The next step after window installation, as documented in the Builder's Manual, is to create the doors. Seems logical to me. The doors are created by cutting them out of the existing fuselage structure which saves the time and effort of having to build them from scratch, and insures a perfect fit. Once removed, the doors are strengthened, as is the fuselage around the door cutout, and latching hardware is installed. Before any of this can happen, however, the manual very clearly states that the hinges should be rigged into place, and the door stops should be fabricated.
Door stop fabrication was interesting in that this was the first lay-up I've done thus far that had to be "released." In other words, the part would be cured in place, then removed from the airframe for permanent bonding at a later time. This was accomplished by first laying down some duct tape around the inside of the door periphery, roughly 4 inches wide centered along the cut line. Then a mold release agent (I used a liquid solution in lieu of the more common mold release wax) was applied to the duct tape and allowed to dry. Before laying up the 2" wide fiberglass strips along the cut line, peel ply was installed. Then 2 plies fiberglass, then another layer of peel ply. After an over-night cure, the whole mess was pried loose from the "mold" and the duct tape removed.
I did this in 4 separate sessions, upper and lower stop for each door, because working above the window line is just no fun and gravity works against you in that case. Instead I turned the fuselage over to build the upper door stops. The completed set of R/H door stops is shown in the photo at right. Once the doors are cut out, these will be bonded to the fuselage on the inside of the door cutout, then trimmed so that they project about .25" into the door opening.
Door Hinge Dilemma
Now comes the frustrating part. When I first received my fuselage sub-kit from Glassic Composites, they backordered all my door hardware, including the hinges. Then they went bankrupt, but you already knew that. I contacted KLS Composites and inquired about getting this badly needed hardware. They said that their machine shop people were pretty busy working on the landing gear, so it would be a while. Not the answer I was hoping for, but at least it was honest. The hinge arrangement on the factory demonstrator SQ2000 was really nothing to brag about--some might even say it was a bit on the cheesy side--so I thought I'd try to come up with a new design.
My first thought was to leave the OML intact and hinge the doors from the inside using gooseneck style hinges. Finding decent gooseneck hinges was tougher than it sounded though. I found some nice hinges by Hartwell Corporation, who coincidentally supplies Boeing with certain parts, but man were they expensive. Hartwell isn't a retailer, so they informed me that I'd have to place a $500 minimum order. Yeah, right. Several Emails later, I found out that Hexcel Structures had a few suitable Hartwell hinges they were willing to part with, but they wanted almost $300 for a set of 4. If I knew for sure that they would have worked for my doors, I probably would have bought them, but since I wasn't sure, I let the opportunity expire.
A few weeks later, when I was strolling around the parts tents at the Arlington Air Show, I happened across a bin of surplus gooseneck hinges. I bought 4 of them. Grand total: $2.00. Pretty nifty.
Now to build a test section to see if these hinges would actually work. I used the scrap piece that was cut out of the bottom of the fuselage as my test article. The curvature wasn't exactly right, but it was a valid cross section of the structure. I had to hack away at some of the core and do a small lay-up to simulate the door joint, but that wasn't too tough. I even installed a simulated door stop and a bulb seal retainer (seal too). Overall a pretty accurate representation of the door-to-fuselage interface I'd say. Then I mounted my $2.00 gooseneck hinges. After experimenting with different placements and orientations of the hinges, I concluded that the concept just wasn't going to work. The kinematics just weren't right. Oh well, at least I didn't spend $300 to figure that out.
By now I was getting a bit frustrated. Although cheesy, I thought maybe I would forget trying to reinvent the wheel and just use the factory hardware... if I could get it, that is. A few gentle reminders (and a couple of months) later, I received a box of door hardware at my front door. Kudos to KLS Composites for sending this stuff to me at no charge, which they were under no obligation to do. The box contained center cams, push rods, locking pins, guide sleeves, but no hinges! Another email to the factory saying, basically, "wazzzuppppp?" My reply was that they didn't send hinges because another builder had come up with a better way to hinge the doors by adapting Velocity hardware. That was good info to get, and I called my fellow builder who was quite helpful, but why didn't they tell me that 2 months ago? Sheesh.
