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#71
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In article , Andy
Durbin writes Ian Strachan wrote in message ... A point I made in an earlier contribution to this thread seems to be being missed but I think is important. That is, where a glider has two hooks, the rear hook can be placed close to the true C of G position. With only one hook, the position will normally be somewhat forward of the C of G position and will be a compromise rather than a true C of G hook. In other postings people talk generally about "CG hooks" without making the above distinction, which could be critical to handling on the launch. "Belly hook" might be a better term, and many will not be true C of G positions unless a nose-hook is also fitted. In a previous posting I stated that the CG hook on my ASW 28, and the only hook on my ASW 19, are in the same place. They are both just forward of the main gear and inside the gear doors. I think they would both be considered to be true CG hooks even though they are forward of the CG. When you say that "the hook is forward of CG" you seem to imply a static measurement. The static on-the-ground measurement of where the glider GC is with respect to the belly hook position is not what matters. It is what happens on a launch (dynamic, not static conditions). What matters is the angle-of-pull of the cable with respect to the centre of motion and control effectiveness of the glider in that dynamic launch situation. If you measure where the CG is statically, that is, on the ground, and placed a tow hook directly underneath it, I think that you would find the subsequent launch pretty unstable either on winch or air tow. -- Ian Strachan Lasham, UK |
#72
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On Tue, 6 Jan 2004 18:39:17 -0000, "W.J. \(Bill\) Dean \(U.K.\)."
wrote: There have been several fatal "aerotow upset" accidents in the U.K. where it seems certain that towing on a hook intended for winch launching was a factor. These include: Lasham new year 1963/4 Auster towing a Ka 6cr or Skylark 2 (I forget which), Tug at Aboyne towing a Ka 6e, Tugs (Super Cubs) towing K 18s at Portmoak and Dunstable (within a few months of each other), this led to the tests by Chris Rollings, Verdun Luck and Brian Spreckley at Booker see http://www.glidingmagazine.com/ListF...Dtl.asp?id=327 . Will that do, or how many others do you need? So that is 4 in 40 years. I think we've managed to kill that many towplane pilots in Aus in the last 15 in mid airs. At least one, maybe more would have had a good chance of survival if he had had a parachute. Something that still isn't required here. The common link with the upsets mentioned seems to be high wing wooden gliders of low wing loading with deep fuselages. These may be prone to pitch up. How long were the ropes in these situations? Were there other circumstances that contributed? Could they have been compensated for? Any glider which launches well on a cable using the aft launching hook, will do the same behind a tug maybe killing the tug pilot in the process. If you really think that the glider pilot can control or stop this process once it starts, READ THE ARTICLE LINKED ABOVE; I suggest that the pilots who conducted those tests were more experienced, more current and just plain better than you. You are suggesting that on a winch launch with much higher loads in the cable that these gliders are not controllable in pitch? To my certain knowledge it is possible to fit a forward hook for aerotow to the ASW 15, 17, ASK 18, ASW 19, 20, and 22 and the Pegase; the ASK 21 and 23 and I think later types were fitted with it as standard. I don't know of any examples of these in club (as distinct from private owner) use which have not been modified. I once owned an ASW20B. The GFA required the nose hook to be fitted. The Scheicher factory job on this was pitiful. Nobody who bought gliders from this batch of 6 put up with it. The releases were taken out and glassed over. When finishing the area it became apparent that the skin had been distorted by the additional release bulkheads. I don't ever recall the 20B having the slightest tendency to pitch up on aerotow on the belly release. I have no aversion to properly engineered nose hooks like in Glasflugel and Schempp gliders but poorly designed retrofits are a bad idea particularly when no testing has been done on that particular type to see if indeed the "solution" is effective or even necessary. The BGA considers 150 foot ropes acceptable. I consider these dangerously short, 200 feet is more like it with around 240 to 260 being much better. Now consider this:: The world's politicians and bureaucrats are forever looking for ways to meddle in our lives to keep themselves in jobs. If we place requirements on