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Auto-Towing - why is this not more popular?



 
 
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  #1  
Old October 5th 15, 05:57 AM posted to rec.aviation.soaring
Sean Fidler
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Default 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  
Old October 5th 15, 10:00 AM posted to rec.aviation.soaring
Bruce Hoult
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Default 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  
Old October 5th 15, 10:29 AM posted to rec.aviation.soaring
Tango Whisky
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Default 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  
Old October 5th 15, 12:01 PM posted to rec.aviation.soaring
gb
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Default 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.

  #5  
Old October 5th 15, 12:13 PM posted to rec.aviation.soaring
Roy Pentecost[_2_]
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Default 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

  #6  
Old October 5th 15, 12:22 PM posted to rec.aviation.soaring
Roy Pentecost[_2_]
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Default 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



  #7  
Old October 5th 15, 12:24 PM posted to rec.aviation.soaring
Burt Compton - Marfa Gliders, west Texas
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Posts: 182
Default Auto-Towing - why is this not more popular?

Chapter 3 of the classic American Soaring Handbook has about 23 pages on Auto Tow with several illustrations including a homebuilt car tow release and a technical discussion of the process. 3,500' of runway is the minimum runway length suggested so the sailplane can (barely) make a 360 degree circle to land. Straight-line auto tow and auto tow with pulley are discussed in detail.

As simple as it appears, auto tow should be carefully researched. Finding a sailplane pilot who has supervised auto tow is essential. A ground-launch endorsement from an authorized CFI per FAR 61.31(j) is required for the sailplane pilot unless "grandfathered" however proficiency is essential for both the pilot and the driver. An observer in the auto is important for safety. Density altitude will affect the power of the auto motor and the speed required for the sailplane to launch.

One possible issue with auto tow on airports with airplane traffic is that the cable cannot be reeled in unless a winch system is mounted on the back of a pick-up truck. Some of the hang glider folks have developed this system.

Read the article in the May-June 1955 SOARING magazine, "The Elimination of Guess-Work in Auto Towing" by Otto Zauner and Art Heavener.

The American Soaring Handbook was a binder of 10 chapters on essential aspects that a SSA club needed to know about maintenance, auto, winch and aerotow launching, instruments and much more. Long out of print this handy 6"x9" blue binder might be found on dusty bookshelves in gliderport clubhouses around the USA. Often listed on E-bay and internet book searches such as Albris, this valuable collection of knowledge written by some of the legends of soaring is essential reading. About $25 if all of the 10 chapters are included in the binder.

For an entertaining (but not instructional) video of auto tow watch the "Reunion" episode of the '50's Sci-Fi TV show, "One Step Beyond".

  #8  
Old October 5th 15, 12:30 PM posted to rec.aviation.soaring
Muttley
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Posts: 89
Default Auto-Towing - why is this not more popular?

Hi Sean
The Dublin Gliding Club is doing every year an expedition to the Beaches on the Dingle Peninsula in the South of Ireland where gliders are car towed see enclosed or others on You Tube
https://vimeo.com/108137453

Regards
Bruno
  #9  
Old October 5th 15, 01:02 PM posted to rec.aviation.soaring
Papa3[_2_]
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Posts: 753
Default Auto-Towing - why is this not more popular?

Two excellent posts above from Roy and Burt. I learned partially on auto tow, with maybe 25 launches done by that method over the space of two winters (we would put the towplane away for the winter and revert to auto towing).. Roy summarizes the operational aspects beautifully. As far as equipment, we used "junker" big-block American iron from the early and mid 1970s. The Oldsmobile Custom Cruiser wagon was ideal, since it has a built-in observer seat in the rear. We found that for whatever reason, auto-towing seemed to put a lot of wear and tear on the transition and drive train. Moderately hard acceleration with the load of the glider followed by near-panic stopping repeatedly at the other end meant that I got to be a pretty decent auto mechanic. At our facility, we had 3,000 foot paved with 800 or so grass overrun. With the glider's tail right in the weeds, the car was just on the runway. That gave us the full 3,000 to accelerate, cruise, then stop. We normally got about 600 feet of altitude, though 700 or even 800 was possible if the wind was right down the runway.

So, it's definitely a viable option, especially for early training. Practically, we ended up getting maybe 8-10 launches during a session before something broke on the vehicle or we had a big rope break. We spent a lot of time fixing per every minute of aviating, but when you're in college, $5 tows are attractive!

Erik Mann (P3)

  #10  
Old October 5th 15, 01:30 PM posted to rec.aviation.soaring
Tango Eight
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Posts: 962
Default Auto-Towing - why is this not more popular?

On Monday, October 5, 2015 at 12:57:33 AM UTC-4, 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


It's only as economical as your space and labor happens to be. Ideal for a dry lake. Hobbs is sort of a paved dry lake :-).

When I was a student pilot, we did 2-33 "cat shots" off Harris Hill with two old tow ropes spliced together, later with a proper 400' cable, into gentle late afternoon ridge lift, all powered by an old 307 Chevelle with questionable brakes (thanks Dave!). A total gas, never to be forgotten. Driving the car (which I did a lot) was even more exciting than flying the glider.. The brow of the hill slopes off in a fashion that makes the nerves a little uneasy... especially with those rusty four wheel drum brakes.

-Evan Ludeman / T8
 




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