Modern launch vehicles are long slender bodies with high flexibility and hence are prone to aeroelastic instabilities
during their flight. These instabilities may adversely affect
the performance of the vehicle or may even cause its failure, It
is therefore necessary that a rigourous investigation of the
aeroelastic behaviour of the vehicle is done at the design stage
itself to ensure that the vehicle is free from such instabilities
during its atmospheric flight,
Important among the instabilities that a launch vehicle may
experience are response to ground wind loads, divergence,flutter
06 control surfaces and panels, buffeting, coupled oscillations
and fuel sloshing, Because of the complex nature of the
aerodynamic input forces and aerodynamic-elastic-inertial
interactions involved in most of these phenomena, it is often
difficult and at times almost impossible to predict accurately
the behaviour of the flight vehicle through theoretical means,
Hence the designer has to take recourse to experimental means
involving design and testing of aeroelastically scaled models,
In this technique an aeroelastic model in a suitable wind tunnel
is used as a mechanical analog of the mathematically complex
problem requiring solution, The model in the wind tunnel first
generates the correct aerodynamic input forces, and the measured
response of the model to these input forces is then used to
predict the response of the actual vehicle using appropriate
scaling laws, The importance of scaled models in the study of
aeroelastic problems of launch vehicles is amply demonstrated by
the work done in this direction at the aerospace research
Laboratories of NASA and elsewhere,
With the importance of aeroelastic problems in the design of
aerospace vehicles in mind, the Structures Division of the
Laboratory, with active support from the Aerodynamic Division*
initiated work on aeroelastic model studies in the early 1970's,
mainly to understand the technique of aeroelastic model design
and fabrication and to gain experience in aeroelastic testing.
Early works in this direction were related to aircraft, involving
design and testing of flutter models of typical aircraft wings
(Ref.1&2).The know-how gained out of these studies was thus very
useful while undertaking studies related to aeroelastic problems
of launch vehicles for the ISRO in the early 1970°s, This paper
gives a brief review of the past and current aeroelastic studies
at NAL on Satellite Launch Vehicles SLV3, ASLV and PSLV
developed/being developed by the ISRO
