Structural Dynamics, Aeroelasticity, and Certification
So, with all of this background on theoretical methods, what are some of the ways aeroelasticity and structural dynamics analyses are actually used? We must recall that for every aircraft, there may be dozens to several hundred combinations of fuel and payloads that must be verified as stable within the aircraft’s flight envelope before clearance for flight is given. The use of computational results is crucial because we cannot possibly test every combination of fuel and hardware mounted on the fuselage and wings (e. g., stores, armaments, fuel tanks). Computational results then become our main work tool for every go/no-go decision made in flight-testing and ultimate airplane certification for flight.
To proceed with this monumental set of tasks, we first need to identify the most critical combinations (i. e., those with the lowest flutter speeds). If possible, these should be compared with previous experience in terms of computation and flighttesting. Once the most critical configurations are identified, we set them aside for special wind-tunnel and flight tests. In particular, we need to ascertain the flutter mode’s shape, frequency mF, speed UF, and severity g’ = dg/dU, all evaluated at the flutter speed (i. e., where g vanishes). Identification of all four items allows us to distinguish between various cases with comparable flutter speeds and, together with previous experience, to decide about further needed ground and flight tests to verify computations and flight clearance.