Matt's RV-7 Project

RIP Jerry

Matt — Wed, 12 Nov 2008 03:00:12 +0000

On the way home from the grocery store this evening, I got a call telling me that a friend from work was killed in a plane crash earlier today. Jerry was one of the nicest and most energetic guys you'd ever hope to meet, and one of the best stick and rudder pilots I've ever known. I talked to him on the phone just this morning, and he was his same old self - eager as ever to get back into the air. It's far too early to know what happened, but the weather all across the midwest was pretty crummy today.

In 2005 Jerry and I flew his Super Decathlon to Idaho and back, a trip of 3000 miles in a single week. We went into a lot of the back-country strips and high-altitude airports, and he taught me a lot about taildraggers and mountain flying. The memories from that trip are ones I'll never forget.

Then the next year we went to Florida together to earn our seaplane ratings, which was another unforgettable experience. He got a real kick out of flying a J-3 Cub off the water. I remember we went to this really terrible fish restaurant one night to prepare for the oral exam and checkride, and spent as much time laughing as studying.

Mary and I had planned to spend last weekend at his place in the Ozarks, but I begged off at the last minute because I was tired from getting over a cold. Now I wish I'd gone anyway, but I'm glad I at least had the chance to talk to him a couple times this week.

Jerry was a teetotaler, but you can bet I'm having a drink for him tonight. He was one of my heroes and I'll miss him.

Sorry for the interruption. I promise the next post will not be such a bummer.

Alternate static air valve

Matt — Mon, 10 Nov 2008 03:28:48 +0000

I decided to install an alternate static air valve in my airplane. I figure that for the amount of effort involved, it's cheap insurance against loss of air data due to a drop of rain getting into the static system - see here for a real-world example of why you might want such a thing. Lots of RV builders use a simple fuel drain fitting under the panel as their alt static valve, but (of course) I wanted to use something fancier.

I bought this miniature pneumatic toggle valve for twelve bucks, which is a smoking deal in the aviation world. It works like a SPST switch for air, and the form factor is almost identical to a standard 15/32" electrical switch.

Since the valve wasn't fitted with any kind of anti-rotation mechanism, I used my Dremel to cut a groove in the threads for a keyway washer.

I mounted the valve in the extreme outboard corner of the instrument panel on the pilot's side. It was a little tricky to locate this hole accurately, since the panel frame makes things pretty tight in this area.

To protect against accidental activation of the alt static valve, I put one of those cool spring-loaded switch guards on it. It's fastened to the panel by the nut on the switch body, and I also drilled and tapped holes for a couple of 4-40 screws to improve its resistance to rotation.

These switch guards are so cool. I wish everything had these. A coffee machine, a vacuum cleaner, your iPod - you name it, it becomes more awesome when the switch that turns it on looks like it came out of a T-38 cockpit.

I'll finish plumbing the alt static valve once I get all the rest of the instruments installed. It will be minimally complex - just one extra static air line to run to the valve. Under normal circumstances, the valve is closed and that extra line does nothing. When the switch is flipped, the static system is opened to the cabin. Very simple.

Stick grips

Matt — Fri, 07 Nov 2008 03:10:20 +0000

I bought a pair of custom carved teakwood grips for my control sticks. These are made by a guy in Washington state who, as far as I know, does nothing but turn out these amazing pieces of airplane sculpture. He might also practice zen meditation and catch flies with chopsticks - I really can't be sure. No website, but if you know how to contact him, he can make you a custom set of grips to your specifications. Super nice guy too.

Then I gave them to a friend from work, who very generously ran them through his laser and engraved labels for the switches right onto the wood. It turned out looking great:

The passenger's stick has a push-to-talk (PTT) button and a four-way trim switch. The pilot's stick has switches for PTT, trim, autopilot disconnect, and engine start. Yes, I am putting a start switch on the stick… with a fuel-injected taildragger, you normally need three hands to start the engine: one to turn the key, one to monkey with the throttle and mixture, and one to hold the stick back to keep the airplane from going over on its nose. Since I'm not a Hindu deity I can't manage this very easily, so I will put the starter control right on the pilot's stick grip. There will still be a key switch in series with the button for safety, so you won't be able to accidentally engage the stater if you bump the stick with your soda.

Wiring

Matt — Tue, 28 Oct 2008 02:00:16 +0000

I made a cable to connect my bench power supply to the airplane, where the battery would normally be hooked up. This will let me test the wiring as I go. I also bought the totally sweet mechanic's creeper that's visible in the background. I've always wanted ~~a flimsy excuse to buy~~ one of those.

Mary, ever a good sport, agreed to crawl into the fuselage to help me rivet some tie wrap anchors in place.

