More cowl mating work

So, after the last session, I spent some time reading up on cowl fitting. One particular point I wondered about was whether it might be a good choice to just cut off the overlapping flange around the prop spinner, in order to simplify getting that interface the way I wanted it. I figured it should be fairly simple to add a flange back later on, and when I found a post from Dan Horton, one of the RV fiberglass gurus, suggesting this same path, I decided to go for it.

So I sawed off those flanges, enabling to me to work on that junction as a simple butt joint. This made things easier, but still not 100% easy –  the new issue was figuring out how to fit the portions of the flanges that extended aft. If I just have the cowl halves on the floor, I have to take a pretty wild guess at where they should be positioned at the aft end, and this in turn affect the mating angle at the front. I felt like what I needed was a way to test-fit the halves on the plane to see how the junction was going.

The problem here was figuring out a way to support the front of the lower cowl. Eventually there will be nutplates holding the two halves together, but not only can that not be done until the fitting here is done, it’s really out of the question now that I removed the flange. Eventually I decided to just drill a pair of temporary holes, one below each air inlet. Each hole has a cleco installed, and then a piece of string can go between the checks and over the prop spinner, thus providing a way to roughly hold the lower cowl in position.

With that done, I made my first fitting of the lower cowl on the airplane. The string+cleco idea worked pretty well up front:

…and to bring the rear into alignment, I used the usual method of wrapping a ratchet strap around and using it to pull the lower cowl up against the fuselage:

Doing this allowed me to check the mating angles at the spinner joint, and make some marks to fine-tune them. I removed the lower cowl, sanded it to shape a bit, and hung it once again. This showed that my joints were getting pretty close, but the right side didn’t quite want to pull flush. I suspect that the inboard part of this is interfering, but it’s impossible to see with the cowl on the airplane…which is a new issue with this approach.

But I realized that the main purpose of this was to figure the relationship between the cowl halves when roughly in place. Being on the fuselage was necessary to establish that relationship, but not to maintain it. With the halves pulled together, I just used a Sharpie to trace the upper edge of the untrimmed lower cowl onto the upper…and now I can use that to join them in alignment without being on the airplane, which should allow me to to the last bit of fine-tuning of this interface up front.

That will be for another night, though.

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