August 2011 Archives

Worked on Cowl Joints

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I drilled both lower side hinges to the cowl.



I then clamped a section of MS20001P4 hinge to the lower cowl on the left side and laid out some holes on approximately 1" centers.



I then drilled all of the holes.



Here's a closeup of the joint.  I'm using MS20001P3 on the upper half since I don't need the extra width.  I installed the P4 on the lower half so that I could bias the hinge up enough to have a small strip of solid hinge material at the joint line.  Doing it the way the plans specify would mean that you would be able to see the hinge ears through the joint which looks pretty crappy.



I received one of two AveoMaxx taxi landing lights from Aircraft Spruce today.  These lights are very compact and very bright, but all LEDs for low power consumption, heat, etc.  They come in a nice anodized aluminum enclosure that will be mounted in my wing tips.  Since they will be mounted a lot farther forward than the typical wingtip landing lights, I'm hoping the longitudinal face of the wing tip cutout won't shade the area in front of the plane from receiving light.  The holes on the top will be used to mount the nav/strobe lights.  There are actually two separate lights in the enclosure.  The center light is the landing light and is comprised of a single massive (nearly 1 square cm) LED that is focused in a fairly tight spot.  Surrounding that is a ring of small LEDs that form the taxi light.  These have a much greater dispersion to more evenly light up the ramp.  I came out at night and tried these, and the light output is very impressive.  Since I'm installing two, I'm hoping that will be plenty of light for night ops.



We got back from a short vacation in Yosemite National Park yesterday, so I got back to work tonight.  I drilled the other P4 hinge to the right side of the cowl then mated the P3 hinges to both sides and installed the upper cowl.  I transferred the hole positions and then drilled the upper half of the hinge to the cowl.  Here's the right side of the cowl.



And here's the left.



Now that the cowl was locked in its final position, I drilled the rest of the holes along the top of the firewall.  The cowl is amazingly rigid now.  Pushing even gently on the cowl moves the whole airplane and there is no perceptible flex in the cowl itself.  If it's this still with just clecoes, I can only imagine how much stiffer everything will be when the hinges are riveted and glassed in place.



The front left corner of the cowl has a small alignment problem.  I'll have to build out the upper cowl to bring it out flush with the lower cowl.



The front right corner also needs a bit of work to make things line up nicely.



Started Oil Door

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I decided to get started on the oil door tonight.  I started by grinding down the edge of the flange to create a better defined joggle.



I then trimmed the door itself and radiused the corners so that the door fits down nicely in the cutout.  The trims on the cowl itself are a little sloppy as you can see below, but that won't matter.  Once I have the door exactly where I like it, I'll put some structural filler here and use the door itself to to mold it perfectly.



I then drilled the hidden hinge to the cowl and door.



The hinge has a spring that will hold the door open while I'm checking the oil.  The door is pretty flimsy right now.  I'm going to need to stiffen it in order for it to work.



Finally, I spent a little time debarring all of the holes I drilled in the cowl attach hinges.  I still have a few more to go, but this makes a big dent in the deburring.



Worked on Cowl Hinges

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Tyson Weihs, one of the co-founders of ForeFlight, stopped by tonight to check out the project along with my buddy Andre.  We spent an hour or so talking about RVs before I got started building.

I spent most of the night working on the cowl attach hinges.  First up was to pull the lower cowl and finish drilling the stainless hinges along the bottom edge of the cowl.  Drilling steel is a pain, and you really want to drill the hinge before drilling the cowl to avoid elongating the hole in the cowl.  Next up, I removed some of the eyelets in the hinge that runs along the top of the firewall.  The hinge pin has to be removed and installed in two separate pieces through the oil door.



I then drilled additional holes in all of the hinges that will bond to the cowl (nine total) and deburred everything.  The small holes will be used for AN426A3-5 rivets (not AN426AD rivets since that can crush the fiberglass).  The larger holes will allow the epoxy/flox mixture to squeeze up through the holes and bond to the layer of glass that will be laid over the rivet shop heads.  This will provide a far stronger joint than just rivets alone.  I will be using West Systems G/Flex epoxy which has a modulus of elasticity of 150,000psi.  This is substantially more flexible than their 105/205 epoxy which has a modulus of elasticity of 450,000psi, but substantially more rigid than adhesive sealants like the MC-236-B2 sealant I used on the tank.



I started prepping the inside of the cowl for a seal coat of epoxy.  I'm going to tint the epoxy white so that it will be easy to see oil or fuel drips.  I've seen other builders just spray paint the inside of the cowl white, but that won't be impervious to solvents like a coat of tinted epoxy will be.



I mixed up some epoxy and microlight filler along with some white tint and applied it to the inside of the bottom cowl.  It started stiffening up before I could finish, but I got about half of it down.  This fills in the pattern left by the honeycomb core to provide a smooth finish and fill in any pinholes.  I'll seal this with some neat epoxy tinted white to provide an easy to clean surface.



I decided to go ahead and mount the com antenna.  My wife gave me a hand with the nuts since you can't reach both sides at the same time.



I then installed a BNC connector on the coax and installed it on the antenna.



I also fabricated a doubler for the transponder antenna.  I'll need a little help riveting this on.



Finally, I fabricated the transponder antenna cable.  It has a BNC connector on one end and a TNC connector on the other.



Finally, I vacuumed out this bay and reinstalled the shelf in preparation for riveting it in place.



With the final trimming of the cowl complete, I pulled the forward top skin off so that I could do some further wiring.  All of the exterior light wires have been coiled up on the cabin floor for the last couple of weeks.  With access to the VP-X again, I finished running all the wiring runs.  I'm probably done with 80% of the load wiring at this point.  I mostly just have the avionics left to do.



I also ran the static tubing up behind the panel so that it can be plumbed to the alt-static switch.



