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#1
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OT WWII Memoirs (was SAFE Winch Launching ...)
At 17:15 26 July 2009, brianDG303 wrote:
On Jul 26, 12:15=A0am, Derek Copeland wrote: We Brits get tired of always being airbrushed out of history by Hollywood= .. For example there were more British and British Commonwealth (e.g. Australians, Canadians) troops involved in the D Day landings than US troops, but you might not have noticed this if you watch 'Saving Private Ryan' and many other similar movies. Throughout WW2 we bombed Germany by night without fighter cover, using bombers such as the Lancaster and the Mosquito, which where less heavily amoured than a B17, but could carry a much greater weight of bombs as a result. In fact even the little unarmed twin engined Mosquito bombers mad= e out of plywood could carry more bombs than a B17. I believe that they didn't show up very well on radar because of their construction, so they were probably the original 'stealth bomber' =A0 On entering the European war the USAAF was warned by the RAF that dayligh= t bombing raids over Germany would be pretty suicidal, as they had already found out the hard way, but of course the Americans (as usual) thought they knew best and had better technology. The rest, Schweinfurt etc, is history! I have to say however that the US bomber crews who took part in such raid= s must have been very brave men, knowing that their tight, straight and lev= el formations where sitting ducks for German radar predictive flak guns and = a well organised fighter force. It was only towards the end of the war when the Mustangs shot down many German fighters that the odds became a little more favourable for them. Derek Copeland =A0 =A0 Derek, Taking a single statistic (the number of troops landing on the Normandy beaches) may be a fact but obscures the truth. The ritish consider the invasion of Normandy to have begun on June 6 and ended on August 29 of 1944, and the casualties (Killed, missing, wounded) of British, Canadian, and Polish troops (there were very few Australians, with about a dozen casualties I think) totaled 83,045 as against the US losses of 125,847. These are the British numbers from the War Diary, 21st Army Group, but other estimates are similar. Also: Hollywood movies are intended to make money and not portray history. Your comment about French gratitude, we Americans like to forget that without the French we could never have won the war of 1776 and the cost to them of that help. We never thanked them much for that either. Your comment about fighting Germany to a draw is simply not supportable. Hitler's direction was always east but he turned west when England and France declared war on Germany following his invasion of Poland. He defeated France and put England in a box, then turned east again. Two fatal errors in judgment, of which he was in the habit of making. Come to mention it, we Brits have never received much in the way of gratitude from the Yanks for supporting George W Bush's futile and counter productive invasions of Iraq and Afghanistan! So much for the 'special relationship'....! Hitler's Germany tried very hard to invade the UK as they had already done to Poland, Belgium, Holland and France and were beaten off, losing a fair proportion of the Luftwaffe in the process. As well as shooting down many attacking aircraft, the RAF also bombed the invasion fleets in the French ports pretty well non stop, making the invasion non-viable. These are historical facts. Derek Copeland |
#2
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OT WWII Memoirs (was SAFE Winch Launching ...)
