Sunday, September 18, 2011

A Tale of Two Canopies

Canopies: they are the best of airplane enclosures, they are the worst of canopy enclosures, they are works of wisdom, they are works of foolishness, the are the epoch of in-flight visibility, they are the epoch of build complexity, they provide gobs of Light, their construction brings days of Darkness, they are the spring of hope, built just before the winter of despair....

with abject apologies to Mr. Dickens. I have two to deal with, one being attached to a flying RV-6, the other being a recalcitrant detriment to an RV-12 ever taking flight.

The RV-6 canopy was not mine to build and has, if the truth be told, been pretty reasonable when it comes to maintenance chores. Basically over the years it has all come down to cleaning the bugs off of it now and then. Until yesterday, that is.

Yesterday was one of those days that you wish you could squeeze into a ZipLoc back and put on the snack shelf in the pantry to be parceled out as a tasty snack every now and then when the weather gets bad.

I had to fly.

I had to fly!

The choice of destinations was easy: my Dad's birthday is next week and through the accident of ordering a hand drill whose price was lower than the $25 minimum for free shipping from Amazon, I had on hand a book that just happened to be the Y in the equation X + Y = $25.01, where X = hand drill. And a good book it is, too, being one of the multitude of means available (yet ignored) to lawmakers and Supreme Court Justices to help them determine just exactly what the Founders meant when the plain English that they used in writing our Constitution requires "interpretation."  Of course, one cannot expect them to be in need of shipping charge padding in precisely the amount needed to pick up a copy of the Federalist Papers or, in my case, the thousands of words shared between Thomas Jefferson and John Adams.

So it was that I found myself descending into the pattern at Darke County (KTZR) International with 180 mph showing on the speedometer, wondering just what in the world that horrendous slapping/buzzing sound emanating from the bow of the canopy just behind me was. Upon landing I was quickly able to discern the problem: the airplane, which is mad at me for trying to sell it, had decided that it would quite willingly trade away some of the weather stripping around the edge of the back windshield simply in order to irritate me. A ten inch section of the stripping had worked its way loose and was flapping in the hurricane force winds that come with the awesome speeds the RV-6 can attain.

I didn't want to fly it back that way, but an interim solution was easily at hand: I "borrowed" a length of duct tape from the local mechanic. Here it is, still in place and unruffled after the return flight.

There is simply nothing that duct tape can't do, with the possible exception of surgical suturing.

Sunday morning dawned equally gorgeous and thus seemed perfect for the work of finishing up the mounting of the canopy to its frame, and if all went well, the installation of the canopy latch too. Pete was along to help again, so I figured we'd get these little jobs done in no time. The first thing to do was to rivet on the canopy skirts. That took very little time since, as is the norm when riveting, the job went three times as fast with two people working. After that we had to install the screws, nuts, and washers that attach the canopy sides to the frame.

I thought the same kind of division of labor as used in the riveting would ernder the same time-saving results, but it didn't quite work out as well. As Pete was on one side of the canopy getting the screws and nuts in place for me to tighten, I would be on the other side tightening the ones that he had already started. It worked well enough, but every now and then the movements of the canopy resulting from his work would get out of synch with the coffee palsy my hands get after a large McDonald's cuppa and I wouldn't be able to get the screwdriver aligned with the moving screw.

I had the shop radio tuned to the local NPR classical music station in an attempt to elevate the culture of the shop, but that only led to such high level discourse as:

Me: "You know, all of this classical music sounds the same."

Pete: Silence.

Me: "No, really. There's only one piece of classical music that can be readily identified by 99.999% of people."

Pete: "The 1812 Overture?"

Me: "Hmm, no, I was thinking Beethoven's Fifth, but you might be right about the 1812 Overture too. Although I imagine most people don't get it until the cannon fires."

See? More cultured already!

It was right after that burst of intellectualism that we noticed something. Pete pointed out that the directions called for me to "cut off the threads that protrude beyond the end of the nut " on the most aft screw on each side. Fortunately, we were all brained-up on classical music and recognized the word "protrude." Still, it seemed odd to cut off all of the threads, what with the standard airworthiness measurement being at least two threads sticking out protruding from a lock nut.

