Cabin top/doors – finally DONE! [320.0 hours]

I’ve been on a mission since April to get the fiberglass work on the Cabin Top and Doors behind me rather than in front of me. It’s been a bit of a marathon, the cabin top molding is not famous for its accuracy and everything has to be hand crafted to fit. Here’s the finished product:

I had planned to roll the thing in and out of the workshop to help with this work, but the weather’s been too cold to safely work with the plexi or cure fiberglass, so it’s all been done inside. I’ve had a pair of heaters going in the workshop 24/7 for the past month, and was finally able to turn them off last night. The shop vacuum copped a beating during this time, and I had to regularly clean out the filter.

Here’s all the steps I went through to get this job done. Skip to the end for the pictures.

1. Fit the rear windows

I used Lord Adhesive (available from Aerosport Products) for all windows. The forward surface of the rear windows needs to line up with the aft surface of the doors, which means spacing the windows up from the fuselage molding. I then built up the rear door pillar with a few layers of fiberglass cloth and flox until it matched. There is a flat spot on the left hand door pillar of all RV-10 cabin top moldings, this was the worst place and had to be built up about 5mm – too much for just micro/filler.

I used West Systems G/Flex with some microballoons to fill in any voids not filled with the Lord Adhesive, and trimmed any excess Lord Adhesive with a scalpel. I then taped and scuffed the window (and fuse), and applied 3 layers of fiberglass cloth on the outside. After sanding any high spots, and scuffing, I used regular West Systems epoxy with microballoons and Cabosil to fill and blend the outside surfaces into the cabin top.

2. Paint the inside door sills and cabin top pillars

The lower cabin top pillars had to be blended in, and painted, along with the door sills, to match the rest of the interior. This painting is best done before the front window is installed. Unfortunately, the inside of the cabin top and overhead is already finished, so I had to mask it all off with cardboard and tape. I didn’t want to have a yellow polyurethane primer leak splattered across the ceiling. This all took a fair bit of time, and I wound up spraying each side in sequence rather than together, because I didn’t trust myself leaning across wet paint to get to the other side.

The job took time but went OK, and you can’t tell where the paint transitioned into the existing painted part of the pillars.

3. Install the windscreen

Once again I used Lord Adhesive. It helps to have a second person helping, cleaning up any excess adhesive squeezed out on the inside using Q-tips and white spirit. I used a combination of clecos and weights to hold the plexi in position while the adhesive cured.

3.1 Extend/fill lower edge and prepare for fairing

I scuffed the upper forward fuselage area, acid etched it, and wiped some Alodine over it to prevent the oxide re-forming. I then filled the lower edge of the windscreen using Micro-balloons, with black dye to prevent it being seen from the inside. After the micro cured, I sanded it to align with the outer surface of the windscreen, taped off and scuffed the windscreen. All I used to figure the tape position was a cardboard cutout section with a 7 inch radius.

3.2 Construct the windscreen fairing

Once again using black dye. Preparation is the key to this layup, I cut all of the glass cloth strips, and allowed several hours to do this in one operation. It worked out quite well and a day later I sanded it into the correct shape, using a wooden block cut with a 7″ radius (using the band saw). I used a stick-on flexible perma-grit strip for this operation, which surprised me by staying in place. Gotta be very careful though, not to encroach onto the tape because the coarse perma-grit is a weapon.

After this I switched to 80 grit sandpaper, and finally 120 grit to carefully sand down to the top layer of tape. I used micro to fill low spots. It took a few iterations to get the entire fairing correct, and blend it into the fuselage at each side.

3.3 Glass in windscreen over the top

Fiberglass cloth across the top and down each side, once again fairing it with micro, matching it with the front edge of the door. To do this, I used packing tape on the door as a release agent, slathered micro through a section of the pillar, and closed the door onto it. The following day, a hard yank on the door would release it, and I can sand down any excess.

4 Door edges and cabin top alignment

Whenever I use packing tape as a release agent, I apply it over a layer of masking tape. It is easier to get off, and then any goo left behind simply comes off with the masking tape.

I worked sections of the doors at a time, applying micro to the pillar edges or anywhere that required building up, closing the door with packing tape in place, letting it cure, and then opening the door to release it. This is a good reason to leave the door windows out and fit them last – you’ve got the entire window opening to use rather than the door handle, and in some cases it requires quite a yank to release the door.

