Air Ministry Specification F.18/37 was concerned with the design and development of two advanced interceptor fighters with one of two 24-cylinder engines in the 2,000 h.p. class then under development - the Napier Sabre "H" type and the Rolls-Royce Vulture "X" type: one with a Rolls-Royce Vulture engine was identified initially as the R (Rolls-Royce) type fighter; the second, with a Napier Sabre engine, was known as the N (Napier) type.
Sydney Camm had commenced investigating the possibilities of just such a fighter in March 1937, and had already roughed out a design built around the Napier Sabre engine and housing twelve 0.303-in. Browning guns with 400 r.p.g. in its 40-foot wings. At the proposal of the Air Ministry, Camm also prepared studies for an alternative version of his fighter powered by the Rolls-Royce Vulture engine, and increased the ammunition capacity of both machines to 500 r.p.g.
Further discussions over military loads and equipment followed, and revised tenders were submitted to the Air Ministry at the beginning of 1938 for both the Type " N " and the Type " R ", as the alternative Sabre and Vulture powered fighters had become known. These tenders were formally accepted on April 22, 1938, and four months later, on August 30, two prototypes of each fighter were ordered. Structurally both types were similar: the wings were all-metal, the front fuselage was of steel tubing, and the aft section consisted of a stressed-skin, flush-riveted monocoque - the first Hawker designs to employ this form of construction. Uniformity between the two fighters was, in fact, achieved to a remarkable degree, but the designs did differ in the Vulture powered fighter made use of a ventral radiator while the Sabre driven machine had one of "chin" type.
Construction of the two fighters proceeded in parallel, and work progressed simultaneously on the preparation of production drawings. As a result of the slightly more advanced development status of the Vulture engine which had been designed along more conventional lines than the Sabre, the Type " R " was the first of the two fighters into the air, flying on 24 February 1940.
The initial flight trials of the prototype were promising, and a production order for 1,000 Tornados was placed at the beginning of November, it being proposed that the new fighter should be built both by Hawker and by A. V. Roe at Woodford. However, the flight test program soon began to run into trouble. Compressibility effects, about which little was known at that time, began to manifest themselves, and it was decided that the ventral radiator bath was unsuitable for the speeds approaching 400 m.p.h. that were being achieved for the first time. The radiator was, therefore, moved forward to the nose, a position already selected for that of the Type " N ", by now dubbed Typhoon; but the first prototype Tornado (P5219) only flew long enough to indicate the beneficial results of the change before it was totally destroyed.
On December 30, 1939, the first Napier Sabre engine had been delivered to Hawker Aircraft, and the first prototype Typhoon (P5212) emerged from the experimental shop to fly on February 24, 1940. It too became the subject of a quantity production order which, it was planned, should become the responsibility of Gloster Aircraft, whose assembly lines were emptying of Gladiator biplanes and whose design office was already immersed in the development of the Gloster Meteor, the first British turbojet-driven aircraft. Although, like those of the Tornado, the first flights of the Typhoon prototype indicated a promising fighter, the machine proving relatively easy to fly at high speeds, its low speed qualities left much to be desired, and it had a marked tendency to swing to starboard during take-off. The "X" form of the Tornado's Vulture engine had not permitted installation above the front spar as was the Typhoon's Sabre and, in consequence, the overall length of the former was 32 ft. 6 in. as compared with the 31 ft. 10 in. of the latter. Owing to the size and weight of the Sabre and the need to preserve c.g. balance, the Typhoon's engine was fitted so close to the leading edge of the wing that severe vibration was experienced as the slipstream buffeted the thick wing roots. On an early test flight the stressed-skin covering began to tear away from its rivets, and the Typhoon's pilot, Philip G. Lucas, only just succeeded in bringing the prototype in to a landing.
Apart from structural teething troubles, the Sabre engine, although a compact and exquisite power plant, called for a considerable amount of development, and it was perhaps fortunate for the future of the Typhoon that, in May 1940, the war situation led to the cancellation of all priority for Typhoon and Tornado development in order to allow every effort to be put into the production of sorely needed Hurricanes. Design development was allowed to continue, and development on the Typhoon included the design of a modified wing containing two 20-mm. Hispano cannon in place of the six 0.303-in. Brownings, the construction of an experimental set of wings containing a total of six cannon, and the initiation of a design study of a Typhoon variant with thinner wings of reduced area and lower profile drag. This latter study was later to arouse interest at the Air Ministry and eventually result in the Tempest. By October 1940 enthusiasm had been revived and production of the Tornado and Typhoon reinstated, production deliveries of both being scheduled for the following year.
The first production Typhoon IA (R7082) with the 2,200 h.p. Sabre IIA engine was completed by Gloster and flown on May 26, 1941. Production of this version, with its twelve Browning guns, was in limited quantity, and those built were used principally for the development of operational techniques. Typhoon IA production aircraft began to enter RAF service in September 1941, and went into action in the summer of 1942. Initial usage proved a great disappointment, with unsatisfactory high-altitude performance, inferior rate of climb and frequent engine breakdowns. When structural failure of the tail unit caused a number of fatal accidents it was suggested that the Typhoon should be withdrawn from service. Fast action was taken to overcome the shortcomings, and introduction of the Sabre II engine brought improved reliability. Typhoon I A were armed with 12 x 7.7mm Browning machine-guns.
