Matt's RV-7 Project » Fuselage

Fuel plumbing rework

Matt — Mon, 03 May 2010 02:03:20 +0000

Lately, most of my free time has been taken up by house chores and other pursuits, leaving little time for the airplane. Today I did manage to redo the fuel plumbing that I'd previously discovered was interfering with the center tunnel runs.

I replaced the straight bulkhead fittings with 45-degree ones:

A view of the new plumbing run on the left side:

Right side:

There's sufficient clearance between the wiring and plumbing now:

Here's what it looks like from the aft side, once the fuel pump/valve/filter assembly is removed from the airplane. Lots of intertwined pipes here and not much room to fit them.

After changing the angle of the banjo fittings on the fuel selector valve, I tightened and safety-wired the nuts:

This is a common sight when you're working with rigid tubing. Cut a line too short, or overbent it, or kinked it, or scratched it? Toss it and start over. My recycle bin has plenty of 3003 aluminum in it this week.

VOR antenna

Matt — Mon, 02 Nov 2009 01:00:55 +0000

A forum thread convinced me to buy and install a traditional cat whisker VOR/ILS antenna on the bottom of the fuselage, rather than the hidden wingtip type often seen on these aircraft. I'm happy to give up half a knot for reliable navigation performance.

I decided to mount the VOR antenna just aft of the F-710 bulkhead, which is just barely accessible when the empennage is attached. A doubler ties into the bulkhead and the F-779 bottom tail skin.

The doubler is made out of 0.063" alclad. Here it's drying after having alodine applied, although in retrospect I'm not exactly sure why I bothered to do this – the "puck" part of the antenna is plastic, and the mounting fasteners don't make electrical contact with anything in there. Oh well, at least it won't corrode.

Here it is riveted in place with the antenna attached via nutplates. The brown stain is alodine that ran downhill while it was drying.

It would be pretty easy to use driven rivets here during the initial build of the tailcone, but on a nearly finished fuselage with the empennage installed it's essentially impossible. Cherry Max rivets to the rescue.

Test-fitting the VOR antenna using some random bolts… when I go to install it for good I'll use AN525 screws instead:

When the rudder and elevators are installed, you won't be able to step on the VOR antenna, so no danger of tripping over it while walking around the back of the airplane.

Yeah, it's hanging out in the breeze, but the airflow down there will be pretty disturbed anyway, so it shouldn't cause too much drag (he said, despite having only a journeyman's understanding of aerodynamics). At least the nav radio reception should be pretty good!

Now that all seven of the antennas on the fuselage are mechanically installed, it's time to move on to wiring them… but that will have to wait for a future work session.

GPS antennas

Matt — Sun, 01 Nov 2009 01:00:52 +0000

My airplane needs a bunch of external antennas on top of the fuselage… one WAAS GPS antenna for each 430W, and a combined GPS/XM antenna for the G3X system. I cut up some 0.063" alclad and made a doubler for each antenna:

I chose to put the two WAAS GPS antennas on either side of the canopy track, about halfway between the F-706 and F-707 bulkheads. As long as they're not placed too far forward, the canopy will pass over the top of them as it lifts up and slides aft. I couldn't put them all the way at the aft end of the canopy track, since the upper fuselage stringers taper together and make it too narrow to for the antenna doublers to fit. I used a yardstick as a spacer to make sure I drilled the doublers parallel to the fuselage centerline, and to ensure adequate space for the canopy slider block to pass by.

Lots of big and small holes drilled in the top of the fuselage… no turning back now! The doublers will be riveted to the inside of the skin, of course, but it's way easier to drill them from the outside. I also had to shape them a bit with hand seamers, since a perfectly flat doubler won't quite lay down on the curved fuselage skin.

The third antenna doubler is located just aft of the F-707 bulkhead. There's plenty of room for the canopy slider block to fit between the antenna and the end of the track, so there should be no problem removing/reinstalling the canopy.

I alodined the doublers and fuselage skin for good electrical bonding, and riveted on floating nutplates.

John came over to help buck the rivets, while I crawled back into the tailcone to drive them from the inside.

The actual riveting went pretty quickly:

A shot of the finished rear antenna doubler:

Now the fuselage has sprouted a crop of antennas:

Victory! Thanks to John for the help.

