I have been reading past posts and have a few questions pertaining to kit building.

I have read about people fiberglassing the firewall for reinforcement.
I have to guess that they are fiberglassing the back of the firewall to the sides and top of fuselage. Is this correct?
I'm also confused about how to use the fiberglass tape or mats.
I went to Tower Hobbies and they sell the fiberglass mats but they want you to buy some adhesive also to glue the the mat down before using the resin - I would have thought the resin would bond the fiberglass to the wood.

What is finishing resin and do you use the finishing resin with the fiberglass or use 30 min epoxy?

Should I use fiberglass tape on the center wing joint when building kits (40-60 sized)?



Rick

as far as the first question goes i have not done it but i believe they are running the fiberglass around the front of the firewall kind of like a limmiter strap incase the glue lets loose. I dont think it neccecary in most cases. but never hurts to have a little extra support if you want to do it. the second question there is a couple ways you can do this one is by putting some epoxy down 30 min then pressing the mat down on top then come back with some more epoxy and smooth it all out. the second is to glue the mat down with a adhesive I ussually use the stuff in the aresol can from the hardware store. then smooth the mat and push the epoxy in from the top getting it flat and smooth as possible. i have better luck with second option. oh ya i just use a scrp thin piece of wood about 2 to 3 inches wide to smooth and spread epoxy happy building and flying

Fiberglassing the firewalll is pretty much making more work for yourself that you don't need. For most planes a good tight fit, 30 minute epoxy, and triangle stock will be more than enough to make a strong firewall. Use the triangle stock on the backside of the firewall where the firewall meets the fuselage sides. (maybe we can talk Minnflyer to do a one of his great graphics showing this). If you do this you shouldn't need anything else to secure your firewall in for most planes

Hope this helps.

I'd also have to agree with the posts in this forum. Fiberglassing the nose of the airplane really isn' necessary unless specifically called for during the assembly of the airframe. What "is" necessary is "fuel proofing" the nose section so that the oil and nitro won't migrate into the wood and glue joints and then start to do bad things. What I've used to fuel proof mine is epoxy finish resin which works well for me.

If you are concerned about the firewall being secure with the airframe there two thing that I've done which has worked well. One is to drill about 4 1/8" holes through the side of the fuselage and about a 1/2" deep into the firewall and then glue some 1/8" hardwood dowel stock in them. A little work but once completed and sanded smooth it would be hard to tell when covered. Believe me you'd total the airframe up before that firewall will let loose.

Another more simpler way is to glue some triangle stock on the front side of the firewall and the fuselage side. Not as pretty but it works well.

Hope this helps.

No graphic needed Ken, I think your description sums it up well. No fiberglass needed either, not for a firewall anyway.

To answer one of your other questions, the adhesive the hobby shop was talking about is not really for structural adheasion. If it's what i think it is, he's referring to a simple spray adhesive. The idea behind this is simple: If you were going to fiberglass a wing center section, you would get a (roughly) 3" wide band of FG cloth. Spray the center section LIGHTY with the spray adhesive and put the cloth in place. The spray will hold it while you get all of the wrinkles out and make it conform smoothly to the shape of the wing. Now, you can wet the cloth with fiberglass resin (which will penetrate down to the wood - one reason not to use too much spray)

I think NEW was reading about fuel proofing and mistook it for fiberglassing??? I sometimes ues resin for fuel proofing if I'm low on epoxy. Instead of 1/8th inch dowles I drill and just use tooth picks plus the triangle stock behind the wall. My last crash the fire wall and fuse front were about the only things that didn't come apart, it was A very hard hit.[]

What got me thinking about the fiberglass and the firewall was reading about the Hanger9 Corsair.

I only have a 40 sized trainer and I did run a small bead of epoxy along the back of the firewall were it meets the plywood sides.

I had never heard of finishing resin before coming to this forum and now I know I can use the finishing resin for fuel proofing and for laying down fiberglass cloth.

One question is how do you go about fiberglassing the back of the firewall if the plane is an ARF - just seems like a mess to me.
I know I don't need to fiberglass the firewall in the trainer but I would really like to know how poeple are pulling this off.


Rick

Are you asking about fiberglassing or fuel proofing, they are both different things?? A lot of the ARfs come with no fuel proofing on the fire wall at all and I have never seen one with the tank compartment or area fuel proofed. Everything depends on the type of plane it is too, some are easy to get at and some are very hard.

I had to fuel proof were the tank is located on the trainer.
The factory had fuel proofed the firewall area.

What I was asking about was how do people go about fiberglassing the back of the firewall for reinforcement if the plane is an ARF.


