cjensen

cjensen

Well Known Member
I'm going to put a styrofoam rib in each of my wingtips, but I'm not sure which type of foam to get. Menards has the pink board, no blue. I've been told that some of the foam won't jive well with epoxy, and that the blue is better.

Anyone? :confused:
 
The pink worked fine with west systems epoxy. See if they have some scrap they can give you. I bought a whole sheet and only used about 1 square foot of it. Only $7 though if I recall.

Jekyll
 
Colored foam the same

Chad,

The pink board and the blue board are the same stuff called exstruded polystyrene. Just a different manufacturer. I have used the foam board on my cowling and to make the custom fiberglass parts I have made so far. No problems. But, I have wrapped them all in duct tape before putting it on the foam, so there was no direct contact. Try some first. If you need some to try rather than buying some, I have all kinds of scrap pieces. But Yes, I think some of the epoxys and resins are destructive to the foam. Make sure you use the foam that is a solid extrusion, and not the stuff that is made of the little white balls.
I can tell you that Gorilla glue will not damage the foam, and does a very good job of holding it together.
 
Perfect! Thanks gentlemen! I have the West Systems epoxy to work with.

Ben, if you have some larger pieces, I'll take 'em. If not, it's cheap stuff in Menard's aviation department...

Takin' a break from the little one already!!?? ;) :p
 
My guess is that the solvents used are the real problem, not the adhesives. Cannot say for sure, but Id guess that foam is more likely to be incompatable with the styrene resin (used with fiberglass) or the solvent used with urethane resins more than epoxies. Generally speaking, the thinner the materials you work with, the more solvents they probably contain. Bottom line, test your materials on a scrap piece first.

Ive wondered why the spray can urethane expanding foams are not used more to fill open spaces like wing tips. Its available everywhere and cheap. Once it cures it is easy to cut and shape, it sticks to everything in any orientation or shape, and it is very lightweight and durable- waterproof, weatherproof. Warning: dont overdo it (it really expands) or use it in closed spaces (it really expands ;) )- it can be very messy:confused:
 
Chad,

The blue (Dow) foam worked fine for me with the West System. Don't know about the pink stuff as I didn't have any.

Check out the pictures and text on the bottom of this page.
 
re: foam eating

Always be sure to throughly cook foam before eating :D

Seriously, though, just as an FYI, some epoxy will attack foam. 5 minute epoxy in particular can get hot enough during cure to damage foam. I just mention this because it's tempting to use the 5 minute stuff to make a quick repair on some non-structural piece.
 
epoxy option

I used Hysol 9462. It's thixotropic, ie. stays where you put it, and it's easy to sand. I have used it a lot in my model jet construction. It sticks to everything. In fact the material around the glue joint will probably break before the glue lets go.

Antony
 
Interesting word Antony!

Thixotropic was explained to me as the way sand at a beach works its way around your feet as the tide washes over.

For you people in the heartland, I got nothing for ya!

:) CJ
 
Captain_John said:
Interesting word Antony!

Thixotropic was explained to me as the way sand at a beach works its way around your feet as the tide washes over.

For you people in the heartland, I got nothing for ya!

:) CJ
Click to expand...
Pretty much like mayonaise.... sits there and stares at you until you whip it up with a knife, and then it will flow :eek:

Ketchup in a bottle is pretty much the same for you non-mayo types :D
 
cobra said:
Ive wondered why the spray can urethane expanding foams are not used more to fill open spaces like wing tips. Its available everywhere and cheap. Once it cures it is easy to cut and shape, it sticks to everything in any orientation or shape, and it is very lightweight and durable- waterproof, weatherproof. Warning: dont overdo it (it really expands) or use it in closed spaces (it really expands ;) )- it can be very messy:confused:
Click to expand...
I have a friend who bought an '83 Chevy Blazer with some really bad body rot (project vehicle). Upon dissecting the body, he found a previous owner had shot that house-sealing expanding foam into various places on the truck's body. Care to guess which areas were rusted the most heavily???

