We met up at Linton today to get cracking on finding out why the X-Air had no electrics. I took my little Robin electrical multimeter which has proven invaluable in the past in tracking down electrical problems and was keeping my fingers crossed that it wouldn’t let me down this time either. Ken and Peter had the X-Air pulled out ready when I arrived and had replaced all the blade type fuses so we got straight down to it.
Whenever I have an electrical problem in an installation I don’t know I like to start by checking that the circuits are connected correctly and that there is continuity in them. Otherwise, if you find a break and just reconnect the power you run the risk of having a short on your hands with all sorts of nasty consequences, especially in an aircraft. Everything checked out top-side so it was time to get our heads under the panel and check all the wiring out down there. Easier said than done because it’s very cramped under there and part of the time you have to lie on your back, but I was used to that having had to do the same in MYRO, which is even more cramped for space. Fortunately everything more or less checked out compared to the official wiring diagram with one change being that the starter button isn’t fused as shown in the diagram, but that wasn’t important.
But still no power. Not quite true actually because there is a miniature switch labelled ‘Intercom’ with an LED that lit up green when you switched it on, showing that power was getting down under the panel. But the main ‘red – live’ lead wasn’t! Time to investigate, so back up top again.
My initial thought was that the wiring had been cut and modified but I discounted that as there were no obvious tell-tale signs. The wiring diagram showed the main red lead connecting straight to the +ve battery terminal but, surprise surprise, there was only one such lead apart from the heavy cable connecting to the ‘heavy’ side of the starter solenoid and that was the one running down to the intercom switch. My conclusion therefore was that that had been specially run to power up the radio system, so I had to look elsewhere to see where the system harness should be deriving its power from. And I didn’t have to look too far.
The starting point was the main plug and socket mounted on the side of the engine. I already knew that there was continuity – but no power – to the right through the loom running down under the panel, so the place to look was to the left of the plug and socket. I traced along the red line from the socket which logically should have been live but wasn’t and when I traced it around to the other side of the engine I found it connected to – an engine earth point. Problem solved!
It was an easy mistake to make. When Peter had been reconnecting the electrics after refitting the engine after its overhaul in the dim light at the back of the hangar, he had found a wire with a bolt-type connector on it which he had assumed should go to earth. In fact it should have been connected to the live side of the starter solenoid which was just close by and as soon as I made this change, the system came alive. It was some relief I can tell you, because we had spent quite a lot of time by then finding nothing wrong but could still not explain why there was no power and I was beginning to run out of ideas.
So basically that was that. We re-cable tied the wiring under the main panel and refitted the front access panel, tidied everything else up and re-cable tied the wiring top-side so it couldn’t move around and chafe. Then we were ready to run the engine. Fate smiled upon us at last because it started and ran beautifully and sounded as sweet as a nut. I thought afterwards that we hadn’t checked the plugs but decided that as it was running fine, we could do that some other time. After letting it run for a few minutes (it needs to be ground run-in for an hour or so as it’s just had a major overhaul) we gave the aircraft a taxi. It felt just right, nicely balanced and with very good toe brakes on the pilot’s side. After going up and back along the main taxiway we went back up again and taxied onto the winter runway so I could check that we were getting full take off revs, which we were. We stopped and checked the coolant level a couple of times, which was fine, and found one problem in that the water temperature gauge wasn’t registering. All the others with the exception of the fuel pressure gauge were working fine though, and that was suffering with the same problem that I found with the old gauge that I got for MYRO, that had been in use in MYME but hadn’t been run for some time. It seems that they then get stuck up internally with goo from the fuel, and this seems to have happened with the X-Air’s one which moves a small amount but doesn’t register the true fuel pressure.
So that just leaves a new fuel pressure gauge to be purchased and possibly a new water temperature gauge too, although with that we can’t presently discount if maybe the sensor is the problem rather than the gauge. I have an old Westach water temperature gauge in front of me that we might be able to use to test the existing sensor but it may be better at the end of the day just to buy a new gauge as, frankly, the existing one does look a bit old fashioned, and if that doesn’t work, then go for a new sensor as well.
But in any event, I doubt that either is a show-stopper when it comes to permit inspection, so really the X-Air is now ready for its inspection and weighing. I think it will zip through with no problems so it’s now very close to having its first permit since 2008. I think today was a job well done, even though it took a while, as along the way we all learnt a bit about the aircraft that we wouldn’t have known otherwise. And that’s always worthwhile and a Good Thing 🙂