« Archives on March 9, 2019

Time To Fix Some Stuff.

For a while now, the MGL RDAC XD engine monitor module has been a little weird, mostly in the form of erratic oil pressure and temperature readings. To wit: Whenever the oil temperature would get above a certain point, the reading would bounce around all over the place, and the oil pressure reading would do the same, resulting in a low pressure warning. It’s very important that neither of those two lie to me, so I installed a steam gauge for the pressure. Oil pressure is solid on the steam gauge, no matter what shenanigans the temp and pressure sensors are up to.

The story so far…

Oh, that’s just a bad ground, you’ll say. Check your connections. Yeah, been there, done that. A lot. And it’s no use. A couple of weeks ago, I went for a nice flight after all the rain, and on takeoff from OXR, I had a complete failure of the RDAC module. Every measurement flashed “rdac fail.”

This, as you may imagine, was almost a code brown, at least until the RDAC came back to life, upon which I promptly flew back to SMO. Popped the cowl, checked the connections to the EFIS, to the grounding block, to all the things. Went for another flight. This time, the RDAC packed up over Malibu and didn’t come back. I flew home old-school, with only the sound of the engine (which I know by heart) as my RPM indicator.

Eventually, I made the connection: When the RDAC gets heat-soaked, it fails. It’s mounted on the firewall, which is extremely convenient because only a couple of wires go through the firewall port back to the panel. Unfortunately, it’s a harsher environment than I anticipated, and after less than 200 hours, I suspect the RDAC has succumbed to the heat and vibration of the engine compartment.

So now I have a job to do: Replace the RDAC, with MGL’s shiny new RDAC XF unit, and this time, don’t mount it low on the firewall where the engine radiates all the heat into it. And maybe, figure out some sort of enclosure for it to keep the worst of the engine’s emissions off it.

When I first installed the RDAC, I had no engine, no accessories, and no clue. I had a vast, untouched expanse of stainless steel where just about anything could go. Over the course of the build, the left side of the firewall got really crowded, and I think the logic was to avoid running data wires along the main power cable coming off the battery on the right-hand side. What we have is a job broken into two lists, for starters: stuff to buy and things to do.

Oh, and by the way, it’s time to start thinking about plumbing the mandated ADSB equipment for 2020. But that’s a whole ‘nother post.

To Buy:

  • MGL RDAC XF
  • CHT probes and wire (2x probes, 4x wire, steel crimp connectors)
  • EGT probes and wire (2X probes, 2x wire, steel crimp connectors)
  • Heat-resistant shrink tube
  • 3-wire shielded cable (+, -, and ground, plus shield). See http://spectrum-instruments.com/resources/documents/splicing_STP.pdf
  • 4″ SCEET tube (See the oil cooler scoop post, the tube’s getting ratty).
  • 1″ Fire sleeve for firewall port
  • 3″ Fire sleeve for cable wrap in firewall port
  • Aluminum Z-channel to mount new RDAC (this is a maybe)
  • Blast tube (look for this in the garage)
  • EZ-Up (to keep the sun off while working. Yeah, I park outside at SMO)
  • Fire barrier goop
  • Tarp/cover (in case I have to leave the cowl off overnight. Or for a whole damn week)

To Do:

  • Dismount Oil Cooler Scoop, gain access to old RDAC
  • Dismount CHT probes from 1 and 4 (these are the ones that work intermittently)
  • Dismount old RDAC, fill firewall holes
  • Mount new RDAC. Somehow.
  • Extend fuel flow wires to new RDAC location
  • Extend fuel pressure and oil pressure probe wires to new RDAC location (Do this at home)
  • Run and wrap all wires to new RDAC location (The existing Adel clamps will work)
  • Wire up new RDAC.
  • Remount Oil Cooler Scoop
  • Devise a way to keep the hose clamps from cutting up the SCEET tube
  • Install SCEET connection from baffle to cooler scoop (Do it right this time)
  • Test all connections!
  • Fly.