Aerodynamics and Design for Ultra-Low Reynolds Number Flight

FIGURE 3.10 NACA 0002 and NACA 0008 boundary layer development at Re=6000.
Chapter 3
A second effect of increasing thickness is a more rapid reduction in the lift curve slope
once past the quasi-linear lift range, attributable to earlier and more severe trailing edge
separation. The NACA 0002 is fully attached up to stall, however the NACA 0008 is
not, as presented in Figure 3.5. Figure 3.5 begins at α=2.0, the edge of the quasi-linear
range. The flow is almost fully attached at α=2.0, with visible trailing edge separation at
95% chord, but by α=3.0 there is significant separation at 75% chord. This moves to
60% at α=4.0. These separated regions result in a large displacement of the flow within
the aft boundary layer, increasing the decambering effect and resulting in larger
reductions in the lift curve slope compared to the fully attached NACA 0002.
3.4 Effect of Camber
The boundary-layer decambering effect just described suggests that the introduction of
camber may offer the potential for significant performance gains over a simple flat plate.
The effects of camber do not differ significantly from those at much higher Reynolds
numbers, but the fact that the detailed geometry is still an effective driver of performance
at such low Reynolds numbers is itself a useful conclusion.
α = 4 deg.
0 deg. 2 deg.
α = 4 deg.
0 deg.
2 deg.
A comparison of the NACA 0002 and NACA 4402 airfoils indicates the gross effects of
camber on performance. Lift curves and drag polars are provided for Re=1000,
Re=2000, and Re=6000 in Figures 3.11 and 3.12. As at higher Reynolds numbers, the
first order effect on the lift curve is a translation towards lower zero lift angles of attack
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