One inconvenient peculiarity of the rotary was that, as a heavy, rapidly spinning mass, it imposed gyroscopic forces upon the airplane. Fortunately, these forces were only moderately strong, for a number of reasons. The single-engine fighters were very compact, and their engines were close to the airplane’s center of gravity. The rotating mass of the engine, furthermore, was concentrated near the crankshaft because the cylinder walls and heads were remarkably thin. Finally, rotaries did not spin very fast; 1,200 rpm was typical.