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Aviation History
1936
1936 - 2271.PDF
202 FLIGHT. AUGUST 20, 1936. Mignet's latest. The H.M.18 will probably be the French factory-built version of the Pou. Note that the wings do not overlap, and that the front wing is placed much higher than in the original Pou. Flight photograph.) DE-VICEING the POU Preliminary Results at Chalais-Meudon : Full Control in a Dive The Stability Question PRIMARILY intended to discover if the Pou-du-Ciel has any vices, and, if so, whether there are means of curing them, the tests in the full-scale wind tunnel at Chalais-Meudon have now been completed so far as the first part of the problem is concerned. They are, however, being continued with a view to determining the stability characteristics of the machine. The machine submitted to Chalais-Meudon for tests was one built by the brothers Lambert, at the request of the French Aerial Association, which paid for the experiments. The machine was rigged and trimmed in accordance with what has become known in France as Mignet's "Polygon of Safety." Before submitting the machine for tests at Chalais-Meudon, M. Mignet laid down certain dimensions for the position of the centre of gravity in relation to the front wing, which he, from his very long experience, had found to provide controllability at all speeds. The dimensions, in centimetres, laid down by M. Mignet as representing correct trimming, are shown in the diagram. It will be observed that the vertical through the centre of gravity passes 70 cm. behind the leading edge of the front wing, that the struts which support the front wing should not be shorter than 75 cm. from the top of the fuselage decking to the bottom of the front wing spar, and that with the machine in cruising attitude the gap between the trailing edge of the front wing and the top of the rear wing should not be less than 40 cm. when the front wing is in the mean position. At cruising speed the top of the fuselage, and therefore the rear wing, should have an angle of +6 degrees, and the axis of the airscrew should be parallel with the top of the fuselage, and for preference be in continuation of it. If airscrew clearance permits, M. Mignet prefers that the axis should be below the level of position shown in the diagram, out does not regard this as very important. Many in this country have held that the amount of overlap (the extent to which the trailing edge of the front wing covers the leading edge of the rear wing) is important in connection with the tendency of the machine to go into an uncontrollable dive. M. Mignet does not share that view, and gives a range of overlap from 5 to 15 cm. Another dimension on which M. Mignet gives a certain amount of latitude is the position of the e.g. in relation to the wheel axle, although he stipulates that it should be 35 to 40 cm. behind the axle. The machine tested at Chalais-Meudon was rigged and trimmed in accordance with this " Polygon of Safety," and was thoroughly flight-tested beforehand by M. Mignet himself and by M. Robert Robineau and the brothers Lambert. The engine was a 25 h.p. Mengin. During the tests the Pou-du-Ciel was '' piloted'' in the wind tunnel by, among others, M. Mignet himself. The tests were, of course, carried out with the engine running, so that the effects of the slipstream were repro duced. It was found that in normal flight and stalled flight the machine was controllable. When, however, a certain small angle of incidence was reached the machine became uncontrollable and steepened its dive until, had it been free to do so, it would have gone over on its back. (It may be remembered that in some of the fatal accidents which have occurred the machine got into a steep dive and ultimately crashed upside-down.) No possible movement of the front wing would bring it out. In order to try to cure this loss of control, the struts which carry the front wing hinge were lengthened, as it M. Mignet's "Polygon of Safety." The dimensions (in cm.; are those which, coupled with an increase in the maximum angle of the front wing to +14 degrees, are now held to give full controllability of the Pou under all conditions.
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