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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. |
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