Applications

Free-flight models are complementary to other tools used in aeronauti­cal engineering. In the absence of adverse scale effects, the aerodynamic characteristics of the models have been found to agree very well with data obtained from other types of wind tunnel tests and theoretical analyses. By providing insight into the impact of aerodynamics on vehicle dynam­ics, the free-flight results help build the necessary understanding of crit­ical aerodynamic parameters and the impact of modifications to resolve problems. The ability to conduct free-flight tests and aerodynamic mea­surements with the same model is a powerful advantage for the testing technique. When coupled with more sophisticated static wind tunnel tests, computational fluid dynamics methods, and piloted simulator technology, these tests are extremely informative. Finally, even the very visual results of free-flight tests are impressive, whether they demonstrate to critics and naysayers that radical and unconventional designs can be flown or identify a critical flight problem and potential solutions for a new configuration.

The most appropriate applications of free-flight models involve eval­uations of unconventional designs for which no experience base exists and the analysis of aircraft behavior for flight conditions that are not easily studied with other methods because of complex aerodynamic phe­nomena that cannot be modeled at the present time.[464] Examples include flight in which separated flows, nonlinear aerodynamic behavior, and large dynamic motions are typically encountered.

The following discussion presents a brief overview of the historical applications and technological impacts of the use of free-flight models for studies of flight dynamics by the NACA and NASA in selected areas.

The most important applications have been in

• Dynamic stability and control.

• Flight at high angles of attack.[465]

• Spinning and spin recovery.

• Spin entry and poststall motions.