Airworthiness

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I

It’s like this: 1) Physics tests airworthiness, 2) Airworthiness is a measure of craftsmanship, 3) Craftsmanship can be measured against aircraft construction standards.

This was true for the Wright brothers and it was true for me and my Zenith CH750 project.

The difference was that I was taking advantage of over one hundred years of aircraft production experience and testing, countless expert application of changes, many small and large successes, uncountable catastrophic fails.  All of that experience about airworthiness could be applied to my project, even if indirectly. So while I was solely responsible for the quality and reliability of my aircraft, at least I had 100 plus years of hindsight to help guide the way.

Wright brother's first powered flight

First airworthy powered aircraft

II

The Zenith rudder kit arrived very well packed in a heavy, vertical-stabilizer shaped wooden crate. I lugged it up the caliche drive to my shop. I’d just shipped my engine core off to Florida in a lightly reinforced cardboard box.  It had been damaged in transit. But not the rudder kit — the folks at Zenith plainly knew what they were doing.

I didn’t. But that was really the main point. I was going to learn how to know what I was doing.

I set the case on the aircraft building table I’d constructed the week before and gazed at it. It was the beginning of the beginning, a personal challenge I’d taken on for reasons obscura. I stood on a path now, self-chosen, and it stretched out before me leading to an indeterminate end.

First step: Take the drill out and remove the screws holding the lid on.

Crated Rudder Kit from Zenith Aircraft

This is how carefully packed aircraft components get shipped

III

There were only 13 individual pieces in the rudder kit. Some had been pre-drilled. I had carefully read all the instructions. I had ordered all the necessary tools.

“This should be easy.”

I began to carefully work to put the rudder together. I’d spent days of my childhood assembling all kinds of model planes and spaceships. Plastic and glue. Now it was aluminum prefabricated parts I was handling, using clecos to hold the pieces together, a pneumatic drill, and — eventually — a rivet gun.

I was slightly anxious, taking the drill in hand for the first time and using it on the rudder spar and doublers. Inside I felt electric. I didn’t want to screw up. There was only one thing to do: My finger pressed the trigger and I drilled, the bit eating into the aluminum, spinning at 4000 rpm, and suddenly there was a neat hole.

Giddy, I drilled more. This went on for a couple of hours. Carefully lining up the drill and bit on the part, pressing the trigger, drilling another perfect hole. I quit while I was ahead. It was just after midnight.

Rudder Spar partly drilled out with clecos

Drilling the holes in the rudder spar to attach doublers

IV

The next day I became comfortable. It was easy and clean. I drilled into the parts repeatedly with no issues. I liked the warm sound of whirring air drill and metal bit on aluminum. Spiralling fibrous strands of metal littered the table. I didn’t know it, but my technique sucked, and all of the sudden I learned the hard way: A horrible grinding sound ripped across my ears as the metal bit poked way too far into a hole. Idiotically, I moved to the next hole and did the same thing. I got frustrated — and did it again and several more times.

It was Einstein’s lament: Doing it the same way over and over and expecting a different result is the definition of insanity.

Finally, I dared to look and see what I’d done.

It was agonizing to behold.

Further inspection made me freak out. I examined my assembled skeleton parts and how they fit together. I was suspicious and unsure. Cross referencing the instructions and drawings did not resolve my suspicion, but made me even more dubious, and then it made me fall into despair.

I turned off the shop lights and went into the house and got in bed. My wife was snoozing happily. I stared at the ceiling. It seemed like I’d destroyed everything.

V

In the dark, I envisioned small cracks turning into large tears that led to the rudder being ripped off the plane.

Uncontrollable descent.

I was certain I’d followed directions to the letter. I had been calm and collected. How was it that the parts didn’t fit as I expected them to fit? How much money would it cost to replace them? How much time? Could I really do this? Would my plane pass the earth, wind, and fire test or would physics and gravity (to be more accurate) have me slamming into the earth and bursting into flames?

My brain wandered for hours, into dreams, most of which had nothing to do with airplanes, but were agonizing distortions of reality.

When I woke up I had a plan. I would replace any and all parts the tech support people recommended. I took pictures that illustrated my concerns and sent them off to Zenith.

Then I waited.

Rudder spar rudder horn fitment

This turned out to be proper fit according to Zenith.

VI

The response was clear: My concerns about fitment of the assembly were unfounded. The photos I sent illustrated that the parts were fitting together exactly right, according to the plans. But the drill-munged bottom rib? I could put a doubler on and address it that way. Or I could get a new part to replace the damaged one.

bottom rib flange damage

Not airworthy. The bit seriously munged the flange that attaches the bottom rib to the spar. Unacceptable.

My brain cleared and the answer was immediately obvious.

I ordered a replacement part.

Advice: Consider buying some drill bit collars and using them correctly to prevent over-penetration of the bit.

There is no reason to walk the path wrong at the very first. While 2020 was going to be the Year Of The Build — it was clearly going to take more time than one year to build the airframe and install the powerplant, even though I was going to be able to work on it often in the evenings. Besides, I wanted to form some of the parts myself. All I had to do was give myself space and peace of mind to do the job right — to work with care, not haste. To repeat, if necessary. To learn, build — fly.

There were plans and construction standards, there was craftsmanship that had to be achieved to meet those standards. For my own sanity and ability to sleep at night I would ensure my plane was airworthy beyond any doubt whatsoever. I had enjoyed working on the rudder so far. I wanted my craftsmanship to rise to a level that physics would measure and find acceptable.

Because at some point, just like the Wright brothers, I would have to take my first flight in the airplane I had built.