Like BK said, not all planes will do a knife edge or will not do them very well. All my Extras do them great and I have a Hots that I did a few mods on and it will pull a knife edge loop on those days I have the guts to try them. My old Bridi Kaos didn't hold them very well, the tail moment is too long and the fuse is too narrow. On my last rebuild I made some mods. I added to the rudder and made a big long fin. That did the trick, now it will hold one for a long time. At full power You pull up at about a 20 degree up angle then start the roll with the ailerons and start adding in the rudder slowly until you are in the knife egde. then just hold. If the plane starts to couple you have to add in some elevator to compensate.