our own operations (Like compulsory nose releases)that are not firmly founded in proper testing and rational analysis we weaken our case in resisting the idiot requirements that come in a never ending stream from these people. I've yet to meet anyone who has flown on a 250 foot rope who hasn't admitted it was easier than on shorter ropes. When I aerotow I want to go soaring for maybe several hours and maybe the enviroment on the ground was stressful due to heat, humidity etc. I really don't need a 5 minute adrenaline thrill to begin a cross country. I would like tows to be a non event. Longer ropes and tow pilots who don't try to thermal or do other sudden manouevers all aid in this. The scariest tow I ever had was in my Salto (with nose release) behind a tow pilot who was not paying attention and who pulled back hard on leaving the ground as we encountered a gust leaving me dangling low from the end of the rope with decreasing airspeed. Followed by a hard push just as I was climbing slowly back up into station(low tow) leaving me very high followed by another hard pull which put me very low again wherupon I released and did a 180 back to the strip. Probably my shortest ever aerotow flight, closest to disaster and on the 130 foot or so ropes that were fashionable at the time. I never ever want to do this again. It was 30 years ago and I remember it clearly. A rope twice as long likely would have made this a non event. The surprisingly easy tows were at Minden in an ASW20(belly release) through the rotor behind a 182. Long rope, no problem at all. Mike Borgelt |
#73
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Earlier, Mark Zivley wrote:
If someone can afford the cost of a new glider, it isn't going to break them to pay for BOTH nose and CG hooks. I don't see why SH (or any other manufacturer) would waste the time with "options" on this subject... The issue here isn't getting the buyer to pay for both hooks. It's getting them to pay _more_ for them. That's where the profit margin is. A year or so ago, I had the experience of observing a friend select and purchase a brand-new European racer. Just about everything that wasn't absolutely required was optional. Even the canopy sliding window was "optional." With that experience in mind, I'd say that the factories play the "option" game for the same reason that car dealers do it: It's a relatively easy way to make the basic price tag look attractive, while increasing the profit margin on the typical sale. It's not at all a time-waster, except perhaps for the purchaser. For all the relatively high prices the factories charge for new sailplanes, they are still operating on relatively slender profit margins. Even high-production types are pretty much hand-built by skilled workers using some pretty expensive materials. It's hard to fault them for getting all the market will bear, any way they reasonably can. Thanks, and best regards to all Bob K. http://www.hpaircraft.com/hp-24 |
#74
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"Mike Borgelt" wrote in message Snip------ I don't ever recall the 20B having the slightest tendency to pitch up on aerotow on the belly release. Snip------ Mike Borgelt Mike, I have flown a number of different gliders on air tow using a CG hook. None of them had a tendency to pitch-up either. My Nimbus 2C tows just fine with a CG hook. Airtow with a CG hook isn't a problem -- as long as the tow is flown normally. It is after the glider gets seriously out of position that the problems arise. With a CG hook, it is easier to get out of position through pilot inattention, and once there, the situation can very quickly become unrecoverable. It is difficult to believe how fast things can go from seeming normal to horribly wrong unless you have been there and done that. It is so dangerous that no instructor would deliberately subject a tow pilot, a student and himself to it just for training. I encountered this once more than 40 years ago. I was a young student pilot flying a glider known for it's challenging flight characteristics. At the time, no weaklinks were required in the 200 foot, 9/16" nylon rope. Note that I don't claim that this would not have happened anyway with a nose hook, but it wouldn't have happened as easily. I was inattentive, lulled into complacency by the smooth air. Instead of watching the tug, I was watching the scenery. Sudden G forces woke me up as the glider soared above the tug and to the right. Both the gliders and the tug's releases jammed under the stress. The tug dove to the left and pulled me it into the dive after it. It was only because the aerodynamically clean glider could outdive the tug that the rope went slack and both releases functioned simultaneously. We both landed safely, but I bought beer for that tug pilot for several years afterward. Had this occurred under 1000 feet, we both would have died. I never looked at air tow the same way again. The concern about airtow with CG hooks is for a condition that lies well outside the experience of 99% of glider pilots. If you airtow with a CG hook, keep in mind that a dragon lurks outside the normal airtow box. Don't go there. Bill Daniels |
