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Aviation History
1936
1936 - 2274.PDF
•i, —, ML AUGUST 20, 1936. FLIGHT. 203 The H.M.I8 is a cabin single- seater with Mengin engine. It takes off in a very short run and has an excellent climb. (Flight photograph was thought that the gap between the wings might be too small and might possibly cause the diving moment. The results were, however, sensibly the same. Then the machine was so re-rigged that the e.g. position was 64 cm. Instead of 70 cm. behind the leading edge of the front wing. Still the critical dive took place. Changes in e.g. position and gap having been found not to effect a cure, the range of incidence angles through which the front wing could be moved was increased. The lower angle, — 1 deg., was retained, but the maximum angle was increased from +9 deg. to +14 deg. It was found that with this range of angles, from -1 deg. to + 14 deg., the machine was controllable in any attitude, even upside-down. It now rests with constructors to scheme out ways of increasing the maximum angle of the front wing while still retaining the ability to decrease the smallest angle to — 1 deg. Unofficially, Chalais-Meudon also tried a shorter cabane to see if a reduction in gap would nullify the cure previously effected by increasing the maximum angle to + 14 deg. The machine was rather more "tricky," but control was still retained with the 14 deg. angle. The French Section Technique insists upon certain minimum stability characteristics for all military and transport aircraft. Chalais-Meudon carried out the usual tests on the Pou also, and found that at large angles, i.e., in stalled flight, the stability of the Pou was perfect. At cruising speed the stability was less, but still sufficient by the standards applied to orthodox aircraft. At small angles, corresponding to high speed, the machine was un stable and required constant correction by the pilot. Many will argue that this is totally unimportant, as the Pou-du-Ciel' is fundamentally different from the normal aeroplane, and that to expect from it the sort of stability with controls locked which is demanded of normal aero planes is rather ridiculous. The Pou is rather by way of being a bicycle of the air and therefore kept in equili brium by the rider, quite instinctively and without effort. The way several Poux were flown in a strong gusty wind at Ramsgate the other day without trouble rather seems to bear out this contention. In this connection the Editor of our French contem porary, Les Ailes, M. Georges Houard, remarks very sensibly that of the two, the Pou which is "officially un stable '' and the orthodox aeroplane which is stable fore and aft, but goes into a spin if left to itself, the Pou, with its total absence of spinning tendencies, is certainly to be preferred. The Chalais-Meudon tests are being continued, partly to see if the Pou can be made to conform with the official French stability criteria, arid partly to test the effects of different overlaps. About this latter point there is still some uncertainty, and opinions are divided. M. Mignet himself, as already mentioned, does not think the amount of overlap plays- an important part in the flying charac teristics, but others believe that the results of the slot effect with large overlap may be considerable. A British Pou has just been installed for tests at Farnborough. A "TUFTED" POU Some Interesting Results : Front Wing Stalls By W. E. GRAY AT a time when wind-tunnel tests are being carried out on full-sized Poux in France and at the R.A.E , k it was thought that it would be of general interest if the airflow over this type of machine were studied in free flight, especially at the stall. The writer therefore asked Mr. Baynes if he could arrange for the Cantilever ou to be flown for the purpose of securing photographs ; this was promptly done, and Mr. Appleby flew the machine a few da VS ago while photos and some brief film shots ^ere taken ; two of the photographs are shown in Figs. 1 and 2. It should be mentioned here that the Cantilever Pou outers considerably from M. Mignefs design as described |ii 11s book. One gathers from Mr. Baynes that before ldmg the cantilever machine he went into the stability Problem carefully, and came to the conclusion that it was essential for safety te have the C.G. at about 0.4 of the front wing chord instead of at about 0.5, as in M. Mignet s design, and that the rear wing should not carry more than 10 per cent, of the total weight; this makes an interest ing comparison with the writer's free spinning tests on a model Pou described in Flight in April, 1935, when the more forward positions of the C.G. were found to be much better than the rear ones. Mr. Baynes also decided to give his Cantilever Pou a different wing section and a bigger gap. It should be mentioned, further, that it is understood that M. Mignet holds the view that the rear wing so in fluences the flow over the front wing as to increase its lift, and in fact even to prevent it stalling; it seemed very doubtful if this latter could be the case, and it was largely for this reason that the test was made.
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