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!
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.
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.
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.
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.
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)
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.
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.
I’ve started work on the firewall penetrations. Since I’m using SDS/EFI there is a need for more wiring through the firewall than is the case for a conventional Lycoming installation. There is also a return fuel line associated with the duplex fuel system, and a fuel regulator. The location of all the parts and pass-throughs needs to be determined, so that I can drill the necessary holes. In accordance with current “best practice” for firewall insulation (in case of an engine compartment fire), I’m installing a Fiberfrax insulation layer on the engine side of the firewall. This requires a thin metal retaining layer on the front of the Fiberfrax. I bought some 0.002″ stainless steel foil for this purpose, but decided there was no way I could work with it without winding up with a crinkly mess, so I have switched to some 0.008″ Titanium.
I temporarily lifted the (Barrett) engine into position to ensure there’s plenty of room around the pass-through positions. I installed doublers for the AntiSplat air/oil separator and the A/C line pass-throughs, as well as various nutplates that are in addition to the plans.
Speaking of the engine, apart from desiccant plugs I’ve been using a home made “conditioner” to help preserve the engine until its first start. I placed about 2kg of (orange) silica gel in a sealed plastic cake container with an aquarium pump. The outlet of the aquarium pump goes through a respirator filter (to prevent any silica dust from entering the crank case), and then into the oil filler hole. A tube from the breather outlet goes into a glass bottle, and a separate tube from the bottle for return air into the plastic container. A humidity sensor in the bottle shows that the crankcase is being maintained at a humidity level of less than 10%, whereas the outside air humidity is often above 50%.
I also worked on the cowling mounts at this time. I’m going to use the Van’s hinge method for the firewall sides, and between the two cowl halves, but have decided to use Skybolts for the upper cowl firewall mount. To that end, I bought a kit of parts from Skybolt. Included in the kit are these nifty looking interlocking flanges, but when I started to work out how to lay them out, I found that I would have to adjust the spacing between skybolts in a fairly arbitrary way to have rivet holes in the flange overlaps occur in sensible places with adequate edge spacing. I really didn’t like the resulting uneven spacing, so I decided to make my own Skybolt flange mounts.
I used two sections of 0.032″ Alclad, overlapped in the middle (top). Marked out, drilled, cut, and then match drilled into place from the firewall edge with the top skin in place. I made a small overlap between the two halves, and dimpled all of the #40 holes to match the firewall. I also added a 0.02″ Alclad spacer to the assembly, same as would be used with the hinges, to allow for some filler on the cowl edge. With these cowl brackets complete, I put them aside since they can’t be riveted on until the upper front fuselage assembly is ready to rivet on. The hinges on each side, and spacers, were made in accordance with the standard plans and riveted in place. I haven’t done anything with the bottom hinges, since these are not used for the Showplanes cowl. I’ll most likely add a Skybolt or screw/nutplate on each bottom side but can’t really do that until I’ve fitted the cowl.
After a lot of preparation, I sprayed the clearcoat onto the overhead console. I’m not much of a painter so I’ve got one run to scrape out and the whole thing will need a cut and polish, but it turned out fairly well and I got the effect I was looking for in terms of the transition from the light grey overhead colour into the carbon fibre console. More importantly, the overhead console is now UV protected with the Durepox clearcoat product I used.
I’ve put the overhead aside for now, time for a break from fibreglass and painting so I’m going to get back to the firewall and work towards getting the fuselage up onto the gear.
My long battle with the Cabin Top is coming to a close, at least for the interior. Various choices made the task harder than it should be, but the end result is now in sight, and I’m happy with how it’s turning out.
Including A/C in this aircraft meant an overhead console would be needed, so I bought the Aerosport Products carbon fiber overhead console. I wanted wiring conduits up each front pillar to make wiring easier, so that brought about a whole load of work to glass these in and finish the pillars appropriately. I’m installing Visors so that requires mounting points, but Van’s have taken the position that holes should not be drilled in the front pillars because the holes have an unknown impact on the rollover protection, so I made up some metal inserts with Nyloc nutplates and glassed them in.
I bought the Aerosport cabin headliner kit, but the headliners were compromised during shipment. I could have repaired the problems, but overall I decided against using a headliner, which meant that I had to finish the entire cabin top interior. This amounts to a lot of work, because the Cabin Top as it comes from Van’s is quite rough, and there are a lot of complex shapes and curves involved, especially after glue-ing in the overhead console. The headliner would not have helped much either, the hardest parts are outside of the area that a headliner would encompass.
I decided to keep the Carbon Fiber look for the overhead console, this added yet another layer of complexity because it had to be masked off while the rest of the interior was painted, and masking off the line between the interior paint and the overhead console is difficult because of the afore-mentioned complex shapes.
Previous choices had an impact as well. Some time ago I chose to use the McMaster Carr door seal, so as described in previous posts I used a length of seal as a mould and built up the door frame to a constant 1/4″ width all the way around. When you do this, there is a “jag” on the inside of the seal which winds up making a nice groove on the interior side of the door edge. This is a good thing, because when you put the “real” seal in place, the seal jag slots into this groove and helps to hold it in place. While spraying fill primer, I didn’t want this groove to fill with with primer and disappear, so I had to tape off to just beyond the small groove around all the door frames. I removed this tape before spraying the primer and topcoat.
If you’re building an RV-10 and want to minimise the work on the cabin top interior, then don’t do any of the things I’ve done. Otherwise, here is the entire process I’ve used:
Fit the cabin top etc., and create the door gap for the McMaster seal (see previous post)
Fit the overhead console, and glue it in. I used Lord adhesive for this (see previous post).
