5.8.1 Static aeroelastics

In classical aerodynamic design, the aircraft shape is designed for one design point M(: (cruise Mach at a given weight and altitude). Knowledge based margins provide the ability to cope with the off-design points. Some still cover the (cruise) flight regime (like Мод = maximum operat­ing Mach. Mcs e subsonic cruise Mach, other aircraft weights for begin of cruise or end of cruise, altitude variations…). Others concern exceptional points which do not occur in normal cruise, but only e g. for emergencies like MD (dive Mach).

Aerodynamics assume the geometry to be rigid Once the aerodynamic shape is fixed and the aerodynamic loads arc known, structure loads arc determined, structure is designed and static aeroelastic deformation is calculated. This deformation at the design point is taken into account when the shape to be built is defined. The procedure reestablishes the designed aerody­namic shape at the design point flight loads (Mc. design weight and altitude). For any deviation of the design point the aircraft will have a different shape. This deviation becomes important if the wing is not very stiff and if the deviations from the design point are large. Both occur for SCTs with thin wings and multipoint design conditions.

To find the best compromise for an clastic wing flying at different design points, acroc – lastic deformation must be considered in the aerodynamic design. For aerodynamics this can be a rather simple formulation, like a beam formulation for a slender arrow wing or an OFW. or a simple shell formulation for some kind of delta wing, including bending and torsion. The diffi­cult problem is the ‘simple” estimation of structural values because this requires simultaneous estimation of loads, mass distribution and structural thicknesses.

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