November 2011 Archives

I mentioned a few weeks ago that there was a flaw in my annunciator control circuit.  I redesigned it to provide a pull down resistor for the transistor base and a pull up resistor for the transistor collector.  I received the circuits yesterday and quickly assembled one, but it was not working as expected.  It was late, so I put it off until tonight.

I got started tonight trying to diagnose the misbehaving circuit.  The first three annunciator lights were working as expected, but all of the others (both some high and some low triggers) were misbehaving.  I measured the voltages at various points in the circuit, but they really didn't make sense.  It was almost as if I had installed PNP transistors instead of NPN transistors.  I checked the bag from Radio Shack and they were indeed NPN.  I breadboarded a single light control circuit and still couldn't get it to work properly.  At this point, I was beginning to wonder if I had completely forgotten my circuit design skills from university.  I was disassembling the breadboard circuit and noticed that the transistor was smoking hot.  This shouldn't have happened because the transistor should either be fully off or fully saturated.  In either case, the power dissipated in the transistor should have been essentially zero.

It was really starting to seem like the only explanation was that it was a PNP transistor.  I looked up the part number on the transistor and sure enough it was a PNP.  I went through the whole bag from Radio Shack and sure enough, every transistor was a PNP despite the bag indicating they were NPN.  I started desoldering the transistors off of the board and noticed the first three (the circuits that worked) were NPNs that I had left over from the first circuit I built.  This really pissed me off.  I wasted hours trying to diagnose a problem caused by Radio Shack's mislabeled transistors.

Anyway, I replaced all of the incorrect transistors and unsurprisingly, the circuit worked flawlessly.  All of the annunciator lights have nice sharp on/off transitions and work exactly as expected.



Mated the Wings

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My brother Seth flew out from KY yesterday to help me mate the wings.  The weather was spotty in the morning, so we got started a little later that I'd have liked.  We pulled the plane out into the driveway and temporarily fit the wings with some hardware store 7/16" bolts.



Next up, we leveled the fuselage laterally and hung two plumb bobs off of each wings.  I tied a piece of fishing line to the cord on the outer two plumb bobs so that I could easily compare the position of the inner two plumb bob cords to the line to see if the wings had any sweep in them.  I also took some measurements from the tail to make sure each wing had the same amount of sweep.  Finally, I checked the wing incidence on both sides to make sure they were the same.

With the wings straight, I installed the flaps to see how they fit against the fuselage.  The good news is that the height on both sides is perfect and the inboard end of the flap skins just kisses the bottom of the fuselage.  Unfortunately, with the wings perfectly straight, the joint between the flaps and the side of the fuselage wasn't uniform.  The gap got progressively wider towards the trailing edge of the flap.  I decided to sweep the wings back slightly to make the gap uniform (I probably only brought the wing tips back 1/4" or so from straight across).  This will make no discernible difference in the flying qualities, but the aesthetics of the flap/fuselage intersection are significantly improved.



After triple checking everything, I laid out some marks to ensure that I had 5/8" of edge distance (from the center of the bolt) in all pieces, then progressively drilled out the hole to just under the final size.  I then used a 0.3115" reamer to bring the hole up to final size providing a snug fit for the bolt.  I used a drill cup on the first three sizes to ensure that I was drilling absolutely perpendicular to the material.



My buddy Andre dropped by to check out the progress, and we drilled the bottom wing skin and the wing root fairings for #8 screws and my brother trimmed them to the fuselage.



Next, I installed the flaps and pushrods and cut out the flap pushrod holes.  These are odd shaped holes due to the changing geometry between the flap weldment and the flap as they're moved up and down.



Heres a rough idea what the hole on the left side looks like.



The side of the fuselage has an arch shaped hole to clear the end of the flap pushrod when the flaps are fully retracted.



The bottom of the fuselage has a slanted and tapering hole to provide clearance for the pushrod and it moves through its range of motion.  I have about 1/8" all around the pushrod in all positions.



