Gear leg fairings, is clay the best option

[jibby212]

I bought the foam and gave it one try and found it to be messy and hard to work with, I am now using 20 minute drywall mud, going back to my construction roots I guess. I put 3 coats on so far and it cuts good with a metal binding strap before it is totally cured, there is a large window of time to do this cutting and pre forming. I will sand to the final finish once it sets up fully. That's where I am at now, waiting for the final cure, so far so good. I wouldn't use the pre mixed dry wall mud, that stuff just dries, don't actually chemically "set up" , it would take a long time to dry when using as thick as needed for the fairings.

[David Paule]

In those thicknesses, it would crack, too. You'd have to make several layers and let each dry before doing the next, using the pre-mixed compound.

Dave

[DanH]

Originally Posted by Aviacs

How do you apply for a fairing base - are any of the densities trowlable?

The basic plan is to tape a piece of cardboard or typing paper into place to act as a dam, mix/pour the urethane, and stand back while it expands. Do not try to trowel it, shape it, or guide it in any way, because you'll make a change to local density. Just let it expand and harden, then hack off the excess. A hacksaw blade or a crosscut handsaw works real well, then it's shaped sanding blocks or tubes.





More elaborate parts are possible:



Sometimes a mixed approach (pour foam and block foam) is best.

....cast several sets of urethane rubber rolls for feedworks on woodworking equipment, e.g. for custom apps and a couple customers. After a pour one time, quite a bit was left over, so i saturated some fabric strips cut from polyester knit fabric, and draped it in layers over the side of a PVC pipe. My curiosity was whether it might be useful to cast odd-ball or obsolete MC intake or airbox parts.

Flying that idea about 900 hours now.

http://www.vansairforce.com/communit...t=rubber+ducts

[Aviacs]

Dan -

Thanks for the very clear tutorial, pics, and link for supplies!

Re the "rubberized" fabric - my suggestion was that the 90A duro might be good for flexible fairings as mentioned by another poster, besides the manifold ideas i had and you implemented. Also on that subject, DOW Corning makes a 2 part castable red silicone that is good for over 300?C * (aprox 600?F).https://pilotshq.com/dow-corning-rtv...g-p-12944.html At that point the fabric matrix could be the limiting factor. I did not compare tear strengths directly with an specific urethane, which are often tougher.

smt

[DanH]

BTW, do not try to use 2lb density pour foam as core in a finished part. I've not tried 4lb and higher as core, but I'd be real shy about it. Altitude pressure change made 2lb expand and contract in ways that left lumpy waves on the finished glass surface. So, use it for forms, but then remove it all.