Cowling Mismatch

[Rick6a]

Overall, I'm quite pleased with the cowl fit.....to one another and the airframe. But as the photos show, a serious mismatch exists in a very noticeable location. I want to fix this right. For those practiced in the subtle ways of fiberglass, I ask....what is the best way to address this problem that will insure pleasing, lasting results?

[Ironflight]

I had a similar - probably a little less- underbite...but you asked how to fix it RIGHT, so I will let the fiberglass gurus answer and sit back and find out what I should have done.....

Truly, all I did was build up the top cowl with a mixture of West System's goops and stuff until everything matched!

Paul

[Kahuna]

Its the long and short story off fiberglass. Sand and fill

I have never seen 2 cowl halfs come together perfectly in the front.
This area of the frontal intake takes quite a beating. I recommend flox. West 2 part epoxy and milled glass fibers. Both avail from ACS. Cotton would probably work, but you might as well get the glass. Its strong stuff. Here is a short lesson that can help get you started.
http://www.torreypinesgulls.org/epoxy.htm
Best,

[RV7Guy]

Looks like you already have the hinge set up. My first recommendation is BEFORE you begin any cowl fit work to the fuselage fix the intake fit. Work on the overlaping flanges with your Dremel. With a few minutes of work you can greatly improve this fit.

Now, before you do any other work, scrub the cowl with soap and water and a stiff nylon brush. Rinse thorough. I then go a step further and wipe down the entire cowl with acetone or lacquer thinner.

Tape the edge of the cowl that won't get filler applied. Put the cowl together and tape to hold in place.

Mix a thick batch of Micro filler (WS 410) and epoxy. Before application, wipe the area with acetone. Apply with a squeegee and work on blending with the other cowl half.

If you do this carefully you'll minimize the sanding and additional fill needed.

Repeat as necessary until you get that perfect look. Small patches and minor fill can be completed with Rage auto body filler. This is a catalyzed filler that will not shrink and will bond great. This will save you time.

On my cowl I covered all the fill work with a layer of 1 oz glass cloth to lock everything together. As Kahuna noted, this area takes a beating. It probably would have been fine but I wanted to be sure.

The cloth I used is very thin. I used Rage to feather these edges.

The process is not to bad. Work in steps and you'll be done in no time.

[brianwallis]

Why dont you just sand the rear of the cowl untill they match in the front?
Best
Brian
ps.. I'm not an expert in fiberglass... so no flaming please...
Thanks

[Ironflight]

Originally Posted by brianwallis

Why dont you just sand the rear of the cowl untill they match in the front?

'cause he already mounted the hinges, which fix the relative positions of top and bottom cowls....

[cytoxin]

Originally Posted by brianwallis

Why dont you just sand the rear of the cowl untill they match in the front?
Best
Brian
ps.. I'm not an expert in fiberglass... so no flaming please...
Thanks

but the center meets up and the sides dont. so he needs to build up. maybe if the hinges were not on he could have pulled them some. but you dont want to pre load things or else you'll be seeing broken eyelets on your hinges.

[carguy614]

Hi all...
I came up with the same problem, although not quite as much Overbite. My solution was to clean up the INSIDE radius of the cowl, and lay up additional layers of cloth, followed by resin and flox to thicken the area. then I ground away the offending overbite slightly beyond the needed amount. Then I laid up some bid cloth over the cowl on the OUTSIDE and sanded to contour. Final fairing with micro , and it really fit well. Nice and strong, and only took about 3 hours to do.
Just one solution, I am sure there are many more!!
Hope this helps....Chris

[Rick6a]

Originally Posted by brianwallis

Why dont you just sand the rear of the cowl untill they match in the front?....

Brian,

Fair question. The cowls were trimmed at the rear to achieve a butt gap with the firewall relative to the desired prop spinner gap, in this case I went with 1/8". After some preliminary trimming, the cowl halfs mated together fairly well and the final trim to the airframe and installing the hinges essentially completed the cowl installation and turned out well if I do say so myself. But the fact is, even though the cowl halfs mate close enough everywhere else including the centerline structure behind the spinner, the upper and lower cowls at the outboard front area do not match each other perfectly....and never would regardless of what the builder does. This is probably due to the molds...something we have no control over. Like Kahuna, I have never seen cowl halfs mate up perfectly right out of the crate. Still, the area in question takes an aerodynamic beating and mine will require a significant build up of material to achieve surface flushness with the bottom cowl. I just want to make certain that the measures I take now will insure I won't regret what I did a couple of hundred flying hours later.

[JonJay]

Originally Posted by carguy614

Hi all...
I came up with the same problem, although not quite as much Overbite. My solution was to clean up the INSIDE radius of the cowl, and lay up additional layers of cloth, followed by resin and flox to thicken the area. then I ground away the offending overbite slightly beyond the needed amount. Then I laid up some bid cloth over the cowl on the OUTSIDE and sanded to contour. Final fairing with micro , and it really fit well. Nice and strong, and only took about 3 hours to do.
Just one solution, I am sure there are many more!!
Hope this helps....Chris

Mine was less severe, and only on one side, but I did the same as above. Very strong and easy to do. Holding up nicely.