So I contacted Hiroo, a Velocity SUV builder, who sent me some shots of his hinge installation. I also got in touch with a fellow SQ2000 builder, Norman Caruana, who was very helpful and sent me some photos and drawings of his installation. He also gave me Velocity's part number for the hinges, so I placed a call the Florida and ordered 4. They cost around $50, if I recall correctly. Turns out their hinges are just MS20001 piano hinge extrusion, which is available from Wicks, cut into 2" widths.
The first step in adapting these new hinges was to strengthen the fuselage in the hinge area. The modification drawing I received from Norman called for 6 OML plies and 6 IML plies common to each side of the fuselage. This seemed like overkill to me, so I called the factory for a re-evaluation. They said all 24 plies were necessary to compensate for the larger fuselage skin cutouts. So I reluctantly layed up the OML plies, all the while thinking extra plies = extra weight, and grumbling that I had already faired, primed, and sanded the roof, and now I was going to mess that up.
Once the plies had cured, I roughly faired the edges with SuperFil, then marked the new cut line. There was no template for this... I just took a few measurements and drew what looked reasonable. Transferring the design to a piece of mylar allowed me to flip it over for use on the other side. Now there was nothing left to do but break out the saw and start cutting. Nothing too tricky about that; just had to keep a steady hand so that the cut lines would be smooth.
With the doors now removed, I bonded the door stops that I built earlier to the inside of the door frame. This was done with a structural adhesive, per the instruction manual. I only had so many clamps, so I bonded each of the 4 sections on different days.
After cure, the door stops were trimmed and sanded so that they projected about .15" into the door opening. The next step was to build the door seal backstop. The backstop is 2 plies of S2 glass layed up over a temporary foam spacer to provide a fixed (3/8") distance from the door stops. After the cure, the foam was removed by means of plastic scrapers and a Dremel tool then trimmed to project ½" beyond the door stop. This "backstop" now serves as a mounting platform for the door seal, which clips in places and will provide a tight seal (hopefully) when the doors are closed. There is mention in the Builders' Manual of an inflatable door seal option, but I don't know of any SQ2000 builders who actually have such a thing.
The nice thing about the KLS Composites hinge design was that it used spherical bearings at the fuselage attach points, which allowed for a certain amount of slop and misalignment. No such luck with the Velocity-style hinges; alignment was critical or the hinges would bind. I maintained alignment by attaching the hinges to a piece of aluminum "L" stock, then built up the door "tabs" with filler and a couple of fiberglass plies so that they were planar. Sounds pretty easy, but it took me a few iterations to get both doors just right.
On the fuselage side, I began by removing the foam core where the hinges would reside. By doing so, I left the inner plies intact for added strength. With the hinges fastened to the doors and the doors duct taped into place, I match-drilled the hinge hole pattern through the OML plies and countersunk them with a 100° countersink (purchased from Boeing Surplus for about $2, by the way). Before installing the screws, I liberally spread some structural adhesive on the top side of the hinges to make up for the roof curvature and inconsistencies inside the "pocket," then torqued the fasteners and let it cure. After that I filled the remaining volume of the pockets with potting compound. One thing's for sure: Those hinges are never coming out. I sure hope I don't damage one of them during the construction process.
The door side of the hinges were tapped with 10-32 thread, so each door can be easily removed from the airplane by removing 8 screws.
With that complete, I finished the layups on the inside of the fuselage around the hinges to close out the area and provide a constant sealing surface. The photo at right is shown before the peel ply and surplus foam core was removed (fuselage upside-down in the photo).
Now that the hinges were basically complete, the next step was to strengthen the doors. This was accomplished by fabricating and bonding a ¾ inch thick by 2 inch wide "frame" of foam core around the door, then glassing over it with S2 glass. It was a fairly straight forward process, but care had to be taken to avoid messing up the windows. This photo shows the foam bonded in place, shaped and smoothed before the fiberglass was installed over it.
