Construction work has been spotty for the past few months due to some work commitments. Time to catch up on a few posts.
I received the prototype 3D printed inlet plenum, after a very long delay caused by Covid-19, a shipment lost in customs, reprinting a replacement, more shipping delays etc. This part was printed in ASA material by a vendor in Sweden. Quality is good apart from some areas where the wall thickness should have been greater.
The part fitted perfectly around / through the compressor, the air filter shroud mount etc. The inlet ramp was also good, perfectly horizontal and lined up with the opposite side (standard Showplanes fiberglass plenum) within 1mm, which is good enough for me. The front edge of the inlet ramp is too far forward, requiring me to trim too much of the cowling. While it would work, it doesn’t leave as much of the cowling inlet hole as I’d like, to get nutplates and some sort of overlapping seal in there. This is one of the areas where the wall thickness is also a bit low. Clearance on the bottom side to the cowling is good, a bit over 1/8″ at the closest point. The rear scat tube connection for a heat muff is also good.
Overall, close to a hole in one which I’m relieved about given how complex the part is. I can now proceed to finish the front of the baffles and around the governor. I’m going to need to address the wall thickness issue and trim back the front edge, which means re-printing the part. These are simple adjustments but I’m going to also look at whether any better alternatives exist than the ASA material I’ve used.
It’s really hard to see much from the pictures, because the 3D printed part is black, but they show the general idea.
Since I didn’t use the Skybolt flanges, I needed to drill out both the cowl and the custom built flange holes that I’ve been cleco’ing so far for holding the cowl in position. I used a step drill to take a section of holes out to 15/32″, removed the cowl, and drilled the flange holes further to provide enough clearance for the retainers. A tapered hand reamer is handy for touching up the 15/32″ cowl holes slightly to fit the rings.
I used floating retainers for the lowest position on each side. These allow a bit of up/down movement, not sure they were necessary but I put them in anyway as they were part of the kit.
While waiting for the 3D printed inlet plenum, I went back to complete a few cowling jobs.
The hole that I cut out of the lower cowling to clear the A/C compressor needed to be filled in. To do this, I taped a 1/4″ thick cardboard spacer in front of the A/C compressor, then applied play-doh to build up a shape that looked aerodynamically reasonable. I applied more masking tape over this, and then packing tape to act as a release agent. I then took the bottom cowling off, and applied two layers of fiberglass cloth over the taped off area. Once this cured, I pried it off, trimmed the excess, and scuffed the resulting shape all over.
After removing the tape and packing, I epoxy’d and cleco’d the shape piece in place, turned the cowl over, applied thickened epoxy to fill the gaps around the cutout, and then applied two layers of glass cloth over the entire inner area. Once cured, I applied a layer of micro to the outside, and sanded it back to form the final shape. There were a lot of crater sized pin holes and these will have to be filled, apart from this the A/C compressor bump on the lower cowling is done.
I also did the oil door. I stiffened the door with a piece of 0.063″ Alclad, bent into shape by hitting it with a rubber mallet. In retrospect, I should have either drilled some lightening holes in it or perhaps 0.032″ would have been OK, the door is quite heavy. I used a pair of Cessna KM610-64 Camloc’s for the catch, building up the button area with thickened epoxy to match the oil door thickness.
I also fitted the Aerosport RV-10 emblem covers to the cowling halves. Just follow the instructions, being careful not to epoxy the cowl halves together anywhere except where you intend to.
Over the past month I’ve had to deal with something that was always going to stop the project dead in its tracks – sorting out how to mount an Airflow Systems A/C compressor inside a Showplanes cowl. The main problems are:
The A/C compressor doesn’t fit – it smashes into the cowl
The A/C compressor occupies almost all of the space normally used for the left hand air inlet plenum
I’ve seen other build efforts that range from leaving out the left hand induction air plenum entirely, to an A/C compressor mount position that occupies a good part of the area of the left hand inlet duct – in turn compromising the cooling air for cylinders #2, 4 and 6.
Recent efforts in Australia, such as this one, use a longer arm on the A/C mount to drop the compressor down low, and make a bump on the bottom cowling to suit. Armed with the latest mount kit from AFS, I proceeded to test mount the A/C compressor, and immediately ran into quite a bit more trouble than I had expected.
