A hybrid airfoil design method for icing wind tunnel tests

Modern commercial aircraft wings are far too large to be tested full-scale in existing icing wind tunnels and ice accretion scaling methods are not practical for large scale factors. Thus the use of hybrid scaling techniques, maintaining full-scale leading-edges and redesigned aft sections, is an attractive option for generating full-scale leading-edge ice accretions. The advantage lies in utilizing reduced chord models that minimize blockage effects in the icing tunnels. The present work discusses the design of hybrid airfoils with large scale factors that match the ice shapes of the full-scale airfoils predicted by LEWICE. Assessments of the effects of scale factor, extent of the full-scale leading-edge, nose droop angle, zero-angle of attack pitching moment coefficient (C_m0), and droplet size are also presented. Hybrid or truncated airfoils are shown to produce ice shapes accurately, even at angles of attack different from the design angle of attack with the proper application of either flap, adjusted test angle of attack, or both. Further results suggest that hybrid circulation does not need to match full-scale circulation in order to match ice shapes, resulting in decreased loading for higher scale factor hybrid airfoils. Matching the flowfield around the hybrid airfoil to the full-scale flowfield provided a superior method for predicting ice shape agreement, stagnation point location being a first order and suction peak magnitude a second order parameter. This goal can be accomplished by varying the aft geometry, through C_m0 and nose droop angle.