|Gull Wing Doors:|
The original Glasair I airframe had a very simple to make gull wing door or the option of an in-slider on one or both sides. The first two pictures are examples of each of the old designs. If you look closely at the old gull wing design, you can see that it does not incorporate a bulb seal. Basically the builder was left to fit a piece of stick-on household weather strip for a seal. This allowed a lot of air and rain to seep in. The in-slider was no different in the sealing area.
For this reason, I decided to upgrade my doors to the new style. The only problem, as with all the stuff on this plane, was money. I decided I would manufacture my own doors from the skin of the fuselage instead of purchasing molded doors from Stoddard Hamilton.
I started by measuring several of the newer Glasairs equipped with the molded doors. From these measurements I was able to determine the size of the cutout for the Plexiglas installation and where to draw the cut lines for the door frames.
The Plexiglas was easy to install after drawing the lines. To accomplish this I used the method described for installing the rear window option. Here is how the glass installation looked before removing the doors from the fuselage.
The next step was to draw the outline of the door frames on the outside of the fuselage. Sorry, I didn't take any photos of this part of the process. After drawing the outlines, I used a small cut-off wheel on my Dremel tool to cut the outer fuselage skin. This cut has to be made very carefully. The gap will be sanded to an even width later.
After the outside cut, the cut lines have to be marked on the inside skin. To do this, I used a Mini Mag light shining from the outside cut onto the inside skin. I marked this line and then drew a parallel line 1.25" closer to the Plexiglas. This was the "step" that the bulb seal would be sandwiched between.
This cut has to be made very carefully and, as with the outer cut, the gap will be sanded to an even width later. This photo shows the relation of the inner cut line to the outer cut line. I recommend protecting the Plexiglas better than I did in this photo. I have a lot of clean up to do before I fly.
After cutting the inside skin, the real fun begins. The canopy frame has to be removed from the fuselage
This takes some finesse. This is accomplished with an automotive gasket scraper (sort of like a putty knife, but more rigid) and an razor knife. First I ran the razor knife around the cut in the inside skin to a depth that kept the knife from contacting the outer skin. Do not cut into the outer skin. Don't even scrape it with the razor tip. This will weaken the flange that you will be using to seal against the new bulb seal.
Next, slide the gasket scrapper into the cut, perpendicular to the inside skin. While prying the scraper toward the Plexiglas, push on the canopy frame portion of the inside skin just until you hear the foam start to come loose from the outside skin. Remove the scraper and reposition it about 1" down from the first place that was pried. Then repeat the prying just until the foam starts to come loose from the outer skin.
When you reach the point where you started, repeat the prying process. This time pry the foam away from the outer skin until it is free. When you get completely around the frame the second time, remove the door. Then scrape the foam from the door frame until the door frame looks like the picture to the right. Do not remove the foam from the fuselage opening yet.
The next step is to make the canopy frame into a solid structure. To do this I used a micro balloon mixture of resin to form a smooth transition between the inside frame skin and onto the back of the outside frame skin. This .PDF shows a cross section of the frame and fuselage. This photo shows the build up area around the hinge, but gives a general idea of how it turns out. Once the transition is formed it is covered with a two-layer laminate all around the door frame. I added two additional layers over the hinge area and overlapping onto the inner frame skin.
Next I installed the latches. To do this, I laid the latch assembly over the inner door skin in close relation to where it would be when installed. I drew a rough line around it, cut the inner skin away and removed the foam. Then I potted the latch bushings into the frame with a mixture of milled fiber, micro balloons and resin. I shaped them with gentle tapers at the top and bottom where the bulb seal would contact the frame.
Note in the photo of the inside of the door latch area the darker color to the rear (left side of photo) of the handle cup. This is a 10-layer laminate that I made on the inside skin so I could router the outside handle relief area into the skin. Remember; the handles are sunk into the outside skin. I traced the handle outline onto the outside skin and used a small router to create the sunk-in area for it.
Next I cut the grooves into the ceiling for the installation of the hinge bushings. With the frame latch bushings potted in place, I installed the hinges to the frame and placed the frame over the opening. I used spacers to set the height of the door flush with the outer skin. I had to remove a small portion of the inner skin where the latch bushings on the frame came into contact. Then I installed the hinge pin and bushings. With the door taped in place, I potted the hinge bushings in place.
One other area of concern with these doors is at the top rear of the door. Stoddard Hamilton used 1/4" foam in this area. To keep the doors from bulging up here, I decided to counter sink the bulb seal flange. From the inside it looks bad, but, it will be covered with headliner material. From the outside you can't even tell.
After potting the hinge bushings in place, I laminated over the bushings and troughs with a 4-layer laminate to reinforce the ceiling in this area.
Next I had to rough finish the doors. I packed the latch opening with spray foam. After this cured, I sanded it to shape to form the cap covering the latch mechanism. I overlapped this onto the outer skin even around the latch pin bushings. I only left a small amount open as a maintenance access to the latch. After that cured, I removed the foam with a long piece of wire attached to a drill. It was a real pain to get all the foam removed. Luckily it's just a housing for the latch. No one will see it.
Next I assembled the latch and packed the remaining opening with clay. I applied a release agent to the door and laminated a two-layer cover over the opening, overlapping it about an inch all the way around. This will be my maintenance cover.
The next photo shows the latch and cover assembled and installed. It also shows the bulb seal in place.... wait a minute, we haven't gotten that far yet.
Next I had to pot the latch bushings into the fuselage sidewall. This was done by installing the doors and removing the inner fuselage laminates and foam so the bushings would just fit. Then I removed more of the foam under the remaining fuselage laminates. I placed the bushings on the latch with the handle in the latched position and taped the door in place again. I used a milled fiber mixture and packed it around the bushings and shaped it smooth over the top. After that cured, I used clay to build a bump over the door-mounted bushing and up to the fuselage flange as a mold for the new inner bulb seal flange at the latch area. I applied a two-layer laminate over the clay. Once cured, I removed the door and the clay and shaped the flange to fit the bulb seal.
Next I had to laminate over the exposed foam in the fuselage opening. To do this, I needed something to laminate to. I didn't want to have to sand and smooth laminates onto the outer skin. The solution was to remove about 3/16" of foam from just under the outer skin all the way around the opening. I thoroughly cleaned the foam from the underside of the outer skin. Then I packed this trough with milled fiber taking the place of the foam. This created
a solid connection between the outer skin and the two-layer laminate that I applied to the entire door opening. I applied an extra two layer laminate over the latch bushings just for insurance.
These next three photos show the finished product. All that is left is filling and smoothing the final layer.
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