Ski design discussion

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Akiwi
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Ski design discussion

Post by Akiwi » Wed Feb 15, 2017 1:17 am

I wanted to start a discussion on ski design, where people could perhaps discuss a few ideas, and maybe encourage out of the box thinking and help push the boundries of ski building.

I had a couple of topics that I think are interesting and would be interested in what other people think.

1. Asymetric skis?
by asymetric skis, I mean different radius on the outside and inside of the ski.
Logically thinking as we use both skis in a turn, you would think that skis should be designed with a larger radius on the inside edge, and a tighter radius on the outside edge.

It would also give you the option to swap skis, if you want to cruise at highspeed doing GS turns, of crank the turns more slalom style.
I know skis like this exist, but why is it not the standard?

2. Why are the tips and tails of most skis so thick?
Why do we need to use spacer material at all?.
Wouldn't it be logical to take the core down to almost nothing, and just have glass in the tips and tails resulting in a lighter ski end and therefore reducing swing weight?
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PowderCad
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Post by PowderCad » Wed Feb 15, 2017 5:52 am

1. Asymetric skis?

My company did this. It was very successful. Definitely our most popular ski. The feedback I received for those who were skeptical was "What if you break an edge?" In this case the skier would swap skis putting the bad edge on the outside. If you have an asymmetric ski you wouldn't have that option.

Elan does asymmetric skis very well too.

Asymmetric skis work best on hardpack and ice. When you get into the deeper stuff it won't matter as much.

I'm a believer in this type of design but only for specific applications. with regards to swapping skis for doing different styles of turns... well that won't work because, as you pointed out, the inside ski in a turn needs a smaller radius (outside edge) than the outside ski (inside edge). swapping skis would not be a fun ride.

2. Why are the tips and tails of most skis so thick?
Durability, stiffness and vibration damping. If you have a very thin tip/tail it won't be stiff. Flexural stiffness in a sandwich composite comes from separation of the top and bottom fibers. Flexural stiffness is important at the tip when plowing through powder and variable snow.

The added weight up there helps with damping so when you do plow through variable snow conditions the mass assists in this. Adding rubber foil up there helps as well but again it is more effective with distance from the center of the thickness.

Durability. It helps to have a blunt edge rather than a sharp edge when the skis hit each other, trees, rocks or other hard objects. Capped construction is best up here if you can do it for that reason.

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Akiwi
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Post by Akiwi » Thu Feb 16, 2017 12:12 am

Thanks for your coments.
I also saw the new Blizzard Spur at Ispo last week, which is what made me start thinking about it.
http://www.ispo.com/awards/ispo-award/w ... -2017.html
I think I will possibly try it with my next skis. with perhaps a 16 and a 20m radius, so good for cruising, and
If ever I have trashed an edge, I have normally binned my skis, so that argument doesn't hold.

I would think a lighter tip would generate less vibration, and would be better for quick turns. OTOH I understand that the thickness adds strength.

I still think that some ski tips are way too thick, and therefore heavy.
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Post by PowderCad » Thu Feb 16, 2017 8:52 am

16m outside radius with 20m inside radius is a big delta.

For an asymmetric design you're trying to match the true difference in radius between your skis. When you are deep into a turn you won't have that big of a difference unless you put a lot of weight on your outside skis which I doubt you would. I would try a 1-2 meter difference to start.
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Post by Akiwi » Fri Feb 17, 2017 12:56 am

Ill try that with probably a 2 m difference.
I'm building a 16m radius ski at the moment... Ill see how it works and how I like it.. then design something based on that.
I guess if the difference is too great, and you are skiing the tighter radius on the inside edge, then the other ski will be wanting to go straight ahead..
Admitedly most weight is on the outside ski so I am not sure how much of a problem that will be. Normally as we have more weight on the outside ski, that ski will get a lot more flex, and with symetrical skis is probably a much tighter radius than the inside ski.. so obviously we can handle the difference... the question is .. how much?
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Post by pmg » Sat Feb 18, 2017 4:44 am

Had the same idea regarding different radiusus on ski inside/outside of the ski. Thinking about the normal radius difference which is how far your legs are apart when skiing, more than 1.5m max seems too much. Basically half a meter would do if one skies technically perfect.

