Bruno Nagler began wind tunnel experiments into helicopter design in 1926 and developed the first practical swash plate.The Nagler NH-120 was developed to test the idea of counteracting rotor torque with a small separate rotor. The engine was mounted above the main rotor on a shaft, and the anti-torque rotor was mounted above both. The NH-160 had a conventional helicopter engine and rotor layout, with the exception of the smaller anti-torque rotor mounted under the fuselage between the landing skids.[2] Yaw control on both was effected through changing the difference in rotational speed between the two rotors, using a series of disc brakes. A small tail surface provided directional stability in forward flight. The smaller rotor would spin at a higher rpm, with about 60 percent of the load,. the main rotor being adjustable for lift control.
The NH-160 proved to be much more stable in tests than the NH-120 which had a higher center of gravity.