The performance of the Typhoon was such that speeds of around 805km/h could be attained in a dive. It was, therefore, numbered among the high-performance aircraft of World War II which began to be affected by the problems of compressibility, with the accelerated airflow over the cambered upper surface of the wing beginning, locally, to approach the speed of sound. It was in April 1941 that discussions were opened between Hawker and the Ministry of Aircraft Production on the subject of Typhoon development. Proposals for a Typhoon Mk II included the installation of a Sabre IV engine of higher power and driving a four-bladed propeller, improved view and a cleaned-up tail.
Hawker proposals (submitted in August 1941) included the suggestion that the Typhoon Mk II should have thin elliptical wings of 12.8m span and 27.9sq.m area, with a 15% thickness/chord ratio at the root and 10% at the tip. The introduction of a new thin-section wing made it necessary to reduce the amount of fuel carried in the wings and an extra bay was inserted in the fuselage behind the engine to accommodate an additional fuel tank. The lengthening of the fuselage called for increased fin area.
Work had been going on in the Hawker design office since 1940 on the development of a new thin wing section. It had already been established that the N.A.C.A.22-series wing section employed by the Typhoon was entirely satisfactory at speeds in the vicinity of 400 m.p.h. but encountered compressibility effects at higher speeds. In dives approaching 500 m.p.h. a very sudden and sharp increase in drag was experienced, accompanied by a change in the aerodynamic characteristics of the fighter, which affected the pitching moment and rendered the machine nose heavy. No actual design work on the new wing was begun until September 1941, and the wing section eventually adopted for development had its point of maximum thickness at 37.5% of the chord. The thickness/cord ratio was 14.5% at the root and 10% at the tip, giving a wing five inches thinner at the root than that of the Typhoon.
This thin wing could not contain a comparable quantity of fuel to that housed by the Typhoon's wing, so a large fuselage tank had to be adopted. This necessitated the introduction of an additional fuselage bay, increasing the overall length by twenty-one inches forward of the c.g. This added length found its inevitable compensation after initial prototype trials in a larger fin and tailplane. The wing area was also increased, and an elliptical planform was adopted, presenting a chord sufficient to permit the four 20-mm. Hispano cannon to be almost completely buried in the wing. All these modifications added up to a radically changed Typhoon, but it was as the Typhoon II that two prototypes were ordered in November 1941. However, in the middle of the following year the name Tempest was adopted. Alternative installations of the Sabre engine were designed for these prototypes; the first (HM595) had a Sabre II and a front radiator similar to that of the standard Typhoon, while the second (HM599) had a Sabre IV engine and wing leading-edge radiators.
In June 1942 it was proposed that six Tempest prototypes should be completed: one with a Sabre VI (Tempest I); two with Centaurus (Tempest IIs); one with a Rolls-Royce Griffon 2B (Tempest III); one with a Griffon 61 (Tempest IV); and one with a Sabre III (Tempest V). Owing to heavy commitments Hawker could not undertake to build more than three and the Mks I, II and V were chosen.
Piloted by Philip Lucas, the first prototype Tempest was flown on September 2, 1942, but prior to this, in February 1942, a production order had been placed and the first production machine flew in June 1943 with Bill Humble at the controls. During flight trials the first Tempest prototype had exceeded 477 m.p.h. in level flight, and the first production model was essentially similar to the first prototype with the chin-type radiator. This was designated Tempest V, and the initial production batch, the Series I, had Mk. II cannon which projected slightly ahead of the wing leading edge, but the Series II had the short-barrelled Mk. V cannon which did not project, and also featured a detachable rear fuselage, small-diameter wheels and a rudder spring tab. Powered by a 2,420 h.p. Sabre IIB engine, the Tempest V attained a maximum speed of 435 m.p.h. at 17,000 feet. The 820-mile range of the Tempest V in clean condition was an appreciable improvement over that of the Typhoon, and was due not only to the small additional quantity of fuel carried but to the aerodynamic refinement of the later machine which permitted a higher cruising speed for the same power.
