Avro 720

Avro 720

National origin: United Kingdom
Manufacturer: Avro
Status: Cancelled before completion of first prototype
Number built: 0

The Avro 720 was a planned British single-seat interceptor of the 1950s. It was to be of mixed propulsion, with a rocket engine to give high performance and a small jet engine for cruising flight. At least one prototype was ordered, but the project was cancelled before any were completed.

Design and development

In the early 1950s, the British Air Ministry, impressed by the performance of the rocket-powered Messerschmitt Me 163 fighter, and facing the potential threat of Soviet supersonic bombers armed with nuclear weapons, issued Specification F.124T for a rocket powered point-defence interceptor. This was to be of similar concept to the Me 163, using its rocket to climb rapidly to meet its target, before gliding back to earth, fuel exhausted, to land on a retractable skid. Proposals to meet the specification were received from a number of companies, including Avro, Bristol, Blackburn, Shorts and Saunders-Roe. It was soon realised, however, that a rocket-only fighter with the performance required by the specification, which would have to glide back to ground from heights of up to 100,000 ft (30,500 m), land without power many miles away and then be recovered and taken back to the airfield by ground vehicle, was impracticable. Revised specifications were therefore issued to Avro and Saunders-Roe for aircraft with auxiliary turbojet engines, giving sufficient power to allow the aircraft to fly back to its airbase after combat.

Avro's design, the Avro Type 720, designed to meet specification F.173D, was a small tailless delta-winged aircraft. It was constructed of metal honeycomb sandwich. The main power-plant was an 8,000 lbf (36 kN) Armstrong Siddeley Screamer rocket engine, using liquid oxygen as oxidant and kerosine fuel. This differed from the competing Saunders-Roe SR.53, which used a de Havilland Spectre powered by Hydrogen Peroxide and kerosine. Both types used a 1,750 lbf (7.8 kN) Armstrong-Siddeley Viper as the auxiliary turbojet, with the Avro design fed with air from a small chin inlet under the aircraft's nose. Two de Havilland Firestreak Infrared homing air-to-air missiles could be carried on underwing pylons.

Two prototypes were ordered, and the Screamer engine successfully completed flight clearance tests in December 1956. Official concern about the practicality of using liquid oxygen, which boils at -183°C (90 K), in an operational environment lead to the Screamer engine being cancelled late in 1956, together with the Avro 720. One structural test airframe was part complete at the time of cancellation, and photographs of this airframe, with the port wing fitted and the serial number XD696 painted on are sometimes claimed to be the "almost complete" first prototype. The Avro 720 had cost £1 Million by the time of cancellation, while its Screamer powerplant cost a further £0.65 million.

Specifications (Performance estimated)

Data from The British Fighter since 1912

General characteristics

Crew: 1
Length: 42 ft 3 in (12.88 m)
Wingspan: 27 ft 3.5 in (8.319 m)
Wing area: 166 sq ft (15.4 m)
Empty weight: 7,812 lb (3,543 kg)
Max takeoff weight: 17,575 lb (7,972 kg)
Powerplant: 1 x— Armstrong Siddeley Screamer liquid-fuelled rocket, 8,000 lbf (36 kN) thrust
Powerplant: 1 x— Armstrong Siddeley Viper ASV.8 turbojet, 1,750 lbf (7.8 kN) thrust

Performance

Maximum speed: 1,320 mph (2,120 km/h; 1,150 kn) at 40,000 ft (12,200 m)
Maximum speed: Mach 2.0
Service ceiling: 60,000 ft (18,288 m)
Time to altitude: 1 min 50 s to 40,000 ft (12,200 m)

Armament

Missiles: Provision for 2x— de Havilland Firestreak infra-red homing air-to-air missiles

Comparable aircraft

Republic XF-91 Thunderceptor
Saunders-Roe SR.53
SNCASO Trident

Bibliography

"Armstrong Siddeley Screamer". Flight, 27 July 1956. pp. 160-164.
"Cancelled Projects:The list Up-Dated". Flight, 17 August 1967, p. 262.
Jackson, A. J. Avro Aircraft since 1908. London:Putnam, 1990. ISBN 0-85177-834-8.
Jones, Barry. "Saro's Mixed-Power Saga". Aeroplane Monthly, November 1994. London:IPC. ISSN 0143-7240. pp. 32-39.
Mason, Francis K. The British Fighter since 1912. Annapolis, Maryland, USA:Naval Institute Press, 1992. ISBN 1-55750-082-7.
"Mixed-Power Interceptor". Flight, 24 May 1957, pp. 697-700.

Avro 720 Pictures and Avro 720 for Sale.

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Source: WikiPedia