Sunday, August 15, 2010

Crickets in my canister

One could be forgiven for alleging that my belfry is inhabited by bats, what with the heat and humidity today being barely within the upper legal limit for being safe to sustain in a sauna and me crazy enough to be endeavoring to fashion a left side longeron right out there in it. Steeped in it, as it were. Stewing in my juices. One would have to be nuts to work on such a frustration-infused project in conditions such as these. Yes, "he must have bats in his belfry to be out there in this awful muck."

'Tis a fair cop.

But... it's the first chance I've had in days, and it was becoming ever more difficult to suppress the feeling that my project is foundering on the hostile shores of Neglect Island.  I've been busy with various and sundry chores, tasks, obligations, and to be perfectly honest, less energy-sapping forms of recreation. Fearing that all of the precious momentum gathered in my most recent effort for force my will upon the seemingly immutable 90 degree angle of the longeron was dissipating, I felt that I had to at least make an appearance at the hangar today. Having a fresh look at the plans might also serve to build a more complete mental image of the steps involved in finishing my first longeron.

Be careful what you ask for, or so they say. It took only moments to realize that the angle that I had opened on the end of the longeron was complete in that it was the required 95.4 degrees (strikingly similar to the ambient heat index, as it transpires, but those are different types of degrees), but stunningly incomplete in its length. I had successfully opened a two inch length to 95.4 degrees, leaving only another dozen or so inches to go. I had been visualizing this opening as something that was needed only at the far extremity of the longeron; such is not the case. It actually needs to go 12 11/16" inches down the length. So, back in the vise went the longeron, and the steel coupling was called back into play.

You may recall that I had also brought the big mallet into the mix by using it to pound on the handle of the vise to force the jaws of the vice to close on the coupling, thereby spreading open the angle on the longeron. I started doing that again, but soon realized that I needed a more refined and humane method. I also realized that I needed to better protect the vertex edge of the longeron. I put the longeron between two pieces of scrap wood to protect it. As can be seen, there are tremendous forces at work here, and the wood wasn't really up to the task.

In fact, it split apart with a sharp "BANG!" and flew high up into the air, almost reaching the ceiling of the hangar.

I needed a new method of getting a lot of leverage to apply force to the vise. I put the vise handle through the open hole in the end of my big adjustable wrench.

I decided that a thicker piece of scrap wood might be a better buffer and be less likely to get decapitated when the going got tough. Using the wrench, I was able to get a lot more force onto the vise without the brutish and somewhat uncontrollable mallet.

All was going well in getting the angle to open, but there was a little unwanted bending going on as well.

Once I had the full length of angle opened up, I turned the longeron around in the vice and took the unwanted bend back out of it by bending it.

There it is, ready for the next step.

In theory, by having opened the 90 degree angle to 95.4 degrees, I would have imparted an unwanted 2.7 degree angle to both of the sides. No one cares about the vertical side, apparently, but the horizontal (top) side needs to be flush the length of the longeron. To fix that, a "metric crescent wrench" (as called for in the plans) is used to twist the 2.7" out of the top and therefore put the entire 5.4 degrees on the side. Now, there's no such thing as a metric crescent wrench, what with them being infinitely adjustable in both SAE and metric sizes, and any other size you might come up with. So it must be a joke put there by Van's.

Tell me, do I look like I'm in the mood for a joke?

Fortunately, the 2.7 degree bend was very easy to make, even with my Harbor Freight faux-SAE crescent wrench. Yes, that's a joke. I guess I was in the mood after all. Go figure.

It was finally time for The Big Bend. Which reminds me of something that happened at dinner when I was up at Oshkosh. The Jackson Two had come down to where we were staying in West Bend to have a nice dinner. I knew of a place right on the banks of the river where we could sit out on the patio and have the river as a nice background for our meal. The question came up as to just what the name of the river we were sitting by was. I replied that it must be the Milwaukee River. A woman at the next table over interjected with the comment that if it was, in fact, the Milwaukee River, then said river must take a bend that she was unaware of. I replied that I not only guessed that the river did  take a bend, but went a step further and postulated that it very likely took a bend to the west. How ever did I arrive at that preposterous supposition, she wondered. I suggested that maybe, just maybe, that's where the name West Bend came from.

She had never thought of that, or so she said.

