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#1
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Auto-Towing - why is this not more popular?
I had an interesting conversation with a pal about auto-tow glider launching method recently. It seems academic really.
When cost is considered, auto-towing has to be far more affordable than even winching. Maybe $1.50 per tow, max? In aviation, the cost is always critical. Especially in gliding club environments. Aerotows are $30-50 per tow. Winches are extremely expensive to purchase, to maintain, and insure and require skilled operators. Auto-tow procedure seems fairly simple. 1) Steady strong acceleration until the glider comes airborne, then 2) add 5mph and 3) hold that speed until you hear differently from the pilot. Of course, 4) stop at the end of the runway :-). Why is auto-towing not a mainstream method of getting gliders airborne? I saw auto-towing happen regularly at Hobbs this year (my first visit). It was quite graceful and almost exotic. To be honest, it looks even more fun than winching. I am very interested in learning what you know, your thoughts and your opinions. Sean 7T |
#2
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Auto-Towing - why is this not more popular?
On Monday, October 5, 2015 at 7:57:33 AM UTC+3, Sean Fidler wrote:
I had an interesting conversation with a pal about auto-tow glider launching method recently. It seems academic really. When cost is considered, auto-towing has to be far more affordable than even winching. Maybe $1.50 per tow, max? In aviation, the cost is always critical. Especially in gliding club environments. Aerotows are $30-50 per tow. Winches are extremely expensive to purchase, to maintain, and insure and require skilled operators. Auto-tow procedure seems fairly simple. 1) Steady strong acceleration until the glider comes airborne, then 2) add 5mph and 3) hold that speed until you hear differently from the pilot. Of course, 4) stop at the end of the runway :-). Why is auto-towing not a mainstream method of getting gliders airborne? I saw auto-towing happen regularly at Hobbs this year (my first visit). It was quite graceful and almost exotic. To be honest, it looks even more fun than winching. I am very interested in learning what you know, your thoughts and your opinions. Sean 7T Because it needs a LOT of space, unless all you want to do is get something with a sustainer engine off the ground? (or you're at a ridge-top site) |
#3
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Auto-Towing - why is this not more popular?
Am Montag, 5. Oktober 2015 06:57:33 UTC+2 schrieb Sean Fidler:
I had an interesting conversation with a pal about auto-tow glider launching method recently. It seems academic really. When cost is considered, auto-towing has to be far more affordable than even winching. Maybe $1.50 per tow, max? In aviation, the cost is always critical. Especially in gliding club environments. Aerotows are $30-50 per tow. Winches are extremely expensive to purchase, to maintain, and insure and require skilled operators. Winches can be homebuilt. They are not expensive to maintain. At least in Europe, they are not expensive to insure. In most European clubs (maybe except Southern France), most club members are trained to operate a winch, and do so based on a rooster schedule. So why exactly do you want to replace them with a car screaming down the runway? Bert TW |
#4
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Auto-Towing - why is this not more popular?
Good question. Seems to me reverse car tows(fixed pulley windward car drives toward the glider) would be the way to go. Has there been any sailplane work with car mounted pay out winches? Pay out winches are what the hangglider and paraglider community have mostly settled on using. Both of these solutions somewhat mitigate the space needed to auto tow.
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#5
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Auto-Towing - why is this not more popular?
I once flew for an ESPN video on flying (Secrets of Speed). One of the
launch methods used was an auto pulley tow wherein the pulley was mounted to the receiver on the back of the car and the cable was staked to the ground near mid field. The car drove in the takeoff direction during the launch and, with the 2:1 advantage of the pulley, it was every bit as exciting as a winch. The car drove at about 1/2 the speed of the glider. We were using a 3,400' runway and I don't recall the release height, though it was not as high as a winch with a full runway length of cable. On 10/5/2015 5:01 AM, GB wrote: Good question. Seems to me reverse car tows(fixed pulley windward car drives toward the glider) would be the way to go. Has there been any sailplane work with car mounted pay out winches? Pay out winches are what the hangglider and paraglider community have mostly settled on using. Both of these solutions somewhat mitigate the space needed to auto tow. -- Dan, 5J |
#6
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Auto-Towing - why is this not more popular?
Dan, a pulley tow launches a glider just fine - but then you need to reset for the next launch. Often, this means untangling the rope. Straight auto tow or winch launch rarely tangles the rope.
There are very few pulley tow operations in the world and cycle time is the usual reason why they gave up on pulleys and moved on to winch launch. On Monday, October 5, 2015 at 9:16:28 AM UTC-6, Dan Marotta wrote: I once flew for an ESPN video on flying (Secrets of Speed).* One of the launch methods used was an auto pulley tow wherein the pulley was mounted to the receiver on the back of the car and the cable was staked to the ground near mid field.* The car drove in the takeoff direction during the launch and, with the 2:1 advantage of the pulley, it was every bit as exciting as a winch.* The car drove at about 1/2 the speed of the glider.* We were using a 3,400' runway and I don't recall the release height, though it was not as high as a winch with a full runway length of cable. On 10/5/2015 5:01 AM, GB wrote: Good question. Seems to me reverse car tows(fixed pulley windward car drives toward the glider) would be the way to go. Has there been any sailplane work with car mounted pay out winches? Pay out winches are what the hangglider and paraglider community have mostly settled on using. Both of these solutions somewhat mitigate the space needed to auto tow. -- Dan, 5J |
#7
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Auto-Towing - why is this not more popular?
