« Posts tagged firewall

Fiddly bits.

8 hours.

So yesterday, I joined EAA 723 at Camarillo airport. I dunno why, but I’m drawn to Camarillo. Maybe it’s because my cousin finished and flew that little hot-rodded Vari-EZE out of there many years ago, maybe it’s because it was the first place I took passengers when I got my private ticket, who knows? But I like Ventura county, and I like KCMA. It also doesn’t hurt that the EAA hangar is right near the Commemorative Air Force hangar, where there are a multitude of interesting flying machines to gawp at. Everyone seems friendly, and the guest speaker for the meeting was an FAA official, who gave us the rundown on ramp checks and a few FAR’s that are very much misinterpreted by the likes of you and I.

The goal of this is to find a nest for my bird where I can final-assemble, certify, and test fly 313TD. Currently, there isn’t any room in either of the hangars, but one gentleman is 20 hours into phase 1 on an RV7A and another is getting ready to go fly, so maybe a spot will open up soon.

Another benefit to membership is that the chapter has a flatbed trailer suitable for moving a project to the hangar, which I will hopefully need very soon. Yet another is several more sets of eyes looking at workmanship and assembly techniques.

As for actual work on the plane, I got the left intercylinder baffle and the replacement fuel pump installed, which is nice. All the wiring is re-secured where it was, and the fittings on the sensor are properly installed with thread seal.

Today, the morning was spent with my neighbor’s vast crew-cab contractor truck, schlepping stuff to and from two different Ikea stores, one in Carson, one in Costa Mesa. We’re doing this kitchen remodel, and our designer was a complete monkey: he ordered a ton of stuff we can’t/didn’t use and failed to get a bunch of things we need, so Shelley and I had to kill our morning putting everything right in preparation for the final cabinet install tomorrow.

I did get some work in on the plane, but it’s cold in Los Angeles right now, down in the 50’s during the day. You East-coasters, Northerners and Midwesterners chuckle all you want, but the little space heater in my shop wasn’t able to take the edge off, so it kind of sucked to be out there today. Cold hands bashing on metal structures when wrenches slip reminds me way too much of college street surgery, changing out a part lying on my back under a car in an icy parking lot. One of the many reasons I moved out here and stayed.

So no, it didn’t go well. First event of the day was an oh-shit moment, when I snapped the head off one of the bolts holding the throttle bracket on. That was a study in anger manangement, and I had the presence of mind to self-soothe through the initial impulses of throwing the torque wrench through the sliding glass door. Tantrums do not fix airplanes.

Fortunately, there’s an O’Reilly Auto store not a city block from my house, so I picked up an EZ-Out (sorry, screw extractor- generic) and through some miracle, managed to get the offending bolt out of the sump. I guess I’m now 1 for 5 using those things. At least I didn’t snap the drill off inside the broken bolt like I did with the wing attach adventure from a couple of years ago.

I installed the breather tube and safety-wired the mixture bracket bolts after torquing them with a different torque wrench (A Snap-On dial-type I bought used) and those are fine. I’m hoping I’m nearly done messing around with Adel clamps. Space is getting tight.

Power feeds wired.

3 hours.

Most of them, anyway. Turns out I need a couple of different switches. I need a dual-pole on/off switch for the battery master, because I’m deleting the alternator field enable. The idea with the alternator field enable is that if for some reason your alternator goes blooey and starts up with runaway voltage, you can shut off the field before it zaps all your goodies. This is a throwback to the days when alternators sucked, some time in the early sixties, and the chances of you interrupting the field before your fancy MFD’s and other computerized avionics surge out are next to nil. Modern alternators are usually pretty bulletproof, unless you switch the field on and off while it’s spinning. Doing that can reduce the life of the alternator from thousands of hours to hundreds, so the battery master is going to be a DPST switch that engages the battery master and the alt field simultaneously. I had to order another couple of switches from B and C also: the one from Van’s sucks. It has no keyway or tabbed anti-rotation ring, and it doesn’t even have a hex nut on the panel side. So I ordered a DPDT switch for the flaps. I also brain-farted on my initial layout, and forgot the heated pitot switch. Ran the circuit for it, allotted amperage for it, forgot to put it on the panel. So I needed another SPST on/off switch for that, because the one I had originally for the pitot heat was repurposed for the pax enable switch.