#75
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On Wed, 7 Jan 2004 19:06:40 -0700, "Bill Daniels"
wrote: The concern about airtow with CG hooks is for a condition that lies well outside the experience of 99% of glider pilots. If you airtow with a CG hook, keep in mind that a dragon lurks outside the normal airtow box. Don't go there. Bill Daniels I completely agree Bill. I'm a long rope fan because the normal box is larger. In fact I think it is not a linear function of rope length as the first 100 feet of rope is probably counts for little due to pilot/sailplane perception/reaction times. There are other dragons which have happened in Oz. Get too low on low tow, put a large bow in the rope and have it catch in the aileron/wing gap. Good reason to have a weak link at *both* ends of the rope. Having once done a cross country tow in low tow on a 130 foot rope and then discovered that the towplane exhaust system was about to fall off makes me not a low tow fan. I worry about the "we've required nose tow releases so we've fixed that problem" thinking. The problem didn't get fixed because nobody had the gumption to require a retrofit on ALL gliders. Politically impossible because when the chips were down it would be impossible to justify. Instead just stick the owners of new gliders with the cost because if they are buying a new glider they can afford it. The LBA/BGA/GFA/insert your civil aviation bureaucracy name here bureaucracy get to feel good because they have "improved" safety and can boast about this, most of the glider pilots don't care one way or the other as they are unaffected and tow pilots are at just as much risk as before as the fleet replacement only occurs slowly. Great! Requiring longer ropes would have been cheaper and would give immediate benefits but here we are still thinking 150 feet is adequate. Wonderful. Meanwhile we've had one mid air on tow in Oz. One side benefit of 250 foot ropes is that you do have time to look around while on tow instead of maintaining station with all your attention. Anybody who hasn't towed on a 250 foot rope I suggest you try it. It took one tow in 1982 for me to be a convert. Meanwhile realise as the tow pilot opens the throttle that you are potentially less than a minute from proving that youve thought about the low altitude tow emergency enough to carry it out successfully. It could be a rope break, engine failure or getting out of station or any one or more of quite a number of other things. Tom Knauff had a good article about this that I saw in Gliding Kiwi. Mike Borgelt |
#76
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The Australian Poster Dave refers to was actually line
drawings of the photo's taken of the tests I described. Chris Rollings At 10:30 07 January 2004, Dave Martin wrote: At 09:18 07 January 2004, Marc Ramsey wrote: Chris Rollings wrote: In launching on a C og G hook you are risking the tow-pilots life more than your own, and this I will not defend. Marc Ramsey wrote I personally prefer to fly aerotow with nose hooks, and both of the gliders I now fly have them. But, I'm not convinced that anyone has provided actual evidence of an observed safety issue with CG hooks. Some numbers like these for, say, the past 20 years in the UK: How many aerotow operations were there per year? What percentage of aerotow operations used CG hooks? How many aerotow upset accidents were there during that period? What percentage of the aerotow upset accidents involved CG hooks? If these figures aren't available, is the use of CG hooks being discouraged based simply on the assumed lack of positive longitudinal stability during aerotow? Marc I hate to agree with Chris Rollings but he sums it up quite well. The questions posed by Marc Ramsey, difficult to obtain that no one will even try, so they will not get answered. Whatever we write here, I cannot see the owners of C of G only aircraft rushing out to retrofit a nose hook. Having towed on both, the worst being an Olympia 2B with only a C of G hook and a powerful tug, I prefer the nose hook every time. Some years ago, mid 1908’s I believe, the Australian Gliding Association, following a number of tug upsets produced a very graphic illustration showing the various stages of a tug being upset by a glider on tow, wherever the hook. It clearly and simply illustrated the difficulties this caused the pilots at each end of the combination. C of G hooks merely increase the likely hood of this happening with an inattentive pilot. The short answer is educating the pilots on the particular hook to be used and hammering home the consequences of inattention to all. The Australian poster should be displayed at all gliding sites. To try to answer the question that started this thread, the B4 pilots problems could be solved by asking the tug to accelerate a little faster from the start, having due regard to the problems this may cause. IE Things may go wrong even quicker! Dave |
