THE "WASH " OF AN AEROPLANE.

King Country Chronicle, Volume IV, Issue 291, 3 September 1910, Page 2

THE "WASH " OF AN AEROPLANE.

Those of our readers who have sat in a racing shell, or stood at the wheel of a racing yacht, will remembee how troublesome is the "wake" of a competitor, whether it takes the. form of the wash of his sculls, nr of the disturbance of the air as it sweeps from the leach of the mainsail of a weatherly yacht that is beating out to windward some distance ahead. In the case of twe racing: yachts that arc thrashing it out on the same tack in a struggle to windward, there is a certain relative position of the two, in which the disturbance of tlie air, caused hy its passage over the sails of the leading yacht, will prove extremely troublesome to the second boat, especially if she be" but a few lengths astern and sailing close to the wake of the other. When this occurs, there. is nothing for it but to put about on the other tack, and so get clear of the interference. With the rapid development of mechanical flight, says the "Scientific. American," the remarkable extent of which was shown so clearly in the recent brilliant performances at Rheims, it has become evident that the "wash" or interference, which is inconvenient to a sailing yacht may become positively disastrous to that yacht of the air, the aeroplane. It was not until the Rheims contests that an opportunity was presented to determine the effect of one aeroplane upon another, when, in meet- > ing or overtaking, they passed in rather close proximity. It is quite possible that the question of interference had never occurred to the aviators at Rheims, but it is certainly a surprising fact that the existence, of such interference, and its evidently serious character as shown when several machines were in the air at once, should not have excited more' attention, both at the time and in subsequent expert discussions of the Rheims contests. When such a large body as an aeroplane, spreading several hundred feet of surface, and weighing from a quarter to half a ton, is driven at fifty miles an hour by propellers that are revolving at from 1,000 to 1,200 revolutions per minute, it is certain to leave in its wake a complicated series of aerial cross currents, whirlpools, and vortices. Now, judging from the description of eyewitnesses of the Rheims races, the behaviour of the aeroplanes, when they swept into rather close proximity to one another, indicates that these arti-ficially-created wind storms were present, and that they seriously affected the equilibrium of any aeroplane that came within their influence. The "wash" from propellers driven, as in the case of Bleriot's monoplane, by an 80-horse-powei engine, and the air waves set up by the passage of his planes must be very great indeed ; certainly the air will not regain its equilibrium until long after the machine has swept by. Two notable instances of this interference occurred when several aeroplanes were in the air together. During one race, when Farman was rapidly overhauling opponents who were flying at the same level, he encountered the wash of the machines, and his own aeroplane was thrown into ' rather violent oscillation. Before he could pass, It was necessary to make a wide detour to the right or left, or swing up to a higher level into undisturbed air. On another occasion when Latham, flying high, overtook a competitor who was travelling at a lower level it was noticed that his own aeroplane made a sudden dive, as though drawn downward by the suction of the machine below him. We attach no little importance to a question which must become increasingly serious as the number of flying machines is multiplied, and the favourite lines of travel become populous with these mechanical birds of the air. "Leeway," as the sailors ?all it, will become even more necessary to the air yacht than it is now to the sailing yacht. Woe to the aviator who, flying low with scant clearance between himself and the ground, is overtaken by some aeronautical scorcher, who sweeps up from behind, and with the characteristic snort of triumph whirls onward, giving him his aerial dust. Happy for him if he recover his rude-ly-disturbed equilibrium at the expense of a broken wing and not of a broken neck. Perhaps after all we have been a little too previous in felicitataing ourselves upon the unlimited room that will he afforded for flight through the air ; evidently the clearance demanded by our sixty-milc-an-hour aeroplanes must be measured by something far wider than the stretch from tip to tip of the planes, or the length from head to tail.