Composite fuselage formers and wing ribs
 

Hello,

I would really appreciate some guidance regarding an alternative to 1/8 lite ply that is called out for formers and ribs on my jerry bates 1/5 Hellcat.
Playing around with the 1/8 lite ply I found it relatively heavy and not very strong and this has prompted me to look for an alternative. I made a few 4x4 inch test pieces and compared them to the lite ply. One piece was made from two laminates of 1/16 balsa and .2 oz carbon fiber veil. Balsa at 90 degrees. The balsa was laminated using 3M 77 spray adhesive (it was quick ) and the carbon veil was attached on both sides with two coats each of Sig nitrate dope. This 4x4 piece weighed half of what the lite ply weighed and was considerably stiffer. I am thinking of using this layup for the fuse formers but using thinned epoxy instead of 3m adhesive. The other test piece was the same balsa core but using 1/64 ply on each side. This was about 1/3 lighter than the lite ply but very stiff, more so than the carbon veil,balsa,carbon vel laminate. As it stands now I feel I will use West epoxy, since I have quite a bit of it, and will take the small hit of increased weight from using it. Any benefit from using carbon cloth instead of carbon veil or 1/64 plywood?
Obviously many planes are fly just fine with lite ply but I enjoy messing around with a bit higher tech stuff. Any ideas or suggestions will really help

I recently made a test lamination with 5.9 oz carbon and an end grain balsa core. It was .165" thick and a 6" x 6" square weighed 22 grams. I cut the end grain balsa with a bandsaw from a block of balsa. The laminate was vacuum bagged using West Systems epoxy. The result was much stronger that 1/8" aircraft ply. Depending on your budget, you might consider some 2.1 oz spread tow cloth from CST Sales. It would be a lot stronger than veil.

http://www.rcuniverse.com/forum/atta...mentid=1940628

Scott

Hi Scott,
Thanks Scott, I'll look into your suggestion later tonight. I have an old robinair vacuum pump that I used on a project years ago, that will go into my vacuum bagging system that I'm building now.. I would like to cut the carbon laminated formers on my band saw but read that it is not a good idea, even when using a metal cutting blade. Any thoughts about that? I looked into a bandsaw blade with tungston carbide particles on the cutting surface but it was around $130. Took a pass on that.

Thanks again, Richard

I have not done a lot of cutting of carbon, but from everything I've learned, the big problems with most regular saw blades is that they can cause a lot of fractures in the carbon and can dull standard blades quickly. I trimmed the carbon overlay on my sample piece with an exacto #11 and then sanded the edges with good results

For straight cuts, a diamond blade in a small circular saw like the Rockwell or Roto Zip, or a mini table saw like the Proxxon or Microlux would work good. for curved cuts, a diamond bladed jigsaw, bandsaw, or scroll saw would work. With a single layer of carbon on each side, you may even be able to cut it with a titanium blade utility knife. You could also use a dremel with a cutoff wheel. One thing to keep in mind is that carbon dust from cutting could get into your electrical saws and cause damage shortening it's life or even completely shorting it out. I recommend using a vacuum while cutting.

Scott

Aside from your band saw blade, consider the carbon dust you create and inhale. Use a respirator.

Can be done. If you use a carbon weave it looks cool. Between two pieces of thick acrylic plate, you will get the same high gloss of the acrylic.
Especially in the engine area if using a gas engine.

Steve

Nomex honeycomb with a skin of just about anything. I have used 1/16 balsa skins and made not only light formers but tail surfaces too. Much easier to cut and still super strong.

The hi-end hi-tech stuff only adds to the time of building from plans. What is called for on the plans will work. I do understand the use of these things in a glider/racer/pylon competition arena but on a warbird is really not needed IMHO. Like Steve says not good inhaling the carbon stuff. I do enough work with epoxy so I limit the process of cutting and sanding carbon materials. I agree it can be made stronger but nothing stronger than terra firma.

The idea of Nomex honeycomb sounds like a good idea. I have a sample piece of .125 thou that i'll try to laminate. How do you laminate it without a bunch of resin pooling down into the honeycomb core? apply the epoxy resins and use a squeegee to remove most of the resin from the balsa ? Roger that on the CF dust. Looks like I may get a carbide coated band saw blade.
This is just like building a 1:1 scale aircraft...Cost over runs.
Just finishing up on my vacuum pump.

Thank you all for the ideas...Richard

Richard, you are correct, a thin film of epoxy on the balsa and then bag it up. It ends up being super light but ridged. If you need more honeycomb I have more then I can use and am selling most of what I have at great prices.