…while I was on the creeper below, pulling rivets:

We put in two rows of plastic tie wrap anchors between the firewall and spar. They are attached to the floor with blind rivets that are flush on the exterior skin. Here you can see I've started to run a few wires back to the cargo bay area.

More tie wrap anchors are riveted to the sides of the center tunnel between the forward and aft spars. These will be used to keep the wire bundles away from the elevator pushrod. Some of these were kind of tricky to rivet in, but I'm glad I went to the extra effort instead of cheating by using the self-adhesive kind. I just don't trust them to not eventually come unglued.

So far, most of the wires I've run through the center tunnel go to the aux battery.

I'm still playing with the exact configuration of the aux battery charging circuit.

Planning the routing of wire bundles and then actually running the wires is a delicate, fiddly, and complicated business - so of course I love it. But I'll admit that it doesn't make for very exciting photographs. I will try to post interesting things here, but don't expect a picture of every wire! Once I get farther along I'll post an updated schematic of the airplane, for those who are really into this kind of thing.

Temporarily securing wire bundles

Matt — Mon, 20 Oct 2008 02:45:40 +0000

I've been stringing wires around behind the panel, and experimenting with ways to keep the wire bundles organized as I build them up one wire at a time. A lot of folks do this with tie wraps, but that seems like it could be very wasteful - especially if you're freaky about keeping your wires neat like I am. Every time you need to add another wire to a bundle, you have to clip off the old tie wraps, throw them away, and install another set.

I tried masking tape instead of tie wraps, but I was almost immediately annoyed by how fiddly it was to peel the tape off the wire bundles. So, time for a new idea.

I've had this box, which contains several yards of self-adhesive velcro, laying around my shop for years. I cut out some small pieces and stuck them to each other, so I ended up with a handful of velcro strips with hooks on one side and loops on the other.

These velcro strips can be temporarily wrapped around a wire bundle to keep it from unravelling, and of course being velcro they come off without fuss.

Another way to temporarily keep wire bundles tidy is to use twist ties. I made a bunch out of three-inch lengths of some solid-core copper wire I had laying around. The red insulation will help me remember to eventually replace them with actual tie wraps when I'm finished running wires.

As you can see, this helps keep the wires together in neat bundles (but I'm not wasting a pile of tie wraps).

You can even run the wire ties through one of those little nylon tie wrap anchors I love so much:

I've found that I tend to use both methods in conjunction - velcro strips to hold things when I'm pulling a new wire and I just need an extra hand, and twist ties when I'm through adding a wire to a bundle.

Wiring

Matt — Mon, 20 Oct 2008 02:26:49 +0000

Yes, I am alive… I was laid up and unable to work on the airplane for several days, thanks to my lovely wife who works with sick people and sometimes brings her work home with her. Ahem. Anyway, I have been running a few wires here and there, which is both interesting and challenging - however, it unfortunately does not always lend itself to exciting and dynamic photographs for one's world-wide-web-log. But here are a few pictures nonetheless.

I soldered wire leads to a 5W, 5Ω resistor, then mummified it with heatshrink tubing per this method - the better to keep the resistor leads from breaking off thanks to vibration. I probably didn't really need to label it, but I wanted to see if my heatshrink label printer could do an omega symbol.

I used a clamp to affix the resistor to one of the subpanel ribs, and also bolted in a power diode. These components are part of the circuit that trickle-charges the aux battery.

I ran some wires to the bus master switches, which should soon provide me the ability to turn the various buses on and off. See the next post for an explanation of the red twist-tie looking things.

Here's another view of the festivities. I put in a few snap bushings here and there to allow wire bundles to be routed to various places.

Flap switch guard

Matt — Mon, 29 Sep 2008 02:32:26 +0000

I've been flying a DA20 lately, and in addition to the various things I like about how it handles, I particularly like the little guard thingy that Diamond puts on the DA20's flap switch. I decided to make one for my airplane too, starting with a chunk of 1"x2"x1/16" extruded aluminum.

I drilled a hole for the switch in the exact center of the piece I cut, then sawed off one side of the rectangle. The flap switch handle fits perfectly between the two sides.

After much cutting and filing, I ended up with a halfway decent looking switch guard:

Here's how it looks with the switch handle removed. I drilled and tapped holes for a pair of 4-40 screws; one into the spacer behind the panel, and the other one into the panel frame. Between the screws and the switch mounting nut and keyway washer, the switch guard isn't going anywhere.

A small hole on one side admits a hex wrench, so I can tighten the set screw that keeps the switch handle from spinning off the shaft.

See, it works - you can easily actuate the switch with your finger:

…but foreign objects flying around the cockpit can't accidentally make the flaps go down. Also, please recycle.

