Cowl Clean Up

Well, we have returned from our Italy trip. We had a great time and now it is back to work on the long Ez. By and large, the finishing on the bottom of the wings and strake is complete at this point. I do have 3 or 4 areas to repair in the micro filler and will get to those soon.

The next goal is to get the wings removed, and lower the fuselage to a comfortable working height for doing the rest of the finishing on under surfaces. But before we take the wings off we have a few loose ends to tie up.

Recall that our cowl cooling air exits are a bit too large. The details are explained in a previous post. But suffice to say I have to reduce the height of the cowl exit by 1.5 inches total, or .75 inches each top and bottom. This still leaves plenty of exit area and room around the spinner and flow guide for vibration. While doing this, it also gives an opportunity to make a nice rounded trailing edge for aesthetics.

The basic process started with adding blocks of foam to create a build up that is .75 inches high and extends 3 inches into the cowl. This foam area was tapered back to meet with the carbon fiber inside of the cowl to create a smooth transition for the exiting cooling air.

Then to create a consistent round trailing edge I made small 3/4 diameter circle templates. These were nailed into a small block of blue foam. This allowed me to Hotwire cut cylinders. The cylinders were then taken to the band saw and cut in half to give half round foam stock.

This half round stock was cut into small segments and bonded to the foam build up along the trailing edge. This gave a relatively continuous trailing edge shape. There were some gaps due to the “segmenting” affect especially around the tighter curves. This was easily filled with dry micro during layup. Shown below is the upper cowl. Foaming at the mouth, so to speak.

Since there will be an overlap between the lower and upper cowl along this rounded trailing edge, I did sand an inch of the trailing edge down by approximately .020-.030 inch to minimize the joggle in the finished overlap.

In addition to adding a finishing touch to the trailing edge of the cowl, this fairing will also act as a stiffener. That is why it is important to do this before the wings are removed. It is important that this layup cures while the cowl is accurately located and clecoed into position.

Just before doing the layup I surprisingly had the foresight to install the cowl an spinner to check for proper clearance. Much to my dismay, the gap around the spinner was inconsistent and on one side was about .5 inch. I was aiming for a consistent .75 inch to allow for engine movement.

The cowl used to have that consistent desired gap, so it obviously warped slightly. No big deal! To repair I simply cut the stiffener. This allowed me to insert wedges between the starter ring gear and the cowl until I had the consistent gap I was looking for.

The cowl was removed for ease of access to wet out the carbon fiber and the layup was completed. While still curing the cowl was re-installed and jigged in place to give the consistent gap around the spinner. This was allowed to cure and then in a second operation the stiffener was repaired.

Once the upper cowl (remember the airplane is upside down) was cured, the cured carbon fiber was trimmed. Then I started in on the lower cowl. The same process is going to be followed with one exception. Where the two cowl halves meet, the round trailing edge will go over top of the last inch of the upper cowl. This will tie the two together and provide for a finished seam area.

Once again, the lower cowl was warped significantly. The stiffener was also in the way since the rounded trailing edge was an after thought. So to kill two birds, the stiffener was removed. Again, the new trailing edge will serve as a stiffener.

While doing all of this work, the oil cooler air exit was also just a raw unfinished edge. So it warranted some attention. Again, the same basic process is being followed.

However, this lip does not need to be as big, so to create the round edge, I used a piece of 3/8 inch nylaflow and 5-minute epoxied that to the edge with a consistent reveal. Foam will taper that edge into the cowl.


I didn’t have enough time on this block of days of to finish adding and shaping foam or do a layup, but a few more hours of work and we should be there. I think it is going to look great and provide a finishing touch!

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