Source: 2018 Q1 Beartracks, Jared Yates
It wasn’t something I planned to do, but a few months ago I managed to take off with the right side cowl door unlatched. How could this even be possible, you might wonder? The first link in the chain was obviously an inadequate preflight. It wasn’t a non-existent preflight, but clearly the pilot missed one important step. The second link in the chain that surprised me was that the problem wasn’t obvious as soon as the prop started turning. It must have been closed enough to have partial engagement of one of the camlocks, because everything seemed normal until after I had been flying around for a few minutes. At first it popped up a little, which prompted me to close the throttle and head back to the runway. Shortly after, it opened fully and began whapping itself back and forth a couple times per second.
The pilot on board figured there was not much to be done about it at this point, and resolved that the door would probably separate shortly. A few different slip angles and pitch angles didn’t seem to make any difference, so he focused on landing safely. The mechanic, occupying the same seat as the pilot, was already frustrated about having to mix three batches of paint, and quite dissatisfied with his pilot counterpart. Good news for the mechanic, the door did not separate, which meant being able to salvage the camlocks. This was something the underwriter of the operation (that is, the pilot) was able to appreciate. The other good news about this was that the windscreen was not damaged by a separating cowl door, which would have been bad news for everyone involved. And above all, the door didn’t land on something important on the ground.
After parking back in the hangar, the manager of the parts department ordered a new 3 foot length of hinge (ACS part number 03-000493, MS20257P3) because the old one was starting to crack at the leading edge. The aluminum panel was obviously not salvageable, but fortunately the spare parts warehouse (conveniently behind the tool box in the hangar) had an extra piece of aluminum sheet in stock.

While waiting for the hinge to arrive, the mechanic was able to sort out a strategy for making the holes match on the new cowl door. The problem is that camlock receptacles don’t lend themselves well to any of the hole transferring fixtures in my toolbox. Rather than starting at the hinge line and rolling the cowl door down to try and match the holes, he decided to start at the camlocks and roll the door up to the hinge. The old cowl door was suitable as a template for marking the camlock holes, and for marking the rough outline of the new door. At first the old door was not willing to help with this, being that the old door was all crumpled up. The mechanic beat it flat with a mallet, which yielded complete compliance.
After attaching the new door to the airplane at the bottom (left photo) the mechanic made marks for where the door should be pre-bent. He removed it from the airplane and carried it across the dirt road to the bending die facility, to find a tree of the proper diameter and branchlessness to serve as a die. This prebending got the door pretty close to its final position, and a ratchet strap held it the rest of the way. He then attached the new piano hinge to the blue part of the old cowl top, and match drilled the door and hinge simultaneously, starting at the middle and working outward on alternating sides.

Upon initial construction, the cowling only had camlocks along the bottom. It didn’t seem necessary at the time to add any others, but in the process of making this cowl door, I realized that the nose bowl had deformed a little, just in front of where the hinge line meets it. This explains the gradually degrading clearance between the cowl door and the #1 cylinder, which has worsened over the past few years. In the photo to the left, notice how the light blue lines show a slight V-shape where they should be flat. This problem wasn’t obvious until it came to trimming the leading edge of the new cowl door. When I pressed down on the apex of that blue V, it flexed the nose bowl, changing the geometry of the front of the door. It’s hard to capture with still pictures, but compare the two photos below. One is with no pressure, the other is with downward pressure. Notice how the unpainted part moves aft relative to the nose bowl parts. Or more accurately, the painted parts move forward relative to the unpainted cowl door. When the nose bowl moves forward, it also pushes the aluminum door outward, providing more clearance between the cowl door and the #1 cylinder.


The obvious solution here was to add another camlock in that section of the door, to help support the nose bowl and keep it from moving aft and steepening the V-shaped distortion at the hinge line. In a case where it would have been nice for the mechanic and pilot to actually be two separate people, I pressed down on the hinge from the top while I drilled through the cowl door and into the fiberglass for the camlock. Hopefully this new camlock will help stabilize the cowl and provide a little more distance between the door and the cylinder. In my case, the new camlock is as high as it could be on the bottom half of the nose bowl. Since the fiberglass is not very well-suited to receiving fasteners, I riveted the receptacle to a small tab of .020” 2024, and then attached that tab to the inside of the fiberglass flange with JB weld. The tab also increased the width of the flange just enough so that I can align the wing nut camloc into the breeze. If that doesn’t seem sturdy enough, I might attach a similar tab to the outside of the flange and squeeze some flush rivets through the whole sandwich, to help spread the load out on the fiberglass. If anyone is tempted to only run camlocks along the bottom of the cowl, I’d recommend reconsidering. Most other builders seem to have done it right the first time.