Single skin foil stiffeners

[merl]

I've got a single skin foil that I think could benefit from some stiffeners down to the trailing edge - like in the peak 5.

I just sewed a test and the curve of the filament (thick garden strimmer line) is too pronounced. Anyone know how to straighten this stuff? Or maybe there is a better kind of filament?

[JakeFarley]

You can straighten it out in hot water (almost boiling) and then fastening it on both ends and letting it cool. You can also curl it up on a spindle to make a coiled leash (but it is not as springy as commercial ones).

[merl]

Well, first attempt: stretch it for a few days

[merl]

Ah nice one Jake - hot water sounds perfect - will try it

[RTL78901]

I used lawn trimmer filament to shape the leading edge of some of the single skin kites I made. It looks very much like that. The first time around, I wanted to straighten it so it would take the shape of the curve built in, rather than the tighter coil it came from. Tried various things including boiling, a heat gun, weights, etc. Nothing worked very well. I finally just put it in place and flew the kite. As it turn out - the wind shaped it for me to the built in curve and it worked fine. It might work the same way down to the trailing edge. You might give it a try (maybe just one of two of them) and see if it works. If not, pulling it out should not be difficult.

[merl]

Agreed. Putting the filament in boiling water before stretching it (24h) improved it quite a lot but the memory of the coil is still there. I tried it out in the kite. Let's see if the remaining curve matters.

[Regis-de-giens]

I used once some tennis raquette strings to reinforce the LE of my ex-speed2 cut into single skin. Thin and rigid enough (at. Least in light wind). So flexible that i did not have to "shape it" to insert it in-between the existing seems, directly.

And unbreakable

Remember that since the stiffner is locked in a plane (imposed by both leading edge combined to cells separators) , it mechanically "works " in hoop stress "compression" so quite efficient even if it is extremely flexible when free in your fingers.

As an illustration, just put the stifner on a table, force it to be fully in contact with the table, curve it and try to push it in its middle ... Hard to bend...

[Schietwedder]

Ratioparts Alucut is what is used in most foilkites.

Buy a big batch (not expensive) and it will be relatively straight because of spool diameter.

Its a big difference compared to normal hardware store nylon lawn mowing filament as its more flexible.

When sewing it into batten pockets leave space at the end of the pocket of roughly 5mm. It will expand when getting moist and if it has nowhere to go it will get very curly and will stay that shape when drying again.

Actually when soaking (soaking soaking wet) the kite with water (swimming in) and then flying it bonedry the nylon will adapt to the shape of the airfoil when drying out.... Quite neat.

Inflating the kite in the basement when it's wet helps also keep this shape until the water is out of the nylon

[merl]

Great tips. I just ordered some. BTW it *is* lawn mowing filament...Suprised to hear that it expands!