abufletcher

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.

TFF

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.

abufletcher

I'll look for some hi-temp paint (hopefully clear) and give that a try.

Teus

Don remember all paint need to dry and harden a certain time. One day is definatly not enough. Some needs a week, some two or more to get the final hardness.

abufletcher

I'm sure you're right. And the fact that it's cold in the workshop probably doesn't help. Today I bought a 2-part "urethane" spray and tried that. It looked promising. But three hours later, even though it was completely dry to the touch (and had no smell and fingerprints didn't show), the methanol fuel wiped it right off like lipstick.

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.

TomCrump

In my opinion, you're testing the paint too soon.

I don't expose my freshly painted models to glow fuel, or gas, for 2-3 weeks after painting.

abufletcher

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.

TFF

Just put a pinstripe on it and go fly the sucker. I liked in in aluminum.

abufletcher

Maybe I should have left the handles on the pot too!

abufletcher

Hmmm...

abufletcher

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.

Instructor

My Feedback: (16)

Take a long threaded rod, screw on a nut and a washer, drill a hole on the centerline of the firewall. Insert the long thread rod through the firewall so the washer is on the front of the firewall. Add another washer and nut on the backside of the firewall and tighten up both nuts. Make a plywood washer the same diameter as the inside of the cowl. Drill a hole through this wood washer and attach it to the rod the same way you did the firewall. Fit your cowl to the washer and adjust the nuts to get the proper clearance for your engine. Leave the brackets bolted to the firewall. Install your engine and then the cowl. I have done this a lot and it works....

Larry

foodstick

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.

abufletcher

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.

abufletcher

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!

foodstick

geezeraviation

My Feedback: (3)

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

RBACONS

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.

abufletcher

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.

geezeraviation

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

abufletcher

That 26cm works out to about 10.25 inches. Just out of curiosity I weighed the glass cowl that comes with the ARF and it was 134gm. So yeah really not a difference worth bothering about.

abufletcher

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.

Teus

Don,

Did you use a dedicated aluminum primer before starting your paint tests? Lot of paints don't like aluminum very much.

abufletcher

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.

geezeraviation

My Feedback: (3)

re peg, round hole.lol
Doc