Engine Mount Fuel Proofing

you would sand after that application or not? should the epoxy be thinned out?

ZACATTACK wrote:you would sand after that application or not? should the epoxy be thinned out?

I've thinned it with alcohol, heated it with a gun until it's thin, and just slathered it on like it is. It's all about the same. If you thin it, you can brush it on slightly more evenly. It'll look nice and glassy when it's hard but it won't be perfectly flat, a little wavy. I never worry about that, just prime(or not) and paint right over it. But if you want to sand it to perfect flatness it sands pretty well. I finished painting mine today, I'll go get a picture and you may be able to see what it looks like over the epoxy. I'll put it in my Flite Streak thread, so when you see it pop up take a look.

ZACATTACK wrote: Am I on the correct path here guys?? Have not done alot of fuelproofing to engine mounts made of balsa.

I hope this is a mis-statement.

George

gcb wrote:

ZACATTACK wrote: Am I on the correct path here guys?? Have not done alot of fuelproofing to engine mounts made of balsa.

I hope this is a mis-statement.

George

+1

Didn't pick that up on the first read.

Not recommendable but it does work with PeeWee engines...

Definitely plywood. Maple is great. You can get it at Hobby-Lobby if you don't have a real LHS.

RknRusty wrote:Definitely plywood. Maple is great. You can get it at Hobby-Lobby if you don't have a real LHS.

all: i have used plywood for engine mounts for more than 30 years + earlier years before during my teens. anywhere from 1/16inch to 1/4inch plywood depending on the size of the engine. and i definitely approve of fuelproofing or epoxing the entire area around the engine mount. what's it going to do besides add strength?? i also tended to use triangular braces on both sides of the mount if it was for a Cox babe bee type engine. very happy happydad

gcb wrote:

ZACATTACK wrote: Am I on the correct path here guys?? Have not done alot of fuelproofing to engine mounts made of balsa.

I hope this is a mis-statement.

George

I think, that is, I hope, he means a mount that is not plastic or metal.

After all, the last time I mounted my McCoy .35 on balsa beams they didn't last very long for some reason!

hm, i'm not even sure what my mount is made of.. it seems to be a lot harder, but just as light as balsa.

RknRusty wrote:Definitely plywood. Maple is great. You can get it at Hobby-Lobby if you don't have a real LHS.

My local cabinet shop lets me rummage through their scrap bin, and I have procured, free of charge, a lift-time supply of maple and cherry stock for beams and other such parts. For me, good ply is best for the radial flat firewalls, but these beams last almost forever with Tee Dee's and other railers, though you will need a means of cutting them to size.

happydad wrote:

what's it going to do besides add strength??

Add weight. Just don't use an insane amount. Epoxy is one of the densest glues.

Just noticed that my post was off-topic...sorry...possibly due to "Lack-o-Folgers" this morning!

Giving engine compartments and mounts a coating of catalyized finishing resin works well for me and is a good way to use up small quatities for resin that you might have remaining from a previous application.

Kim wrote:
My local cabinet shop lets me rummage through their scrap bin, and I have procured, free of charge, a lift-time supply of maple and cherry stock for beams and other such parts. .........

If you don't have access to a cabinet shop, the craft section in Walmart carries hardwood square stock (called square dowels) for under $2.00. I've found several other things in the craft section that can be useful in building. There is also a extensive selection of acrylic paint branded as "Applebarrel" that has come in handy.

I use 30 minute epoxy for fuel proofing --- apply a coat, then use a heat gun to thin and smooth it out. Heating it, besides leaving a smooth surface, also seems to help it soak into the plywood.

GermanBeez wrote:hm, i'm not even sure what my mount is made of.. it seems to be a lot harder, but just as light as balsa.

There is more than one kind of plywood. For our purposes, there is regular birch plywood that is heavier, stronger and made of more plys than...lite-ply, which is lighter, not quite as strong, but great for most applications.

For my purposes, I use birch ply for most firewalls. For a Pee Wee, 1/16" ply should do. I like hard balsa behind the firewall if using screws (I prefer sheet metal screws to wood screws).

Many use epoxy when gluing plywood because air drying types (esp. white glues) take a loooong time to completely dry if gluing ply to ply. The layers of glue that hold the individual layers of plywood together provide a barrier to air drying.

Sorry for getting off on a tangent. Epoxy or surfacing resin should supply enough fuel proofing. If not fuel proofing, you might want to avoid using CA around that area.

George

RknRusty wrote:Definitely plywood. Maple is great. You can get it at Hobby-Lobby if you don't have a real LHS.

I think I misspoke, I meant birch.

I think Zacattack is in the final stages of his Jr. Satan build. The plans call for balsa mounts but, the mounting bolts go through the balsa and are secured through the plywood skid.

microflitedude wrote:

happydad wrote:

what's it going to do besides add strength??

Add weight. Just don't use an insane amount. Epoxy is one of the densest glues.

in the context of the original posting of course i meant to use sparingly, but i understood the aircraft was not an ultralite so i didn't think a gram or two of thinned epoxy would make that much difference.
my apologies to the microflitedude.
another very light strong wood is basswood which has apparentely replaced birch wood in most hobby shops.

happydad

Personally I have always used a coat or two of polyurethene varnish, it's fuel proof and why get overly complicated? Mounting an engine is not a major civil engineering project!

happydad wrote: another very light strong wood is basswood which has apparentely replaced birch wood in most hobby shops.

Also replacing spruce. SIG site has comparisons of weight and strength for basswood vs. spruce.

Basswood is about twice the weight of balsa: my current project uses 6 pieces of 1/4 x 1/4 x 24 for spars and LE. Balsa weighs 1.1 oz for all 6, basswood is 2.4 oz. Using the basswood for one spar, take the half oz hit for extra strength.

Basswood stock is a good substitute for dowel used for joining split elevator halves: square cross section makes a tight glue joint.

When substituting woods, in addition to strength you should take flexibility into account also. For some applications where strength must include flexing, or shock absorption, balsa and spruce rank at the top.

When discussing plywoods I left out basswood plywood which is also excellent for model airplane use. If you haven't used different plywoods, check out the plywood information available at Aircraft Spruce. Lotsa good stuff.

Back on subject, I believe that the Lil Satan uses a 3/32" or 1/8" lite-ply firewall radial mount, and the Jr. Satan uses maple beam mounts mounted to a 1/8" lite-ply sheet that includes the landing skid. I have an old Jr. Satan (with hangar rash) out in the garage that was once a home for a OS MAX .15.

If a Li'l Satan is built lite for a Pee Wee you could probably get by with hard balsa for a firewall. In that case You might try the thinned epoxy or finishing resin so it would penetrate the balsa and add structural strength.

Of course there is seldom only one way to do things and we are guided by OUR results, so if you discover a better way, please share.

George