More Wood!

Ok, so I got the necessary braces installed. I also set up the seat well enough to take some measurements with a laser level simulating the horizon from my height when seated, and used that to generate templates for the canopy. However, in the meantime, there were a few more pieces of woodworking to attend to. The first is that, because of the way the fuselage is built, the plywood that stretches over the crossmembers behind the seat doesn't have a good way to glue to the longhorns.

The solution the previous builder used was to glue on more spruce to build the sides up to level, and it makes sense to me. So I went ahead and did the same. First I shaped some pieces of wood to follow the contours of the plane:

Then I glued them on, came back a day later, and started planing. I had to build up the center crossmember as well, because of the compound "dip" in the fuselage (Only needed about .02" or so, but it was easier to glue on a much thicker piece and plane it down later.) I used a hand plane held at an angle, so that the center x-member was being cut while the plane used the forward and rear x-members to set the height. Once the x-members were all co-planar, I planed the sides to match.

I didn't get a picture of the finished product, apparently. I was about ready to glue the plywood on, when I realized I'd want all of the gussets in place first; they'd be hard to add later! So I spent some time sanding tiny wood blocks to the right compound angles. It's not very difficult, but it was a little time consuming. I ended up needing 12; I was able to finish and glue 9 before I ran out of time.

The next time I was down, I finished making the gussets I needed and glued them overnight.

After everything had time to set, I planed and sanded everything down and cut the plywood to fit. This is pretty thin stuff, and I've found that by using a utility knife to cut through it, I can usually avoid sanding it except to break the sharp edges.

After several passes with the knife, it usually only needs a touch with sandpaper to get the edges smooth, and as long as you marked it right, it's bound to fit. All that was left was to glue it all together and clamp it down.

Next time I'm down, I'll pull the clamps off and start re-working the fiberglass seat backs. They need to be trimmed a little bit in order to fit the new angle. I'll probably cut the holes for the control sticks too, which will allow me to install those again and start fiddling with their location. I'm gearing up for all of the non-fiberglass things, since winter is almost upon us here. I've been working on designing a prop in CAD, as well as a control stick grip. Unfortunately, it looks like the canopy/aft deck/front deck is going to have to wait another winter... at least I have a plan for that now.

Seats (Part 5)

Continued from Seats (Part 4)
I attached piano hinge to the seat back at the bottom, so I can access the back really easy. While that was curing, I glued in four 5/8" spruce braces for the seat back, to make sure they won't buckle under load. I also cut a 1/4" piece of spruce for the other side of the seat back hinge to attach to.

Once those had set, I cut the seat pan to fit around them, then connected the seat back to the 1/4" spruce with the other half of the hinge. These I lined up with the seat pan in the plane, then epoxied the spruce hinge plate to the seat pan.

Once that had cured, I drilled holes all the way through the seat pan and the spruce hinge plate and epoxied nuts underneath the seat pan, so the hinge can easily be unscrewed from the seat pan. Honestly, that was probably overkill, because it's easiest to pop the whole seat assembly out of the plane and pull the hinge pins. However, it makes me feel better that the hinge is screwed down instead of just epoxied on, and even if the epoxy holding the spruce hinge plate failed, the screws go through that *and* the seat pan, so it's not coming apart unless I want it to. I have a close-up of the hinge and spruce, but it's too blurry to post, so I'll have to take another one.

I went ahead and cut the seat back into two pieces after this was all cured. I didn't cut it before because I wanted to make sure both seat backs were hinged in exactly the same place and direction, so they won't interfere with each other. The last thing I did was seal the edges using 1" fiberglass tape, then sanded them all smooth. I'll probably paint the seat back, but I didn't feel the need to do that yet. With the seats hinging separately, I can use the passenger side as a flat surface when I'm flying solo. The only part that I haven't figured out yet is where to put the seat foam if I do that... but I'm hoping I won't have a reason to need a work surface while I fly. Much of my cross country flying has been done with an instructor in the right seat, which leaves no room for charts in a C172. As a result, I've got a nice kneeboard that will hold a folded chart. I'll be running iFly software on a Nexus 7 on the instrument panel, so in theory the only time I'd need a physical chart would be if my electronics went south, and I probably wouldn't bother moving seat foam and flipping the seat back down in that case.

