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History & Justification
When the taildragger modifications were done, the top cowling was split and a hinge added per STC to make it easier to get at the engine for normal maintenance. A nice idea, but not really compatible with the 160 HP upgrade and the speeds I usually fly. As shown in the Before picture above, I found that the cowling edges were being rapidly worn away from vibration.
I added some 10-32 hold-down screws front and rear, which helped a bit, but that really wasn't enough. I also added internal blisters at the latches to reduce the amount of hot air exiting the sides of the cowling. The photos below show the state of the cowling as of January 2002. Click on any photo to see it bigger.
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Cowling Improvements
The first step in geting a better cowling was to try to find a decent used AA-1 cowling to use as a template. This was not easy! FletchAir managed to dig up one that wasn't too badly thrashed and sold it to me for $750!, without the oil door or the latches, with my current cowling to be returned someday as a core. At this point I was not sure whether I would actually use the 1-piece cowling on the plane, or only as a template for a new one.
The next step was to find a shop willing to do good work for a reasonable
amount of money. Of course, in the aviation business, the definitions of
"good" and "reasonable" are up for interpretation. I decided to go for
good and let reasonable slide a bit. After all, we don't fly to save money,
do we? I ended up choosing Andy Estes of Red Mountain Aircraft Services,
right here at Falcon Field (480.396.9008). These guys
are mainly in the restoration business and have an associated paint shop next
door. I was able to see the results of some of their previous work and
was pleased.
Design Concept
I came up with a cowling design that is supposed to reduce the vibration-induced wear, while completely eliminating the unsightly and leaky old latches. Originally, I was hoping to use some kind of ¼-turn fasteners, but this ultimately turned out to be too costly (for me) to get installed. I settled for a lot of 8-32 CS screws and nutplates, plus some larger 10-32's in the holes where the Camloc's used to be.
Structural Repairs
It turned out that the cowling was a lot worse that it appeared, and that a lot of additional metalwork was going to be needed on both the cowl itself and the supporting structure. The lower cowling rails and firewall flange all needed some help before the nutplates could be installed. Getting the flush pathes into the compound cowling curves was also more difficult than anticipated. In the lower rail photos, you can see the holes where the latch hooks and the blisters uses to be. Click on any photo to enlarge it.
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Painting
Quite a bit of pre-painting work was required to try to get a smooth surface for painting. This was done by B&F Aircraft Painting at FFZ. The final coat looks pretty good before mounting it on the airplane. Click on any picture to enlarge it.
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Final Comments
Well, this whole idea turned out to be a lot more expensive than I expected, requiring an inordinately large number of man-hours to turn the piece of metal I got from FletchAir into something like what I wanted. On top of all that, after a few hours of flying, the outlines of the flush patches began to show through the paint as tiny cracks.
I can certainly understand why people build their own airplanes. The "right" thing to do would have been to either make a mold for a fiberglass cowl, or to start from scratch and try to make a new cowl on the English wheel. However, getting either of those ideas past the FSDO would be very difficult, whereas the changes I made were pretty easy to pass off as "minor repairs and improvments" and the 337 was approved fairly easily.
Of course, now that I have a 337 for the improved cowling, I guess I could
start on making one from sheet metal
Andy Elliott
9 March 2002