The Accelerometer Methods of Obtaining Aircraft Performance from Flight Test Data (Dynamic Performance Testing)

There are, in general, two basic methods of obtaining aircraft performance from flight test data. The first of these methods, the Direct method, is to fly a particular maneuver of interest and mathematically correct this maneuver to a given set of standard conditions. Several similar maneuvers at different flight conditions are then combined in a composite map representing one aspect of the aircraft performance. The Indirect method is more subtle and has its basis deeper in theory. By this method, a group of aerodynamic and propulsion parameters are developed which in themselves are only numbers and do not represent performance. These parameters are not tied to a specific maneuver or maneuver type, but in general relate the physical forces required to achieve a certain flight condition. Such parameters for an aircraft would be the drag coefficient, lift coefficient, thrust available, fuel flow requirements, etc. However, these parameters can be combined with known facts about the airframe and propulsion system in such a fashion as to compute airplane performance. With the advent of highly accurate accelerometers, the dynamic maneuvers have become attractive for development of aerodynamic data when obtaining aircraft performance using the Indirect Method.