It comes up the firewall with the other wires and then heads over to the left side of the plane and then aft to the instrument panel.



I got up early this morning and finished sealing the inside of the lower cowl.  It doesn't look like applying tinted epoxy is going to work very well.  The coats of epoxy are so thin that they're translucent.  It would take so many coats to make an opaque white layer that it would be pretty heavy.  I'm going to end up just painting this white like most builders do.  The epoxy and filler still did a great job sealing the surface to keep oil from soaking into the fiberglass though.



My buddy Andre stopped by mid-morning and helped me finish riveting in the ELT shelf.  Afterward, I reinstalled the ELT.  We also riveted in the transponder antenna doubler that I fabricated and then I installed the antenna cable.



Finished Tailcone Wiring

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With the ELT shelf riveted in, I wanted to finish up all of the tailcone wiring.  One of the final items on the list is the cabin light wiring.  I ran three 22awg wires from the front up through the top of the baggage bulkhead.  This will be inside the cabin frame support and will connect to a small LED spotlight that will have both white and green lights in it (hence the two red wires and one black ground wire).



I then secured all of the wires from the left conduit with an adel clamp on the ELT shelf rib and some zip ties.



I also ran an additional RG-400 cable through the right conduit for the Garmin GTN-635 GPS antenna.  I had originally planned to mount both GPS antennas (the Garmin and the Dynon) under the cowling, but the Garmin install manual stipulates that GPS antennas not be installed closer than 9" from each other and require a 7.5" minimum radius ground plane under the antenna.  Though under the cowling would likely work just fine most of the time (and I'm still going to mount the Dynon antenna there), I want the highest possible antenna performance for my primary IFR navigator.



I finished all of the wiring runs up to the area behind the subpanel, though the cabin light ground is the only wire I could actually hook up to anything.



I started countersinking the cowl for the rivets used to attach the hinges.  I was originally planning on using a permagrit countersink, but I tried my regular countersink and it did a great job.  I've heard it can dull them, but buying a new one would be cheaper than a permagrit countersink so I don't think it's worth it.



Now that I know where the side hinges will rivet to the firewall, I riveted the sides of the firewall flange above that point.



Then riveted the hinges on below that.  The bottom seven rivets can't be reached with the squeezer, so I'm boing to have to shoot and buck them somehow.



I've been planning on mounting the Dynon GPS antenna under the cowl.  Most builders fabricate a little shelf that runs between the engine mount and the firewall, but that would get in the way when changing the oil.  Since I only have one antenna to mount, I decided to fabricate a small mount that will attach directly to the engine mount.  I placed the straightedge between the top of the firewall and the spinner to see how high I can go.  The actual cowl in convex through here and will actually provide more clearance than this.



The mount is just a short piece of Z channel that I trimmed to fit the antenna.  I'll drill a couple of holes in the bottom flange and attach it to the engine mount with a couple of adel clamps.



For some reason, I decided to install the throttle cable bracket tonight.  I fabricated this bracket months ago, but it needed to be powder coated before it could be installed.  I sprayed a couple of coats of white powder coat on it and baked it for awhile in my toaster oven.



I then drilled the heads of a couple of coarse thread AN4 bolts and installed the bracket to the boss on the front right of the engine.  It was a little tight getting the safety wire installed, but I managed to get it done on the first try.



I'm not sure why I took this picture, but here's a shot of the other side.



Ordered Avionics Stack

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I ordered my avionics stack today.  I'm going with a PS Engineering PMA8000BT audio panel and Garmin GTN 635.  I went back and forth about both units a bit.  I was originally going to install the PMA5000EX audio panel, but ended up deciding the Bluetooth functionality would be worth it for making phone calls and listening to music.  I was also originally planning on installing the GTN 650, but ultimately didn't think I would use the VOR/Loc/Glideslope functionality much.  Switching to the 635 not only saved me about $1,000, but the unit is 0.8 lbs lighter and I probably saved another several pounds of antennas and wiring (not to mention hours of time that I would have spent hooking up the additional antennas).

Tidied Up Wiring

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I spent a little time tonight tidying up some wiring runs under the seats.  I installed an adel clamp on the wires to the left of the center tunnel.  I haven't tightened either of these down fully yet since I want to wait until the GPS antenna cable is adjusted to length and I still need to run the wires for the control sticks.



I installed the adel clamp supporting the wires coming out of the left conduit and added a couple of zip-ties to tie everything together.  It's amazing how solid these wire bundles become when zip-tied together.



I added an adel clamp to keep the pitot/AOA lines held down to avoid interfering with the aileron push tube.  I might have been able to use a zip-tie base attached with a pop-rivet, but I really don't want there to be any possibility of anything coming loose around the flight controls.  You can also see at the top of this picture that I took all of the snap bushings out of the forward holes in each seat rib.  I have no idea why Van's has you drill holes here.  It's a really poor place to put them since they'd have to snake around the control stick brackets.



I also tidied up the wiring aft of the baggage bulkhead.  Everything is firmly secured and well supported.



I stopped by my avionics shop over lunch today and picked up the GA 35 antenna for my GTN 635.  Dynon recommends installing any GPS antennas at least 1' from the ADAHRS, and Garmin recommends installing the GPS antenna with at least 7.5" ground plane all the way around the antenna.  These two recommendations necessitated moving the antenna behind the F-707 bulkhead.  I fabricated a doubler from 0.040" aluminum that matches the outline of the antenna and then installed it to the fuselage.



Here's where the antenna is relative to the aft window.  The ADAHRS is roughly under the aft edge of that piece of paper, putting it roughly 18" from the GPS antenna.



Afterward, I crimped on a TNC connector and ran the antenna cable along the underside of the upper rib next to the Dynon network cable.



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