Yesterday was a bit of a milestone. I installed the firewall grounding plate, which is a brass plate with a bunch of fast-on tabs on one side. The other side is in contact with the firewall, and a big 5/16 brass bolt goes through the firewall, where it becomes the attach point for the negative battery cable and the braided strap that connects to the engine block. With this in place, I ran the wires for the master battery switch. For the first time, I connected the positive power lead to the battery. When the battery master switch was turned on, there was a satisfying >clunk< from the firewall, which meant that the master contactor was working. I checked the main and endurance busses and read 12.5 volts on the multimeter. I didn't hook up the starter switches. I'm still puzzling out wiring runs, But I'll get to that soon enough.

Firewall fail.

5 hours.

Yesterday, I should have stayed in bed. It was that bad. I started out the day by attempting to mount the RDAC (engine monitor module) on the firewall. I did this by drilling out one rivet in the F-601L stiffener along the top of the firewall, then match-drilling the rest of the holes. Would have been a great plan, except when I was drilling the second hole in the firewall and stiffener, something moved and I put the hole about 3/32 of an inch below where it was supposed to go. Boom, violated edge distance. I have an email in to Van’s tech support to find out whether I’m going to have to replace that stiffener, which would suck like nothing has ever sucked before. It would involve removing the engine mount and the landing gear. The other possibility, since I’m not really placing a load on the stiffener with the 5-ounce RDAC, is that they’ll tell me to “build on.” If that happens, I just have a slightly crooked RDAC, but otherwise it’s fine. So I’m kind of freaking out about that, and really hoping I haven’t bought myself a ton of work with this one stupid mistake.

Then it started to get better: The LA public library emailed and said my copy of William Gibson’s ‘Zero History’ was available for pickup, so Shelley and I rode our bikes down there to get it. But on the way home I almost got run over by an idiot backing out of the car wash. What does this have to do with airplane building? Not much, other than it’s difficult to work on critical things in a state of elevated stress. But I needed a win of some kind, so I decided it was time to mount the heated pitot tube in the wing. Of course, that ballooned into wing wiring.

This pic doesn’t show the tubes, but I originally had the AoA and pitot lines running through the two grommets in the rib in the bottom of the frame.

But it’s a couple of years later, and I now know a lot more about EM interference than I did back then, as well as what equipment I’ll have on board. I pretty much rewired the whole thing. First thing I did was pull out all the wires and cut a section in the PVC conduit to allow the pitot heat wires and AoA tube an exit to mid-wing. I rounded off the edges of the PVC to mitigate chafing, then ran AoA tube, NAV antenna wire, pitot heat, landing light, and position light wires down the conduit, breaking out the pitot heat wires and the AoA tube, while sending the rest down to the wingtip. The strobe cable I ran through one of the grommets from wing root to wingtip, which will help isolate the strobe pulses from the NAV antenna. Supposedly RG400 cable keeps this from happening, but I’m going to be making a lot of connections at the wing root (building in the guest house, remember?), so I want to keep the strobe cable and the antenna as separated as possible. Unfortunately, I can’t close the deal, because I need two more 1 1/16″ Adel clamps for the cut ends of the conduit, otherwise they’ll vibrate against the ribs. Those should show up from ACS in a couple of days, but it really irks me to leave things unfinished because I don’t have supplies. It makes more to double check later.

The other wing got the same treatment, but I’d already cut a break in that conduit to allow for autopilot wiring. I still ran the strobe cable through the grommets near the spar, because I’m not terribly interested in having the strobes make the autopilot twitch. Also, depending on the performance of the Archer NAV antenna, I might put another one in the right wing for a second NAV radio at some point.

After all that, I didn’t get the pitot heat module actually mounted. That’s next.

MGL Avionics rocks!

3 hours.

Yesterday I took a long lunch and drove down to TOA (Zamperini Field in Torrance) and hung out with Matt at MGL Avionics for a demo of the Voyager EFIS. The Voyager is the Odyssey’s little brother, but it’s essentially the same EFIS. Matt showed me a lot of the features and a quick run-through of navigation techniques, as well as walked me through the setup screens for various aircraft parameters, and If I wasn’t sold before I walked in the door, I certainly was when I left. I was going to buy everything on the spot, but their stock got cleaned out over the holidays and they’re waiting for a fresh shipment from MGL South Africa.

