Aerotow towrope instructions

Don't have time for a lengthy reply, however, we use a combination of very strong on the primary length and not so strong on each end.

The long, too strong part is sold by Samson Rope, and is called Tenex. We use 1/4 inch for most gliders. Each end has a short section of 1/4 inch Polypropylene (about two feet) serving as the required weak links. No kind of knots are permitted.

The ropes used on the ends as weak links must pass a breaking strength test using a simple lever arm and weights to verify the rope meets the breaking strength requirements.

A major problem is the quality of the rope. In some cases the brand new rope has broken strands, or knots on individual strands, which causes the rope to fail during breaking tests.

Probably a good magazine article.

Tom Knauff

Tom, we get our rope from an industrial supplier of safety and climbing equipment, the rope has to meet specs.
The 1/4 inch 3 ply twisted poly meets specs for FAA weak link requirements for most gliders. The Janus C requires a stronger weak link, so we use 5/8 ind dia for that. We also use 5/8 inch for auto tow. We could use 5/8 for aero tow, but it does not stand up very well to the abuse.

BillT

On Wednesday, April 6, 2016 at 6:35:43 AM UTC+3, Bill T wrote:
Tom, we get our rope from an industrial supplier of safety and climbing equipment, the rope has to meet specs.
The 1/4 inch 3 ply twisted poly meets specs for FAA weak link requirements for most gliders. The Janus C requires a stronger weak link, so we use 5/8 ind dia for that. We also use 5/8 inch for auto tow. We could use 5/8 for aero tow, but it does not stand up very well to the abuse.

Does any glider truly *require* a stronger rope? PTT should never be an emergency situation.

Gliding New Zealand specifies a 750 kgf weak link for all gliders, but I think all clubs I've flown at use a rope of the correct strength without any weak link. The rope gets replaced when it looks worn. I've seen a few old ropes break at initial towplane acceleration but breaks in mid air are very rare.

http://gliding.co.nz/sites/gliding.c...s/AC3-02v5.pdf

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

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.

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