acted to eliminate the high frequency vibrations that had plagued the Typhoon.<ref name=Thomas106>Thomas and Shores 1988, p. 106.</ref> The design team also chose to use the new [[Napier Sabre|Mark IV version of the Napier Sabre]] H-block 24 cylinder engine for the Tempest, drawings of which had become available to Hawker in early 1941.<ref name=Mason67_4>Mason 1967, p. 4.</ref> In February 1941, Camm commenced a series of discussions with officials within the [[Minister of Aircraft Production|Ministry of Aircraft Production]] on the topic of the P.1012.<ref name=Mason67_4/> In March 1941 of that year, clearance to proceed with development of the design, referred to at this point as the Typhoon II, was granted. The design at the time encompassed the Sabre E.107C (as it was then known) with a four-blade propeller, 42 ft span elliptical wing with six cannon armament; while the front of the fuselage was redesigned the rear was unchanged from the Typhoon.<ref name=":0">Buttler 2004 p18</ref> At this point, work was undertaken by a team of 45 [[drafter|draughtsmen]] at Hawker's wartime experimental design office at [[Claremont (country house)|Claremont]], [[Esher]] to convert the proposal into technical schematics from which to commence manufacture.<ref name=Mason67_4/> In March 1941, the [[Air Ministry]] issued [[List of Air Ministry Specifications#1940–1949|specification F.10/41]] that had been written to fit the aircraft. The performance estimate given to MAP was 455 mph at 26,000 ft.<ref name=":0" /> In September Camm was told that the Air Ministry's Director of Technical Development that they had decided to have two Typhoons converted to the new design. By October 1941, development of the proposal had advanced to the point where the new design was finalised.<ref name=Mason67_4/> === Prototypes === [[File:Hawker Tempest II LA602 - Prototype.jpg|thumb|First prototype Tempest Mk. II ''LA602'', again with the small tail unit.]] On 18 November 1941, a contract was issued by the Air Ministry for a pair of [[prototype]]s of the "Typhoon Mark II"; the new fighter was renamed "Tempest" on 28 February 1942.<ref name=Thomas105/><ref name=Mason67_4/>{{#tag:ref|The renaming of the "Typhoon II" to "Tempest" was considered to be an indication of the level of changes and increasing number of refinements that had made the two aircraft more unique and distinguished from one another.<ref name=Mason67_4/>|group=nb}}{{Efn|Buttler gives 6 August as the official renaming, and notes the suggestion came from Camm in January.<ref>Buttler 2004 p18</ref>}} Complications were added to the Tempest program by external factors in the form of engine issues: the [[Rolls-Royce Vulture]] engine and corresponding [[Hawker Tornado]] aircraft which was being developed in parallel to the Typhoon were both terminated. This measure turned out to be prudent, as engine development was not trouble-free on some of the variants of the Tempest.<ref name=Mason67_4_6>Mason 1967, pp. 4-6.</ref> The [[Bristol Centaurus]] radial engine was now also considered for equipping the Typhoon and Camm was forewarned in October 1941 to expect a request for a Centaurus to be fitted. This was confirmed in February as an order for six prototypes with the Centaurus; the DTD stating that the development was highest priority.<ref>Buttler 2004 p18</ref> Delays with the Sabre IV development affected the project. With the expected first flight date for the Tempest was September 1942, the engine for ''HM595'' was changed to a Sabre II complete with the Typhoon cooling system and under nose radiator.<ref name=":0" /> Due to this previous experience on other programmes, the Air Ministry was sufficiently motivated to request that Tempest prototypes be built using different engines so that, if a delay hit one engine, an alternative powerplant would already be available.