UM...depends on the plane....A LOT!

BTW a ST .50 (I didn't know they made that size yet), is a small plane. But it should hover...a Saito .82 would be barely enough, but I am just guessing...depends on the weight. That target for extreme 3D is as close to 2:1 as you can get (thrust to weight). Although I have never seen a small plane actually reach a 2:1 ratio other than foam, the bigger ones ARE easier to hold a hover with, (100cc and larger).