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Post by skidesmond » Thu Feb 23, 2017 7:10 pm

I too have thought of an asymmetric ski, same as PMG. I made a ski accidentally where the side-cuts were different, ie the bases warped. The skis were wonky and found they wouldn't carve equally. One ski always wanted to go more straight. Maybe if they were purposely made engineered to spec things would be different.

As for tip and tail thickness, use carbon fiber with thinner tip fill and you'll have a more elegant looking tip and tail and it will be very strong.

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Akiwi
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Post by Akiwi » Fri Feb 24, 2017 1:30 am

skidesmond wrote:I too have thought of an asymmetric ski, same as PMG. I made a ski accidentally where the side-cuts were different, ie the bases warped. The skis were wonky and found they wouldn't carve equally. One ski always wanted to go more straight. Maybe if they were purposely made engineered to spec things would be different.

As for tip and tail thickness, use carbon fiber with thinner tip fill and you'll have a more elegant looking tip and tail and it will be very strong.
WIth the asymetric skis, I'll just have to try it... Got to get my process down so I don't need so much time to create a pair of skis..

My current skis which I have just finished, I built in about 15 hours.
Much less than my previous efforts... A lot of that time was finnishing.. graphics etc, so a prototyp which isn't pretty could be done much quicker I think.

The tips are nice and thin and elegant.. I ran the core to the tip at about 1,, and strengthened with carbon and fiberglass.
I'll post them later when the clear coat has hardened a bit and I can take a photo.
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Akiwi
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Post by Akiwi » Fri Feb 24, 2017 8:04 am

Here is a picture of the tip.
Image

Image
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skidesmond
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Post by skidesmond » Fri Feb 24, 2017 6:06 pm

Skis look great! Not sold on the asymmetric design. If you were to figure the radius difference of the arcs based on feet separation, the radius would not be very dramatic. I don't know what arc difference is on asymeteric skis.

Check out ScottyBob skis. They have different length tails.

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Post by skidesmond » Fri Feb 24, 2017 6:17 pm

Here's an old thread about asymmetric skis. Basically my thoughts are the same

http://www.epicski.com/t/3007/asymmetric-side-cut-skis

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Post by PowderCad » Sat Feb 25, 2017 6:43 am

When we were prototyping asymmetric designs we also looked into offsetting the turning center from the inside and outside edges.

Conceptually, when you are in a turn your inside foot will be ahead of your outside foot. We tried compensate for this by skewing the center of the turning radius slightly back on the inside ski and slightly forward on the outside ski. we used the same radius on both side of the ski for this prototype so we can isolate that variable.

Our first prototype on the skewed sidecut didn't work out well. We were testing asymmetric radiii skis at the same time and had great results with that design so we abandoned the skewed design.

My guess was either the skew was too dramatic or we didn't have the boot center zeroed in. With more time we could have gotten t to work but relative to the results of an asymmetric radius it would have been more a gimmick.
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Post by Akiwi » Sun Feb 26, 2017 1:35 pm

I like the look of Scotty Bobs skis, but I think his offset design is more for telemarking where the inside ski is further back, so he has moved the edge part that touches the snow forward.
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satch
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Post by satch » Mon Feb 27, 2017 12:50 am

I'm pretty sure it's not worth experimenting with asymmetric skis. When skiing most of your weight is on your outer leg (in a turn) which automatically bends that ski more than the inside ski. Now to have both skis exactly parallel you'd have to factor that deflection in as well. Also the distance between your skis is not constant when skiing. The faster you into a curve the bigger the distance between your skis.
To really notice an effect you'd have to build two pairs both having the same inside radius and especially exact same bending stiffness.

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Post by Akiwi » Tue Feb 28, 2017 1:00 am

I ski pretty aggresively most of the time, with probably about 90% of my weight on the outside ski, so I guess in these situations it isn't important what the inside ski has. However at low to moderate speeds on relatively flat terrain you initiate the turn by rolling both skis onto their edges and weight is pretty eveny distributed over both skis.. I can see that in this situation having the same radius on the inside and outside ski would be a good thing. I think I will drop this idea untill I hear something else that changes my mind.
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