Trim top cowling or bottom cowling

[alpinelakespilot2000]

After test fitting the cowling it has become pretty obvious that the top and bottom cowlings will have to be trimmed where they meet. Am I correct in believing that, since the top cowling is fitted first, you fit the top cowling and then trim the bottom cowling (side seem) as necessary to fit it to the whole/intact upper cowling? Or do you have to take some material off the top cowling side seam as well?

Thanks.

[jsharkey]

I used the joggle line on the bottom cowling as the datum and trimmed the top cowling to fit it. In the end however I trimmed off the joggled lip to fit the hinge.
Jim Sharkey
Rv6

[grover]

I ended up doing some trimming from top and bottom - to get a presentable appearance.

[pierre smith]

....is to cut both simultaneously. On my friend's -4, the cowls overlapped by an inch or more at the firewall and less toward the front. He suggested that we could draw a straight line from front to rear, tape them up with vertical strips of duct tape and cut both with a disc.

My response was that, "heck yeah, it ain't my cowl". let's go for it. So we did....with me cutting and him holding the two halves firmly together as I cut through both sections and the duct tape as I arrived at each strip. They were clecoed at the firewall and clamped to the prop back plate so that steadied things up. Worked like a charm...caveat!! Your mileage may vary

Regards,

[andrew phillips]

I places both halves on a f flat surface (granite countertop) and found that the top was already pretty good. I scribed a line all the way around based on the counter and sanded off somewhat less than 1/4" in the worst areas. I then used the top to create a nice straight line on the bottom. Worked our well for me.

[Steve]

I took very little from the top cowl edges. Just enough to get them straight. I used a 12" length of oak 2x4 (from the cabinet guy next door) wrapped in 100grit emery to help get the straight edge.

Steve

[Mark Burns]

Originally Posted by Steve

I took very little from the top cowl edges. Just enough to get them straight. I used a 12" length of oak 2x4 (from the cabinet guy next door) wrapped in 100grit emery to help get the straight edge.

Steve

I did almost the same, except I used a trick a long time RV builder showed me.
You glue sheets of sandpaper to a flat table top and just rub the whole cowling back and forth. Works great, and talk about a staight edge!

Mark

[N941WR]

and all have worked.

My thinking was that you will see how the top cowl fits long before you see the bottom cowl. Thus, I fitted the top first and then worked on the bottom.

Just don't forget to take into account engine sag. I did, just not enough.

Before you start fitting them to the airplane, work on getting them to come together around the flange easily first. Once you solve that problem, the fitting the rest is much easier.

Similar to what was described above, I used a sanding board to smooth the edges. I worked long and hard to get smooth and straight edge on the sides of the top cowl first. The board I had in my hand was 24" long w/ a 120 grit belt 3M 77 glued to it. That worked out well for me, YMMV.

To support the the canopy while fitting, I used roles of paper towels, which worked great. Once the match drill the top cowling to the firewall, you can return the paper towels to the kitchen.

My bottom cowl had to be trimmed in length and on the sides, so a lot more sanding with the long board was required.

[alpinelakespilot2000]

Thanks all!

I've kind of figured that the flanged area around the spinner had to be fitted first and then once that was set the rest of the cowlings would have to be sanded as necessary. Sounds like I can just make sure the sides of the top cowl are straight and then fit the bottom cowl to what remains.

Long boards with sand paper sounds like good advice too.

Again, the help is much appreciated.

[jsharkey]

I double side taped the emery paper to one of the faces of my 24" level. Easy to grip and dead flat. Don't think it damaged the level.
Jim Sharkey