elliptic radius?

Post by **skywalker** » Saturday 3 August 2002, 11:36

Hello,

first I want to say that I'm very glad about finding Your HP. Thanks for it!!

My question is: many people are talking about elliptic sidecut of carving boards. I've been thinking al lot about it and in the end I did a 3D-construction of a board with the aim of a perfect round radius in an extreme angle to the ground. The line, Your board is making under an angle to the snow will always be elliptic if the edge is an round radius. This might cause the look of sliding in Your videos because the way of the front doesn't fit to the way of the mittle of Your board edge. What about Your boards, did You think about this point, do You think it's important? The ellipses which resultet of my construction had an extreme ratio of the axis lengths.

regards

Tom

Post by **rilliet** » Sunday 4 August 2002, 9:35

Hi Tom,

This problem is not simple at all.

The question to me is: is there a sidecut shape that makes a board versatile and able to carve in any situation and any board angulation?

Answer:
Yes, but it doesn't depend on the sidecut only.

Let's consider the two limit situations:

1. A "carved" turn is made with the board nearly flat on the snow (1° to 10°). Here, the turn radius will be the sidecut radius. It is obvious that the only sidecut shape able to perfectly match a circle arc is a circle arc. So in that case, the shaper will choose a radius.

2. An extreme carved turn is made with the board nearly vertical on the snow (let's say 60° to 85°). In this situation, the board should be bent and twisted, sothat the whole edge is in contact with the snow.

The line, your board is making under an angle to the snow will always be elliptic if the edge is an round radius.

No, it also depends on how the board is bent and twisted.
It is possible to force it to bend and twist in a way that, with a round radius sidecut, the line on the snow is still a round radius.

You can do the following experiment: take a narrow piece of cardboard. Cut out a cicle arc on one of its sides. Place the cardboard piece with a angulation like a snowboard, on a table in a way that the whole edge is flat on the surface. Try to shape a perfect circle arc.

If the board (or cardboard) is bent but not twisted, you will have to bent it like an ellipse to make the whole edge touch the snow. in this case, the line on the snow is actually an ellipse. This means that a board with an infinite torsion stiffness is unable to carve...

If you bend and twist the board, you can give a round shape to the line. In this case, the board deformation is conical.

This is why the flex and torsion stiffness distributions are each one so important. The rider can only push on the board, so the board must have the mecanical characteristics that makes it bend and twist naturally in the right way.

Our torsion control system that is independent of the flex and allows a very fine adjustment of the torsion stiffness makes the reach of this mechanical ideal possible.

Jacques

Post by **skywalker** » Sunday 4 August 2002, 19:06

Hello Jacques,

Thanks for Your answer, I guess I can understand now how You think about this theme. My thinking started from another side of the problem. If You want the hole edgr to grib, You need a rather flexible board in longitudinal direction. But for enough grip of the edge at the front and the tail of the board, it must not have much torsional flex. That's why I tried to think about a board with hardly any torsion...

When I try to follow Your thoughts, it becomes clear, that there is no elliptic sidecut necessary, if You find the perfect realtionship between longitudinal and torsional flex. I think I understood this point.

But there is another point in Your posting I cannot agree with: I already wrote to You in my mail, that it's mechanically impossible to change torsional flex with no influence to longitudinal flex. I know, that You can build a soft board with high torsional flex and vice versa. But if You start with a board with specific longitudinal flex adding some torsional stiffness, You always will change longitudinal flex, too. You're right, that it is possible to build the board with more longitudinal flex to eliminate this influence again, but the influence will always exist.

(Believe me that I know what I'm talking about, I've been studying mechanical engineering for more than tree years now and will finish in 7 month)

You gave me a beautyful example for the sidecut problem, if You like, I can give You one to show You the effects of torsinal and longitudinal stiffness...

Sorry for this, I know that's no main theme of extremecarving. You have found a great way for our sport and I'm glad having found Your HP! I know that it is important to show the snowboarding world, how much fun You can achieve in that easyer way!! I hope to see You at an european meeting this winter. Then we can talk about an EC-board for me, maybe the topic might be something to talk about, too

I will need quite a small and rather soft one, because I'm only 1,72m of highth on only 66 KG of weight.

Greetings

Tom

Post by **rilliet** » Monday 5 August 2002, 6:46

Hi Tom,

But there is another point in Your posting I cannot agree with: I already wrote to You in my mail, that it's mechanically impossible to change torsional flex with no influence to longitudinal flex. I know, that You can build a soft board with high torsional flex and vice versa. But if You start with a board with specific longitudinal flex adding some torsional stiffness, You always will change longitudinal flex, too. You're right, that it is possible to build the board with more longitudinal flex to eliminate this influence again, but the influence will always exist. (Believe me that I know what I'm talking about, I've been studying mechanical engineering for more than tree years now and will finish in 7 month)

Sorry but it so.
I cannot change the longitudinal flex without changing the torsionnal flex (because of the sandwich construction), but thanks to my system, I can change the torsional flex without changing the longitudinal flex (or so few that it is totaly negligeable).
Of course a board with stiffer torsion seems harder in the turns because the longitudinal flex is better transmitted to the edge. But the pure longitudinal flex, that everyone can test in the surfshop (the heel on the ground, the nose in one hand, the other hand pushing on the center of the board), remains unchanged.

If I had to prove it, I should reveal the secret.

So please trust me.

Jacques

Post by **skywalker** » Monday 5 August 2002, 18:44

Hi Jacques,

I've been thinking about what You wrote and talked about it with my mates and I now think I got this point, too. Certainly, You're right

And, certainly too, I got one more question. When I bought my asymmetric Generics IQ in 1993 I thought about buying a wild duck crusher world cup. Have You been at wild duck at that time? Did You have any influence to the design of the board and what do You think about it. A friend of mine is planning to buy a used one

Are there any news about an european meeting???

Greetings

Tom