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Aviation History
1936
1936 - 2408.PDF
SEPTEMBER 3, 1936. FLIGHT. c as regards the depth of the stalled region and the angular change of the downwash at the stall; these are the "further peculiarities of flow " mentioned at the end of the first article. The fact that the depth of the stall varied with yaw on the Swallow was seen and filmed latei, and '' still'' photos were taken afterwards. Two typical specimens appear in Figs. 6 and 7, and in a way they are perhaps more interesting than some of the others, as showing a different side of the problem; pig. 6 shows a shallow stall, with the wing forward 5 deg., and Fig. 7 shows a deep stall when the wing was yawed back 10 deg I with no yaw tne stalling was intermediate. Now, it will be seen that in Fig. 6 a little aileron was needed to hold the wing down, and in Fig. 7 rather more was needed to hold it up; these confirm the amounts of yaw, which are no longer readable. In Fig. 6 the stall has had long enough to develop to have swept the "yaw-meter" right forward, the surface flow is reversed except near the L.E., and yet the tur bulent region is quite shallow; this, in fact, seemed to be its permanent state so long as the attitude could be held. Fig. 7 shows a very different state of affairs; the stall was caught in the act, and although the surface flow at the masts is reversed it has not had time to sweep away the nearby yaw- meter, nevertheless the flow has at once been disturbed to a great depth, and its final state is somewhat worse than that shown. The exposures were 1-150th sec. The only explanation of this behaviour that I can offer at present is that when the wing is forward the bending of the surface flow causes the dead air to accumulate at the inboard end of the wing, or, if it is truer, to be sucked away from the tip, whereas when the yaw is the other way the reverse holds good; the T.E in the two photos was 15 deg. forward and normal to the wind, respectively in Figs. 6 and 7. In the tunnel tests it was found that with considerable sweep- forward there was no sudden change of the downwash angle even though a shallow layer of surface stalling had taken place, and that the downwash angle even went on increasing with increase of incidence for a very considerable time—in fact, one could hardly say that the outer part of the wing had stalled in the ordinary sense at all; this was with a 2.5 to 1 taper and 10 deg. or more sweep-forward of the L.E. It was impossible to check if the Swallow behaved in this way because the stalling of the rearward wing caused it to fall so rapidly with 10 deg. yaw that the forward tip could not be made to stall at all: a number of film shots were taken while the wing-tip came up overhead without any sign of a stall. It would be interesting if it could be confirmed on a machine with control surfaces of sufficient power to force it into the attitude required—something like a flick roll, in fact. In connection with the depth of stall it is interesting to study the diagrams in R. and M. 1203, for it is fairly obvious that something of the sort was happening there, too; the pressures in different Concluded overleaf.) IN SEARCH of the PRIVATE OWNER'S IDEAL The four machines designed to the order of the U.S. Bureau of Air Commerce and mentioned by "Indicator" in "Topics of the Week'' in the Private Flying section of this issue. Above is the fairly conventional all - metal Curtiss-Wright monoplane and on the left is the far-from-conventional Weick pusher in which all normal manoeuvres are carried with only two controls. The slot-cum-aileron can be seen in the centre of the wing. First of the Bureau experiments was the Hammond, shown above. On the left is the Waterman mono plane, which is somewhat similar in general layout to the Hammond and the Weick, but which has no tail and is vaguely reminiscent of the original Westland Pterodactyl.
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