...Pop

[Nick's Sticks]

I moved this discussion on pop to the design/layup section. I think there is a lot that could be said about 'pop.' Everyone seems to know what pop is and what it feels like. I am hoping this thread might help quantify it and help us get figure out how to get it.

Just one more thing. Can anybody give me a definition of "pop" in terms of engineering quantities (like force or Young modulus)?
Thanks.

nope, "tons of pop" is too vague a thing still.

to me it is the ability of the nose/tail to spring allowing you to pop off jumps or ollie just a pinch higher. I dont know what other people think it is and i cant quantify it.

i guess it's the ability of a board to rebound when flexed, without being underdamped so that it wobbles or too stiff.

one unit of 'Pop' is equal to or grater than the force necessary to transform an ordinary smile into a sh** eating grin...

one unit of 'Pop' is equal to or grater than the force necessary to transform an ordinary smile into a sh** eating grin...

My skis have plenty of it.

[Nick's Sticks]

I am not an engineer but like most scientists I like to try to quantify qualitative elements. I agree that something like resistance to deflection would be one way to measure 'pop.' I tried to figure out the 'pop' of an old pair of k2 x15's. I measured the deflection of the ski when loaded with a 31.8kg weight at its midpoint.



I used the deflection of a beam formula: deflection=(W*L^3)/48EI.
Since calculating I would be hard, at least for me, and since I was being less than scientific, I used EI as my unit of 'pop' (P).

where:
defleciton=.06m
W=downward force/load=312N
L=length=1.86m
E=modulus of elasticity
I=moment of inertia

.06=(312*1.90^3)/48EI
in this case EI=P=743

When I did the same test to a flexier pair of skis that I built I got P=637. It should be noted that I eyeballed a tape measure for all my measurements and did a lot of rounding to make things simple. But it was clear that the softer ski had less pop on the snow and deflected much more under weight. If anyone else has a way to calculate 'pop' stiffness, etc I would be interested in hearing it.

This said, I think there is a lot more that goes into the feel of poppyness than the physical ski itself. The technique, strength, and mass of the rider have as much or more to do with how a ski behaves than the ski's parameters. Flex of a ski is also dynamic since one can flex a ski in many different ways: leaning back, stomping with the heal, etc. Not to mention that the shape of the tail will change how the ski compresses. Even if a rockered tail is stiff as a board you will have to lean much farther back to get it to load than a flat tail.

Just some thoughts.

[jono]

I have 6 thoughts on pop.
1)Would it work to just measure the percentage of camber lost when the ski is set on a flat surface? It seems that my skis with more pop are less prone to losing camber when set down on a flat surface. This would be a measure of how a ski's flex interacts with its mass and original shape/camber. Isn't this what pop is?
2)It might help to not have bindings on the skis (or use the same bindings on every pair or a standard weight on the mid sole mark) to test the percentage of camber lost. Differences in ski weight, length, location of running surface, etc contribute to pop and would not need to be standardized in any attempt to measure pop.
3)If reverse camber skis can have pop it might be indicated by how much the raised parts droop.
4)Zero camber, or low camber, skis would need to be placed on an apparatus that allowed the ski to deflect downward. The beam deflection function would work well for these skis.
5)Maybe pop could be expressed as how much a set force (the ski's own weight) changes a ski's form. Less change would indicate more pop. Instead of measuring a simple deflection we need a way to quantify amount of a change in the form of a ski in order to quantify pop.
6)A rockered ski's (or any type of ski's) pop might not be evident until the shovel of the ski is loaded or deflected by oncoming snow. The amount of "load" could contribute to the ski's pop. In this type of ski just measuring the change in form would yield meaningless information since the ski's original form is dynamic and dependent on load. I remember hearing about rossignol making skis with an adjustable rocker and wondering if these skis would feel dramatically different at various rocker settings.

[Steevner]

I think pop could be measured by bending a ski a certain distance, or a certain force, and then releasing the bend and seeing how high the ski can shoot a random object.

[knightsofnii]

i dont think it's enough to measure "pop" by a simple beam deflection test and bending moment diagrams.


not sure about skis, but snowboards are now reinforced differently in different spots everywhere along the board. No two spots of a snowboard are going to deflect or react the same way.

I could go even farther and say that no two cores are the same, so no two snowboards are truly the same, but just forget I said that for now


Like I said I really dont know if there is a definition of pop. But yea anyone you ask about pop says SOMETHING along the lines of how a board flexes in SOME part of the board. like "dude i can ollie so good on the thing its got so much pop"

but someone else will say "dude this thing is soft and buttery but it has huge pop!" how can you have both? Some boards actually have both.
They can flex, but they can spring or rebound really well too, they feel lively instead of like dead wood or a broken bat.

