The Hawker Tempest is a British fighter aircraft that was primarily used in its Mk.V form by the Royal Air Force (RAF) in the later stages of the Second World War. The Tempest, originally known as the Typhoon II, was a significantly 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.Beamont, Roland. Tempest over Europe, 1994, p. 13.
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".Thomas and Shores 1988, pp. 18, 105. 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.J. A. D. Ackroyd. "The Spitfire Wing Planform: A Suggestion." Journal of Aeronautical History, Paper No. 2013/02.Both the Spitfire and the Typhoon were designed when little was known about the behaviour of air at high subsonic Mach numbers, 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. Other problems had been experienced with the Typhoon, such as engine unreliability, lack of structural integrity, and the inability to perform high altitude interception duties.Mason 1967, p. 3.
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.Thomas and Shores 1988, p. 105. 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.Mason 1967, pp. 3–4. 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).Tempest V Pilot's Notes 1944, pp. 6–7, 31.
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.Bentley 1973, p. 95. 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.Thomas and Shores 1988, p. 106. 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.Mason 1967, p. 4.
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.Buttler 2004 p18 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 programme 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.Mason 1967, pp. 4-6. 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:Mason 1991, p. 331.Mason 1967, pp. 4–5. 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) One Tempest Mk.III (serial number LA610), equipped with the Rolls-Royce Griffon 85 engine (originally planned for the Griffon IIB) 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. 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 & 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.Buttler 2004 p21