Since Wankel engines operate at a relatively high rotational speed, at 6,000rpm of output shaft, the Rotor makes only 2,000 turns. With relatively low torque, propeller driven aircraft must use a propeller speed reduction unit to maintain propellers within the designed speed range. Experimental aircraft with Wankel engines use propeller speed reduction units, for instance the MidWest twin-rotor engine has a 2.95:1 reduction gearbox. The rotational shaft speed of a Wankel engine is high compared to reciprocating piston designs. Only the eccentric shaft spins fast, while the rotors turn at exactly one-third of the shaft speed. If the shaft is spinning at 7,500rpm, the rotors are turning at a much slower 2,500rpm.