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Building Tips and technical articles. => Building techniques => Topic started by: Dane Martin on March 19, 2016, 08:48:27 PM
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So the Strega was built and flown on a ro-jett 61, and then i believe a .75. But no pipe. I want to run a ro-jett 61 on a pipe. Because it was built with no pipe in mind, i am now tasked with installing a hole... Haha.
Before getting started, i decided to make a tunnel out of foam. If nothing else, it's a good starting point for a mold. I'm thinking of slotting the belly, installing the foam tunnel and light glassing it over. Then paint it to match. Sounds easy enough i suppose...
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Shown above is pastor Kevin and my friend Donald cutting the foam on the hot wire table. It's a little excessive for modeling, but whatever it takes, right? Lol
Here's the section that will be trimmed and fit into the plane. Or, used as a mold... I don't have it figured out yet. I'm just winging it.
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How warm do things get around a pipe? CF-epoxy can survive much higher temperatures than foam.
Just thinkin', here -- dunno if it's a valid worry or not.
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I was immediately thinking that fuselage rigidity would be a problem with the foam tunnel. Many are just 1/64" ply rolled into a "U" and glued into the cavity, which would help a lot. A layer of .5 oz FG or CF wouldn't hurt. Make sure you have some clearance for air circulation. Can't say how much is enough, but 1/16" on a side would probably be minimum. I had to butcher a big oblong duct under the header. Not sure if air goes in or out there, but it helped. n~ Steve
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All excellent points. I don't know about temp... The main thing i wanted the foam for was just a shape. I'm thinking more and more it's only going to be a mold to make a fiberglass tub.
For the fuse rigidity, I'll add formers that are shaped to the tub, and inside the fuse.
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Just my 2 1/2 cents. When I first started using pipes maybe a decade ago I know I way over-thought this and tried to shape the inside of the tunnel and thought it should be glassed, etc. I learned it wasn't worth the trouble and was far too heavy. Today I just have the hole in the bottom, close the area off from the rest of the airplane with 3/32" balsa- just boxed in not shaped and a few dope coats. Done. Make a standoff mount about 2/3 rds of the way back. Allow plenty of clearance around the pipe and the tunnel open enough to get plenty of air around the pipe. Most of my pipes are exposed from the bottom. I've never had any heat issues and the airplane is lighter and uncomplicated.
Dave
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Looks good Dave. I'm thinking something like that. Even easier, will be the fact that on the Strega, the belly over the wing is more shallow. So, maybe just box it in with balsa, fuel proof paint and done? Sounds a lot easier.
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All excellent points. I don't know about temp... The main thing i wanted the foam for was just a shape. I'm thinking more and more it's only going to be a mold to make a fiberglass tub.
It doesn't get that hot towards the back. I would suggest you leave the foam in place, put medium glass over the foam, and move on with your life.
BTW, the danger point where anything will melt, if it ever will, is about a minute or two *after* a flight
Brett
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Here's the starting point. Dave, it looks like your pipe sits in the plane deeper. This Strega has a much more shallow belly pan. I'll cut into it tonight to find out how easy this will be. Thanks Brett. Sounds like heat won't be a huge factor here.
PS, i flew this yesterday with no pipe. The power is great. I chickened out and only did loops and stuff.... But the power was great, and the break was very nice. If it wasn't so loud, I'd consider leaving it alone. But our field is very noise sensitive...
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Doesn't Dubby have a mini muffler for that? I have one on the Ro-Jett 40 RE.
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Yes John he makes a header muffler which works fine but there are advantages to the pipe. If you go with the 'Randy' pipe which I use mostly, and noise is a very big deal to you, you might ask him if he still has those multi chamber resonator pipes I recall that were some quieter. I have one from the '.40' days but don't know about current larger versions. My RO Jett .40s may find their way into classic airplanes some day and header mufflers will be the ticket for those.
Dave
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It's a Randy pipe Dave. Here it is laying into the chamber i cut. I'm thinking my thoughts of the job were bigger than what the job is ending up being. The entire section of the fuse was hollow enough to accommodate the pipe. I'll use a Macs pipes mount basically on the wing inside the fuse. Then just box in the hole i cut as you described. I'll clean up the cut out with a dremell and sand paper. Should come out pretty good.
Doc, i thought about the mini muffler, but i bought a ro-jett so i figure I'll make the most of it. Dive all the way in, you know?i could have just bolted in my k&b 61 or the saito 72 fs and made it really simple. But i just wanted to learn how to tune a pipe set up.
Oh, and pic two shows the only former in the way. I'll notch it down about 3/16 and it'll clear the joining area
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Well, it's looking pretty neat the way it sits in there.
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Ok, here it is before the paint. I just boxed in the area. The pipe mount is a piece of 1/2x1/2 hard wood jb welded to the wing (which was glassed). I cut it to the same angle as the wing, so the top mount portion is parallel to the pipe. Then the mount piece is bolted to that hardwood.
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"Great" Dane,
Looks good so far, keep at it.
We flew our R/C pattern ships with exposed pipes. I never had one that had the pipe inside.
Any CL guys flying CL models with exposed pipes on the outside of the fuselage? Sure would make the install a lot easier.
BTW. What do you have for a camera?
Charles
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Hey Charles. I'm just using my phone camera.
I wanted to just leave the pipe outside completely, but the header sinks into the fuse, so the pipe had to be lower. I didn't build this plane, it's pretty descent but not too pretty anymore. Lots of flight hours. Seen a fair number of contests too. So i know the plane flys. Great test bed to learn about piped engines!
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"Great" Dane,
Looks good so far, keep at it.
We flew our R/C pattern ships with exposed pipes. I never had one that had the pipe inside.
Any CL guys flying CL models with exposed pipes on the outside of the fuselage? Sure would make the install a lot easier.
BTW. What do you have for a camera?
Charles
Pipes on Precision Aero planes are hidden because we have appearance points and pride,, dont want that hunk of carbon hanging out in the breeze like you left your pants unzipped LOL
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I guess that depends on the size of the pipe? Oh!
Oh, and i glassed it after sanding a lot. It came out better looking than that, but i don't have a pic i guess. I'll get it after paint