You're probably using more pitch than you need to. Stationary flips are all about timing, not jamming the left stick around. If you use too much pitch, and collective you'll bog the motor and lose headspeed. On the sim, try flipping with as little collect ive and as little pitch as possible to get a feel for what you need. Remember, in a flip you only need a few degreees negative, about the same as you'd use to hover inverted. Start your flip by pulling back on the right stick. You don't need it to rotate fast. At the same time, add a little positive pitch to get it climbing, just to give yourself an advantage. As the nose approaches vertical, center the left stick to give zero pitch. This will accomplish two things: one, it will keep the heli in one place, two, it will increase your headspeed. As it goes inverted pull the left stick just a bit below center. If your pitch curves are set up right tha's all you'll need. Then center the stick again when the nose is pointing down and smoothly add positive pitch as it becomes upright. Don't panic, and don't overcontrol. THe heli is designed for this move. As long as you do your job right, so will the heli. Practice this move a bit high until you get the feel for it.