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It has been my observation that most major problems can be greatly reduced or eliminated if builders would spend extra time getting better fits when laying up the joints. In this section I will share some techniques I've developed in dealing with these trouble spots.

Joint Basics

Look closely at the joints, all of them. Make sure they are below or even with the rest of the parts.

Whenever possible, fill up to and over two pieces that match or fit to each other. Use the tape covered cardboard method discussed below to get a perfect 1/8-inch gap.

I have found 20-minute epoxy to be very useful for filling big areas on the bottom, at the wing tips, and wing root to fuselage fillets. If I had a choice between this type of epoxy and the slower curing brand used for structural building, I would use this, especially instead of thick buildups of bondo. However, it is not as strong as the slower epoxy and should not be used in the high impact areas such as wing leading edges and nose. I also would not use it around the canopy and cabin areas because it will get abused beyond its strength.

It is important to use micro on all edges; anywhere something opens, closes, or fits up against. Bondo has no strength and if you close your hatch or cowl down on something, it will chip or break off.

Cowl

Cowls need special attention. You must install the complete engine with propeller. Let it settle two weeks. Then fit the cowl. If it's too short or you have too big of a gap top to bottom, fix it with glass, not with filler later.

After you have the cowl fit as good as possible and it is screwed on the plane, step back and plan out your moves. You will find that it needs to come out somewhere and go in somewhere else. Mark this on the fuselage and the cowl. Fill under the cowl between the fuselage and the cowl to make it go out and remove to get it to go in. This is an important spot on the plane.

Next remove the cowl and tape up the fuselage with 2-inch 3M masking tape. Tape 3 inches past the seam so that the tape is between the cowl and the fuselage and up on the fuselage 2-3 inches. Now screw the cowl back on and mix up a batch of micro and generously apply this all over the seam and the tape; go back onto the cowl about 6 inches. Let it set up and pull the cowl off. Look inside of the cowl and you will see the joint seam. Sand half-way through the seam, leaving the cowl a little longer. At this time do not sand the outside of the cowl, just the seam length. Then put the cowl back on the plane and tape up the cowl this time. Generously apply micro all over the seam, going back onto the fuselage about 6 inches. When you are done you have no gap and plenty of material to sand level on the outside. This is where you would start.

Sand the outside reasonably smooth and you will see the line from when you sanded the cowl from the inside. This will give you a good start on the gap. It will be straight (assuming you sanded it straight when you had it off the plane). Now carefully mark off the gap by taping off the gap as straight as possible and then mark it with a pencil, using the tape as a ruler.

Next take a piece of .020 aluminum, 2 inches by 7 inches, and put 80-grit gold Stickit sandpaper on one side. Using the edge, sand the gap slowly up to the line you penciled in. It is important that you do this slowly and carefully. Just work up to the line you marked off with the pencil. Now set the width of the gap by turning the sand board around and sand the other direction. This will not deepen the gap as the paper is just on the side of the aluminum.

All you have left is to final sand the contour on the outside. The trick to getting a good gap is to work slowly and precisely and to draw a line to sand up to. Do not try to eyeball it as you sand. You will keep removing here and there, meanwhile the gap keeps getting larger.

Canopy

I have developed a technique that works really well to set good, consistent gaps. Take a piece of corrugated cardboard and cut it into 2-inch wide strips about 2 feet long. Coat both sides with 2-inch 3M masking tape. Lay the strips on the floor and beat them flat with a rubber hammer. Now put these strips end to end all the way around your canopy and close your canopy onto them. Micro up to both sides of these strips. Wait about two hours and wiggle the cardboard a little to separate it from the micro slightly. The next day take the cardboard out completely and now you have perfect 3/16-inch gap all the way around with micro built up for a good, even fit. Redo this wherever you need to redo it. It really works well.

Make sure you install the seal and let the canopy sit for a few days with the latches in place before you determine this is the final fit.

Use 3 to 4 layers of tape between the canopy and the longerons for clearance on the shoebox fit over the sides. By the time you fill, paint, and surface this, it will be barely enough clearance. I suggest some clear Teflon tape over the canopy underside when you are done or the paint will surely fail over time.

Control Surface Gaps

You need .042 all around the control surface. I have found that a .020 piece of aluminum with a piece of self-adhering 80-grit sandpaper on both sides makes a great gap setter. Put it between the surfaces and sand back and forth until the control surface is free. If you need to just sand off of one side, then pull the paper off the side you don't want to remove material and it acts as a guide. Then when you paint it, the gaps will close to about .020 as you will have put about .010 worth of sealer, paint, and clear on the edges because it builds up more there. If you don't take the time now, you'll pay for it later with sticky control surfaces, not to mention the appearance problem of rubbing.

Wing Tips

If you have a bulge at the joint, you will have to fill on both sides of it to make it smooth. This will increase weight as well as work load.

Gear Doors and Access Panels

One thing that works great for me is to outline the gear door with cardboard that has been both flattened with a rubber hammer on the floor and coated on both sides with 2-inch masking tape. Cut into 4-inch strips 1 1/2 feet long. Push this into the gap between the door and the wing. Fill from both sides of the door and the wing so that you get enough micro to make a level transition. After 2-3 hours, wiggle the cardboard to see if it separates from the micro. If it does, wiggle it loose all around. Let this sit till morning and then remove it all together. Now you have a great 3/16” gap all around the door and enough material to block out with the 36 grit on a 16” fileboard.

The extra slow cure micro on the gear door affords some strength against pressure/vacuum opening them in flight and gives you some material to make the wing flat. This saves you 25% weight juxtaposed body filler and adds strength to boot.