Tensioner wheel, bracket
The supplied drive system simply didn’t work. The tensioner (idler) wheel, using the supplied bracket, hits the starter motor. I can see that with the previous “short” arm, the system would swing up higher and that would free up enough room for the idler wheel to swing past the starter motor. I sent feedback to AFS about this but received no reply. After consulting with the Australian builder referenced above, it turns out the solution was to:
Add spacers, for a total of 7/16″ of spacing, to the engine mount. This moved the entire compressor assembly “away” from the starter motor by 7/16″.
Machine a replacement idler pulley, which was the same size as the AFS supplied pulley, but without the ridges on each edge – saving around 1.5mm of edge distance.
Make a longer arm, even longer than the “long” one AFS supply
I started making up additional spacers (AFS supplies three 0,063″ spacers), using 0.063″ Alclad, but I was only able to add two of these before I ran out of threads on the engine studs used for the A/C mount. I didn’t want to replace these studs, and I didn’t want to switch over to low profile lock nuts – the A/C compressor is quite heavy. So, my spacing limit without resorting to these measures was 0.3″.
The guy who did the VH-BKK installation referenced above graciously had another idler pulley made, and sent it down to me. Armed with this, I still needed to change the position of the idler mount, which means I have to build a new idler mount bracket. I’ve ordered some 6061-T6 plate to do this, in the meantime I drilled a new hole in the existing bracket (rendering it structurally unsound) just to prove I have the hole position correct. This is shown in the following picture, along with the new idler pulley. The clearances everywhere around this are very small, but this is typical and they will be adequate. The idler pulley can now swing up past the starter motor with about 1.5mm of clearance.
I also had to change the Serpentine belt, for this arrangement I fitted a 4PK1130 belt, rather than the 4PK1113 belt provided with the kit – just 17mm longer.
It is necessary to cut out a section on the front of the Showplanes cowl and fiberglass a bump in place to provide adequate clearance for the front of the A/C compressor. There’s nothing hard about this, and one good thing about the Showplanes cowl installation is that the Serpentine belt does not overlap the inlet at all (unlike with the Van’s cowl) – so there is no air leakage associated with treatment to clear the Serpentine belt, and no compromise to cooling air inlet area.
LHS Inlet Plenum
I had expected to solve this problem with various cuts and balloons etc. to the existing inlet plenum. After looking at the problem, I didn’t even attempt it because (a) this was going to beyond my fiberglass skills, and (b) this is probably beyond anyone’s fiberglass skills. There simply isn’t a clear enough path through the maze to make an adequate shape, and unless I could turn the plane upside down, gravity was always going to work against me.
After some soul searching, which included consideration of leaving the A/C system out, I decided to go ahead and create a 3D model of the entire system as a means to 3D print a replacement inlet plenum. The top end is identical to the Showplanes system, using the lower 1/3 of the circular inlet hole for induction air. The plenum has to step down and change shape, wrap around the bottom of the A/C compressor while clearing the bottom cowling, and then join in to a replacement shroud around the existing Showplanes air filter system. Here are some screenshots which include various early prototypes and the final model, which includes an air takeoff to account for the standard Van’s 2″ scat tube outlet for air to a heat muff.
The inlet plenum as shown can be 3D printed in one piece. It is secured at the bottom by three screws in the LH air filter shroud, using nutplates, same as the standard Showplanes arrangement. Around the compressor, two places mount to the A/C compressor lugs using Buna-N rubber spacers, AN3 bolts and washers. The vibration-damping spacers are rated to 200 degrees F which should be adequate. At the top, a flat Alclad plate which extends down from the existing #2 cylinder mounting flange is secured across the heat muff air inlet area, and at the very front of the inlet, using #6 countersink screws with nutplates on the underside of the inlet plenum. One of the front positions uses a low profile nut, embedded in a hex shaped hole, instead of a nutplate.
For the plenum material, the choices are currently between UV resistant ASA, or the more expensive UV resistant tough resin. Both have high glass transition temperatures and adequate chemical resistance. The plenum does not extend back too close to cylinder #2.
To prototype the system, I printed the plenum in sections on my cheap consumer grade 3D printer, using PLA, and taped the parts together. It takes about 100 hours of printing time to do the complete model, and I’ve made several revisions to refine the design and fix up the various maths mistakes I made along the way. It’s been a laborious process but I’m happy enough with the end result. It takes a high end desktop platform 15 hours to render the model in suitably fine detail, and a bit of repair processing to derive the final STL file. I uploaded the (64MB) STL file to http://www.craftcloud3d.com and was quoted just over U$200 to print the model in Black UV resistant ASA, with 40% infill.
