Low Reynolds Number Testing of the AG38 Airfoil for the SAMARAI Nano Air Vehicle

Abstract

Development of flying vehicles in the centimeter-scale size range based on fixed wing, rotary wing, or flapping wing concepts has met with renewed interest in recent years. The Defense Advanced Research Projects Agency’s Nano Air Vehicle program sought to develop vehicles of 7.5 centimeter length and 10 grams total mass that can fly for 20 minutes with a range of 1 kilometer. Under this program Lockheed Martin participated in wind tunnel studies of an AG38 airfoil for application to a mono-wing rotorcraft at very low chord Reynolds numbers (Re) of 15K to 60K. This paper discusses the experimental models, instrumentation and methodology used to obtain data in this challenging low Re regime. A summary of experimental aerodynamic data is presented for the AG38 airfoil in clean condition and with a turbulator. A turbulator is developed for operation at Re 20K to lower drag and reduce undesirable non-linear lift and moment behavior associated with laminar separation bubbles. Experimental data are compared to computational results from XFOIL for both forces and pressures showing good correlation. Data are presented for plain and split flaps at Re from 15K to 40K showing that these flaps are effective for airfoil lift control.