Now for the crappy part. When I originally cut out the R/H door, I noticed that it "stress relieved" itself a little bit. By that I mean that the contour changed slightly. The L/H door did not do this and went back into the cutout perfectly. I didn't worry too much about it, figuring that between the hinge attach points and the latching mechanism it would be forced into conformity. Well, that was a bad decision. I should have corrected the problem before doing the door reinforcement because now I had stiffened the door into the improper contour. I attempted to re-contour the door by bending it with clamps, dead weight, and straps while heating it to 175° F. I had marginal success getting it back into shape, but the fit was still unacceptable.
Begrudgingly, I had to commit to rebuilding the upper aft corner of the door. Damn... as if I hadn't spent enough time monkeying with this door already, now it was going to take another week to rebuild it. So I added some filler and more plies to the inside frame until it made good contact with the door stop. This required removing and replacing a section of the foam "stiffener." Then I broke out the grinder and removed material from the outside, just below flush. Finally I added a couple of S2 plies to the OML and sanded the whole mess until it was smooth and flush all around.
There were some other areas around the door that were just a bit beyond flush, but a little SuperFil on the fuselage took care of that.
I also found that the gaps around both doors where pretty good, but could be better. Strategic applications of epoxy/flox, epoxy/micro, and/or SuperFil combined with duct tape and mold release remedied this. Oh yeah, and sanding. Was I spending too much time on this? Would anybody even notice the gaps around the doors? Weeks were turning into months. Yeah, it's got to be right. I don't like doing things "half assed."
After reading Paul Lee's web page, I see that he had a similar problem with his door(s), but he was smart enough to correct it before adding the stiffeners.
Getting near the end of this long chapter now. All I had left to do at this point was to install the handles and latching hardware. I opted not to use the KLS Composites door handles since they projected into the air stream about 2 inches. Instead I bought 2 door handle assemblies from Lancair. Pretty slick design with (nearly) flush handles. A bit pricey at $300 for the pair, but what the heck. There wasn't much modification required to adapt the Lancair parts since the locking action was similar to KLS's system.
I used KLS's locking pins despite the fact that they're over-designed by a large margin: 7/16" diameter steel pins, 4 per door, that slide into tubular "receivers" on the fuselage. It would take a tremendous amount of force to shear one of those suckers. I considered using ¼" aluminum instead to save weight but couldn't find a "receiver" tube of the correct diameter. Aluminum is a bit soft anyway, and may tend to wear out and get sloppy after several door latching cycles. The locking pins were connected to the door handles by means of push rods. Here again I deviated from KLS's design by using thick-walled 6061 aluminum tubing, internally tapped with 10-32 threads, for the push rods. I finished them off with spherical bearin
The last piece of the puzzle was to install the gas struts. The struts hold the doors in the open position, and due to their placement, will also hold the doors closed. The neutral point is about ¼ open. Quite a bit of force is transferred by these struts, so the attach brackets are bonded in place with structural adhesive and have several glass plies over the top. The unfortunate part about this rig is the gas struts alter the "door closed" position a little bit. It doesn't really affect the fit-and-fair, but it does affect the operation of the locking pins. Without the gas struts installed the locking action is cucumber-smooth. With the struts installed, it takes quite a bit of force to lock the doors. For you builders (and potential builders) who haven't completed your doors yet, I would recommend postponing the installation of locking pin receivers until after your gas struts are in place. Too late for me: I'll either have to live with it or grind out the receivers and relocate them slightly.
That about wraps up the door chapter. Certainly that was the most challenging task to date. According to my construction log, I invested 318 hours in the doors. No wonder it's taking me so long to build this airplane.
Update 1: I decided that I had invested too much time in these darn doors to live with the high locking forces, so I ground out the aft locking pin receivers (4 total) and repositioned them to compensate for the twist imparted by the gas struts. Then I re-bonded them and re-did the fiberglass overlays. Chalk up another few hours to the door installation.