Sam James Cowl - Skybolts on Split

My Skybolts have been installed around the firewall. I will give a separate shot-out for Debra Bowers at Skybolt for her help. I had to respace the SB's along the sides to make the split line SB's line up with a single one on the firewall. I just was not going to be satisfied unless I did. I have been using the Skyloc tabs and they worked on OK on the firewall. With others coaching, including DanH, the split line was not going to work with the jagged pattern of the tabs so a single line was chosen to avoid catching a painted cowl in between “teeth".

I got fasteners on the nose prepared by using a fiberglass overlay in the notch between the cooling air inlet and the spinner. A learning experience, but a good one. I learned to use several layers of PVA as a proper mold release!

OK, now to the sides. This is where the vacillation occurred. I quickly ordered a 2” strip of .063 from Van’s to form the rails and hold the SB’s. .050” would have worked, but Van’s did not have that only .063 and they are a lot cheaper than the alternative sources. Suddenly it occurred to me that the straight strip was not going to work because of the compound curves toward the nose. So, I prepared 3” strips of 8.9oz for the process and sandblasted the inside of the cowl to etch the surface for adhesion. (a story in itself) I was still drawn to the metal, but feared the process and failure to achieve the result. Well, I got over that and after all, I had the metal and it was going to waste anyway. Out came the body hammers, one good one and others kinda junk, but I polished the faces, tightened the handles, and found some 5/16 rubber belting to use for a backing plate. I experimented with some shorter, thinner pieces and they came out ok as compound curves. I went to lowes and got a contour gage and marked the SB stations so the curve matching could begin. Pounding and checking worked pretty well and after about 30 min I had a check. Oops . . . the length needs to curve too!?!?! OK, after sleeping on it I had an idea, I took the back rivet plate and the rivet gun with a mushroom set and used 100 psi to run up and down the strip until it bowed ¼ end to end against the width. - - Perfect! Following are some pictures of the finished piece and of the process steps.

Thanks to DanH for the fiberglass advice, I hope he is not disappointed in the metal part.

Nose bridge done, using 4-40 screws to hold until nut plates are installed, edges are tight to ensure correct alignment.



Fiberglass all ready for split line, but am I?


The hammering did not take to much. Many blows with controlled force. The snap-on hammer worked as a planisher pretty well.


Crummy photo, but the curve is clear.


Using the rivet gun to compress and stretch the side and curve the piece. Working both sides prevented added curve 90 deg to this.

And finally installed with clecos. Nice fit all along, using the count our gage helped ensure a match before even fitting it.

Precisely Locating the Skybolts.

There are instructions for how to get the cowl fitted where one shines a light behind and drills the locations for the SB fasteners in the cowl. As we know Sometimes the light method is less than precise and the hole ends up elongated. Further, drilling a large diameter precisely with a single hole, let alone an elongated one is a challenge. Here is how I approached that problem.

First there are these little inserts from SB to allow using a cleco for the fit up process. I could not get them in position, so I made some little plates and used 4-40 flat head screws for the process.



Then, came elongated holes. After I was satisfied with the cowl location, each cleco in the SB location was removed and an arrow used to indicate which side of the hole was to be used.



Then came to drilling. I made a drill guide and an alignment plug. The plug was plug w/pin was forced with the arrow's aid then two vice-grip c-clamps were used to hold the guide in position. The holes were drilled with a hand held 1/2 drill to 1/64" size smaller than desired. A dowel wrapped with sandpaper quickly fitted each hole to the SB ferrule.



So that's that.

Couple of extra Photos

Here is the split rail installed. An inside view



A quick look at the contour gage at work. I marked the split line on the gage to know where to locate the gage against the part. The copper cleco is the SB location station. There was surprising change from the one to another. Only the first 15 inches inches was curved on the vertical.

The FWF progress continues. I had reason to remove the SB fasteners in the upper cowl to begin eliminating the weave surface and make it smooth to use as a form for the plenum construction.

I saw a post talking about using circlips rather than the SB retainers. It was nice idea and I tried it. Unfortunately they don't work. Needing to proceed and getting hand cramps removing the SB retainers, I got some o-rings. They are perfect!!

Here is a picture of the package from Grainger. I got a pack of 100 for less than $5.

Just came across this thread. Impressive. I love to see inventive techniques.
Thanks for posting.

BillL said:

Then came to drilling. I made a drill guide and an alignment plug. The plug was plug w/pin was forced with the arrow's aid then two vice-grip c-clamps were used to hold the guide in position. The holes were drilled with a hand held 1/2 drill to 1/64" size smaller than desired. A dowel wrapped with sandpaper quickly fitted each hole to the SB ferrule.

Click to expand...

This is a good plan. I did a similar thing, but out of thick aluminum. It worked well, but the steel version would be far more durable. My step bit just about ate up the full aluminum thickness by the time I was done. If you can make it from tool steel, do it and then sell it here for 10x what it cost when done! That would be a great buy (and would have a great resale value)