4.1 Door gaps, fairing across the top of the door

At this point, the doors closed properly but with basically no gap. Starting at the very top, I used a small piece of 120 grit sandpaper, and worked it from side to side through the gap, closing the door until it jammed, then lifting the door a fraction so I could keep sanding. I mostly sanded the cabin top – since it was micro and easy to sand, but also since the doors already had a nicely formed flat angle which I didn’t want to distort.

Once I could move the sandpaper side to side with the door closed and locked, I moved onto the front and back curves and did the same thing, working my way down each side in turn. Finally I sanded across the bottom and around the bottom corners, getting to the point where I could insert the 120 grit paper, and with a bit of friction still there, slide it all the way around the door.

I measured the 120 grit paper at about 0.01″ thickness. The gap will need to be wider prior to painting, but at this point I left it as is – as long as there is a gap the door is hanging freely, attached by the hinges and the door pins only. Setting up this gap allows the door to drop slightly, maybe a fraction of a mm. This required a bit more fairing work around the top of the doors, to match the door level with the cabin top.

4.2 Bottom of the doors

The bottom of the doors was a close match to the outside of the fuselage, aligned within perhaps 0.5mm across the entire length, but it is a simple matter to match it precisely. Once again, using packing tape as a release agent, I built up the door where required, and the surrounding fuselage area(s) where required, with a thin layer of micro, and then sanded it back to get an exact matchup. This introduces lots of pin-holes which of course have to be filled later.

4.3 Check the seal gap

Since the doors adjusted position a “bit” with the initial gap set, it’s important to go back and ensure that the “seal” gap for the McMaster seal is still correct – between 1/4″ and 5/16″ in my case. I made a few adjustments across the top on each side.

5 Fit the door windows

With the doors an exact match and a 0.01″ gap all the way around the doors, it was finally time to fit the door windows. These are the easiest windows to fit, you can take the doors off and use gravity to your advantage.

6 Optional – prime and fill pin-holes

I elected to spray on some primer and surfacer to seal everything up and fill almost all of the pin holes. I only sprayed two layers of surfacer, sanding most of it off each time. There are still some low spots, it’ll need more work prior to painting, but it’s good enough for now.

All of these operations took two months to complete, and it was with some relief that I took all the masking and protective film off, and wound up with a good result.

 

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    f44a
    Fixing in rear window with Lord Adhesive
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    f44b
    Window spaced up to align with door
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    f44c
    Fiberglass cloth overlaid across window
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    f44d
    Micro-balloons fairing filler
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    f44g
    Priming the door sill
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    f44e
    Topcoat on door sill
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    f44f
    Topcoat on door sill
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    f44h
    Front window ready for installation
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    f44i
    Lord Adhesive applied to rear/top edge
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    f44j
    Inside view of front window installation
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    f44k
    Metal scuffed, etched and Alodined
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    f44l
    Ready for window edge filler
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    f44m
    Micro-balloons (with black dye) applied
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    f44n
    Window edge filler sanded, window scuffed
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    f44o
    Windscreen fairing - some assembly required
  • f44p
    f44p
    Completed windscreen fairing layup
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    f44q
    Fairing sanded to shape
  • f44r
    f44r
    Applied micro (with black dye)
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    f44s
    Sides/Top glassed in, more filling/shaping
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    f44t
    Fairing transition to match the door
  • f44u
    f44u
    Filling low spots
  • f44v
    f44v
    Sanding the door gap
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    f44w
    Fairing door/fuse alignment
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    f44x
    Fairing door/fuse alignment, some low spots left
  • f44y
    f44y
    Left side door/fuse alignment fairing
  • f44z
    f44z
    Fitting door windows
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    f44za
    Fitting door windows
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    f44zb
    Glass cloth for door windows
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    f44zc
    Door windows glassed in
  • f44zd
    f44zd
    Preparing to spray primer and surfacer
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    f44ze
    Preparing to spray primer and surfacer
  • f44zg
    f44zg
    Light coat of polyurethane primer
  • f44zh
    f44zh
    First coat of surfacer
  • f44zi
    f44zi
    Filling pin holes
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    f44zj
    Tearing down after spraying
  • f44zk
    f44zk
    Removing window tape, protection
  • f44zl
    f44zl
    Cabin top and doors - finished!
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    f44zm
    Cabin top and doors - finished!
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    f44zn
    Door gap
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    f44zo
    Front view

Up on the gear [10.5 hours]

I agonized over how best to raise the airframe to install the gear legs. I gathered some family muscle to lift it up onto a workbench, but aborted the attempt after it became clear we couldn’t do the lift with enough control.