<ref name="Mason67_4" />An order was approved for six more prototypes with alternate engines in May and the contract for two with Sabres, two with Centaurus and two with [[Rolls-Royce Griffon|Rolls Royce Griffons]] followed in June.<ref name=":0" /> [[File:Hawker Tempest Mk III.jpg|thumb|Tempest Mk. III prototype ''LA610.'']] The six prototypes built were as follows:<ref name=Mason91_331>Mason 1991, p. 331.</ref><ref name=Mason67_4_5>Mason 1967, pp. 4–5.</ref> * One Tempest Mk.I ([[serial number]] ''HM599''), equipped with the Napier Sabre Mk.IV engine * Two Tempest Mk.II (serial numbers ''LA602'' and ''LA607''), equipped with the Bristol Centaurus Mk.IV engine (LA607 later receiving a Centaurus Mk.V)<ref name="hawkertempest.se/markii"/> * One Tempest Mk.III (serial number ''LA610''), equipped with the Rolls-Royce Griffon 85 engine (originally planned for the Griffon IIB)<ref>{{Cite web|date=2018-02-21|title=HAWKER'S FASTEST FURY – LA610|url=https://navalairhistory.com/2018/02/21/hawkers-fastest-fury-la610/|access-date=2021-08-14|website=navalairhistory.com}}</ref> * One Tempest Mk.IV (serial number ''LA614''), which was never completed but planned to be equipped with a Griffon 61 engine * One Tempest Mk.V (serial number ''HM595''), equipped with the Napier Sabre Mk.II engine The Tempest Mk.I featured other new features, such as a clean single-piece sliding canopy in place of the car-door framed canopy, and it used wing radiators instead of the "chin" radiator.{{#tag:ref|The use of wing radiators was a point of controversy, with Air Ministry officials approaching Camm with doubts concerning its vulnerability to battle damage.<ref name=Mason67_5/>|group=nb}} Due to development difficulties with the Sabre IV engine and its wing radiators, the completion of the Mk.I prototype, ''HM599'', was delayed, and thus it was the Mk.V prototype, ''HM595'', that would fly first.<ref name=Mason67_5/> {{Multiple image|total_width=230|perrow=1|header=Cockpit and rudder evolution|image1=Hawker Tempest ExCC.jpg|caption1=Tempest Mk.V prototype ''HM595'' with early "car door" cockpit structure and small tail unit.|image2=Hawker Tempest V parked 1944 (cropped).jpg|caption2=Tempest Mk.V production model with late "[[bubble canopy]]" cockpit structure and large tail unit.}} On 2 September 1942, the Tempest Mk.V prototype, ''HM595'', conducted its [[maiden flight]], flown by Philip Lucas from [[Langley, Berkshire#Langley Airfield|Langley, Berkshire]], England.<ref name=Mason67_5/> ''HM595'', which was powered by a Sabre II engine, retained the Typhoon's framed [[Canopy (aircraft)|canopy]] and car-style door, and was fitted with the "chin" radiator, similar to that of the Typhoon.<ref name=Mason91_331/> It was quickly fitted with the same [[bubble canopy]] fitted to Typhoons, and a modified [[fin]] that almost doubled the vertical tail surface area, made necessary because the directional stability with the original Typhoon fin had been reduced over that of the Typhoon by the longer nose incurred by the new fuel tank. The horizontal tailplanes and [[Elevator (aircraft)|elevators]] were also increased in span and chord; these were also fitted to late production Typhoons.<ref name=Mason91_331/><ref name=Mason67_6/> [[Test pilot]]s found the Tempest a great improvement over the Typhoon in performance; in February 1943 the pilots from the [[Aeroplane and Armament Experimental Establishment|Aeroplane & Armament Experimental Establishment]] at [[MOD Boscombe Down|Boscombe Down]] reported that they were impressed by "a manoeuvrable and pleasant aircraft to fly with no major handling faults".<ref name=Thomas106/> On 24 February 1943, the second prototype ''HM599'' first flew, representing the "Tempest Mk.I" equipped with the Napier Sabre IV engine; this flight had been principally delayed by protracted problems and slippages encountered in the development of the new Sabre IV engine.<ref name=Thomas106/> Construction had been on hold (so parts could be used for possible repairs to the first prototype) until ''HM595'' was converted to Sabre II.