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user guide

To the users of BT- cable drogues:

This manual for the BT- drogue is meant to be for serious information, for contemplative moments or whimsical minutes, as well as for cheering up dull club meetings and a gripping read for the bored cable-winch-operator.

Dear glider-pilot friends, dear cable-winch operators, dear cable fetchers, dear cable engagers,

when I first started to produce drogues for gliders in the 70’s, I aimed for the best possible quality to ensure a long life and a high standard. Nevertheless I have noticed that drogues which come back for repair, have been treated extremely ‘step-motherly’ at some airfields. (I won’t mention names).

So I felt inspired to summarize everything that is necessary and worth knowing about this neglected aspect of the towed take-off. Always consider: a drogue, which is not ready for take-off can spoil the best weather conditions as can a torn shock-absorbing rope, or a cable recovery car that won’t start.

An aerial sports enthusiast from LSV Gronau, rang me just recently. He wanted to know, if the drogue –bought in 1990- would be repairable. He apologized that “we have so bad conditions on our field”. I replied that it’s a good result when the drogue has done the job for 9 years, despite the conditions. Obviously they are doing everything right in Gronau and they don’t need to read the following manual.

  1. The drogue is directly engaged behind the winch cable, so that the long harness straps and, as a result, the base of the drogue point towards the winch. Otherwise the drogue will not open. I feel a bit daft writing the last sentence but I had to mention it – you never know…

  1. The shock–absorber rope with the shear- link is sitting between the drogue and the glider – you will know that yourself.

  1. Those who have a double drum winch can afford the luxury of engaging a purple coloured drogue on the left hand cable, and a red drogue on the right hand cable. I am immensely proud of this innovation, which shook the world of glider aviation to its foundations. Here a decisive hint from glider pilots from Verden/Germany: they discovered that there is no threat to safety when you swap over the colours on the cables. But the ground crew has to pay more attention to cope with left and right, red or purple, north or south, east or west, forest or field, hill and valley- drogue. Glider sport requires you to ‘ test your intelligence’!

  1. You almost always have to disentangle the long harness straps, when the drogue has been disconnected from the winch cable. Otherwise the harness straps differ in length and will be stressed unevenly until they tear. This shortens the long life and durability immensely. Especially older drogues reward thorough ‘strap care’ otherwise they may just give up the minute the weather conditions are perfect.

 

  1. And because we are all experts we know about the most critical moment in the take-off procedure: The first 50 metres. There is a problem if the cable winch slackens (the ‘cable-winch hole’), or the pilot slackens – or worse- both slacken and the drogue is doing exactly what it is supposed to do: it opens up! There is no reason to complain to the manufacturer -which would be me- but try to eliminate the error either in your gear or in your proceedure. This phenomenon doesn’t occur with older gliders like the KA6 or the ASW13 but more with competitive gliders –where the better pilots are flying…

  1. In support of these pilots I have to say that it is more likely to be a problem caused by the higher weight of the gliders, and the low acceleration of the cable-winch. The drogue is only a ’indicator’ of an error. We tried to stop this happening in our club in Braunschweig by sticking small slabs of beech wood onto the ground of the winch-drums/by enlarging the winch drums using small beech boards to achieve the necessary acceleration at the start. Obviously, it is never the drogues fault- NEVER!

  1. Well, finally the plane is in the air, the drogue rattles a bit because it hasn’t got much else to do.

  1. After the pilot releases the cable, the drogues big moment has finally come. It opens quickly and reliably and indicates to the winch-operator that he/she isn’t finished yet with the tow. The winding-in of the drogue should be done in a responsible and circumspect manner, just like towing with glider attached. You are mistaken if you think it works better at full throttle! A Mr. Tost told me when very small drogues are towed, or you constantly tow at full throttle, then the winch engines will wear out prematurely. And nobody really wants that. Even though the drogues survive it.

The drogue is towed to the winch with medium rev’s, but under tension, because the cable should wind onto the drum without any loops. The drogue is designed to have enough drag to fly back to the winch. This works better without side winds, I must admit. But the drogue will lift off the ground when towed horizontally to collect the last cable of the day. If you tow–in with too much thrust, not only does your winch break down quicker, but the drogue starts to spin (which also can be a sign for ‘tangle’- also see above).

8) When the “side wind effect” comes into play (I loved using this word when I was an instructor, because it made me sound so competent), the drogue can come down on the left or right of the winch. It is completely wrong to continue as if everything is normal. This ignorance caused the death of a cyclist in Oerlinghausen, when she was knocked off her bike by the cable. It is hard to imagine such a serious situation, but it still can happen. Obstacles you also must avoid are hedges, trees, masts and landing lights (very expensive). They shouldn’t be taken at speed. The winch-operator should –when in doubt- climb down and fetch the drogue from the field. On foot! Or send the recovery–car driver, if it is really necessary.