Spar holes and wiring

Matt — Tue, 08 Sep 2009 02:21:35 +0000

How was your labor day weekend? I drilled two big holes through my airplane's wing spar:

Relax, I got approval from the factory first:

Matt,
Yes, you can provide additional holes within reason. Use the same diameter as we have, and also keep in mind the proper edge distance (2D). Also keep clear of other structure such as seat ribs, spar bars, flanges, brackets, etc.
Joe Blank Builder Support Vans Aircraft Inc.

Since doing this incorrectly would basically ruin the airplane (or at least be extremely time-consuming and painful to repair) I spent a lot of time measuring and contemplating various locations. I eventually picked a spot outboard of the F-716 seat ribs and inboard from the F-783 cover support ribs.

Vertically, the new holes are equidistant from the upper and lower spar reinforcing bars, and have more than enough distance from the existing holes I've been running wires through. I had to pull the wire bundles out of the way to drill the new holes, and I had to use an extension to keep the drill chuck from grinding up the ribs, but it all went just fine.

You can bet I deburred the heck out of these holes.

I wasted no time putting the new wiring holes to use… this is the coax for the transponder antenna, which runs down the right side of the forward cabin floor, goes up through one of the new holes, and then turns inboard before running down the right side of the center tunnel.

After passing through the rear spar, the transponder coax jogs outboard again and runs down the F-727 rib before passing through a bushing in the baggage bulkhead.

This is as far as I got before I had to go mow the lawn. Later on I'll figure out a way to secure the coax to the floor, and put on the BNC connector. By the way, this particular piece of coax is actually the same one I had previously cut and run to go to the nav antenna connection in the left wing root. Subsequently, this thread on VAF convinced me that it would be a better idea to instead use a V-shaped dipole antenna under the tail instead, so I ripped that cable back out. By happy coincidence, it was the perfect length to use for the transponder, so nothing is wasted.

I ran a few other wires this weekend too. The tail and each wing got power wires for the nav and strobe lights, plus a wire to synchronize all three strobes. I have decided to go with LED nav/strobe lights, although since I am an inveterate bet-hedger I made sure to size the wires for the strobe lights so they'd each be sufficient to run a single-output power supply for a more traditional certified light head, should I have a change of heart and decide to go that way instead. I also ran a spare wire to the right wing with an eye towards eventually using it to power an APRS tracker (someday).

Many feet of wire are ready to be run back to the tail too, although not everything is in place yet.

New game! Whenever you drill a hole in your spar, you have to take a drink. Tonight's beverage was a summer seasonal from Blue Moon, which was not half bad.

Riveted transponder doubler

Matt — Mon, 10 Aug 2009 02:00:59 +0000

Al Stuber put his CH 750 project on hold long enough to drop by and hold the bucking bar against the belly skin while I crawled inside and backriveted the transponder doubler. Thanks Al.

The brown discoloration in the above photo is alodine, by the way. Don't want any surface corrosion forming here and messing up my antenna ground plane.

Here's a shot of the transponder antenna bolted to the bottom of the fuselage… nothing to it, just a plastic shark fin thingy:

One more thing checked off the to-do list.

Elevator/aileron speed controller

Matt — Mon, 27 Jul 2009 02:00:32 +0000

One of the things that always annoyed me about my last RV was that the electric elevator trim was incredibly sensitive at normal cruise speeds… trying to trim out control pressures would always turn into a game of "how fast can I press and release the trim button so the airplane doesn't get out of trim in the opposite direction". So to improve that situation with this airplane, I bought a Safety-Trim two-speed trim control unit, which gives you the ability to slow down the trim servos when flying faster than a preset airspeed threshold. It also provides some protection against trim runaway due to a stuck switch, which is nice.

To mount it, I made some little standoffs from scrap alclad:

I attached it to one of the ribs under the pilot-side baggage floor. It's a pretty short run forward from there to the control sticks, and the wires to the servos can go fore and aft through the center tunnel. I'll run the wires to it later – right now I'm just trying to get all my boxes mounted where they need to go so I can plan my wire runs.

