The Hawker Typhoon (Tiffy in RAF slang), was a British single-seat fighter-bomber, produced by Hawker Aircraft. It was designed to be a medium-high altitude interceptor, as a direct replacement for the Hawker Hurricane, but several design problems were encountered, and it never completely satisfied this requirement.
Its service introduction in mid-1941 was plagued with problems, and for several months the aircraft faced a doubtful future. However, when the Luftwaffe brought the formidable Focke-Wulf Fw 190 into service in 1941 the Typhoon was the only RAF fighter capable of catching it at low altitudes; as a result it secured a new role as a low-altitude interceptor.
Through the support of pilots such as Roland Beamont it also established itself in roles such as night-time intruder and a long-range fighter.
From late 1942 the Typhoon was equipped with bombs, and from late 1943 RP-3 ground attack rockets were added to its armoury. Using these two weapons, the Typhoon became one of the Second World War's most successful ground-attack aircraft.
Even before the new Hurricane was rolling off the production lines in March 1937, Sydney Camm had moved on to designing its replacement. The two preliminary designs were very similar and were larger than the Hurricane. These later became known as the "N" and "R" (from the initial of the engine manufacturers), because they were designed for the newly developed Napier Sabre and Rolls-Royce Vulture engines respectively. Both engines used 24 cylinders and were designed to be able to deliver over 2,000 hp (1,491 kW); the difference between the two was primarily in the arrangement of the cylinders – an H-block in the Sabre and an X-block in the Vulture. Hawker submitted these preliminary designs in July 1937, but were advised to wait until a formal specification for a new fighter was issued.
In March 1938, Hawker received from the Air Ministry Specification F.18/37. F.18/37 asked for a fighter which would be able to achieve at least 400 mph (644 km/h) at 15,000 feet (4,600 m) and specified a British engine with a two-speed supercharger. The armament fitted was to be twelve Browning machine guns with 500 rounds per gun, with a provision for alternative combinations of weaponry. It was in response to this specification that Camm and his design team started formal development of the designs and construction of the prototypes.
The basic design of the Typhoon was a combination of traditional Hawker and more modern construction techniques; the front fuselage structure, from the engine mountings to the rear of the cockpit, was made up of bolted and welded duralumin or steel tubes, while the rear fuselage was a flush-riveted, semi-monocoque structure. The forward fuselage and cockpit skinning was made up of large, removable duralumin panels, allowing easy external access to the engine and engine accessories and most of the important hydraulic and electrical equipment.
The shallow-angle inverted gull wing had a span of 41-foot-7-inch (12.67 m), with a wing area of 279 sq ft (29.6 sq m). The airfoil used was a NACA 22 wing section, with a thickness to chord ratio of 19.5% at the root tapering to 12% at the tip. The wing possessed great structural strength, provided plenty of room for fuel tanks and a heavy armament, while allowing the aircraft to be a steady weapons platform. The inner wings, outboard of the fuselage had a 1° anhedral, while the outer wings, attached just outboard of the undercarriage legs, had a dihedral of 5½°. Each of the inner wings incorporated two fuel tanks; the "main" tanks, housed in a bay outboard and to the rear of the main undercarriage bays, had a capacity of 40 gallons; while the "nose" tanks, built into the wing leading edges, forward of the main spar, had a capacity of 37 gallons each. Also incorporated into the inner wings was an undercarriage with a track of 13 ft 6¾ in.
Although the Typhoon was expected to achieve over 400 mph (644 km/h) in level flight at 20,000 ft, the thick wings created a large drag rise and prevented higher speeds than the 410 mph at 20,000 feet (6,100 m) achieved in tests.The climb rate and performance above that level was also considered disappointing. In addition, when the Typhoon was dived at speeds of over 500 mph (805 km/h), the drag rise resulted in buffeting and trim changes. These compressibility problems led to Camm designing the Typhoon II, later known as the Tempest, which used much thinner wings with a laminar flow section.
As was usual with front line Second World War RAF aircraft, the Typhoon was modified and updated regularly, so that a 1945 production example looked quite different from one built in 1941. In the last months of the war, a number of older aircraft were taken out of storage and overhauled, sometimes seeing active service for the first time; for example, R7771 was from one of the first production batches, built in 1942 with the car-door canopy and other early production features. This Typhoon was delivered to, and served on the Fighter Interception Unit in 1942. In February 1945 R7771 was listed as being in front line service on 182 Sqn.; by then it was fitted with a clear-view "bubble" hood, rocket rails and other late series features.
