WIND-TUNNEL EXPERIMENTAL METHOD. FOR AERODYNAMIC COEFFICIENTS

Once the baseline configuration of an aircraft is selected, the WT experiments are conducted on the (physically) scaled (down) models of the vehicle. WT testing mainly yields the aerodynamic coefficients. Static rigs are used to obtain the steady-state aerodynamic characteristics. The tests are conducted in low-/high – speed WTs. The effectiveness of various control surfaces is tested. To determine the dynamic derivatives, the forced oscillation test rigs are used. The aircraft’s physical model is oscillated and force/moment measurements are made. Rotary rigs are used to determine the characteristics at high AOA and AOSS.

To extend the force and moment coefficient measurements made in the WT for small-scaled models to full scale, it is necessary to match the similarity parameters, e. g., Reynold’s number, Mach number, and Froude number. The Froude number is

related to the ratio of inertia force to gravity force as mass *acceleratlon = YL which is a

mass * g dg

dimensionless quantity.

The matching of Reynold’s number is essential at low-speed tests while Mach number is matched for WT tests carried out at high speeds. Generally, it suffices to match these two similarity parameters for models held fixed within the WT. For a free-flight model, however, it becomes necessary to match the Froude number.