Building my first 2m pattern ship which has a composite fuse and honeycomb formers, etc. I studied a lot of pics from PL Prod's web site and it appears from the pics that silicone adhesive was used almost exclusively for attaching the honeycomb items to the fuselage. The only exception is that in some pics it looks like epoxy might have been used on the firewall, but then in other pics it looks like silicone... maybe it wasn't the same plane in both pics... I don't know. I'm not 100% sure I'm looking at silicone in the pic, but the adhesive fillets look more like clear silicone than epoxy with micro-balloons to me.

My question is: Has anyone used silicone adhesive on honeycomb/composite fuse? Any tips or tricks with using silicone? Pros/Cons vs epoxy? Weight... is it lighter than Epoxy? Quieter?

Thanks, John.

Attached is a sample pic of what I was looking at.

On my Sam Turner, 'Pursuit', the last two formers in the fuse are held in with rtv silicon. These formers are located rearward from the canopy opening. This method is easy to do and in my opinion holds just as well. I don't know about attaching formers that are forward of the canopy opening. I used epoxy for these.

I believe the picture is showing a mixture of microballons and epoxy. It could also be aeropoxy from hysol or BVM. IT is a premix of epoxy with microballons.

Mark L
Baltimore

Lots of guys use Zap-a-Dap-a-Goo.by Pacer.
Erick Hawkins swears by it.

Monkey Boy,

I am pretty sure that it is epoxy with microballoons like Mark Lamos said. I have seen many PL airplanes up close and that is what it looks like. I think they mix it and then put it into a syringe to make the bead so neat all the way around. Hope this helps.

That picture is showing a firewall. I would not use silicone or Zap-a-dap-a-goo on a firewall. I'm almost positive you are looking at epoxy with microballoons in that picture. I would definitely use epoxy on the firewall and other high stress areas.

Jim

Is goop fuel proof ? I used this the other day for my tank floor to get some flexibility when I need to pull the tank out. I did some evaluation and it seems to be tougher than silicone but remains flexible. However, I only use epoxy for hoigh stress areas, certainly not silicone or goop or ca.

Polyurethane glue now gaining acceptance for holding formers to glass fuselages. Among it's advantages is it is very light and the long working time allows for accurate alignment of the parts. It also expands as it cures filling gaps, and creating a fillet that will help firmly secure the pieces. I am going to try polyurethane on my EAM T-45 Goshawk.

Turbines,

Have you heard any news about Sam Turner? I bought a Saturn from him last year. He seems to have dropped out of just about everything shortly after he delivered my airplane. I wish he'd come back. He builds wonderful airplanes.


Rob

The polyurethane glue is really nice for some applications. I sheeted my wings with it and used it in numerous other places.

When doing my removable stab I was able to reduce the weight by using polyu rather than epoxy when gluing the wing tube in. Using the Bob Noll approach to doing a removable stab takes quite a bit of epoxy and polyu is lighter and expands quite nicely in the channel cut for the wing tube.

However keep in mind that when using the polyurethane glue you are supposed to "clamp" the items you're gluing together (normally just place some weight on it) or the glue will dislodge the item you're gluing when it expands.

I'm not sure about using it for a firewall, it may work fine but I'd be a bit concerned that the expansion could shift the firewall out of place. On the other hand, if you have it hanging from your engine and you place an equal amount all the way around it may be fine. Interesting idea for sure.

One more thing, don't over do it on the polyu glue. One of the guys I fly with put a ton when mounting his main wing tube and it started spreading the foam apart and seeping all the way from the wing tube to the surface of the foam. I have no idea how much he used, but it must have been a lot .

Keith

The material used for bonding the formers, and anything else for that matter, to honeycomb structure is NOT microbaloons with Epoxy, but a mixture that is epoxy and microfibers. These give a finished appearance to balloons but are many times stronger. They are essentially a product that is micro fibers of cellular cotton. when cured the strength is astounding. The ones I have used are marketed by WEST SYSTEMS. When producing a laminate of Carbon\Honeycomb it is essential to add a small quantity to the epoxy mix due to the small gluing area on the edge of the honeycomb, the mix then forms a small fillet to increase this glue area by forming a bond slightly down the vertical edge of the honeycomb. I can not comment on the other glues mentioned due to no experience with them in this sort of application but the above does work well and is far less prone to vibration problems than a mix with balloons as these are for filleting applications, not strength.
Cheers
Zotandy

I have used Silicone in the past...but found it to be heavy...when compared with epoxy. For the Firewall I use Epoxy actually Zpoxy finishing resin...and mix it with micro balloons until it is a paste....

I then use my finger and make a nice fillet front and back of the firewall....and use a small piece of balsa with the corner sanded round or at an angle like 1/8" corner...maybe 3/16"...then scrape all excess resin off and it will give a perfect and clean joint without any excess resin...

For the Nomex plates and formers I use epoxy in the tail end but up front like on my Smaragds and Hydeaway kits I have used Foam safe CA to secure the nomex trays...also the epoxy and micro balloons works very well in the this situation also...Just put lots on and get good coverage then scrape it all off except a very thin fillet at the joint..Works good every time and they don't come loose.
I just test flew my 5th ZN line kit before Christmas a Hydeaway and this works every time.

Zap a Dap stuff will melt the foam....and its heavier than Silicone! the epoxy if you clean off all the excess is very light..the foam safe CA is even lighter....Firewalls, and tail formers should always be glued using epoxy....Pro-bond makes an ugly and non consistent surface and silicone type adhesives are just too heavy...


Years ago I compared the weight added by using silicone and the weight added by using just epoxy on two separate planes...weighed before firewall install and after firewall install the result was the silicone was almost double the weight.....If you sand the inside of the fuse the epoxy works just as well holding things....the silicone tends to have a better grip on the inside of the fuse....be careful though some planes like the Piorin kits are not epoxy glass and I think the silicone will reach with the resin....

Not positive here but.....I know the resin henry uses is more like a polyester type than a Epoxy type....

Troy

Thanks for the info and help. Somehow I was convinced the fillets looked like silicone... glad I was set straight... you guys probably saved my bacon on this one. I was ready to use silicone. Finally got engine thrust set and the firewall drilled and ready to be glued to the fuse. Based on your collective info I plan on using a good epoxy and a micro-balloon/milled fiberglass filler. Thanks again. John.