I borrowed a 500kg lift table, removed the handle, and made up a frame that provided support under both the main and rear spar. I wanted a backup in case there were any problems with the lift table, so I crudely extended the forks on the tractor, added a bit of padding, and held these an inch below the airframe, as shown. As it turns out, the table did fine and the tractor was not required.

I fitted the left main gear leg and wheel, then had to cut the old dolly apart (committed at this point!) to get it out of the way and fit the right main gear leg and wheel. After fitting the nose gear, I let the table down and the fuselage settled in a nose high position (because of the missing engine weight). It looks awkward like this, but it’s still quite a milestone to get it up onto the gear.

  • f43a
    f43a
    Raised by lift table, getting backup tractor forks in position
  • f43b
    f43b
    Raised by lift table, tractor forks for safety
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    f43c
    Raised by lift table, tractor forks for safety
  • f43d
    f43d
    Cutting away the old dolly
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    f43e
    Left main gear on, ready to do the right
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    f43f
    Left main gear on
  • f43g
    f43g
    Both mains and nose gear on
  • f43h
    f43h
    Back down, on the gear, nose high with no engine weight

Avionics goes live [5.0 hours]

My current plan is to get the airframe up on the gear so I can roll it in and out of the workshop to do the remaining fiberglass work outside. I decided to do a trial fit of the Avionics before doing this, just to make sure everything fitted properly after riveting together all of the sub-panel brackets.

The trial installation took about 3 hours, and no adjustments were required. I only did the minimal amount of wiring to get power to the panel, installing a single master switch controlling the primary (left) system master solenoid. Power came from a car battery on the floor next to the baggage door. I left out the Transponder/ADSB system, the Avidyne IFD didn’t have a GPS antenna, and of course with no engine there were no EMS sensors. I taped a COM Antenna, and the Dynon GPS puck, onto a chair outside the workshop. I ran the ADAHRS cable through one of the conduits and connected the primary ADAHRS only, sitting on a shelf in the rear. Didn’t worry about the harness cables much, just crammed them in – a real installation will take a lot longer when it happens.

It all worked at first turn-on, apart from warnings associated with the pieces that were left out / not connected. Nothing calibrated but I was able to use the COMM’s, enter flight plans, wobble the ADAHRS and see the screens update correctly etc. It was a useful exercise and helped firm up how I was going to route some of the wiring.

Now I get to take it all out again (which won’t take long) and get back to the plan – up on the gear and a month or so back in fiberglass hell.

Trial installation of Avionics


Firewall insulation [7.5 hours]

Now that the upper forward fuselage assembly is riveted on, I can go ahead with the firewall insulation, using the Titanium foil and 1/8″ Fiberfrax I had previously prepared.

In order to prevent the Titanium from puckering, I used 1/8″ stainless steel spacers (available from McMaster Carr) for all #8, #10, 1/4″ and 5/16″ holes, and stainless steel washers for larger sizes. I used RTV to hold the spacers “in place”, a few swizzles of Fire Barrier 2000+ to hold the Fiberfrax in place, and then put on the Titanium. I used machine screws to retain the Titanium in place, these will later be replaced by whatever their respective position calls for. There’s a few pulled rivets across the bottom, and for most of the pass-thru’s I had left one rivet position open so that retaining rivets can be used here as well. The rivets I used are stainless steel, and have a closed end cap, so they should seal up quite well.

I installed the A/C pass-throughs and steel AN fittings for the duplex fuel system, and riveted on the oil cooler mount. I previously made up a Titanium insert for the center recess. I subtracted 1/8″ all around from the recess dimensions, and made the insert accordingly. The thing’s a work of art, but it turns out I should have allowed more wiggle room so I’m going to toss it and make up another one.

I went on a bit of a campaign mounting various items on the firewall, to get them off the shelf and out of the way. Finally, the engine mount went on and that’s another large item no longer on the floor.

