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

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)

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

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.

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

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

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

Thanks, Bill.

I only did a couple of pulley tows for the filming of the ESPN thing.
Some of the raw footage (not shown on TV) shows the rear end of the car
being lifted sufficiently that the driver lost control of the car.
Fortunately the passenger/observer was Emerson Fittipaldi and he reached
across, took the wheel, and straightened out the car. When I released,
it was quite a sight seeing the rope literally slamming down on the
runway. I can easily imagine the tangles this caused in the pulley
system. =-O

Dan

On 10/5/2015 6:18 PM, 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

--
Dan, 5J

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

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