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.

New Rudder is On!

The new rudder is on, and the plane flies well. I think it may even fly a little better than before, but that could be a placebo effect. A couple of notes though:

  • The rod bearing distance measurements on the drawing referencing the inner surface of the spar is farking stupid. It means you have to subtract the thickness of the spar and doubler plates if you want to adjust your rod bearings using the accessible side of the spar as your starting point.
  • There’s also no way I can think of to get a 1/64″ accurate measurement of the rod bearing hole center to the spar without some weird contraption.
  • Salvage as much as possible from the old piece. In this case, I was only able to get the counterweight and the fairing attach strips, but it provided an excellent opportunity to practice drilling out rivets.
  • Use a plastic zip tie to cut out the excess pro seal from the rivet holes on the trailing edge before riveting. This works way better than it should and won’t scratch the work.

Once I actually got the parts and a solid block of time to work on it, it went really quickly. 10 years ago, I spent a lot of time puzzling things out and correcting mistakes. This time around, it was almost easy.

Rudder 3.0

It was easier to build new than repair the old one. Here are various stages – riveting skins to spar, and the dreaded trailing edge pro seal. Fortunately, I still have the drilled angle aluminum I used to do the last one, so of course it worked out fine.

Pro tip: use the end of a plastic zip tie to carve out the excess sealant that squeezes out into the dimples.

Test

Foo bar bar

Rudder 3.0

This time around, I kind of know what I’m doing. I’ve done the stiffeners, removing the plastic, all that Jazz. The only part I was able to salvage from the old rudder was the counterweight, and this time, I know the order of riveting in such a way that I’m not fighting the counterweight to do the top rib.

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.

Oil Cooler – Day 5. Progress.

Today sucked a lot less than yesterday.  I got the oil cooler attached to the engine mount, which is a significant milestone.  I also learned that you can attach anything at any angle using this One Weird Trick, which I’ll describe later.

The oil cooler itself doesn’t weigh all that much, and there are no significant loads placed on it.  The attachment method is Adel clamps, which serve to isolate it from some of the engine’s vibration.  Given that, it seems that the beef I put into the brackets is unnecessary and an example of overengineering.  That said, it’s really, really important to me that the oil cooler stays firmly attached and that it retains its structural integrity until the end of time.

Forward Bracket - Oil Cooler

Forward Bracket – Oil Cooler

The  Weird Trick I mentioned earlier is shown below.  On the right of frame, there is a large-ish piece of angle connected to another angle bolted to the cooler.  The way this works is that there’s enough span on the opposite side to cover the distance needed  by two Adel clamps when the angle is laid up alongside the tube and the adjacent side lines up with the angle connected to the cooler.  This made for a much easier test-fitting, and the same technique is in use on the bracket shown above.

So it’s come to this.  The oil cooler is suspended where it needs to be to get air to it from the big hole in the baffle. At this point, the whole setup will take nearly my full weight, so I’m not terribly concerned about the parts failing.  At this point, the weakest parts are the flanges of the oil cooler itself, and they can be reinforced with angle or bent sheet.

This is the best fit possible for access, airflow, clearance from other important things (fuel line, for example).  There should also be enough room to get a  fiberglass intake plenum between the cooler and the middle engine mount tube.  I measured.  But “best fit” means the least hideous compromise.   Now for shaping the  plenum.  Yay, fiberglass.

Happy New Year.

Oil Cooler, Day 4

This suuuuucks.   I usually feel a certain smugness when my predictions come true, but not this time.  I knew this was going to blow going in, that’s why I delayed it for so long.  I was on the money with this one.  Not one part of this has gone smoothly.  Most of it has to do with the fact that it’s impossible to suspend an oil cooler in mid-air in the place it will eventually go so measurements for bracketry can be taken.

I guess if it was easy, everyone would do it.  Today I took a different tack, and unfortunately I didn’t take any pictures, because there was nothing to shoot.  Just a lot of head scratching and pondering, followed by some fairly intense metal work.  Oh, and I managed to burn the f**k out of my left thumb and forefinger trying to grab a piece of hot angle off the bandsaw table.

At least I have a proper metal shop to do stuff in, even if it is at the opposite corner of the hangar from where my plane is.

Eventually, I was able to draw up some rudimentary plans plans based on some measurements.  That actually worked and I have a main bracket that should, in theory suspend the oil cooler in the correct position from the engine mount tubes in three places. There is also no chance in hell it’s going to break. It’s reinforced at the cooler mount point with .062 angle.

I also need a new oil hose, which is shaping up to be around $250.  Argh.

