An analysis of steady straight flight with inclined thrust

Abstract

Griffith's proposal to achieve vertical take-off and landing at the usual attitude demands sea-level thrust considerably greater than the weight and continuously rotatable through 90 deg. A study of the steady states of such a system is necessary as a preliminary to work on the flying techniques involved in the project. In this survey a vectorial method of analysis has proved useful in displaying the special features of the performance of such aircraft at both high and low speed. The main conclusions are: (a) The high-speed performance is sensibly a maximum when the thrust is along the axis of minimum drag. Hence inclining the thrust is useless except in the grounding operations. (b) When the thrust exceeds the weight by a Substantial margin, steady flight is confined to very high speed in a very small incidence range. In this regime there are two flight-path angles for every incidence. (c) Handling may therefore be difficult until, with increase of height, the thrust has fallen below the-weight. If this proves to be so, it is suggested that the full thrust should be used to climb out of the 'excess thrust' region as quickly as possibly. The aerodynamic dividends in increased height and speed of economic cruise are obvious, but no attempt is made at a project assessment. (d) At very low speed, the attitude corresponding to any given inclination of the thrust is almost constant, and a large range of low speeds and flight-path angles is possible.