Ski Builders Forum

Yepp, I guess it’s the high tech stuff that makes us come alive
This sounds really interesting

I'm at Oppdal every weekend during winter. Just give me a hint it you are in the area.
I'll make Erik brief me regarding his flex analyzer. I hope It's more high tech than his directly-on-the-skull-molded-powder-helmet

Cool.

Guess we´ll bee seeing each other at Oppdal then.

We should keep each other posted on developments of the measuring equipement. Might be some good possibilities for technology transfer and cooperation on different stages of design.

Svimen: I was a student at the machine engineering faculty some years ago, and I guess that’s a good place to start looking. As far as I know accelometers are rather rugged.

In my previous job we used accelometers to do vibration analyzes. By analyzing the results, I think it would be possible to determine the flex pattern as well. However, this requires at set of accelometers uniformly distributed on the ski, a laptop to log the result (or maybe a PDA) and some software. I guess it’s possible to work out a way to make it easy to transfer the setup to different pairs of skis. The accelometers we used are not that big or heavy.

Sounds good. How many accelerometers do you think are necessary to get a meaningful result?

Ideally, both skis should be instrumented at the same time, making comparisons of inside and outside ski possible, it might even be desirable to instrument both edges of both skis, as this might give some clue to the torsional stiffness and the torsional behaviour of the ski as well.

I might get a friend of mine at the cybernetics department to help with the programming and all the tech, sadly he´s not a skier though...

I know some BASE jumpers who once tracked a jump using a high-speed gps, this might be too coarse for our purpose, but on the other hand it could tell us something of the actual movement of the skier and how this affects the forces applied to the ski. I´ll try to find out the frequency of sampling and precision of such a thing.

I hope It's more high tech than his directly-on-the-skull-molded-powder-helmet

are you kidding? He made it! I think I talked to him about that idea last year at oppdal.

anyway, it was not a flexanalyzer, it was a vibration analyzer.

endre wrote:He made it!

Yepp, I know. Good story, but maby a bit of topic

Hi Endre,

I've found very interesting all the work you have done regarding the tests in the "measuring ski flex post". I've seen it first in the TGR forum and then here.

You published most of the category charts but I've seen a chart on the magazine that you haven't publish yet in the post here.

It's the one with the Blizzard Titan Pro, Dyanstar Legend Pro and the Volkl Mantra.

Would you be so kind to also post this graph in the thread? Thanks.

Svimen, the system used in the article G-man linked to could most probably also be used under the boot if you use a slightly different pressure mat. It is a system used primarily for medical research but has some mats for other areas as well and they have started to do some work in the ski business as well. This link; 3w.novel.de/generalinfo/news-intro.htm , scroll down, shows some test done last year with in shoe pressure though. It is linked with a Blue Tooth so you do not need the computer in your backpack. Might be a bit hard to get your hands on the system though as there only is 4 systems in Scandinavia that I am aware of and it is expensive to buy.

I have made a pdf with the curves of 85 2006/07 freeride and jib skis.

to visualize the different curves, open the layers pallette on the left side of your pdf browser and click the "eye buttons".

here is the PDF:
http://www.endrehals.no/Flexcurves%202007.pdf

Endre,
awesome work! Thanks for sharing.

-kelvin

endre wrote:here is the PDF:
http://www.endrehals.no/Flexcurves%202007.pdf

this is just amazing ! Thx !

Interesting post! Endre, just curious as to why you selected F/L as your stiffness measure? From the old beer & johnston text, could you not calculate section stiffness as EI, solved from the cantilever equation.

y=(PL^3)/3EI

I am probably missing something but I'd be interested to hear your thoughts.

Because I am not predicting stiffness, I measure it.
I assume that Hooks law counts for ski constructions in general, I use the same sections for all measurements, etc.

Not shure what explanation you want, your question was very general and needs a loong answer, can you be more precise?

Hi endre, thanks for the reply! My thoughts were that the EI ratio would give a better representation of stiffness than F/Lsection. It seems to me that F/L kinda gives a dummy ratio, in that it can only be used experimentally to compare skis. If you wanted to correlate testing to analytical stiffness, etc getting more out of your data, it seems that EI would might be the best choice as you get the same stiffness profile and with all the same inputs but you have the advantage of being able to design with it. You could probably still design around the F/L method but I would imagine you'd need a complicated FE model.

I have noticed in some literature wrt ski design two measures of stiffness both EI and "flex" - F/L.

Those plots are killer btw, give a great baseline for optimizing a ski to fit a profile.

Endre & others,

Have you flex tested any skis from the 90's or 80's? I'd be interested to see the evolution in flex from straight to shaped. My intuition is that they decreased stiffness due to the change in skiing style, from pure waist pivoting to more fluid steering motions. Any other thoughts? Again, wow'd by this topic.

Cheers.