Oil Cooler, Day 3.

I thought this was going to be a fairly easy exercise.  After all, what’s the big deal, right?  Attach a flange to the baffle, mount the cooler, fab up some fiberglass ducting, slap on a length of SCEET, and presto, done.

Nah.  Slow your roll, dude.

First thing that needed to happen was removing the old cooler mounting flange.   Rather than take the baffles apart, which may have been a poor decision, I figured I’d just unzip all the rivets along the top and left of frame so the baffle can open up, swinging open from the bend right about where the spark plug wires go in.  That hypothesis was borne out.  After some less-than-stellar de-riveting, I have the baffle exposed, but even opening up, it was difficult to get any kind of squeezer or rivet set into the area by the engine mount tubes.  Before anyone freaks out, yes I did clean up the mangled rivet holes, and a couple of them went away entirely when I cut out some excess for the 4″ flange opening, seen in the next shot.

So now there’s a big plate of aluminum doubling up the baffle, to which is attached a beefy 4″ aluminum duct flange from an industrial dust collection system.  Fun fact about that:  Originally, this duct was two pieces, which included a sliding gate to control the amount of air going through the duct.  Cool setup, but it was not to be.  I either had edge-distance issues or conflicts with other parts of the structure, and it didn’t look like I would be able to set up the control cable and mount it.  Bummer, but that’s the way it goes.   I want to return to flight ASAP, I don’t want to be back to project status for any longer than necessary to make this a safe, effective modification.

The final configuration looks a little different from the above.  The flange is flipped over to provide material to rivet along the top where the baffle parts connect, and I cut one of the tabs off to allow for clearance of something else.   But it looks like I have enough room for a 90 bend of SCEET (or one of those boy-racer intercooler inlet elbows) and a diffuser.

This is where I plan to put the oil cooler.  I’ve checked for clearance to mount tubes, wires, and my fuel line (important, that), and it also clears the lower cowl.  I think I can connect to the engine mount with Adel clamps in at least 4 places, both from above and below.  It also looks like there are no immediate obstacles to exit air, but I’m not sure how airflow will be affected by the proximity of the engine mount tubes, but there is nothing directly up against the fins on the bottom.

So I guess my New Year’s resolution for 2018 is to solve all my cooling issues.  Among the things that keep me awake at night is the possibility that the 4″ duct will now steal too much cooling air from the cylinder heads.  Also on the list is to rework the baffle seals to be fewer, more continuous pieces, made of silicone instead of the black rubber baffle material.

Today is New Year’s Eve.  It’s unlikely I’ll be making more headway on this until after I go back to work, but if I keep it chill on tonight’s festivities, I might be able to put in some work tomorrow.

Happy New Year, everyone!

More oil cooler fun

Finding a spot for the new oil cooler was just part of the adventure.  I needed to make room by disconnecting the plug wires and temperature probes from the left side so I could work.  I also needed to find a new spot for the fuel pressure sensor.  Fortunately, that’s easy. I can clamp it to the top strut of the engine mount, pretty much where you see it resting now, top middle of the frame.

Ordinarily, I hate working with steel.  it’s sharp, unyielding, and awkward to work with.   This all changes when you have the proper tools. EAA 96 has a plump machine shop, with a shear, two sheet metal bending brakes, numerous drill presses, grinding wheels, table saws, a massive lathe, and two Bridgeport mills, one of which is working, but neither of which I know how to use.  There are also a number of projects in the hangar that utilize the tube-and-fabric method, so there’s a scrap can full of 4130 steel tubing and sheet cut-offs.  So that’s where I went to get the brackets I needed.   I’m sure there’s some fancy engineer-y math I could have used to bend a bracket so it works in one piece like papercraft, but I was able to get this together with two pieces.  This connects to an angle brace on the cooler and suspends it from the engine mount at the angle and distance I’ll need to get a fiberglass plenum on it, which will connect to the baffle via 4″ SCEET tube.

I chose steel because it was available, I have the tools to work it, and I can get away with less material.  I don’t have the right circumstances to do a solid aluminum webbing, so steel it is.

There will also be a support member on the bottom of the cooler, where I have to battle the mechanics of attaching to the engine mount without blocking the airflow from the cooler.  I paid for 10 rows of cooling, I want all 10 rows cooling.

New oil hoses will also be a necessity.  The top one barely made it to the cooler with an acceptable bend in the line.  There’s no way it makes it now.   I may be able to repurpose the from-cooler line as the to-cooler line, but that’s doubtful, given the fittings necessary.