Shortfinals – aviation and more!

By: shortfinals

Jun 29 2013

Tags: 'blown flap', 'fishtail' nozzles, 'jet flap', aircraft, Bedford, Bristol Siddeley Orpheus BOr.3 Mk805 turbojet, British Aircraft Corporation, California, Chief Test Pilot, Cosford, Desmond 'Dizzy' Addicott, Great Britain, Hunting Aircraft Ltd, Hunting H-126, Le Bourget, Moffett Naval Air Station, museum, Museums, NASA, NASA Flight Research Center, National Gas Turbine Establishment, Paris Air Show, Pyestock, RAF, RAF Gaydon, RAF Museum, Royal Air Force, Royal Aircraft Establishment, Stanley 'Olly' B. Oliver, USA, warbird, wind tunnel, XN714

Category: aircraft, Aviation, England, military, Museums, RAF, Royal Air Force, warbird

4 Comments

Pure research aircraft are rare beasts. Usually, for reasons of economy, the aerodynamicists or propulsion engineers or radar technicians, can ‘make do and mend’ and modify (sometimes almost to the point of the original aircraft becoming almost unrecognizable) a redundant Service airframe. Some aircraft types are surprisingly successful in this regard; the Fairey Battle, an RAF WW2 light bomber, which was SO bad it suffered almost 100% casualties on certain missions, turned out to be a superb engine test bed, flying many different high-performance piston engines. In the modern era, the Anglo-French SEPECAT Jaguar, an attack jet of some note, proved to be very useful in ‘fly-by-light’ experiments.

However, sometimes there arises a special set of circumstances which means that the ONLY thing you can do is BUILD an aircraft to test the theory! Such an aircraft is the ‘Yellow Peril’, the Hunting H-126 (RAF Serial, ‘XN714’) seen above. In the immediate post-war period, research was being undertaken to see if jet aircraft could be made to fly very slowly, in safety, so that they could use shorter runways. The ‘jet flap’ principal (to become known as the ‘blown flap’ in the United States), had been the subject of extensive research at the National Gas Turbine Establishment at Pyestock, and, indeed, was subject of a patent in 1952. This was a process by which a large proportion of a jet engine’s output was ‘blown’ across its flaps, so that its stalling speed was radically reduced. The Ministry of Aviation issued a specification, ER. 189D, to cover the construction of two jet aircraft to investigate this extremely low-speed jet flight.

Hunting Aircraft Limited, of Luton (part of the British Aircraft Corporation) won the contract to build two aircraft (XN714, 4 degrees wing dihedral – built; XN719, 8 degrees wing dihedral – partially built, then cancelled). XN714 had certain fuselage elements in common with Hunting’s Jet Provost, but turned out to be singularly ‘plain’ looking! Powered by a Bristol Siddeley Orpheus BOr.3 Mk805 turbojet of 4,000 lbs static thrust, and carrying just a single pilot, it was to employ a fully blown wing. The hot engine exhaust was sent to a distribution ‘manifold’ (nicknamed, ‘the dustbin’). Here, up to 50% of the gases were ‘bled’ across the wing flaps via a series of ‘fishtail’ nozzles and complex ductwork. A proportion of the exhaust was used for forward thrust via a pair of jet nozzles, one each side of the lower fuselage. There were two nozzles, one at each wingtip, which controlled the aircraft in the roll axis at slow speed, and others at the extreme tail which served the same function in pitch and yaw; these were needed, as use of the ‘jet flaps’ caused large changes in trim. A variable incidence tailplane also helped overcome these.

XN714 was completed by August 1962, and taxi trials were initially performed at the Luton facility of Hunting Aircraft by their Chief Test Pilot, Stanley ‘Olly’ B. Oliver, then the aircraft was taken 30 miles by road to the Aerodynamics Flight of the Royal Aircraft Establishment at Bedford. On the 26th March 1963, XN714 took off on its first, 20 minute long, test flight. It was accompanied by not one but TWO Gloster Meteor two-seater chase planes! Take off took place at 80 knots after a run of 600 yards.

A series of test flights ran through June 1965, and pilots were warned not to attempt flight at less than 35 mph! On the 19th June, 1965, the H-126 was demonstrated at the Paris Air Show at Le Bourget by Desmond ‘Dizzy’ Addicott, that well-known Scottish test pilot and racing driver. Unfortunately, ‘Dizzy’ had to land cross-wind and burst a tyre.

On its last ‘public appearance’ XN714 was flown to RAF Gaydon for the local Battle of Britain Air Display on the 17th September, 1966. The very last flight took place on 9th November, 1967; the flight was 25 minutes long, giving a total flight time of 141 hours and 318 landings, in the 100+ flights.

Sadly, there were no more research funds available, and directed jet thrust (as in the Hawker P.1127) was proving more efficient than ‘jet flaps’. One critical factor was the fact that the brake units on the fixed ‘Electro-Hydraulic’ undercarriage were completely worn out. However, there was one last, very surprising, chapter to be written in the history of XN714.

The Ministry of Aviation agreed to loan XN714 to NASA! On 3 April, 1969, the crated aircraft was loaded onto an RAF Short Belfast transport (serial XR366) and flown to the NASA Flight Research Center at Moffett Naval Air Station in California. There it was subjected to a comprehensive series of tests in the NASA Full Scale Wind Tunnel. It is not recorded what the NASA engineers thought of the Yellow Peril !

In May, 1970, it arrived at Holme-on-Spaulding-Moor (Hawker Siddeley Aviation) from NASA, where it was temporarily stored. Eventually, it was shuttled to RAE Bedford, where it sat, crated, for a number of years, until it was finally delivered to the RAF Museum, Cosford in 1974, to take its place in the ‘Flight Test’ section of the Museum.

The H-126 might not have had the good looks of the F-86 or the Hunter, but this early research jet, with a stalling speed lower than many light aircraft, had a useful working life in one particular area of aerodynamics, and is well worthy of being preserved.

Operation Husky