FW 190
I agree totally with what you say, however I believe I have two good reasons to do what I'm doing. One is to learn to use different materials and two to keep the aft end light. I will use a respirator instead of a dust mask though.

Hi speedracer...Do you have any 1/8" honey comb?

Thanks,
Richard

Richard, I do have some 1/8". You can PM me with a size requirement and zip code and I can give you a price.

Honeycomb is not a very good material for structural components, even more so if you have no idea what you are doing in terms of its design , utilization and layup.

Any carbon greater than about 4oz/yd is overkill as well for 95% of the people in this hobby.

And finally

multiple light layers will be stronger than one or two layers of a heavier cloth when the total fabric weight is equal.

if honeycomb is such a poor material why do soo many aerospace and aviation companies use it??? I call nonsense on this assertion

I don't know but they use it in flooring, aluminum+honeycomb+aluminum, in some, aircraft...Is that considered structural ? Or was it meant to be critical structural members ?

Very few if any use them for major structural components. In my full scale maintenance experience i have primarily seen aluminum honeycomb panels for floor panels, interior partitioning, non stressed access panels, etc. i have never seen its use for wing spars, major fuselage bulkheads, etc. the reason is the fabric layers have very little surface area to attach to the honeycomb itself. It is also never used in an application requiring a Bolt through application without an embedded and pottes hardpoint mounted into the panel.
you will also notice that much of the full scale aircraft use an aluminum skin, on each side of a honeycomb panel.

Again, improperly designed and utlized honeycomb panels are worthless except for adding weight.

It would depend on the aircraft design, but the majority of the time, i would say flooring is not considered structural to the aircraft itself and only structural in holding whatever is being attached to it. Seat rails are typically through bolted through the floor panels and then straight into the aircraft structure itself, so the floor panels become semi structural to keep the aircrafts main structure from flexing, but the stress parts (seat track fasteners) are transferred to the main aircraft structure and not the flooring.

Again, it all depends on how the airplane was designed, so theres no blanket statement for every situation.

Balsa/foam and glass/carbon is much easier for the average hobbyist to do well.

Hmmmm then you are saying I should stop making firewalls from honeycomb-carbon laminates. Geez in 10 years or more now, I never had any failure of such a composite and I've used 1/4" material and have mounted up to a 55cc gas engine. Cross grained balsa-carbon laminates also. And guess what? The middle of the firewalls is removed allowing the carb better breathing from inside the fuse. The hard points are simple carbon tubing sized to fit the bolts I want to use. Blind nuts are backed up with a birch ply disc, 1/8" thick...

BTW- for small things, a food vacuum sealer works great with the correct bags of course. Nice thing is that if you are restless, put the bag in hot water for an hour or two to really kick the epoxy

Shaun,

Would you please send me a quote for both 1/8" and 1/4"? PMs thru RCU are iffy so email me directly. 3-5 sq yards of each....Thanks

I see some modelers think that full size aircraft construction crosses over to our toys.

As pointed out in post #12 by Invert, I believe his early comments are directed at our toys.

A structural engineer once said to me " a good engineer, engineers, a bad one over engineers".

steve

I never said that, YOU did.. I said "Improperly designed and utilized honeycomb structures are worthless".. Obviously you have found what works best for your applications (or have done enough research into what would work prior to attempting the parts (which 90% of people are to lazy to research something now a days and just want a quick and easy answer).

You guys get all bent out of shape when someone comes in here and starts poking a needle at your balloons.. This is why i don't post nearly as often as I used to, everyone is so touchy when someone has a different opinion than the next guy.

If you want to look at how improperly designed and utilized honeycomb structures can work out for you, just look at the Numerous FEJ (Fly Eagle Jet) structure failure threads in the RC jets section..

Like i said, the average hobbyist who has little experience or knowledge (in composites) is more likely to have better experience and success with glass/carbon and balsa laminates, especially if they are making the panels themselves

Thomas,
Far from being "bent out of shape" I and I'm sure many other respect and appreciate your talent and willingness to share your hard won knowledge when it comes to composites. Constructive criticism is invaluable...Too bad some folks take it personally. Please don't stop sharing your know how.

Here's a nice tutorial on cutting carbon fiber.

http://www.youtube.com/watch?v=EWzN6GZeEzs


Cheers,
Scott

Thanks Scott Good find. I have quite a few perma grit tools mentioned in the video. They sure work fine.

Regards, Richard

I can not agree more about the honeycomb wrong utilization but only to illustrate where the right honeycomb usage is applied.

http://www.rcuniverse.com/forum/atta...mentid=1945731

FEJ ... the anti-NASA engineers.