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Low Speed Tunnel Measurements of the Ground Effect on a 1-5th Scale Model of the Swift

Although theoretical methods of estimating ground effect have never
been very reliable, a good deal of information is available for aircraft
with unswept wings, and it has been found that this can be applied reasonably
well to delta—winged aircraft where again the trailing edge is unswept.
With swept wings the position seemed less satisfactory, and tests have been
made on a model of the four—gun version of the Supermarine Swift, both in
free stream and near a ground board, to collect data on ground effect for
comparison with flight tests and theoretical estimates. Some effort has
been made to extend the scope of the results by using two tailplane heights
and several flap configurations, and the results are compared with theoret—
ical estimates of ground effect.

The model used for these tests was a 1/5th scale model of the Swift
with four—gun wing1; the undercarriage was not represented. The main
dimensions are given in Table I and the general arrangement is illustrated
in Fig. 1. Tests were made with the actual aircraft flaps, which are of
irregular shape, and also with alternative 500 split flaps, which were
suitable for joining with a fuselage flap and extending as full span flaps.
(Figs. 2 and A). These consisted of an unswept body flap B1, constant
chord trailing edge flaps B2 over the inner wing, and 3Q% chord trailing
edge flaps B5 over the outer wing. The gaps between adjacent flaps were
sealed.

Tests were made without tailplane and with the two tailplane positions
illustrated in Fig. 3. The upper tailplane was the same as that used in
the tests of Ref. 1, and represented the position on the aircraft. The
lower tailplane position was obtained by inverting the rear fuselage of the
model, giving an anhedral of 100.

Transition was free on the aerofoil surfaces, but was fixed on the
fuselage at 10% of its length and on the cabin and intake lips. The ground
(Fig. 5) was represented by a wooden board two inches thick spanning the
tunnel. It had a length of thirteen feet, two feet of which formed a
chamferred nose, the chamfer being on the side of the ground nearer the
model. A note on the problems involved in the use of a ground board and in
calibrating the tunnel is given in the Appendix.