stiffness of the strut

I´m thinking of making a T-bar for myself. To get a reference for the rigidity a made some measurements on my carafino T-bar.
bending rigidity: the distance between the supporting points was 84cm. The dumbell right in the middle was 15 kg. the deflection was 3mm.
https://i.servimg.com/u/f74/15/74/67/59/img_0513.jpg

torsion rigidity: distance between rotation axis and the targetpoint of the dumbell was 315 mm; deflection was 13mm; corresponds to 2,36° twist at 46,35 Nm
https://i.servimg.com/u/f74/15/74/67/59/img_0514.jpg

Anybody who made similar measurments on his T-bar? What do you think how rigid a T-bar has to be? I wonder that moths can use NACA 0012. This corresponds to a thickness of 14,5 mm at a profil length of 12cm. The overall weight of boat and sailor is about 140kg. This means they have a lot more forces on their mainstrut.
@FaF : if you have a strut profil close NACA 0012 and a thickness of 16mm this would mean that you chordlength of more than 13cm?! Est-ce vrai?

cheers
mario

The Moth has a mot more torsional pressure because they have a hull with outriggers on both sides from which the sailor forces his body weight - it is a completely different set up on the kite foil, so in theory we should be able to use much finer (shorter chord lengths) and still be able to ride with comfort and structural strengh. However, moulds and the correct use of Carbon, Kevlar re-enforcement are key to making the vertical / horizontal leg torsionally strong enough once you begin to make things thinner etc. It's a kind of catch 22 and you have to know that your design will work otherwise it can become a very expensive mistake. Regards Chris

foiler a écrit:

I´m thinking of making a T-bar for myself. To get a reference for the rigidity a made some measurements on my carafino T-bar.
bending rigidity: the distance between the supporting points was 84cm. The dumbell right in the middle was 15 kg. the deflection was 3mm.
https://i.servimg.com/u/f74/15/74/67/59/img_0513.jpg

torsion rigidity: distance between rotation axis and the targetpoint of the dumbell was 315 mm; deflection was 13mm; corresponds to 2,36° twist at 46,35 Nm
https://i.servimg.com/u/f74/15/74/67/59/img_0514.jpg

Anybody who made similar measurments on his T-bar? What do you think how rigid a T-bar has to be? I wonder that moths can use NACA 0012. This corresponds to a thickness of 14,5 mm at a profil length of 12cm. The overall weight of boat and sailor is about 140kg. This means they have a lot more forces on their mainstrut.
@FaF : if you have a strut profil close NACA 0012 and a thickness of 16mm this would mean that you chordlength of more than 13cm?! Est-ce vrai?

cheers
mario

I use a Tbar in Steel, 30x15x2. With 15Kg in the middle, and a mast about 85cm. I use a soft find on the net : http://jean.lamaison.free.fr/flexion.php
I have a deflection = 1,71mm with lateral force (roulis).
And a deflection = 0,54mm with axial force (tangage).
I don't calculate in torsion.

And you are right, the first foils has about 130mm of chordlength with NACA0012. Now, i reduce to NACA0014. And chordlength is about 110mm.

I think a NACA 0014 is a good option. Another common section for struts on moths is the NACA 66014. It is a laminar profil with the thickest part further back then the NACA 0014. This could be an advantage for the rigidity. Furthermore the NACA 66014 has a so called
"drag bucket", this means it has less drag within a narrow range of AngleOfAttack. Laminar profils have to be done very properly to get this advantage. The best would be a moulded strut.

watch upper part of naca63412.i think NACA66014 is faster than naca0014.For me 120mm width is too much.Le bord d'attaque des naca 0012 ouOO14 est trop épais et fait perdre de la vitesse pour moi!!!!!

On the picture we can see the difference between a laminar and a non-laminar profile. So yes, within a narrow range the NACA 66014 has less drag than NACA 0014 (non-laminar profile). If the strut is done very precisely it should benefit of the "drag bucket".
But the radius of the front of the section should not be smaller then 1 percent of the chordlength, otherwise we risk ventilation and noise. (At least that´s what I read in a moth forum :-)
https://i.servimg.com/u/f74/15/74/67/59/images10.jpg

The moth expérience is realy usefull.My tBar is very near the 66014 and it's very fast.For sure that it's risky, if the leading edge is too sharped.Good luck and sorry for the bad english

hi franck,
I really apprecciate that I can join a french forum, write in english and you even answer me in english. I remember you are also able to speak german. And I guess it is way better than my french. I use the google translater to get an idea what you guys are talking about :-)
whether french, english, german, esperanto...
it´s great that we can share our passion

bonsoir

what is the material!!!!
merci thanks

genau!wir werden uns vieleicht in sudfrankreich treffen.Laurent wird ein" meeting" in mai fur alle foiler, am strand ,in der nahe von Monpellier organisieren.Du wirdst uns die Osterreicher" TOUCH" bringen.Sonst, die Speed2 12m must ganz shnell fur leicht wind mit einem foil sein.