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Old Dec 05, 2012, 03:02 AM
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prefer lift over drag anyday
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Joined Jun 2005
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When you speak of auto soaring, whether it was the bird toy in thermals or the automatically turning into a slope wind, it doesn't make sense to me. Can you explain further?

For slope soaring, maybe you imagine that if you fly along the slope with the hill on your right, you would feel wind blowing in from your left wing (the wind that is hitting the slope). This is not the case - you would not feel any sideslip from wind relative to the ground. Sideslip is measured relative to the aircraft body. Aerodynamic forces do not care about what direction or speed the ground is moving beneath you - only the relative air on the body.

For thermal soaring, I do know of a trick to make a glider "auto soar" by carefully tailoring wing twist along the span. Basically you design the wing to stall asymmetrically and then trim it to fly a very stable glide near stall. When such a plane encounters a vertical gust which increases AOA on the plane, it will always stall one wing first, creating a nice turning action that causes it to naturally turn around updrafts. This has been successfully designed, built and flown. But this requires careful tailoring of both airfoil section and spanwise lift distributions at low reynolds numbers, along with a very good understanding of the dynamics (have to have stable spiral mode) of free flight models.
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