reducing tip flapping

sir.orange · Post by **sir.orange** » Tue Dec 18, 2012 2:39 pm

I noticed that most of my skis that have rockered tips (20cm onwards) start to flap at certain speeds. My designs have always 2 or 3mm thickness in the tip/tail section. i tried full length woodcores (a 15mm tip/tailspacer) surrounds the wood core, but also abs spacer over the total tip/tail length. My cores are 100% and 750gr / 24oz triaxial glass.

What are your experiences in tip flapping, how did you eliminate it?
I think Titanal might be an option for industry but not for me/us!?

twizzstyle · Post by **twizzstyle** » Tue Dec 18, 2012 3:56 pm

If it's off the snow, it shouldn't effect how the ski performs, just looks a little ridiculous.

You need something to dampen the vibration. More weight would help, it would at least lower the natural frequency, but adding weight is never a good thing. I wonder if some strategically placed strips of VDS above/below the core could help?

vinman · Post by **vinman** » Tue Dec 18, 2012 4:07 pm

Carbon stringers? I use some carbon tow to stiffen my laminate selectively. Maybe some extra carbon right at the base of the rocker transition running into the tip and back into the running length some???

rsotak · Post by **rsotak** » Wed Dec 19, 2012 9:45 am

Some strips of metal in the tip section will also help lessen this without adding much weight.

Volkls are a great example of how a metal topsheet can dampen a ski.

prospectsnow · Post by **prospectsnow** » Mon Dec 24, 2012 9:16 am

I was getting this with some prototype boards this year.
When I press these I do it without a topsheet and start with no added reinforcement. I was getting the same result.
With no topsheet I then added in some carbon after the fact and took it out for another test. Adding carbon was more to stiffen a the tips that were too flexible, but the Chatter dropped significantly.

My take, the carbon is more assertive making the tip resistant to flexing over terrain. The rocker portion is inside the turn radius so I'm getting better stability too.

My question, VDS, marketed to dampen skis... How effective is it in reality? Over the space of the turn radius I can see it making a diff, but in isolated areas? Not claiming to be the expert here, just thinking VDS is 95% for bonding 5% for Dampening while marketing has us thinking the reverse.

For the guys that have tried VDS in a few variations. What would you say is the effectiveness?

twizzstyle · Post by **twizzstyle** » Tue Dec 25, 2012 10:14 am

Adding carbon fiber (or anything that increases the stiffness) doesn't damp out the vibrations, but it increases the natural frequency of the vibration, so it's less likely to happen.

Adding weight does the opposite, it lowers the natural frequency. Doing one or the other should help.

sir.orange · Post by **sir.orange** » Thu Dec 27, 2012 2:33 am

another theory that made me thinking and makes sense in my eyes is to put different amount of fibre-layers in the flapping areas, to increase the "destructive interference" in those areas.
for example: you have one layer triax above and one below the core. if you add carbon stringers you should add different amounts above and below. like 2 above and 1 below. the unequal composition results in different frequencys of the below and above layer while flapping. the optimun would be, the two crests of the waves meet both on their top and eliminate each other.

having the exact same layers of fibres above and below the core, results in two equal frequency that add their crests up.

(destructive) intereference
http://en.wikipedia.org/wiki/Interferen ... agation%29

i just pick that up from a skibuilding friend, but it makes sense in my eyes. what do you think?

skidesmond · Post by **skidesmond** » Thu Dec 27, 2012 3:32 pm

prospectsnow wrote:I was getting this with some prototype boards this year.
When I press these I do it without a topsheet and start with no added reinforcement. I was getting the same result.
With no topsheet I then added in some carbon after the fact and took it out for another test. Adding carbon was more to stiffen a the tips that were too flexible, but the Chatter dropped significantly.

My take, the carbon is more assertive making the tip resistant to flexing over terrain. The rocker portion is inside the turn radius so I'm getting better stability too.

My question, VDS, marketed to dampen skis... How effective is it in reality? Over the space of the turn radius I can see it making a diff, but in isolated areas? Not claiming to be the expert here, just thinking VDS is 95% for bonding 5% for Dampening while marketing has us thinking the reverse.

For the guys that have tried VDS in a few variations. What would you say is the effectiveness?

I'm not an expert on VDS either but there are some very detailed posts about what VDS really does. It's called Vibration Dampening System (I think) but it's really acting as a shear layer and a medium to aid in keeping materials bonded together like steel and FG or UMHW and wood. Somewhere in here a member ran extensive testing with "real" measuring equipment and found it did almost nothing in the way of damping.

twizzstyle · Post by **twizzstyle** » Thu Dec 27, 2012 4:24 pm

I think everybody has their own acronym for VDS

I've always known it as "vulcanized damping sheet".

skidesmond · Post by **skidesmond** » Thu Dec 27, 2012 6:43 pm

twizzstyle wrote:I think everybody has their own acronym for VDS I've always known it as "vulcanized damping sheet".

You'll probably right... I sort of guessed....

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reducing tip flapping

reducing tip flapping