But I hope someone can figure it out

[Nick's Sticks]

I think, like you said, shape and stiffness probably has the most to do with a skis' performance. Even though I called the measurements I took a measure of 'pop,' it was really just a test to see how stiff the ski was. Another test could be to suspend a weight from the tip or tail of a ski and see how far it flexed when supported from the middle. I know other people have done similar test to see how stiff their skis are.

I have found that the skis I have built that have a longer tapers in their core seem to be livelier (no surprise). By long tapers I mean ones with cores that stay thick farther towards the tip and tail. I also prefer skis that have a round flex in front of the bindings but less flex in the tail. Kinda like a sideways J rather than a C. It may be that the liveliness and pop come from a combination of a more flexy tip and less flexy tail. Something like =(tip flex)/(tail flex).

When going into a turn I load the tip of the ski and for an explosive exit one can spring off the tail. Really stiff skis might not feel as lively because they are harder to load the tip in the turn. I can elaborate further but it is time to go have a beer. Cheer.

one last thing.
After poking around on the interweb I found this article about ski flexing. It isn't really about a skis 'pop' but interesting nonetheless. http://www.springerlink.com/content/266 ... lltext.pdf

[davide]

I measured the deflection of the ski when loaded with a 31.8kg weight at its midpoint.

1)Would it work to just measure the percentage of camber lost when the ski is set on a flat surface? It seems that my skis with more pop are less prone to losing camber when set down on a flat surface.

All these definitions mean pop=stiffness.

In my opinion, pop is related to the amount of elastic energy that is converted back into mechanical energy. Imagine dropping a ball made with an ideal elastic material, it will bounce back to same height. In a real case, it will bounce back only to 90% (a lot of po) or 40% (little pop) of the initial height.

I think pop could be measured by bending a ski a certain distance, or a certain force, and then releasing the bend and seeing how high the ski can shoot a random object.

They can flex, but they can spring or rebound really well too, they feel lively instead of like dead wood or a broken bat.

That said, I think that all the woodcore/glass sandwich skis have almost the same pop. Probably a ski with rubber from tip to tail will have less pop, because the rubber dissipates more energy that wood or glass.

[sieg01]

I have thought about this too. What makes good pop??? I don't hardly freestyle alpine ski. But I have been trying more and more freestyle snowkiting. Maybe the two translate??


With kiteboarding on the water, You get good pop when your kiteboard has pretty straight edges and a stiff board... You edge hard in the water and release to pop up.


With snowkiting... I have been working on doing the same thing on the snow (I haven't been doing very good so far). One of the thoughts of other people was that some risers under the bindings will help you to load up that edge more. Any thoughts to that?

I also was wondering if having a large camber and a stiff ski would help load up so you could get your pop.



Is the pop your talking about when your riding your skis relatively flat? Or does it come after edging your skis?

[sieg01]

Another question... In alpine skiing... can no camber skis give good pop?

[endre]

I made an identical subject about pop once, it went on pretty much like tis one does. It seems to me there are quite a lot of theories about pop and what it is, I have stopped using the term totally, since it does nothing but confuse people (noone agrees what pop describes)


here's the thread:
http://www.skibuilders.com/phpBB2/viewt ... hlight=pop

[doughboyshredder]

I think of pop, as the rebound that a board has. In other words how badly the board wants to go back to it's molded shape. If the camber / rocker is weighted out, and the weight is removed how much kinetic energy is released as the board goes back to it's unweighted shape?

I think. But like has been said, it really depends on the rider, and I would think the set up of the bindings. Probably the type of binding has an effect on this. (moreso with snowboards than skis).

[Three31]

Chack out this blog - it is a good discussion (more like q&a) with techical information . . .

http://www.wagnerskis.com/blog/2008/ene ... n-and-pop/

[chaka]

Chack out this blog - it is a good discussion (more like q&a) with techical information . . .

http://www.wagnerskis.com/blog/2008/ene ... n-and-pop/

Iteresting article and responses, of course....
Once you pop, you can´t stop.

[sammer]

I knew I'd seen this topic before,
http://www.skibuilders.com/phpBB2/viewt ... sc&start=0

My thinking is flex is relative to stiffness but pop is a reactive force.
I have two skis that are the same flex(beam), similar camber, but one feels more bouncy.
When it springs back seems to transfer more energy (If this makes sense)
Perhaps one is heavier so loses more energy in rebound?
If this is the case would pop not be the opposite of dampness?

No conclusions from me. Just an observation, and a link to an old posting of a familiar topic.

sam