Firewall tips
10-25-2003, 04:49 PM
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Firewall tips
Hi Guys,
OK next round of questions, what is everyone using for firewall these days. I just made up a laminate firewall that is 1/2 " thick that is light and strong. Let me know what you think. It is two plates of 1/8 " 5ply birch with 1/4" balsa in between. I laid 1 oz glass between the balsa and ply. I made up a sheet like this in my press and just cut out 4 firewalls from it. I compared it to 1/2" ply and it is about 1/2 the weight.
I want to get the nose real stiff.
Rob
OK next round of questions, what is everyone using for firewall these days. I just made up a laminate firewall that is 1/2 " thick that is light and strong. Let me know what you think. It is two plates of 1/8 " 5ply birch with 1/4" balsa in between. I laid 1 oz glass between the balsa and ply. I made up a sheet like this in my press and just cut out 4 firewalls from it. I compared it to 1/2" ply and it is about 1/2 the weight.
I want to get the nose real stiff.
Rob
10-25-2003, 06:56 PM
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RE: Firewall tips
1/2 thick for a firewall sounds like way overkill. I have used only 1/4 thick ply ever. I cut an 1 1/2dia hole through my firewalls, what is left has no deflection. With a back plate mount the screws are out in the corners. What is left in the middle is doing nothing. The stiffnes is required in the sides, top and bottom of the fuselage behind the firewall. usually achieved with 1/16 ply doublers on the sides. I assume we are talking about balsa fuselages.
Ed S
Ed S
10-25-2003, 07:21 PM
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RE: Firewall tips
Hi Ed,
Yes I do use 3/16 balsa sides with 1/64 plywood doubler and 1 oz glass between them. I opted for the 1/2 thick because it was easier to cut in the angles on each side to get good gluing surfaces. I like the idea of the hole in the middle.
Rob
Yes I do use 3/16 balsa sides with 1/64 plywood doubler and 1 oz glass between them. I opted for the 1/2 thick because it was easier to cut in the angles on each side to get good gluing surfaces. I like the idea of the hole in the middle.
Rob
10-25-2003, 10:59 PM
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RE: Firewall tips
Robert,
I use a 1/2" thick firewall of aircraft ply, and I cut a 3/4" hole in the center.
I've been told its overkill also, but it works for me. I believe a strong front end transfers the engines power much better than a thinner firewall.
I use a 1/2" thick firewall of aircraft ply, and I cut a 3/4" hole in the center.
I've been told its overkill also, but it works for me. I believe a strong front end transfers the engines power much better than a thinner firewall.
10-26-2003, 11:08 AM
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RE: Firewall tips
Hi Dave,
Yeap that is what I was thinking, You should try making up one of these laminated firewalls, they are very light and stiff. Do you run dowels through the fuselage sides into the firewall. We used to do this years ago in some of the old F-1 kits. I was thinking about just using toothpicks, 3 on each side.
Rob
Yeap that is what I was thinking, You should try making up one of these laminated firewalls, they are very light and stiff. Do you run dowels through the fuselage sides into the firewall. We used to do this years ago in some of the old F-1 kits. I was thinking about just using toothpicks, 3 on each side.
Rob
10-26-2003, 02:35 PM
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RE: Firewall tips
I have pinned my firewalls in the past, but since I went with the 1/2" firewall, I don't think its neccessary. I use 1/8" lite ply on the top and bottom of the nose. When you glue this all together with good epoxy (I use M310, Mythackralyte (sp?)) there is no need to pin also, although it probably doesn't hurt.
When I did pin, I found that 1/8" dowels worked better than toothpicks. I would just use 1 in the top and 1 in the bottom through the 1/8" lite ply. I still don't think pinning through balsa sides does that much good.
As to a lamintated firewall, I would be concerned about compression in the center by using balsa. I haven't had a big issue with keeping fuze weight under control, so the 1/2" firewall hasn't been a problem.
When I did pin, I found that 1/8" dowels worked better than toothpicks. I would just use 1 in the top and 1 in the bottom through the 1/8" lite ply. I still don't think pinning through balsa sides does that much good.
As to a lamintated firewall, I would be concerned about compression in the center by using balsa. I haven't had a big issue with keeping fuze weight under control, so the 1/2" firewall hasn't been a problem.