A closer reading showed that we were to consult the figure on the following page for more information. It's good that we did!

That was a job for the Dremel.

That finished the mounting of the canopy, so we pressed on with the installation of the latch. The first thing to do there was to insert the D-handle through the tube in the canopy frame. If the handle was loose enough in the tube that it could rotate on its own accord with no more motive force than the weight of its handle, I was to "carefully pinch" the ends of the tube. The handle did, in fact, rotate quite freely, so I proceeded to pinch the end of the tube, but apparently not carefully enough since the handle would then no longer fit into the tube at all.

This left me with the perplexing quandary of how exactly one goes about un-pinching a tube. As it turns out, that can be accomplished by inserting the end of a large drill bit slightly into the tube and using it as a kind of pry bar to separate the sides of the tube back out. It might also require a little cleaning up with a small file. After fiddling with it for a little while, I got it to a state where the handle would fit through the tube and turn only with physical motive force.

All that remained was to attach the handle, which I had placed somewhere where I wouldn't lose it. And we all know what that means. As we were hunting for it, I cupped a hand to my ear and said, "Oh, there it is! It's in the radio!"

 To which Pete, quite naturally, said, "Huh?"

"Oh, never mind," I replied, "that's Handel, not 'handle'."

And that was that for any hope of elevated culture.

That done, the matching latch parts needed to be installed on the roll bar. The first part is a Teflon-esque plastic block that will provide a soft-ish latching mechanism for the handle to latch into. The holes in the roll bar need to be tapped to 8-32 to provide two holes for the screws that will hold the latching block in place to screw into. This operation entails a number of steps that seem somewhat make-work and silly until you realize that the entire purpose of them is to get the tap perfectly straight as it works its way into the roll bar. One wonders why they don't just tell us why we're doing odd things now and then.

That was all going swimmingly (even though we had yet to figure out why we were going through all of the seemingly silly steps) until it came time to cleco the latching block into the two holes in the roll bar that were mysteriously left open wwwaaayyyy back on page 24-05.

I had left the wrong two holes open:

In my defense, when I was wwwaaayyyy back on page 24-05 I didn't have the drawings and parts that I have now, and the quality of the drawing that I had to work from was somewhat less than could be desired.

So, out came the mistakenly placed rivets and in went the new. Screwing and tapping and more screwing ensued.

We did a quick test fit of the latching handle and found that it wouldn't fit into the latch block. The plans allow a .020" removal of material from the latch, so I worked on it for a little while with a small file.

Upon a second test, I made an interesting discovery. I discovered that it is possible to get the canopy latch to latch, but to be completely unable to get it to un-latch. Luckily for me, I had a Sharpie(tm) marker in there with me and was thus able to communicate with the outside world:

The latch proved to extraordinarily difficult to get working properly, but we eventually tracked the problem down to the outside handle holding the D-handle up too high. That was caused primarily by a slightly off-center drilling of the screw hole that holds it onto the shaft of the D-handle. There were a number of possible solutions that we kicked around, all of which involved re-ordering parts or trying to remove material from the parts on hand. A consultation of the Van's online store showed the following:

Ruin this part:         Buy a new one for:

plastic block                $8.50
outside handle             $16.00
canopy frame              don't even ask

Neither of us wanted to be considered cheap, nor did either of us want to re-build the entire canopy on a new frame so we decided to concentrate our efforts on the handle. With that level of decision-making prowess brought to bear, we soon decided that I would remove 1/16" off of the bottom of the outside handle. The band saw was perfectly capable of that, although that handle got so hot that I was able to use it to finally defrost the little freezer portion of the hangar fridge. Still, it solved the problem!

Everything else fit perfectly and was in reasonable alignment. I was happy to see that the canopy skirts overlapped the fuselage sides perfectly and didn't require the installation of any spacers.

There are a couple of more little plastic blocks to install, and then the fiberglassing begins. This was the point where I had decided that I'd place my order for the engine, but I think I'm going to hold off for another couple of weeks. I don't foresee the fiber glass work going all that quickly.

No comments:

Post a Comment