Just today I pulled the trigger and ordered the final article, it’s being printed by a vendor in Sweden, and will be delivered here within two weeks. There is still a chance that the final piece will require some small adjustments. There’s a limit to how far I can go with taped together sections, and how many times I can re-measure everything. The final model is way more complex than I had expected, and has consumed far too much time, I’m tired of fretting about it so it’s a relief to get it off my desk.
In the meantime, there are a few other, much simpler pieces I can design to help with the baffling around the governor etc. I’ll complete these, but mostly I’ll be getting back to actual, real, physical work on the project – there is a lot still to do.
Very slow progress recently due to various issues, travel and otherwise. I’m also way behind with build log posts, so here’s the first catch-up one.
I started looking at the engine baffles, and fitted some of the rear ones. I can’t trim the baffles until I fit the cowling. I can’t fit the cowling without knowing where the spinner is located, and I can’t figure that out without mounting the propeller. So, out of the farm shed came the propeller crate, and I unpacked and fitted the Hartzell 3-blade composite propeller. Then I was able to bolt the spinner in place, and measure the distance from the flywheel to the spinner.
Just about every builder seems to make up a simulated spinner from a circular piece of wood, as described by VAN’s. I didn’t have any bolts on hand that would suit such a thing, and it seemed to me the real spinner hub was already a pretty good reference for setting up the cowl. So that’s what I did, and it worked out great. There is of course the issue of also having the real composite propeller blades in harm’s way during the cowl fitting process. This is just a workshop discipline issue as far as I’m concerned, and simply means being clean and methodical – so maybe it actually helps.
The Showplanes cowl itself is a work of art – a very high quality moulding and the fit to the fuselage is excellent. The instructions that come from Showplanes, though, are quite poorly written. For the initial cowl fitting the message is to simply follow the VAN’s instructions from the RV-10 build manual. That’s what I did, and if I was going to do it over, I would do the top cowl aft edge final fit differently, as I’ll note below.
Here then is the complete procedure I used to fit the cowl. With this procedure, I found that I only had to get the bottom cowl in position once, i.e. trimming of both the aft and side edges were done in-place, so by the time I removed the bottom cowl for the first time, it was fitted with all four side and rear hinges riveted in place.
Trim the front flange of the upper cowl, so that the two cowl halves fit together with a circular front surface that is a good fit with the spinner. I drilled six #30 holes at the positions recommended in the Showplanes instructions, so that I can easily fit the two halves together in the same position with cleco’s. Don’t drill out for nutplates yet.
Run a piece of 2″ masking tape across the top of the fuselage, with trim lines at 3″ and 4″ back from the edge of the fuselage where the top cowl aft edge will need to be trimmed. After marking these trim lines, I also ran a piece of 3/4″ masking tape around the top of the fuselage, about 1mm back from front edge. This was simply to protect the top skin when I did the final sanding of the top cowl aft edge “in place”.
Put the top cowl in position. I wadded up a towl around the top of the flywheel to get the top cowl in place. For the cowl to spinner gap, I used 3/16″. There’s a debate about spinner gaps on this VAF thread and by the time I was all done with both cowls the gap was more like 7/32″. Tape the cowl in place, and measure back from the 4″ trim line to establish the trim line on the aft edge of the top cowl.
Take off the top cowl, and cut off the excess, leaving around 2mm aft of the trim line to allow sanding back to the final fit.
Here’s why I would do it differently a second time around. I sanded the top cowl back to the trim line at this point, per the instructions. Then I drilled (from underneath) and cleco’d the aft points of the top cowl into place. The problem with this is, when I put the bottom cowl into place, and cleco’d the two cowl halves together at the front, I found that the position I had the top cowl wasn’t quite right. It only takes a tiny deviation at the front, to change the aft corners a lot. In the end, I decided the cowl had to be right, so I set it up in the correct position around the spinner (allowing for a bit of engine droop over time), adjusted the holes on the top aft edge by drilling (most) of them out to 3/16 (gold cleco’s, and I’m left with a gap of about 1.5 mm across the right rear corner of the top cowl where I’m going to have to do a layup to extend the cowl back to where it needs to be, because as it turns out I trimmed too much off it in the first place. So step 5 below is what I SHOULD have done:
Back when I made the brackets for the Skybolts, I would have drilled the center locating hole #40, instead of #30, just to give more options if I had to finesse locating holes. Now, before putting the top cowl back in place (still with 2mm of excess material on it), I would have made up a few “flaps” of cardboard that are taped to the top fuselage and can be flipped over to show the location of several of these #40 holes across the top cowl aft edge – so that enough holes can be drilled through from the top (I’d do #40, then #30) to secure the top cowl in position as it gets sanded back to fit against the fuselage. Now, with this all prepared, set the top cowl aside, still with ~2mm to sand/trim back on the aft edge. This sanding to size will only be done with the bottom cowl in place – because that’s the way we can guarantee that the top cowl is in the correct position.