I'd avoid any expanding foam that's not made for aviation or marine use. "Epocast" is the aviation brand that springs to my mind first... but it's probably super-expensive.
 
Thanks for the replies and advise everybody! I ran to Menards aviation department on Sunday, and spent a whole $10 on an eight foot piece of the pink stuff. This will be plenty for me and the next guy, and the next guy to make little filler ribs for fiberglass stuff.

11-19-06-013w.jpg


11-19-06-014w.jpg
 
Are you going to fiberglass over that Chad, or just epoxy in place? Either way, make sure you put the tip on the wing while it's setting up!
 
I'm not sure yet if I will epoxy or glass them in. Good tip on making sure they're on the wing while setting up. I probably wouldn't have thought of that until afterwards... :rolleyes:
 
Do you really need to add filler ribs on the H stab tips and fin tip? I noticed Vans didn't add the filler ribs on the red RV-7 they built a couple of years ago. I didn't add them on my -7A. What am I losing in efficiency for not having them?

The wingtips are a different story. They are rather flexible when unmounted and I'm sure there is some "oil-canning" in flight. But, in my book, they stiffen up well enough when riveted to the end wing rib. Also, I installed an Archer antenna inside the right wingtip. It certainly was quite a bit easier to do without a foam rib "in the way".

Mike

-7A with 160 flight hrs.
 
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I decided today that I may not put a rib in there permanently. It certainly will help keep the tip from flexing when I drill my holes to the hinge pin, but after that, I may just remove it.

Who else has put this rib in there? Is it needed?
 
Jarhead,
I believe the only real differences in foam, besides the resins used, is whether the air pockets are sealed or open, and the obviously the added cost for repackaging for an aviation or marine market. The resin used in expandable foam is urethane, which is very durable and flexible.

Regarding rust, last time I checked fiberglass does not have a rust problem :)

The purpose of the foam filler is to eliminate any spaces for water to collect, and to support the structure of the empty tip- in both cases, I believe the expandable stuff would do a better job than a cut-to-fit solution.

Any reason an antenna cannot be molded into the tip using expandable foam, assuming it can be removed through a disconnect of some sort? Vibration or electrical short issues would be eliminated.
 
Why the foam?

I decided pretty early on that I'd make little foam rib-letts to fill in the end areas on my HS and elev, and VS. But I'm missing something on putting foam in the wing tip. Is it for rigidity of the fiberglass tip? Or for some other reason?

I'm definitely getting my "educational purposes" out of this kit! :D
 
I'm not real sure. That's why I've decided to hold off on permanently installing them until I find out if this is something people are doing regularly. :confused: I'm installing my tips with piano hinge, and the guy that did this before me put foam ribs in his tips, but not sure why...
 
I've read that the top surface of the wing tip can oil can in flight. With my wing tip clecoed in place with the trailing edge rib in there, it doesn't take much pressure to make the top surface oil can. I'm in the homestretch, so I'm going to wait and see if it's really a problem once I'm flying.

Dave
 
Wait and see

My impression is that oil canning is hit or miss on the RV-7 bat wingtips. Some folks get it, some don?t.

Personally, I am taking a wait and see approach. Good luck.
 
Wing Tip enforcment

I built small ribletts to keep the tips from flexing. The tips on the RV-7 are quite flexible, even when mounted. FYI what I did was to shape V extrusions from the pink foam. The top edge got rounded and cut notches on the back so that they could flex. I laid them parallel with the wing spars and glassed them in place.

Round the top edge of the foam so the glass does not lift up and create voids. Rough up the surface to glass a lot!! and clean up with MEK (I know I know) or acetone or something. It has to be clean. Glued the foam strips in places using some flox. Lay 3 layers of 2.5 - 3" tape over the setup and work/brush wet out the cloth with resin. Came out nice... I put the archer antennas in there also. There is lots of room. I think I put 4-5, (20 total) ribletts on each surface with tighter spacing towards the aft edge where it was most flexible. Looks like ribs in a boat. This lets you finish up the tips without worrying about the final fit. They flex and screw in place but will not oil-can.
 
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