Aerotow towrope instructions

The whiffle ball is free to slide on the tow rope. It slides up against the nose of the glider, including the release and pitot tube, but does not affect the airspeed indication.

We use hollow braid rope. For most of the gliders, 1/4 inch is strong enough. A stronger rope is used for the big, heavy gliders. The short piece, serving as the weak link, on both ends of the entire tow rope is only 3 feet or so long, and loops back, then weaves in and out three or four times, ending up inside the hollow braid rope.

The resulting loop is fed through the larger of the double Tost rings we use, then the free end of the weak/link tow rope (without the loop) goes through the loop in the rope before weaving in and out of the 1/4 inch rope serving as the weak link.

The other end of this weak link is fished inside of the actual, much stronger tow rope. We make it come in and out 3 or 4 times to keep it secure so it does not slip. No knots are used.

Of course both ends of the tow rope are assembled in the same manner, but the tow plane end does not have the whiffle ball.

The weak link / tow ring on the glider end of the tow rope is subject to the most abuse, and is carefully inspected by the wing runner, and pilot before each launch.

Most landings of the towplane at Ridge Soaring Gliderport are on grass. If we landed on a hard surface runway, we would have to re-think this. As a minimum, it might be necessary for the towplane to drop the rope.

Tom

On Monday, April 4, 2016 at 6:17:41 PM UTC-4, Paul Remde wrote:
Hi,

I am trying to find a good online resource with instructions for assembling
a glider aerotow towrope. I can't seem to find anything. I suspect that
every soaring club has a document explaining how they make their towropes..
I'd love to have links to a few on my web site.

Best Regards,

Paul Remde
Cumulus Soaring, Inc.

Slightly off the main topic--has anyone heard of a Tost ring failure? I can't find specs on the Tost site for rejection/replacement of the ring. Rough calculation says the small ring is 7 times stronger than the 5/16 poly rope. I doubt the rings are notch sensitive. So-what criteria do you use for relaxing them? Thanks

I think the FAA regs state the tow plane weak link must greater but no stronger than 25% more than the glider-side weak link. It is sounding like most people who even try to put in weak links are using the same weak link rope on both ends. How are you ensuring the tow plane weak link is stronger but not by 25% more than the glider side weak link?

Is this a case of it being difficult to live to the letter of the law but we can at least get closer to the spirit of the regs than not trying at all?

BTW, thanks for this thread, I will be building all the ropes for 3 nationals in the upcoming weeks and it is always great to hear what others are doing...

Bruno - B4

On Wednesday, April 6, 2016 at 5:44:11 PM UTC+3, wrote:
The whiffle ball is free to slide on the tow rope. It slides up against the nose of the glider, including the release and pitot tube, but does not affect the airspeed indication.

We use hollow braid rope. For most of the gliders, 1/4 inch is strong enough. A stronger rope is used for the big, heavy gliders. The short piece, serving as the weak link, on both ends of the entire tow rope is only 3 feet or so long, and loops back, then weaves in and out three or four times, ending up inside the hollow braid rope.

The resulting loop is fed through the larger of the double Tost rings we use, then the free end of the weak/link tow rope (without the loop) goes through the loop in the rope before weaving in and out of the 1/4 inch rope serving as the weak link.

The other end of this weak link is fished inside of the actual, much stronger tow rope. We make it come in and out 3 or 4 times to keep it secure so it does not slip. No knots are used.

Of course both ends of the tow rope are assembled in the same manner, but the tow plane end does not have the whiffle ball.

The weak link / tow ring on the glider end of the tow rope is subject to the most abuse, and is carefully inspected by the wing runner, and pilot before each launch.

Most landings of the towplane at Ridge Soaring Gliderport are on grass. If we landed on a hard surface runway, we would have to re-think this. As a minimum, it might be necessary for the towplane to drop the rope.

How does the pilot carefully inspect the rope, given that they should be strapped in checks done before the towplane arrives?

We have the wing runner quickly inspect the last third or quarter or whatever of the rope while bringing it in front of the glider, and hold up the last arms-span of it to show the pilot there are no knots in at least that part, but the pilot is several meters away and isn't going to be inspecting the rings of detailed condition of the rope.