Prepare the bottom cowl. I used a laser to establish a center line, by trial and error of the cowl position on a workbench while checking the horizontal measurements at (a) the front, and (b) the rear of the cowl. This center line turned out to be almost exactly in the center of the slot in the lower part of the cowl, but I didn’t want to rely on that – too used to VAN’s mouldings I guess. Removing the lower cowl with a 3 blade propeller can be a problem – I chose one of the common solutions which is to cut the slot for the nose gear leg fairly deep, and I’ll need to install a cover over it as part of the installation procedure. Before cutting the slot, I match drilled four #40 holes into a piece of scrap 0.032″ Alclad, that can be used to retain the aft edge in place after the slot has been cut. Without this retainer plate, after the slot is cut, any attempt to pull up the aft edges of the lower cowl will distort the cowl by pulling the two halves apart around the slot. Now cut the slot. I used a 2″ hole saw, and located the center of the hole 2″ down from the forward most part of the solid surface on this part of the cowl – see the pictures. This places the top part of the hole 1″ from the edge where the honeycomb filler starts. I then used a jigsaw to cut out both sides of the resulting 2″ slot. This created a long slot, wide enough to get around the gear leg without the gear leg fairing – I’ll widen the slot later to fit the fairing. That gives me a bit of wiggle room if the slot is not quite in the center, since this can be checked against the un-faired gear leg once the lower cowl is in position. Tape up the front gear leg with some masking tape, to protect against scratches, and sand any rough edges off each side of the slot.
The untrimmed lower cowl, even with this long slot, is still difficult to get into position with the 3 blade propeller. I used an engine lift to lift the engine up until the nosewheel was off the floor by about an inch, this gives just enough room to get the untrimmed lower cowl into place. By the time I took the lower cowl off again, it is trimmed and all hinges are fitted, and I was able to get it out without the engine lift. This is how I want it – no special tools required to get the cowl off for maintenance. To get the cowl on this first time though, it’s a bit of a trick and definitely takes two people. I positioned the propeller blades as shown in the pictures – the blades are not quite at the 4 and 8 o’clock position – measure from the blades (at around the places where the cowl sides will have to pass) to the floor and get them about even. This was perhaps 5 degrees after the 4 / 8 o’clock position, in terms of normal engine rotation, because of the blade twist. Protect the propeller blades with some tape.
Now, with one person each side, slide the lower cowl up between the blades. It’s a tight fit, but by going a bit sideways and bending the aft corners of the cowl as they pass the blades, you can do it. Another option would be to temporarily remove the bolt holding the gear leg up, but I didn’t need to do this. Once the cowl had cleared the propeller blades, I slid a short table with some padding under the cowl just so it can’t slide back down into the propeller blades.
Crawl underneath, and cleco the retaining plate into place on the bottom aft center of the cowl, behind the gear leg, to hold the two halves together at the constant slot gap of 2″.
See the pictures. I drilled two small holes at the top rear of the lower cowl excess, put a loop of 0.04″ safety wire through each as shown, and then used a light 1″ tie down strap run across the top of the fuselage to hold the lower cowl in place. Don’t tighten it down yet, and when you do, don’t tighten it down much at all – it’s just to hold the aft of the lower cowl in place. You could also use rope, if you’re good at knots.
Lower the engine lift, so the nose wheel is back on the ground, and remote it, we don’t need it any more.
Place the top cowl back on, and insert the six #30 cleco’s that hold the front of the two cowl halves together near the spinner. I had placed a folded up towel around the top of the flywheel so the front cowl assembly sits in around about the correct place.
Make up a pair of metal brackets as shown in the pictures, I made mine in an “L” shape out of scrap Alclad, drilled a #40 hole in the end that will retain the bottom cowl, and carefully drilled two holes (By memory they were 75mm apart) to match the existing holes in the spinner backplate. See the pictures. Screw these brackets, one on the left and one on the right, as shown in the pictures. The bracket part that touches the lower cowl will bend against the lower cowl, but do not drill the #40 holes into the lower cowl yet.
Now, get the front of the cowl in the correct position with respect to the spinner – with the spinner gap you want, even all the way around, centered left/right, and with top/bottom alignment according to what your selected guess is for the amount the engine will drop over time. Most people seem to use about 1/8″ for this guess. Spend plenty of time with this. Also check the alignment of the entire cowl. I didn’t use plumb bobs like the VAN’s instructions, I previously used a self leveling laser to check the left/right alignment of the door sills at the same point on each (rolling one main wheel up onto a piece of 1/8″ thick wood got this alignment right), and then set up the same laser to check the left/right alignment of the cowl intake holes. After making a dozen or so adjustments, most of which simply undid prior adjustments, I tightened up the bottom cowl rear strap (just enough to retain it in place), and carefully drilled #40 through the two spinner brackets and installed cleco’s. This secured the lower cowl into place, and the front of the upper cowl as well.
Never bump the prop from this point on – you want to keep the alignment set up by the two cleco’s into the lower cowl.
Now, using the flip-over cards previously taped to the top of the fuselage, drill #40 through the top center hole of the top cowl, and a hole about 12″ each side of the top. These three cleco’s set the position of the top cowl, although at this point the rear edge of the top cowl is not yet trimmed. Drill these holes out to #30 since the alignment may have been out slightly from the flip cards.
Remove the three cleco’s. Check the top cowl aft edge and convince yourself that the trim line is still correct. Fix it up if it is not. Now, remove the top cowl by removing the six front #30 cleco’s, put it on a bench, and begin sanding down to the trim line across the center section of the cowl.
Place the top cowl back in position, cleco the front, check the aft edge, remove the cowl and continue sanding down to the trim line. I probably did this about 8 times to get the top cowl trimmed. The best tool to use for this is a long perma-grit sanding block. I always hand sand edges that I want to be accurate. Leave the machine sanders in the cupboard. Work from the center of the top cowl, out to each side. As you do so, you might want to drill more cleco holes, if you had done more flip cards. You can’t really trim the side corners of the top cowl unless it is properly secured in place across the top. I don’t know how you do this if you use the Skybolt mounting plates that already have the large hole drilled in it. Tape the cowl in place I guess. I’m glad I made my own brackets.
Once you’re happy with the aft edge of the top cowl, you could release the lower cowl, including the two #40 cleco’s at the front, let it slip down out of the way, and then using a long flexible 90 degree drill extension and the top cowl held in place with the holes already drilled, get your arm up under the aft end of the top cowl and drill/cleco the remaining top cowl aft edge holes from the inside out. This only works if you make your own brackets with #40 (or #30) holes. The top cowl aft edge is now done, and since it was done with the lower cowl in place, it will be right – unlike mine that I need to fill a bit.
Remove the top cowl and set it aside. Move the bottom cowl back up into position, cleco’d to the spinner brackets at the front and held with the strap over the top at the rear. I used a couple of high lift jacks on each lower aft edge to take up any gap at these points.
Enough talk for now, here are a first set of pictures:
Continuing now with the bottom cowl:
Mark the aft edge trim lines, per the plans, using lines previously measured back 4″ on the fuselage.
Remove the bottom cowl, and trim to within under 1/8″ of these lines. Using a long straight (course) permagrit sanding block, sand down close to the trim lines on each side.
Fit the bottom cowl, check for alignment, and continue sanding until the cowl fits properly. I did the final sanding to fit “in place”, by just allowing the cowl to drop down a bit, and spread out on the side I was working on. I stopped at the point where the fit was good, I’ll worry about paint gaps closer to painting time.
With the bottom cowl supported in place, and each pre-drilled aft edge hinge pin fitted, match drill the aft edge hinge pins from the inside out using a right angle drill extension. There may be a few that are hard to get to, skip these and do them once the cowl is removed.
Drop the bottom cowl out, match drill any holes that had to be missed, clean out all debris, and refit the cowl putting a #40 cleco in every hole. Using a countersink cage and a 3 flute countersink with #40 pilot, countersink each hole in turn for an ad3 rivet head.
Clean out any final debris, and rivet the hinge on each side. I used a pneumatic squeezer, and actually did this in place with the cowl dropped down and stretched out a bit.
Refit the cowl with the hinge pins on each side, and the two cleco’s on the front (to the temporary spinner brackets).
