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The Hawker Tempest was a British fighter aircraft primarily used by the Royal Air Force (RAF) in the Second World War. The Tempest, originally known as the Typhoon II, was an improved derivative of the Hawker Typhoon, intended to address the Typhoon's unexpected deterioration in performance at high altitude by replacing its wing with a thinner laminar flow design. Since it had diverged considerably from the Typhoon, it was renamed Tempest. The Tempest emerged as one of the most powerful fighters of World War II and was the fastest single-engine propeller-driven aircraft of the war at low altitude.
Upon entering service in 1944, the Tempest was used as a low-level interceptor, particularly against the V-1 flying bomb threat, and as a ground attack platform, in which it supported major events such as Operation Market Garden. Later, it successfully targeted the rail infrastructure in Germany and Luftwaffe aircraft on the ground, as well as countering such attacks by German fighters. The Tempest was effective in the low-level interception role, including against newly developed jet-propelled aircraft such as the Messerschmitt Me 262.
The further-developed Tempest II did not enter service until after the end of hostilities. It had several improvements, including being tropicalised for combat against Japan in South-East Asia as part of the Commonwealth Tiger Force.
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 cumulated in the Hawker P. 1012, otherwise known as the Typhoon II or Thin-Wing Typhoon. 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, 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 4 digit series wing section, had a maximum thickness-to-chord ratio of 19.5 per cent (root) to 12 per cent (tip), 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.[nb 1] 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.
In March 1940, engineers were assigned to investigate the new low–drag laminar flow wing developed by NACA in the United States, which was later used in the 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. 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. The wingspan was originally greater than that of the Typhoon at 43 ft (13.1 m), but the wingtips were later "clipped" and the wing became shorter; 41 ft (12.5 m) versus 41 ft 7 in (12.7 m).
The wing planform was changed to a near-elliptical shape to accommodate the 800 rounds of ammunition for the four 20 mm Hispano cannons, which were moved back further into the wing. The new wing had greater area than the Typhoon's,[nb 2] however, 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 21 in (53 cm) fuel bay in front of the cockpit, with a 76 Igal (345 l) fuel tank. 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).
Another important feature of the new wing was Camm's proposal that the radiators for cooling the engine be fitted into the leading edge of the wing inboard of the undercarriage. This eliminated the distinctive "chin" radiator of the Typhoon and improved aerodynamics. 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. 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. The design team also chose to adopt the new Napier Sabre IV engine for the Tempest, drawings of which had become available to Hawker in early 1941.
In February 1941, Camm commenced a series of discussions with officials within the Ministry of Aircraft Production on the topic of the P.1012. 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. At this point, work was undertaken by a team of 45 draughtsmen at Hawker's wartime experimental design office at Claremont, Esher to convert the proposal into technical schematics from which to commence manufacture. In March 1941, the Air Ministry issued specification F.10/41 that had been written to fit the aircraft. By October 1941, development of the proposal had advanced to the point where the new design was finalised.
On 18 November 1941, a contract was issued by the Air Ministry for a pair of prototypes of the "Typhoon Mark II"; the new fighter was renamed "Tempest" on 28 February 1942.[nb 3] 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 were both terminated. Due to this previous experience on other programs, the Air Ministry was sufficiently motivated to request that a total of six Tempest prototypes be built using different engines so that, if a delay hit one engine, an alternative powerplant would already be available. This measure turned out to be prudent, as engine development was not trouble-free on some of the variants of the Tempest.
The six prototypes were built as a single Mk.I, HM599, powered by a Sabre IV, two Mk.IIs (LA602 and LA607) equipped with the Centaurus IV, a Mk.III (LA610) with a Griffon IIB, a Mk.IV (LA614) with a Griffon 61, and a Mk.V (HM595) with the Sabre II. 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.[nb 4] 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.
On 2 September 1942, the Tempest Mk.V prototype, HM595, conducted its maiden flight, flown by Philip Lucas from Langley, Berkshire, England. HM595, which was powered by a Sabre II engine, retained the Typhoon's framed canopy and car-style door, and was fitted with the "chin" radiator, similar to that of the Typhoon. 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 elevators were also increased in span and chord; these were also fitted to late production Typhoons. Test pilots found the Tempest a great improvement over the Typhoon in performance; in February 1943 the pilots from the A&AEE at Boscombe Down reported that they were impressed by "a manoeuvrable and pleasant aircraft to fly with no major handling faults".
