torsional flex

[BigG]

Hi,

I was thinking about how to minimize the torsional flex in a ski.

I was thinking about really small carbon rods in de width of the skis.

What are your ideas?

Geoff

[davide]

Carbon biaxial (+-45°) is better, because the fibersare aligned to the torsional forces and it seems it is also effective in damping vibrations.

[burny]

the best, most reliable, solution would be in my opinion to build a torsion box ... but I havent figured out how to construct one, or to be more precisely, how to make one that fits into the amateur pressing process I do.
However, I've cut one of my old racing slalom völkls (racing lab, wc ski, p30 topsheet) in half, i will post pictures soon, and this ski contains a torsion box as far as I can tell. to my surprise a "normal" völkl p40 ski had much more metal inside than the racing ski and it seems like this normal ski has a (thinner) torsion box as well.
from my experience i can tell, the slalom ski is almost unhandable for normal skiers, its just waaaay to stiff at the tail and really gets speedy if not ridden with a good skiingtechnic. (well, thats what we wanted, we wanted a ski that puts the pedal to the metal when leaning backwards, you can see this pretty well on television how fantastic those skis accelerate when driven out of a turn leaning backwards). The p40 was, in my eyes, a good ski for anyone who can ski but nothing extraordinary. Thats why i was so surprised to see them beeing constructed almost equally. Probably different kinds of wood, fibers and metal are used.

[plywood]

well, elan have on their page a very interesting construction. they call it wave flex or something like that....

the ski has a 3D-waved surface.... should also prevent torsional stability. they have some videos there where they show how it should work...

but this is maybe a bit difficult to build by yourself.

[sam]

A torsion box is jut when the core is wrapped in fiberglass right. If so then couldn't you have the same effect by laminating fiberglass inbetween the strips on a vertically laminated core? This would also add verical strips of fiberglass to the ski. Has anyone tried this?

[endre]

this is what goode does, just with carbon and foam

[sam]

this is what goode does, just with carbon and foam

Does it work?

[endre]

goode skis are actually crazy torsionally stiff. way too stiff for my taste, But I think it has more to do with the way he puts the carbon fibres, probably all in 45 deg. or something.. not shure about the construction, but when I measured them they were allmost twice as stiff torsionally as the average ski. I believe that this is a good (bad) example of a too t-stiff ski

[BigG]

If you have a look at their website you will be able to read they are using 2 biaxial and 2 UD layers of carbon at both bottom and top.

It doesn't surprise me they are so stiff.

I'm wondering however how they build up their cores.

Geoff

[endre]

strange how two different discussions go parallell like this..

here is the picture davide posted of the goode core construction in the "foam core discussion"

[BigG]

I know about that topic but it doesn't explain about the type of foam and what type of strips are used.

On the goode website you can road those strips are dampening vibrations.

Geoff

[endre]

i think it's mainly to hold the ski together, if it's for dampening it's not very successfull. (my personal oppinion) incredibly light though!

[davide]

I know about that topic but it doesn't explain about the type of foam and what type of strips are used.

On the goode website you can road those strips are dampening vibrations.

Geoff

Foam is C70.75 I think, and carbon is damper than glass.

[Car_ve_diem]

k2's torsion box construction are torsional noodles compared to goode's design. (my personal experience) thats why you need metal in k2's to carve (like the crossfire/recon rather than the apache stryker)

goodes are probably the most torsionally rigid ski i've ever skied (race skis included) but as mentioned before they are so light that deflection is abundant and you feel every little crystal (despite carbon's terrific dampening abilities)...

out of curiousity...has anyone or would there be a way to laminate the different core materials together using carbon???..(see the above GOODE diagram but use wood in place of foam)...

[davide]

...they are so light that deflection is abundant and you feel every little crystal (despite carbon's terrific dampening abilities)...

Well, deflection does not depend on weight, but on stiffeness.
I skied them (two runs), wind-blown, piste, hard and soft snow, and I liked them a lot.

By the way, they told me that that the central part of the ski (over about 1 m) should be stiff in torsion, while tip and tails, it is better (moreforgiving) if they are a bit softer.