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DIY intersection fairings Q.

az_gila

Well Known Member
I've made one lower intersection fairing and I am 1/2 way through the second. Working in a cold (well AZ cold) hangar I haven't been able to get the modeling clay really smooth. I think this will create more thickness than needed when the fairing fiberglass will be finally finished.

For the upper intersection fairings I think I would like to use the expanding foam method, but I'm not sure of the exact product to use that can be sanded smooth. I've used Dow "Great Stuff" on home projects but I'm not sure how well it can be sanded/formed.

Has anyone used this foam approach and can they describe what tools they used for forming the smooth curved surfaces required?
 
I've made one lower intersection fairing and I am 1/2 way through the second. Working in a cold (well AZ cold) hangar I haven't been able to get the modeling clay really smooth. I think this will create more thickness than needed when the fairing fiberglass will be finally finished.

For the upper intersection fairings I think I would like to use the expanding foam method, but I'm not sure of the exact product to use that can be sanded smooth. I've used Dow "Great Stuff" on home projects but I'm not sure how well it can be sanded/formed.

Has anyone used this foam approach and can they describe what tools they used for forming the smooth curved surfaces required?

Gil, I did mine in a normal temp basement, but the clay worked a lot better with heat, I took the bricks in a baggie and dropped in hot water for a while, then applied while warm. A heat gun only melts the surface if too hot.

I use 80 grit auto body paper to sand foams to near net, then use 220 to make smooth. Be careful with drywall compound, it takes a long time to dry, and will crack if heated to accelerate.
 
Use drywall mud on top of the clay then wax it, after it is smooth and hard.

I hadn't thought of that combination. I won't need to buy the good expanding foam and also won't have to worry as much about getting the clay smooth.

Thanks. :)
 
Gil,

Get a large sponge, like the kind you can get to wash your car. Get the sponge wet and use it to smooth the plaster. (That's a great tip on fixing your walls too.)
 
Heat the clay

Gil,I have done this many times and in the cold too. Heat the clay up first by leaving in the house overnight. I use a heat gun when needed and also heat regular eating spoons and use both sides (not from your wife's place settings). I have heated clay to almost melting with no bad effects.

Steve, Fairings Etc.
 
I've heard the "great stuff" foam isn't all that great for modeling and sanding but have never tried it.
Decent results with X-30 from spruce
http://m.aircraftspruce.com/catalog/cmpages/x30foam.php

I've used Great Stuff to form a diffuser (duct) for a heat exchanger. Easy to sand to shape using rasps, coarse sandpaper, etc. Very open cell foam; will need to be sealed with drywall mud or something similar to get a slick mold surface.

Make sure you have a release agent on the underlying structure if you're using it on the plane. It's tenacious stuff.

Charlie
 
Gil,
Try some bondo over the clay. Dries quick and easy to sand.
The drywall mud should work too. I built the full size movie prop for the B2 bomber for the movie Broken Arrow. You can not believe the amount of bondo and drywall mud we used.

One question I have about rolling your own fairings is how do you make sure they are the same on both sides? I suspect if they are different they could cause the plane to not fly true. Maybe Im over thinking it but I have heard stories of the gear fairings not being aligned correctly and needing to correct with trim.
 
I actually used my gear fairings to center my slip indicator. Several iterations with duct tape to get it where I wanted it. My fairings are not identical.

Don
 
Gil,
.......

One question I have about rolling your own fairings is how do you make sure they are the same on both sides? I suspect if they are different they could cause the plane to not fly true. Maybe Im over thinking it but I have heard stories of the gear fairings not being aligned correctly and needing to correct with trim.

I lifted the plane up level and used the string method shown on the plans to get the correct "twist" of the gear leg fairing. I locked the top into place with the hose clamp and then gently lowered the plane. There seemed to be no detectable movement at the wheel pant end, and if there was a minor shift it should be the same on both sides...:)
 
Gil,I have done this many times and in the cold too. Heat the clay up first by leaving in the house overnight. I use a heat gun when needed and also heat regular eating spoons and use both sides (not from your wife's place settings). I have heated clay to almost melting with no bad effects.

Steve, Fairings Etc.

Right from the expert...:)

Thanks Steve, I'll try hot spoons.

I have your fairing on the nose gear, but my mains have -
Sam James wheel pants
Tracy Saylor(? I think) leg fairings
Non-standard brake line exit at the fuselage bottom.

Buying your nice parts would have been a lot easier...:D
 
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