#77
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The Capstan and Olypia 2 really have 'compromise' hooks,
halfway between nose hook and C of G hook. Not quite so good for winch launching but not as wildly unstable on aerotow as a true C of G hook. Not sure about the accident statisics for those days, my close involvement only began when I started work at Booker in 1970 - certainly there were aerotow accidents back then. Chris Rollings At 10:48 07 January 2004, Silent Flyer wrote: Chris Rollings wrote in message ... SNIP Let's look at the numbers. I will use the UK as an example, since I have a fairly accurate knowledge of the statistics there, but the pricipals are the same for any of the World's gliding nations. SNIP Chris I learnt to fly at an all aerotow operation back in 1967 at the old Leicestershire club at Rearsby. Training was on a Slingsby Capstan and pupils were then sent solo in an Olympia 2b, (in my case after twenty seven flights). These of course like virtually all gliders of that time had only CoG hooks. What do the accident statistics say when comparing that period with the present day ? Don Brown |
#78
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Todd is right in every respect, at least one of the
aerotow upset fatals involved a largly winch launch experienced pilot and the cicumstances he surmised. Chris Rollings At 15:06 07 January 2004, Todd Pattist wrote: Eric Greenwell wrote: The US might have less trouble with CG hooks than a country where aero tow isn't as common. There are a couple of things that might make the U.S. experience a little different in view of our training and operating procedures and the different experience of our pilot base. Many/most U.S. pilots are unfamiliar with winch launching and are extremely uncomfortable with any kind of nose high attitude on launch. I have occasionally wondered if some 'kiting on tow' accidents might be related to the pilots control response in a situation that is dangerous for an aerotow, but not for a winch launch. Another potential difference is the prevalence of U.S. training in the venerable 2-33, which typically produces a very high nose up attitude as the roll commences and requires a strong forward stick to compensate. Of course, despite those comments, we also experience too many towing accidents. The CG hook can be implicated in more than the kiting accidents, and I know several pilots who have purchased or retrofitted the nose hook after a loss of directional control during the initial roll on a CG hook aerotow launch. Todd Pattist - 'WH' Ventus C (Remove DONTSPAMME from address to email reply.) |
#79
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Yes the pull can be enough to affect stability, that
was what the test I descibed demonstrated. Chris Rollings At 18:36 07 January 2004, Greg Arnold wrote: Marc Ramsey wrote: If these figures aren't available, is the use of CG hooks being discouraged based simply on the assumed lack of positive longitudinal stability during aerotow? Is the pull on a CG hook during aerotow ever great enough to have much effect on the longitudinal stability of the glider? I have never noticed such an effect, so I wonder if pilots who fly from a winch (very quick acceleration and doubtless a significant effect on longitudinal stability) are unfairly extrapolating their experience there to the aerotow situation. Doubtless a nose hook is better for aerotow, but I wonder if the alleged advantages aren't being oversold by some posters to this thread. |
#80
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The point is not 'does a Cof G hook cause a glider
