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EGT and CHT Wiring, Annunciators – 9 hrs

September 8, 2013 Leave a comment

Sunday Sep 8, 2013

I been moving more into the electrical wiring work this weekend. For the audio panel I did a test installation of the connector backplate onto the tray to determine how this goes together. The instructions in the PSEngineering installation guide are rather limited.

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Next I assembled the second annunciator controller module and tested it. This one is wired to sense two circuits going to ground and two circuits going high to 12V. Everything checked out as expected so these are ready to be installed in the airplane.

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The next adventure was cutting and terminating the exhaust gas temperature (EGT) and cylinder head temperature (CHT) sensor leads between the engine and the engine monitoring system (EMS). I hoped this would be straightforward but I stumbled upon some posts on VAF and the Dynon forum about problems with erratic EGT readings and bad crimps seem to be the cause. On further investigation I learned that the thermocouple wire used in these leads is a hard metal and does not crimp well to typical copper terminals. So at least I was alert to the issue. I started by doing a sample crimp on a short piece of scrap wire and sure enough it pulled off when I did a pull test. The EGT wire is seven strands and the gauge is a little small for a 18-22 AWG terminal. So I tried again by stripping the wire twice as long and folding the wire back on itself to double the area inside the crimp. That was too large and would not go into the barrel so I cut three of the seven strands at the mid point of the fold so it effectively had 11 stands in the crimp area. That fit into the terminal barrel and produced a good crimp that passed the pull test. I did not measure the force but I pulled on it pretty hard.

For the CHT wires the strands seem to be slightly finer and the wire would fit into the barrel folded back double without trimming any strands. That too produced a strong crimp.

After experimenting to get this solution I was able to terminate all the EGT and CHT leads on the left side (cylinders 2 and 4). I cut pieces of shrink sleeving to go over each mating pair of Faston connectors but have not shrunk them because I may install some fireproof expandable sleeving over this bundle later. The routing I chose provides plenty of slack for the relative motion of the engine without getting too extreme.

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Here is a better view that shows how I spread the terminations out to avoid a big bulge in one region. The Dynon instructions recommend against trimming any of the armored sections of the cables so I did one loop back on the EGT4 cable to keep the terminals in a reasonable region. Otherwise they would have been up inside the firewall pass-through and I was not going with that.

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With all the wiring planning I have been doing I was able to get a list of the wires and sizes that route through the fuselage center section. The holes to pass wires through the center section is limited to four snap bushings about .450 diameter each and one of those is filled by the elevator trim cable. When I saw the full list of wires that have to get through there it was clear they were not going to fit with the two pitot hoses (pitot and static) that need to go to the Gemini PFD. So I decided to reroute the pitot hoses under the canopy sills to make more room for wires. This picture shows the static line (white) rerouted from behind the baggage compartment beneath the main longerons through a hole I added to the F-706 bulkhead (as a contingency) when I originally built it.

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The hose comes out behind the fresh air inlet  behind the panel which is perfect for routing to the Gemini. I did the same thing on the left side with the green pitot hose. I still need to add a few tie bases to tidy up the routing but I think this will help the wire routing problems considerably.

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Categories: Avionics, Engine Sensors

Installed EGT Probes – 3 hrs

July 7, 2013 Leave a comment

Sunday July 7, 2013

You only get one shot to drill the holes for the exhaust gas temperature probes – unless you want to ship the pipes back to Vetterman to weld up the holes. Consequently, I researched the subject of where to mount the probes and how to orient the wires. The Dynon manual says they should be 2 to 8 inches from the cylinder. It also says “This spot should be on a straight portion of the exhaust manifold, as this provides a better fit for the hose clamps. For best results, mount all probes the same distance from each cylinder.” Well that turns out to be impossible with the Vetterman crossover exhaust. The #3 cylinder is the main driver and it has a welded fitting that is about 3 inches below the flange that prevents the probe from being installed anywhere but just above it. You can see it in the center of the picture below. I put the probe 2.6 inches from the bottom of the exhaust flange. Keeping consistent with the 2.6 inch offset causes the probe to be on the bend of cylinder #1. But my research from other builders indicated this would not be a problem. To maintain cowl clearance I pointed the probes forward on this side away from the respective spar plugs so as not to block them. The wires will loop forward and upward and join the spark plug wires clamped to the valve covers.