On Jul 26, 11:45*am, Del C wrote:
At 17:15 26 July 2009, brianDG303 wrote: On Jul 26, 12:15=A0am, Derek Copeland *wrote: We Brits get tired of always being airbrushed out of history by Hollywood= .. For example there were more British and British Commonwealth (e.g. Australians, Canadians) troops involved in the D Day landings than US troops, but you might not have noticed this if you watch 'Saving Private Ryan' and many other similar movies. Throughout WW2 we bombed Germany by night without fighter cover, using bombers such as the Lancaster and the Mosquito, which where less heavily amoured than a B17, but could carry a much greater weight of bombs as a result. In fact even the little unarmed twin engined Mosquito bombers mad= e out of plywood could carry more bombs than a B17. I believe that they didn't show up very well on radar because of their construction, so they were probably the original 'stealth bomber' =A0 On entering the European war the USAAF was warned by the RAF that dayligh= t bombing raids over Germany would be pretty suicidal, as they had already found out the hard way, but of course the Americans (as usual) thought they knew best and had better technology. The rest, Schweinfurt etc, is history! I have to say however that the US bomber crews who took part in such raid= s must have been very brave men, knowing that their tight, straight and lev= el formations where sitting ducks for German radar predictive flak guns and = a well organised fighter force. It was only towards the end of the war when the Mustangs shot down many German fighters that the odds became a little more favourable for them. Derek Copeland =A0 =A0 Derek, Taking a single statistic (the number of troops landing on the Normandy beaches) may be a fact but obscures the truth. The ritish consider the invasion of Normandy to have begun on June 6 and ended on August 29 of 1944, and the casualties (Killed, missing, wounded) of British, Canadian, and Polish troops (there were very few Australians, with about a dozen casualties I think) totaled 83,045 as against the US losses of 125,847. These are the British numbers from the War Diary, 21st Army Group, but other estimates are similar. Also: Hollywood movies are intended to make money and not portray history. Your comment about French gratitude, we Americans like to forget that without the French we could never have won the war of 1776 and the cost to them of that help. We never thanked them much for that either. Your comment about fighting Germany to a draw is simply not supportable. Hitler's direction was always east but he turned west when England and France declared war on Germany following his invasion of Poland. He defeated France and put England in a box, then turned east again. Two fatal errors in judgment, of which he was in the habit of making. Come to mention it, we Brits have never received much in the way of gratitude from the Yanks for supporting George W Bush's futile and counter productive invasions of Iraq and Afghanistan! So much for the 'special relationship'....! Hitler's Germany tried very hard to invade the UK as they had already done to Poland, Belgium, Holland and France and were beaten off, losing a fair proportion of the Luftwaffe in the process. As well as shooting down many attacking aircraft, the RAF also bombed the invasion fleets in the French ports pretty well non stop, making the invasion non-viable. These are historical facts. Derek Copeland Derek, agree with the facts, just not the conclusions. The UK won the Battle of Britain (good job that!) but if Hitler's #1 goal had been to defeat Britain he probably could have done so, I'm not convinced GB 'fought him to a draw'. Hitler was defeated in large part by the temperature and terrain of Russia as was Napoleon before him, along with Russia's ability to take almost unlimited casualties in the process, and Russia was always the goal. Perhaps we should leave the Iraq/Afghanistan theater for another day. Do they winch-launch there? I'll be over in six weeks walking the ground of the AFalaise if you can come over we could get into it and enjoy |
#3
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SAFE Winch Launching
As interesting as it is the discussion about who did what in the last war
has about as much relevance to gliding and safe winching as a tesion controlled winch. The differences are too numerous to mention except that a Spitfire, Hurricane and Mustang all worked and did a useful job, unlike the mythical tension controlled winch. |
#4
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OT WWII Memoirs (was SAFE Winch Launching ...)
At 18:45 26 July 2009, Del C wrote:
Hitler's Germany tried very hard to invade the UK as they had already done to Poland, Belgium, Holland and France and were beaten off, losing a fair proportion of the Luftwaffe in the process. As well as shooting down many attacking aircraft, the RAF also bombed the invasion fleets in the French ports pretty well non stop, making the invasion non-viable. These are historical facts. Germany could have swept up the British troops at Dunkirk, and then immediately invaded with a pretty good chance of success. But Hitler dithered, and listened to Goering, and blew his chance. He really did make quite a few decisions that, in hindsight at least, were disastrous. We should, I suppose, be grateful for that. Jim Beckman |
#5
