What speed do planes need to go to stay in the air?

The speed a airplane needs to go to stay in the air, depends on the plane. Each plane has different factors, such as weight, manureverability and the conditions which it is flying in.

In general, the speed a plane needs to stay at, is the level of it's "Stall Speed". A "Stall", is when a airplanes engine/propeller stops moving. This gradually slows down the aircraft, which then will bring the plane lower and lower. Also the planes "Flaps", the parts of their wings that can tilt, can change the speed and how long it will travel until it will come to ground level.

google Stall Speed and the plane you are inquiring about to get the exact figures.