You are currently browsing the monthly archive for July 2007.

Like many builders, I made my turtleback 1.5″ taller to provide more room and a better fit to a slightly larger canopy. This caused me some grief, though. There wasn’t time to do the layup after installing the foam, so I left it overnight. Well, apparently the humidity and cool evening weakened the 5-min epoxy hold where I had to lengthen each piece. The joints were at the ends, where the curve is the sharpest, and they just snapped overnight. I spent all evening Thursday repairing them, and here’s hoping it will hold, because I can’t get back in there until next week!

A few things would have prevented this, and I strongly encourage other builders raising their turtlebacks to do one or more of the following:

  1. Install more slats. The plans number of support slats is just barely acceptable , and when you raise the height, it puts you over the top. I recommend at least 2 additional slats per side, more closely packed the farther you go up the curve. They’re VERY fast to install, especially if you cut their slots when you cut the rest, and could save you a lot of heartache.
  2. Make sure the flashing that supports the edges of the foam pieces is firmly attached at every spot, and especially at the top, where if you simply tape it, the tape may peel off the duct tape lining. I had used a roll of aluminum foil tape that John had lying around, and it was great at first because it was so thin, and held its position. The problem was that it didn’t stick very well, so it gave way at the top and was part of what allowed the foam pieces to buckle.
  3. Don’t do the joints at the ends. You want them even, on both sides, so you don’t get a noticeable line on one side but not the other, but that doesn’t mean they have to be at the lip. Instead, cut each foam strip in half in its middle and add the extension piece there. There’s not much flex in that section, so you don’t have stress on the j0int, and if you’re careful to use very little glue, you won’t get a joint line (it’s easily sanded, anyway).
  4. Use twice as many foam strips. This is probably annoying, but if you used 3″ strips instead of 6″ strips, they would be easier to shape for a good fit and install. You’d also need more flashing, of course, but by the time you were done you’d probably be ahead of the game.
Advertisements

Well, the foam is installed in the turtleback jig. It took quite some doing, but it’s good to have that out of the way. More and more I find myself getting frustrated with some of the build techniques. It’s when you see things like the masking tape to cover the remaining gaps, and you realize that you aren’t the only one who, at some point, has said “screw it, good enough.” Yup, the designer did, too.

I share a hangar with John Slade, and have had the pleasure on a number of occasions to ride right-seat with him and experience first-hand what I’m getting at the end of all this labor. On each ride I notice something new, something that changes how I think of the build cycle in terms of the final, flying aircraft. John suggested that I put these thoughts down here, in the hope that other builders might gain some benefit from them. Here goes!

My theme this week is complexity. Flying in a Cozy has changed how I view what’s important and what’s not. I’ve read a recent discussion about switch guards that illustrates this point perfectly. The argument was that it should be made difficult to make mistakes through flipping the wrong switch, and to prevent passengers from doing the same. It’s a perfect topic for me, because I was an adherent – I had all sorts of switch guards and locking toggles in my original panel design.

No.

Way.

The Cozy is SMALL. I’m not talking about Cessna vs. Beech Baron here, I’m talking about Cessna vs. Boeing 747. It’s easy to focus on the width factor, and it’s true that you sit right next to your passenger, legs nearly touching. What you don’t see much talk of, though, is where the panel is. The panel isn’t like a car dashboard – it’s RIGHT in front of you, and it’s not exactly hard to see. You can throw the ‘passengers’ argument out the window immediately (or just throw out the passenger) – if they’re reaching for something, you know it, and you can politely break a finger or two to suggest that they consider another idle-time toy.

As for flipping the wrong switch yourself, most big toggles take a surprising amount of force to actuate, and thus it’s unlikely that you’ll hit the ‘wrong’ switch by simply bumping against it, even due to turbulence. You can’t bump one of these from the side to move it; you have to push it straight up or down.

Switch guards are fine, in principal, but they don’t protect against deliberate actions. Putting one on the arming circuit for a missile is one thing. Putting it on something you flip all the time, like a fuel pump, is a really bad idea. The trouble is, you get USED to flipping it just to manage fuel flow, so after a while the toggle cover becomes just an irritant, not something that makes you think twice. At that point it’s worse than useless. It may even be a hazard, because it may make the pilot clumsy in responding to emergencies, like running a tank dry. That’s not exactly unheard of, and has killed more pilots and planes than hitting the wrong switch ever has.

I think a better answer to address safety concerns is switch segregation.  I plan to put some of the more critical, engine-related switches in front of the pilot’s stick. John has his there, and I’ve discovered that in the Cozy, this is an easily-reached area but also one that is NEVER in a ‘bump into’ zone, because your hand is always on the stick. You would have to either reach across with your right hand and deliberately hit something, or take your hand off the stick – neither action is something that would happen accidentally.

For fuel switches, where you do want rapid access and easy control, I will put them in a group together away from other switches, such as lighting. Beyond that, I think additional time could be better spent in other areas if safety was truly a concern.

The turtleback jig is now done, and three of the foam strips are installed. I wanted to wait until next (this) week to do more – it was late, and I was tired. Still, it feels good to make this kind of progress even with a limited amount of time available. I’ll post pictures when I have a chance to get them off the camera.