10-27-2003, 11:40 AM
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RE: Firewall tips
If you look around, you can find 1/4" end-grain balsa sheet. This would be a good substitute for ordinary 1/4" balsa sheet in the middle of the sandwich.
A while back, I made some firewall material for the QM40s using 1/4" end-grain balsa sheet between two layers of 1/16" aircraft ply, with some thin CF mat under the ply on one side. It works fine, and the extra thickness gives me plenty of gluing area for better adhesion to the sides. However, the weight saving turned out to be negligible. And if you cut a big hole in the middle, even that advantage goes away. FWIW, if I had it to do over again, I'd just use a high-quality 3/8" ply.
D.
A while back, I made some firewall material for the QM40s using 1/4" end-grain balsa sheet between two layers of 1/16" aircraft ply, with some thin CF mat under the ply on one side. It works fine, and the extra thickness gives me plenty of gluing area for better adhesion to the sides. However, the weight saving turned out to be negligible. And if you cut a big hole in the middle, even that advantage goes away. FWIW, if I had it to do over again, I'd just use a high-quality 3/8" ply.
D.
10-27-2003, 01:29 PM
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RE: Firewall tips
Talking about the stiffness of the nose, I think a good advice would be to use the carbon fiber and epoxy on all the corners of the nose for a Q500, for me it has really worked well, and helps as prevously said, transmitting the engine power more effectively.
Regards
Regards
10-27-2003, 10:22 PM
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RE: Firewall tips
Hi Guys,
Do you use chopped glass and epoxy or triangle stock on the back side of the firewall. I usually go whith chopped glass.
Rob
Do you use chopped glass and epoxy or triangle stock on the back side of the firewall. I usually go whith chopped glass.
Rob
10-28-2003, 12:10 AM
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RE: Firewall tips
I used chopped carbon fiber mixed with finishing resin.
Heres a picture, complete with my Overkill 1/2" firewill.
This is one of my earlier attempts at using the carbon fiber and finishing resin. I now use about 1/2 as much carbon fiber, and about 1/4 as much finishing resin. It is absulutely amazing how strong this makes your nose section.
Heres a picture, complete with my Overkill 1/2" firewill.
This is one of my earlier attempts at using the carbon fiber and finishing resin. I now use about 1/2 as much carbon fiber, and about 1/4 as much finishing resin. It is absulutely amazing how strong this makes your nose section.
10-28-2003, 10:22 AM
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RE: Firewall tips
Dave,
That CF epoxy glob just has to be stronger and quicker to do than the triangle wood corners I have been using forever. Do you also put a bead on the missing corners through former A after the bottom plate is installed?
Dan
That CF epoxy glob just has to be stronger and quicker to do than the triangle wood corners I have been using forever. Do you also put a bead on the missing corners through former A after the bottom plate is installed?
Dan
10-28-2003, 11:52 PM
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RE: Firewall tips
Dan,
I'm not positive I understand your question. For the top nose piece, I glue triangle stock to the sides, and sand flush with the top. I then glue with epoxy, and clamp down with 6 good clamps making sure I get a good bond at the firewall, in between, and at the 1st former.
That picture was an early attempt. My recent quickees use much less epoxy and CF, and are MUCH stronger than balsa triangle stock. Weight gain is extemely neglible.
I've also started using the finishing resin / CF under my wing hold down blocks and landing gear blocks. Its stronger than the triangle stock, and I don't need to pin the blocks anymore. Real easy to do all the blocks, and nose with one batch of glue and CF.
I'm not positive I understand your question. For the top nose piece, I glue triangle stock to the sides, and sand flush with the top. I then glue with epoxy, and clamp down with 6 good clamps making sure I get a good bond at the firewall, in between, and at the 1st former.
That picture was an early attempt. My recent quickees use much less epoxy and CF, and are MUCH stronger than balsa triangle stock. Weight gain is extemely neglible.
I've also started using the finishing resin / CF under my wing hold down blocks and landing gear blocks. Its stronger than the triangle stock, and I don't need to pin the blocks anymore. Real easy to do all the blocks, and nose with one batch of glue and CF.
