The Royal Aircraft Establishment at Bedford

Puma XW241

This helicopter was the eighth of a development batch hand built by the French firm Aerospatiale at Marignane.

It first flew on 20 July 1968 as an SA330A, later being upgraded to an SA330E. It was delivered to Westland Helicopters at Yeovil on 10th October 1968 as a pattern airframe for the RAF Puma HC1.

It was acquired by Aero Flight at RAE Bedford in May 1973 where it was then extensively instrumented for a wide range of helicopter research and system demonstration activities.

It was also equipped with an internal power winch for use in the dropping of a variety of un-powered models used in spinning and aerodynamic stability trials.

The photo shows the aircraft in July 1980 fitted with an early instrumentation probe and a rotor hub instrumentation installation.

During the 1970s a research emphasis was placed on rotor aerodynamics. In forward flight the helicopter blade tip operates at high Mach numbers on the advancing blade while possibly encountering low speed stall on the retreating blade. Also, large local fluctuations of blade loading are caused by the vortices from preceding blades. An understanding of these complex phenomena was considered essential to the design of rotors possessing maximum lifting power while having minimum vibration and reduced structural fatigue loads.

Puma XW241 in July 1980

In support of this research objective, XW241 was employed in a successive number of classic experiments, using specially modified main rotor blades, to gain an understanding of rotor performance aerodynamics – the first time this had been done in flight. A number of blade configurations were examined, including innovative cambered aerofoils, and culminating in a full set of blades having swept tips . Much of the flight work was considered to be high risk, since the aircraft was often required to operate significantly outside its design flight envelope, and great care was taken in the monitoring of blade and structural loads using ground telemetry and frequent mechanical inspection. The blade aerofoils tested were found to significantly improve the performance of the aircraft as a whole while reducing its noise signature.

Puma XW241 at Bedford Airfield

The analysis of these measurements made an invaluable contribution to the development of the theoretical models of rotor systems – an essential input to the design of advanced rotors – and facilitated the design of the sophisticated swept rotor blades incorporated in the record breaking Lynx helicopter and, subsequently, the rotors of recent military aircraft, such as the Merlin.

The work was a significant input to the British Experimental Rotor Programme for which a Queen’s Award for Industry was made to the Defence Research Agency and Westland Helicopters.

Similar programmes were later carried out on this aircraft into the associated aerodynamics of tail rotors, and an investigation was made into the in-flight kinetic heating of rotor blades, an issue related to the understanding and modelling of blade ice formation.

Research interest later moved towards methods of assessing rotary wing handling qualities and the development of comprehensive flight simulation mathematical models for the Puma and other helicopters. The assessment work was carried out on XW241 using carefully designed pilot control inputs and the selection of specific flight conditions. The analysis of the response of the aircraft also included aerodynamic data from the rotor system and has provided a richer understanding of the nature of the flight mechanics involved. In turn this work has contributed strongly to modern design tools for helicopters and their handling qualities.

Where is it now?

At the end of its long serviceable life, XW241 was used as an EMC test-bed by DRA/DERA and, finally, QinetiQ, before being donated to the FAST Museum where it is now on static display.  [IS IT STILL HERE? NOT LISTED ON FAST MUSEUM AIRCRAFT PAGE – https://airsciences.org.uk/aircraft-on-display)

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