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Avionics Master Switch

3 hours.

Originally when I built the electrical system, I was of a mind that an avionics master switch is a single point of failure and should be avoided.  I have since changed my mind.  First,  my comm2 radio has no off switch (MGL V6), second, I really want my comm and audio panel volume settings to be set and left alone.   Third, and this is the most important thing, I want to minimize the danger of transient voltage spikes damaging very expensive equipment when starting and shutting down the engine.

The simple fix is adding an avionics fuse block inline with the Endurance bus with a switch in between.   The EFIS has its own power switch and will remain on the E-bus.  So far so good, and the install went smoothly, except for the time I dropped the passenger stick through-bolt down the hole between the center section ribs.  That was fun, because my fat hand doesn’t fit past the stick through the access hole, and I wasn’t about to take the floor panel off.   I then fished around with a magnetic screwdriver bit holder, and that sort of worked, but then somehow, I dropped that in there too.   After a brief bit of grumbling (seriously, how long can you stay mad being at an airport), I was able to fish that out of there with a couple of long aircraft drill bits held like chopsticks.   After that, I got my bolt back.

I forgot to bring little zip-ties to re-secure the DB25 connector on the pax stick.  Also, I forgot to bring my little screwdriver so I could tighten up the connector on the back of COMM 2, which will get fixed tomorrow morning before work.

So now I’m less worried about blowing up my avionics than I was.  But the process was suspiciously painless, right up until that last bit.

Magneto Mystery Solved.

7 hours.

So remember when I was trying to debug a nasty popping, backfiring, horrible magneto?  Yeah, like it was yesterday.   Matter of fact, it was yesterday.  And today.  Every engine test since first start has been a mess and the reasons are plentiful, going back to when David and I first tried to get it running a while ago. This has been going on for 3 weekends now.

First, I modified Bob Nuckolls’s electrical system diagram to include a pushbutton starter switch in addition to the spring-loaded (ON/OFF/(MOMENTARY ON) switch.  Turns out you can’t have both.  What wound up happening here is that when the spring-loaded switch was set back to center ON, it was grounding out the one magneto capable of running the engine.  I’ll get to that in a second.  In addition to that, we were never sure which wire went to which magneto, because those two bits of shielded cable never got labeled.   Lesson #1.  We did eventually test that and got the wires running to the correct mags.  We think.

If I wanted to keep my stick pushbutton start, the  On/OFF/On switches would have to go and be replaced with dual-pole ON/ON switches, which would allow me to disengage the start circuit as well as ground the mags, making them cold and safe.   I replaced those switches, and maybe here, maybe the step before, the wires got switched again and left went to right and right went to left.  The good news is that with these switches installed, the engine fired up.  Ran a little rough, but it was a damn sight better than last week.   OK, shut down right mag for RPM drop.  No drop.  Shut down left mag for RPM drop.  Bang, boom, sput, cough.

As you might expect, shutting down the “left” mag caused the engine to pop and misfire, so it was assumed that something was wrong with the right magneto.  First thing we did was switch it out for a good one, the one my hangar mate had in a plastic bag for eventual installation on his RV9.  Timed it to the engine, buzzboxed it, fired the engine up.  Same thing.   At this point it was a head-scratcher, because here we’ve just put a brand new Slick 4300 series magneto on the right side of the engine and we’re still getting popping, misfiring, the same thing.

Oh, one important detail I’ve left out of this story so far:  I don’t know how many times we pulled the magnetos and checked and rechecked the engine timing.  During this process somwhere, I the timing pin (an allen wrench or a pop rivet)  in the distributor block when we pulled the engine through to set up the engine timing.  Maybe I even did it at home before moving to the airport.  At one point, I pulled a very bent allen wrench out of the left mag and a bent pop rivet out of the right one.

I assumed that because the “left” magneto was working fine, it was the right one that was messed up, but that couldn’t be because I’ve just replaced it with a brand stinking new one.   Matter of fact, when I opened up the mag I’d pulled out of the airplane, everything looked fine.  The distributor gears were OK, the rotor was fine, and the distributor block wasn’t cracked or anything.   I left Ron’s spare mag on there  because I had more debugging to do and I didn’t want to change back to the original mag, which may have been compromised in some way, even though none was evident.