The first problem encountered with the Typhoon after its entry into service was the seepage of carbon monoxide fumes into the cockpit. In an attempt to alleviate this, longer exhaust stubs were fitted in November 1941 ("Mod [modification] 239"), and at about the same time the port (left) cockpit doors were sealed. The Pilot's Notes for the Typhoon recommended that "Unless Mod. No. 239 has been embodied it is most important that oxygen be used at all times as a precaution against carbon monoxide poisoning." Despite the modifications, the problem was never entirely solved, and the standard procedure throughout the war was for Typhoon pilots to use oxygen from engine start-up to engine shut down. In addition to carbon monoxide seepage, pilots were experiencing unpleasantly high cockpit temperatures; eventually a ventilation tube helped alleviate, but did not solve the problem. In addition two small, rear opening vents were added below the port side radio hatch, just below the canopy.
A major problem, afflicting early production Typhoons in particular, was a series of structural failures leading to loss of the entire tail sections of some aircraft, mainly during high-speed dives. Eventually a combination of factors was identified, including harmonic vibration, which could quickly lead to metal fatigue, and a weak transport joint just forward of the horizontal tail unit. The loss of the tailplane of R7692 (having only 11 hours of flight recorded) on 11 August 1942, in the hands of an experienced test pilot (Seth-Smith), caused a major reassessment which concluded that the failure of the bracket holding the elevator mass balance bell crank linkage had allowed unrestrained flutter which led to structural failure of the fuselage at the transport joint.
Starting in September 1942, a steel strap was fitted internally across the rear fuselage transport joint, although this soon superseded by Mod 286 (modification number 286), in which 20 alloy "fishplates" were riveted externally across the rear fuselage transport joint, while internally some of the rear fuselage frames were strengthened. This was a permanent measure designed to stop in-flight rear fuselage structural failures and was introduced on the production line from the 820th production aircraft; between December 1942 and March 1943, all Typhoons without Mod 286 were taken out of service and modified. Modified balance weight assemblies were fitted from May 1943. Finally the entire unit was completely replaced with a redesigned assembly from August 1944.
Although these modifications reduced the numbers of Typhoons being lost due to tail assembly failure, towards the end of the Typhoon's life there were more tail failures, this time caused by a change to the undercarriage latch mechanism in late 1944; in high-speed flight the undercarriage fairings were pulled into the slipstream, creating an uneven airflow over the elevators and rudder resulting in tailplane and then rear fuselage structural failure. In total 25 aircraft were lost and 23 pilots killed due to tail failures.
The Typhoon was first produced with forward-opening side doors (complete with wind-down windows), with a transparent "roof" hinged to open to the left. The first 162 Typhoons featured a built-up metal-skinned fairing behind the pilot's armoured headrest; the mast for the radio aerial protruded through the fairing. From mid- to late 1941 the solid metal aft canopy fairing was replaced with a transparent structure (later nicknamed "The Coffin Hood"), the pilot's head armour plate was modified to a triangular shape and the side cut-outs were fitted with armoured glass; the first production Typhoon to be fitted with this new structure was R7803. All earlier aircraft were quickly withdrawn and modified. From early 1942 a rear-view mirror was mounted in perspex blister moulded into the later "car-door" canopy roofs. This modification was not very successful, because the mirror was subject to vibration. Despite the new canopy structure, the pilot's visibility was still restricted by the heavy frames and the clutter of equipment under the rear canopy; from August 1943, as an interim measure, pending the introduction of the new "bubble" canopy, the aerial mast and its associated bracing was removed and replaced with a whip aerial further back on the rear fuselage.
Starting in January 1943, R8809 was used to test a new, clear, one piece sliding "bubble" canopy and its associated new windscreen structure which had slimmer frames which provided a far superior field of view to the car-door type. From November 1943 all production aircraft, starting with JR333, were to be so fitted. However, the complex modifications required to the fuselage and a long lead time for new components to reach the production line meant that it took some time before the new canopy became standard. In order to have as many Typhoons of 2nd TAF fitted before "Operation Overlord" conversion kits were produced and Gloster, Hawker and Cunliffe-Owen modified older Typhoons still fitted with the car-door canopy.