RV-14 Top Cowling Fitment in Roll

[Meat]

Hello All,

I'm fitting my top cowling laterally per page 45-08 using the dual plum bob technique described in the plans. The cowling was trimmed to the scribe lines around the inlets and spinner opening and fits nicely with the trimmed bottom cowling. I'm using a clear Plexiglas spinner template in place of the actual prop and spinner bulkhead. I can cleco the cowling to the template and the 3/16" spinner gap is built in. I haven't yet drilled the cleco holes in the cowling.

My issue is getting the top cowling within the 1/16" tolerance laterally (in roll) that Vans directs. Mine is about 5/16" off between sides when measured from several spots on each side of the cowling front to the floor. The floor is level. There's no amount of moving the aft edge of the cowling left/right per plans that will reduce that difference significantly without severely distorting the cowling.

Has anyone else seen this amount of variation between top cowling sides? If so, how did you deal with it? If I accept the 5/16" difference what problems, if any, am I creating with baffling, inlet ramps, appearance, etc.? I'm trying to figure out if this is a big deal or not and how to fix it. Van's specified a 1/16" max difference for a reason.

Thanks all for your time and any advice.

Scott Davis

 

[Reflex]

Scott,

I too found this to be a difficult part of the build. Having completed this only a few months ago, it's still pretty fresh in my mind.

First let me answer your question. I don't know if 5/16 makes a huge difference in the finished product....but it would to me. What I'm finding at this point of the build is that the better the cowl fits the easier it is to install inlet seals, have accurate front baffle alignment, spinner/back plate fit, etc.

When I initially trimmed, I was within about 5/32 or so. One thing I've learned on this build is that I know what perfect is, but I still don't know what "good enough" is. When I doubt, I try to make something perfect. The key word being "try". I rarely achieve it. Yes...it adds time.

Ultimately, I found that a very, very small amount of movement on the back left or right of the cowl on one side creates a large amount of movement on the front. If I put slight pressure on the back left side of the cowl, the top right would move up significantly and vise-versa. In short, even though I thought I had the back of the cowl where it joins the fuse properly fit....I didn't. I thought it looked good and fellow builders ooo'd and ahhh'd, but it was just a few thousands "off".

In the end, I went back and re-evaluated my fit against the fuse. Even though the fit was very good, I decided that I need to remove a bit of material on one side to allow the front to fit/measure properly. It's tough to take a bit off of one side as to keep the fit straight as you "technically" need to remove material from almost entire back edge of the cowl to keep the rear edge straight. I must have had that top cowl on and off 75+ times.

I'd encourage you to experiment with moving (by hand) the back left and right portions at the apex of the fuse curve and below to see if it raises/lowers the left and right measurements from the floor. Remember, if you're 5/16 out on one side, when level your only out half of that. It doesn't take much to move it.

By the way, I thought one of the toughest parts of this process was to find the exact center of the upper cowl. If that isn't right, your doomed from the beginning.

Pictures below with explanations.

Sorry for the long post.

I thought this looked good, but it wasn't right.

What I settled for (left side)

What I settled for (right side)

Final fit.

 

[rvbuilder2002]

Because the cowl is a molded, composite part, even though it was produced in a mold, it is possible to have cured with a slight twist in it, when allowed to just lay statically.
Sometimes you have to clamp the forward end at the orientation you want and then use the tape to pull it to the position you want at the back.

 

[Meat]

Thanks so much for the quick feedback. Very helpful.

Scott

 

[Meat]

Thanks so much for the quick feedback. Very helpful.

Scott