Fit the wiring conduits to the front struts, and glass them in with 3 layers of glass. See previous post for details on how I used a Nylon 3D printed part to transition into the overhead. I used straight epoxy, blackened with die, to seal the Nylon transition pieces into the overhead. The same technique was used to seal around the (black Aerosport) door strut brackets.
Make metal inserts with Nyloc nutplates for the visors. Position these so that the visors just miss the overhead console when (unextended and) pushed to the front. Glass these inserts in at the same time as step (3) above. Triple check their position with the real visors before doing so!
Apply filler (epoxy + micro-balloons + cabosil) to the front pillars to create the desired shape around the conduits, and transition into the visor mount points which must be kept flat.
I didn’t like the amount of material left on the cabin top roof after the front seat belt mounting bolts were countersunk, so I added three layers of glass around these points to create a slight “bulge”. I added filler around this “bulge” to transition smoothly back into the cabin top.
Apply filler everywhere else around the interior, and to transition from the overhead console back into the interior. This took several iterations to get right, so fill, sand, fill, sand, fill, sand ….
I cleaned everything off with wax and grease remover, and scuffed the overhead console to prepare it for later clear coat, with a 600 grit wet sand. Then I cleaned everything off again and taped up the overhead, and fussed over the edge that I was going to tape to. This edge I made about 1/4″ back from the corner of the overhead – it’s really impossible to tape a straight line on the corner when you have to go around bends in three dimensions.
After cleaning off again, I applied a thin glaze of straight epoxy over the “flat” parts of the cabin top, i.e. the parts where I could use a squeegee. This was to fill pin holes. Around the curves and steps, I didn’t do anything in particular for pin holes at this point.
I rolled on a coat of Wattyl UC-230 primer-surfacer, let it dry, and sanded it back. I wouldn’t bother with this step again, I was still left with a zillion pin holes and it’s much more effective to just spray it on.
Without bothering about pin holes, I sprayed on a second coat of UC-230, using a cheap gun I bought for priming that had a 1.8mm nozzle. Once this dried, I sanded it back. The result was a zillion pin holes, a lot of small low spots where further sand/surfacer operations were required to render the interior flat, and a few larger low spots that required a bit more filling.
I filled the few “larger” low spots as required, and applied Ever-coat 440 express pinhole filler. Be careful if you use this product, it is highly toxic. After this, another coat of UC-230 and sand it back.
I repeated the process – spray on UC-230, sand it back, fill pinholes – about another three times. Each time I probably sanded 80% of the material off – but never back to the previous layer – and got down to the point where (a) I couldn’t find any more pinholes, and (b) when I sanded it back, there were no “low spots” left. It’s easy to see the low spots, they remain shiny in reflected light while the material you’re sanding doesn’t.
Once I was happy with all the surfacing, I sanded the surfacer down to the level of the tape along the transition line to the carbon fiber console, removed all the tape, and then carefully sanded the edge down further, leaving a very slight rise where the surfacer began (180 grit for this sanding). I used a sharp knife to scrape away surfacer in a few tiny places where it had crept under the tape. I removed the electrical tape around the door surrounds (to stop surfacer filling up the groove for the seal jag). Then I cleaned everything up with wax and grease remover, and finally with alcohol.
I re-taped the centre console, putting down a careful line with 3M vinyl tape, just “inside” the edge of the UC-230. I fussed over this taping a lot, because the next step – polyurethane primer – is much thinner paint and will creep under a bad taping job. Moreover, it will stick to just about anything and be impossible to get off. I left the door surrounds un-taped.
I sprayed PPG polyurethane primer, two coats. One in the evening, one the following morning. Drying time is 4 hours. It was a perfect day outside, so I decided to spray the top coat in the afternoon. For this I used my better quality spray gun, with a 1.2mm nozzle.
I sprayed two coats of PPG polyurethane topcoat, 1.5 hours apart. The 1.5 hours is just to allow the first coat to flash off. After each of the PPG primer operations and each topcoat, I rushed the cabin top back inside the garage (which is closed up) and threw a drop cloth over the whole thing to try and reduce dust, since I don’t have booth that I could fit the cabin top in.
Drying time for the topcoat is 12 hours, full cure in a week. Seven hours after the second coat, I carefully pulled up the vinyl tape. A sharp knife and tweezers helps, and it’s important to avoid dropping any “shards” of paint from the vinyl tape (which it doesn’t adhere to) back onto the topcoat – it’ll stick.
After the topcoat had cured overnight, I removed the rest of the masking on the overhead.
Unavoidably, a few small bugs landed on the topcoat and suffered a cruel death. I waited two days so that the topcoat had hardened up, and used a very sharp/pointy knife to remove the remains. I think I did this in 4 places, fortunately they were all very tiny bugs. These, and a few dust spots, will clean up OK when I cut and polish the topcoat. I’m not going to do this until after the topcoat has fully cured.
The next job is to spray clear-coat on the carbon fiber. I’m going to tape off the grey paint along the transition line, protect the rest of the interior with plastic etc., and spray the clear. I’m using a marine product called Durepox for this. I haven’t done it yet, so I’ll update this post once it is done. I did a little test piece and the chemistry between this and the PPG polyurethane seemed OK. I do expect to run into some pinholes in the carbon fiber, I can see them under a magnifier, so I’ll probably have to use a small brush to fill them, sand back, and do several coats of the clear before it is good enough to finish with 2000 grit wet and a buffing polish.
Once the clear is done, I’ll cut and polish the grey topcoat, glue the windows in with Lord adhesive, and the cabin top will finally be ready to fit to the fuselage for good. To finish the interior window transition, I plan to cut a rubber seal in half and cement it in place, as described in a Van’s Air Force post some time ago.
Of course, once the cabin top is on, I get to do a lot of this all over again, filling in around the lower door surrounds, filling and joining everything up with the existing finished paintwork, in theory so that it is not possible to see where the join is.