Supermarine Type 224

Supermarine Type 224

Company type	Prototype fighter aircraft
Industry	Aerospace
Founded	1934
Founder	R.J. Mitchell
Headquarters	United Kingdom
Products	Fighter aircraft prototype

Template:Infobox aircraft The Supermarine Type 224 was a British gull-wing monoplane fighter crafted by R.J. Mitchell at Supermarine as a response to Air Ministry Specification F.7/30, which aimed to replace the Gloster Gauntlet with a new fighter. It was equipped with a Rolls-Royce Goshawk engine featuring an innovative evaporative cooling system.

Due to issues with this cooling mechanism and underwhelming trial results, the Air Ministry dismissed the Type 224, awarding the production contract instead to the Gloster Gladiator. Nonetheless, the experience gained from designing the Type 224 informed Mitchell’s later success with the Supermarine Spitfire.

Air Ministry Specification F.7/30

In October 1931, the British aircraft industry received Air Ministry Specification F.7/30, which evolved from Operational Requirement O.R.1. This specification mandated an all-metal fighter capable of both day and night operations, armed with four machine guns, delivering high top speed and climb rate, while maintaining a landing speed below 60 miles per hour (97 km/h). Emphasis was placed on excellent cockpit visibility. Although any suitable engine could be utilised, preference was given to the then-developing Rolls-Royce Goshawk. Designs were submitted by manufacturers including Bristol Aeroplane Company, Hawker Aircraft, Westland Aircraft, Blackburn Aircraft, and Supermarine.

Among these proposals, three were selected for prototype construction by the Air Ministry: Supermarine’s Type 224, Blackburn’s (Blackburn F.3), and Westland’s (Westland F.7/30). Both Hawker’s biplane and monoplane designs were rejected; however, they proceeded with the privately funded Hawker P.V.3. Similarly, Bristol financed development of the Bristol Type 123 biplane and the monoplane Bristol Type 133 after their official entries were declined. Gloster did not submit a bid due to their focus on the Gloster Gauntlet but later developed the Gloster SS.37 as a private venture incorporating Hawker construction methods to enhance their Gauntlet design.

Building on Supermarine's achievements in the Schneider Trophy races, chief designer R. J. Mitchell was confident in delivering a high-speed fighter. Within four months of receiving Specification F.7/30, Supermarine presented their monoplane design: the Type 224.

Mitchell's design

Mitchell's concept for the Type 224 featured an inverted gull-wing configuration, selected to reduce the length of the undercarriage legs and consequently minimize drag. Unlike the airfoil profiles used on Schneider Trophy racers, he opted for a thicker wing airfoil.

The aircraft's fixed landing gear were enclosed within substantial fairings. The fuselage employed a monocoque structure, with one pair of guns positioned on each side of the cockpit, while an additional pair was installed within the 'trouser' fairings of the fixed undercarriage.

The wing was constructed around a single main spar. The engine's cooling system incorporated condensers that extended along the entire leading edge of the wing, forming a 'D-box' spar that provided considerable torsional rigidity. The section behind the main spar was covered with fabric.

The Type 224 was equipped with the 600 horsepower (450 kW) Goshawk II engine. Its evaporative cooling system operated by maintaining the cooling water under pressure to allow it to surpass 100 °C (212 °F) without boiling as it circulated through the engine. This superheated water was then depressurized to vaporize into steam, which was subsequently condensed back into liquid form in condensers and recirculated. While this system had been tested in other aircraft—primarily biplanes where condensers and water collection tanks were located in the upper wing—in the Type 224 these tanks were housed within the undercarriage fairings. Because the condensed water remained near boiling temperature, minor pressure fluctuations often caused it to vaporize again inside the water pumps, frequently resulting in pump failure.

Tests and subsequent development

Although Mitchell was generally skeptical about wind tunnel testing, certain elements of the Type 224 design underwent evaluation in the Vickers wind tunnel. These tests confirmed that a gull-wing configuration offered aerodynamic advantages. Additionally, wind-tunnel assessments were performed on a full-scale model of the open cockpit area to verify that the pilot would not experience excessive buffeting caused by the windscreen design.

Supermarine provided performance predictions for the Type 224 to the Air Ministry based on wind-tunnel data, which forecasted favorable results. Consequently, the ministry authorized production of a prototype. The aircraft's maiden flight took place on 19 February 1934 with pilot "Mutt" Summers at the controls. However, its actual performance fell short: it achieved a top speed of only 228 miles per hour (367 km/h) and required 9.5 minutes to reach an altitude of 15,000 ft (4,600 m), compared to anticipated figures of 245 miles per hour (394 km/h) and a climb time of 6.6 minutes to 15,000 ft (4,600 m). The wing design also led to challenges with lateral stability, prompting additional wind-tunnel testing before finalizing modifications that included enlarging the fin.

Fate

Mitchell engaged in talks regarding several enhancements to the Type 224, including a redesigned wing, tailplane, and engine configurations, which were expected to boost its maximum speed to approximately 265 miles per hour (426 km/h). However, the Air Ministry concluded that developing an entirely new aircraft was preferable to modifying the Type 224. This decision was made in 1933. By January 1935, further production was halted. Mitchell expressed dissatisfaction with the Type 224’s inadequate performance and began to question the accuracy of wind-tunnel test results.

Gloster proceeded with its own private project, resulting in the Gladiator, which was commissioned in mid-1935 to serve the expanding RAF.

On 25 May 1937, the Type 224 was transferred to the Aeroplane and Armament Experimental Establishment at RAF Martlesham Heath. The aircraft’s operational life concluded during the summer of 1937 when it was utilized as target practice at Orford Ness, Suffolk.

Legacy

Despite the Type 224's shortcomings following the earlier successes of Schneider racers, Mitchell retained confidence in his fighter design capabilities. He undertook a complete redesign, producing an aircraft featuring straight wings and a thinner airfoil profile.

The Air Ministry quickly recognized that Mitchell’s revised concept constituted a new airplane altogether. It sought a fighter designed by Mitchell and his team, leading to the issuance of Specification F.37/34 in January 1935, specifically aimed at covering Supermarine’s new design. This specification essentially supplemented F.7/30 by referencing Supermarine’s specification 425a and accompanying drawings, paving the way for the development of the Supermarine Spitfire.

Supermarine requested that the name Spitfire be officially reserved for this model. The designation was accepted; however, Mitchell personally disliked the name, and it was subsequently discontinued for use with the Type 224.

External links

• Photographs of the Type 224 hosted by Destination's Journey (Archived version dated 29 March 2024).