September « 2007 « Matt's RV-7 Project

Archive for September, 2007

Aux Battery Box

Sunday, September 23rd, 2007

One component that I've designed into the electrical system of my airplane is a small auxilliary battery, which will help keep a few critical systems online during engine start. Unfortunately there aren't a great many places where you can easily mount a second battery. I thought for a while about putting it under the baggage compartment floor or even under the seats, but in the end I decided to choose a small battery and mount it to the F-721A forward canopy deck, behind the panel on the passenger side.

I went to the local battery mega-store and picked up this 3.3 Ah VRLA battery. It is a store-brand clone of a Panasonic LC-R123R4P and is the same size, so I should be able to get replacements in the future if I need to. This is a pretty small battery (note the tape dispenser for reference) but it's the biggest one that will fit between the panel and subpanel.

I fabricated some parts out of scrap…

…and made this simple battery box. The base is 0.050" alclad, with 1/8" angles riveted to it (double-flush where necessary). It's probably way overbuilt, but I just used the materials I had on hand. I'm not sure why I primed it – force of habit and superstition, I guess.

Just like the main battery box, this one features a bar to hold down the battery. Unfortunately the battery's terminals are both on top, putting them close enough to the hold-down bar to make me worry about them shorting to it. I worked around this by riveting the bar to a strip of 1/4" nylon that is wider than the bar is, this preventing the bar from being able to contact either terminal. I'm not sure why I had nylon sheet stock in my junk bin, but I'm glad I did.

Here's the box bolted in place, with the hold-down bar temporarily taped on until I can pick up some long bolts of the correct size. Note that the bolts all come up from the bottom – this is because the fuselage skin prevents you from lifting the battery straight out of the box. To remove the battery, you actually have to undo all four bolts and slide the whole battery box out first. Hopefully this won't be too much of a hassle, as I don't anticipate needing to replace this guy more often than every few years.

Here's what it looks like with the skin clecoed in place. There is about 1/8" of clearance between the skin and the aft corner of the battery, which explains why I had to let the rear hang off the F-721 a little bit.

After I took this picture, with the skin still clecoed in place, I unbolted the battery box and removed it just to prove to myself that it can be done. It's actually not a terrible process – I've done worse maintenance on airplanes and lived to tell the tale.

I've also been working on some schematics for the airplane's electrical system. I put together a first draft, along with some notes, and sumbitted it to the Aeroelectric list for review by the learned elders. If you're interested you can cick here to see my current electrical diagrams and some text, including an explanation of how the aux battery will be used.

Posted in Electrical/Panel |

Fuel tank manometer test

Saturday, September 22nd, 2007

John loaned me his fuel tank leak testing kit a couple weeks ago, and I've been using it to do some extended testing of my fuel tanks. It's a simple water manometer that plugs into the tank outlet – you cap off the vent line and then use a Schraeder valve threaded into the drain flange to pressurize the tank.

I filled the first tank to 27 inches of water, which is about 1 psi, and marked the height of the water column.

Then I left it alone for a week. The water level fluctuated up and down with local pressure and temperature changes, but at the end of a week the tank was still holding approximately the same amount of pressure. After that I did the other tank, and it tested fine too. Hooray!

You can buy the fittings to make one of these setups from Van's, but you have to supply the plumbing and yourself (or borrow a buddy's).

Posted in Wings |

Put the canopy to bed

Sunday, September 16th, 2007

To keep the canopy from having to sit on its own side skirts when it's not on the airplane, I threw together this very simple storage rack out of scrap lumber:

To capture the rollers, I knocked a 1" hole in a chunk of scrap 2×2 with a spade bit, then cut it half to make these little cup thingies. A wood screw from beneath holds each one in place.

In the back, the rear pins rest on wood blocks that are screwed to the bottom piece:

I carried the canopy upstairs and stored it carefully on its rack, on the guest bed. The exterior handle in the back makes it a snap to carry the canopy around solo – I think you'd need a helper if you didn't have the handle to grab.

And now I have a canopy bed again! I swear, that joke never gets old.

Posted in Canopy |

Canopy finishing touches

Saturday, September 15th, 2007

A while ago I ordered a nice machined aluminum handle for the exterior part of the canopy latch from Rivethead Aero. They took my payment and then disappeared for a couple months, but after repeated badgering I finally received my latch handle. It's really a work of art, which makes their disappointing customer service even more of a shame.

Anyway, I cut the latch shaft to the proper length after some fiddling and measuring. The handle is secured with a couple of setscrews, and for safety's sake I used a drill to put a couple of little dimples in the steel shaft for the setscrews to bite into. I just didn't feel right about the handle being attached solely by friction. Speaking of which, I used Vibratite on the setscrews, which should hopefully keep them from departing the aircraft.

The handle looks awesome:

And of course, me being me, I spent a bunch of time fiddling with the alignment of the handle to get it perfectly parallel to the centerline of the fuselage when the canopy is closed and latched.

At the forward end of the canopy slide rail, there's a brace that stiffens the overhanging portion against the F-706 bulkhead. The plans show this brace being constructed from a piece of threaded rod and some jam nuts, with a big ugly nylock nut on the end. I have a thing about wanting the interior of my airplane to not look like I built it in my garage, so I decided to dress this area up a bit. I used a piece of aluminum tubing, painted to match the rest of the interior, to cover the threaded rod and make it look a little nicer. At the forward end, I replaced the nylock nut with a swanky looking self-locking stainless steel acorn nut, which is a bit more professional looking.

I decided to keep going with the acorn nuts, using them in place of nylock nuts to attach the rollers to the canopy frame, as well as on the screws that act as the axles for the roller wheels.

Along the sides, I replaced all the #6 nylock nuts with more acorn nuts. I also used acorn nuts on the interior faces of the C-677 rear pin mounts, although it's hard to see in this photo. Now there are no exposed fastener threads visible on the inside of the canopy whatsoever. This is a purely cosmetic modification, but I really like the way it dresses up the interior.

I used Vibratite on all the screws and bolts in the canopy. At one point I had a regular assembly line going:

Next, I installed the canopy lock for good:

I cut a slot for the lock arm into the canopy track. In its normal unlocked position, the arm points forward, parallel to the track.

When it's locked, the arm swings down into the slot and prevents the canopy from being slid open more than a small fraction of an inch. Well, unless you were to beat on it hard enough – it's not particularly sturdy.

This is a photographic record to remind myself where I stashed the keys:

In the spirit of checking off the remaining items on my canopy to-do list, I installed the little track for the canopy shade:

Then I whipped up these little air baffles out of some leftover angle stock, and fitted them to the fuselage and canopy. They'll eventually be painted to match the interior, and will be attached to the longerons with a couple rivets. They butt up against the inside of the side skirts at the rear of the canopy, and will serve to seal up the small gap back there.

After thinking about it for a few days, I decided to drill out the front two rivets on each side of the canopy, where the leading edge of the fiberglass aft skirt attaches to the side skirts. I replaced the previous 3/32" rivets with 1/8" rivets sitting inside tinnerman washers, which makes me feel better about the rivets not puling through the fiberglass. The airflow is going to try to peel the fiberglass skirt back in this area, so I wanted to beef up the attachment a bit.

Well, that about does it for the canopy. Next I'll build some kind of a frame or platform to set it on, and stash it in the house so it will stay out of the way and not get scratched.

Posted in Canopy |