Now it’s time to do the side hinges:
Refit the top cowl, allowing the sides to overlap on the outside of the bottom cowl. Now mark a trim line on each side, using a long straight edge. I used a 40″ steel ruler, and a laser which I set up so that the trim line was in the same pitch as the door sill on each side – this is the horizontal pitch when the aircraft is in cruise. This is not horizontal on the ground.
Remove the top cowl, cut and sand down to this trim line on each side, using a long straight sanding block. Refit the top cowl.
Mark a trim line on each side of the bottom cowl, using the top cowl as a guide. Cut and sand down close to this line, but not to it. At this time I also marked in the position of the Aerosport cowl hinge pin covers, and left material forward of this hole on the lower cowl as shown in the pictures.
Fit the top cowl, and keep sanding the bottom cowl sides until they fit properly, with a small gap. At some point during this process I also cut out the holes for the Aerosport cowl hinge pin covers, and trimmed the front section each side of the lower cowl so that it was a good fit with the upper cowl, which wraps around the bottom cowl at each front corner.
Prepare the hinges for each side, and drill #42 all rivet holes in the lower hinge halves. I used a drill press set at 4,000 rpm for this step, to allow drilling accurately and without distorting the hinge half. I elected to use AN257-P4 hinge halves on the upper cowl, so that the hinge eyelets on the lower cowl were below the edge of the cowl. This gives a little bit of extra room when sliding the lower cowl out under the three blade propeller. Clamp the AN257-P3 hinge halves onto the lower cowl (with the upper cowl removed), using a spacer block to set the desired depth all the way along the hinge (I used a scrap of 0.063″ Alclad). Using a right angle drill extension, drill #40 from the inside of the hinge through the lower cowl on each side. Clean out debris, reattach the hinges, and countersink the outside of the cowl for -ad3 rivets. Rivet each bottom cowl side hinge in place. Again I used a pneumatic squeezer.
Set the top hinge half in place on one side, and determine the exact height above the split line where the rivet holes will go. Select a position around the midpoint, and using a foam block wedged/taped between the hinge and a cylinder head (without pushing the side of the cowl “out”), sit the upper cowl in place. Mark where this first hole will be in the upper cowl half, using the previous measurements.
Using an air drill (=> high speed), with a #42 bit, drill this hole through the cowl and hinge. Apply very little pressure, take your time and let the drill bit do the work. I used a 0.025″ metal spacer between the cowl halves for this first hole, which allows for a slightly wider gap after a bit of “spring back” occurs. Pop the cowl up, clean away any debris and de-burr this hole in the hinge, reassemble and put a cleco through the cowl and hinge for this first hole.
Mark hole positions along the length of the top cowl, using a piece of masking tape (see pictures). Working forward and aft of this hole, drill through the cowl and hinge #42 and cleco each hole. I stopped using the 0.025″ metal spacer at this point, and simply eye-balled the gap because I didn’t have three hands. Once all holes are drilled, remove the top cowl, clean up the debris and cleco the top hinge half in place. Ream #40 all holes, clean up, and refit the top cowl, hinge and all clecos. Now, remove one cleco at a time, countersink, and reinstall the cleco. Once all holes are countersink, remove the top cowl, clean up, deburr the hinge holes, and rivet the hinge in place.
Refit the top cowl, slide the hinge pin in for the side just completed, and repeat steps 33-35 for the other side.
That’s it for the initial cowl fit. Next step is to fit the two support fairings supplied by Showplanes that fit around the front gear leg, that support the center section of the lower cowl.
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.
Fiberglass hell continues (apart from two weeks off while I did an awesome flying trip) in the form of the two doors – an infamous part of the RV10 build. Each door comes as an inner and outer shell. You epoxy the two halves together, using the cabin top as a mold. Then you trim and sand each door until it fits. Sounds simple enough, but after installing the door, checking the fit, and taking it off for the umpteenth time it all gets a bit tiring.
There have been many incidents of RV-10 doors coming off in flight. Van’s released a supplement to the design, a “safety catch”, after the first few incidents. An aftermarket design from Planearound is generally regarded as the best solution. It provides a central gearbox with a CAM that “pulls the door in”, and 180 degree handle travel that provides longer pin penetration than the standard kit’s 90 degree travel. In addition, I’m fitting an external handle made by Aerosport Products along with a lock which is keyed the same as the baggage door lock.
