The Hawker Tempest was a British fighter aircraft primarily used by the Royal Air Force (RAF) in the Second World War. The Tempest was an improved derivative of the Hawker Typhoon, and one of the most powerful fighter aircraft used during the war.
Design and development
During development of the Typhoon the design team, under the leadership of Sydney Camm, were already planning design improvements, this process resulting in the Hawker P. 1012 (or Typhoon II). Although the Typhoon was basically a good design, Camm and his design team were disappointed with the wing which proved to be too thick in its cross section; this created airflow problems and inhibited flight performance, especially at higher altitudes. The Typhoon's wing, using a NACA 4 digit series wing section, had a maximum thickness to chord ratio of 19.5% (root) to 12% (tip). In March 1940, engineers were assigned to investigate the new low drag laminar flow wing developed by NACA in the United States, which had been used in the new North American P-51 Mustang. A laminar flow wing adopted for the Tempest series had a maximum thickness to chord ratio of 14.5% at the root, tapering to 10% at the tip. The maximum thickness of the Tempest wing was set further back at 37.5% of the chord versus 30% for the Typhoon's wing.
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 an elliptical shape to accommodate the 800 rounds of ammunition for the four 20 mm (.79 in) Hispano cannons, which were moved back further into the wing. The new elliptical wing had greater area than the Typhoon's.[nb 1] 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 gal (345 l) fuel tank. In addition, two inter-spar wing tanks, each of 28 gal (127 l), were fitted on either side of the centre-section and, starting with late model Tempest Vs, a 30 gal (136 l) tank was carried in the leading edge of the port wingroot, giving the Tempest a total internal fuel capacity of 162 gal (736 l).
In service, Tempests also carried two specially designed, streamlined, drop tanks of 45 gal (204 l) giving a maximum of 360 gal (1,636 l) and an operational radius of 500 mi (805 km) Another important feature of the new wing was Camm's proposal that radiators for the new Napier Sabre IV engine were to be fitted into the leading edge of the wing inboard of the undercarriage. This eliminated the distinctive "chin" radiator associated with 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. Fortunately for the pilots, the new wing and airfoil, and the four-bladed propeller unit, eliminated the high frequency vibrations that had plagued the Typhoon.
Tempest I prototype HM599
; when first flown, it had the "car-door" canopy and small tail unit.
The redesigned main undercarriage legs were longer and had a wider track (16 ft/5 m) to improve stability at the high landing speed of 110 mph (180 km/h), and to allow tip clearance for a new de Havilland 14 ft (4 m) diameter four-blade propeller. The main undercarriage units were Dowty levered suspension units incorporating trunnions which shortened the legs as they retracted. The majority of the Tempests built used 30 by 9 inch (76.2 by 22.9 cm) four-spoke wheels, while the prototypes and early production Tempest Vs used the Typhoon's larger 34 by 11 inch (83.4 by 28 cm) five-spoke wheels. The retractable tailwheel was fully enclosed by small doors and could be fitted with either a plain Dunlop manufactured tyre, or a Dunlop-Marstrand "twin-contact" anti-shimmy tyre.
Camm and the Hawker design team placed a high priority on making their aircraft easily accessible to both air and ground crews; to this end the forward fuselage and cockpit areas of the earlier Hurricane and the Tempest and Typhoon families were covered by large removable panels providing access to as many components as possible, including flight controls and engine accessories. Both upper wing roots incorporated panels of non-slip coating. For the pilot a retractable foot stirrup under the starboard root trailing edge was linked to a pair of handholds which were covered by spring-loaded flaps. Through a system of linkages, when the canopy was open the stirrup was lowered and the flaps opened, providing easy access to the cockpit. As the canopy was closed the stirrup was raised into the fuselage and the flaps snapped shut.
The new design was finalised by October 1941 and the Air Ministry issued specification F.10/41 that had been written to fit the aircraft. A contract for two prototypes of the "Typhoon Mark II" was issued in November, and the new fighter was renamed "Tempest" in January 1942. The problems experienced with delivery of engines finally led the Air Ministry to ask for six prototypes with different engines so that if a delay hit one engine an alternative would be available. This resulted in a single Mk.I, HM599, with a Sabre IV, two Mk.IIs (LA602 and LA607) with the Centaurus IV, a Mk.III (LA610) with a Griffon IIB, a Mk.IV (LA614) with a Griffon 61, and the Mk.V (HM595) with the Sabre II.