But back to The Big Bend. The idea here is that the longeron will provide support for the side skin where it of necessity ends its upward trek at the edge of the canopy. That area of the fuselage has a graceful outward bend to provide room for my bulky shoulders. The way to determine that the longeron is correctly bent is to use the canopy sill part as a template.

It took me awhile to figure out where exactly to position the template on the longeron. The line that I marked 'A' is at the end of the area where I had just finished opening the angle. There is another line marked as the 'START OF TEMPLATE', but the line drawn to show it was open to interpretation. Luckily, a measurement was also provided. If I am reading it correctly (and yes, there is still some doubt in my mind), the edge of the template should line up with a mark 1/4" (or 4/16" if you don't want to simply the resulting fraction arrived at by subtracting 12 7/16 from 12 11/16) from the 'A' mark. The drawing seemed to support that interpretation, so I made the mark and test fit the template.

You can see how much bend is going to be required.

The plans say that the part to be used as the template can be set aside and the opposite part used in its stead (albeit flipped upside down) if the original part doesn't work with the longeron in the vise. I could see that this was going to be the method I would need to use, but I figured that it would have to be done cautiously to avoid making the bend in the wrong direction. Visions of the shipping costs for having to order a replacement longeron sharpened my focus on this issue quite distinctly.  I carefully placed the opposing part, clearly marked with an 'R' to differentiate it from the 'L' piece that will eventually be riveted to this, the left, longeron in place.

The hash marks on the longeron are 1 inch apart. The idea is to clamp the longeron in the vise and apply some bend at each of the 1 inch marks until everything lines up with the template. The plans also warn that a vertical component can be introduced at the time of bending in the horizontal plane, and that one should be on the lookout for that and correct it when it happens. So, in the vise with it, and start bending. The plans suggest checking the bend against the template early and often to ensure that one isn't actually over-bending the longeron. If one is very, very careful, it is possible to match the curvature of the template very precisely. Which it appeared that I had done a simply admirable job of. Still, it's not official until the longeron is matched with the real template, not the inverted stand-in. Which I did.

Only to find that I had very precisely matched the inverse of the bend. Merde! How could I have bent the thing backwards?? Well, simple really. I had neglected to mark the front and rear of the template, and I had managed to use it backwards.

As it turns out, if one is motivated enough, the longeron bending can be very carefully reversed and re-accomplished in the correct direction.  If anything, it turned out even better the second time.

It seemed prudent at this point to forgo the pleasure of doing the right side longeron. I've been disciplining myself into cleaning a new portion of the hangar every time I go out there, so I decided I'd do a little shop-vac cleaning and call it a day. The target area was the back corner of the hangar where the crickets like to gather. My friendly bird hadn't come back, and I could hear a new batch of the irritating buggers back there. The little fiends are clever - they hear me coming when I go hunting for them and quiet down until I give up and leave. They then chirp up (so that's where that expression comes from...) and call me insulting names.

Well, the joke's on them. While evolutionary adaptation has taught them to be quiet when an irate human comes after them, their species has apparently failed to adapt quickly enough to recognize the danger of the shop-vac. It sucked up a good half dozen of them. I'm just crazy enough to laugh out loud when I hear them chirping away inside the belly of the vacuum. In fact, one could be forgiven for saying that I have crickets in my canister!


Anonymous said...

I see the problem now. You didn't have your lucky orange mallet colored Hawaiian shirt on. Don't ever do that again.

Co-Pilot Rick

Torsten said...

Hm, the Big Bend is causing more problems than I thought. First I over bent it trying to precisely match the bend a few inches behind the start - overlooking that the rest of the template was shifting way out of alignment - and now I'm having the hardest time avoiding a significant bulge in that same area that wants to curve outboards more than the template wants me to. How did you get that done so perfectly?

DaveG said...

Trial & error - a LOT of it. I remember going an inch at a time with little bends on the first pass, then taking a high level look at to to see it it needed a bend further along the length (which would affect the entire length) or closer to the starting point (which would affect only a short length)

I also ended up getting bend in the up/down plane that I had to take back out. That, of course, meant that I had to touch up the front/back bend. It's very hard to describe.

I didn't get the left side perfect. It was an up/down bulge that ended up causing a (sadly permanent) 1/32" gap between the side skin and the canopy shelf skin.

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