This weekend I took the P51 mustang and made it a sloper. To do this I customized the stock P51 with these specs.
power plant: none powered.
CG: x=0, y=5.50, z=0
The rest are stock.

I found I could roll launch. After launch I could retract the gear and fly around. I could even come in and let down the gear and to a touch and go. I would just roll back down the slope and relaunch.

The wind need to be blowing around 20 mph.