Also, Mary was in town this weekend, so here's the usual photo of her looking cute:

Started panel for real

Matt — Sun, 21 Sep 2008 02:45:58 +0000

A month after I submitted the initial set of drawing files, I got the finished panel back from the machine shop. The total bill was… well, I don't even want to write down what I had to pay, but suffice to say it was about quadruple what I was expecting. It turned out pretty nice, but there's no way I would use that same shop again. I would have been better off sending the design to one of the several places that specialize in CNC cutting of airplane panels. Anyway, let's forget that ugliness and keep moving forward.

I fit the various switches, breakers, etc. to the pilot's side panel. Everything fit very well after a little bit of work with a file.

A view of the other side:

Closeup of the alternator circuit breakers… you can see where the machine shop guy made a booboo. The CNC machine was programmed to drag the cutting tool across the surface of the panel, making a nice little trench. Luckily this is not a big deal, since I was already planning to put an engraved placard over the top of this area. If it had been anywhere else, I'd have been pissed.

I used a 1/8" drill to make some little divots on the back side of the panel, for the circuit breaker keyway washers to catch on.

Passenger-side panel installed in the fuselage:

Zero hours on the Hobbs!

Pilot-side panel installed, and looking pretty sweet if I do say so myself. By the way, my plan is to get everything wired up, drill holes for miscellaneous other stuff like parking brake and heat valve cables, and then take it all apart for painting or powder coating (haven't yet decided which).

Same thing from the other side. The canopy deck intrudes a bit on the available behind-panel space, forcing you to think three-dimensionally when locating your panel components. Luckily I got it right, and nothing runs into anything else.

I temporarily installed the radios, and cut some 0.090" filler plates to cover the unused area at the top and bottom of the radio stack.

This is the money shot:

At Oshkosh I good a good deal on this fancy flap switch. It has a little flap-shaped piece of aluminum for a handle, which is a cool touch.

In order to get the switch body to clear the panel frame, I had to make (I hesitate to say "machine" since my tools are fairly primitive) this spacer out of 3/16" stock. Right now it's just captured by the switch, but I may end up riveting it to the panel just because.

I never finished wiring the two buses together at the bus tie diode, so I finished that tonight. This is a power diode with a hefty heatsink, which provides an alternate power path from bus 1 to bus 2, but not the other way. The heatshrink over the terminal ends is just to prevent a short circuit if I drop a wrench across the two terminals while power is applied. Although they are protected by fusible links, I don't want these big power wires flopping around, so I used an adel clamp here. Probably overkill but it makes me feel better.

Here's a view from the other side of the subpanel. All the wires are cinched down tight with tie wraps.

Here's a cool trick… Avery sells these tie wrap bases that have a hole in the middle that's just the right size for an LP4-3 blind rivet. Need to secure a loose wire but don't have anything nearby that you can put a tie wrap around? No problem, just use one of these little guys. I have a feeling I'll be using these by the truckload, all over the airplane.

Engine ground straps

Matt — Wed, 17 Sep 2008 02:36:21 +0000

I installed a braided ground strap between the back of the engine and the firewall ground block. This is the heavy-duty conductor that carries the hundreds of amps of starting current back to the negative terminal of the battery. It's fastened at both ends by adel clamps, so there's no strain on the actual terminal ends.

Closeup of the attachment to the engine… it's secured to one of the auxiliary alternator mounting studs with a nut and lockwasher, and is clamped to a neighboring stud.

Then, because I have equal love for both belt and suspenders, I installed a second one. If the first one were to somehow come off, the full current of the starter would flow back to the negative battery terminal through all the various sensor wires, control cables, etc… quickly turning them into smoke. Thus, a backup ground strap. This one goes between a sump bolt on the left side of the engine, over to a nutplate on the lower firewall. I couldn't find a way to provide strain relief for the ends, but it's only a backup.

There's so much stuff back there that it's hard to get a good picture, but you can sort of see where I put some heatshrink tubing over the second strap. There's no danger of a ground wire shorting to ground, obviously, but I wanted to guard against it accidentally rubbing against the engine mount. It doesn't touch it currently, but it's possible that it might flop around and tear up the powder coat.

Propeller arrived

Matt — Mon, 15 Sep 2008 02:00:54 +0000

Eight and a half weeks after placing the order, the propeller arrived. It is a thing of beauty. Heavy, expensive beauty.

The box is like eight feet long and weighs ninety pounds. With it sitting like this, there's barely any room to walk. Or store empty beer bottles.

I dragged it over by the wings, and raised it up on some boards so the cardboard doesn't soak up moisture from the concrete garage floor.

For reference, here's the current status of the fuselage:

And the rest of the garage… what a mess.