Seth removed the tank attach brackets and bent them so that they're flush against the side of the plane and flush with the back of the fuel tank attach bracket.  Afterward, I drilled the fuel tank attach bracket for the bolt that ties these together.  Once the wings are back off the plane, I install a nutplate on each bracket to allow these to be screwed together.



I was getting really damn cold.  I was still in shorts and a long sleeve t-shirt, and it had dropped to 46º before I gave up and decided to call it a night.  Hopefully I can rig the ailerons tomorrow morning pretty quickly.

Rigged Ailerons

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I got started this morning by adjusting all of the aileron pushrods so that both ailerons are aligned with the flaps when the sticks are perfectly vertical and I had the same number of threads showing on each end of the pushrods.  I then torqued all of the jam nuts down and applied torque seal.

Next, I figured out what will work for the aileron stops.  These are 1/2" long, 5/8" diameter spacers with a 3/16" hole in the middle.  I probably need to shorten them slightly to allow me to insert the appropriate washers to give the bearing some play.



This gives me 30.2º upward deflection (25º-32º is the recommended range).



And 16.5º downward deflection (15º-17º recommended range).



My brother and I pulled the wings off and got them covered and the plane back in the garage just as the rain started.  I wasn't able to fabricate the fuel lines, but those can happen after the wings are installed for good.



I deburred and dimpled the center bottom skin for #8 screws.  These will attach this skin to the bottom of the wing.



I also deburred the holes in the rear spar carrythrough.



I wired the copilot's headset jacks tonight.  I wired the pilot's side weeks ago, but for some reason didn't get around to the copilot's side until tonight.



On this side, I routed the wires over the duct like I meant to do on the pilot's side.  I'll secure these wires a little better later.



I drilled a small hole in the canopy latch handle and tapped it for a spring.  Unfortunately, when I installed the spring, the plastic tip sheared off, so I have to order another one.



Since I had to stop working on the canopy latch handle, I decided to install the DB-37 shell on the annunciator control circuit connector.



More Misc Fuselage Tasks

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My wife and I celebrated our 11 year wedding anniversary tonight.  She had to get up early for work tomorrow though, so I came out to the garage for a few minutes tonight to knock a few tasks off the to-do list.  I got started by crawling under the fuselage and deburring/scotchbriting the flap pushrod holes.

After that, I decided to torque and seal a bunch of the fuselage fasteners that are in for good.  First up, I retorqued the center pushrod jam nuts and sealed them.



Next, I torqued and sealed the bolts that secure the center pushrod to the control sticks.



Finally, I torqued and sealed the bolts that attach the tank attach brackets to the fuselage.



Rigged Elevators

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I finished drilling the aft deck and longerons to the elevator up stop.



I also finished drilling/reaming the forward vertical stabilizer support bracket to the forward spar of the horizontal stabilizer.



The elevator down stop needed quite a bit of material removed to achieve the recommended amount of deflection.



With the up stop manufactured to plans, I get 31.1º of upward deflection (25º-30º is the specified range).  It looks like a number of builders have ended up with slightly more than the 30º limit.



With the adjusted down stop, I can reach 24º deflection from neutral (20º-25º is the specified range).  Since I plan on doing quite a bit of acro, I wanted to get near the upper limit.



Afterward, I adjusted all of the elevator pushrods to length and torqued the jam nuts.



I had to lengthen the servo pushrod from 6" to 6 3/16" center to center to put it at 90º to the servo arm when the elevators are neutral.  I also took the opportunity to prime the servo pushrod and torque everything down.  I still have the forward elevator pushrod to do and the final bellcrank connections to install/torque.



I finished up the forward elevator pushrod and installed it for good.  Putting the washers between the bellcrank arms and the bearing was a real pain in the ass and required using a washer wrench and looking in a mirror to see what I was doing.  I just noticed that I forgot to add torque seal to the jam nut on the rod end bearing.



I also installed the forward end of the aft elevator pushrod for good.  This didn't need washers since it uses a larger bearing.



Installing the forward end of the forward elevator pushrod was also a real pain because the aileron interconnect pushrod really gets in the way.  This also needed washers between the forks of the arm, but at least I didn't have to use a mirror to see what I was doing.



