Stefan,

It sounds like your motor is a bit weak. What is your Fox turning with that 9x4 prop? Also, what prop is it? How heavy is your plane?

Be sure your elevator trim is level! (just checking, I'm sure you know this already). When I say "level", I actually mean just slightly up (1/16 to 1/8") from absolute neutral. It's scary how little elevator travel is actually needed to make the plane turn, so setting up your elevator trim won't be easy until it's airborne.

From my experience, it really helps to run when throwing a Gremlin. Have a helper do this for the first flight and tell him to throw it AWAY and UP SLIGHTLY. A 30 degree angle is good. Once released, the plane will still need a little space to gain speed, but it will be about a second until you can start flying it.

With higher power setups, engines turn a 9x4 prop anywhere from 18K to 21K on the ground, and launching a 2.25 lb plane is simply a matter of letting go. With less power and / or more weight, you should run to launch, and be extra careful to manage that prescious altitude until speed is gained.