9 out of 10 control systems on the B-24 were hydraulic. Back then Hydraulic fluid was flammable. While the Liberator had farther range, speed & weight carrying capabilities due to the "Davis" wing,the B-17 could take much more of a pounding and still make it home.I read a study recently comparing all factors of the two planes and the B-17 comes out ahead do to less maintance issues,thus greater "availability" for missions.