I moved the paint booth out and tossed it in the farm shed. I don’t really have much use for it in the coming months, and moving it out clears up a lot of room in the workshop. At the very least it needs re-lining, it’s more like a dark room these days. It might get torn down, I think its usefulness is over after four years of dedicated service – an entire slow-build RV-10 got primed in that little paint booth!

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    f41a
    1/8" spacers RTV'd to firewall
  • f41b
    f41b
    All spacers and washers RTV'd to firewall
  • f41c
    f41c
    Trial fit of Titanium, taped together in correct alignment
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    f41d
    1/8" Fiberfrax in position
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    f41e
    Titanium in place, oil cooler mount riveted on
  • f41f
    f41f
    Fuel fittings, heater box holes
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    f41i
    Engine mount on
  • f41g
    f41g
    Moving paint booth out
  • f41h
    f41h
    Moving paint booth into farm shed

Upper forward fuselage [85.5 hours]

With all the avionics in hand I decided how everything needed to fit behind the panel. This included not only the avionics, but also the SDSEFI system. Cable routing is another consideration – D connectors, and in some cases a “straight” section of cable running into the D connector – have to be accounted for. Suffice to say, the final layout turned out to be different than the layout I had previously worked out simply based on box dimensions.

I made up brackets for securing the rear of the IFD GPS chassis, and added stiffeners to the sub-panel where required in accordance with Van’s guidelines. I had to mount one item – the secondary system voltage regulator – on the back of the sub-panel. To make it easily removable I added nutplates to the mounting flanges. These will be easy enough to drill off and mount on another regulator if/when it must be replaced. I also drilled two fan mounting holes in the top skin, using a circle cutter in the drill press set to 250 rpm.

Once I was happy with all of the brackets and stiffeners, I primed them, riveted together the forward front fuse subassembly – including all of the brackets and stiffeners – and painted the exposed interior and top shelf area in a flat black polyurethane.

While the forward fuse was still open, I trimmed and fitted the Aerosport interior side panels, installed nutplates for these side panels, installed the NACA vents, and installed the rudder panels for the last time. I also completed all of the tunnel work, permanently installing the brake lines, fuel lines, fuel filter and wiring for the fuel pumps.

Finally the time came to rivet the subassembly onto the fuselage. One advantage of the Control Approach rudder pedals is that access is quite good through that area, once you’re upside down with your head under the panel. The riveting went fine and I was also able to complete the firewall riveting, including the brackets and spacers I had previously made up for the Skybolts.

Next job is to fit the firewall insulation and engine mount.

  • f40a
    f40a
    Drilling and cutouts in Aerosport 310 panel backplate
  • f40b
    f40b
    Making brackets for AFS ACM module
  • f40c
    f40c
    Making brackets for rear of GPS tray mount
  • f40d
    f40d
    Fitting brackets for rear GPS tray support
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    f40e
    Fitting brackets for rear GPS tray support
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    f40f
    Fitting brackets for rear GPS tray support
  • f40g
    f40g
    Fitting brackets for rear GPS tray support
  • f40h
    f40h
    Remote audio module fits in same bracket
  • f40i
    f40i
    Figuring out nutplate positions for Adel clamps
  • f40j
    f40j
    Drilling nutplate holes
  • f40k
    f40k
    Modified B&C regulator for rear sub-panel mount
  • f40l
    f40l
    Modified B&C regulator for rear sub-panel mount
  • f40m
    f40m
    Trimming Aerosport side inserts
  • f40n
    f40n
    Priming extra sub-panel brackets and parts
  • f40o
    f40o
    Cutting Fan holes in front forward subassembly skin
  • f40p
    f40p
    Riveting brackets to forward front panel assembly
  • f40q
    f40q
    Fitting skin to forward front subassembly
  • f40r
    f40r
    Upper forward fuse subassembly riveted together
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    f40s
    Upper forward fuse subassembly riveted together
  • f40t
    f40t
    Ready to paint flat black on upper forward fuse subassembly
  • f40u
    f40u
    Painted upper forward fuse subassembly
  • f40v
    f40v
    Painted upper forward fuse subassembly
  • f40w
    f40w
    Fitting Aerosport side panels, NACA vent proseal'd in
  • f40x
    f40x
    Bucking rivets the hard way
  • f40y
    f40y
    Upper forward fuse riveting complete!
  • f40z
    f40z
    Upper forward fuse riveting complete!

