From: "Sean H. Breheny" > Why are you saying the AOA would be so small? There shouldn't be anything > to stop the pilot from raising the nose and increasing the AOA, as far as I > see it. AOA is directly related to airspeed for a given AOA, the glider will fly at a given airspeed. This is a property of the airfoil used and cannot be changed (except for w/ flaps and other devices that adjust the shape of the wing). If the pilot raises the nose, he will increase the AOA and slow down. This is all dependant on the power to weight ratio of the aircraft in question, of course. Aircraft with lots of power may maintain a given AOA at a high pitch angle. For sailplanes, however, a given AOA (and pitch angle - without power, they're equivalent) will result in a given airspeed. > Do sailplanes have a "best climb" speed? I thought that was for powered > airplanes only, as a compromise between engine power, lift, and drag. > AFAIK, a sailplane cannot perform a sustained climb relative to the air > around it, so technically there is no such thing as a sustained climb for a > sailplane. A thermal just means that the air around the sailplane is rising > faster than the sailplane is falling in it. There are two "performance" speeds in gliders. You have the minimum sink speed (usually 5 or so knots above stall) which the glider uses to stay in the air for the longest period with a given altitude. This is equivalent to maximum climb angle in a power plane (Vx, I think). The second speed is best L/D speed, the speed at which the lift to drag ratio is greatest. At this speed, the glider will travel the greatest distance over the ground for a given altitude loss. This is equivalent to best rate of climb in a power plane (Vy?). Minimum sink is used for thermalling because it permits a tighter circle in the thermal. Best L/D is used between thermals or on long cross-country runs. Your definition of a thermal is correct, in that a positive rate of climb relative to the surrounding air is impossible. However, minimum sink speed results in the least altitude lost per unit of time in the thermal and thereby permits more efficient use of the rising surrounding air mass. The lower the glider's sink rate, obviously, the higher the rate of climb in a thermal, when compared to a glider with a higher sink rate. - Robert -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.