<ref name=":0" /> ''HM599'' was at first equipped with the older Typhoon cockpit structure and vertical tailplane. The elimination of the "chin" radiator did much to improve overall performance, leading to the Tempest Mk.I quickly becoming the fastest aircraft that Hawker had built at that time, having attained a speed of {{convert|466|mph|km/h|abbr=on}} during test flights.<ref name=Mason91_332/> The Sabre IV was failing testing and so the Mk I Tempest was abandoned by the MAP.<ref>Buttler 2004 p21</ref> On 27 November 1944, the Tempest Mk.III prototype, ''LA610'', conducted its first flight; it was decided to discontinue development work on the Mk.III, this was due to priority for the Griffon engine having been assigned to the [[Supermarine Spitfire (Griffon-powered variants)|Supermarine Spitfire]] instead.<ref name=Mason67_4_6/>{{#tag:ref|''LA610'' went on to serve as the prototype for the later [[Hawker Sea Fury|Hawker Fury/Sea Fury]], what would be the ultimate offshoot of the Typhoon and Tempest family as well as the fastest of all Hawker-built piston-engine fighters.<ref name=Mason67_6>Mason 1967, p. 6.</ref>|group=nb}} The Air Ministry had seen the Mk III as a replacement for the Hurricane in ground attack, with the narrower engine giving a better view as well but the Typhoon would be the interim aircraft for the role. In practice the Typhoon proved very good for ground attack.<ref>Buttler, 2004 p 20</ref> Work on the Tempest Mk.IV variant was abandoned without any prototype being flown at all.<ref name="Mason67_4_6" /> The Tempest Mk.II, which was subject to repeated delays due to its Centaurus powerplant, was persisted with, but would not reach production in time to see service during the Second World War.<ref name="Mason67_6" /> Continual problems with the Sabre IV meant that only the single Tempest Mk.I (''HM599'') was built; consequently, Hawker proceeded to take the Sabre II-equipped "Tempest V" into production instead.<ref name="Thomas107">Thomas and Shores 1988, p. 107.</ref> In August 1942, even before the first flight of the prototype Tempest V had been conducted, a production order for 400 Tempests was placed by the Air Ministry.<ref name="Mason67_5">Mason 1967, p. 5.</ref>{{Efn|At the start of March 1942, the contract had been for 400 Mark I<ref>Buttler 2004 p 20</ref>}} This order was split, with the initial batch of 100 being Tempest V "Series I"s, powered by the {{convert|2,235|hp|kW|abbr=on}} Sabre IIA series engine, which had the distinctive chin radiator, while the rest were to have been produced as the Tempest I, equipped with the Sabre IV and leading-edge radiators. These 300 Tempest Is were intended to replace an order for a similar quantity of Typhoons placed with the [[Gloster Aircraft Company]].<ref name="Mason67_5" />{{#tag:ref|It had been intended that prefabricated Typhoon components could be reused on the Tempest, this proved to be impractical as the design production Tempest had diverged considerably from the Typhoon.<ref name=Mason67_5/>|group=nb}} As it transpired, the difficulties with the Sabre IV and the wing radiators led to this version never reaching production, the corresponding order was switched to 300 Tempest V "Series 2"s instead.<ref name="Mason67_5" /><ref name="Ovc1">Ovčáčík and Susa 2000, p. 1.</ref>{{#tag:ref|Although JNxxx serialled Tempest Vs are called "Series 1" and later ones called "Series 2", these definitions first appeared in 1957, and there is room for doubt about them being used by Hawker during the Second World War.<ref>[http://www.rafcommands.com/forum/showthread.php?s=3b945437fb56fc153bd6de6c7f848d7d&t=460 "Discussion on first 100 Tempest V."] ''rafcommands.com.'' Retrieved: 1 January 2012.</ref>|group=nb}} === Tempest Mk.V === [[File:15 Hawker Tempest (15834185691).jpg|thumb|left|Tempest Mk. V prototype with [[bubble canopy]] and Mk. V tail, but with 20 mm Hispano Mk. II guns.]] During early 1943, a production line for the Tempest Mk.V was established in Hawker's Langley facility, alongside the existing manufacturing line for the [[Hawker Hurricane]].