An experimental investigation of the subsonic drag and pitching moment characteristics of slender cambered bodies with pointed noses and tails

Abstract

It is known that supersonic aircraft are liable to possess some trim drag under cruise conditions. Fuselage camber has been suggested as one means of reducing this component of the drag, and the purpose of this investigation was to obtain quantitative data on the pitching moment increments obtainable from fuselage camber and incidence, and the associated increments in fuselage drag.

Lift, drag and moment measurements have been made on a body representative of the fuselage of a supersonic transport aeroplane. The fineness ratio of the body was 15:1, the cross-sectional area distribution being of modified Sears-Haack form. Parabolic nose and tail camber was used, the nose and tail portions being made removable so that a variety of different configurations could be tested. The Reynolds number of the tests was 14.1 x 106 based on the length of the model, and the Mach number was 0.2. The tests were made with a transition wire attached to the model at 10% of the length from the nose. A preliminary investigation indicated that the Reynolds number was probably sufficiently large to ensure that the results would give a good guide to the full scale characteristics.

The experiments showed that nose camber produces a pitching moment increment in very close agreement with the predictions of inviscid slender body theory. The increments in lift and drag, whilst not zero as predicted by inviscid theory, axe small. Tail camber on the other hand gives rise to much larger lift and drag increments, and the increment in pitching moment is quite different from that predicted by inviscid theory. In the present tests the pitching moment increment due to tail camber amounted to about 10% of the theoretical value.

The scope of the experiment was insufficient to answer the question “What is the optimum fuselage shape for minimum trim drag?" However, the indications are that an uncambered fuselage at incidence will provide a given pitching moment for less drag than any cambered fuselage. This however neglects the interference effects of the wing and tail unit on the fuselage, and of the fuselage on the wing and tail unit. For reasons of (i) tail clearance on take-off and landing, (ii) cockpit layout and view, and (iii) cabin layout, fuselages with camber may be required. Some indication of the fuselage drag penalties likely to be sustained by these modifications of the fuselage are given by the results of this experiment.