The Fairey Firefly FR.4 saw a major redesign of the basic Firefly design, with leading-edge radiators installed to provide cooling for a more powerful Griffon 61 engine. The first attempt to install a two-stage supercharged Griffon 61 in the Firefly, the Firefly F.3, ended in failure, partly because the new engine needed a larger radiator. On the F.3 this was carried under the engine, as on the F.1, causing drag and instability.
Early in 1944 Fairey began work on an alternative design. This used wing leading edge radiators (as seen on the de Havilland Mosquito), eliminating the need for the big 'chin' radiator of the Mk.I. As a result the FR.4 had a neatly curved nose. This was emphasised by the removal of the under-engine radar pod, which was replaced by a new radar nacelle mounted on the starboard wing. This was balanced by a 55 gallon fuel tank in a similar nacelle on the port wing. The FR.4 was also given shorted clipped wings to improve the Firefly's rate of roll.
After testing the basic design in mock-up form on a Mk I, Fairey produced a true prototype, which made its maiden flight on 25 May 1945 (at this stage it had the standard Mk I wings). Over the rest of the year this prototype was repeatedly modified to bring it up to the eventual FR.4 standard. A second prototype made its maiden flight on 21 February 1946, and the first production aircraft took to the airs on 25 May 1946.
This aircraft was delivered to the Fleet Air Arm in September 1946, but the type wasn't cleared for shore-based operations until 12 February 1947, and even then a series of limitations were imposed that weren't lifted until the summer.
The FR.4 entered service with the Royal Canadian Navy in August 1947, going to No.825 Squadron. No.810 Squadron of the Fleet Air Arm received its first aircraft when it reformed on 1 October 1947, and was followed by Nos.812 and 814 Squadrons. The FR.4 had a short front-line career. No.810 Squadron used it for two years, to October 1949. No.812 Squadron converted to the FR.5 in mid 1948 and No.814 Squadron in the first half of 1949.
A night fighter version of the FR.4 was ordered, but didn’t enter service.
Engine: Griffon 74
Power: 2,004hp at take-off, 2,245hp at altitude
Wing span: 41ft 17in
Length: 37ft 11in
Height: 13ft 11in
Empty Weight: 9,674lb
Loaded Weight: 15,615lb
Max Speed: 367mph at 14,000ft
Service Ceiling: 31,900ft
Range: 760 miles
Armament: Four 20mm Hispano cannon
Bomb-load: Sixteen 60lb rockets or two 1,000lb bombs
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