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Aviation History
1948
1948 - 2128.PDF
7i6 FLIGHT DECEMBER I6TH, 1948 Suction-wing Glider Interesting Australian Exp eriment with Griffith-type Aerofoil FIRST official intimation that,although complete laminarflow right up to the trailing edge is not likely to be achieved bysuction, the principle can be applied to give low drag for a very thickwing section was given by Mr. E. F. Relf in his very remarkable WilburWright Lecture in 1946. Since that time, work has been going on toobtain experimental verification of the possibilities indicated by theory. It may be recalled that in hislecture Mr. Relf showed an aerofoil section with a thickness of 38 percent of the chord, and stated that, with a single slot, the theoreticalmaximum lift coefficient should be in the region of 2.5, and the dragno greater than that of a thin wing. The critical Mach Number of such a wingwill be low, and so its application would probably be confined to aircraft of moderateperformance, but the advantages which it would confer on an all-wing aircraft of rela-tively small size are obvious. It still re- mains to be seen whether a wing of thissection would lend itself to the vee plan form necessary, bearing control and stabilityproblems in mind, but in the meantime full- scale tests on a "straight" wing are beingmade in Australia by the Division of Aeron- autics of the Australian Council for Scientificand Industrial Research, under the direction of Mr. L. P. Coombes. A glider of 56ftspan has been built, and has already made some flights, the first of which took place inOctober, when the glider was towed to a height of 10,000ft by a Dakota and thencast off. The photographs show the complete gliderand some of the structural details of the wing. It will be seen that the main struc-ture is a spar box, behind which the concave top surface curves down to the trailingedge. The suction slot is located near the beginning of the concave part of the curve, Below, a wing section partly covered, showing tunnel for slot suction. On the right, the skeleton of the spar and leading edge. rr- KT Wheeling out the glider from the shops at Fishermen's Bend. The picture on the left gives a good idea of the wing construction. an arrangement which appears to differ slightly from the section shown by Mr. Relf. Air is exhausted from a spanwise tunnel, and it would ap- pear that the wing structure is such that different slot widths can be tested in order to determine the most effec- tive compromise between adequate suction effect and volume of air to be removed from the boundary layer of the wing. No information is yet avail- able concerning the plant used in the glider for exhausting the air from the slot tunnel. In his lecture Mr. Relf pointed out that under good conditions it was only necessary to suck away about half the quantity of air in the boundary layer, but that this needed a very narrow slot, which would give rise to rather high velocities just inside the slot, which might involve considerable internal losses. C 12
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