Yesterday, I thought, hm, maybe the wire going to the magneto is shorted somewhere.   So I disconnected the terminals from the mag (and took the harness cap off to be safe) and tested them for continuity.   With the switch set to “ON” there should have been no beep from my multimeter.   I got a beep.   AHA!   There’s a short in the shielded P-Lead wire!  So what do i do then? Cut the ends off the wire to the “right” mag at the switch, thinking maybe the connection shorts intermittently because I cut the insulation of the wire and the shield’s touching it.   Still beeped.   OK, that wasn’t it.. Maybe it’s at the mag end.   Cut that off.   Strip back some cable so I can test the ends.   Still beeped.   At that point the day was pretty much over.

Last night I was falling asleep reading Book 7 of Stephen King’s Dark Tower cycle and it hit me.  What if the wires were on the wrong switches?  Left is right, right is left.  That would mean three things:  One, the “short” in the P-lead cable isn’t a short at all.   The other switch was cold, so the multimeter would have beeped no matter what, because disconnecting from the switch and still connected to the other mag, there’s enough continuity for a beep.   At the mag end, testing the wires would produce a beep because they’re going to a switch in the cold/safe position.   Two, this would also mean that I’ve been debugging the wrong magneto for the last two weekends in a row.  All my attention was focused on the wrong part of the system and it didn’t occur to me to check something as simple as wiring because I’d already gone down that rabbit hole and figured I’d verified it multiple times.   Three, I’m an idiot.  Once for leaving the timing pin in the left magneto, twice for not checking the wiring, and three times for assuming things were correct in places where they weren’t.

I hadn’t planned to go to the airport today, but I did.  I figured it would only take me a couple of hours to sort this out, so I loaded up the bike and headed to OXR.   First thing I did was pull the right magneto and check the internal parts for damage.   This was onerous.  I routed my hoses and cables so they trap the magneto in a cage with no hole big enough to let it exit.   I had to take the oil pressure sensor hose off to extract the magneto.  It always makes me nervous doing that.   All I need is for a lock washer to fall down inside the engine accessory case and I’m totally screwed.   I did manage to extract it, and got it up on the bench, where I was able to remove the back cover and the distributor block.   Guess what I found:

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That right there is the rotor gear.  This spins on the shaft that opens and closes the points, making the spark.  Notice that there are two teeth missing, and several of the others are damaged.   The bottom line here is that no matter how carefully the engine timing is done, there is no way in hell this gear will drive the distributor gear in any way that will provide a spark at the right time.  To prove this out, I reassembled and installed the old right mag on the left side of the engine.   I have two impulse-coupled mags, I can do this.   I remembered to take the timing pin out, say thankya and may it do ya fine (Dark Tower, remember?).   Then, miracle of miracles happened.   The buzzbox timing process, which I am now intimately familiar with, went just like all the documentation, descriptions, and YouTube videos said it would.  Snap the impulse couplers, back off enough to get rid of gear lash, then move the prop forward to 20 degrees BTDC.  twist one mag until the light just goes on or off, depending on what it’s doing when you turn the box on.   Back the prop off again, then move it back to 20.  The light should go on right there.   Twist the other mag until the same thing happens.   The trick is to get both lights to come on at the same exact time.

With two teeth missing off the rotor gear that wasn’t ever going to happen either, so wiggling the mag back and forth on the dead spot betwene those teeth isn’t going to do squat.

But joy of joys, sing hosannah to the heavens, with two properly timed and synchronized magnetos, that engine runs smooth and strong, like a big cat purring.   Ron helped me push the ship out into the sun and I fired it up.  Rock solid, dead on.  RPM drop on both mags, just like that beat-up Cherokee I learned on.

Now I get to go back in and clean up the mess I made testing everything.  Re-wrap my wires, safety-wire the governor, everything back int its place.

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5 hours.

Today was about putting things back together and getting a handle on some of the chaos.   The first bit of good news is that the oil temperature probe works fine.  I pulled it out of the engine and hit it with a heat gun and sure enough, it gave me a reading.  So I’m not going to worry about that anymore.   I secured the wires back in their bundle and i’m calling that squawk done.

I also wasn’t real happy about the weird way I had the fuel pressure sensor set up.  The Adel clamp holding it was maybe a size bigger than it should have been, and this way seems more secure:

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As I mentioned last time, I flipped the governor arm over and it seems to work just fine:

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My biggest problem with doing it this way was where the injector line was going to go.   A piece of angle solved that.   Now it’s out of the way, and less likely to be heat-soaked down near the cylinder.  I still haven’t safety-wired the screws yet, or put the cotter pin in the cable attach nut, But I think this is how it’ll stay.