On Monday, October 5, 2015 at 6:18:15 PM UTC-6,
http://www.coloradosoaring.org/think...ey/default.htm Reverse pulley is the best way to autotow. Cotswold no longer does this, but did so for about 30 years. Frank Whiteley wrote: Dan, a pulley tow launches a glider just fine - but then you need to reset for the next launch. Often, this means untangling the rope. Straight auto tow or winch launch rarely tangles the rope. There are very few pulley tow operations in the world and cycle time is the usual reason why they gave up on pulleys and moved on to winch launch. On Monday, October 5, 2015 at 9:16:28 AM UTC-6, Dan Marotta wrote: I once flew for an ESPN video on flying (Secrets of Speed).* One of the launch methods used was an auto pulley tow wherein the pulley was mounted to the receiver on the back of the car and the cable was staked to the ground near mid field.* The car drove in the takeoff direction during the launch and, with the 2:1 advantage of the pulley, it was every bit as exciting as a winch.* The car drove at about 1/2 the speed of the glider.* We were using a 3,400' runway and I don't recall the release height, though it was not as high as a winch with a full runway length of cable. On 10/5/2015 5:01 AM, GB wrote: Good question. Seems to me reverse car tows(fixed pulley windward car drives toward the glider) would be the way to go. Has there been any sailplane work with car mounted pay out winches? Pay out winches are what the hangglider and paraglider community have mostly settled on using. Both of these solutions somewhat mitigate the space needed to auto tow. -- Dan, 5J |
#9
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Auto-Towing - why is this not more popular?
Having done both in the UK, at two different sites, I can compare and
contrast: 1. Auto-tow needs a hard surface, realistically at least 1000m and preferably nearer 2000m long. Winch launch can be done off grass surfaces needing only a route for cable tow out using a tractor or 4x4. 2. Winching only accelerates the glider (plus a small amount of engine, transmission and drum inertia) thus reaching take-off speed takes much less time than auto-tow where you also accelerate close to 2 tons of auto as well as the glider (say about 0.6 tons). Typical winch launch reaches take-off speed in 2-3 seconds whereas auto tow takes 10-15 seconds to get airborne. This longer ground roll also exacerbates cable wear (along the hard abrasive surface for auto-tow, compared to soft grass surfaces on winch strips). 3. The angle of pull is more favourable as the winch is always further away than the auto would be at any given point. There is rather more down than forward pull with an auto, mid-climb onwards. This increases cable tension (limited by the weak link) for a given level of 'thrust' so makes cable breaks more likely and reduces the amount you can use back pressure to increase the angle of attack and hence climb rate. 4. With an auto, you have to terminate the climb before the end of the runway so you can stretch out the cable, as it falls by parachute, so it does not end up in a big knotted pile. This reduces the effective useable runway length. 5. Heavy cars with auto transmission generally need a lot more maintenance than a winch (lots more effort in accelerating and decelerating the tow vehicle itself). My experience is that, all other things being equal, you typically get around 50% higher for a given runway length using a winch. Ther may be occasions, such as on expeditions, when auto-tow is expedient but for regular training operations such as those done in Europe, you can't beat the winch. Regards, Roy Pentecost |
#10
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Auto-Towing - why is this not more popular?
Yes I've also done reverse pulley. It solves a few of the auto-tow issues: Angle of pull, length to tow out cable after release but still leaves the others: Time and distance to accelerate great moving mass. It also introduces much more cable wear as part of the cable is always on the ground. Reverse pulley is better than straight tow but still less effective than the winch. At 11:13 05 October 2015, Roy Pentecost wrote: Having done both in the UK, at two different sites, I can compare an contrast: 1. Auto-tow needs a hard surface, realistically at least 1000m an preferably nearer 2000m long. Winch launch can be done off grass surface needing only a route for cable tow out using a tractor or 4x4. 2. Winching only accelerates the glider (plus a small amount of engine transmission and drum inertia) thus reaching take-off speed takes much les time than auto-tow where you also accelerate close to 2 tons of auto a well as the glider (say about 0.6 tons). Typical winch launch reache take-off speed in 2-3 seconds whereas auto tow takes 10-15 seconds to ge airborne. This longer ground roll also exacerbates cable wear (along th hard abrasive surface for auto-tow, compared to soft grass surfaces o winch strips). 3. The angle of pull is more favourable as the winch is always further awa than the auto would be at any given point. There is rather more down tha forward pull with an auto, mid-climb onwards. This increases cable tensio (limited by the weak link) for a given level of 'thrust' so makes cabl breaks more likely and reduces the amount you can use back pressure t increase the angle of attack and hence climb rate. 4. With an auto, you have to terminate the climb before the end of th runway so you can stretch out the cable, as it falls by parachute, so i does not end up in a big knotted pile. This reduces the effective useabl runway length. 5. Heavy cars with auto transmission generally need a lot more maintenanc than a winch (lots more effort in accelerating and decelerating the to vehicle itself). My experience is that, all other things being equal, you typically ge around 50% higher for a given runway length using a winch. Ther may be occasions, such as on expeditions, when auto-tow is expedien but for regular training operations such as those done in Europe, you can' beat the winch. Regards, Roy Pentecost |
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