Leading edge fillet.

[inzersv]

The instructions say to use Super-Fil or structural adhesive with microballoons to create a smooth transition from the rip capstrips to the front spars and from the front spars to the leading edge. Can Bondo be used to do this also? Pros or cons? Thank you very much. If Bondo can be used, I will be doing this on my left wing Christmas Eve morning.

[HighWing]

Only weight. It might seem a small thing, but ounces here and there add up to never to go away pounds. Consider the carbon fiber kit in development - big bucks to shed pounds.
Lowell

[jtpitkin06]

Many bulders have used automotive fillers without problems.

A quick check of the MSDS will show Bondo, Dynalite, 3M Lightweight Body Filler (all made by 3M) and many other other automotive body fillers, are made with polyester resin as the adhesive and talc as the filler.

I tend to shy away from it for a few reasons. First, it’s heavy. Bondo is about 10 pounds per gallon. Superfil Epoxy filler is about 4 pounds. Second is the talc will absorb water if continuously exposed. However, there is little chance of continuous submersion unless you are building a seaplane.


On the plus side, Bondo cures quickly and may be sanded in 20 minutes. For aircraft use Bondo will adhere with proper surface preparation, If used in limited quantities the weight should not be an issue.

Superfil from Polyfiber is an epoxy resin with microballoons premixed. It is non-hazaradous. The epoxy resin will stick to anything short of Teflon. It is ideal for aircraft. The only negative is the slow set time. It takes about 12 hours before you can sand it.

I think there are reasons to use both products. Cure time being the biggest issue. For making the tiny fillets at the front of the ribs and false ribs, either product will work fine. Just do a little prep work with a Scotchbrite pad and clean with alcohol before applying the filler.

One word about the weight issue. While you may think you are only using a limited quantity it does mount up after a while. By the time you fillet all the ribs, form and smooth the flaperon and empanage tips, fill in low spots on the fuel tanks and smooth the cowling you can go through a gallon of filler in a blink. Using Bondo instead of Superfil you will add six pounds.






JP

[HighWing]

I've always used the mix your own with microballoons and epoxy. I like a hard epoxy rather than the structural type because it sands a bit easier. I will mix to consistency depending on what the application is. When doing the final layers, I will use a single edge razorblade as a spreader. It has usually been a last of the day task - ready to sand in the morning. In warm weather two coats a day are possible. Occasionally for very small batches, I will use 5 minute epoxy.
Lowell

[jtpitkin06]

When forming the filets at the front of the ribs, tape off both sides of each rib. Also tape off the forward limit of your filet. The back edge where the filet extends below the rib doesn't matter as it will never show. Terminating the filets the same distance at the front will give an even appearance to the fabric dimples. Leave the tape in place when you do your sanding to avoid scratching the spar.

[WISDAN]

I agree with using Polyfil for filling. The weight can really add up ... take my word for it!

Dan G.

[WISDAN]

The correct name is Superfil. My bad.

Dan G.