Towrope tensions....Part II

On Monday, October 15, 2018 at 10:20:53 AM UTC-4, Retting wrote:
Looking for towrope tensions information applied during a typical AERO tow. Singles and twins up to 600kg/ 1500#.
Perhaps testing was done back in the 60’s before Al Gore invented the internet. Prefer some numbers over methods of achieving.
The Uganda Information Award is still in play .... this thread only .
Credible Best Wag will be considered.
Civil disagreement with counter points encourage.
Numbers boys numbers.

R

As posted in Pt I


-
Steady state calculations are interesting but irrelevant.
Tow rope failure happens on a snatch, because a loop has developed
and then the rope suddenly becomes taut; then the load depends on the
separation rate, the extensibility of the rope and the mass of the glider.

John F

Agree, but if I can get support for a reasonable starting point, a consensus, then I can work it from there.
R

On Monday, October 15, 2018 at 12:04:33 PM UTC-7, Retting wrote:
Agree, but if I can get support for a reasonable starting point, a consensus, then I can work it from there.
R

The answer depends on the strength of the weak links you intend to use. In fact, consistent with most tow release STCs, you should have a placard in the towplane with the weak link limit listed (our does). Typically the installation should be good for 150% of the design load (listed weak link strength). The design load for the installation needs to be considered for all possible orientations. If the rope/weak link is stronger than the installation, the release may depart the aircraft instead of breaking the weak link.

As noted previously:

Try AC43.13-2B Chapter 8 rather than do your own guessing

I have no decent answer, you can skip from here..........

Soft tire, wet ground, deep grass vs. pavement, dragging brake (or pilot that holds divebrake part way through initial acceleration, yada, yada, yada........), many variables.

Max is usually initial acceleration of the towplane. Soft throttle is less load than "ramming it".

You can find a "range", but it can be huge.

OK, I will bite, why are you asking? The mission statement can yield closer answers to your question vs. the nebulous question you asked.

Not an engineer.
Not trying to be a PITA, although, I usually end up in that pot.

It seems like the practical answer is the one you want is some fraction more than the rope you intend to use. We typically use a 1600 lb tow rope, you want to be sure the mount stays on the plane, and the rope will break when you need it. In our club, we had a contingent that tried to use 1200 lb rope. The result was several rope breaks, all on the ground, mostly with 2 place ships, as the rope came tight after slack takeup or initial roll out.

Rick

1.5 to 2 x's the weak link strength for the attachment point. Someone at Tost could tell you the shear strength of their mounting kit bolts. It depends on what you want to fail first. Pull apart the mount or part of the tail still attached to the mount.

SF

4,000 lbs or 50% of the yield strength of something you dont want pulled apart.
SF

We are almost there.......RR threw out a nugget of using 1600# towrope which is a good established practice. That will be my start point. Then SF tacked on the ‘shear’ strength of the tow hook attachment system, which is where I am at now. I am using 125,000 psi tensile strength bolts which , if I remember my engineering from years pass using the 60% rule, equates to approx. 75,000 psi shear strength.
So, the tow hook/tailwheel assembly is attach to a 1� rod with two bolts which in turn attach to the aircraft fitted assembly. Does the tailwheel assembly system strength exceed the breaking strength of the rope, and by how much?
I do not know how to convert psi to pull strength (pounds).
R

Retting- If you got reasonably decent advice from RAS, you should count your lucky stars and be grateful. Don't be a cheap *******. Send SF 200 Ugandan shillings, or really look like an early Microsoft investor an send a Zimbabwean $100,000,000,000 bill to the guy!

https://www.ebay.com/itm/Zimbabwe-10...S!-1:rk:2:pf:0

Lucky? I knew someone would arise to the challenge.
Cheap? How many people you know have 100 Uganda Shillings.
A fair trade.

R