Line strength

[R Moore]

I am opening this discussion because I think there is some myths, misconceptions and exaggerations about line strength required and kite pull.

I don't know of many people who actually measure kite pull and line breaking strain.

My 23 ft Conyne Delta (165 sq ft) will not pull me off the ground and I am 180 lb. I have measured the line tension at wind speeds of 40 mph + and it did not exceed 120lb. I use a digital tension metre.

My 120 sq ft kite was caught in 60 mph winds last year. The line tension was no more than 155 lbs but the winch motor burned out. I don't know many people who have flown a large kite in high winds.

Using 300 lb Spectra for the first time, I initially felt uncomfortable and thought the line may break until I actually measured the tension.

Of course larger kites or harder pulling flow forms can generate very large line tension, requiring 500 - 1000 lb line. These are the exception and would require good anchorage. I can't see any point in trying to hand fly a kite with a consistant pull of over 100 lbs. If you do, your arms must be like gorillas.

The maximum pull of most kites is much less than their owners percieve.

Even a 50lb pull is difficult to hold longer than a few minutes.

Thin, Spectra and Dyneema exagerate this perception because they are slippery and difficult to hand fly even with gloves, they also make more whistling noise and so give the impression of high tension. It's a good excercise to actually measure your pull on a line and with the help of an assistant record your estimate of tension and compare it with real values.

I have heard claims about anchored inflatibles snapping this 1 ton rope or that 800 lb Dacron but the traction kite is a 50 square ft parafoil, incapable of tension a greater than 100 lbs. On inspection I saw the achor lines were only 300 lb Dacron and the reason for the break was a sharp edge on a crowd barrier base.

The benefit of using lines 4 times the estimated line pull is the allowance for knot strength reduction, abrasion and cuts will still see the line with more than enough residual strength and can be kept for longer before discarding. But, the kite that is up first and down last usually one that is carefully constructed for lightness, stability and has the smallest line diameter consistant with the kites actual maximum pull. I know people prefer larger line diameters because they can be held in the bare hands but better performance is gained by using thin strong lines such as Spectra/Dyneema. The Dyneema and Spectra I use is much tougher than Dacron and I think will outlast the Dacron 3:1. I think with good care, a Spectra or Dyneema line should last 8 - 9 years. They are very resistant to UV radiation. Dacron, on the other hand, while it is much cheaper than Spectra, ony lasts 2 - 3 years. I always use gloves these days anyway so it doesn't make any difference to me from potential for cuts or burns.

In fact, I have been badly burned by 100 lb Dacron when a small (10 sq ft) kite took off in a gust.

As far as the risk of injury to others, I don't think there is much difference between running in to a 200 lb Dacron line or a 200 lb Spectra line. Both will cause similar injury except maybe the Spectra will cut a little deeper. Spectra does hold an advantage over Dacron line crossovers on a crowded flying site. It is far less aggressive than Kevlar which has been banned by many kite clubs for use on group flying activities.

Line often breaks at tether points because of poor knots and the line is not checked regularly for damage. I don't know if this kite pull thing is an expression of machismo. Many lines chosen for single line kites are overkill and dull the performance. A kite with a max of 50 lbs pull only needs 100 lb line. As long as the line is loop spliced and sleeved at the kite end and is free of damage, you can trust the stated breaking strain. It is still double what is needed. Actually, 50 lb pull is quite stout. I can't hold this longer than 10 minutes. Perhaps I am getting too old!!?

Bob Moore

High altitude flyer

Australia

[Progcraft]

Great post Bob.

I know I always go with the overkill on line strength. Frankly, I'm paranoid really.

I also never hold my kites. Well, very rarely. I always stake them, so I can fly more kites I even stake my Eddy kites that only has, what? 2 lbs of pull? and I fly it on 50 lb line.

As for Kevlar line. I have some kites that's I've built that I value very highly. As such, I only fly them on overly strong, Kevlar cored line. I do not want to lose those kites and will take every precaution to make sure I win if they tangle with another kite. I don't see that as being the least bit wrong to do, or want to do.

Because I also fly traction kites, I know what 200 lbs of pull really feels like. So I know that my big flowform (5m long, 4m wide) does not generate that much pull, but I fly it 1000 lb, Kevlar core line anyways. (I used to fly it on 1800 lb rope, but that caused just too much drag).

Say, would you mind re-posting this over at kitebuilder.com forums too please? I'm sure it would be much appreciated.

Thanks.

P.

[ant man]

60 mph winds !!!!!!!!!!!!!! now thats sick