In the photo above, you can also see that I've riveted a bunch of plastic tie wrap anchors to both sides of the left and right tunnel ribs. They'll get put to use soon when I start running wires through the tunnel

Transponder antenna doubler

Matt — Mon, 27 Jul 2009 01:00:16 +0000

I bent a doubler for the transponder antenna out of 0.050" alclad and drilled a bunch holes for rivets and mounting studs and antenna connectors through it:

Then I crawled into the fuselage and match-drilled the doubler to the belly skin and the F-729 bellcrank rib, about a foot behind the baggage bulkhead. In terms of the length of coax needed to reach this location, I'm right at the limit of what the Garmin install manual allows, but I couldn't find a better place to put it. Not to mention, I hope the transponder-rays won't do anything weird to the pitch servo. Also, I shortened the doubler slightly between these two pictures, since I'm thinking about moving the ELT back here and I wanted to be sure to leave plenty of room.

A view from the outside. I need to deburr, dimple, and alodine the mating surfaces, and then see if I can coax Mary into helping with the riveting duties.

Flap motor wiring

Matt — Mon, 20 Jul 2009 02:00:12 +0000

Since I had one of the required components in hand already, I decided to also work on the flap motor and associated wiring this weekend. Here I've mounted the flap positioning system control box on the new backrest brace:

Here's another view to show how it stands off from the underlying rivets, thanks to a few nylon washers. That dimpled hole in the foreground is for mounting an adel clamp.

As I previously threatened, I cut the wire harness between the control box and position sensor and crimped on some connectors. Now the motor and control box don't have to both come out of the fuselage at the same time.

Since the flap motor is now no longer permanently tethered to anything else, I couldn't think of a reason not to (semi) permanently attach it to the flap actuator channel. This photo is proof that I did put the cotter pin in:

Then I spent several hours running wires to the flap switch and pulling wires back to the flap motor. Properly bundling and securing new wires takes me about ten minutes per linear foot per wire (longer if I have to drill new grommet holes or install new clamps or tie wrap anchors) so consequently this took all afternoon. I left the flap switch hanging from the panel for now, since there's no need to go to the trouble of bolting it in place for an electrical test.

Once I had all the connectors installed, I plugged it in and gave it a floor run… it works! Bump the switch, and the flaps move one notch up or down. Nice. I'll clean up the wires in a future work session.

Made new backrest brace

Matt — Sun, 19 Jul 2009 02:00:14 +0000

At some point in the last year I managed to bend my F-785 backrest brace – that's the vertical piece that goes between the F-705 bulkhead and the baggage floor, and forms the aft end of the flap motor housing. I'm not sure if I accidentally put too much weight on it from above, or inadvertently kicked it while crawling around inside the fuselage, but I definitely buckled one of the flanges. I bought the parts to make a new one many months ago, but only got around to building it this weekend.

Similar to Bob Collins' idea, I decided to reinforce the new backrest brace by riveting some angle-aluminum doublers on the inside:

The finished product, after several hours of fabrication… note how the rivets at the bottom end tie the doublers into the attach angle. Compared to the old one, the new brace is a couple ounces heavier and a heck of a lot stiffer.

Installed in the fuselage for final fitting:

Pneumatic squeezer and beer… you can theoretically build an airplane without either one, but why would you want to?

Comm antennas

Matt — Tue, 31 Mar 2009 02:13:10 +0000

My brother helped me install the belly-mounted comm antennas while he was in town this weekend. In the photo below we're lining up the antennas and drilling the mounting holes… much easier to do it with the antennas inside the fuselage than outside:

My camera was low on batteries so I didn't get a picture, but we made doublers for the antennas out of 0.050" alclad. You can kind of see one in this photo:

Since the antennas are grounded via their mounting screws, ensuring good electrical contact is essential for proper antenna performance. I used an alodine pen to corrosion-proof all the mating surfaces:

Here's a better shot of the fuselage doublers, with the alodine drying. It looks blotchy but that doesn't really matter.

I likewise cleaned, scuffed, and alodined the areas of the fuselage floor destined to be covered by the doublers:

Adam helped me rivet the doublers to the floor:

They're also attached to the seat ribs with blind rivets – plenty strong. Each antenna is attached with four screws that go into floating nutplates, and the BNC connector protrudes through the hole in the middle.

Voila, antennas. This arrangement should make for easy wiring, keep the antennas out of the plume of exhaust gunk, and satisfy the radios' requirement for minimum antenna separation distance.