Last week, Owen recommended tightening up the tailwheel chains.   Van’s recommends a half an inch of slack, but if you ask ten different people how they like their tailwheel chains, and you’ll get at least five different answers. But my chains had an inch of slack, and if I took a link out, I’d have none.  But I did take a link out of each side, and while there isn’t really any dangling slack, I can move the chains up and down by about a half an inch, and I’ll tell you, based on today’s test, it taxis just fine:

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That little gap in the rudder fairing is kind of annoying.   Not exactly sure what to do there, except put nutplates in there and hope for the best.

Today’s test was all about seeing how things went with the cowl on.  First, I wanted to make sure I could actually get the cowl on with the flipped-over governor bracket making the cable rise a bit more than it did before.   Turns out, I’ve got about 1/8″ of clearance between the cable and the top cowl, which is good enough.   And from what I remember, the cowl inflates a little in flight, so that 1/8″ becomes a little more.   And that’s fine.   I just don’t want to have to put a clearance wart in the cowl to accommodate the cable.

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But before taking it out for another test, this adjustment had to be made to the baffle material on the lower cowl.  I had to cut it back a bit, because it was covering up about 6 square inches of air intake.   Bad.   So with this mod in place, I put the top cowl on, and pinned it down.   Then I put a few of the floor panels in, and you’d be surprised how much the plane stiffens up with the reinforcing action of the panels.   I ran it up, then shut down the left mag.  Engine died.   Started it again, repeated.   OK, right mag dead.   Grr.   Still runs fine on one though.

So I said screw it, let’s taxi it around.  The new tailwheel chain tension was much better.  Now it’s more like Mickey’s Citabria, and the ground handling is nice!  I took it to the end of the hangar row, turned right, went down the next row, turned right again, then went back to the barn.  CHT’s never got above 210.   As soon as I get this mag situation sorted out, it’s time for ground runs.

\Last time, shutting off the left Mag made a lot of popping and missing, which I attributed to timing.   This time, I’m pretty sure the timing’s right, but now shutting off the right mag shuts off the engine.  Now, it might have something to do with the fact that I left the pop-rivet I was using for a timing pin in the hole when I pulled the prop through, but I can’t say for sure.   What I do know is that before, on the right mag, I had backfiring.   Now I’ve got squat.

 

Equal parts forward and back.

6 hours.

One of these days, I’ll move forward without moving backwards.  Today I had to dismount the EFIS in preparation for taking it to MGL Avionics.   Apparently the OAT module is fried.  I tried it with a new probe last week, no dice.   Maybe, if I’m lucky, I’ll be able to drop it off tomorrow on my lunch hour.   Other than that annoyance, I got the tailwheel hardware primed, something I should have done long ago, and I got my spark plugs torqued in.   But now, for some mysterious reason, the tailwheel steering chains don’t reach their mounting points on the rudder anymore.   It’s possible I had the steering link on upside down/backwards, which would have accounted for the missing 3/4″ of chain necessary to bridge the gap between what I need and what I’ve got.   Looks like I’ll be ordering another set of tailwheel chains.  Grumble.

Anyway, once I get my EFIS back from the shop, it’ll be time to prepare the engine for first start.

On another note, I’m progressing nicely in my tailwheel training.   We flew from Torrance to Hawthorne, where I did 8 landings, unassisted.   Apparently I CAN land a Citabria in 3-point attitude.   At least when the wind is coming at me and I set up the approach right.

Still more connections.

6.5 hours.

A bit of a late start.   Since I took this week off, yesterday was my first weekday commute to OXR.   I went via PCH, which is nice enough, but it took a little longer, especially during rush hour.

I finished installing the rudder cable linkages to the pedals, so that’s another thing done.   I also got the pitch trim servo wired in.  I’ll need to adjust the throw on the trim servo, but that’s essentially done.

Then I went back to wing wiring.   I got the strobe and lights connected for the right wing, plus the autopilot servo.  It was lots of tedious, fiddly stripping and crimping in small, awkward places, which has an extra coating of suck because I did something to my right elbow and now operating hand tools like crimpers is fairly painful.

Left to do is connecting the VOR antenna wire (This may become an ADSB antenna wire if they phase out VOR) in the left wing and putting in a couple of pieces of UHMW tape here and there.  If I can have lights, strobes and VOR by the weekend, I’ll count myself lucky.

 

The Tall Tail

4 hours.

Finally got the tail on.   After some struggles with the rudder bottom and some adjustment of the bearings to make it swing more freely, I got the rudder on, listening to Larry Niven’s “Draco Tavern” on audiobook.   It’s amazing how well audiobooks pass the time.