<ref name=Mason67_6/> Production was initially slow, claimed to be due to issues encountered with the rear spar. On 21 June 1943, the first production Tempest V, ''JN729'', rolled off the production line<ref name=Mason67_6/><ref name=Thomas107/> and its maiden flight was conducted by test pilot [[Bill Humble]].<ref>Mason 1991, p. 333.</ref> [[File:Hawker Tempest V JN729 - Langley - 1943.jpg|thumb|The first production Tempest Mk. V ''JN729''. Long-barrelled Hispano II cannon and Typhoon five-spoke mainwheels were identifying features of the first production batch of 100 Tempests Vs.]] During production of the first batch of 100 Tempest V "Series Is", distinguishable by their [[United Kingdom military aircraft serials|serial number prefix ''JN'']], several improvements were progressively introduced and were used from the outset on all succeeding Tempest V "Series 2s", with serial number prefixes EJ, NV and SN. The [[fuselage]]/[[empennage]] joint originally featured 20 external reinforcing "fishplates", similar to those fitted to the Typhoon, but it was not long before the rear fuselage was strengthened and, with the fishplates no longer being needed, the rear fuselage became detachable.<ref name=Bentley>Bentley 1973, pp. 92–93.</ref> The first series of Tempest Vs used a built-up rear spar pick-up/bulkhead assembly (just behind the cockpit) which was adapted from the Typhoon. Small blisters on the upper rear wing root fairing covered the securing bolts. This was later changed to a new forged, lightweight assembly which connected to new spar booms: the upper wing root blisters were replaced by small "teardrop" fairings under the wings.<ref name=Bentley/> The first 100 Tempest Vs were fitted with {{convert|20|mm|in|abbr=on}} [[Hispano-Suiza HS.404|Hispano Mk.II cannon]] with long barrels which projected ahead of the wing leading edges and were covered by short fairings; later production Tempest Vs switched to the short-barrelled Hispano Mk.Vs, with muzzles flush with the leading edges.<ref name=Ovc1/> Early Tempest Vs used Typhoon-style {{convert|34|by|11|in|cm|abbr=on}} five-spoke wheels, but most had smaller {{convert|30|by|9|in|cm|abbr=on}} four-spoke wheels.<ref name=Ovc2_4>Ovčáčík and Susa 2000, pp. 2, 4.</ref> The new spar structure of the Tempest V also allowed up to {{convert|2,000|lb|kg|abbr=on}} of external stores to be carried underneath the wings.<ref name=Thomas107/> As a result, several early production Tempest V aircraft underwent extensive service trials at Boscombe Down for clearance to be fitted with external stores, such as one {{convert|250-1000|lb|kg|abbr=on}} bomb or eight "60lb" air-to-ground [[RP-3]] rockets under each wing. On 8 April 1944, the Tempest Mk.V attained general clearance<ref name=Mason67_7/> to carry such ordnance, but few Tempest Mk.V deployed bombs operationally during the war.<ref name=Mason67_6/><ref>Mason 1991, p. 334.</ref> Rockets were never used operationally during the war by the Mk.Vs.<ref name="hawkertempest.se/armament"/> As in all mass-produced aircraft, there may have been some overlap of these features as new components became available. In mid-to-late 1944 other features were introduced to both the Typhoon and Tempest: A [[Rebecca/Eureka transponding radar|''Rebecca'']] transponder unit was fitted, with the associated aerial appearing under the portside centre section. A small, elongated oval [[Pitot-static system|static port]] appeared on the rear starboard fuselage, just above the red centre spot of the [[Royal Air Force roundels|RAF roundel]]. This was apparently used to measure the aircraft's altitude more accurately.