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. 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 466 mph (750 km/h) during test flights.
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 Spitfire instead.[nb 5] Work on the Tempest Mk.IV variant was abandoned without any prototype being flown at all. 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. 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.
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. This order was split, with the initial batch of 100 being Tempest V "Series I"s, powered by the 2,235 hp (1,491 kW) 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 for the Gloster Aircraft Company.[nb 6] 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.[nb 7]
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. 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 and its maiden flight was conducted by test pilot Bill Humble. Several early production aircraft were used for experimental purposes; a number of these underwent extensive service trials at Boscombe Down including clearances to be fitted with external stores, including 500 lb (227 kg) and 1,000 lb (454 kg) bombs and 3 in (76.2 mm) RP-3 rockets, although few Tempest Vs deployed such ordnance operationally during the War. On 8 April 1944, the Tempest V attained general clearance.
During production of the first batch of 100 Tempest V "Series Is", distinguishable by their serial number prefix JNxxx, 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. 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.
The first 100 Tempest Vs were fitted with 20 mm (.79 in) Hispano Mk.IIs 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. Early Tempest Vs used Typhoon-style 34 by 11 inch (83.4 by 28 cm) five-spoke wheels, but most had smaller 30 by 9 inch (76.2 by 22.9 cm) four-spoke wheels. The new spar structure of the Tempest V also allowed up to 2,000 lb (907 kg) of external stores to be carried underneath the wings.
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 transponder unit was fitted, with the associated aerial appearing under the portside centre section. A small, elongated oval static port appeared on the rear starboard fuselage, just above the red centre spot of the fuselage roundel. This was apparently used to measure the aircraft's altitude more accurately.
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 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 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.
Two Tempest Vs, EJ518 and NV768, were fitted with Napier Sabre Vs and experimented with several different Napier-made annular 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. NV768 was later fitted with a ducted spinner, similar to that fitted to the Fw 190 V1. Another experimental Tempest V was SN354, which was fitted with a Vickers 47 mm "P" anti-tank gun, under development but never deployed, under each wing in a long "pod".[nb 8]
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. 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. 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.[nb 9] 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. 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, production was delayed.
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, while Hawker were to build 1,800. This switch delayed production even more. 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. 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 at Bristol's Banwell facility, 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.
Physically, the Tempest II was longer than the Tempest Mk.V (34 ft 5 in/10.5 m versus 33 ft 8 in/10.3 m) and 3 in (76 mm) lower. The weight of the heavier Centaurus engine (2,695 lb/1,222 kg versus 2,360 lb/1,070 kg) was offset by the absence of a heavy radiator unit, so that the Tempest II was only some 20 lb (9 kg) heavier overall. Performance was improved; maximum speed was 442 mph (711 km/h) at 15,200 ft (4,633 m) and climb rate to the same altitude took four and a half minutes compared with five minutes for the Tempest Mk. V; the service ceiling was also increased to 37,500 ft (11,430 m).
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 (2,590 hp/1,932 kW) Centaurus V driving a 12 ft 9 inch (3.89 m) diameter Rotol propeller. Tempest IIs produced during the war were intended for combat against Japan and would have formed part of Tiger Force, a proposed British Commonwealth long-range bomber force based on Okinawa. The Pacific War ended before they could be deployed.
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 2,340 hp (1,700 kW). 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. Other changes included the strengthening of the rear spar and the inclusion of spring tabs, which granted the variant superior handling performance.
The original Tempest V prototype, HM595, was extensively modified to serve as the Tempest VI prototype. On 9 May 1944, HM595 made its first flight after its rebuild, flown by Bill Humble. In December 1944, HM595 was dispatched to Khartoum, Egypt to conduct a series of tropical trials. During 1945, a further two Tempest V aircraft, EJ841 and JN750, were converted to the Tempest VI standard in order to participate in service trials at RAF Boscombe Down.
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. For a long time, it was thought there were Tempest VIs that had been converted for target towing purposes; however, none of the service histories of the aircraft show such conversions and no supporting photographic evidence has been found. The Tempest VI holds the distinction of being the last piston-engined fighter in operational service with the RAF, having been superseded by jet propelled aircraft.
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