NASA Technical Paper 1865
Design and Experimental Results for a
Flapped Natural-Laminar-Flow for General Aviation
M. Somers Virginia
Langley Research Center Hampton,
National Aeronautics and Space Administration
Scientific end Technical Information Branch
INTRODUCTION Research on advanced-technology’ airfoils for general aviation applications has received considerable attention over the past decade at the NASA Langley Research Center. The initial emphasis in this research program was on the design and testing of turbulent-flow airfoils with the basic objective of producing a series of airfoils which could achieve higher maximum lift coefficients than the airfoils in use on general aviation airplanes at that time. For this series of airfoils, it was assumed that the flow over the entire airfoil would be turbulent, primarily because of the construction techniques in use (mostly riveted sheet metal). A summary of this work is presented in reference 1. While these new NASA low-speed airfoils did achieve higher maximum lift coefficients, the cruise drag coefficients were essentially no lower than the earlier NACA four- and five-digit airfoils. Accordingly, the emphasis in the research program has been shifted toward natural-laminar-flow (NLF) airfoils in an attempt to obtain lcwer cruise drag coefficients while retaining the high maximum lift coefficients of the new NASA airfoils. In this context, the term “natural-laminar-flow airfoil” refers to an airfoil which can achieve significant extents of laminar flow (?30-percent chord) solely through.’ favorable pressure gradients (no boundary-layer suction or cooling). Research on natural-laminar-flow airfoils dates back to the 1930’s at the National Advisory Ccmmittee for Aeronautics (NACA). (See ref. 2.) The work at NACA was culminated with the 6-series airfoils (ref. 3). The 6-series airfoils were not generally successful as low-drag airfoils, however, because of the construction techniques available at the time. The advent of composite structures has led to a resurgence in NLF research. The initial applications were sailplanes, but recently, a number of powered general aviation airplanes have been constructed of composites - most notably, the Bellanca Skyrocket II (ref. 4) and the Windecker Eagle (ref. 5). In Europe, powered composite airplanes have also been produced. One such aircraft, the LFU 205, used an NLF airfoil specifically tailored for its mission (ref. 6). Thus, the introduction of composite construction has allowed aerodynamicists to design NLF airfoils which achieve, in flight, the low-drag characteristics measured in the wind tunnel (ref. 7). The goal of the present research on NLF airfoils at Langley Research Center is to combine the high maximum lift capability of the NASA low-speed airfoils with the low-drag characteristics of the NACA 6-series airfoils. As part of the present research, an NLF airfoil, the NLF(l)-0416, was designed using the method of reference 8 and verified experimentally (ref. 9) in the Langley Lm-Turbulence Pressure Tunnel (LTPT) (ref. 10). Based upon the success of this airfoil and the excellent agreement between the theoretical predictions and the experimental results, a second, more advanced, airfoil was designed using the method of reference 8. An experimental investigation was then conducted in the Low-Turbulence Pressure Tunnel to obtain the basic low-
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speed, two-dimensional aerodynamic characteristics of the airfoil. The results have been compared with the predictions from the methcd of reference 8. Use of trade names or names of manufacturers in this report does not constitute an official endorsement of such products or manufacturers, either expressed or implied, by the National Aeronautics and Space Administration.
Values are given in both S1 and U.S. Customary Units. Measurements and calculations were...