On the Stability of Flight Vehicles in the Low Reynolds Number Non-Linear Regime

This report addresses some issues associated with dynamic stability of vehicles flying at speeds such that the flight Reynolds number is of the order of a few hundreds of thousands. In particular the wing loading and speed are such that the flight occurs at relatively high angles of attack. Under these circumstances the aerodynamic characteristics of the vehicle are likely to be non-linear in nature. Here the nature of the flight itself could be significantly different from that expected under those conditions where the aerodynamic characteristics are linear. As a result of this study the authors conclude that the usefulness of the linearized stability analysis is limited when applied to flight at high lift coefficients at low Reynolds numbers. This study highlights the need for additional reliable data in this Reynolds number range in several forms: (1) Static aerodynamic characteristics; Dynamic stability derivatives measured with small amplitude at a variety of set points; and (3) Some trajectory simulation data using a dynamic, perhaps a magnetic model suspension system, to probe for unexpected, non-linear aerodynamic coupling.