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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.
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.
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.
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.
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