Avionics [2.0 hours]

Last October I decided to use Advanced Flight Systems for the Avionics. They were great to work with and were able to take my hand written sketches, various CAD drawings and models, E-mails, and verbal descriptions and turn it into a coherent package of avionics and panel insert designs.

I signed off on all the drawings after about a month of dialog and more or less forgot about the whole thing until a wooden crate arrived here today containing the panel and avionics. AFS did a great job of packing it all up properly and everything arrived in pristine condition.

With all the avionics now in hand, I can finally work out where to mount the various boxes behind the panel, and do the necessary sub-panel cutouts and reinforcement. Between all the avionics and the SDSEFI equipment, there’s quite a lot to pack in behind the panel.

Apart from checking that everything arrived OK, I temporarily mounted the TFT display bezel on top of the LH panel insert. It took quite a bit of CAD work last year to ensure this bezel would squeeze in above the AF5600T EFIS, and match the contour of the panel insert. It fitted perfectly. I need to buy some black S/S #6 screws, so that the four mounting screws melt into the background rather than shine in my face.

  • f39f
    f39f
    Panel crate arriving
  • f39a
    f39a
    Ready to open
  • f39b
    f39b
    Well packed
  • f39c
    f39c
    Working through the layers
  • f39d
    f39d
    Panel out of the box
  • f39e
    f39e
    All this has to fit behind the panel
  • f39g
    f39g
    TFT Bezel fits
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    f39h
    TFT Bezel fits
  • f39i
    f39i
    TFT Bezel

Cabin top on – for good [11.5 hours]

I’ve fitted the cabin top – for good. It’s riveted on and retained with structural epoxy, so it isn’t coming off again. The RV-10 is often described as the aircraft kit that is 90% metal, and 80% composites. The cabin top goes on and off many times before it is “right”. I finally decided there was no reason for it to come off again, so … on it went. This time I scuffed the door channels and slathered on some flox, dropped the cabin top in place, did up all of the bolts along the door channel and installed rivets along each rear side of the cabin top. Now I have to fill the vertical parts of the door channels with structural epoxy, fit those bolts, and then finish the inside of the door channels with micro, fill primer, then prime and paint to match everything up with the already-painted cabin top interior.

I also primed, assembled and painted the tunnel cover pieces I’ve had laying around for a few months. These are cut and modified because of the control approach rudder pedals, which require slots and doublers in the front most part of the tunnel cover. The spray booth has just about outlived its usefulness, so I’m going to move it out of the workshop to free up some room.

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    f38k
    Tunnel covers primed
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    f38j
    Front most tunnel cover section, slots for Control Approach rudder pedals
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    f38i
    Tunnel cover primed
  • f38g
    f38g
    Overhead ready for final installation
  • f38f
    f38f
    Scuffed door channels before final overhead fitment
  • f38e
    f38e
    Overhead riveted in place
  • f38a
    f38a
    Cabin top riveted on
  • f38d
    f38d
    Front pillars in place for good
  • f38c
    f38c
    Conduits from overhead will fit inside Aerosport Cabin inserts
  • f38b
    f38b
    Fitting cabin top

Firewall insulation [31.0 hours]

I’ve been working on the firewall insulation. There’s a lot of material on VAF about this, I won’t repeat it here. Suffice to say I’m using an insulation material called Fiberfrax, 1/8″ thick, on the outside of the firewall. In order to hold it in place, a thin metal foil layer is required. I’m using 0.008″ thick Titanium for this layer (I previously bought some 0.002″ Stainless Steel foil but decided I couldn’t work it without having it crinkle up and/or tear. Impossible to drill a hole through it). The main purpose of firewall insulation is to give me some time to get the aircraft on the ground in some sort of controlled manner, in the highly unlikely event of an engine fire. A secondary purpose is to minimise the amount of heat that can be transferred into the RV-10 tunnel.

I found the best tool to cut the Titanium foil was an ordinary pair of scissors. Drilling small holes wasn’t a problem, but enlarging them with drill bits is not possible. I used a series of reamers for the smaller holes, the angled end of the flutes works well. To drill a #12 hole, for instance, I would first drill a #42 hole, then #39, #35 using drill bits, then #30, #19 and finally #12 reamers. The back of the foil must be supported of course.