If you go to the MGL Avionics website, you’ll see some video of the EFIS in action, but I have to tell you, the images on the website do not do justice to the actual unit. On the site, the screen looks really loud and playskool, but on the EFIS, it’s as high-quality and pleasing to the eye as any of the Garmin or Dynon full-synvis offerings. The unit itself is a very nice powdercoated black and the buttons are a nice metallic silver, with extremely good tactile response. My only gripe is a minor one: Terrain above you on the HSI flashes red. Not a primary, saturated red, but the flashing is annoying. I assume this is to let you know that you are potentially flying into a mountain, but a nice option would be to turn off the flashing unless you’re within a certain distance of the terrain.

I wrote a check and left with an RDAC X-D engine monitor module, while Matt packaged up the probes and senders to ship out later. All in all, a very good experience.

After work, I went home to find my shipment from B & C had arrived. Problem is, I ordered two extra E-bus diodes, so now I have to ship them back. Lesson: Always review your online order when the “review order” page comes up. I did manage to get one of them mounted, but I didn’t have my computer with me at the time, so I couldn’t wire it based on my schematic. I also got the 60 amp current limiter for the main bus mounted on the firewall. That was a 10 minute job that turned into an hour because I had to make a doubler and rivet it to the firewall, which sucked for mainly ergonomic reasons.

I’m also ordering the MGL current sensor to replace the 50mV shunt. I was originally going to go with this, then decided against it, now I’m going with it again. It simplifies wiring, and Matt has assured me that it shouldn’t be so messed up by the Earth’s magnetic field that it will be unreliable.

Tonight, when I get home, I’ll wire the E-bus feed and diode, then maybe clean up some wiring back in the Jeffries tube.

Stainless Steel Providers.

5 hours.

Oh yeah, it was a good day. Not only did it not require the use of an AK-47, I got a lot of momentum going on firewall-forward wiring. The overall schematic is still rather nebulous, but it’s based more or less on Bob Nuckolls’s Aeroelectric Connection, drawing Z11. In this scenario, there’s a main bus, an endurance bus, and a small always-hot bus. I’m toying with the idea of deleting the always-hot bus and just putting in a switch for the alternate e-bus feed because quite honestly, an always-hot bus is an excellent opportunity to drain every last molecular twitch out of an otherwise healthy battery.

Also, with the acquisition of a Garmin GNS430W, my avionics stack is now complete. EFIS, audio panel, transponder, nav/comm/gps, done. Good god, I’d love a cigarette right about now… But the upshot of this is that the the electrical picture is now complete. I have to provide power for these devices, plus the various other implements of flight, namely trim, strobes, lights, and autopilot servos. How does that work? Common wisdom is to start at the battery and work your way back. Instead, I ran loads for lighting and strobes, and today I ran starter and e-bus feed, and they’ll collide behind the panel in a Gotterdammerung of switchgear and fast-on tabs.

So the next step is, how to get the electrons from where they are to where they need to be? I had a few simple rules, gleaned from the Aeroelectric Connection and the mighty oracle of Van’s Air Force, to wit:

1. Thou shalt not run thy strobe cables alongside thy data cables.
2. Thou shalt not run thy data cables alongside thy power wires
3. Thou shalt provide ample room to service thy components after the holy top deck skin is on.
4. Thou shalt not run thy wires below tubes which carry fuel, for the drips from leaks onto that which arcs may beget the inferno.
5. Thou shalt not allow breath or light to pass between cabin and engine compartment.
6. Thou shalt not expose thy wires to sharp metal edges.

The first step was to figure out where to make holes in the firewall for pass-through of electrical cable and sensor data.

A little off from my original guesstimate, but this’ll do.  A 1-inch hole accommodates the SafeAir1 firewall Passthrough, a stainless steel gizmowith a rounded outlet to let wires exit in any direction without chafing on one side, and get sealed with fireproof tape and goop on the other.

After a little cleanup, it looks OK.

