First off, I would go with the second core layout...in fact, if you are using inserts, I would do all three center strips with the balsa. If you arent doing inserts, DONT plan on wood screwing into balsa. Having your higher modulus woods on the outer strips will give you a higher torsional stiffness (basically creates a horizontal I-beam for your horizontal force). Second, why put all of your carbon on one side of the core and your glass on the other? This is going to greatly offset your neutral axis...creating an unnecessarily high shear stress between the balsa and your glass facings. Just my two cents.
I was planing to put also birch or pine in waist instead of balsa, just for inserts.
Firstly i also wanted to put carbon under and over core but i read on this forum that carbon has got better tensile strength and glass compressive strength, and so that carbon over core is easy to break.
I'm building flying models for 10 years and from my expirience i would give: base/VDS along edges/glass +-45/vds upright the ski/ 2 x carbon 0/90 / glass +-45 / core / glass +-45 / carbon-kevlar 0/90 / glass +-45 / topsheet
But as i have written i read that carbon over core is bad idea though there is a lot of skis with carbon over core and this is why i'm asking
This seems like alot of fabric to me...most of us just do 22 oz of 0/+45/-45 on each side of the core. It seems like you could do 0 carbon/+45 glass/-45 glass/core/+45 glass/-45 glass/0 carbon. additional fabrics seem unnecessary (and expensive).
I think the compression vs. tension you are talking about is that glass's compression properties are better than glass's tension properties. Likewise carbon's tension properties are better than carbon's compression properties. This does not mean that glass's compression is better than carbon's compression. Your carbon wont fail.
Yes it seems to be here a lot of fabric, but i have to test few versions.
Look that balsa is't a strong wood, i want to make as light core as possible and get durability and stiffness from fabric.
On the other side freestyle ski must be flexible, i think that maybe combination glass/carbon/glass on each side of the core (project2) should be good. if it will be not stiff enough i can always put few small strips of carbon rowing
^ park skis are generally stiffer (for pipe and big air). they have only recently become softer due to changing styles and people wanting more of a 'play' ski.
As far as the amount of composite, I would agree that less is preferable, but yes, you do just need to try some things out. so as far as im concerned, go for it. you could also add a very small amount of thickness to your core to stiffen it up, instead of adding additional carbon. Also remember that carbon makes a very snappy ski (too much will result in a very non-damp (word?) ride).
Again, give it a shot, but I would choose different woods for a park ski.
well... I'm not terribly experienced, and there have been skibuilder 'studies' that have suggested core material has little to do with physical characteristics. My time on skis and my feeling, however, is that it has a pretty big impact. I plan on doing a number of tests and experiments to quantify, or at least better understand, these influences.
anyways, i wouldn't recommend a specific wood, but I would look to something that is light, strong, fairly stiff, but still with the ability to bend, and with resilient fibres that will stand up to repeated distortion... of course. I basically spent a lot of time just looking at wood characteristic comparison charts, other manufacturers materials and essays/descriptions of wood responses to various situations. A good understanding of wood mechanics and biology wouldn't hurt either. sorry, i made this way more complicated than you likely are looking for. I don't know... I would consider things like bamboo, maple or maybe douglas fir. these should be fairly available, reliable and produce solid results.
hope that is helpful. i'm just leary about using balsa in a park ski, and am not really a fan of pine or birch either. feel free to examine the structure of these woods and prove me wrong, this is just my general feeling.
like I said, I hope to do some really good research with regards to the effects of wood in skis, but as of right now, i don't know a whole ton.
ps. i have some pretty good resources at school as i'm taking a number of wood products processing courses and am developing some good knowledge and contacts. hopefully it all works out and in the future I can write up some conclusive stuff.