The rudder wasn’t the only thing I got done; I installed the tailwheel chains and torqued down the tailwheel attach bolts.   Cannot believe I didn’t do those bolts earlier.  I’m lucky I didn’t find the tailwheel rattling around in the truck once we got to the airport.

The rudder bottom may have to have a few things fixed.  I ate away a lot of glass trying to get it to fit properly, so I might have to build it up a bit. I still owe a couple of wraps of UHMW tape around the strobe and light wires.

The only real struggle came from the trim control wire.  I had to get it to pass through a couple of rubber grommets and make its way to the area forward of the VS spar under the empennage fairing.   This was not fun, but my hangar mate Ron helped out by shining a light inside the HS so i could see to jam the wire into the grommet with the two fingers I could stick through the lightening hole.

Somehow I misplaced the cut-off DB9 connector which would have showed me the pinouts for wiring the two ends of the trim wire together.   I remembered writing it down somewhere, but it wasn’t where I thought it was: I devoted an entry on this website to wiring color codes and pinouts but I didn’t remember that at the time.   I called Shelley to see if I’d written it down on some papers I’d stuck to the cork board in the erstwhile shop and she sent me photos of them, but no joy.   I didn’t think to look on this blog, but searching for stuff like that through an iPhone is no fun.

So that’s that.   Just have to get the the trim wired up and a couple of loose ends and the tail is on and attached.   I pushed the plane out into the sun for a photoshoot before I headed home.

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Attaching the rudder.

6 hours.

Today was both  productive and frustrating.   The intent was to finish up all things rudder, which didn’t happen, but got pretty close.

I spent a bit of time making some more clearance between the rudder/elevator tips and their corresponding stabilizer tips.   To get a perfectly matched arc shape, I wrapped successive layers of coarse-grit sandpaper around the tip and counterweight, and swinging the part through its travel sanded the stabilizer tip into the shape I needed.   Easy.   But the main focus of the day was the rudder, both wiring and attaching the rudder bottom.

First thing I needed to do was set up the rudder bottom attach, which involved putting  platenuts on the attach strips so I can remove the rudder bottom later if I need to.  This was a time-consuming process, which does not fit well with my “final assembly” ethic.    It needed to be done, along with wiring the tail lamp and strobe.    That went better than expected, but I had to run a ground wire for the tail lamp, which I’d forgotten to do the whole time I was working on stuff back there.

 

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Platenuts.   But not many.

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I have no idea why I took this shot.   But this is right about when it started to go south.  When I put the vertical stabilizer on, I put it on with the bolt heads on the inside of the fuselage, with the threads pointing aft.   When I put the rudder on and tried to fit the rudder bottom to it, there was no way in hell the rudder bottom was going to fit.   So I started shaving down the fiberglass on the rudder bottom, which helped.   The major issue was that with the bolts pointed in the wrong direction, the rudder bottom interfered with the center bolt.

Now, this is where you’re saying “turn the bolts around, dude.”   If you had said that when I ran into this problem, it would have helped.  But no, yours truly had to do it the hard way.   I removed the rudder, and figured, hey, I’ll just let the rod end bearings, the ones holding the rudder to the stabilizer, out a bit and see if I can clear those threads.   Nope.   Several tries. Nope.   Without my fancy rod-end-bearing tool, even.   Nope.   After a few rounds of this, I smartened up and flipped the bolts around, and everything clears just fine.   But now my rudder is way out of alignment, and even though it travels nicely and freely, there’s  much bigger gap at the bottom than there is at the top and this will not do.

The good news is that the tail lamp works fine, no smoke, no blown fuses.   The strobe doesn’t, but that’s probably because the strobe pack was last switched on and run some time during the Bush administration and the capacitors are hosed.   I’ll be needing a replacement, and soon, because the wings are going to go on and I’ll need to test that all the blinkenlights work.

So for next time, bring the fancy rod end bearing tool (a couple of scrap pieces of PVC pipe).

 

 

Wings closed, part 1

7 hours.

Yesterday, my friend Derek came by for a few hours and helped me rivet the bottom wing skins on. Derek is peripherally responsible for me being where I am today with regard to aviation: Flying leads to skydiving, skydiving leads back to flying and flying lessons, rental airplanes lead to homebuilts. Before he arrived, I did some pondering about the best way to rivet the wing skins on, and the first two things that needed to happen were the removal of the aileron push tubes and the flaps, so I did that.

