The uncommon Whirlwind

In 1935, with war with Germany looking more likely, the British Air Ministry issued a requirement for a 400 mph single seat fighter armed with the incredibly heavy (for the time) armament of four 20 millimeter Hispano HS.404 cannons.

The number of engines was not specified, and the requirement – simply called “the cannon fighter” after its approval – resulted in a number of innovative design submissions, but the challenges were formidable.

To get the desired speed, the wing had to be very small, but the weight of the cannon meant the aircraft would be heavy, and a heavy aircraft with a small wing meant very high landing speeds. The technical director of Westland Aircraft Limited, W.E.W “Teddy” Petter, offered up a small, sleek twin engine fighter with thin, low mounted wings, a bubble canopy and the four cannons in the nose for maximum concentrated firepower.

To offset the potential high landing speed, Petter installed Fowler flaps – a type of flap that slid backwards before hinging downward, which increased both camber and chord and created a larger wing surface for lower speeds. These heavy flaps were unusual for a fighter and were installed between the engine nacelles and along the bottom fuselage.

The Whirlwind was powered by two liquid-cooled 885 horsepower Rolls Royce Peregrine engines – the ultimate development of the highly successful Rolls Kestrel. The engine nacelles, wings and the associated plumbing were designed to fit tightly around the Peregrine.

At the same time, Rolls Royce had developed the 1,000 horsepower Rolls Royce Merlin engines that were powering the new Hurricanes and Spitfire. But even with the smaller Peregrine, the highly streamlined Whirlwind was much smaller in terms of frontal area, and its top speed of more than 360 mph was the same speed as the two other Royal Air Force fighters. Its four 20 millimeter cannons had a rate of fire of 600 pounds per minute, which made it the most heavily armed fighter in the world, and their close grouping in the nose concentrated the fire in a very tight pattern.

 The Whirlwind had several innovative design features. The horizontal stabilizer was mounted high on the vertical tail to keep it out of the wing and prop wash during heavy maneuvering, magnesium was extensively used in the construction, and most of the ancillary systems were hydraulically operated.

When the test program began, the Whirlwind proved to have excellent performance and handling characteristics, though it did have a limited combat radius – under 300 miles – that limited one of its intended roles: bomber escort. Its relatively high landing speed, even with the Fowler flaps, also limited the number of airfields it could operate from. But the biggest problem was with the Peregrine engine.

It had a “ground level” supercharger and it was initially felt the Peregrine would be the standard fighter engine for RAF. However, as fighters rapidly increased in size, the Peregrine was simply too small to be useful. The larger Merlin had its share of problems, but because of its greater potential, Rolls Royce devoted its resources to quickly bring the Merlin into service and the Peregrine was relegated to a secondary status.

The result was that Whirlwind did not enter squadron service until May 30, 1940, and because of slow deliveries of the engines, the fighter only flowed fitfully into the operational units. In the end, only two squadrons – 137 and 263 – were equipped with the fighter.

In service, the Whirlwind was extremely well liked. The Peregrine engines limited its high altitude capability, but at medium altitude its high speed and excellent maneuverability made it very effective in air-to-air combat, and its heavy armament made it an ideal ground strafer.

The pilots also appreciated the placement of the wings and engines ahead of the cockpit, which allowed the aircraft to absorb a great deal of damage while the cockpit area remained largely intact, as well as the extra margin of safety provided by the second engine. Because of the Whirlwind’s excellent characteristics, there was some thought given to re-engining it with the Merlin, but ironically its beautiful design worked against it.

 Since the wings and nacelles were designed specifically for the Peregrine, re-engining would have involved rebuilding the entire aircraft, which, given how fast fighter aircraft were evolving, was not feasible.

By December 1943, the two Whirlwind squadrons had turned in their planes and converted to the Hawker Typhoon, ironically the only fighter in the wartime RAF inventory that took more time to develop than the Whirlwind. As a further irony, the Napier Sabre engine in the Typhoon proved far less reliable than the Peregrine.

For questions or comments, contact Dr. Michel at marshall.michel@ramstein.af.mil.