For larger holes, a step drill works, but to finish the hole or enlarge anything beyond around 9/16″, I used a 1/2″ round sanding attachment in a die grinder. These wear out quickly, I went through around twenty of them. Doing these large holes with the die grinder worked well, as long as the foil was supported right up against the stainless steel firewall.

In an ideal world, all of the firewall nutplates and pass-through positions would be known when the firewall was laying on a bench, before ever being attached to the fuselage. That doesn’t happen, so I had to find a way of accurately drilling holes through the foil for all of the nutplates etc. To do this, I 3D printed a lot of disposable drill guides. For any purpose, I designed a drill guide, printed it, and used it to accurately drill a #42 hole through the center of whatever I needed to. In this way, I worked around the firewall and made all of the holes required in the Titanium foil. I used #6 screws through the AN3 nutplates to hold the foil in place while I worked on it, and clecos where appropriate.

With the foil prepared, I cut the Fiberfrax to shape, sandwiched it between the foil and firewall, and then worked my way around all of the holes, cutting the Fiberfrax as necessary with a sharp modelling knife. For the engine mount points, I completely removed the foil and ‘frax. All of the gaps will be filled in later with Fire Barrier 2000+.

I then set the Fiberfrax and foil aside. I can’t attach it permanently until the upper forward fuselage assembly is riveted in place. In fact, all I seem to have done for months now is to prepare parts, and set them aside.

One of the downsides of adding firewall insulation like this is that it makes future firewall modifications difficult. It is possible to drill through the foil and firewall, but deburring is a problem. I tried to anticipate everything I could, and for pass-throughs I put in more than I needed, it’s easy enough to plug up unused pass-throughs. I also made a separately mounted plate that attaches to the right side of the firewall, for mounting electrical components on. At some future time, if the electrical requirements change, I can simply make up a new mounting plate for them, rather than rely on firewall mounted nutplates for each individual component.

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    f37a
    3D printing a drill guide
  • f37b
    f37b
    Drilling holes in Titanium foil
  • f37c
    f37c
    Drill guide to go through AN3 nutplate
  • f37d
    f37d
    Drilling center hole through Titanium, from the rear
  • f37e
    f37e
    Drilling holes for oil cooler mount
  • f37f
    f37f
    Marking out upper Titanium foil sheet
  • f37g
    f37g
    Cutting upper Titanium foil sheet
  • f37h
    f37h
    Holes cut out in top Titanium sheet
  • f37i
    f37i
    Titanium foil insert for center section
  • f37j
    f37j
    Titanium foil insert for center section
  • f37k
    f37k
    All the drill guides used for Titanium foil
  • f37l
    f37l
    All holes and cutouts done, except for center
  • f37m
    f37m
    Engine mount cutout
  • f37n
    f37n
    Engine mount cutout
  • f37o
    f37o
    All holes and cutouts done, except for center
  • f37p
    f37p
    Fiberfrax stored for later use
  • f37q
    f37q
    Pass-thru's riveted on

Annunciation with “attitude” [15.0 hours]

There were quite a few early RV10 incidents with doors opening in flight. Most were due to doors not being properly latched in the first place. Van’s added a safety latch, but most builders choose to install the awesome Planearound safety latch. In addition, Vans supplies magnetic reed switches to sense each door pin being closed, together with panel lights to provide a visual “door open” indication. Some EFIS’s can also accept an input and provide a door indication.

When I did the panel layout, it was clear that space was at a premium. The door annunciator lights seemed like a single function waste of space, albeit an important one. I started looking at a TFT display to combine several annunciation functions, and narrowed the search down to a small TFT touch display module made by Matrix Orbital, the GTT38A. Readable in daylight, dimmable, and being a touch display, the possibilities multiply.

The fit was tight. I designed a bezel and verified the fit by printing prototypes on my (cheap, consumer) 3D printer. Checked the 3D model when integrated into the panel models. Finally, I had the bezel printed in black UV resistant epoxy, which cost me a total of $25.