{{Citation needed|date=January 2015}} Unusually, in spite of the Tempest V being the RAF's best low- to medium-altitude fighter, it was not equipped with the new Mk.IIC [[Gyro gunsight|gyroscopic gunsight]] (as fitted in RAF Spitfires and Mustangs from mid-1944), which would have considerably improved the chances of shooting down opposing aircraft. Tempest pilots continued to use either the Type I Mk.III [[Reflector sight|reflector gunsight]], which projected the sighting graticule directly onto the windscreen, or the Mk.IIL until just after the Second World War, when the gyro gunsight was introduced in Tempest IIs.<ref>Ovčáčík and Susa 2000, p. 30.</ref> Two Tempest Vs, ''EJ518'' and ''NV768'', were fitted with Napier Sabre Vs and experimented with several different Napier-made annular [[radiator (engine cooling)|radiators]], with which they resembled Tempest IIs. This configuration proved to generate less drag than the standard "chin" radiator, contributing to an improvement in the maximum speed of some 11 to 14 mph.<ref>''Flight'' 1946, p. 91.</ref> ''NV768'' was later fitted with a ducted spinner, similar to that fitted to the [[Focke-Wulf Fw 190|Fw 190 V1]].<ref name=Mason91_332>Mason 1991, p. 332.</ref><ref>Thomas and Shores 1988, p. 112.</ref> ==== 47 mm anti tank gun trials{{anchor|Vickers 47 mm Class P}} ==== [[File:47mm P.jpg|thumb|Tempest ''SN354'', outfitted with experimental 47 mm class P guns and standard smaller four-spoke wheels.]] Tempest V ''SN354'' was fitted with two experimental underwing Class P 47 mm guns (built by [[Vickers-Armstrongs|Vickers]]) just after the war.<ref name="Williams, A. G.">{{cite web|last=Williams |first= A. G. |url=http://www.quarryhs.co.uk/Pgun.htm |title=The RAF'S 47 mm Class P Gun Project |archive-url=https://web.archive.org/web/20160319192518/http://quarryhs.co.uk/Pgun.htm |archive-date=19 March 2016 |website=quarry.nildram.co.uk |accessdate= 16 March 2012}}</ref><ref name=Mason67_13>Mason 1967, p. 13.</ref>{{efn|The weapon has been misidentified as a 40 mm cannon in many references, such as Mason 1991.<ref name=Mason91_336>Mason 1991, p. 336.</ref>}} These guns were part of a project started in mid-1942 to develop a more powerful airborne [[anti-tank gun]] than the [[Vickers 40 mm Class S gun]] which had been used on the Hurricane IID.<ref name="Williams, A. G."/>{{efn|Vickers, Rolls-Royce and the [[War Office]] Design Department produced competing designs but Rolls Royce stopped work before completing a weapon<ref name="Williams, A. G."/> }} The Vickers guns were housed in long slim streamlined [[gun pod]]s carried on the bomb racks<ref name="hawkertempest.se/armament"/> and had 38 rounds each.<ref>http://i.imgur.com/brlZOwU.png {{Bare URL image|date=March 2022}}</ref> Surviving photographs suggests that the 20 mm wing guns were removed for this installation. Testing of the guns revealed that the weapon had potential, but no production was undertaken.<ref name="hawkertempest.se/armament"/> === Tempest Mk.II === [[File:Hawker Tempest II Hawker Tempest II (17145743791).jpg|thumb|left|Tempest Mk. II prototype with [[bubble canopy]] and Mk. V tail, but with 20 mm Hispano Mk. II guns.]] As a result of the termination of the Tornado project, Sydney Camm and his design team transferred the alternative engine proposals for the Tornado to the more advanced Tempest.<ref name=Mason67_4_5/> Thus, it was designed from the outset to use the Bristol Centaurus 18 cylinder [[radial engine]] as an alternative to the liquid cooled engines which were also proposed. A pair of Centaurus-powered Tempest II prototypes were completed.<ref>Mason 1991, p. 337.</ref> Apart from the new engine and cowling, the Tempest II prototypes were similar to early series Tempest Vs. The Centaurus engine was closely cowled and the exhaust stacks grouped behind and to either side of the engine: to the rear were air outlets with automatic sliding "gills". The carburettor air intakes were in the inner leading edges of both wings, an oil cooler and air intake were present in the inner starboard wing. The engine installation owed much to examinations of a captured [[Focke-Wulf Fw 190]], and was clean and effective. On 28 June 1943, the first Tempest II, ''LA602'', flew powered by a Centaurus IV (2,520 hp/1,879 kW) driving a four-blade propeller. ''LA602'' initially flew with a Typhoon-type fin and rudder unit. This was followed by the second, ''LA607'', which was completed with the enlarged dorsal fin and first flew on 18 September 1943: ''LA607'' was assigned to engine development.