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On the left side the probes are also 2.6 inches from the flange but here they are oriented pointing aft, again away from the spark plugs. The hose clamps on all the probes were too long, leaving more than 2 inches of “tail” poking out so I cut the excess off with a dremel cutting disc. Now I need to route all these wires!

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I started another small project today that has been on my To-Do list for quite a while. I made a plate to hold all the LED annunciator lights for the instrument panel. In the photo you can see the dimensioned sketch I used to make the plate and the functions designated for the lights. These lamps operate on 12 Vdc and don’t require external resistors. I’m still working on the wiring plan and I’m trying to find a way to add a push-to-test function for the entire annunciator array.

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Finished Hinge Pin Covers – 4 hrs

June 9, 2013 Leave a comment

Sunday June 9, 2013

I have been using the brass pins that came with the horizontal hinges in the cowl since I installed the hinges months ago. The plans say to replace them with stainless steel pin wire included in the finishing kit so I worked on that Saturday. Bending this wire such that it looks good is not that easy so I have been putting it off. I started by forming a 180 degree bend at the end of the wire. The radius is just large enough for my finger to fit into the loop. I used the shank of a 3/8 inch socket wrench handle to bend the curve. Then I bent it slightly further to maybe 220 degrees . I laid the loop against the side of the cowl to make sure it fit within the tear drop opening and I marked it for another tight bend right where it enters the first hinge eyelet. That was about a half inch from the start of the loop. I put the wire in a vise and bent it there to make a shape like a question mark. Finally I bent it slightly out of the plane of the question mark so it leans out of the opening as you see below (click it for a bigger image). This makes it easier to insert and remove.

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Then the trick is to rotate it 180 degrees in the hinge so the loop leans into the opening and is just flush with the cover. It tuns easily so installation and removal is a cinch. The stainless steel pin seems to go into the hinges a little easier than the brass did so that is nice also. I trimmed the other end of the pin wire to be just flush with the last hing eyelet.

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I shaped the other hinge pin the same way and I put both covers on and used a little epoxy/micro filler to smooth out the surfaces on and around the covers and fill flaws. After sand this looks pretty good and I can declare this mini-project done.

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This morning early I installed a couple of nut plates on the right subpanel rib of the forward fuselage for the manifold pressure sensor. With the nut plates installed I mounted the manifold pressure sensor for good and put a piece of safety wire on the plastic tube fitting.

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Installed Red Cube – 2 hrs

May 30, 2013 Leave a comment

Thursday May 30, 2013

After some consideration about where to mount the “Red Cube” fuel flow sensor I decided to contact Don Rivera and Airflow Performance for a recommendation. He sent me a few photos showing the sensor mounted on the engine mount near the right lower Lord isolator. That looks like it will work with my set up so I made an aluminum plate and attached it to the engine mount tubes with two adel clamps. In order to give the fuel line more clearance to the engine mount gusset I made a spacer from 3/4 inch thick HFMW to go under the Red Cube. This photo shows the spacer and the steel AN fittings I installed in the Red Cube.

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Here is the Red Cube installed on the plate which bridges across two engine mount tubes. Now I can measure the length of the fuel lines that go between the AFP servo and the Red Cube, and the Red Cube to the fuel spider and get those on order.

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Manifold Pressure Lines – 6 hrs

May 16, 2013 Leave a comment

Thursday May 16, 2013

The PMags each have a pressure port that needs to be connected to the engine manifold pressure line. I had installed the hose from the engine to the firewall recently but I had not yet hooked up the manifold pressure sensor or the PMags. The PMags came with a piece of black silicone tubing that fits the PMag port so I installed that with a T (McMaster-Carr part number 53055K171) and routed it along the engine mount with adel clamps to the pass-thru port on the right as you can see below.

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Once through the firewall I installed another T to split off to the Dynon manifold pressure sensor and the firewall fitting from the engine. The fitting at the firewall has a small orifice and the clear plastic line there is quite small to help smooth out pressure pulses in the line. The adapter to connect black PMag tube to the larger clear tube that came with the manifold pressure sensor is McMaster-Carr part number 53055K127.

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On other fronts I drilled the two rails for the VPX box to the ribs in the forward fuselage. Clecos installed for now.

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I also installed adel clamps to hold the oil breather tube securely above the exhaust pipe.

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While I was having fun I installed the cylinder head temperature probes into the ports on the engine. I used a little anti-seize compound on the threads.

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And finally I installed the fuel pump drip line according to the instructions.

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