The cannon-armed Typhoon IB was following the Mark IA, and the Air Ministry was pressing for its rapid service introduction to counter the new Focke-Wulf Fw 190. Nos. 56 and 609 Squadrons based at Duxford began to receive their Typhoons in September 1941, before the fighter was fully developed, and these squadrons were forced to take on part of unearthing the new machine's numerous faults. In the first nine months of its service life far more Typhoons were lost through structural or engine troubles than were lost in combat, and between July and September 1942 it was estimated that at least one Typhoon failed to return from each sortie owing to one or other of its defects. Trouble was experienced in power dives - a structural failure in the tail assembly sometimes resulted in this component parting company with the rest of the airframe. During the Dieppe operations in August 1942, when the first official mention of the Typhoon was made, fighters of this type bounced a formation of Fw 190s south of Le Treport, diving out of the sun and damaging three of the German fighters, but two of the Typhoons did not pull out of their dive owing to structural failures in their tail assemblies.
Despite this start to its service career, operations continued and the accident rate declined as the engine teething troubles were eradicated, although the tail failures took longer to solve, despite immediate strengthening and stiffening as soon as the trouble manifested itself. In November 1942 No. 609 Squadron, led by Wing Commander Roland Beamont, was moved to Manston in an attempt to combat the near-daily tip-and-run raids which were being made by Fw 190s and could rarely be intercepted by Spitfires. The Typhoon enjoyed almost immediate success. The first two Messerschmitt Me 210 fighter bombers to be destroyed over the British Isles fell to the guns of Typhoons, and during the last daylight raid by the Luftwaffe on London, on January 20, 1943, five Fw 190s were destroyed by Typhoons.
On November 17, 1942, Wing-Commander Beaumont had flown a Typhoon on its first night intrusion over Occupied France and, subsequently, the fighter was employed increasingly for offensive duties, strafing enemy airfields, ships and railway transport. The success of the Typhoon in the ground-attack role led to trials with two 250-lb. or two 500-lb. bombs which were carried on underwing racks. This load was later increased to two l,000-lb. bombs, but the Typhoon was not to find its true element until it was adapted to carry airborne rocket projectiles - four under each wing. By D-Day, in June 1944, the R.A.F. had twenty-six operational squadrons of Typhoon IBs. Without its underwing load the Typhoon IB weighed 11,300 Ib.; and with two 500-lb. bombs and the necessary racks, 12,400 lb. Maximum speed was 398 m.p.h. at 8,500 feet and 417 m.p.h. at 20,500 feet, and an altitude of 20,000 feet could be attained in 7.6 minutes. Between the prototype and production stages several design changes had been made. These included the re-design of the fin and rudder, the redisposition of the wheel fairings and the introduction of a clear-view fairing behind the cockpit. On the first few Typhoon IAs the solid rear fairing was retained; later a transparent fairing was fitted, but this was abandoned in favor of the first sliding " bubble " hood to be used by an operational fighter.
The Typhoon IB, by now affectionately known as the "Tiffy", distinguished itself particularly in the Battle of Normandy, where it decimated a large concentration of armor ahead of Avranches, disposing of no fewer than 137 tanks, and opening the way for the liberation of France and Belgium. For use in the tactical reconnaissance role, the Typhoon F.R.IB was developed early in 1945. In this version the two inboard cannon were removed and three F.24 cameras were carried in their place. One Typhoon was also converted as a prototype night fighter, with A.I. equipment, special night-flying cockpit and other modifications. Production of the Typhoon, which was entirely the responsibility of Gloster Aircraft, totaled 3,330 machines.
Typhoons were operated by 32 RAF squadrons, and used by the RCAF and Free French squadrons within the RAF.
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.
By the end of 1945, none remained in front-line service.
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.
Typhoon Mk. IB
Engine: 1 x Napier "Sabre IIA", 1605kW / 2150 hp
Max take-off weight: 5170 kg-6,010 kg / 11398 lb-13,250 lb
Empty weight: 3992 kg / 8801 lb
Wing loading: 40.8 lb/sq.ft / 199.0 kg/sq.m
Wingspan: 12. 67 m / 41 ft 8 in
Length: 9.74 m / 31 ft 10 in
Height: 4. 67 m / 15 ft 5 in
Wing area: 25.9 sq.m / 278.79 sq ft
Max. speed: 673 km/h / 418 mph
Cruise speed: 530 km/h / 329 mph
Service ceiling: 10360 m / 34000 ft
Initial climb rate: 3,000 ft/min / 914 m/min
Range w/max.fuel: 1530 km / 951 miles
Range w/max.payload: 980 km / 609 miles
Armament: 4 x 20mm cannon, 900kg of weapons / 8x rockets
Engine: Napier Sabre IIC, 2260 hp