Cowl fitting question (RV 6/7/9 engine cowl)

[PaulvS]

The question is: when in the cowl fitting sequence to cut off the rebate along the side edges of the lower cowl where the upper cowl overlaps and where the piano hinge attaches. (It is unclear why the rebate is molded in, unless it is to help during fitting.)

There isn't any mention of the rebate in the construction manual, but the drawing shows the shaded area that needs to be trimmed off.



I have so far installed the top cowl and cleco'd on the boot cowl piano hinge. The bottom cowl is trimmed and fitted on temporarily with straps. The next step would be to either: 1) attach the vertical piano hinges at the sides or 2) trim off the horizontal rebate flange first and only then attach the vertical hinges.




Thanks if you know the answer!

 

[Stevea]

The question is: when in the cowl fitting sequence to cut off the rebate along the side edges of the lower cowl where the upper cowl overlaps and where the piano hinge attaches. (It is unclear why the rebate is molded in, unless it is to help during fitting.)

There isn't any mention of the rebate in the construction manual, but the drawing shows the shaded area that needs to be trimmed off.

View attachment 55284

I have so far installed the top cowl and cleco'd on the boot cowl piano hinge. The bottom cowl is trimmed and fitted on temporarily with straps. The next step would be to either: 1) attach the vertical piano hinges at the sides or 2) trim off the horizontal rebate flange first and only then attach the vertical hinges.

View attachment 55282View attachment 55283


Thanks if you know the answer!

Hi Paul.

I think (fuzzy memory warning inserted here) I installed the bottom cowl to firewall side hinges first, then trimmed the overlap for the top/bottom side seam hinge, and finally installed the top/bottom side seam hinges. Of course I don’t have any photos to show that…..sigh, even with digital photos I didn’t manage to take any during that part of the build. But hey, I did have the green/honeycomb core cowl like yours!

 

[Mike T.]

I Just finished doing this on my 9a. The order was as follows: Fit the upper cowl, trim, and install hingers. Next, fit the lower cowl and cleco together at the spinner. trim and drill bottom at the floor / firewall seam, then trim vertical sides to length and install hinges. Let the top cowl overlap the bottom cowl and mark the bottom cowl to trim the horizontal seem. Last thing is installing the horizontal hinges between the upper and lower cowl.

 

[PaulvS]

Hi Paul.

I think (fuzzy memory warning inserted here) I installed the bottom cowl to firewall side hinges first, then trimmed the overlap for the top/bottom side seam hinge, and finally installed the top/bottom side seam hinges. Of course I don’t have any photos to show that…..sigh, even with digital photos I didn’t manage to take any during that part of the build. But hey, I did have the green/honeycomb core cowl like yours!

I Just finished doing this on my 9a. The order was as follows: Fit the upper cowl, trim, and install hingers. Next, fit the lower cowl and cleco together at the spinner. trim and drill bottom at the floor / firewall seam, then trim vertical sides to length and install hinges. Let the top cowl overlap the bottom cowl and mark the bottom cowl to trim the horizontal seem. Last thing is installing the horizontal hinges between the upper and lower cowl.

Thanks Steve and Mike for the clarification, that order worked out well. It took longer than expected (!) to sand all of the edges straight for the top and bottom to fit together properly.



The front of the cowl behind the propeller has an uneven gap due to the way that the part was molded and this seems to be a common problem. I've built up the inside of the ring with epoxy glass and will grind off 1/8" on the outside to even up the gap.

 

[Stevea]

Filling the nose ring gaps so that the cowl halves line up and are parallel to the spinner backplate seems to be standard procedure. Mine were off enough on one side I built it up with balsa wood, and then covered it with two layers of fiberglass (old school surfboard construction). Lots and lots of sanding to blend the added fiberglass back into the cowl. Came out great…..just took forever until I thought it looked good.

 

[PaulvS]

Filling the nose ring gaps so that the cowl halves line up and are parallel to the spinner backplate seems to be standard procedure. Mine were off enough on one side I built it up with balsa wood, and then covered it with two layers of fiberglass (old school surfboard construction). Lots and lots of sanding to blend the added fiberglass back into the cowl. Came out great…..just took forever until I thought it looked good.

There's still some more minor filling and sanding to be done but the gap behind the spinner is quite even now.



I added some balsa to the bottom half and ground off fiberglass on the top half. Our molded parts seem to be consistent in the areas of distortion that need to be fixed.

 

[Kiwifly]

Also worth noting that the lovely constant gap achieved during this phase is likely to change when the engine sags, I have allowed for this by making the gap at the top less than the bottom, with the hope that when the sag occurs it will even up.

 

[Stevea]

Also worth noting that the lovely constant gap achieved during this phase is likely to change when the engine sags, I have allowed for this by making the gap at the top less than the bottom, with the hope that when the sag occurs it will even up.

Maybe, maybe not. Mine never showed much visible change between the spinner and the cowl. When I did end up changing engine shock mounts (after about 1000 hrs, 8 years in service), it was because the gap from the air box to the nose gear leg got way too small. It was a bit on the small side to begin with.