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SAFE Winch Launching - Constant Tension
The 'constant tension' theory of winch launching was dreamed up by
someone in the US who has no practical experience of winch launching whatsoever! So far nobody has managed to built a true tension winch (which would measure actual cable tension), so we don't know if the theory would work or not. The concept seems to have become a bit of a Holy Grail in the US, which is probably inhibiting the design and building of more conventional winches that would work just fine. On the Yahoo Winch Design site I have suggested carrying out some autotowing experiments, where it would fairly easy to mount an in-line load cell to find out if CT would work, but this suggestion was rejected by the above person and his followers as not being relevant due to the mass and inertia of the towcar. Such an experiment would work in calm conditions. There are a number of constraints in real life winch launching. 1) The minimum airspeed has to be at least 1.3 x the normal stalling speed (Vs), to avoid the risk of stalling or spinning at the increased wing loading due to the cable pull. At the high levels of pull suggested this might increase to 1.4 Vs. 2) The optimum climbing airspeed for best gain of height seems from practical experience to be in the range 1.5-1.6Vs. 3) Most gliders have a fairly low maximum winch launching speed (Vw), which is set for structural reasons. There should also be a weak link (fuse) included in the cable line which will break before the glider does. 4) Many gliders, particularly older ones such as the K13, only have a very limited speed range in which they will climb safely and well without exceeding Vw. The stalling speed of a K13 can increase to over 50knots near the top of the launch, its optimum climb speed is about 56knots and its Vw is 58knots. Some more modern types such as the K21 are a bit more speed tolerant. 5) You have to fly the glider in such a manner that you can always recover from a cable break or winch power failure, and not risk a stall or flick spin. This entails a fairly shallow initial climb followed by a controlled rotation rate of not more than 10 degrees per second. I believe the Germans once managed to kill 12 pilots in one year (1995) by carrying out what are known as 'kavalier starts' where the glider climbs very steeply straight off the ground to maximise height. We have also had a few such accidents in the UK, always on very powerful winches so rapid acceleration doesn't make them safe. The theory behind constant tension is you provide a pull or tension that is close to the breaking strain of the weak link. Thus you maximise the pull and the height gain in accordance with the Goulthorpe formula: h = P/W/(1+P/W) x l where h = height, P= Pull, W = glider weight and l = notional cable run from the point of rotation. Thus for a Pull equal to the weight of the glider you would expect to get a height of 50% of the effective cable length. However, the above equation is idealised and assumes zero cable weight and zero drag, and is based on 100% transfer of energy. For many years I launched on very powerful manually driven Tost winches. Many of the launches were way over Vw until you signalled too fast, but it was quite rare to break a weak link in the early part of the climb. I therefore suspect that the constant tension as a large fraction of the weak link strength idea would just vastly overspeed the launches. In order to contain the speed according to the theory, you would have to climb at an achieved climb angle of about 60 degrees. Most gliders run out of up elevator well below this angle. Such an angle would also represent more than a 'kavalier start' as described above! The other idea in the 'constant tension' theory is that the glider pilot would control the speed by pulling back harder to slow the launch down and easing forward to speed up. However I worry that a pilot trying to control the speed at the same time as the winch is trying to sense and control the tension would just lead to an oscillating or hunting situation. As a winch driver myself, I always try to avoid 'chasing the glider pilot' as this generally makes things worse. If I have to make a speed adjustment I just move the throttle to a slightly different setting and then hold it still again. The technique for controlling the airspeed from the glider end does work on a Skylaunch winch where you are giving a constant power setting and also works on constant torque Supacat (diesel + fluid flywheel)) winches. With either type of winch you have to start backing off the throttle setting near the top of the launch to avoid overspeeding the glider. We don't know if constant tension would give a constant and appropriate airspeed, or whether it would need to be varied for different stages of the launch to achieve this. Derek Copeland At 19:45 26 July 2009, Don Johnstone wrote: As interesting as it is the discussion about who did what in the last war has about as much relevance to gliding and safe winching as a tesion controlled winch. The differences are too numerous to mention except that a Spitfire, Hurricane and Mustang all worked and did a useful job, unlike the mythical tension controlled winch. |
#6
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SAFE Winch Launching - Constant Tension
As I see it the "constant tension" theory relies on being able to measure