<ref name=Mason67_11/>{{#tag:ref|''LA607'' was presented to the [[College of Aeronautics]] at Cranfield, Bedfordshire and is currently ({{as of|2011}}) preserved at [[Fantasy of Flight]] at Polk city, [[Florida]].|group=nb}} The first major problem experienced during the first few flights was serious engine vibrations, which were cured by replacing the rigid, eight-point engine mountings with six-point rubber-packed shock mounts. In a further attempt to alleviate engine vibration, the four-blade propeller was replaced with a five-blade unit; eventually, a finely balanced four bladed unit was settled on.<ref>Mason 1991, p. 339.</ref><ref name=Mason67_12>Mason 1967, p. 12.</ref> Problems were also experienced with engine overheating, poor crankshaft lubrication, exhaust malfunctions and reduction-gear seizures. Because of these problems, and because of the decision to "tropicalise" all Tempest IIs for service in the [[South-East Asian theatre of World War II|South-East Asian theatre]], production was delayed.<ref name=Mason67_11/><ref name=Ovc2>Ovčáčík and Susa 2000, p. 2.</ref> [[File:Hawker Tempest II at Hawker plant c1945.jpg|thumb|New Tempest IIs of the first production batch at Hawker Aircraft. Note the closely cowled engine and the carburettor and oil-cooler intakes in the starboard wing's inner leading edge.]] Orders had been placed as early as September 1942 for 500 Tempest IIs to be built by Gloster but in 1943, because of priority being given to the Typhoon, a production contract of 330 Tempest IIs was allocated instead to [[Bristol Aeroplane Company|Bristol]], while Hawker were to build 1,800. This switch delayed production even more.<ref name=Ovc2/><ref name=Mason67_11_12>Mason 1967, pp. 11-12.</ref> On 4 October 1944, the first Tempest II was rolled off the line; the first six production aircraft soon joined the two prototypes for extensive trials and tests.<ref name=Ovc2/> With the end of the Second World War in sight, orders for the Tempest II were trimmed or cancelled; after 50 Tempest IIs had been built by the Bristol [[British shadow factories|shadow factory]] near [[Banwell]], production was stopped and shifted back to Hawker, which built a total of 402, in two production batches: 100 were built as fighters, and 302 were built as fighter-bombers (FB II) with reinforced wings and wing racks capable of carrying bombs of up to 1,000 lb.<ref name="Ovc2_7_8">Ovčáčík and Susa 2000, pp. 2, 7–8.</ref> Physically, the Tempest II was longer than the Tempest Mk.V ({{convert|34|ft|5|in|m|abbr=on}} versus {{convert|33|ft|8|in|m|abbr=on}} and {{convert|3|in|mm|abbr=on}} lower. The weight of the heavier Centaurus engine ({{convert|2,695|lb|kg}} versus {{convert|2,360|lb|kg}} was offset by the absence of a heavy radiator unit, so that the Tempest II was only some {{convert|20|lb|kg}} heavier overall. Performance was improved; maximum speed was {{convert|442|mph|km/h|abbr=on}} at {{convert|15,200|ft|m|abbr=on}} and climb rate to the same altitude took four and a half minutes compared with five minutes for the Tempest Mk.V; the [[Ceiling (aeronautics)|service ceiling]] was also increased to {{convert|37,500|ft|m|abbr=on}}.<ref name=Mason91_342/> Tropicalising measures included the installation of an air filter and intake in the upper forward fuselage, just behind the engine cowling, and the replacement of the L-shaped pitot head under the outer port wing by a straight rod projecting from the port outer wing leading edge. All production aircraft were powered by a ({{convert|2,590|hp|kW|abbr=on}} Centaurus V driving a {{convert|12|ft|9|in|m|abbr=on}} diameter [[Dowty Rotol|Rotol]] propeller.