jg1501

hi everyone
i have a balsa f-18 that im gonna make fiberglass molds of then make a fiberglass hornet out of. my question is to reinforce the fuse how can i figure the distance to place reinforcement wood or my molded reinforcement? so i dont get to much weight on one end or the other. the other question is what would be ideal thickness of fiberglass so as not to make it to heavy? i was figuring 1/4 inch thick. then i was going to weight each part after that to make identical parts(wings) same weight. does anyone think im on the right track? thanks

myersflyers

My Feedback: (33)

jg1501,

Check out the previous post. http://www.rcuniverse.com/forum/m_3617179/tm.htm.
If your talking 1/4 thickness of just fiberglass and epoxy, your plane is going to weight a ton.
With a layup of several layers of fiberglass, you should not be over 1/16 - 3/32". ( 3/32 in reinforced, thick build up areas only)
I've found that you can keep things pretty light if you use a combination of fiberglass, Kevlar and carbon fiber.

Try this as a test sample; take a piece(6 or 8" sq.) of 2oz. FG cloth, a smaller piece(4"sq.) of 1.7oz aramid cloth
and 6oz FG cloth (6 or 8" sq.) and wet them out sparingly with epoxy and sandwich the aramid between the FG pieces.
Place the test sample between two pieces of glass(a little wax to the glass just so it pulls up with no problem) or
mylar and weight it down until dry.

After a day or two you'll notice the test piece getting stiffer, yet flexible.
The smaller piece of kevlar added tremendous strength and does not have to cover every inch of the FG,
but be used in critical areas. You would add Carbon were stiffness is required and this could be sandwiched as well
during the layup process. (Aramid adds strength and flexibility, carbon adds strength and rigidity)

PS. Use the test piece for a gear door, etc.

jg1501

so if i got this right ill try your test method you suggested but when i actually go to make the plane from the mold lay it up with the 2oz then 2 layers of 6 oz and reinforce with carbon fiber or kevlar.where need, as done in the other thread. or what ever i find to be the best after the tests i do. just want to make sure im clear on this. thanks for your help

myersflyers

My Feedback: (33)

jg5101,

I probably need to get a clearer understanding. Are you asking about the plug, mold or the final product?

I suggested your test be with 1-2oz FG, 1-aramid, 1-6oz FG. You should o try other combination, but don't
forget it will take a few days to get a good feel of the strength and rigidity of your layup.

My main point, according to your original question, is to show you will not need 1/4" of fiberglass to
mold your F18. One of things to consider when doing your lay up is where the most strength vs. weight
vs. rigidity needs to be applied. This is if your questioning is about the layup of the final product.
The plug and mold are another animal.

Consider that a giant scale 35% acrobatic full composite plane(100+ WS., 90+fuse) that flys with a
twin engine, fuel and smoke tanks, and 9-11 servos can fly superbly at 27-28 lbs. This is without a lot of
serious beefing up. Whereas, a turbine weighing 26-27 lbs (wet) with a WS of 70+- and fuse of 85 +- is
much smaller, but the stress on the ariframe is tremendous at the speed in which they fly.
So, how you layup the model in stressed areas has a great deal to do with weight.

An example of what I mean is the tail cone and nose area (minus the nose gear area) on a jets can
be layed up lightly (i.e 1 2oz. FG + 2-6oz. of FG), but the wing and stab section will require a hefty layup
of FG & Carbon [ie. (1-2oz FG) + (2-6oz FG) + (1-2.9-3.5 aramid) + final layer of 1-6oz. FG].
These are only example because much depends on the type and size of the aircraft.


If your are building a prop jet, you could layup the entire fuse with 2-6oz FG. and use carbon tow to add
ridigity to the empennage, wing saddle area and firewall. This will come out nice and light for you.

jg1501

Thanks for your help with this. I got some carbon fiber and arimid on the way to me right now. My question was about the final lay up. I found a nextcraft web site that let me see it visually that help ,and that was my plan to do as mike did. I just wasnt to clear on how thick i should make my final lay up. The aircraft im doing is a 1/10 scale atleast that what i figure it at. It has a 55 inch wing span and about 56 inches nose to tail. It will be a pusher prop at first, then when i get more funds im putting a ducted fan on it.

I have about 9 yds of 1.7 oz fiberglass cloth now and getting about 9 of 6oz. I also have that 3 yrds of arimid and carbon fiber coming.The plugs im making from autobody fiberglass blankets that can be split to make them thinner and easyer to shape with. I plan on making them as ridgid as i can get them so i get no twisting or anything and they last. As for the wing saddle areas i was planing on using the carbon fiber as you suggest as with the landing gear area. One of the things i worrie the most about is reinforcing the inside of the fuse. Would it be better to use balsa wood for that or carbon fiber?

again thanks alot for your suggestions and help

myersflyers

My Feedback: (33)

jg1501,

Wishing you well with your project. Keep us posted.
I suggest carbon for the interior support. Balsa is good for side wall support,
but it soaks up a lot of epoxy too.