Space/Science — HabitableZone

Space/Science » in reply to Stick a couple of aero flaps on it if you have to.

Hypersonic aerodynamics are very nonintuitive
Gary — (archived)

The rule-of-thumb with hypersonic aerodynamics is one's intuition is the exact opposite of reality. For example, a flat plate in normal incidence is statically stable in hypersonic flow. The stability is driven by the shockwave and not by vorticity or viscosity. Hypersonic vehicles tend to have poor lift. The way to increase the L/D ratio is to devise a geometry that has a reduced drag while keeping the original lift. Just sticking a flap on the Apollo CM would increase the drag and probably offer no significant increase in lift (again this is counter intuitive).

The Apollo AS-501 test flight came in at 11.17534 km/sec inertial at 121.92 km (lunar return velocity). The average L/D for AS-501 based on flight data was 0.37 . An axisymmetric biconic entry vehicle can achieve a maximum L/D of 1.0 . A manned return-from-Mars vehicle should be either a lifting body, biconic or a raked conic.

Gary

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