Composites

[Elapid]

I'm learning to work with composite materials now, i thought i'd share some pics...

I purchased some 1/8" Nomex honeycomb and nondirectional carbon fiber cloth on ebay a few months ago. I finally got enough epoxy resin to start work on a new project. I'm starting with the fins, the plan was to use the cf mat with a fiberglass veil. on both sides of the nomex honeycomb. the problem i found was that with the cf mat is that it soaks up a lot of resin and when it is put under vacuum without anything to absorb the excess, the honeycomb fills with the excess resin.

after the first fin, i decided to use one pump to do each side of the fins. this worked, keeping the honeycomb empty of excess resin, however, there were many dry spots.

i sanded the edges flush with the nomex, then used thin CA glue to repair any delaminations/dry spots.

satisfied with the results, i then proceeded to mount the balsa strips to the edges of the fins to create an airfoil shape. I used trailing edge material from model airplane stock and aileron/elevator stock for the leading edge.

and here's the final result, sanded and ready to go!

 

[GL-P]

I got some CF too and I'm starting some experiments with ultralight tubes.

Can't wait for the CF sleeves!!!

Nice fins!!!

 

[rocketsonly]

Exactly what my TARC team plans on doing in the new future! Do you think it would be easier to apply epoxy to the cloth first and let it cure in order to become and panel, and then to just epoxy the panel to the honey comb, one side at a time?

 

[Elapid]

i was going to mention that.. thanks!

what i will do next time is to put a thin layer of fiberglass on the nomex honeycomb to seal it, then do the cf/fg layers.

 

[gerbs4me]

nice work on the fins
I couldn't of done better myself

 

[Elapid]

Originally posted by gerbs4me
nice work on the fins
I couldn't of done better myself

thank you!

 

[rocketsonly]

Originally posted by Elapid
i was going to mention that.. thanks!

what i will do next time is to put a thin layer of fiberglass on the nomex honeycomb to seal it, then do the cf/fg layers.

Sorry, I don't understand that, please explain further!

 

[Elapid]

what my plan is, is to wet out a piece of 3/4oz fiberglass and adhere it to the honeycomb. since the 3/4 oz wets out with such a small amount of resin, the chance of filling the honeycomb is minimal. once the skin is cured, the honeycomb will be sealed against any excess resin from successive layers filling the voids.

does that make sense?

 

[rocketsonly]

Ahhh! Much better! Sounds great, let us know how it fares!

 

[Elapid]

i supported a fin at the edges and stood in the unsupported center section, balanced on one heel... ~175lb

i don't think it even flexed.



i'm going to be making bulkheads and centering rings...most likely using end-grain balsa rather than the nomex to facilitate hole-cutting. i think it would be difficult to get a nice round hole in the nomex.

the fins are about 1/4 the weight of the same thickness of G10, about 63g each.

I found the .rkt file that i got the fin layout from, it is the RDS Star Quest

 

[GL-P]

I'm gonna try 1/32" basswood with tip to tip 2oz cloth or some CF. Should be real light and super thin!!!

 

[rocketsonly]

Originally posted by Elapid
i supported a fin at the edges and stood in the unsupported center section, balanced on one heel... ~175lb

i don't think it even flexed.



i'm going to be making bulkheads and centering rings...most likely using end-grain balsa rather than the nomex to facilitate hole-cutting. i think it would be difficult to get a nice round hole in the nomex.

the fins are about 1/4 the weight of the same thickness of G10, about 63g each.

I found the .rkt file that i got the fin layout from, it is the RDS Star Quest

From my conversations with John Coker (www.jcrocket.com), he prefers endgrain balsa for fins, and honeycomb for tubes.

To those who don't know of endgrain balsa: it's not the same as regular balsa wood! The cuts are perpendicular to the directional plane of the grain. If that makes sense.

 

[Elapid]

pretty cool!

i don't have nearly enough honeycomb to attempt it.
maybe if i get to like this stuff i'll pick up more

 

[rocketsonly]

Mr. Fiberglass (one of our sponsors) carries tons of neat composite materials you should check out.

https://www.mrfiberglass.com/

Just tell him Rocketguts/Matthew suggested you to go to him!

 

[Elapid]

thanks!

i finished a couple panels made from nomex and e.g. balsa cores

finished weight is 1.9g/sq in for both the balsa and the nomex honeycomb. 5mm balsa panels, 7mm Nomex.

i used the 3/4 oz fiberglass to seal the honeycomb and it seems to have worked out nicely.

here's a couple pics

i covered the table outside with a trash bag to protect me (from my wife's ire).
lots of ash has been falling...fire season in california, ya know!

here's my custom curing oven

 

[GL-P]

That release cloth you're using doesn't look like waxpaper. What are you using?

 

[rocketsonly]

Originally posted by GL-P
That release cloth you're using doesn't look like waxpaper. What are you using?

Doesn't the release cloth need to have pores so that the epoxy can seek through and become absorbed by the breather material? Does wax paper have pores?

 

[Elapid]

release films, breathers, etc.?
i'm not using any.
that's because i'm doing it wrong.
you know what>?
it's working OK, so i'm not too concerned.

i just stick the epoxy-impregnated parts into a vacuum bag, and apply the vacuum.

i bet i could save a good .1g/sq in with the proper technique.
i'm not looking gor any altitude records, so an extra gram or two overall isnt' an issue at this point.

so, at 1.9g/sq in (doing it wrong)...this stuff is about the same weight as the same thickness of wood, but many times stronger, and is about 1/3 of the weight of the same thickness of G10!

i was considering using mylar with pinholes in it for release film and using paper toweling for a breather...maybe it would have helped. i think it is mostly useful when using an excess of resin to help keep the weight down. i didn't use excessive amounts of resin so i mostly fight dry spots, not heavy areas.

it is interesting to note the difference between how i brushed the resin on the first time, compared to how i do it now...practice makes perfect.

thanks for looking!

 

[Elapid]

it seems to be working out!

the finished fincan weighs in at 380g
the original bits from the rocksim file come in at 480g

a total savings of 100g over standard plywood fins and a much stronger result! and all the weight is off the rear of the rocket.

here's a pic of the finished unit.

 

[edwardw]

Isn't weight at the rear of the rocket not a good thing - because it shifts your CG back and then that might make it unstable?


Edward

 

[Elapid]

Originally posted by edwardw
Isn't weight at the rear of the rocket not a good thing - because it shifts your CG back and then that might make it unstable?


Edward

yup!
It's not a huge savings, but every little bit helps!
and the lighter rocket can fly on smaller motors, or go faster on the bigger ones...maybe even higher.

 

[DumasBro2]

Giant Leap has panels that look just like what your making. It's not cheap however. I used the 1/2" Nomex honeycomb/fiberglass panel for the main wing on my Bomarc. The stuff is amazingly light and strong. https://www.giantleaprocketry.com/hpdefault.asp scroll to the bottom of the page.

steve

 

[DumasBro2]

ok, that link is just the main page. Hit products; What's New; then New Composite Fin Material.

steve

 

[Elapid]

that's where i got the idea.