Glide Ratio
When flown at a constant speed in still air a glider moves forwards a certain distance for a certain distance downwards. The ratio of the distance forwards to downwards is called the glide ratio. The glide ratio is numerically equal to the Lift-to-drag ratio under these conditions; but is not necessarily equal during other manoeuvres, especially if speed is not constant. A glider's glide ratio varies with airspeed, but there is a maximum value which is frequently quoted. Glide ratio usually varies little with vehicle loading however, a heavier vehicle glides faster, but maintains its glide ratio.
Glide ratio is also known as glide number, finesse and is the cotangent of the downward angle- the glide angle. Alternatively it is also the forward speed divided by sink speed (unpowered aircraft):
Read more about this topic: Gliding Flight
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