Clever ways to mount a round cowl?
#26
Thread Starter
I've been testing paints. It seems unbelievable that automotive body paints are not fuel proof...not even close to it. Are the auto touch-up paints sold in hardware stores different from the stuff actually used to for car finishes? If I were to splash RC fuel on my car, would I be able to wipe the paint off with a paper towel? Seriously, this seems ridiculous.
I also tried a spray paint advertized on the can (if I understand the Japanese correctly) as being for "outdoor" use, for example, on a garage door. It fared no better than model enamels even after curing overnight. The only thing that's worked so far is a "high zinc" silver paint that I think it designed to resist corrosion.
It's times like this that I envy you guys in the US, who can just run over to Home Depot and pick up some Rustoleum.
I also tried a spray paint advertized on the can (if I understand the Japanese correctly) as being for "outdoor" use, for example, on a garage door. It fared no better than model enamels even after curing overnight. The only thing that's worked so far is a "high zinc" silver paint that I think it designed to resist corrosion.
It's times like this that I envy you guys in the US, who can just run over to Home Depot and pick up some Rustoleum.
#27
Many of the one part paint is not fuel proof. It use to be, but EPA killed most. Some get by with stuff I cant make work. I have used Duplicolor auto touchup lacquer and I have coated it with Clear Hi Temp paint. Does OK.
#30
Thread Starter
Guess I need a new testing protocol. I'll reapply both the auto paint and this 2-part urethane (which together have already cost me $30) and then test them both over several days. For example, fuel test #1 after two days, #2 after four days, #3 after a week. So I guess I have plenty of time to work on other things.
#32
Thread Starter
It's just so frustrating thinking that I won't get to see that brightly painted cowl on my model for several weeks! I certainly wouldn't paint it before I made absolutely certain on a test piece that it would be fuel proof. So it sounds like I need to paint the test piece (I already have two different paints on it and will add two more) and then put it away for a few weeks.
There are plenty of other things to do. Just getting the mounting of the on-board glow system and "fuel injection" (since the Seidel needs to be primed before starting) worked out will take some thinking. Then I need to make an extension for the needle valve. Even on the cowl itself, I need to make the brackets (probably metal L-brackets), fill some holes with JB Weld, and do some finally edge finishing. And the plumbing. And of course all of this will require mounting and remounting the engine at least a couple more times.
I suppose there's no hurry. The weather has been far too windy to maiden this beast anytime soon.
There are plenty of other things to do. Just getting the mounting of the on-board glow system and "fuel injection" (since the Seidel needs to be primed before starting) worked out will take some thinking. Then I need to make an extension for the needle valve. Even on the cowl itself, I need to make the brackets (probably metal L-brackets), fill some holes with JB Weld, and do some finally edge finishing. And the plumbing. And of course all of this will require mounting and remounting the engine at least a couple more times.
I suppose there's no hurry. The weather has been far too windy to maiden this beast anytime soon.
Last edited by abufletcher; 01-17-2015 at 07:45 AM.
#36
Thread Starter
Returning to the topic of mounting the cowl, I've had a week or so to ponder the problem and all the ideas posted here. I had just about settled on the idea of riveting brackets to the cowl (and even bought a riveting tool) and then bolting the brackets to the firewall. But then I realized that wouldn't work. The brackets wouldn't be able to slip over the engine (and the exhaust ring) from the front. Another challenge is the the basically rectangular firewall is significantly smaller than the diameter of the cowl. Each of the suggestions posted above have merit, e.g. the ply ring, the dowels+magnets, the "rotate and lock" idea.
I feel like the answer is right in front of me but that I can't quite see it. Somehow it will need to involve either brackets or a ply ring attached (in some way) to the firewall, then I'd slip the cowl over the engine and bolt it to the ring/brackets.
PS. A secondary issue is how to ensure that the cowl is properly centered on the engine.
I feel like the answer is right in front of me but that I can't quite see it. Somehow it will need to involve either brackets or a ply ring attached (in some way) to the firewall, then I'd slip the cowl over the engine and bolt it to the ring/brackets.
PS. A secondary issue is how to ensure that the cowl is properly centered on the engine.
Last edited by abufletcher; 01-21-2015 at 09:41 PM.