I reviewed the information available about doors coming off in flight. The exterior of the door is a low pressure area, which tends to suck the door outward. The bottom of the door can flex and bow outward. If the door is poorly constructed, or if one of the pins is inadvertently not engaged properly, the door can disengage from the bottom and once that happens in flight, it is guaranteed to tear off around the hinges. Many RV-10 pilots never allow passengers to close the doors, electing to always do it themselves to ensure the door is correctly closed. Here is a list of what I’m doing during construction to avoid future door problems:
Install the Planearound safety lock (180 degree), instead of the Van’s safety lock. It seems overall a better design, there is greater pin travel and the centre cam lock doubles as a means to draw the door in so that the front and back pins cannot go anywhere but into their respective pin blocks.
Install four door pin proximity switches, which will act in series to switch a panel mounted annunciation light from “red” to “green” indicating all four door pins are correctly seated.
Adding some supplemental “stiffening” to the bottom edge of the door. To the extent the bottom of the door resists any tendency to “bow outwards” in flight, it is less likely to put stress on the door locking mechanisms.
Adding backing plates to the hinge mounting points for both the door and cabin hinge mounts. These came as a kit from Air Ward a long time ago. Not sure if I’ll use the exterior cabin support parts (since the standard screw heads are directly applied to the steel hinges), but for the cabin interior, which winds up hidden by the overhead, and the door interior, the support plates distribute the load across a larger area of fiberglass than four individual washers and nuts. Same for the door exterior mounting plates.
In addition to the above, I’m using an aftermarket bulb seal sourced from McMaster Carr. This seal is applied to the cabin side, and provides a more professional automotive style finish than the standard kit seal, which is applied to the door itself. There’s a bit more work though in that the cabin needs to be sanded down to a 1/4″ gap all around the door, and in turn built up to a 1/4″ edge all the way around to support the McMaster seal.
For the “additional structure” along the bottom of the door, I simply laid some 12mm conduit along the bottom edges in the inner shell, and secured it in a few spots with epoxy. In addition, I cut a handful of conduit sections, just under 3/4″ in length, and epoxy’d one end in place distributed around the large open areas of the lower door, as shown in the picture. When it came time to glue the two door halves together, I put down a couple of layers of glass across the conduits that ran across the bottom of the door, and then filled around it as normal with extra epoxy/flox/cabosil. When the two door halves were brought together, this created a “box section” along most of the bottom of the door. For the other open areas, I simply deposited a clump of flox on top of each short conduit, filling up the inside of each small conduit, and then securing onto the outside surface of the door once the halves were brought together.
I also pre-installed the Planearound gearbox and supports before the doors were glued together. I haven’t seen this done before. It means you don’t have to cut the bottom of the door open after the fact, and fill it back in. I simply drilled a hole in the right place on the inner shell, until the shaft just fitted inside the hole, then used the gearbox itself to match drill the four mounting holes, in turn countersinking these from the inside surface of the door. I pre-lubricated the inside of the gearbox with some Boelube, and then wrapped up the gearbox in packing tape, except for (a) some plain plastic on the rear under the packing tape so that the back of the shaft wouldn’t bind with the packing tape, and (b) the two rectangular holes in the sides of the gearbox where the racks go.
One concern is epoxy from the Parabeam draining down onto the gearbox, into the rack holes, and in turn into the gearbox – that would be a disaster. To ensure this couldn’t happen, I made up a thin Alclad plate which ran along the top of the gearbox, with a flange on each end. I epoxy’d this along the bottom edge prior to bringing the two door halves together. This means any epoxy that ran down after the door halves were brought together would drip down well away from the rack holes. I applied some thick epoxy/flox/cabosil mix along the top of this flange prior to bringing the door halves together, so that any (runny) epoxy from the Parabeam would tend to run away to each side rather than down the outer door shell. This all might be overkill, but it worked out OK because after the doors were cured, neither gearbox was seized up!
Gluing the two door halves together is definitely a two person operation. I had “Rosie” mixing up epoxy/flox/cabosil while I applied it. We both carefully placed the two halves together, and then onto the cabin/mold. I previously drilled #40 cleco holes through the door halves into the cabin. These are easily filled with (structural) epoxy later, and they allow uniform pressure to be applied while the door cures. Clamps can easily be over tightened, causing flat spots around the natural curve of the doors. After the doors were epoxy’d and placed on the cabin, I left for a two week flying trip, so there was plenty of time for the epoxy to cure!
