INTRODUCTION TO AEROELASTICITYScience which studies the mutual
interaction between aerodynamic forces and elastic forces, and the
influence of this interaction on flight vehicle design.
This definition is not complete , since many important
aero-elastic phenomena involve inertial forces as well as
aerodynamic and elastic forces.
Static aero elasticity Dynamic aeroelasticity
Divergence, load distribution etc Flutter, buffetting*
AEROELASTICITY *
What is DIVERGENCE ?VKFInteraction between aerodynamic and
elastic forcesDeformation of body/wing due to aerodynamic forces
produce more incidence angle and hence more aerodynamic loads
Speeds below critical value (divergence speed), the disturbing
force due to aero loads will be less than restoring force offered
by stiffness. Hence stable equilibriumBeyond critical speed,
Disturbing force > restoring force, hence divergenceFor WingAt
critical speedMo+L*ec = K , ec is the distance between elastic axis
and aerodynamic axisL= q*CLc=q*(dCL/d)c*(+), c is the chord
lengthMo= qCmo*c2=qec2(dCL/d)/(K- qec2(dCL/d) )
qcr=K/ ec2(dCL/d) AEROELASTICITY - contd*
Control Effectiveness:Influence of elastic deformation of the
structure on the controllability of vehicle
Control system reversal:The intended effects of displacing a
given component of the control system are completely nullified by
elastic deformation of the structure
Load Distribution:Influence of elastic deformation on the
distribution of aerodynamic pressure over the structure
Aeroelastic effects on StabilityInfluence of elastic
deformations of the structure on dynamic and static stability of
flight structure*
Tachoma Narrow Bridgetx Aircraft wingWHAT IS FLUTTER ?Dynamic
aero-elastic instabilityInteraction between aerodynamic, elastic
and inertia forcesInteraction of flexural and torsional
motionsHarmonic oscillations with increase in amplitude
(exponentially)Fatigue failure PreventionDe-couple the constituent
motionsInertial coupling prevented by coincidence of CG with
elastic axisAerodynamic coupling is eliminated when aerodynamic
centre coincide with elastic axis
AEROELASTICITY - contd*
BuffetingTransient vibrations of flight vehicle components due
to aerodynamic impulses produced by the wake behind wings, fins and
other components
Dynamic ResponseTransient response of flight vehicle structural
components produced by rapidly applied loads like gusts,
gunreaction, abrupt control motions, moving shockwaves, landing,
etc *