#37
My Feedback: (16)
Returning to the topic of mounting the cowl, I've had a week or so to ponder the problem and all the ideas posted here. I had just about settled on the idea of riveting brackets to the cowl (and even bought a riveting tool) and then bolting the brackets to the firewall. But then I realized that wouldn't work. The brackets wouldn't be able to slip over the engine (and the exhaust ring) from the front. Another challenge is the the basically rectangular firewall is significantly smaller than the diameter of the cowl. Each of the suggestions posted above have merit, e.g. the ply ring, the dowels+magnets, the "rotate and lock" idea.
I feel like the answer is right in front of me but that I can't quite see it. Somehow it will need to involve either brackets or a ply ring attached (in some way) to the firewall, then I'd slip the cowl over the engine and bolt it to the ring/brackets.
PS. A secondary issue is how to ensure that the cowl is properly centered on the engine.
I feel like the answer is right in front of me but that I can't quite see it. Somehow it will need to involve either brackets or a ply ring attached (in some way) to the firewall, then I'd slip the cowl over the engine and bolt it to the ring/brackets.
PS. A secondary issue is how to ensure that the cowl is properly centered on the engine.
Larry
#38
Abu has this been mentioned?
L brackets screwed to the firewall, the pieces that come out from the firewall have epoxied plywood on them to fit out to the cowl. then by drilling your holes very nicely on the cowl they screw right into the wood. They look nice from the outside,removing 6 or 8 screws and the cowl comes off leaving the cumbersome brackets on the firewall.
Thats the way I did it on the 1/3 pup.
L brackets screwed to the firewall, the pieces that come out from the firewall have epoxied plywood on them to fit out to the cowl. then by drilling your holes very nicely on the cowl they screw right into the wood. They look nice from the outside,removing 6 or 8 screws and the cowl comes off leaving the cumbersome brackets on the firewall.
Thats the way I did it on the 1/3 pup.
#39
Thread Starter
Thanks for that suggestion. I think it would have to be something like that. I'm also considering the idea of silver soldering a nut onto the inside of the brackets. One thing that makes the brackets a less than perfect option is that they have to extend well past the edge of the firewall (at least an inch) and I can only use four (at something like X positions) because of the "lips" on the side edges of the firewall. Of course, I could cut through those or make brackets that bend around them.
This is turning out to be a trickier problem than I had imagined.
This is turning out to be a trickier problem than I had imagined.
#40
Thread Starter
Hmm...you know, I may have been looking at this problem from the wrong way around. Since the cowl diameter is much larger than the firewall, maybe I don't need to access the mounting bolts from the front at all. Maybe I can bolt the cowl on from behind!
#42
Senior Member
My Feedback: (3)
Cowl fixings
With the weight of the engine I'd be using a glass cowl to save some. I have a glass cowl on the pictured airplane and you can see (sort of ) the wood blocks around the perimiter of the firewall that the cowl ataches to with button head sm screws. There are lots as it helps it survive with the vibration of the gas engine. It's 10 years old and they haven't wallowed out.
Doc
Doc
#43
My Feedback: (3)
I use stand-offs made from 1/4" or 3/8" ply. Epoxied and pinned to the firewall. Cowl has rectangles of G10 epoxied inside with "U"-shaped cut outs that key to the ply stand-offs. Once the cowl and stand-off are drilled, I glue a piece of inner yellow nyrod into the stand-off and use 2-56 button head screws to secure the cowl. For a 1/5 scale cowl, 4 stand-offs are sufficient. For the 10" or so cowl for the Seidel, I upped it to 5 stand-offs.
The method is quite secure. Had an engine throw a connecting rod on takeoff. Impact was hard enough to punch the engine through the 1/4 ply firewall but the stand-offs are all still affixed to the firewall, including the one that was snapped in half.
The method is quite secure. Had an engine throw a connecting rod on takeoff. Impact was hard enough to punch the engine through the 1/4 ply firewall but the stand-offs are all still affixed to the firewall, including the one that was snapped in half.
#44
Thread Starter
Doc, I wonder how much a glass cowl would weigh relative to my 26cm diameter aluminum pot version, which weighs 203g without any mounting hardware. I sure wouldn't be keen on making a glass cowl.
I've got a basic solution in mind. It would involve soldering a nut to the back of small L-bracket and then riveting that bracket to the cowl. The L-bracket would turn inwards but be short enough to clear the exhaust ring when the cowl is removed. Then I would have another sort of Z-shaped bracket extending out from the firewall. A bolt (M3?) from the rear would hold the two brackets together.
