Skybolt SJ Cowl Dilemma

I have been preparing for the cowl installation. I have the sky bolt installation and have looked at many builders sites. I plan on using the sky bolts on the cowl halves. To make the installation look good from the outside, I wanted to have line of fasteners on the cowl split line up with one fastener on the firewall.

I made an assumption (BAD) and confirmed it with two sources. I assumed that the cowl split line was parallel to the longeron along the side of the cabin. Further, that line would intersect the center of the engine crank. Will James confirmed, and a view on dwg 45 also indicates, but does not state the same. So I proceeded to finish the spinner and then located that point on the fuse along the firewall. See picture below. The plan was to locate the tabs in the lower cowl half.

The firewall Skybolt tabs have been installed. (Pict below) I began today to proceed with the upper cowl fitting. SHOCK - - the upper half does not extend down to the "centerline" . I also have the stock Vans cowl but it is only 1/2 " lower.

Oh- BTW - I called Vans - spoke to Ken this AM. In spite of the Vans drawing #45 "showing" the cowl split parallel to the longeron, it is not. Apparently it may have been but in the build of the prototype, the cowl was cast in place and then removed and sent to the supplier. Not Vans problem, but it is what it is.

It seems I have three options:

1. Respace all the tabs on the firewall.

Result, cost, delay of tabs, and issues with reaching some rivets.

2. Extend the upper cowl or have Will James make me a new one that has a longer side skirt.

Result: Issues with with a smooth extension of the side or $ of ordering and shipping a new half, IFF Will James will/can do it.

3. Locate the tabs on the upper cowl instead of the lower cowl so that the fasteners appear below the cowl split rather than above.

Result: Possible PITA in every time the cowl gets reassembled.

4. Proceed with cowl fitting, see how it goes when it gets to cutting the cowl split.




Last thought - if I do #1, or #3 then the line of fasteners will not be parallel to the longeron, it probably won't be noticeable. I checked the engine - it with in .3 degrees of being parallel to the longeron.

I tried like you to have them line up and like you I failed. Mine is closer than yours, but I will tell you I never notice it now that it's flying. Bet you won't either

Looking at your picture your tabs are virtually identical to mine based on rivet location (mine on the sides might be a little higher). You will need to shim all of the tabs. I think I have .025 shims between the tabs and fuse on all the tabs. After the upper firewall line is cut on the cowl, the split line will be closer to the bottom. With shims to make it flush with the skin, it gets even better.

Kind Funny . . .

Kind of Funny - - - Don, I used yours as a guide, but selected that single location all by my self. I am going to find out what the real design dimension is and publish it so others are not surprised. I am now suspecting it is 3 degrees from longer on centered on the crank at the front of the cowl.

What do you think about the tabs fastened to the top cowl? It might allow the external fasteners to be in line. Will it be an issue for installation?


Thanks

BillL said:

Kind of Funny - - - Don, I used yours as a guide, but selected that single location all by my self. I am going to find out what the real design dimension is and publish it so others are not surprised. I am now suspecting it is 3 degrees from longer on centered on the crank at the front of the cowl.

What do you think about the tabs fastened to the top cowl? It might allow the external fasteners to be in line. Will it be an issue for installation?


Thanks

Click to expand...

No way would I put the tabs on the top cowl. I did not use the tabs on the split line. I glassed a flange to the lower cowl to mount the recepticles in. The scallop of the tabs would be obnoxious to deal with trying to get the top cowl in place and would be really really bad if the tabs were on the top cowl. It's hard enough to remove now. The cowl is so stiff near the front it's hard to get the fasteners to come out of the recepticle. The whole process takes a lot of patience, but the results on mine are terrific.

By the way, if you glass a flange to the lower cowl, you will have plenty of tabs left over (18 to be exact) to move the tabs around on the firewall

Bill,

There is enough strength there to just not use that recep.

You will have them on the cowl horizontal line and put one toward the back.

Don't sweat it.

I had a similar, though not identical, problem when I fit my SJ cowl. I proceeded as necessary and made a small modification after the top and bottom cowls were fully fit. That looks like your door #4 to me, Bill.