I finished drilling the vertical stabilizer forward spar to the attach bracket and deburred it.



I also epoxied a washer to the forward side of the vertical stabilizer rear spar on the left side since the vertical stabilizer is twisted to the left slightly to counteract the left turning tendency of the airplane.  I also countersunk and installed an AN426 washer in the center hole here since I had to drill out the AN470 rivet I installed there.



When I drilled the bottom of the vertical stabilizer to the tailwheel mount bracket and aft bulkhead, it left some tiny metal shavings between the two pieces.  Fortunately, I had this chip chaser which did a great job of cleaning these out so that the two pieces lay flat against each other.



This is not an airplane part, but the attach point on my inspection mirror finally broke.  I mixed up some epoxy and flox and glued it back together.  This is probably far stronger now than it was originally.



I realized a couple of months ago that I needed one of the serial input lines on the GTN connected so that the SkyView could share traffic with it.  The avionics shop mailed me a few extra wires with high-density d-sub pins crimped on, but I've avoided installing them because it is such a pain to remove the connectors.  Anyway, I decided to bite the bullet and do that tonight.  It wasn't too bad.  I had everything back together and the wire harness zip-tied in under an hour.  I went ahead and hooked up three serial in lines in case I ever need to hook anything else up.



Hooked up GTN Serial Input

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No pictures tonight, but I hooked up one of the GTN serial inputs to one of the SkyView serial outputs so that the SkyView can share traffic information with the SkyView.  I configured the SkyView to output TIS traffic, but it wasn't clear how to configure the GTN to receive the traffic. I tried configuring it as a GTX with TIS, but then it wanted to put a transponder control box on the screen (though it had a red X through it).  I'll need to ask on the Dynon forums to see if anyone has any ideas.

Prepped Wings for Riveting

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In preparation for riveting on the wing bottom skins, I wanted to take care of a few last items inside the wings.  First up, I installed the remaining fuel tank z-bracket bolts and torqued/sealed them.  Afterward, I installed the remaining screws that attach the tank (only on the bottom of each wing since that's all I could reach.  I also cleaned out each bay and stripped the plastic from the insides of the wing skins.



This bracket ties the pitot tube mount to the adjacent rib.  I primed it and riveted it to the rib with some AN470 AD3-4 rivets.



Finally, I installed the countersunk nutplates on the top side of each wing aft of the spar.  I'll do the bottom side of the wing aft of the spar after the bottom skins are riveted on.  The nutplates around the inboard edge of the tank will have to wait until I can remove the wings from the stand.



My buddy Andre stopped by and we got started riveting the inboard bottom wing skin on the right wing.  We got all of the rivets in the wing walk ribs (the four closely spaced ribs on the left of the picture) except for the last rib which is easy to reach with the squeezer.  We also finished up the next two ribs on either side of the inner inspection cover.  This took us roughly 2.5 hours.  It seems like such a small amount of riveting for this much time, but some of these rivets were really tough to reach and required multiple tries to get the bucking bar on them.  The rest of the bays should be a bit easier to reach.



I came back out later in the night and decided to get the wing root fairings prepped.  I cleaned up the remaining edges and dimpled the holes for #8 screws.  These can now go on the shelf until I get to the airport and the wings are on for good.



Andre stopped by today and helped me finish riveting the bottom of the right wing.  We had a little scare when the holes wouldn't align correctly.  Basically, if the rear spar holes were clecoed in place, the forward spar holes were off by about 1/32" or so.  The holes in the substructure were farther apart than the holes in the skin.  I finally determined that the flanges at the ends of the ribs can flex a little bit and pulling down on the rear spar compressed these flanges enough to allow me to pull the holes into alignment.  The outer skin is definitely easier than the inner skin.  There is a lot more room between the ribs, and we changed our strategy to rivet the rear spar first while I could reach straight up from below in each bay.  It still took us probably 4-5 hours to finish off this wing.



I installed the last few wires in the avionics interconnect connectors and then installed the shells.  Afterward, I tidied up the wiring bundles a bit.  The loops of extra wires there are the other two (currently) unused GTN serial input lines and the dimming bus wires from the GTN and audio panel in case I choose to hook them up to the SkyView at some point.



