Aerodynamics and Design for Ultra-Low Reynolds Number Flight

Chapter 3
Further analyses have investigated the possible benefits of varying the magnitude and
distribution of camber. The design space has been explored using nine airfoils spanning
2% to 6% maximum camber located at 30%, 50%, and 70% chord. All of the sections
are 2% thick NACA 4-digit profiles. All calculations have been completed at
Re=12,000.
The lift curves provided in Figure 3.13 are for 2% and 4% camber at all three of the
chord locations. In both plots, the aft shift of maximum camber results in a less severe
reduction of lift past the quasi-linear range, higher attainable lift coefficients, and higher
lift-to-drag ratios. This correlates with reduced trailing edge separation for a given angle
of attack. The aft cambered sections exhibit separation at a lower angle of attack, but the
growth of separation is retarded. As the angle of attack increases, the majority of the
suction side experiences less adverse gradients than a similar section with forward
camber. The region of separation contained aft of the maximum camber location by
maintaining less adverse gradients ahead of it. The aft concentration of camber
functions like a separation ramp in the pressure distribution [22].
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C l
0.7
0.6
0.5
0.4
0.3
0.2
0.1
NACA 2X02 Lift Curves
Re=12000
NACA 2302
NACA 2502
NACA 2702
0 1 2 3 4 5
α (deg.)
0 1 2 3 4 5
α (deg.)
FIGURE 3.13 Lift curves for 2% and 4% cambered NACA 4-digit airfoils at Re=12000.
C l
0.7
0.6
0.5
0.4
0.3
0.2
0.1
NACA 4X02 Lift Curves
Re=12000
NACA 4302
NACA 4502
NACA 4702