My original estimate for the size of the MGL RDAC engine monitor module was way off, and MGL doesn’t actually publish the dimensions of the unit in the installation guide, which is problematic. So I scoured the newly-minted mglavionicsusers.org forum and found the answer I needed, then made this ghetto-ass mockup from the battery box packaging and a roll of blue masking tape.  This made me reconsider the location for the data wire hole.   In theory, there should only be one data wire going aft, that of the RDAC itself.   All the engine probes and sensors should go from the engine to the RDAC.

How do you make a meal out of stainless steel?   Chew slowly.   Everybody gets all weird about stainless steel, and true, it’s a whore to work with, but remember, if you can scratch it, you can cut it.   This is a 1″ hole saw, about three bucks from B&B hardware.  The trick is to dunk the end of it in Boelube and go SLOWLY.   Make your pilot hole with a #40, then move up to 1/4″, which is the size of the hole saw’s pilot bit.   This one’s so dull it won’t go through warm cheese, but it serves as a good guide for the hole saw.   Then, if the teeth of the hole saw are sharp at all, you should be able to grind your way through the firewall fairly easily.   Keep it from heating up.  If it starts to smoke, put more Boelube on it.    The amazing torque of this Makita cordless drill is also helpful.  It’s relentless.   If you’re working above the battery, cover the battery with a sheet of plastic or something.    You don’t want stainless steel chips grinding away between your battery and the firewall.

For added fireproofing, I used a bead of my leftover Fire Barrier 2000 around the FPT (firewall pass through) flange, just to seal the deal.  Not that it’s very necessary; you get pretty much an airtight lock when the two halves are screwed together with the firewall between them.

And there you have it.   Starter load wire, main bus feed, and e-bus feed, all going through the firewall just like they’re supposed to.  What this photo doesn’t show is the firesleeve I forgot to put on the outside of the FPT before I ran the wires through it. It also doesn’t show the master contactor load wire I put in shortly after.  I put the fire sleeve on and clamped it down with one of the hose clamps provided in the kit.

Since I was feeling inordinately proud of myself, I figured I throw the engine mount isolators on there.   Still not sure how they go, I’ll have to check, but the red bolt protection nipples are a nice touch.

Up in the corner next to the VA-168 manifold, you can see the second FPT.   This will carry a data cable from the RDAC back to the EFIS, with room for future additions should I wish to take my life in my hands with some sort of electronic ignition.

And here I am, sitting in the focus of the Dynafocal brainprobe.   Maybe I can infuse it with some of my own sentience, such as it is.

I just got off the phone with my cousin, Navy SEAL and former SDV electronics tech, who assures me, despite my misgivings, that the switchgear on the panel and the power routing is not a problem.   Nor is anything else.  Where it gets tricky is the audio wiring, where impedances must be matched and other arcane spells must be cast.   I’m going to bring him out here from Yuma for the hard stuff, I think.

Fun with the Firewall

5 hours.

I can walk around that plane all day long and find things to not do because one of the ducks isn’t in its assigned row. Problem is, the days are getting shorter and I can’t wait for everything to fall into place. The firewall has been one of those things. I still need to make holes for wire pass-throughs, and bolt various things to it, some unknown as to their specific configurations and form factors. But sometimes, you have to make a move. Today I fire-sealed the cabin heat box and installed the firewall recess.

This is halfway through the process. The cabin heat box is done, and the battery box is in place. , All the gaps and openings need to be sealed up in case there’s an engine fire. A gasoline-accelerated fire in the engine compartment fanned by a 200mph gale would make every hole, crack, and gap a 2000-degree blowtorch aimed right at the occupants’ legs, something we’d very much like to avoid. I’m using 3M Fire Barrier 2000 in all those cracks. Hi-temp RTV is rated for 700 degrees, this is rated for 2000.

Hopefully this won’t be an issue. You’re not supposed to use rigid tubing from anything fixed to the airframe to anything attached to the engine. The reason for this is obvious: the engine vibration will fatigue and split a hard line in a fairly short amount of time. This is why you’re supposed to use braided steel and flexible, firesleeved hoses for fuel lines between the firewall and the fuel pump.

