Ah, It seems it was a problem with the biplane tail skid from the firespitter mod. It provides more resistance than a wheel, and was preventing my biplanes from budging an inch with such low thrust. Once I switched to a normal back wheel my planes work exactly as you described. But the engines used to have much higher stationary thrust, why the change? Is it more realistic this way? Thank you so much for this mod, I love combining it with a bunch of other mods to make ww1-ww2 dogfights.