The cleco’s came out OK, some requiring a bit of twisting and force to remove them due to the epoxy running down into the cleco/holes. It took around eight hours per door to trim off the excess and sand down the edges to match the cabin top. I used duplicator straps to keep the door alignment left/right during this step, and one on each top corner. I highly recommend the latter – four straps in total – because the top edge of the door is where you start the final fitment, this is where the hinges get drilled. Once the door is on the hinges, it hangs slightly differently because there’s more weight towards the front of the door than the rear (the hinges are not in the door’s C of G), so you can’t trim the lower parts of the door until the hinges are fitted. It’s all a bit of a chicken and egg problem, but after having each door on and off about 20 times the doors are a good fit. I only took enough off the doors to have them fit into place, more sanding will be required after the cabin top is properly fitted to the fuselage in order to set up the gap all around each door.
After all that, I have each door now hinged to the cabin, and quite an accurate fit, the bottom edge of each door is less than 0.5 mm proud on the front and back edges, and perhaps 0.5 mm under in the middle. Ultimately the transition from the door to the fuselage will have to be filled and sanded all around, along with the transition into the cabin top, so +/- 0.5 mm is good enough for now.
The doors (and cabin top) are a long part of the project. I have quite a way yet to go with them, but the weather’s been good so almost all of the sanding I’ve been able to do outside.
Notes from the future for builders:
Don’t drill the bolt holes around the lower doorway from the cabin top into the fuselage, just drill #30 holes on the side and #40 holes on the bottom. You’ll want to remove and reinstall the cabin top on multiple occasions while you work on the doors and overhead/interior, and it’s much easier to use cleco’s than bolts. Enlarge these to the required bolt holes once you’re ready to final install the cabin top.
If you’re going to use the Planearound kit, definitely install the gearbox onto the inner door shell before gluing the two door halves together. For the 3/8″ access hole required – use their measurement for the distance forward from the gearbox, but for the up/down distance, don’t measure it – insert a rack into top side of the gearbox, roll it forward until it intersects the “vertical” line you just drew for the forward distance, and use the hole in the rack as a drill guide to drill a #40 hole through the door. That makes a pilot hole in exactly the correct position, now enlarge the hole to 3/8″. Later on, place some masking tape over this hole while sanding the door, you’ll be creating clouds of fiberglass dust and there’s no need to have that accumulate inside the door or gearbox.
If you’re going to use the Aerosport exterior handle, pre-drill #40 the three holes using the stainless steel striker plate as a template, through both the inner and outer door shells, while the two door halves are all cleco’d together for initial preparation. This is the first step in the Aerosport instructions. Why? Because when you glue the doors together, you can install three #40 cleco’s (could use #30’s) through these holes and that brings together the two surfaces where the door latch mechanism goes. The instructions tell you to coat these surfaces with regular epoxy, but that is fairly runny and once the door is placed on the cabin for the epoxy to cure, the epoxy can run and a poor bond can occur in this area. This happened to one of my doors, I had to use a syringe to squirt more epoxy into it while installing the latch, and this shouldn’t happen. In fact I’d put a thin layer of the thickened flox on this area in the first place, slathered on top of the thin straight epoxy which will run.
Use plenty of the thickened epoxy, and remember on the aft side and the bottom that the final trim is quite close to where the two shells part. Be generous with the amount applied, you need to work fast and there’s no point in trying to economize on the amount of epoxy (it weighs next to nothing) or focusing on making the application pretty.
My formula for the thickened epoxy was 4 pumps of epoxy, 4 pumps of slow hardener, 2 scoops of flox, and 2-3 scoops of cabosil. Mix the epoxy and hardener thoroughly first, then mix in the flox, then mix in the cabosil, until the mixture does not slump if held vertically. We made up 3 of these per door (in addition to the regular epoxy used for the Parabeam). Might have been a 4th on one side, can’t quite remember.
Next job is to install the door latches, which means rationalizing three sets of instructions – from Van’s, Planearound and Aerosport. Fortunately, plenty have gone down the same path before me, so between these instructions and some online reading I should be able to work it out.
Due to other commitments, I’ve had to take a few months off from building, from April through June, but as of July I’m back at it again. Apart from doing the MPC course there was one notable event during this time, with the arrival of the finish kit, propeller and spinner from Van’s, the cowling from Showplanes, and the engine from Barrett Precision Engines. Finish kit inventory didn’t take long. Now I’ve really got to get on with it…