One of the biggest sources of air infiltration in the RV is the large hole in the side of the fuselage that allows the aileron pushrod to exit the fuselage.  When flying at high altitudes, ice cold air comes in through this hole and then comes up through the seat belt attach holes, stick boot hole, etc.  It also makes the seat pans really cold which can make sitting in the plane really uncomfortable.  The solution to this is to install boots around the pushrods to block the air.

I installed the aileron pushrod boots from Classic Aero Design.  These are more expensive than others on the market, but after installing them, I think the extra cost is absolutely worth it.  These are very well designed and really easy to install.  First up is to install the mounting ring.  This is flexed into place so that the foam covered flange tucks between the outer fuselage skin and the adjacent rib.  The ring is then expanded outward until the predrilled holes align.  A couple of pop rivets anchors the rings in place.



Next, a strip of adhesive backed foam is adhered to the outside of the flange.  Notice that the inboard edge of the flange is bent outward slightly.



The boot is then installed over the flange and a zip-tie is used to cinch it down against the foam strip.  The bent edge of the flange keeps the end from popping off the flange.  Once the pushrod is installed for good, another foam strip will be adhered to the pushrod and the inner zip-tie will be used to anchor it.



Finally, I tapped into the pitot tube to run a line up to the Gemini.  I spoke with TruTrak yesterday, and the Gemini PFD has been delayed a couple of months, so they're going to send me the Gemini ADI which has the exact same mounting holes and wiring/plumbing connections.  Once the PFD is available, I'll swap the ADI out for it.



Finished Skinning Wings

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Andre stopped by again today (we both had the whole week off work) and helped me rivet the bottom skins on the left wing.  We learned a few lessons on the right wing and were able to knock these out in only about five hours.  The only thing that was a little more complicated on this wing was the pitot tube mount, but it wasn't too bad.



I installed the pitot tube and connected the tubing inside the wing.



I installed the remaining nutplates on the root ribs and then propped the wing up on the leading edge of the tank.  This looks precarious, but it is surprisingly stable.



This allowed me to install all of the nut plates around the inboard edge of the tank skin...



...as well as install the tank attach bracket nutplates.



Finished Interior Lighting

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I decided to finish up the interior lights tonight.  The final light is a small stick-on LED light strip that will cast a dim glow in the footwell so that I can see where my feet are and see the fuel selector.  I'm going to install it to the bottom of the control cable support bracket, but I need to paint it first, so it's just held on with a piece of masking tape right now.  I put a 39kΩ resistor inline with the lights to dim them down pretty far.  The light should be dim enough that it's not a distraction when flying at night.



With all of the wiring done behind the panel, I started zip-tying the bundles.



I also installed a connector shell over the panel ground block wires.  I *think* all of the wiring behind the firewall is complete now except for the final hookups to the TruTrak Gemini and the elevator trim servo.



I wrapped up the flap position sensor installation tonight.  I installed the 4-40 threaded rod between the bracket I fabricated and the position sensor and adjusted the length so that it moves the position sensor arm through the full range of travel.  I then installed a couple of locking jam nuts to keep the rod from moving.



Next, I configured the flaps with a couple of intermediate stop points.  I'll duplicate these settings in the VP-X so that it will automatically stop at these points when I tap the flaps switch.  I probably won't enable that feature during initial flight testing though.  Here's the indication when the flaps are all the way up.



...and here's the indication when the flaps are all the way down.



I installed the heater control box cable tonight.  The control is mounted on the far right of the instrument panel which provides for a fairly easy routing.  The cable curves down over the rudder bars and is attached to one of the firewall support angles with an adel MS21919-WDG3 adel clamp and then passes through a 1/4" hole in the vertical firewall support angle behind the wire bundle.



The housing will be anchored with another adel clamp to the bolt on the right and the protruding wire will attach to the b-nut on the flapper arm.  There's no point hooking these up now since the control cable has to be removed when the instrument panel comes out for paint and labeling.



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