Archive for May, 2008

Mounted fuse blocks

Thursday, May 29th, 2008

I decided to mount the main and endurance bus fuse blocks on the left side of the subpanel, just behind where the pilot's displays will go. Access to the wiring should be pretty easy after removing one or more glass displays to gain access. Or, I will always be able to go the more uncomfortable route, up from the floor while lying on my back getting poked in the ribs by the fuel selector.

The essential bus diode (with hefty heatsink) is mounted to the other side of the subpanel. I tried to plan its location so that some of the screws used to mount it can also be used to attach adel clamps.

Mary came down to play Bejeweled on her phone and drink wine and watch me work. She composed and photographed this artful scene while I was preoccupied:

Would the isopropyl alcohol in the background count as a dry white? And which do you serve with pneumatic tools, anyway?

Lightspeed ignition mounting

Monday, May 26th, 2008

I mounted the brain box for the Lightspeed ignition system to the starboard subpanel rib. The power and sensor connectors face aft, and the ignition wires exit towards the front, where they have a straight shot through the "noisy" firewall passthrough. (The "quiet" passthrough will be on the other side of the airplane, where all the sensor wires will go)

I used some z-channel material I had laying around, and the box is attached to the channels with screws. The lower bracket is riveted to the avionics shelf, but the upper bracket is attached with screws. I did this to facilitate future maintenance, since I will be able to get to the lower mounting screws from underneath, but the upper ones will be pretty much unreachable from down below… instead, I'll reach in through the forward skin access panel and unscrew the whole bracket from the rib if I need to remove the box for repairs.

Bad day, with hoses

Sunday, May 25th, 2008

Today stated off well but ended poorly…

I wanted to use a restrictor fitting for the connection to the manifold pressure hose, to keep the #3 cylinder from running too lean if the hose breaks. But, Van's only sells a 45-degree restrictor which won't fit on my engine. I had to make my own straight restrictor by filling an AN816 fitting with JB Weld, waiting a day for it to cure, and then drilling a #60 hole through it. Turned out great:

Installed in the port on the #3 cylinder:

The manifold pressure hose attaches to the restrictor fitting, then sort of loops inward:

It's attached to the engine mount with adel clamps, and passes through a fitting I installed in the firewall near the brake fluid reservoir.

The hose that goes between the firewall and the fuel pump inlet is a tight fit, but it works. In this photo I'm using a bungee cord to teach the hose to follow a curve that keeps it away from the engine mount. A couple hours like that and it kept the right shape on its own.

The oil pressure hose exits the right side of the accessory case, loops around to the left, and is secured to the top of the firewall with adel clamps.

The oil pressure hose enters the transducer manifold (top of photo), as does the fuel pressure hose (bottom). Eventually there will be pressure transducers screwed into the manifold, and the unused holes will be plugged.

The fuel pressure hose runs down to a tee on the outlet of the fuel pump (brown hose in center of photo). Also visible in the background is the fuel pump overflow hose, which runs down to the bottom of the firewall.

I have a policy that any hose that carries pressure should be professionally made and tested, but since the fuel pump drain hose doesn't carry any pressure and should rarely even have any fuel in it, I decided to make that one myself. This is Aeroquip 303 hose, using the recommended mandrel for assembly. It's a pain to do properly – I'm glad to leave making the proper hoses to the pros.

Of course, the plans call for the fuel pump overflow hose to be made from plastic tubing, but I thought that was cheesy. My hose is a little heavier but at least it won't melt/crack/etc. The hose runs down to an AN837 fitting that's adel-clamped to the engine mount, and thence a length of aluminum carries the fuel overboard and out the back of the cowling. I drilled out one of the rivets on the firewall flange and used it for a screw and clamp that secures the tubing.

Here's where it all went off the tracks… while installing the very last fitting, the upper one for the fuel pump drain, I accidentally cracked the fuel pump housing:

Another photo with different light. I guess it doesn't take very much torque on a steel fitting to ruin a thin cast-aluminum housing.

After stewing about it for a while, I decided that the fuel pump has to come off to be rebuilt. That meant I had to take off most of the hoses I'd just spent hours installing. I also had to take off the magneto and loosen the prop governor cable bracket just to be able to get at the fuel pump bolts. Nothing on the engine is easy to work on!

After a couple hours of bad language, the fuel pump is now removed from the engine. Hopefully repairing or replacing it won't be too expensive.

I also had to mow the hateful lawn, and the new Indiana Jones movie was not very good, and now I have a headache, so overall this day has been kind of a dud.

Fuel hose

Saturday, May 17th, 2008

Believe it or not, it took me an entire afternoon to install the hose that goes between the engine-driven fuel pump on the back of the engine and the fuel injection servo up front. This seemingly simple task was greatly complicated by clearance problems and lack of space to work in (is this starting to sound familiar?). You want the fuel line to be far away from the hot exhaust pipes, but the ideal routing – up over the "wing" of the oil sump – is blocked by the mixture bellcrank. So, I had to play with various routings of the hose until I could find a way to get it as far away from the exhaust as I could, while still staying clear of the mixture linkage when it's in the idle cutoff (worst case) position.

Since the hose is right there, I put some additional heat shields on the exhaust pipes to keep the fuel line cool. In this photo you can see the somewhat circuitous routing the hose takes, as it exits the fuel pump, crosses under an engine mount tube (the photo doesn't show it, but there's an inch of clearance there) and then climbs up away from the exhaust pipes. A pair of back-to-back adel clamps, shown here partially obscured by the exhaust, secures the hose to the #4 intake tube. I ended up with at least an inch of clearance between the heat shields and the hose. By the way, all my fuel/oil hoses are Stratoflex 124J assemblies with integrated firesleeve, made to my specifications by Precision Hose in Tulsa. Good customer service and good prices too.

These clamps were a giant pain to install, because the normal bolt-flinging properties of the adel clamps were magnified by the almost complete lack of access to the area where I wanted to put them. I managed to scrape a bunch of paint off the #2 and #4 intake tubes, but it's all cosmetic stuff.

I need to do better than one hose per day if I'm ever going to finish this thing.

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: