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Aviation History
1950
1950 - 1537.PDF
FLIGHT, 17 August 1950 1*7 by the holder of a Private Pilot's Licence except in a case where there is no question of " hire and reward " flying. Just before the outbreak of war, " banner-flying," with horizontal banners attached to rollers below the lower wings, was beginning to give way to the vertical advertise- ment, which for purposes of discrimination may be termed " poster-towing." The latter consisted of a word or mes- sage being trailed behind the tail of an aircraft on a long cable, the letters being cut out and readable over a much wider area than was possible with the horizontal banners, which could only be read when the machine passed imme- diately over an observer. One of the firms specializing in poster-towing was Air Publicity, Ltd., and they developed their own method of operation. A description of this method, as it may be applied today, follows. The poster itself consists of block letters, 6 ft high, cut out from canvas, preferably black. A length of bamboo, of ij-in diameter, is inserted into the leading edge of each letter to act as a stiffener. Connecting tapes run horizon- tally across the backs of the letters, with clips on the leading edges and hooks on the trailing edges, so that other letters may be connected to them as required. These tapes are not visible from the ground when the poster is 200 ft up, and the message is readable for about a mile to the left of the poster. From the other side, of course, the message appears backwards, but it was customary for the towing aircraft to make a wide left-hand circuit round a town so that the message could be read by as many people as possible. TTp to 30 letters can be used to form one poster. When all the letters are clipped together in the desired order the poster is rolled up until required. Assembly or taking-down of a complete poster can be effected in under an hour. At the forward end of the poster is a vertical metal rod, or tow-bar. At its lower end is a small adjustable fin to ensure that the poster is kept vertical in flight, and the bar itself is weighted at the bottom. The Avros were fitted with a vertical box structure under the fuselage just aft of the tail-skid. At the bottom of this was the release-gear (operated by a Bowden cable from the cockpit, in much the same way as the present method used for glider- release) to which was attached the 500-ft tow-rope. The rape itself is strong enough to take an 880-lb strain. The other end of the tow-rope is attached to an "8" hook, which allows the poster to ride easily, and the hook is in turn connected to a oridie consisting ot three ropes (the lower of which is arranged to take the greatest strain) joined on to the tow-bar. The various components are shown in the detail drawing. At the extreme end of the poster is a piece of heavy-gauge netting to prevent oscilla- tion and consequent damage to the poster. The method of picking up the poster from the giound is shown in the other sketch. The complete poster is laid out on the airfield, well to the left of the aircraft, and the tow-rope looped round and attached to the quick-release gear under the fuselage. The aircraft illustrated in boih drawings is the Chrislea Ace, which, with its tail-up attitude on the ground, might prove suitable for this sort ol work. It is low-powered (145 h.p. Gipsy Major) and economical to operate, which are important considerations. In practice the aircraft Is much farther behind the poster for the start of the take-off run, but is shown closer in the drawing for convenience. The top of the tow-bar is held up from the ground by an assistant to facilitate the pick-up. The poster is. in fact, peeled off the ground. There is no jerk when it is airborne, so there is little likelihood of its being damaged. The pilot climbs steeply immediately after take-off, and when 1,000ft has been reached assumes level flight ar<>' a suitable cruising speed. The Avros were cruised at about 50-60 m.p.h. with the posters, but a higher speed should be possible with a modern aircraft; obviously, the poster will become tattered it flown too quickly. To see that the poster is flying correctly the pilot must make a gentle turn, for it is immediately behind and belcw —in the " blind spot " in fact—when flying straight. If it is not flying vertically the pilot can make a complete turn round the airfield and drop the poster by means of the release-gear so that the fin on the tow-bar can be adjusted. At the end 0* the display the poster has to be dropped back on to the airfield as, obviously, the aircraft cannot land with it still trailing behind. To do this the pilot flies at about 400ft into wind and, after getting permission from flying control, releases the cable at the right time so that the poster falls in the required place. It is a matter of CD CD (Right) Details of the assem- bly and towing arrangements for a silhouette-letter message. A = Release gear. B — Tow-rope. C = "8 " hook. = Bridle. = Tow-bar. = Stabilizing fin. — Connecting tapes. =- Hooks and clips. (Left) A plan view showing how the message is " peeled- off" the airfield ; the tow-bar is raised at one end to facilitate the pick-up. The woi'd de- picted does not foreshadow Flight's use of this publicity method ! judgment and experience for the pilot, making full allow- ance for wind, to know just when to release the cable. If dropped from less than 400ft there is the possibility that the tail-end of the poster may hit the ground before the cable is released :.nd become damaged. Air Publicity used to have a van equipped with many sets of letters, and spares for the aircraft, to accompany each of their Avros on its tours round the country. Each operational crew consisted of a pilot, a ground engineer for servicing, and a van driver/maintenance man to atten.1 to the poster. It is perhaps important for poster-towing pilots to remember that over a town an aircraft may not be flown lower than 1,oooft above the top of the highest obstacle within a radius of 2,000ft of the aircraft. Finally, the possibility of a total ban must be borne in mind.
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