to pitch up on tow'. The point is that if something (an accidental pilot input, or a gust not corrected for immediately because the pilot in momentarily distracted) causes the glider to pitch up, will it carry on pitching further up of its own accord, stay it the attitude it has reached, or start to pitch back down of its own accord? If the first of those three, how easy is it to stop it pitching up? In the tests on the Ka8, it seemed to me to be (almost?) impossible to stop it, once the pitch angle exceeded about 30 degrees. Don't know about most of the other types mentioned in this thread. I've flown most of them, but even I didn't include 'simulated tug upset whilst aerotowing on C of G hook' in my normal type conversion exercises - I think I would have found it hard to get a tow after a while if I had. Chris Rollings At 00:00 08 January 2004, Mike Borgelt wrote: On Tue, 6 Jan 2004 18:39:17 -0000, 'W.J. \(Bill\) Dean \(U.K.\).' wrote: There have been several fatal 'aerotow upset' accidents in the U.K. where it seems certain that towing on a hook intended for winch launching was a factor. These include: Lasham new year 1963/4 Auster towing a Ka 6cr or Skylark 2 (I forget which), Tug at Aboyne towing a Ka 6e, Tugs (Super Cubs) towing K 18s at Portmoak and Dunstable (within a few months of each other), this led to the tests by Chris Rollings, Verdun Luck and Brian Spreckley at Booker see http://www.glidingmagazine.com/ListF...Dtl.asp?id=327 . Will that do, or how many others do you need? So that is 4 in 40 years. I think we've managed to kill that many towplane pilots in Aus in the last 15 in mid airs. At least one, maybe more would have had a good chance of survival if he had had a parachute. Something that still isn't required here. The common link with the upsets mentioned seems to be high wing wooden gliders of low wing loading with deep fuselages. These may be prone to pitch up. How long were the ropes in these situations? Were there other circumstances that contributed? Could they have been compensated for? Any glider which launches well on a cable using the aft launching hook, will do the same behind a tug maybe killing the tug pilot in the process. If you really think that the glider pilot can control or stop this process once it starts, READ THE ARTICLE LINKED ABOVE; I suggest that the pilots who conducted those tests were more experienced, more current and just plain better than you. You are suggesting that on a winch launch with much higher loads in the cable that these gliders are not controllable in pitch? To my certain knowledge it is possible to fit a forward hook for aerotow to the ASW 15, 17, ASK 18, ASW 19, 20, and 22 and the Pegase; the ASK 21 and 23 and I think later types were fitted with it as standard. I don't know of any examples of these in club (as distinct from private owner) use which have not been modified. I once owned an ASW20B. The GFA required the nose hook to be fitted. The Scheicher factory job on this was pitiful. Nobody who bought gliders from this batch of 6 put up with it. The releases were taken out and glassed over. When finishing the area it became apparent that the skin had been distorted by the additional release bulkheads. I don't ever recall the 20B having the slightest tendency to pitch up on aerotow on the belly release. I have no aversion to properly engineered nose hooks like in Glasflugel and Schempp gliders but poorly designed retrofits are a bad idea particularly when no testing has been done on that particular type to see if indeed the 'solution' is effective or even necessary. The BGA considers 150 foot ropes acceptable. I consider these dangerously short, 200 feet is more like it with around 240 to 260 being much better. Now consider this:: The world's politicians and bureaucrats are forever looking for ways to meddle in our lives to keep themselves in jobs. If we place requirements on our own operations (Like compulsory nose releases)that are not firmly founded in proper testing and rational analysis we weaken our case in resisting the idiot requirements that come in a never ending stream from these people. I've yet to meet anyone who has flown on a 250 foot rope who hasn't admitted it was easier than on shorter ropes. When I aerotow I want to go soaring for maybe several hours and maybe the enviroment on the ground was stressful due to heat, humidity etc. I really don't need a 5 minute adrenaline thrill to begin a cross country. I would like tows to be a non event. Longer ropes and tow pilots who don't try to thermal or do other sudden manouevers all aid in this. The scariest tow I ever had was in my Salto (with nose release) behind a tow pilot who was not paying attention and who pulled back hard on leaving the ground as we encountered a gust leaving me dangling low from the end of the rope with decreasing airspeed. Followed by a hard push just as I was climbing slowly back up into station(low tow) leaving me very high followed by another hard pull which put me very low again wherupon I released and did a 180 back to the strip. Probably my shortest ever aerotow flight, closest to disaster and on the 130 foot or so ropes that were fashionable at the time. I never ever want to do this again. It was 30 years ago and I remember it clearly. A rope twice as long likely would have made this a non event. The surprisingly easy tows were at Minden in an ASW20(belly release) through the rotor behind a 182. Long rope, no problem at all. Mike Borgelt |
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