DESIGN OF AIRFOILS AT LOW REYNOLDS NUMBERS.

A presentation is given on the design of airfoils at low Reynolds numbers (100,000 less than RN less than 500,000), specifically those applicable to radio-controlled model sailplanes. Two common types of airfoil lift and drag hysteresis are illustrated and explained in terms of the behavior of the upper-surface transitional separation bubble which is commonly present at these low Reynolds numbers. The theoretical section characteristics of several airfoils predicted by the Eppler computer program for the design and analysis of low-speed airfoils were compared with the recent experimental data of D. Althaus.