Dynamic Stability Derivatives
Abstract
Measurement and interpretation of dynamic stability derivatives are examined in the context of Aerodynamic Modeling (the technical discipline that deals with representing vehicle aerodynamic responses in a mathematical form consistent with the analyst's needs). Several such techniques are discussed with emphasis on the classic stability derivative approach. Importantly, complications imposed by unsteady aerodynamic responses (those in which the forces and/or moments cannot be taken as simply related to the aircraft's instantaneous motion state) are considered. Furthermore, the implications of using wind-tunnel dynamic testing equipment that cannot isolate the effects of particular motion variables are addressed. The stability derivative concept is still the most widely used aerodynamic modeling technique and is based on two fundamental assumptions: 1) instantaneous aerodynamic loads depend only on the instantaneous values of the motion variables; and 2) they vary linearly with the motion variables. However, these assumptions prohibit a precise representation of unsteady aerodynamic responses to an arbitrary motion input. Specifically, stability "derivatives" with respect to the rates-of-change of the state variables are shown to be terms of an asymptotic expansion of the aerodynamic response to an arbitrary motion input. Therefore they are valid only in the limit as the non-dimensional motion rates approach zero. The insight gained from adopting this point of view is shown to be useful in laying out an experimental program and interpreting the results. Discussions of dynamic testing techniques in the wind tunnel; data reduction methodology; assessment of the validity of the resulting dynamic derivative model; and means for properly expressing measured stability derivatives with respect to the desired flight dynamics coordinate system are provided.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 2015
- Accession Number
- ADA624267
Entities
People
- Jerry E. Jenkins
Organizations
- Air Force Research Laboratory