The methods I have seen across 4 clubs now have been mostly dependant on how the towplanes are operating (Landing vs dropping the rope on pavement vs turf). The methods i have seen to date a

1) Using Solid braided poly rope, a single overhand knot followed by a 1-foot back-splice that goes through the tost ring. Tennis balls with slits cut in them are then threaded over the knot and the first part of the Tost connecting ring. The whole section is then wrapped in duct tape, which is added to regularly on the flight line when it is looking worn down. This is done at the Air Force Academy, where the tows are landing and taxiing on pavement with the ropes attached.

2) Using Hallow-core poly rope, run the end through the tost ring assembly, then thread back inside the main line for 6" or so, then outside for an inch or so, then feed whatever is remaining back into the main line. This seems to be the simplest and fastest method I have seen of making ropes.

3) Using Solid core poly rope, a simple back-splice of 8-10" and tying a knot after the back-splice for your "weak link" capability. This club also used different weak links for schweitzer links or for the lighter ships (1-26 and sparrowhawk).

Chris

FAR 91.309 addresses towing gliders and requires the tow rope to have a strength "not less than 80% of the maximum certificated operating weight of the glider and not more than 200%.

It also provides for special safety links with the same requirements.

The same regulation states the towing aircraft must have a safety link with a breaking strength greater, but not more than 25% greater than that on the glider end, and not more than twice the maximum certificated operating weight of the glider.

On Monday, April 4, 2016 at 3:17:41 PM UTC-7, Paul Remde wrote:
Hi,

I am trying to find a good online resource with instructions for assembling
a glider aerotow towrope. I can't seem to find anything. I suspect that
every soaring club has a document explaining how they make their towropes.
I'd love to have links to a few on my web site.

Best Regards,

Paul Remde
Cumulus Soaring, Inc.

all german gliders that I know about have a weak-link requirement in their operators handbook. I've always assumed US pilots are required to comply with the operators handbook and the FAA standards.

all german gliders that I know about have a weak-link requirement in their operators handbook. I've always assumed US pilots are required to comply with the operators handbook and the FAA standards.

You can also check the TCDS - online if you like. There will likely be something there regarding weak link strength. For example the ASW-27 FAA TCDS specifies:

"Weak Link
Ultimate strength
For winch tow
1455 lbs. (660 daN)
For aero tow
1445 lbs. (660 daN)"

I've also found bulletins from Cessna giving a maximum breaking strength for the rope or weak link when one of their aircraft is used for towing. Most models specify 1200 lbs. maximum. I only have that in paper form from back in the late 60's/early 70's so maybe that has been superseded in the years since. As I recall it was nothing to do with the hook but rather with the structure the hook was attached to. Unfortunately Cessna's current website is kind of a nightmare and I can't find anything relevant on it.

At my club we're using hollow braid polypropylene and the loop that the ring goes through runs the rope through vinyl tubing so the ring doesn't directly rub on the rope. Once the loop is made and the free end tucked inside the rope to secure it we wrap the loop end in rubber tape topped with electrical tape. I'm not sure how much of a benefit the tubing part is because I've never compared wear rate with and without it. We have a soft grass runway so the ropes have an easy life but I still retire them after one year maximum service time. The tow plane end has a Tost ring and the glider end has a Schweizer ring that the various weak links (made in a similar fashion as the tow rope except that one end is a simple loop of rope) is attached to. We no longer have any Schweizer hook equipped gliders flying at our field but I keep a selection on hand in case a visitor shows up with one.

Bruno, our plane side weak link never touches the ground. After a couple of tows dragging the glider side weak link on the ground, the tow side is now stronger. I can see the difference in the glider side weak link.

Yes we use a clear vinyl tube over the weak link rope to keep the ring from chafing the rope.
The Janus C specifies a stronger link, 16xx # I think, the 5/16" rope made into a weak link covers that.
Sometimes we run. 5/16" link on the tow end and for all the other gliders a 1/4" link on the glider end.
From a weak memory I think the 1/4" weak link rope is 1200# strength.

We tired the braided poly, but it did not stand up to our rough conditions. So we stay with 3 ply rope.
We are very good at eye splices. Any solo student can make a respectable weak link.

We also use whiffle balls to keep the whip and sag of the rope at a lower rate.

BillT

Why play around with home made weak links when you can by them ready to go links from Tost for less than a few cents per tow?
http://www.tost.de/ESollbruchstellen.html

All(at least almost all) towingropes in Europe uses some kind of metallic weak link inline with a polyester rope and the Tost rings. It is not only mandatory be the flight manual, it is also national regulations around this.