British fighter aircraft
The Hawker Tempest is a British fighter aircraft that was 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 at low altitude was the fastest single-engine propeller-driven aircraft of the war.
Upon entering service in 1944, the Tempest performed low-level interception, particularly against the V-1 flying bomb threat, and ground attack supporting major invasions like Operation Market Garden. Later, it successfully targeted the rail infrastructure in Germany and "Luftwaffe" aircraft on the ground, as well as countering similar attacks by German fighters. The Tempest was effective in the low-level interception role, including against newly developed jet-propelled aircraft like 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.
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". 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. 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 , but the wingtips were later "clipped" and the wing became shorter; versus .
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, 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 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 use the new 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.
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. 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. 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. The performance estimate given to MAP was 455 mph at 26,000 ft. 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.
Prototypes.
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. 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. 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. 
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. 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.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 Griffons followed in June. 
The six prototypes built were as follows:
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. 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 Aeroplane &amp; Armament Experimental Establishment 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. Construction had been on hold (so parts could be used for possible repairs to the first prototype) until "HM595" was converted to Sabre II. "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 during test flights. The Sabre IV was failing testing and so the Mk I Tempest was abandoned by the MAP. 
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 instead. 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.
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 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. 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.
Tempest Mk.V.
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.
During production of the first batch of 100 Tempest V "Series Is", distinguishable by their 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. 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.