Hysol vs Superfill

[JoeRuscito]

Can someone please help explain to me the advantages/disadvantages of using either for things like the rudder/elevator tips. Is superfill just a weight advantage when used as a filler? I assume superfill is not as strong of a structural adhesive. Also do most people opt to use balsa instead of foam? What is the reasoning here, it sounds like balsa is a bit more durable? I'm not using oratex so heat isn't as issue.

[Delta Whisky]

Joe - you are correct, Superfill is a filler while Hysol is a structural adhesive. I'd rather sand and shape Superfill than Hysol, even when Hysol is loaded with micro-balloons. Superfill should never be used for anything that has to stay bonded together.



As to foam vs. balsa wood - I used balsa. A personal decision as I find carving foam a tougher task: foam is too easy to carve; too easy to remove material that belongs there. It seems to suffer from "shop rash" a lot easier as well.

[Floog]

Hysol is for bonding and strength. Like JB Weld, another 2 part epoxy. Think of Superfil as a cosmetic finish putty. They work well together on the empennage tips. Shape and 'glue' the foam in place with Hysol. Shape the foam to about 1/8" undersize. Now use Hysol to build up and strengthen the foam over the entire finish surface. This will bond the foam to the airframe and create a durable 'eggshell'. After it is sanded with 80 grit, apply a thin layer of Superfil and finish sand. Done in this way, the foam is very light and made extremely durable. Remember, it all gets covered with fabric too. Using balsa instead of foam will produce the same results.

[Shadowrider]

Use balsa and super fill. Balsa and superfill will hold up much better when you accidentally bump them, which you will building in a garage.

[Floog]

If you expect a lot of hangar rash, don't install the tips at all. They're cosmetic only. Or make them out of titanium

[efwd]

Hangar Rash is inevitable. I made balsa wood flapperon tips. Sculpted art as far as I was concerned. I love the way they are shaped but I have rash and Im not even certain how it happens. I would buy the fiberglass flapperon tips if I did it again or I would just fill in the end of the flapperon smooth.

[jiott]

In my opinion, the areas most vulnerable to hangar rash are the horizontal and elevator tips. I would recommend balsa in these areas. The top of the rudder and vertical stab, and flaperon tips are much less likely to get dinged and the foam as Floog describes, or the plastic flaperon tips are fine.

[ken nougaret]

Speaking of top of the rudder/vertical, that was the spot i had slight hanger/garage rash. I was backing my plane in the garage before lowering the tail on the trailer. Luckily it only lacked about 1/4" so it wasnt very noticable and i didnt have to repair. My preference was balsa wood that i used everywhere except the top of the rudder/vertical, where i used foam. I still recommend balsa.

[aviator79]

I did foam on the flaperons tips and top of the vertical stab/rudder and balsa at the horizontal stab and elevator tips like Jim describes. If I did it over again, I'm do balsa everywhere. If you sand through your super fill to the foam while shaping, you have to dig out the foam and re-fill with super fill, let it cure and resand. It's a huge time waster, and I did it more than once. You can sand down to the balsa and it will do just fine.

[Guy Buchanan]

You've already been set straight on Hysol vs Superfill. Definitely don't use Hysol for anything but adhesive, it's just too expensive. Use cheap epoxy filled with West Systems Microlight, or Superfill, whichever's cheaper. (You can even use Microlight with polyester, but you gotta be quick, and work in small batches.)

Foam vs balsa depends on the foam. You can buy foam more dense than balsa, that will actually be stronger. (See Last-a-Foam, available in 10-25 pcf.) However any substrate, once shaped and filled, should be covered with glass cloth. Otherwise you've just got a ding machine you'll be forever patching. (Imagine a surfboard without fiberglass. Not good.) Once covered with glass you then fill the weave with micro or Superfill, sand, fair, and cover. Obviously you'll have to reduce the dimensions of the foam/balsa to account for the glass thickness. About .03" per 8 oz. layer should do it.