Alright I tested the ski today in varied conditions.
Aaaand the verdict: meh. or meh-ish...
There was a lot going on and I have to ski them a lot more before I can give a better feedback. If skied aggressively and fast they performed well. super snappy, agile. But when half-assing things they can be a handful. really nice on the way up obviously tho.
There are a lot of possibilities why this could be:
- weight (definitely a factor, i plan to play around with added weights to increase swing weight. Was the idea from the start actually)
I'm just a hack that doesn't know how to ski "skinny" skis (that's a given)
Magne-traction?
when working with a biaxial layup, there are coupling effects that will result in a concave base when flexing. I don't think this was a big factor in today's condition, but will see if I ski them on a slope.
the pure carbon layup vs my usual mixed layups with ampliTex
For now i will detune the edges in tip and tail a little and hope i can ski them in steeper terrain soon. With the avalanche conditions here we had to stay below 30° for the majority of the day and i have a feeling they will come to life in the steeper stuff. Sounds all rather negative but I am actually super excited as I am learning a shitload in the process.
mammuth wrote: ↑Sat Jan 23, 2021 3:51 am
When changing the direction angle you change the torsional stiffness as well.
(...)
Btw. the top looks excellent. Do you have a pic of the raw carbon you did use?
Yes maybe I have to elaborate a little more on this. The stiffness of the carbon drops dramatically when loaded off-axis, as can be seen in this graph:
Torsion in 0° is the same as traction/compression at 45°. Therefore we can consider the 0° UD layer being 45° off-axis if we talk about a torsional loading. As the stiffness at 45° drops so much the UD layer in a normal ski contributes nearly nothing to the torsional stiffness and only the diagonal layers do any work. same but reverse for the lengthwise flex. So you have two different fibre orientations to do very differents tasks. In my design all I did is finding an angle where my only layer matches the stiffness of what i usually would use at 45°, and then compensate for the lost stiffness lengthwise with a modified core profile (still somewhat hand-wavey as the core thickness also influences the torsional stiffness. Therefore I now have a mixed loadcase in my skis with traction, compression and shear.
So my 17.5° off-axis carbon can be considered being 17.5° off axis to the main direction, and 45°-17.5°=27.5° off axis for the loading in torsion at 45°. This was all verified with a couple of bending tests on a universal test machine.
The carbon I used is a non-woven UD
https://shop.swiss-composite.ch/pi/Verstaerkungsfasern/Kohlefasern/Gelege-Unidirektional/Carbongelege-UD-125g-m-500mm.html
I used 4 thin plies on top and bottom, which will improve mechanical properties over fewer thicker layers. I also added a 8gsm carbon fleece between the UD layers and the core and used a toughened bonding resin on the interface rather than a brittle laminating resin.
carlduke wrote: ↑Fri Jan 22, 2021 12:29 pm
Thank you for posting this! It is a beautiful ski and I'm anxious to hear how it performs and if you were building it again if you would use something more substantial in place of rohacell and instead take some weight off the base and edges.
Did you reinforce the binding area at all?
Yeah the Rohacell is just silly for such a ski. Even if it does hold up i find it hard to justify spending the money to safe maybe 60g per ski over a full balsa core. I just needed it to get under my self imposed 1000g mark...
Binding area is reinforced with a aviation quality 3mm birch plywood and two layers of 163gsm glass in a pocket. So glass at 0/90, +/-45 , birch plywood, then the top laminate.
That's it for now i think. I will keep you posted when i have some more news.
Will you cut your climbing skins in the exact shape or leave them straight in the "uneven" part of the edges underfoot?