Riveting the skins on the wings would have been really tough without help, especially the inboard rows near the bellcrank. As it was, I really had to stretch to get the bucking bar up in there far enough to reach the rivets closest to the aft wing spar. But it gets easier as you move outboard, and we finished off the left wing yesterday afternoon. Derek had to leave at around 3-ish: newborns really don’t care all that much about Daddy’s friends’ projects, but I kept going.

Before he left, Derek helped me get the double row of rivets on the right wing, then I got going on the rest. To say that riveting those big bastards by yourself is awkward would be like saying Stephen King sells a lot of books. Fortunately, the skins do bend quite a bit, and I wish I had a photo to show you how I did it, but the general gist of it this:

With the double row riveted, cleco the spar side and leading edge side holes together. Then climb in between the skin and the ribs, which will allow you to get a hand and a bucking bar in through the lightening holes to just about anywhere you need to go. And it should go without saying, remove the blue stuff from the inside of the skin before it gets riveted on, or you’re going to have a lot of fun later. Good thing I remembered this before we got too far along, but if you’re reading this, I hope it reminds you before you buy yourself a long night of failure-drinking.

I thought the autopilot servo was going to cause a lot of problems, but with the push tubes out of the way, it was really a non-issue. By myself, I got another row done, up to the access panel for the bellcrank, then quit for the day. I was sore and tired. Even with help, riveting wing skins on is like yoga for gearheads.

Left to do: the remaining skin rivets, and some minor wiring cleanup, since I replaced the puny 14-ga wire intended for the landing lights with a much beefier 10-ga flavor.

More odds and ends

4 hours.

A few things here and there. I installed the MAP tubing and put a couple of heat shields on the pipes to protect the throttle and mixture cables. I also installed the canopy seal, which is going to need some assistance from some RTV or proseal. I do think firewall forward is just about done, though. The cabin heat SCAT tube rubs on the engine mount a little, but some UHMW tape should fix that. The two things I did that were of major importance were the autopilot test and getting that ridiculous piece of lead off the flange of the left elevator counterweight rib.

A while back, I’d balanced out my elevators, or so I thought. You’re supposed to put the elevator tips on, then drill holes in the lead weight until the elevator balances. Well, guess what? You’re not supposed to have the elevators connected when you do this. I discovered this, freaked out, then riveted a flat piece of lead (cut from an extra counterweight) to the outboard rib.

When I put that away, thinking I was just about the smartest cat in the whole barn, I started imagining the kind of beating a control surface takes in flight. So what happens to a little piece of lead riveted to this structure with a couple of Cherry countersunk blind rivets? The piece of lead comes off and somehow jams the elevator in the dive position and I go screaming downward like a holed Stuka, straight into a busload of orphans on the 405. This has bothered me for months, but I could never find a good opportunity to fix it until Saturday. I drilled out the rivets and put the lead back in a drawer. I also read about a neat trick you can do when balancing your elevators: Pour some lead shot into the tip through the tooling hole in the rib until th elevator balances out, then stick it in place with epoxy resin. Even if it’s not perfect, bias it a little heavy, because paint will change the balance.

I also mounted the MGL GPS antenna on the top side of the glare shield. It works; I get an intermittent GPS position while still inside the guest house.

Oh and one other thing: I dragged the wing cradle over to the shop and tested out the bank servo of the autopilot. Since I actually followed a wiring plan and wired the fuselage-side and the wing side according to it, I was able to test out both servos simultaneously. I do need to make a new ground connection though. The ground from the servo bracket sucks and I was only able to get a good ground by cleco-clamping the ground terminal to a wing rib.

More bits and bobs

5 hours.

Since we’re now undertaking a remodel of the downstairs (as if it’s not crazy enough around here) the pressure is on to get the plane done and get it out of the guest house. I’ve been finding all the fiddly things to do and doing them, per last week’s list.

The alt air cable adventures continue. The bracket’s done, and now there’s a hole in the firewall. Suck part is that I have the wrong eyeball, I need the .188 and I have the .210, so it doesn’t actually seal much of anything. New one is on order. I reinstalled the flap brace and drilled the horizontal stabilizer to the the fuse. I had to do this because I replaced the HS-710 bracket a while back because it was crap and I never got around to it.

The panel is also labeled! This is quite nice, but I still need to put the N number on it, as well as the placard that says, “I built this plane, so don’t go looking for certification.”

Cooling blast tube for the alternator is installed, but only halfway, it needs to be secured in such a way that it blows on the alternator. Other blast tubes need to be installed for the magnetos, and then I have to get serious about hoses and control cables.