Chapter 10 - Propulsion Devices

Abstract

This chapter focuses on propulsion devices used in aerodynamics and how to apply one-dimensional control-volume analysis or simple momentum theory to examine the performance of propulsion devices. Froude's theory applies to propulsive systems in that work is done on air from the atmosphere and its energy is increased. The theory is based on the concept of the ideal actuator disc or pure energy supplier. Airscrew coefficients such as thrust coefficient, torque coefficient, efficiency, power coefficient, and activity factor are discussed in the chapter. The activity factor is a measure of the power-absorbing capacity of the airscrew that for optimum performance must be accurately matched to the power produced by the engine. The performance of an airscrew may be determined by model tests. Dimensional analysis is used for this purpose that leads to a number of coefficients, analogous to the lift and drag coefficients of a body. The chapter also discusses the momentum theory applied to the helicopter rotor, the rocket motor, the hovercraft and discusses that propulsive force is obtained by increasing the momentum of the working gas in the direction opposite to that of the force, propellers, turbo-jets, and helicopters operating in the Earth's atmosphere.