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Aviation History
1949
1949 - 0542.PDF
348 FLIGHT March 24th, 1Q49 Retrieving Glider Cables How No. 12 Group Gliding Club Saves Ground-time By Wing Cdr. A. J. M. Smyth ASHORT time ago an article* in these pages momen-tarily turned the spotlight on gliding-ground equip-ment. And since everything possible should be done to alleviate the burdens of the financially hard-pressed gliding dubs, No. 12 Group Gliding Club, R.A.F., would like to make public the fruits of an autumn's research. .(Fpr, contfary-tb general belief, we too have to make-ends meet witbjbut jtssistance from the' taxpayer.) • / Early last year an idea was sweeping B.A.F.©. gliding clubs that cables might be retrieved \fy means of a small winch and a piece of string always attached to the main cable. Although I personally visited almost every club in April, I never actually saw such a device working, nor did I ever meet anyone who could describe one in detail. Therefore, as soon as No. 12 Group Club moved to our home station, bringing with it its one decrepit Beaverette, we set about improving our ground organization by the development of such a fabulous mechanism. In this we were very lucky to have with us as a member F. S. Hillyer, who not only designed and manufactured the winch, but also procured the parts at very small cost. Few new developments in aviation are completed with- out blood, tears and sweat; this was no exception. No one knows how many times Hillyer had to start afresh as each winch proved useless, and as trial and error revealed new requirements. We know that an ideal specification should be something like this: — (1) An engine of about 5 b.h.p. We use a Petter Type A developing 3.9 b.h.p., but this is slightly underpowered. (2) A reduction gear. We use a twin belt drive of about 3 to 1, and this seems to give us about the right speed. (3) A clutch to facilitate gear-changing and to provide a quick stop when winding in the cable. We use a stan- dard Borg and Beck single plate. (4) A gear box. When the end of the main cable is back at the main winch, little power is required from the retriever and winding may be fast. When there is a lot of main cable out much more power is requited and con- sequently a lower gear is necessary. We use an Austin Seven gear box. 5) A sensitive brake to prevent over-running yet so designed as not to impose friction at other times. We are now using a hand-operated band-brake, but probably some form of automatic mechanical brake would be ideal. Most of our initial troubles were due to over-running. (6) A free-running drum of not less than gin core diameter. If the drum centre is smaller the revs will become enor- mous, as the string may have to pay off at speeds up to 60 m.p.h. Smaller drums would also produce an* undesirably high ratio of full to empty diameters. (7) A simple feed-on mechanism which will not hinder feed- off. (8) A light cord or string which will break easily in case of hang-up yet will haul-in the main cable without breaking. We find 2-lb kite-cord to be ideal. We may go back to i-lb cord if our technique improves, but find that coarse handling still breaks even 2-lb cord- This cord or string is attached to the main cable where it joins the weak link just before the aircraft attachment:;; Since modifications resulting from experiences of the early stages have been embodied in the specification as given it is not intended to refer to those experiences now.; It may have been that much of our trouble was due to faulty handling, as we still find that a careless initiate can break the string; but we certainly came suddenly upon success. For circuits using up to a thousand yards of cable, retrieving takes about the same time as that during which the glider remains airborne without lift. We have done six complete circuits in 24 minutes, using one Cadet, with a pilot change in the middle. The air time was about three minutes per circuit. But allowing time for briefing we are happy to keep up an average with two aircraft of nine to ten launches per hour. Our one Beaverette is- kept fully employed in aircraft retrieving. But there are limitations which we still have to over- come. Because of engine power, we are unable to use more than 1,000 yd of cable. Not only is the Hillyer winch unable to haul 1,700 yd of our main cable, but this length of cord imposes appreciable drag on a sailplane, and costs it some 200ft of height. Moreover, the increased speed of working magnifies our signalling difficulties, and a speech link between the main winch and the Hillyer at the other end has become almost essential. We hope to use walkie- talkies for this purpose. * " Per Ardua ad Cumuli." by F. G. Irving. December 23rd. 1948. A = Enfilt* D •» tr»k«B = Clutch t - Winch C = Gmr box t =•= f—i-on
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