convex shape?

wingworks · Post by **wingworks** » Mon Jan 21, 2013 5:25 am

megawatt-------- anyone think the deep groves in the top side areas of the megawatt cores is designed to be a weaker area along the edge and allow flex away from the snow under hard pressure?(rounded bottom result?)

MontuckyMadman · Post by **MontuckyMadman** » Mon Jan 21, 2013 11:34 am

twizzstyle · Post by **twizzstyle** » Mon Jan 21, 2013 11:37 am

Just looked up the ski so I had an idea what you were talking about.

I'm sure they have a technical reason they claim as a selling point with the grooves - but more likely than anything, it's there for aesthetics.

skimann20 · Post by **skimann20** » Mon Jan 21, 2013 1:27 pm

It's because they have a cnc and they're trying to show off...

wingworks · Post by **wingworks** » Mon Jan 21, 2013 1:49 pm

yes makes you wonder? and you would think the dip in the path of diagonal strands would also get rid of any torsional stiffness outboard of the groove as well? seems all thier skis have some couture shapes

twizzstyle · Post by **twizzstyle** » Mon Jan 21, 2013 2:06 pm

Perhaps it's a good way to add longitudinal stiffness without adding weight? The diagonal fibers in the triax on the vertical faces act as a shear web. But I think you're right, that is at the cost of torsional stiffness (which isn't as important on a powder ski).

skidesmond · Post by **skidesmond** » Mon Jan 21, 2013 4:33 pm

My guess is the rise down the center is aesthetics and perhaps adding stiffness, somewhat like the Atomic D2 (D2 = double-deck), that has a separate top plate that is raised. To me Atomic is kind of gimmicky since the you need the top plate for the ski, it's not an option but supposedly it flexes/slides/moves over the bottom.

maximegb5 · Post by **maximegb5** » Wed Jan 23, 2013 6:08 am

Yeah, there are 2 attach points on each side of the binding for the carbon plate. When you flex the ski quite hard, you can see the plate move, and it is loosely attached, so that the screws force the plate on the ski, but still allow forward-backward movement. Atomic also has almost the same model without the plate, and it is 600$ less than the D2 model.

In the megawatt case, it seem it would only diminish the torsional stiffness, or increase the longitudinal, depending how you would see it.

mrgooddave · Post by **mrgooddave** » Wed Mar 20, 2013 1:19 pm

I think the milled top surface ADDS torsional stiffness.

The old Atomic Beta's are the first ski I can recall with a shaped top sheet and they promoted the enhanced torsional stiffness. Black Diamond has be doing it since the CrossBow.

In my mind the concept is such: compare a flat bar and a channel of same material and thickness. The channel is harder to twist by far. So each change of direction in the cross section adds an element of torsional strength. This is why a capped ski has good torsional stiffness.

It seems everyone so far agrees that longitudinal stiffness is increased. Butm knowing that the recessed areas on the BD skis are not parallel to length- qqqqqwhy would it not enhance torsional stiffness?

Please help me understand if I am wrong.

MontuckyMadman · Post by **MontuckyMadman** » Wed Mar 20, 2013 5:41 pm

They are maximiseing the torsional and longitudinal stiffness to weight ratio as the core will always weigh less than additional composite especially with relation to swing weight in the tips and tails if you take carbon fiber out of the equation, that and cost.
or at least this is my opinion.

twizzstyle · Post by **twizzstyle** » Wed Mar 20, 2013 6:23 pm

mrgooddave wrote:
In my mind the concept is such: compare a flat bar and a channel of same material and thickness. The channel is harder to twist by far. So each change of direction in the cross section adds an element of torsional strength.

It doesn't work that way. A better analogy would be: take that same original bar, and cut two grooves in it. Does it somehow gain torsional stiffness? No it doesn't. It also doesn't gain longitudinal stiffness, but that's because it is one solid material. Things get more complicate once you start talking composites and fiber orientation.

I am still not convinced that, all else the same, grooves like this increase torsional stiffness. I would have to see some data to convince myself, it just fundamentally does not make sense.

mrgooddave · Post by **mrgooddave** » Thu Mar 21, 2013 3:51 pm

[

It doesn't work that way. A better analogy would be: take that same original bar, and cut two grooves in it. Does it somehow gain torsional stiffness? No it doesn't. It also doesn't gain longitudinal stiffness, but that's because it is one solid material. Things get more complicate once you start talking composites and fiber orientation.

Ok. But to clarify my thought with the steel bar- I was envisioning the bar as the composite layer not the core. By cutting grooves in the core you add complexity and strength where it counts- the composite layer the wraps over each surface of the core. I think? I too would like to see good data. I have no way of performing such a test. I will email BD and see if they will talk.

Appreciate the feedback Twiz and MM.

twizzstyle · Post by **twizzstyle** » Thu Mar 21, 2013 9:18 pm

mrgooddave wrote:By cutting grooves in the core you add complexity and strength where it counts

Torsional strain is in shear, at an angle to the axis of twisting. Stiffness from a fiber composite material acts in the direction of the fibers, so we use diagonal fibers in skis and boards to add stiffness in the diagonal, or shear, direction. Just like normal bending loads, the torsional stiffness is increased as you move the layer further away from the center of the "beam". So now we have these grooves... The bottom of the groove, where the composite is horizontal, is closer to the center of the beam, so you are reducing the effective torsional stiffness from that part of it. The sides of the grooves, where it is vertical, I don't think take up any of the torsional load?

If you wanted to make something that had the highest torsional stiffness with a given sheet of composite, it would be a perfectly round tube!

mrgooddave · Post by **mrgooddave** » Fri Mar 22, 2013 9:14 am

I got a reply from BD:

The CNC shaping of our ski cores allows us to create three ribs towards the tip and tail on skis wider than 100mm underfoot that beef up the torsional stiffness of our boards (i.e. Formula One technology), while skis that are 90mm underfoot and less receive one main CNC channel, creating two ribs out towards the tip/tail (i.e. Dual Torsion Bow tech). Additionally, with the Verdict and Zealot that have metal top sheets, there isn't any metal over the CNC cut-outs - the titanal has the same cutouts, allowing us to shave weight where it's not otherwise needed while still maintaining the same structural integrity tip-to-tail.

Richuk · Post by **Richuk** » Fri Mar 22, 2013 12:22 pm

I know you guys are talking about the same ski ... but the same area on the ski?

I thought Twizz was describing this: http://www.blackdiamondequipment.com/en ... gawatt-ski, but not this: http://www.blackdiamondequipment.com/en ... gawatt-ski

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convex shape?

convex shape?

convex shape?