Gap and Stagger Effects on Biplanes with End Plates: Part II

Document Type

Conference Paper

Publication Date


Publication Source

47th AIAA Aerospace Sciences Meeting including The New Horizons Forum and Aerospace Exposition


Modern flow diagnostics applied to a very old aerodynamic problem has produced a number of intriguing new results and new insight into previous results. Part I demonstrated large differences in lift due to changes in gap and positive and negative stagger. Part I also used downwash to elucidate some of the reasons behind this behavior; however it is noted that the inviscid assumption was not adequate to capture this behavior in the theoretical and computational models used. Part II will present a generalized empirical method for the prediction of lift coefficient as a function of gap, stagger and angle of attack determined from the parametric force balance results. The resulting empirical approach allows for a rapid determination of CL for a biplane having different gap, stagger, AR and taper without the need for a complete viscous flowfield analysis.

The momentum deficit method and Kutta-Joukowski theorem (Trefftz plane Stereo PIV) were applied to the PIV data for the purpose of measuring the drag and lift force. The accuracy of these methods was found to be comparable to the force balance measurements. Trefftz-plane Stereo PIV shows that the positive stagger configuration has significantly different flow morphology. The spanwise and vertical velocity components in the wake can be largely manipulated by the presence and shape of the endplates and the stagger condition of the upper wing. A dramatic lift slope change (C ) was found almost universally on all biplane models tested at an angle of attack around 5o and appears to defy explanation based on the usual viscous arguments.




Permission documentation is on file.


American Institute of Aeronautics and Astronautics

Place of Publication

Orlando, FL