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.