Quote:
Originally Posted by Otto
NASA guy told me ~8 degrees was max slope on aft body, to avoid undue separation and turbulence. German sailplane research showed essentially that, as seen in oil smear tests in wind tunnel.
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Remember,they're talking about sections or bodies of revolution with very low thickness and high fineness,and they're operating in turbulent free air,trimmed for max efficiency,at altitude.
Also,during landing and take-off the wings can survive angles of attack close to stall,and with turbulators ( vortex generators ) they can push that angle another 6-degrees.
With suction slots,wings can maintain attached flow up to around 40-degrees.
Mairs research ascertained that for automobiles,22-degrees would be the limit.
You'll see this angle with Klemperer's Cd 0.16 'minivan',Walter E. Lay's Cd 0.12 'pumpkin seed'.It's also the terminal angle for the L/D 2.5 streamline body which Hucho references as the drag-minimum in ground-reflection,developed by Ludwig Prandtl under inspiration from Edmund Rumpler.
And before you say it,some of the exotic fancy laminar sections with remarkable low drag can suffer up to 300% drag increases when used as 'cars'.