  1. I dedicate this paragraph to the winch driver/operator. This concerns mostly the very dashing ones who want to show the young and inexperienced beginner how to tow in the cable. In this case I am speaking of the male winch operators because I have never heard of the following examples involving female winch operators. They are too hesitant and/or considerate. Anyway, back to Mr. Winch Operator: At full throttle with the drogue very close to the winch. But it doesn’t always work out so well with the “close”. The first shackle, the weak link or the triangular ring of the drogue is then very close to the azimuth rollers. That’s not on! The fellow pilots or the workshop boss will notice it anyway, if you are not careful and circumspect with the equipment.

  2. Let us assume that everything went fine to this point. But a new threat is approaching our drogue in the shape of the recovery car driver. Didn’t I just mention something like “young and inexperienced”? The older club members are happy to fly and aren’t keen to drive; and they’ll try to avoid this job. A great opportunity to digress: I remember the time when I was already eighteen but without a driving license and the old experienced pilots haggled over who should drive an old Volkswagen four-wheeler. We solved the problem neatly in our club by having the flashiest and most modern recovery car that ever existed in the northern hemisphere: a Volkswagen van, diesel/GT, with all extras-very posh! It would be easy to write a book about these vehicles, with lots and lots of pictures. But now back to the point. When unhooking the drogues from the cable and transporting them separately you will get –without trying- a bird’s nest. That’s Murphy Law! Or could it be prevented by taking a bit of care? The drogues should also not be thrown over hot bonnets or exhaust pipes. The cap and the harness straps are made out of polyamide because of its toughness and durability-but they melt like butter under the influence of heat. Lots of “things” can gather in the car (notice how discreetly I mention this collection) and among them could be one or more old car batteries. Drogues don’t like battery acid. I have repaired some drogues in the past now and I can say like Ben Akiba that everything has already happened at some point.

  3. A good method seems to be not to unhook the drogue but to let it dangle off the rack (from top of the recovery car roof) and to drag the shock absorber rope over the runway. It seems like our advantage in Braunschweig/Waggum is in our grass runway, which causes nearly no wear and tear. There must be some very bad and muddy fields out there. Repairs to my problem children bear witness to this. Some clubs even wash their drogues before they send them to me.60C, gentle wash in the machine, great.

  4. Eventually the parachutes do return to the launch point in one piece and one thing remains to look out for. Before the drogue on the downwind side can be operated the one on the upwind side should be disengaged, thus avoiding mixups during the towing back. This is only of interest if you have a twin drum winch or even more drums. In Repke-Schnuckenheide (Hankensbuttel) a Dutch club was operating a four-drum winch during a summer camp. They even washed it after every flying operation! I heard that from a reliable source! Normally the winch operator makes sure that the first towed drogue does not come to rest above the second cable. Otherwise he’d have to get off the winch and he doesn’t really like that. In principle, everything can start again from the beginning unless flying operations are finished for the day..

  5. What else should the club members take care of? Don’t shove the drogues in with the shock absorber ropes somewhere like a pile of crap. Some care and sensitive handling pays off here too. Hang up damp parachutes for drying. Don’t continue using a drogue when you have discovered damage. Send the drogue for repair immediately. And by the way I offer packing courses once a year (01/04) so clubs can learn to put their drogues away nice and tidily. Another course (disentangling of harness straps-for beginners) is planned for the first of January.

  6. And now for a subject that should not be missed out in aviation: what to do when things go wrong.

  1. First thing that comes to mind is what the winch operator should do when a cable breaks or a launch fails and is related to the drogue and safety. Stop, foot off the accelerator and brakes on. The drogue can fall down to earth without causing any harm. An open towed drogue could collide with a plane or vice versa. It is always dangerous.

  2. The drogue comes down outside the air field. Please se Para. 8.

  3. I recommend all clubs to have a substitute drogue. You never know-I don’t promise eternal durability. Use an older but still functioning drogue as a reserve and treat yourselves to a new one.

  4. I have to put in another paragraph. I spoke already of the big braking drogues but want to explain a bit more. While we had our Star Fighter drogues in West Germany our glider friend in East Germany had their MIG drogues. I heard the results were the same. But we also shared the negative side effect. The drogue opened immediately when the cable broke and covered the wing or worse the canopy because the pilot was flying according to the rulebook. Soon afterwards the authorities reduced the diameter of drogues to 6 feet. And the chapter on big braking drogues came to an end.