Since I was fire-sealing everything, I figured why not, let’s put the engine mount on. After sealing the lower firewall corners and the brake reservoir, I got the engine mount on, permanently. I considered being a showoff and putting the plane up on the gear, but then I realized I’d omitted a rather important detail: I’d forgotten to notch out a section of the lower firewall corners to make room for the gear legs. Not one of my prouder moments. But I was able to scribe out a section to remove, which I did, and it would have been really easy if it hadn’t been for the fact that stainless steel sucks to work with. It bites, so you have to file the edges down. It also hardens if you heat it up, with something like a Dremel burr. Finally I was able to get some notches done, but they’re not that pretty. That’s what gear leg fairings are for though, right?

Here’s the firewall recess all riveted in. There’s a bead of fire seal under the flanges in addition to the seams in the recess. I hope that goop doesn’t run too much before it cures.

What happens next? I don’t know. I have the rudder available to work on, maybe I’ll do the taillight.

Let Them Eat Static.

1 hour.

Finished installing the static line. Much easier to crawl down the Jeffries tube with the flap motor bracket removed. I also made some .063 spacers for engine mount. Supposedly they weld it all up in a jig at the factory, and drill the QB fuselages with the same jig, but maybe the welding process stretches the metal a bit. Anyhoo, I had to make two aluminum washers to go behind the lower middle attach points, which, fortunately, are about .063″ off the firewall when the 4 outside bolts go on. They’re probably not exactly .063″, but they will be when everything is tightened down. I have a good feeling about it. I also got out the fiberglass cap that goes on the bottom of the rudder to see how it might accommodate the Whelen A500 position light/strobe assembly, and the answer is: not that well. There will be a need for fiberglass work here, I think. I’ll have to somehow build up enough material to drill and tap threads, or I’ll have to figure out a way to get a backing plate in there. Neither option looks like fun, but there’s gotta be some light back there or we ain’t legal. I know I promised photos, but I forgot to bring my phone. I’ll catch up with that later.

Back to the fun stuff

4 hours.

Saturday and Sunday were somewhat unproductive, given the gloom-induced malaise and subsequent need to eat (organic) cheese puffs and watch TV, but I installed the VA-168 sensor manifold, the cabin heat box, and most of the static line. The sensor manifold and the cabin heat box will have to come off and get fire-sealed before I can call them done, but I need to find an acceptible fireproof sealer for the various firewall penetrations first. If everything works out right, I won’t have too much going through the firewall. Right now, I can think of some: For holes in the firewall, I’ve got 3 control cables, the brake line fittings, the fuel line fitting, cabin heat, the RDAC (engine sensor pod) cable, main bus power, brake cylinder fitting, and the various bolts holding things on. Fewer pass-throughs sits well with my universal hate for goop of any kind. But the idea is to keep windblown flames from burning avgas, smoke, and carbon monoxide out of the cabin. Dead pilots make bad landings. The 2″ hole for the cabin heat box was less traumatic than I thought it would be. I used a 2″ hole saw on a cordless drill at the lowest speed and plenty of Boelube. The trick with stainless is to go slowly and keep it as cool as you can. If it heats up, it hardens, and it will kill whatever tool you use on it. But care is needed: stainless steel makes an extremely sharp edge when cut, and it’ll go after you with near-sentient aggression. File down the edges, or pay for it later in blood.

The static line is still unfinished. I fabbed a bracket for the T-fitting that joins the two lines from the static ports on either side of the fuse, and I drilled a hole in the angle where the canopy latch bar attaches so I can run the tubing up under the left side longeron on its way to the EFIS. I got the cable clamps installed along the bulkhead, but I haven’t yet installed the bracket for the T-fitting or cut the tubing to length. I also wound up removing the flap motor because there’s no good way to winkle my big ass into the tailcone without some pretty decent contortions. I’m not a huge guy, but I’m not as limber as I used to be, and I have a somewhat irrational fear of getting stuck in a position that cuts off my air supply or leaves me unable to extricate myself without assistance. Once I’m prone in the tailcone it’s fine, as long as I remembere to bring all my tools and parts with me. The motivation to plan the job ahead of time is amplified hundredfold by the sheer amount of work it takes to climb into that space. Oh, and also to remember to go to the bathroom before you get started. I’ll post some photos tonight or tomorrow.