the tension being exerted on the glider release at the winch drum. Quite how this might be achieved is very puzzling and has no relevance to the information required to give a safe and effective launch. If you were to say that measuring the tension at the glider release and using telemetry to pass this information to the winch then that might indeed work, however if you were going to the trouble of doing that you might as well send useful information, like the airspeed of the glider, so the winch driver could maintain a constant speed. Cable tension during a winch launch has sod all to do with anything except as an indicator to the winch driver of possible over or underspeed. It is the speed which is of relevance and importance. At 13:15 27 July 2009, Del C wrote: The 'constant tension' theory of winch launching was dreamed up by someone in the US who has no practical experience of winch launching whatsoever! So far nobody has managed to built a true tension winch (which would measure actual cable tension), so we don't know if the theory would work or not. The concept seems to have become a bit of a Holy Grail in the US, which is probably inhibiting the design and building of more conventional winches that would work just fine. On the Yahoo Winch Design site I have suggested carrying out some autotowing experiments, where it would fairly easy to mount an in-line load cell to find out if CT would work, but this suggestion was rejected by the above person and his followers as not being relevant due to the mass and inertia of the towcar. Such an experiment would work in calm conditions. There are a number of constraints in real life winch launching. 1) The minimum airspeed has to be at least 1.3 x the normal stalling speed (Vs), to avoid the risk of stalling or spinning at the increased wing loading due to the cable pull. At the high levels of pull suggested this might increase to 1.4 Vs. 2) The optimum climbing airspeed for best gain of height seems from practical experience to be in the range 1.5-1.6Vs. 3) Most gliders have a fairly low maximum winch launching speed (Vw), which is set for structural reasons. There should also be a weak link (fuse) included in the cable line which will break before the glider does. 4) Many gliders, particularly older ones such as the K13, only have a very limited speed range in which they will climb safely and well without exceeding Vw. The stalling speed of a K13 can increase to over 50knots near the top of the launch, its optimum climb speed is about 56knots and its Vw is 58knots. Some more modern types such as the K21 are a bit more speed tolerant. 5) You have to fly the glider in such a manner that you can always recover from a cable break or winch power failure, and not risk a stall or flick spin. This entails a fairly shallow initial climb followed by a controlled rotation rate of not more than 10 degrees per second. I believe the Germans once managed to kill 12 pilots in one year (1995) by carrying out what are known as 'kavalier starts' where the glider climbs very steeply straight off the ground to maximise height. We have also had a few such accidents in the UK, always on very powerful winches so rapid acceleration doesn't make them safe. The theory behind constant tension is you provide a pull or tension that is close to the breaking strain of the weak link. Thus you maximise the pull and the height gain in accordance with the Goulthorpe formula: h = P/W/(1+P/W) x l where h = height, P= Pull, W = glider weight and l = notional cable run from the point of rotation. Thus for a Pull equal to the weight of the glider you would expect to get a height of 50% of the effective cable length. However, the above equation is idealised and assumes zero cable weight and zero drag, and is based on 100% transfer of energy. For many years I launched on very powerful manually driven Tost winches. Many of the launches were way over Vw until you signalled too fast, but it was quite rare to break a weak link in the early part of the climb. I therefore suspect that the constant tension as a large fraction of the weak link strength idea would just vastly overspeed the launches. In order to contain the speed according to the theory, you would have to climb at an achieved climb angle of about 60 degrees. Most gliders run out of up elevator well below this angle. Such an angle would also represent more than a 'kavalier start' as described above! The other idea in the 'constant tension' theory is that the glider pilot would control the speed by pulling back harder to slow the launch down and easing forward to speed up. However I worry that a pilot trying to control the speed at the same time as the winch is trying to sense and control the tension would just lead to an oscillating or hunting situation. As a winch driver myself, I always try to avoid 'chasing the glider pilot' as this generally makes things worse. If I have to make a speed adjustment I just move the throttle to a slightly different setting and then hold it still again. The technique for controlling the airspeed from the glider end does work on a Skylaunch winch where you are giving a constant power setting and also works on constant torque Supacat (diesel + fluid flywheel)) winches. With either type of winch you have to start backing off the throttle setting near the top of the launch to avoid overspeeding the glider. We don't know if constant tension would give a constant and appropriate airspeed, or whether it would need to be varied for different stages of the launch to achieve this. Derek Copeland At 19:45 26 July 2009, Don Johnstone wrote: As interesting as it is the discussion about who did what in the last war has about as much relevance to gliding and safe winching as a tesion controlled winch. The differences are too numerous to mention except that a Spitfire, Hurricane and Mustang all worked and did a useful job, unlike the mythical tension controlled winch. |
