Another breather hose

June 13th, 2015

So, this was the previous arrangement for the engine breather hose… a 90-degree AN swivel fitting plus a 90-degree hose end:

I was driven to use this setup – which let's face it, was overcomplicated at best – by the limited options for hose routing that are available when you have an angled oil filter adapter, as my engine does. There's practically no good way to point the hose fitting that doesn't cause either the fitting or the hose to hit something else. But then I had a brain wave and thought of a much simpler solution, so I tore out the existing hose and engine fitting:

This is the new arrangement I came up with. The fitting on the engine is now a 45-degree brass hose barb, pointed towards the left side of the engine as well as somewhat forward. This allows the hose to clear the engine mount heading forward, whereupon it takes a medium-sharpish bend and turns 180 degrees back towards and air/oil separator. It does come close to the baffles and the oil cooler plumbing, but there's plenty of room for things to move around without rubbing together.

The hose is affixed to an engine mount tube with a pair of adel clamps, the purpose of which are to pull it down and keep it from rubbing on the inside of the top cowl, which is its natural tendency due to the angles involved. Although it seems at first glance like there isn't enough slack in the hose to accommodate movement of the engine, in actuality there's at least a foot of hose there, with a pretty good loop in it. This MIL-6000 hose is also fairly springy, and you can "boing" it back and forth an inch or two with your fingers. Compared to the fuel hose on the bottom of the engine, there's actually more slack in the new breather hose.

Here's another view, looking across from the right side of the engine. The engine mount and oil separator do not move relative to one another, so the short length of hose between the engine mount and firewall doesn't require any slack in it.

I have now re-engineered every piece of the breather system at least twice! I think it's truly all finished now. Here's hoping, anyway.

Posted in Firewall Forward

Thermocouple heat shields

June 13th, 2015

Even though the thermocouple connectors are made of fairly high-temperature nylon, I didn't like how they were only a couple inches from the hottest part of the exhaust pipes. So, I bolted on a couple more radiant heat shields. Here's the left side:

And the right side:

Posted in Firewall Forward

EGT/CHT wiring

May 25th, 2015

The last major firewall-forward wiring job is to connect the thermocouples that measure exhaust gas temperature (EGT) and cylinder head temperature (CHT). There's two probes per cylinder, so it ends up being a fair number of wires.

Rather than using the old-style ring terminals to connect the thermocouples, I decided to use these cool little connectors from Omega Engineering. A lot of aircraft manufacturers are switching to this method of connecting thermocouples since they're easy to work with and there aren't any concerns about insulating the connections.

I cut off the ring terminals and installed the connectors on all eight probes. By the way, you have to be careful when wiring Type K thermocouples… the red wire is the negative side!

I'll skip over the couple days I spent working out the wiring routes and strain relief arrangements, and just walk you through the final product. Starting on the starboard side of the engine, the thermocouple leads and connectors are all bundled up and secured with high-temp tie wraps:

I made a little standoff out of a strip of 4130 steel, painted for corrosion resistance. It ties into the lower valve cover screw on the #3 cylinder and supports an adel clamp that secures the wire bundle. In this photo it's held on by a cleco since I intend to replace it with a high-temp silicone clamp when I get my next parts order in the mail.

The wire bundle goes down the #3 intake tube, where it's secured by another pair of adel clamps near the bottom:

It's sort of hard to see in this photo, which is looking up at the bottom of the right side of the engine, but the bundle of thermocouple wires loops around a diagonal engine mount tube and attaches to the transverse tube with more adel clamps. Although it doesn't look like it in this photo, there is plenty of space between the wires and the diagonal tube.

Now we're on the left side of the engine, looking across to the right. The wire bundle crosses the aircraft, following the transverse engine mount tube via three pairs of adel clamps:

At the port-side landing gear socket, the wires turn the corner and head up one of the engine mount tubes towards the top corner of the firewall. Yet another pair of adel clamps routes them up the tube, and the wires for the #2 and #4 cylinders split off here as well:

The main wire bundle runs up the back of the tube, where it's attached with… you guessed it, another pair of adel clamps:

At the top of the engine mount, one more pair of adel clamps helps the wire bundle turn the corner, and then it disappears through the port-side firewall penetration:

Meanwhile, the wiring on the left side of the engine is more straightforward. The wires and connectors are all bundled together and tied off – you can also see how I ran a tie wrap through the middle hole in each pair of connectors, to help prevent them from pulling apart:

I used the cable for the alternate air door as a convenient way to route the wires on this side of the engine. I cut some 1/2" lengths of rubber fuel hose, and used more high-temp tie wraps to hang the wire bundle from the cable sheath. The result is a neat way of running the wires that looks nice and keeps them away from the ignition leads:

Inside the fuselage, the thermocouple wires are connected and more or less bundled, although at some point in the future I'm going to have to schedule an epic tie-wrapping session for the behind-panel wiring:

All eight of the probes are reading room temperature, which is a good sign. The fact that the #2 EGT is reading a little higher is just a rounding fluke – the EGT temperatures are rounded to the nearest 5 degrees.

I lost track of the number of adel clamps I installed as part of this little project. It sounds easy now, but each pair of clamps was a mini-nightmare all by itself. These clamps are difficult enough under benign circumstances, but in the FWF area where you can barely get your fingers on them, let alone a wrench, it can seem nearly impossible at times. I hope I don't have to install any more adel clamps for a good long while.

Posted in Electrical/Panel, Firewall Forward

ELT wiring

May 3rd, 2015

The ELT uses a fairly rinky-dink DIN connector for its power and GPS position inputs. Rather than trying to solder these tiny pins while standing on my head inside the airplane, I decided to solder them on the bench instead:

Then I fabricated a short DIN-to-Molex adapter. Inside the airplane I used a mating Molex plug with crimp pins.

What this enabled me to do was to also build an in-situ test adapter, complete with diagnostic LED. Then instead of having to leave the wire for the LED in the airplane all the time, I can just plug this little thing into the harness and watch the LED blink when the ELT gets data. Which is what I did – sorry, it didn't photograph well, so I can't show you a picture.

The ELT also comes with a separate little box, containing a buzzer that sounds when the ELT is activated. I suppose that would help the CAP find a crunched airplane in a forest, for example, but I expect its main purpose is to alert bystanders to an accidental ELT deployment after a hard landing or whatnot. I mounted the audio box on the aft side of the F-707 bulkhead:

The audio box uses its own battery, an unusual 3V lithium number. I'll need to crawl back there and replace it in 2024:

I secured all the wires that go to the ELT, and there are actually quite a few. I used plastic tie wrap anchors to route the wires to and from the audio box, whose mounting screws are visible here on the forward side of the bulkhead:

I fabbed a length of RG400 coax for the ELT antenna, and used more plastic anchors to secure it loosely to the bulkheads and floor.

Everything is shipshape in ELT land now, I believe. Per the manufacturer's guidance, the antenna cable does not penetrate any bulkheads or aircraft structure, and is only loosely restrained elsewhere, so it can still move around and hopefully won't get cut during a… shall we say, "a deceleration that rearranges the configuration of the airframe".

Posted in Electrical/Panel

Transponder antenna cable

May 3rd, 2015

One last job to finish up the transponder installation – crimping the BNC connector and securing the short run of coax that goes from the transponder to the antenna. Done and done:

Posted in Electrical/Panel

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