This paper reports the results of an experimental study of the prototype rotary-piston air motor RPD-4,4/1,75 in the form of speed characteristics. The maxima of the air motor's performance effective indicators have been determined, as well as the rotation change ranges that correspond to them. It has been established that for the intake receiver's air pressure change range within 0.4...0.8 MPa the maximum value of effective power is 1.7...2.5 kW. In this case, the maximum value of the torque and mean effective pressure for a given pressure range in the intake receiver is 17.0...18.2 N∙m and 0.13...0.18 MPa, respectively. The dependence has been derived of the hourly air consumption on the rotations and pressure in the intake receiver. Depending on the test mode, the hourly air consumption is within 25…226 kg/hour. It has been established that the minimum values of the specific effective air consumption correspond to 800...1,000 rpm. Thus, for a maximum value of air pressure in the intake receiver of 0.8 MPa, the specific effective consumption is 60.8...93.2 kg/(kW∙h), for the minimum value of 0.4 MPa – 49.7...81.3 kg/(kW∙h). The potential of the adiabatic expansion capacity has been determined, brought to the air motor, as well as the effective adiabatic efficiency. The maximum efficiency of the air motor corresponds to 800...1,000 rpm. In this case, the maximum efficiency value was achieved at a pressure in the intake receiver of 0.4 MPa; it is 0.41. The dependences have been derived of the change in the pressure of spent air in the exhaust receiver, the maximum value of which does not exceed 0.075 MPa