Rick

Probably the best way to do that is to remove the engine mount (if it's there) and screw the screws back in flush with the rear side of firewall. This is done to keep the glue from filling the screw holes if blind nuts were used to hold the engine mount to the firewall. If there were just some drill holes then disregard and proceed further. Now go and get yourself some glass cloth (medium to heavy weight will do) and with a very sharp pair of scissors cut a piece to match the size of the firewall. Spray the backside of the firewall with a light coat of contact cement and let it get to a tacky state and then place your cut piece of glass cloth on it and smooth it out to where no wrinkles. Then mix a good size batch of 30 or 45 minute epoxy up and with the fuselage vertical on your bench (maybe leaning against the wall or something) pour it in onto the glass cloth and "dab" it into the fibers using a cheap brush or even a foam type brush. Don't go to heavy with the epoxy and try not to push the glue around too much to where it'll move the glass cloth. The idea is to get the epoxy to soak through the fibers of the glass cloth and good contact made to the wood of the firewall. The epoxy will flow a little on its own. Some guys will actually add a small amount of alcohol to the epoxy to thin it out which helps and it'll also increase the amount of working time. Be careful when doing this since very little is needed to change the consistency of the epoxy. Use alcohol soak paper towel to clean up the area's outside of the firewall which may have gotten a drop or a splatter of glue. Let the work sit for a few hours and then go back pull the screws out (if you had them screwed in into blind nuts) and drill out the existing holes on the firewall. Should look pretty nice and added a good deal of strength to your firewall.

Thanks for the explaination tschuy.

Rick

N/P Rick,

Hope it was clear enough for you to understand. If I had some pictures I'd share them.

Cheers,

Tim Schuy

But you're right, fiberglassing the rear of a firewall WOULD be messy... It's also unnecessary.

If you want to fuel-proof that area, you could spray or brush it with polyurethane, or any of the fuel-proof paints that are on the market, or you could use finishing resin, or epoxy thinned with alcohol.

I just thought maybe one day I might need to know how to fiberglass the back of the firewall when building a 60 sized kit.


Rick

Why fiberglass the back of the firewall? That is uneccesary work. All you need to reinforce it is either some 1/2 X 1/2 or slightly smaller square basswood stock, or triangle stock. Get the corner all smeared with 30min epoxy, and place the block into place. Then, smear some more epoxy into the corners that produced (for a little added piece of mind, but not really necessary). You have a joint that will not let go. This is easiest done while building (if it's a kit). If it's an arf, I wouldn't worry about it, unless you are grossly overpowering the model.

Also, yes a lot of people use fiberglass on the center wing joint for strength. I never have as all of my 2 piece wings are arfs. In an arf, you'd have to cut the covering off, fiberglass it, then re-cover it. I don't want to put that much time into an arf. That's why I bougt an arf! Just use 30 min or longer epoxy on the wing halves and you will be just fine. I've had one wing fold up on me, and that was my fault. The plane had added weight for balancing, and was probably close to 1/2 pound overweight. It was still a fun plane to fly (trainer), but heavy. During a dive, I didn't pull back on power. When I pulled out of the dive at the bottom (probably traveling in the neighborhood of 80 plus MPH), the wing folded. I don't think fiberglass would have helped that, but maybe. So, if you are really worried about it, then go ahead. The only kit I've ever built had a one piece wing, so there was no joint. However, when I build a kit with a two piece wing, I will fiberglass it. But that's only because it's easy to do before you cover it!

Minn and the others are correct, fiberglassing the firewall is not needed. IF you feel like you need more strength than triangle stock will give you, then you should pin the firewall. after epoxying the firewall to the fuselage drill through the fuselage and into the firewall. use carpenter's glue in the hole and then tap in a wooden dowel. cut the dowel flush with the fuselage. This is cleaner than fiberglass. it is lighter than fiberglass. and is easier than fiberglass. Built this way, you won't be able to pull the firewall out.

Hey, nice diagram Ken!

Ahhh yes master, thank you for your praise. I am but the young humble grasshopper, and you are the wise master!

thanks mike.

Yea it looks like pinning the firewall would be much easier.

I'm just getting info for future use - I don't think my trainer needs the firewall reinforced.

What got me thinking about the whole firewall thing, I was reading about someone with a H9 ARF Corsair and Satio 100 engine who's firewall came loose on the ground while tuning the motor.


Rick

newtoplanes,
that can be a problem with ARF's. An ARF plane is just like anything else in this world that is manufactured (cars, computers, etc . . .), it's only as good as the person that is putting it together. Somebody could have been having a bad day and didn't attach the firewall in that plane very well. That should be a good practice for everybody that is going to fly an ARF (also applies to second hand planes, even your own builds), check all joints that you can get to and make sure they are secure. If the motor being ran could pull the firewall out, a good tug on it while putting it together should have shown that is was weak.