Now I just need to work out the specifics such as the length of the brackets and their placement to properly align the cowl both centered on the engine and front to back.
I've got a basic solution in mind. It would involve soldering a nut to the back of small L-bracket and then riveting that bracket to the cowl. The L-bracket would turn inwards but be short enough to clear the exhaust ring when the cowl is removed. Then I would have another sort of Z-shaped bracket extending out from the firewall. A bolt (M3?) from the rear would hold the two brackets together.
Now I just need to work out the specifics such as the length of the brackets and their placement to properly align the cowl both centered on the engine and front to back.
#45
Senior Member
My Feedback: (3)
That cowl is 9" in dia and 5 1/4 " deep and weighs 184gm, not that much less, not as much as I thought it would be. I think the method to attatch that you described would work OK I bought that cowl from Fiberglass Masters and I think it was about 45 bucks ten years ago when I bought it.
Doc
Doc
Last edited by geezeraviation; 01-24-2015 at 07:17 PM. Reason: Add data
#46
Thread Starter
That cowl is 9" in dia and 5 1/4 " deep and weighs 184gm, not that much less, not as much as I thought it would be. I think the method to attatch that you described would work OK I bought that cowl from Fiberglass Masters and I think it was about 45 bucks ten years ago when I bought it.
Doc
Doc
#47
Thread Starter
Once the idea of bolting the cowl on from behind occurred to me, making the brackets for the cowl was fairly easy. They are made from sections of steel strap from the hardware store with a 90 degree bend and an M3 nut silver soldered to the inside face of the bracket. Soldering on the nut goes like this: 1) file the face 2) heavily grease an M3 bolt, insert it through the hole in the strap then tighten down the nut 3) carefully wipe away all grease on the nut and the face to be soldered 4) put the bracket into a wooden jig, add flux, and solder. The grease keeps the solder from flowing onto the bolt. I made 7 brackets but so far I only have 5 attached, one at the top and the four others at X positions. I might add the other two on the sides. Each bracket is attached to the cowl with two pop-rivets. Next I need to make the the brackets that will attach to the firewall and then extend out to the cowl brackets. This will be a bit trickier as it involves making sure that everything is aligned.
The second photo shows the temporary arrangement for the radio gear and glow system. The balance seems roughly correct.
Finally, I tested the paints again after letting them all cure for more than a week. The auto paint still failed (rubbed right off) after sitting with a few drops of methanol for a couple of minutes. The "outdoor" (non-latex) paint also failed; it didn't wipe off but it crinkled and the surface became rough. The high-zinc paint seemed ok, but a bit of color rubbed off on the paper towel. The only paint to succeed was the 2-part urethane spray.
The second photo shows the temporary arrangement for the radio gear and glow system. The balance seems roughly correct.
Finally, I tested the paints again after letting them all cure for more than a week. The auto paint still failed (rubbed right off) after sitting with a few drops of methanol for a couple of minutes. The "outdoor" (non-latex) paint also failed; it didn't wipe off but it crinkled and the surface became rough. The high-zinc paint seemed ok, but a bit of color rubbed off on the paper towel. The only paint to succeed was the 2-part urethane spray.
#49
Thread Starter
No primer. As far as I know, no such thing is available at the local hardware store. Wait, come to think of it, I used some kind of small hobby spray can that was supposed to prime metal for painting with hobby paints. Anyway, all this is way too complicated for this non-scale project. The 2-part urethane works and comes in a suitable color. On my WWI models I just use latex or acrylics and then finish with Nelson's clear flat.
I've spent the evening attempting to get the cowl hung. Despite all of my efforts with rulers, and protractors, and compasses, nothing is lining up like it is supposed to. And it looks like the two bottom brackets are just totally in the wrong place and will need to be removed and repositioned. Centering a larger round cowl on a much smaller rectangular firewall is messing with my brain.
I've spent the evening attempting to get the cowl hung. Despite all of my efforts with rulers, and protractors, and compasses, nothing is lining up like it is supposed to. And it looks like the two bottom brackets are just totally in the wrong place and will need to be removed and repositioned. Centering a larger round cowl on a much smaller rectangular firewall is messing with my brain.