bacon2109 wrote: ↑
Wed Dec 13, 2017 12:29 am
been writing to long, some answer were posted;
for a mast , a DIY build, to reach a fair stiffness and torsion, you put 2 to 3 mm wall tickness of fibre carbon on each side.
If using about 200g/m^2 cloth, 1mm thick carbon is 5 layers. 3mm carbon would be 15 layers.
15 layers each side is overkill for DIY, particularly with 6k. This are 30 layers, take or leave, with 60-90 mins pot time for the normal person wrapping a mast. So, not a pro:) If one is really skilled, maybe, just maybe less than 60min to wrap it. That is a huge stress for DIY builder who never attempted to build something similar.
What you're missing completely from the picture is a stringer. Stringer will replace heaps of carbon needed for bending strength.
Also, 30-60 is not a torsional strength. 45 is. No matter how it bends you can't get wrong with 45. The guys who build the moth HF will tell you more 45, the better. I did splat 2 layers each site if remember well. All together 4 layers each side, so less than 1mm. Strong as. Two carbon stringers.
Uni can't be used for 45 (or any angle) simply because it's impossible to align it properly. Remember, the epoxy pot life is your enemy - not what theoretically one can do. So you need to go with biax, plus with woven carbon for non 45 angle if you wish.
To put it simply, all of this is replaced by prepreg. One can do whatever with a prepreg since no epoxy pot life to worry about.
As I see it DIY is a compromise. As an engineer, building a bridge is a compromise too. Actually, everything is. So we're optimising for our application, time and money.
---flex and torsion stiffness increase on shorter beam--- No. The structural property is the same. What's different is the amount of stress or a leverage on shorter/longer mast.
Also, building an asymmetric mast (thinner in the middle), creates wrinkles on carbon. It would be enormously difficult for one off DIY builder to manage this.
Hm...A lot covered. Good luck.