« Archives on July 7, 2019

All Together Now

Finally, after four months of interruptions, priorities, fragmented blocks of time, and truly awful weather, some of which begat the need for a new rudder, N313TD is back to operational status.

When I installed the new RDAC, I had to leave the left side CHG and EGT probes unconnected, because the wires wouldn’t reach the new RDAC location.  Yesterday, I ran the K-type extensions from both sets of probes to the new location and connected them accordingly, and as far as I know, they all go to the right terminals.  To truly test it out, I need to heat up the cylinder head and probes with a heat gun to find out which is which, but that’s not happening at a tie down in Santa Monica.   I know 1 and 3 are right.  It’s 2 and 4 that might not be.  You see, I ran the wires and wrapped them in spiral wrap before I thought to mark which was which.   The photo above shows a messy, but functional arrangement with enough extra wire to allow switching terminals, although I believe I can set them in the EFIS.  At that point, I can clean them up and make them all nice.  But for now, they’re secure and self-supporting, so I’m good.

The other thing that happened on the way to the new RDAC module was that I somehow picked up an extra 2500 ohms between the fuel tank and the Fuel Level inputs.  This new RDAC has a DIP switch for a pull-up circuit on most of the sensor inputs.  The manual says you’re supposed to have the pull-up on for float-type senders, but if it’s on, the resistance drops to zero and the fuel level reads full.  Not useful.

With the pull-up circuit off, ~8 gallons reads about 1500 ohms, according to the raw level reading in the EFIS.   One of my tanks is pretty much there, because I leveled the airplane and the fuel on the left side is juuuuuust touching the outboard rib of the tank.  So I half-assed it using the settings below until I can properly calibrate by emptying each tank and adding back 3.5 gallons at a time.   The gradations are from the previous measurements.

Opinions are strong on this, with most of them in the key of “you should use a totalizer and do the math” and “if you keep track of what you put in and the time you fly, you don’t need a gauge.”   But the saner voices acknowledge that fuel gauges are a good redundancy to a totalizer, and I tend to agree.  Either way, I now have everything I had before the old RDAC went tits-up, and then some.  #1 and #3 CHT’s aren’t randomly dropping out anymore, and the left-side fuel level doesn’t randomly jump from its normal reading to full tank.  The EFIS is still a mess.  I can’t get it to take the latest update and it can’t read any of the raster maps I’ve uploaded, and I’m getting pretty damn good at QGIS, so I’m not as happy with it as I should be.  But it’s still performing well for a 2010 unit that’s no longer being manufactured.

Did I mention I was doing this stuff outside at a tie down at SMO?  Yeah, about that.  No electricity, so no luxuries, specifically, no heat gun, which means yours truly was shrink-wrapping wire with a barbecue lighter and a cupped hand.

All repairs are field repairs, yo.   Can’t wait to install the Fed-mandated ADSB equipment before 2020.