« Archives in October, 2010

Halloween Horror.

8 hours.

My parts arrived from Van’s last week. A couple of ribs and a HS-710 angle that I had ordered because I was tired of that nagging feeling of something not right in the structure of the horizontal stabilizer. Yesterday, I finally got to drilling the offending part off, with the intention of making a new one that satisfied all the edge distance requirements. This is the old HS-710:

You can see how beat up this thing is, and that’s from me sucking at riveting a long time ago. Not only that, see the holes along the flat part, near where the angle starts? Those holes are too close to the edge of the part. The general rule is that the center of a hole should be 1.5x the hole’s diameter from the edge of the part or another hole. This isn’t even close.

This part is one of four structural elements holding the tail onto the airplane, so it’s kind of important and it has to be perfect. No ovaled holes, plenty of edge distance, good rivets, deburred holes and edges. This part connects the inboard ribs and both spars as well, so it’s all got to fit together in such a way that all those requirements are satisfied. The plans for this section suck, and the design could be better too. This is one of the first things you have to do as a builder, and a fit this important could do with a little more explaining of the whys, and some clarification on the steps. It’s almost as if it’s deliberately designed to get your nose off the paper and understand the structural priorities for yourself, and the lessons are taught in mangled metal and UPS shipments from Aurora, Oregon. The main lesson here is that you have to trim off just enough of the nose rib flange to let it fit between the HS-710 and HS-714 angles, and that it’s better to be closer to the edge on the aft rib than on the angle.

So, armed with 4 years of aircraft construction savvy between then and now, I set about replacing the HS-710 angle and the inboard ribs.

This is the shiny new HS-710, ready to install. The tapered ends didn’t get as much of a taper this time, leaving more metal on the edges. All good, right? Wrong.

Another important lesson: Get rid of all annoyances and irritants before you do anything critical. Find your neutral space. My jeans were falling down (belt not tight enough, getting less fat, good news really), the drill charger fan was running, the psytrance station started playing something screechy, tweaky, and annoying, and the shop vac hose and air lines were completely underfoot. I drilled the new HS-710 in exactly the same place as the old HS-710, through the spar in the old hole. I needed a whole new class of profanity to accurately describe the situation at that point. I didn’t have one. So I threw stuff. Nothing heavy or expensive, but even watching my hearing protectors explode in a bright flash of red plastic and skip across the concrete didn’t satisfy the frustration and disappointment. Even the time I drilled a hole in my finger wasn’t this maddening.

At this point, I wasn’t much into taking photographs. I spent the next few minutes contemplating selling the whole mess and buying a Cessna. Slower, but for the money, hauls more cases of wine back from Napa. But then the ‘F— You’ took over. F— You happens at the darkest hour, when you just say F— You, this is not stopping me. F— You, you are just soft metal. F— You, I will get this done. Today. So I made a new HS-710 from some angle stock. That’s right. Made one. And I can make more. I’ve got plenty of angle stock. We can do this all weekend, so settle in, princess. This time, there was way more measuring than there was drilling, and I now have a fully functional, structurally sound, properly installed HS-710. Here are all 3 HS-710’s, old, new, and new new.

Getting that little bastard on was only the first of the fun things to do. This setup is designed to be assembled before the skins are on, and getting it all together requires some basket weaving and the use of the double-offset rivet set, which is a deep, dire pain in the ass. The procedure is: Stick the aft ribs in, drill them through the spar, then use those holes to match drill the forward rib making sure the edge distance is good. Before you drill that, make sure the skin-to-rib flange lineup is good. Get this part locked down, then do the skin holes. But riveting the flanges to the spar is a bitch. The double-offset set likes to walk around, and you really need to secure the assembly and keep the set seated or you’ll mangle the rivets and that will mean drilling out and possibly enlarging the holes. Trust me you do NOT want to go up to an AD5 rivet in there. The rivet gun just barely makes it in there to get a good lock on the rivet heads. Like I said, it was designed to be done without the skins in place.

If you get it right, you end up with something like this:

See how there’s plenty of room between the center of the rivet and the edges of the metal?

Squeezing the skin rivets is easy. I even remembered not to rivet the holes for the empennage fairing this time.

Assembled and resting. The next horizontal stabilizer I build better be on the next airplane.

More odds and ends.

2 hours.

I’m waiting for parts from the Mothership, so it’s all about what I can find to do while I’m waiting. Mostly I sat out there puzzling out wiring runs. The floor panels are in already, so I might have a nice game of Go Fish to look forward to when it comes to running wires for 2 GPS antennae (yes, 2, in case I get hold of a GNS 430W), trim servo, strobe unit power, tail light, then strobe wires forward for the wingtip strobes. What I did actually get done was finally rivet the reinforcing angle that the tank brackets attach to just forward of the main spar. I can’t believe I forgot to do that during wing mating, but I think I probably had other things on my mind at that point. So that’s done, and there are little blobs of torque seal on the accompanying thru-bolts to tell me I don’t have to worry about it anymore. Oh.. remember this thing? F-697?

It’s the canopy jettison bracket. I put it on the subpanel because I was just following the directions. Then I realized I’m not going to install the canopy jettison system (weight, complexity, etc). Now I realize that thing might get in the way if I have to chop holes in the subpanel for some deep avionics, like a GNS 430W or some other surprisingly large piece of gear I think I need. So I took it out. You can never have too much practice drilling out rivets.

