End cap fill

[DaveO]

i am contemplating filling the ends caps of the HS and interior end cap of the elevator with household insulation, the type that comes in a can. It will expand to fit the form, no fiberglass only Resin filling of the small holes of the foam.

I tried it make a "U"of a piece of aluminum. It filled very well and I could cut it to the form of the aluminum.

I was interested in knowing has anyone else done this, what is a potential ramifications ?
thanks
Dave

[Kyle Boatright]

You probably won't be happy with the results. Either short term, it'll over-expand and change the tip profile, or long term it'll do the same thing.

Search the forum for "expanding foam" and I think you'll find several posts on the subject.

[rv7charlie]

If you're committed to it, you might consider the white latex foam instead of the 'Great Stuff' urethane foam. The latex stuff is nowhere near as powerful in its expansion pressure.

[Carl Froehlich]

Originally Posted by Davoakes@att.net

i am contemplating filling the ends caps of the HS and interior end cap of the elevator with household insulation, the type that comes in a can. It will expand to fit the form, no fiberglass only Resin filling of the small holes of the foam. SNIP
Dave

No - keep that product and anything like it far away from your airplane.

What I do:
- Cut a piece of rigid foam insulation to fit in the rib. Make it 1/16? shallower, and 1/16? clearance to the rib sides. Use a little micro to glue it in (just the bottom)
- Cover the foam with 3-4 bids of glass. Tuck the edges of the glass around the foam. Once set, the edges with provide support for the face.
- After the glass set, skim coat of micro on top of the glass. If you did it right, you will not need much to make a flush surface.
- Before you add the last micro, add a small straw (1/8? diameter) at the trailing edge so you leave a path for water to escape.

Finish and paint with the rest of the control surface.

I did this on all end ribs on two planes and it has held up perfectly over 16 years.

Carl

[RV Jerry]

As said in previous post the expanding foam will keep expanding with heat and time and you will probably end up with a mess , I use 3/8 balsa and fiberglass over it

[JonJay]

Originally Posted by RV Jerry

As said in previous post the expanding foam will keep expanding with heat and time and you will probably end up with a mess , I use 3/8 balsa and fiberglass over it

Same here. Epoxied the balsa in place. I believe this is the factory recommended approach.

The only time I have seen the expanding foam used was to close off gear leg fairings. Bad idea. The foam trapped water and corroded the leg. It was stable and didn?t keep expanding or if it did it didn?t deform the fairing. Still a bad idea.

[Bill Boyd]

I just finished a couple of months of doing the same thing. Believe me, if you plan to cover the foam in glass, you're letting yourself in for a LOT of sanding and blending where the cloth wraps onto the control surface skins...

I used the LocTite dense expanding foam from WalMart and let it expand several days before trimming/sanding to final size and covering in lightweight glass cloth and epoxy. Long term creep does not seem to be an issue after several weeks - no bulges noted.

What I did forget was that the inboard upper edge of the flaps likely needs to be trimmed to the fuselage side once the wings are on. This will likely destroy the end cover I did on the inboard flap ends. On the bright side, this is one end rib not really exposed to much slipstream in flight nor easily visible on the ground, so less of an issue than the others for either drag reduction or cosmetics.

I did not attempt to fill the inboard caps on the elevators that are angled to allow rudder travel - I was tired of it all by then, and consider this less aerodynamically significant since the side is "swept" out of the slipstream

[DaveO]

Thanks for your reply on the subject. It seems that there are many ways to do this, but expanding foam may not be the way.
Dave

[vlittle]

Scroll down here to see what I did. A lot of work.

[nilberg]

I completely understand the wish to create sleek control surfaces.
I was on my way down that path, but after a while I convinced myself that I was building an aluminum airplane not a Cozy.

Mostly because I saw many RV's at Oshkosh with cracking (cosmetic) in those areas. You really have to pay attentions to the transitions, micro will look good now, but after a few years... Most builders going that direction are using fiberglass covering the transitions to avoid cracking. Make sure to allow for draining.

I have now gone complete (obsessively) to the opposite philosophy now. I celebrate the lines between the fiberglass and skins, not hiding any rivet, not even the rivets for the fairings.

(Although , I might fill the pop rivet heads, just to convince myself I am not a zealot... )