<ref name=Ovc2_4/> Tempest IIs produced during the war were intended for combat against [[Empire of Japan|Japan]] and would have formed part of [[Tiger Force (air)|Tiger Force]], a proposed [[Empire's Commonwealth of Nations|British and Empire]] long-range bomber force based on Okinawa to attack the Japanese home islands.<ref name=Mason91_340>Mason 1991, p. 340.</ref> The [[Pacific War]] ended before they could be deployed.<ref name=Mason67_12/> === Tempest Mk.VI === [[File:Tempest-rafhist.jpg|thumb|left|A Tempest Mk. VI.]] Various engineering refinements that had gone into the Tempest II were incorporated into the last Tempest variant, designated as the ''Tempest VI''. This variant was furnished with a Napier Sabre V engine with {{convert|2,340|hp|kW|abbr=on}}. The more powerful Sabre V required a bigger radiator which displaced the oil cooler and carburettor air intake from the radiator's centre; air for the carburettor was drawn through intakes on the leading edge of the inner wings, while the oil cooler was located behind the radiator. Most Tempest VIs were tropicalised, the main feature of this process being an air filter which was fitted in a fairing on the lower centre section.<ref name=Mason67_12/> Other changes included the strengthening of the rear spar and the inclusion of spring tabs, which granted the variant superior handling performance.<ref name=Mason67_12/> The original Tempest V prototype, ''HM595'', was extensively modified to serve as the Tempest VI prototype.<ref name=Mason67_12/> On 9 May 1944, ''HM595'' made its first flight after its rebuild, flown by Bill Humble. In December 1944, ''HM595'' was dispatched to [[Khartoum]], [[Sudan]] to conduct a series of tropical trials. During 1945, two more Tempest V aircraft, ''EJ841'' and ''JN750'', were converted to the Tempest VI standard in order to participate in service trials at RAF Boscombe Down.<ref name=Mason67_12/> At one point, 250 Tempest VIs were on order for the RAF; however, the end of the war led to many aircraft programs being cut back intensively, leading to only 142 aircraft being completed.<ref name=Mason67_12/> For a long time, it was thought there were Tempest VIs that had been converted for [[target tug|target tow]]ing purposes; however, none of the service histories of the aircraft show such conversions and no supporting photographic evidence has been found. The Tempest VI was the last piston-engined fighter in operational service with the RAF, having been superseded by jet propelled aircraft. === Drawing board designs === In 1943, Camm initiated work on a new design for fighter equipped with the at that point unbuilt [[Rolls-Royce Eagle (1944)|Rolls-Royce R.46]] engine. The project designated as the ''P.1027'' was essentially a slightly enlarged Tempest with the R.46 engine, which Hawker expected to develop around 4,000 hp (2,980 kW). This engine would have driven a pair of four-bladed [[contra-rotating]] propellers. The radiator was relocated into a ventral bath set underneath the rear fuselage and wing centre section: the wingspan was {{convert|41|ft|m|abbr=on}} and the length was {{convert|37|ft|3|in|m|abbr=on}}.<ref name=buttler30/> However, work upon the P.1027 design was soon dropped in favour of concentrating upon a further developed design, the ''P.1030,'' in September It featured wing leading edge radiators and had larger overall dimensions of {{convert|42|ft|m|abbr=on}} wingspan and {{convert|39|ft|9|in|m|abbr=on}} length. The top speed was calculated as {{convert|509|mph|km/h|abbr=on}} at 20,000 ft, with a rate of climb of 6,400 ft/min (1,951 m/min). Service ceiling was projected to be more than {{convert|42,000|ft|m|abbr=on}}.<ref name=buttler30>Buttler 2004, p. 30.</ref> Work on both was ultimately dropped when Camm decided to focus design efforts upon the more promising jet engine designs he was working on instead.
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