  5. This item might be a bit longer. A letter from aero club Heppenheim brings me to this subject. I’ll quote the most exciting bit: “ An ASK 13 performed a towed take-off at 1000ft when either a big electrical discharge or lightning struck the tow. The pilots hair stood on end and they could not touch the control stick or the release knob because it was electrified. The instructor on the back seat released by foot. A few seconds later it was gone (the electric charge) and the glider could land without any problems.” The club wanted to know if the harness straps are conductive or not. They do not conduct electricity.

  6. I used to buy harness straps which had woven in metal threads to get rid of static charge via the cable. Every pilot has witnessed the electric shock you can get after landing. We had to stop using the special straps after the producer suddenly decided to supply the material only in huge quantities. And we really don’t need much for 100 odd drogues a year. So we had to abandon that gimmick and switch to normal straps. I never heard whether the metal threads worked or not. As the British say, ”no news is good news”!

  7. I found an article in the German Aero Courier in February 1996. “How to get your cable winch fit for the new season”. I found this interesting sentence “ there must not be an electrical connection between the cable and shock absorbers via the drogue, to make sure of the potential disconnection between the plane and the winch” Suddenly I could legitimately produce drogues, which were non-conductive.

  8. I still remember when clubs produced their own drogues. “Take a length of winch cable, wrap some cloth round it, take off!”; the results were appalling. Despite their brilliant conductivity I never heard anything bad about them. I figured that as the controls of a glider have to be connected by copper wires to the toggle the winch is always earthed. No winch operator forgets that .I had to find out more about this. “Braunschweig is the home of research”, they say and I rang up the National Board for Aviation (the LBA). Without wanting to be nasty I can only say that they didn’t have a clue. They recommended that I ring the PTB (the National Board for Physics and Technology) so I did. Only to be told that I’d better contact the professor of High Tension and Electrical Systems at the Technical University in Munich. I outlined my problem in a letter and received an answer soon afterwards from a very nice Professor H. Steinbigler. It would be a service to science if I quote him/her fully. “ If I understand your question right you want to know if the drogue which sits between glider and cable during the towed take-off should work as an isolator or not. You also ask if lightning strikes on gliders are likely. Last question first. It is highly likely that you would be struck by lightning if taking off in a thunderstorm. The electric field of the storm would be enormously charged by the earthed cable even though there is an insulating section of some metres somewhere on the line. The system of glider cable and cable winch would act like a very tall building and have a very high likelihood of being struck (especially by a so-called up-striker) Such effects are used in lightning research. Little rockets carry up steel wires to trigger the lightning charge of a thunderstorm. I strongly dissuade from a towed take off in a thunderstorm.

  9. The question of isolating or conducting connections in the form of a drogue has in my view two different aspects.1: The effect of electrostatic charges.2: The effect of a lightning strike. Electrostatic charges can be avoided by having conductive drogues between glider and earth. A lightning strike cannot be avoided even if an isolating disconnection of some length is available because the disconnection would be flashed along by the lightning discharge. The distance between glider and cable winch is not enough protection against a lightning strike because as I mentioned before the conducting and earthed winch cable massively enhances the electric field of a thunderstorm. The upper end of the cable would be struck and this would influence the glider and its pilot. A conducting drogue would act like a lightning conductor in principle if it were capable of conducting the lightning electricity safely without melting or evaporation (explosion!). Of course a conducting drogue is no protection against lightning strike. To summarise my explanation summarised neither a conducting drogue nor an isolating one are capable of lightning protection. In my opinion a towed take off has to be avoided during a thunderstorm.” Isn’t it exciting to hear of the possibility that you could evaporate or even explode? I won’t comment on this letter because it speaks for itself in its truth and clarity. You probably will be a bit more clued-up now that you have managed to fight your way through to here and respect for the power of nature should not be strange behaviour for us glider pilots.

    1. I’d like to refer to some business matters. Since July 2001 we are producing drogues with interchangeable harness straps. A spring hook substituted the lower triangular ring. You can now order straps to exchange damaged ones by yourself to save costs. The spring hook allows other rings, karabiners, disconnectors or shackles to be set in. You have to be sure to tighten the screw joint again and to tie up the long straps again if you have to exchange any thing. The upper straps are doubled since a long time and keep even better.

    2. And the last information: all drogues are delivered with the label “styled by Giorgio Doga” Italian is always “in” with textiles. There are pants from Bruno Banani as well for instance……….

Yours sincerely Juergen Daube alias Giorgio Doga

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