First prototype Tempest II LA602
, again with the small tail unit.
The first Tempest prototype, the Mark V HM595, was first flown by Philip Lucas from Langley on 2 September 1942. This aircraft retained the Typhoon's framed canopy, car-style door, powered by a Sabre II engine, and 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. 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". The Air Ministry had already ordered 400 Tempests in August but production of the new Sabre IV engine ran into protracted problems and delays. The second prototype, the "Tempest Mark I" with the Sabre IV did not fly until 24 February 1943. This prototype also had at first the older Typhoon cockpit structure and vertical tailplane. Elimination of the "chin" radiator did much to improve performance and the Tempest Mark I was the fastest aircraft Hawker had built to that time, attaining a speed of 466 mph (750 km/h). Continual problems with the Sabre IV meant that only one Mark I (HM599) was built; consequently, Hawker went into production with the Sabre II engined "Tempest V", with the first rolling off the production line on 21 June 1943. [nb 2]
Tempest Mark V
The first production Tempest V JN729
. Small blisters covering the spar securing bolts are visible on the wing root fairing. Long-barreled Hispano II cannon and Typhoon five-spoke mainwheels were other features identifying the first production batch of 100 Tempests Vs.
Even before the first flight of the prototype Tempest V a production order for 400 Tempests was placed by the Air Ministry.The order was split, with the initial batch of 100 being Tempest V "Series Is", powered by the 2,235 hp (1,491 kW), Napier Sabre IIA series engine with the chin radiator, while the rest would be the Tempest I with the Napier Sabre IV and leading-edge radiators. As it transpired the difficulties with the Sabre IV meant that this version never reached production and the order was switched to 300 Tempest V "Series 2"s.[nb 3] The first production Tempest V, JN729 was first flown by test pilot Bill Humble on 21 June 1943. Several of the early production aircraft 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 used such ordnance operationally during World War II.
Examination of captured Fw 190s brought about improvements in the windscreen/ side windows; by careful design and positioning of the frame structure blind spots were reduced to an absolute minimum. The three-piece windscreen had a bullet-resistant centre panel made up of two layers, the outer 1.5 in (38mm) thick and the inner 0.25 in (6.5 mm).
During production of the first batch of 100 Tempest V "Series Is", distinguished 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 rear fuselage 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 new spar structure also allowed the wings to carry up to 2,000 lb (907 kg) of external stores. Also developed specifically for the Tempest by Hawker was a streamlined 45 gal (205 l) "drop tank" and carrier fairing; the redesigned wing incorporated the plumbing for these tanks, one to each wing. The ailerons were fitted with spring-loaded tabs which lightened the aerodynamic loads, making them easier for the pilot to use and dramatically improving the roll rate above 250 mph (402 km/h). Starting with EJxxx series Tempest Vs the improved Sabre IIB and IIC were used, both of which were capable of producing over 2,400 hp (1,789 kW) on emergency boost for short periods of time. All versions of the Sabre drove four-bladed, 14 ft (4.267 m) diameter de Havilland Hydromatic or Rotol propellers.
The first 100 Tempest Vs used long-barrelled 20 mm (.79 in) Hispano Mk.IIs the barrels of which projected ahead of the wing leading edges and were covered by short fairings, while later production Tempest Vs switched to the short-barrelled Hispano Mk.Vs the muzzles of which were flush with the leading edges. Finally, while early Tempest Vs used Typhoon style 34 by 11 inch (83.4 by 28 cm) five-spoke wheels, the majority used smaller 30 by 9 inch (76.2 by 22.9 cm) four-spoke wheels.
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. This was apparently used to more accurately measure the aircraft's altitude.
with experimental 47 mm class P guns. This is fitted with the standardised smaller four-spoke wheels.
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, an asset which was fitted in RAF Spitfires and Mustangs from mid-1944 and one which 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 two Vickers 47 mm "P" guns, one under each wing in a long "pod".[nb 4]