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Acceptable temp for fiberglass around pipe?

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Old 12-13-2012, 09:49 AM
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DrScoles
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Default Acceptable temp for fiberglass around pipe?

I have a skymaster mig-29 with a P180. I don't want to overkill the heat shield/blanket treatment on the back end. Are there any rules of thumb to go by on how hot things can get? I am also curious if anyone has an idea about how much cooling goes on when the plane is in the air with air going over the top and through the plane for cooling versus sitting on the ground? i.e., you can keep it at idle on the ground no sweat, and that is equivalent to full throttle in the air, temp wise.

I have an infrared thermometer, just don't want to test it by seeing paint bubble!
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Old 12-13-2012, 11:36 AM
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Dr Honda
 
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Default RE: Acceptable temp for fiberglass around pipe?

I'm no pro on this... but it depends on how you have things ducted inside.

If you have a full bypass... then the heat is contained, and the exhaust thrust should draw cool air in, around the tubes.

If you have it wide ope inside... and a single wall pipe... you should still have the pipe set up, so that it can still create a venturi, and draw air in. To do that... you should have the inner pipe, inside the outer. OR... if you have a single wall pipe... you should use a cup at the rear. ( it also helps draw a vacuum) And then finally... the exit of the pipe should be just inside the rear of the model. That will pull the hot air out.


Every model is different... but the one model I have, that I thought would be a problem, turns out to run very cool. (tight install, and a single wall pipe) The top of the fuse is barely warm after a flight.


I'm sure guys with more experience can answer for that specific air frame.
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Old 12-13-2012, 11:48 AM
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Default RE: Acceptable temp for fiberglass around pipe?

In my helis, i use this around the exhaust areas where i feel there may be too much heat from the turbine ..


http://www.vario-helicopter.biz/us1/...ducts_id=37041

same as automotive header wrap


~V~
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Old 12-13-2012, 12:19 PM
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dbsonic
 
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Default RE: Acceptable temp for fiberglass around pipe?

With a GSU you should be able to figure this out. Check temps with a run on the ground. And then go up for a flight. If it is no higher than the temps shown on the ground at least you can say it is cooler.
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Old 12-13-2012, 04:55 PM
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LGM Graphix
 
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Default RE: Acceptable temp for fiberglass around pipe?

Mike,
I know this might sound elementary, but honestly, if the fuselage feels uncomfortable to touch while running, it's getting hot. Every jet I've ever had I could comfortably put my hand on the fuselage while it was running. The dark colored jets got hotter sitting in the sun. The point at which the paint will start to bubble isn't until about 250 degrees Celcius, if it's getting that hot you run the risk of starting to soften the resins in the fiberglass (remember, the inside will be much hotter, fiberglass actually insulates pretty good) and more importantly, run the risk of melting servo leads etc inside. I would personally say anything on the outside of the fuse any hotter than about 50 degrees Celcius (around 140F) would be cause for me to start looking at why it's getting that hot.
Jeremy
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