Please tell me why I cannot take off

[gnomechompsky]

After trying about 20 times I still cannot take off in a Spitfire on a grassy runway (playing a mission in the Team Fusion campaign). The plane never seems to get up enough speed despite throttle being maxed. I am able to keep the plane roughly in a straight line using the rudder but as I lift off the front wheels it always barrel rolls left and the wing digs into the ground.

I am able to take off with other planes on a flattened runway so what am I doing wrong?