After that, I fiddled around with the fiberglass rudder tip, and worked on the mounting system for the tail position/strobe. This is genius. At some point, I bought a length of 1/4″ aluminum dowel from the hardware store. What I did was cut 2 half-inch lengths of it, which I’ll drill and tap to 4-40, the same thread as the tail light mounting screws. I’ll put some dimples in the sides of them, then sink them into blobs of flox in the rudder bottom. At that point, they’ll be permanently affixed and I’ll still be able to unscrew them to change bulbs. OH, thumbs down on the build quality of the rudder botttom. The two halves of the rudder bottom don’t exactly line up along the seam, so I’m going to have to clean it up with micro and sandpaper. If I was exceptionally skilled with sheet metal, I’d make my own out of aluminum, but I’m not, so I’ll deal.

Finally, I messed around with the tailwheel springs. I’m going to need to order new chain. I should have looked at the plans. I remember them going together completely differently, and it took me some time to figure out that getting the chain directly on to the spring is no big deal. But the puzzle fooled this monkey, and I missed ‘Castle’ for nothing.

I’m going to pester Tim again this week and see what the deal is with my cylinders.

The Telltale Heart is no longer beating.

4 hours.

Today I started the fix on something I should have done a long time ago. When I first started building this thing in late 2005, I knew FA about how airplane parts go together. I also had pretty weak skills in precision metal cutting. I didn’t know how big the saw kerf was, I didn’t know how much metal would come off from the grinding wheel, and several other things that are pretty much muscle memory now. When I was building the horizontal stabilizer in 2006, I still didn’t quite have the knack of it,

This is what I’m talking about:

This is the forward reinforcing angle that spans the forward spar of the horizontal stabilizer. This part is structural. I probably shaved off too much metal from the bottom when making the angled tab, so that’s what killed me on the edge distance. Then I further beat the crap out of the two inboard ribs during the process of sticking it all together. I sent photos to Van’s of the whole sad-looking assembly and they told me it was ugly but not a problem structurally. Maybe it is OK, but it’s been bugging me for nearly four years. So today I ripped out the ribs and the HS-710 angle. New parts are on their way from the mothership.

It’s going to be rock solid this time, and I know that because I now know HOW those parts are all supposed to fit together, so I’ll have a drilling and riveting strategy that insures everything has the proper edge distance. I also have a tungsten bucking bar that I didn’t have before, and I have a decent array of skills built up over the last 4+ years so I think I can rivet the new pieces together without giving them that hand-hammered bronze-age look.

Fun with the Firewall

5 hours.

I can walk around that plane all day long and find things to not do because one of the ducks isn’t in its assigned row. Problem is, the days are getting shorter and I can’t wait for everything to fall into place. The firewall has been one of those things. I still need to make holes for wire pass-throughs, and bolt various things to it, some unknown as to their specific configurations and form factors. But sometimes, you have to make a move. Today I fire-sealed the cabin heat box and installed the firewall recess.

This is halfway through the process. The cabin heat box is done, and the battery box is in place. , All the gaps and openings need to be sealed up in case there’s an engine fire. A gasoline-accelerated fire in the engine compartment fanned by a 200mph gale would make every hole, crack, and gap a 2000-degree blowtorch aimed right at the occupants’ legs, something we’d very much like to avoid. I’m using 3M Fire Barrier 2000 in all those cracks. Hi-temp RTV is rated for 700 degrees, this is rated for 2000.

Hopefully this won’t be an issue. You’re not supposed to use rigid tubing from anything fixed to the airframe to anything attached to the engine. The reason for this is obvious: the engine vibration will fatigue and split a hard line in a fairly short amount of time. This is why you’re supposed to use braided steel and flexible, firesleeved hoses for fuel lines between the firewall and the fuel pump.

Since I was fire-sealing everything, I figured why not, let’s put the engine mount on. After sealing the lower firewall corners and the brake reservoir, I got the engine mount on, permanently. I considered being a showoff and putting the plane up on the gear, but then I realized I’d omitted a rather important detail: I’d forgotten to notch out a section of the lower firewall corners to make room for the gear legs. Not one of my prouder moments. But I was able to scribe out a section to remove, which I did, and it would have been really easy if it hadn’t been for the fact that stainless steel sucks to work with. It bites, so you have to file the edges down. It also hardens if you heat it up, with something like a Dremel burr. Finally I was able to get some notches done, but they’re not that pretty. That’s what gear leg fairings are for though, right?

Here’s the firewall recess all riveted in. There’s a bead of fire seal under the flanges in addition to the seams in the recess. I hope that goop doesn’t run too much before it cures.

What happens next? I don’t know. I have the rudder available to work on, maybe I’ll do the taillight.

Landing gear put together.

2 hours.

That’s not saying it won’t come apart again. It’s currently in this state:

I think I’m not kosher on the amount of threads showing on the bolts holding the wheel pant bracket on one leg, but I can sort that out tomorrow. But I have this theory: If things are assembled with all the requisite parts, those individual parts are less likely to grow legs and wander under appliances and places of storage to hang out with the dust bunnies. It’s like the Phantom Graveyard of Lost Hardware under there, like that scene in Heavy Metal when the B-17 crash lands on the island full of derelict planes, abandoned spaceships, and zombies. But instead of zombies, I have an assortment of fasteners and other hardware.

The gear is ready to rock, but I need to get fire caulk so I can finish up the firewall installation stuff and put the engine mount on. Then I can put the plane on the gear, just for a hoot . Tailwheel’s on, why not give it a test roll?

The engine is still at Tim’s. He’s backlogged, and my engine is all torn down, waiting for inspection. I’m not in a hurry, but I am in a hurry to find out how things cost, because I need to know what my avionics package is going to look like. The way my luck runs with engines, I’ll probably have enough left over to equip 313TD at about the same level as Kern and Rinker Buck’s Piper Cub.