#7
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SAFE Winch Launching - Constant Tension
At Feshiebridge, Scotland, AIUI they developed telemetry for indicating glider airspeed to the winch driver, and it was said to work very well. IIRC, it did not send an airspeed number in knots, but rather an indication of too slow, a bit slow, OK, a bit fast, or too fast (or something like that) which is what the winch driver really needs to know, they believed. The unit in the glider was calibrated for the glider type. It needs somebody with first hand experience of it to tell more, and I don’t know if it has been kept going. Chris N. |
#8
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SAFE Winch Launching - Constant Tension
I suspect fitting each and every glider with a telemetry transmitter
would be prohibitively expensive and resisted by most. A member of my club did this as an experimental demonstration and I was able to drive the winch to the appropriate airspeed. Getting accurate airspeed from a rope mounted device for the whole fleet could be problematic. Tension telemetry would be much easier to construct and ruggedize and limiting tension by glider type (and loading) is doable, probably more easily with hydraulically or electrically driven drums than with the reciprocating and rotating weight of IC engines in a direct drive (including automatic transmissions and drive trains) where airspeed output would be more easily used. Tension control should allow for wind gradients and shears but the control algorithms need to smooth the changes to avoid surges and hunting. Manually driven winches should not be discounted, but I have some ideas about standardization of controls and operating methods. Frank Whiteley On Jul 27, 9:30*am, Don Johnstone wrote: As I see it the "constant tension" theory relies on being able to measure the tension being exerted on the glider release at the winch drum. Quite how this might be achieved is very puzzling and has no relevance to the information required to give a safe and effective launch. If you were to say that measuring the tension at the glider release and using telemetry to pass this information to the winch then that might indeed work, however if you were going to the trouble of doing that you might as well send useful information, like the airspeed of the glider, so the winch driver could maintain a constant speed. Cable tension during a winch launch has sod all to do with anything except as an indicator to the winch driver of possible over or underspeed. It is the speed which is of relevance and importance. At 13:15 27 July 2009, Del C wrote: The 'constant tension' theory of winch launching was dreamed up by someone in the US who has no practical experience of winch launching whatsoever! So far nobody has managed to built a true tension winch (which would measure actual cable tension), so we don't know if the theory would work or not. The concept seems to have become a bit of a Holy Grail in the US, which is probably inhibiting the design and building of more conventional winches that would work just fine. On the Yahoo Winch Design site I have suggested carrying out some autotowing experiments, where it would fairly easy to mount an in-line load cell to find out if CT would work, but this suggestion was rejected by the above person and his followers as not being relevant due to the mass and inertia of the towcar. Such an experiment would work in calm conditions. There are a number of constraints in real life winch launching. 1) The minimum airspeed has to be at least 1.3 x the normal stalling speed (Vs), to avoid the risk of stalling or spinning at the increased wing loading due to the cable pull. At the high levels of pull suggested this might increase to 1.4 Vs. 2) The optimum climbing airspeed for best gain of height seems from practical experience to be in the range 1.5-1.6Vs. 3) Most gliders have a fairly low maximum winch launching speed (Vw), which is set for structural reasons. There should also be a weak link (fuse) included in the cable line which will break before the glider does. 4) Many gliders, particularly older ones such as the K13, only have a very limited speed range in which they will climb safely and well without exceeding Vw. The stalling speed of a K13 can increase to over 50knots near the top of the launch, its optimum climb speed is about 56knots and its Vw is 58knots. Some more modern types such as the K21 are a bit more speed tolerant. 