Fuselage « Matt's RV-7 Project

Archive for the ‘Fuselage’ Category

Flap motor wiring

Sunday, July 19th, 2009

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.

Posted in Electrical/Panel, Fuselage |

Made new backrest brace

Saturday, July 18th, 2009

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?

Posted in Fuselage |

Comm antennas

Monday, March 30th, 2009

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.

Posted in Electrical/Panel, Fuselage |

Fuel flow sensor

Sunday, May 4th, 2008

If you choose to research the topic obsessively, as I have been doing lately, you'll find that there are about three locations where people have been mounting the fuel flow sensor, and everyone thinks the way they installed theirs is best. You can put it on the cabin floor downstream of the electric fuel pump, near the engine between the mechanical fuel pump and fuel injection servo, or in the line between the fuel servo and the fuel distribution spider on top of the crankcase. I accept the argument that your fuel flow readings will be more accurate the farther downstream your sensor is placed, but there are also vibratory and thermal factors to consider when mounting a somewhat delicate sensor in the harsh environment of an engine compartment. After a weekend of head-scratching, I couldn't settle on a location forward of the firewall that I found completely satisfactory, so I gave up and elected to mount my flow sensor on the cabin floor. I can live with the fact that I may get inaccurate readings when the electric fuel pump is turned on, but that will only occur for a few minutes per flight. There is theoretically an increased chance of vapor lock as a result of adding another restriction upstream of the mechanical fuel pump, but I don't know of any evidence of this actually happening in real life (and if it does, I can still turn on the electric pump). There's also the fact that I put the flow sensor on the cabin floor in my last airplane, and it seemed to work fine.

Anyway, end of rationalization section. I pulled all the fuel plumbing out of the fuselage – it's easier than it sounds: you only have to undo three flare nuts and four screws and the whole works lifts right out.

I cut the line that previously went from the electric fuel pump outlet up to the firewall, re-flared it, and installed the fuel flow sensor.

The sensor body is partially tucked under the mounting plate, so it won't hit the fuel pump housing. It's not attached to anything, just sandwiched between the mounting plate and the floor. I stuck some foam weatherstrip material to the bottom, to hopefully isolate it from exhaust vibrations coming up through the floor.

With the flow sensor spliced in, the fuel line runs up to the firewall as before. Notice that this location satisfies the manufacturer's recommendation to give the sensor 5" of straight line on both the inlet and outlet sides, which is much more difficult on the other side of the firewall.

The housing fits without hitting the sensor or any of the plumbing:

Posted in Fuselage |