At 08:00 PM 27/04/01, you wrote:
>To simplify matters I combine my contribution to those topics.
>
>>From my previous life in Germany I have some limited experience with high
>tow and now a few hundred low tow launches here. The low tow position is
>more comfortable and easier to fly, especially for a beginner. I'm not even
>sure why but thats what i found. I also regard the low tow position as
>significantly safer than high for the tug pilot. Overclimbing of the
>towplane by the glider occurs much easier from high for a number of reasons,
>i.e. the glider starts from high anyway and less time is available to
>correct, the glider accelerates during the process and generates more lift,
>the slingshot effect gives the last push. Without statistics at hand I can
>not prove but I dare say that more tugs were lost due to overclimbing than
>other causes.
>The added safety for the glider pilot due to 50 or so feet more height is
>marginal at best and should not be needed in a well managed tow. For these
>reasons I'm happy to stick with the book and instruct accordingly.
Most of the so called problems go away if you use a longer rope. Nearly 20
years ago Ron Sanders and I stayed a day after the Narromine Nationals to
fly each other's gliders and also the then new Ventus B.
After flying I remarked to John Rowe(the soaring center CFI) about the
length of the rope in use. The Pawnee was out there on the horizon. He said
"you didn't have any trouble did you" No was the answer, in fact it was a
nice easy tow with little energy in the tug wake by the time the glider
passed through it. They had adopted the long rope after finding their
students had a lot of trouble learning aerotow(low tow) which immediately
improved by using the longer rope.(240 feet I think it was).
Incorrect technique can also be a problem. There was a good article about
this in S+G about 10 years ago. Lining up parts of the tug or the tug with
the horizon was shown to be an unstable control loop.
Placing the tug in the correct position on the canopy is the right thing.
50 feet more height may make the difference between hitting an obstacle or
not in the event of a low altitude launch failure.
Consider what will happen with a relatively short rope in low tow if the
weak link breaks. There is a good chance that the rope will drape over the
glider and could get caught in the aileron/wing gap. It has happened. Bits
falling off tugs isn't that unusual either.
Don't forget our book is different from everyone else's including our
friends in New Zealand. Our arguments don't seem attractive to the rest of
the world. I guess they are all out of step.
>
>I do understand the importance of a weak link for the tow plane and pilot
>and don't advocate it's abolishment. As the glider pilot however I would be
>just as happy not to have one. I find it very difficult to see a glider
>damaged due to overload in an aerotow. It is a risk with low probability and
>much easier to manage than the risk of a broken weak link early in the tow.
The same logic means the tug is unlikely to be damaged in flight by lack of
a weak link. There is really little excuse for draping the rope over
approach end obstacles.
I'm a fan of rope retract winches for dedicated tugs. These have been
available for a long time. The weak link if used needs to go on the glider
end of course.
>I know of operations overseas which conciously delete the weak link because
>of that risk, significant in their case as they have nowhere to go once over
>the fence.
Having been towed down the main street of Willaston with full ballast on a
number of occasions and taken off to the west or north out of Waikerie into
the TV masts and orchards I'd say there are plenty of operations in this
country where there are few places to go immediately after takeoff. They
are just not recognised as such and low altitude aerotow launch failures
are mercifully rare so nobody worries about it enough.
>We are discussing the merits of high tow to deal with emergencies at low
>height and at the same time most Australien operations use a weak link made
>from an untested piece of thin rope, worn and UV damaged. The only correct
>weak link is of the certified steel kind close to the tow plane.
Completely agree with the properly designed weak link if we are going to
use one.
Mike Borgelt
Borgelt Instruments - manufacturers of quality soaring instruments
ABN 75532924542
Box 7474 Toowoomba M.C.
Queensland 4352
Australia
Tel 0746 355 784
mob 0428 355 784
0429 355 784
fax 0746 358 796
International
phone: int'l+ 61 7 46 355 784
Cellphone:int'l +61 4 28 355 784
int'l +61 4 29 355 784
fax : int'l+ 61 7 46 358 796
email: [EMAIL PROTECTED]
website:www.ozemail.com.au/~mborgelt
--
* You are subscribed to the aus-soaring mailing list.
* To Unsubscribe: send email to [EMAIL PROTECTED]
* with "unsubscribe aus-soaring" in the body of the message
* or with "help" in the body of the message for more information.