The module sits above the pilot side EFIS and the bezel matches the shape of the panel insert in the Aerosport 310 panel. In order to minimize the depth, it is necessary to modify the GTT38A module, and remove most of the connectors. These will be simply be replaced with a few flying leads which go through the panel to a small connector. The module requires +5V power, ground, and a 4-wire RS-232 interface (TX,RX,CTS,RTS)

Front side of the bezel
Inside of the bezel
GTT38A module (badly overexposed) and 3D printed bezel
Position of TFT module on the left hand panel insert

With the TFT touch module in position, it’s time to get creative and decide what what other useful tasks it can perform apart from replacement of the door annunciator lights. There’s an embedded CPU associated with the power system I’m designing for the SDS-EFI system, with plenty of spare capacity, access to some interesting sensor data, and the Internet if cellular service is available.

There’s a valid philosophy going around about modern aircraft panel design, that says any old pilot should be able to get in and fly the aircraft, i.e. what they are presented with should have the same look and feel of any old Cessna, to avoid safety issues associated with a lack of understanding about the modern avionics. I don’t have a problem with this approach, but I’m building this aircraft for myself, and my better half, and as such I don’t feel tied to having (for example) a legacy keyswitch with “LEFT/RIGHT” magneto positions, despite the fact that there are no magnetos.

The following images are actual screenshots from the GTT38A, driven by early software written to test out a few concepts and verify the functionality.

First thing is the startup screen. You climb in, and turn the masters on. This could be just about anything, including the time, a startup diagnostic report, whatever. For now, it’s just the aircraft callsign:

OK, so I’m now holding the checklist card, and I’m ready to start up. I need to move on from the above startup screen (whatever it ends up being), so I touch the GTT38A display, and I’m presented with the following:

That’s right, if you don’t know the security code in this aircraft, you won’t be going anywhere. I already have one key for the fuel locks and another key for the doors and baggage door. I didn’t want a third key for the ignition. There is no keyswitch in this aircraft. Without the code entered here, the engine start button won’t do anything, and there won’t be any power supplied to some essential parts of the SDS-EFI system.

There’s a design issue associated with this. It’s fine to disable mechanisms on the ground prior to startup, but once in the air, there must be no possibility that a fault in the electronics can disable essential systems. This includes faulty software design, electrical I/O signalling, or any other issue deep in the electronics itself. Suffice to say, once the correct code is entered and the engine is started, there are low-tech redundancy mechanisms in place to override the dis-engagement interfaces that the security lockout employs on the ground.

OK, so we enter the correct code. Here’s the next display:

This is the original purpose of the TFT display. The three “lights” on the right are for left door, right door, and baggage door. In the actual prototype, the lights flash if the doors are open, and the “UNLOCKED” text does as well. There is really no way to ignore or not notice it. When all the doors are closed and the pin sensors are all engaged, there will be “three greens” and at that point touching the display will move on to the next category. Until the doors are locked, touching the display will do nothing.

There’s an issue with such a hard nosed approach. What about wanting to do an engine run on the ground with a door open, for maintenance? The answer is to have multiple security codes, that allow different paths through the procedures. A maintenance code, which might require more digits as well, can be assigned to allow bypassing certain lockouts such as the door lock test.

Assuming we’re in normal operation, after the doors are locked, we will be going through the startup checklist. Most of these items will be covered by panel switches that are outside the scope of the TFT display, but there are a couple of items that are not, such as testing the Coil Packs. When I went through the electrical system design, one aspect was to consider everything I needed for the dual SDS-EFI system, and that included being able to test everything during runups. This exercise made it clear I needed a switch for each Coil pack, in order to test the Coil packs (akin to a magneto test). There was no need for these switches at any time other than during runups. The CPU which monitors the redundant power system has access to a mechanism to disable power to the coilpacks (same in-flight comments as before), so I chose to do these runup actions using the TFT display, saving two panel switches and associated wiring and mechanical connections in the process.

Checklist items that are initiated from the TFT display are simply a sequence of items, and you can sequence back and forth through the items with “NEXT” and “BACK” buttons. Here, for instance is the display for testing the Left Coilpack

With the engine at the selected runup speed, touch the large button to disable the Coilpack. The display will change to this:

In this mode, the Coilpack is disabled, and the “NEXT” and “BACK” switches are also disabled. You can’t go anywhere without re-enabling the Coilpack. The checklist item will call for the pilot to check engine RPM drop, probably 50RPM or less. Once the check is complete, the Coilpack can be re-enabled by touching the large centre button, and the display will revert to the previous state. Clicking the “NEXT” button will proceed to the next checklist item, which would in this case be the right Coilpack:

We go through the same procedure here.

