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Minimum Sink is one of the cardinal speeds which it is important to know when flying a glider of any kind. Min sink, as it is also known, is the speed at which the aircraft loses altitude (in still air) at the slowest rate. This is the airspeed at which to fly to maximize airtime, to stay aloft for the longest time. It is also the best speed to fly when flying downwind (all else being equal), and yields the best climb rate when flying in lift, either thermals or ridge lift.

For a typical hang glider, stall speed is 18-20 mph, min sink is about 21-22, trim speed is 22-24, and best glide speed is somewhere in the 25-30 mph range. Flying at minimum sink speed will keep one aloft longer than flying at best glide, but one will cover less distance across the ground. One must use careful judgement when determining which is more desirable.

These airspeeds can be determined using instruments while flying in still air and recording airspeed vs. descent rate. A plot of these values is called a polar curve, and is an indispensable aid to pilots when racing or trying to maximize any aspect of gliding flight.

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