Thank you all for the reply.

I'm using a OS 50 with 11x7 turning about 13700 rpm. SIG 15% fuel.

The plane fly quite fast and have good vertical pull although not unlimited. I've try to enter with half throttle, apply full rudder and throttle up.....dosen't change anything, the plane still drop. Is this conclude that my plane just wouldn't knife edge?

ALan Pang