There may be additional checklist items, if so they’ll be presented in the same simple form. The idea is not to take over the job of a printed checklist, and not to take over a checklist facility that the EFIS system might provide. The checklist items deployed by the TFT display are simply those that the associated controller has access to, and can’t be accessed elsewhere, i.e. items associated with the SDS-EFI system that are provided and controlled by the redundant power system.

After checklist items are completed, the TFT display will have a number of run-time options. These will probably be selected by swiping the display, to scroll between pages horizontally. The displays will generally be limited to those items not available elsewhere, the idea again is not to try and be another EFIS, but to do things the EFIS can’t do.

For example, current engine monitoring products aren’t set up to monitor electronic fuel injection operation. The power system I’m designing performs redundancy in a distributed manner, each fuel injector has individual power that is redundant and protected. Along with this comes current monitoring, but the injector current is dynamic. ADC’s sample the injector currents, and this data is available for presentation on the TFT display. A typical injector current display might look like this:

The display is deliberately simple. There are no scales, just cylinder numbers and graphs. The last thing a pilot needs is more complex displays flashing in his face. The above injector current data is sampled and will update around 10 times per second. The “shape” of these plots show the familiar “blip” on the leading edge, caused by the back EMF as the pintle opens on the injector.

We can do some simple heuristics on the injector current profile. In the highly unlikely event of an injector going open, wiring going open, or ECU driver failing, the display will look like this:

Obviously the next step would be to switch over the ECU. If the failure goes away, the ECU driver or wiring as far as the injector relay box is a problem. Regardless, the next step would be to land as soon as possible.

Other parameters can be considered – pulse width, presence or absence of the pintle “blip”, area under the curve etc. and measurements that fall outside of a particular range could be highlighted by changing the plot color to red. Again, indication only – no automated actions – and nothing too flashy, just an additional piece of easy-to-interpret data that may help to quickly diagnose a situation where the engine starts running poorly.

I’m sure there will be more applications for the little display, such as:

  • Display Air/Fuel ratio from a wideband O2 sensor
  • Display Coilpack dynamic current
  • Display data from FWF thermal or pressure sensors, for future cooling efficiency testing.

In the meantime I get to delete two annunciators (doors) and two switches (coilpacks) from the panel so in that regard I’m already ahead.

Ground Block Horror Show [0.5 hours]

I ordered a 48 pin ground block from Aircraft Spruce, P/N 07-03464. The block is actually made by B&C Aero. Nothing much to it, just a heap of Faston terminals soldered to a brass strip, with a brass bolt at one end.

Unfortunately, whoever made the block has flowed solder all over the terminals, filling all of the locating holes. There are blobs of solder clumped onto the terminal faces, and flux/resin residue all over the place. In contrast to this, the “representative” photo of the product on ACS’s web site shows the holes clear and the contacts in their original condition.

Faston connectors have a “dimple” on them that positively locates the terminal into a hole on the spade. This locates the terminal to ensure proper mechanical mating, maximum contact area, and provides a measure of protection for the connection from coming loose or free due to vibration.

Since the holes are all filled in with solder on these terminals, this proper mating will not occur, and connections to this ground block could easily come loose and fall off. The solder blobs on the spades will cause distortion of the Faston connector, permanently deforming the lugs and causing a poor connection over time. Moreover, the contact resistance and its properties over time are an unknown quantity, since the original contact material extensively researched by the Faston terminal manufacturer has been replaced by whatever grade of solder was used under the unknown application conditions that existed when this ground block was made.

If ground points start degrading or falling off in flight, the outcome could be very serious, and potentially fatal. Anyone who has ordered one of these products should check its condition before installing it.

I’ve asked ACS for a refund. I could reflow it and clear out the holes, but the blades would still be covered in solder residue and that defeats the dimensional tolerance and contact material the original manufacturer of the Faston contacts has in place.

Description of detent and hole in web section
Product as advertised on ACS’s website
  • bc_gnd2
    bc_gnd2
    Solder and flux all over contacts, holes filled
  • f36a
    f36a
    Solder and flux all over contacts, holes filled