5) You have to fly the glider in such a manner *that you can always recover from a cable break or winch power failure, and not risk a stall or flick spin. This entails a fairly shallow initial climb followed by a controlled rotation rate of not more than 10 degrees per second. I believe the Germans once managed to kill 12 pilots in one year (1995) by carrying out what are known as 'kavalier starts' where the glider climbs very steeply straight off the ground to maximise height. We have also had a few such accidents in the UK, always on very powerful winches so rapid acceleration doesn't make them safe. The theory behind constant tension is you provide a pull or tension that is close to the breaking strain of the weak link. Thus you maximise the pull and the height gain in accordance with the Goulthorpe formula: h = P/W/(1+P/W) x l where h = height, P= Pull, W = glider weight and l = notional cable run from the point of rotation. Thus for a Pull equal to the weight of the glider you would expect to get a height of 50% of the effective cable length. However, the above equation is idealised and assumes zero cable weight and zero drag, and is based on 100% transfer of energy. For many years I launched on very powerful manually driven Tost winches. Many of the launches were way over Vw until you signalled too fast, but it was quite rare to break a weak link in the early part of the climb. I therefore suspect that the constant tension as a large fraction of the weak link strength idea would just vastly overspeed the launches. In order to contain the speed according to the theory, you would have to climb at an achieved climb angle of about 60 degrees. Most gliders run out of up elevator well below this angle. Such an angle would also represent more than a 'kavalier start' as described above! The other idea in the 'constant tension' theory is that the glider pilot would control the speed by pulling back harder to slow the launch down and easing forward to speed up. However I worry that a pilot trying to control the speed at the same time as the winch is trying to sense and control the tension would just lead to an oscillating or hunting situation. As a winch driver myself, I always try to avoid 'chasing the glider pilot' as this generally makes things worse. If I have to make a speed adjustment I just move the throttle to a slightly different setting and then hold it still again. The technique for controlling the airspeed from the glider end does work on a Skylaunch winch where you are giving a constant power setting and also works on constant torque Supacat (diesel + fluid flywheel)) winches. With either type of winch you have to start backing off the throttle setting near the top of the launch to avoid overspeeding the glider. * We don't know if constant tension would give a constant and appropriate airspeed, or whether it would need to be varied for different stages of the launch to achieve this. Derek Copeland At 19:45 26 July 2009, Don Johnstone wrote: As interesting as it is the discussion about who did what in the last war has about as much relevance to gliding and safe winching as a tesion controlled winch. The differences are too numerous to mention except that a Spitfire, Hurricane and Mustang all worked and did a useful job, unlike the mythical tension controlled winch. |
#9
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SAFE Winch Launching - Constant Tension
Don Johnstone wrote:
... If you were to say that measuring the tension at the glider release and using telemetry to pass this information to the winch then that might indeed work, however if you were going to the trouble of doing that you might as well send useful information, like the airspeed of the glider, so the winch driver could maintain a constant speed. Cable tension during a winch launch has sod all to do with anything except as an indicator to the winch driver of possible over or underspeed. It is the speed which is of relevance and importance. We have recently tested the Launch Assistent that is sold by Skylaunch, http://www.skylaunchuk.com/index.htm and have found that is can be (as the name indicates) an *assistant* to the winch driver to help him/her judge the speed of the plane. It helps escpecially unexperienced winch drivers, or in adverse conditions like shearing winds within the launch. After 20 years of experience as a winch driver and winch instructor (Tost winch) I still believe a well instructed and experienced winch driver (and all winch drivers should have a certain minimum of launches per year) is able to judge and control the launch as good (or even better) than any automated (tension-controlled) system, that in the end also relies on the correct behavior of the pilot instead of the winch driver. -- Peter Scholz ASW 24 JEB |
#10
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SAFE Winch Launching - Constant Tension
Skylaunch sell a telemetry system called 'Launch Assistant' which relays
the actual airspeed of the glider to an LCD display mounted somewhere in the view of the driver. It costs a few hundred dollars in total. See: http://www.skylaunchuk.com/ Derek Copeland At 16:49 27 July 2009, Chris Nicholas wrote: At Feshiebridge, Scotland, AIUI they developed telemetry for indicating glider airspeed to the winch driver, and it was said to work very well. IIRC, it did not send an airspeed number in knots, but rather an indication of too slow, a bit slow, OK, a bit fast, or too fast (or something like that) which is what the winch driver really needs to know, they believed. The unit in the glider was calibrated for the glider type. It needs somebody with first hand experience of it to tell more, and I don=92t know if it has been kept going. Chris N. |
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