Subsonic Aircraft Drag: An Appreciation of Present Standards

Abstract

Summary The drag at cruise CL of a number of recent aircraft—mostly large subsonic transports—has been analysed in terms of figures-of-merit derived from Melvill Jones’ original concept of a streamline aeroplane. The values have been compared with those for some representative aircraft from the 1930-1940 period. The paper then proceeds to highlight some of the main sources of excess drag; for the recent aircraft, these are grouped under broad headings such as “excrescences”, “Mach-number effects” and “nacelle installation or interference”. The results of the analysis are somewhat disturbing. Perhaps the most striking feature, bearing in mind that only a restricted class of aircraft have been considered, is the very wide spread between the figures for the poorest and the best of the recent aircraft. Also, the detailed drag breakdown varies widely from one aircraft to another. The evidence in the paper suggests that, in many cases, present drag standards can and should be improved.

Measurement of the drag of various three-dimensional excrescences in turbulent boundary layers

“…9. The subsonic data do not appear to lend themselves to analysis in the form of equation (1). As can be seen in Figs.…”

“…For cylinders which extend further into the boundary layer though still within a region characterised by the wall variables, hid becomes an important parameter because of the formation of horse-shoe vortices. For such cases a wallvariable relationship may be more appropriate than the form given by equation (1). Results in this form are given in Fig.…”

“…In turn, this has provided impetus for research into the drag of excrescences. It has been shown* 1 ' that the drag of most current aircraft could have been lower if more attention had been paid to the avoidance of unnecessary excrescences.…”

Effect of aircraft surface smoothness requirements on cost

“…Haines* 13 ' gave an account of subsonic aircraft drag, comparing post war progress with pre-war technology levels. He reviewed the drag of a number of transport aircraft.…”

The Future of Aeronautics—Dreams and Realities

“…A. B. Haines (12) initiated a much needed revival of interest in subsonic drag in 1968 when much of the country's effort and attention was focused on supersonic and hypersonic flight. With limited resources such choices, although difficult, must sometimes be faced.…”