The first squadrons to be equipped with Tempest Vs were Nos. 3 and 486 at Newchurch, Dungeness, the first of these receiving its equipment early in 1944. By May five Tempest Vs had been lost due to engine failure, and this was discovered to be due to an over speeding of the propellers, resulting in an uncontrollable increase in engine revolutions, the failure of the bearings and the collapse of the oil system. In June modified propellers were fitted which solved the problem, and two days after the invasion of the Continent, on June 8, 1944, the Tempests met enemy aircraft in combat for the first time, destroying three Bf 109G fighters without loss to themselves. On June 13 the first V1 flying bombs were launched against England, and the Tempest, being the fastest low-medium altitude fighter in service with the R.A.F., became the mainstay of Britain's fighter defense against the pilotless missiles, destroying 638 of these weapons by the beginning of September. The Tempest V was also employed on the Continent for train-busting and ground-attack duties.
With the 2nd TAF in Europe, they not only made a valuable contribution in the close-support role, but claimed the interception and destruction of 20 Messerschmitt Me 262 jet-powered aircraft.
Meanwhile the second prototype (HM599), designated Tempest I, had proved sufficiently promising for production plans to be initiated. In the light of experience gained with the Centaurus-powered Tornado and the suitability of the Tempest fuselage for the radial engine, a Centaurus version of the Tempest was also initiated as the Mark II, and production drawings were prepared in parallel with those of the Mark I. In the event, the Tempest I was later abandoned while the Mark II was allowed to proceed to the production stage following the successful flight trials with the prototype, LA602, which commenced on June 28, 1943. The first production Tempest II flew fifteen months later, but the first unit, No. 54 Squadron, was not equipped with this fighter until November 1945, and was thus too late to participate in the war. The Tempest II was powered by the 2,500 h.p. Bristol Centaurus V or VI eighteen-cylinder, air-cooled, two-row radial, and attained a maximum speed of 440 m.p.h. at 15,900 feet and 406 m.p.h. at sea-level. Its range on internal fuel was 775 miles and initial climb rate was 4,520 ft./min.
Schemes for the utilization of the Griffon IIB and the Griffon 61 engines accounted respectively for the Tempest III and Tempest IV designations, neither passing the project stage. Nor did an alternative armament proposal based on the use of 0.5-in. machine-guns. The final Tempest variant was the Mark VI, which, appearing in 1945, was powered by the 2,700 h. p. Sabre VA engine and, except in having small intake ducts in the wing roots, was outwardly indistinguishable from the Tempest V. By and large, both the Typhoon and Tempest escaped the fate of so many aeroplanes of being used as test-beds for a variety of experiments. The Typhoon was designed in a naval fighter variant to meet the requirements of specification N.11/40, and one prototype was converted to this standard under the Hawker project designation P.1009. Another Typhoon modification, the P.1010, was to have had leading-edge radiators and a turbo blower, but work on this was not proceeded with.
As part of their engine development program, Napier's designed an annular cowling for the Sabre to replace the familiar chin-type radiator bath. The first such installation was on a Typhoon IB (R8694), but most of the development was undertaken with a Tempest V (NV768) which flew with several different types of annular radiator and hollow spinner. Another experimental Tempest V (SN354) had a 40-mm. gun under each wing in a long fairing.
The Tempest VI was a tropicalised version of the Mk V with a 1,714kW Sabre V engine. This entered RAF service post-war, as did the Tempest II with Bristol Centaurus power plant.
A majority of Tempest IIs were deployed overseas. Three squadrons were based in Germany with the British Occupation Forces and four squadrons went to India. The large stocks of Tempest II in India in 1947 allowed eighty-nine of these aircraft to be supplied to the newly independent Indian Air Force. The following year twenty-four Tempest IIs were delivered to Pakistan.
The Tempest II, 450 of which were built, was the RAF's last single-seat piston-engined fighter bomber. It was largely replaced by the de Havilland Hornet during 1948, but a few squadrons still flew Tempests until 1951, including several squadrons in Germany.
Many Mk V and Mk VI aircraft were converted subsequently to serve as TT.5 or TT.6 high-speed target tugs.
Tempest Mk V
Engine: 1 x Napier Sabre IIA, 1626kW / 2150 hp
Max take-off weight: 6142 kg / 13541 lb
Empty weight: 4082 kg / 8999 lb
Wing loading: 44.9 lb/sq.ft / 219.0 kg/sq.m
Wingspan: 12.50 m / 41 ft 0 in
Length: 10.26 m / 33 ft 8 in
Height: 4.90 m / 16 ft 1 in
Wing area: 28.06 sq.m / 302.04 sq ft
Max. speed: 370 kt / 686 km/h / 426 mph
Service ceiling: 11125 m / 36500 ft
Range: 1190 km / 739 miles
Armament: 4 x 20mm cannon, 450kg of bombs