Seats (Part 3)

Continued from Seats (Part 2)
I've spent the past few weeks making some solid progress, although it doesn't feel like it. I cut the carbon fiber seat pan to its rough shape, and cut the channel for the elevator pushrod to run through. I've also got a piece of foam cut to shape as a former for the carbon fiber to lay over the channel, creating a tunnel to protect the pushrod from debris (and from being stepped or sat on.)

I wet out two layers of CF, wrapped them around the foam tunnel former, and slid that into the slot I cut.

Once that cured, I removed the foam and flipped the seat over. I wet out two more layers of CF (for four total) and laid those over the tunnel from the last step. This would have created a void at the forward end of the tunnel, so I filled it with a really thick micro mixture ahead of time.

 It looks in the picture like the CF over the tunnel has sharp edges, but they're all quite flat and smooth in real life.

I tried to do the seat back next, using some left over foam from my wing tanks. That was a disaster, and I mostly just wasted time and resources on learning how *not* to lay up fiberglass. I may write up the long version at some point, but I'm not sure anyone else is dumb enough to try it as many times or as many ways as I did before giving up (or getting it right.) Long story short, plastic bagging is a perfectly viable fiberglassing option, but like everything else in fiberglassing, it has to be done just right. So far I haven't figured out how to do it just right. So I'll go back to fiberglassing the way I usually do, because I really want repeatable results (and I really want a seat back!)

Continued in Seats (Part 4)

Seats (Part 2)

Continued from Seats (Part 1)
I spent a lot of time prepping for the actual carbon fiber layup. Some of my brackets didn't fit quite the way I'd like, so I did a lot of fiddling to get everything right. After that, I trial fitted and then shaped the seat to fit exactly how I wanted it.

Once I was satisfied, I began using duct tape and plastic drop cloth to protect the fuselage from any epoxy drips.

After one more trial fit, I got ready for layup. Two layers on the bottom, two layers on the top, each with one layer 45 degrees to the other. I wet out the carbon fiber between two sheets of plastic in order to keep the carbon fiber layers from shifting. It didn't work as well as I hoped, and the epoxy was beginning to set up before I had it on the foam. Apart from that, the process went fairly smoothly. Seat went onto the bottom layers, which was then lifted into position in between the spars. The top layers were then placed on top, and everything was pressed together and smoothed out, then left to cure.

Final trial fit:

With carbon fiber and curing:

After it was cured, I gently but firmly removed the seat from the plane. Next I'll need to cut out and add a tunnel for the elevator pushrod, holes for the control sticks, and then work on the back of the seat.

I found a picture of the plywood cutting process, and am uploading it just for my record below.

Continued in Seats (Part 3)

Seats (Part 1)

After two solid months of doing little nothing projects here and there and generally not accomplishing very much, the weather finally got nice enough to start doing some fiberglassing. So I decided to build my seats next, because 1. it's a smaller fiberglass project to get me back in the swing of it before I tackle the wings, and 2. once I have the seats in place I can set my rudder pedals, my control sticks height, canopy and therefore aft deck height, and also sit on it and make airplane noises. I'm using carbon fiber for its strength to weight ratio, and because the seat giving way in flight would cause the airplane to be uncontrollable, so I want it as strong as possible. At this point I intend to build as much of the plane with vinylester resin as possible, because it cures very fast compared to just about every viable epoxy I've tried. However, there's some solid research that suggests vinylester doesn't bond well with carbon fiber, so I'm using West Systems epoxy instead. West Systems is fantastic stuff, but it takes about 6 hours to cure at 70* F, and that time goes up dramatically as temperature goes down. This week is all warm days, so I'm gonna try to knock this out before the end of the week.

I started with ½" foam, sliced into 2" strips. I epoxied 3/32" plywood in between each strip, so the strips of wood and foam are oriented length-wise in relation to the aircraft.

Once that had cured, I cut the panel into two pieces, one to match the seat back, and one to make up the flat bottom of the seat. I also built about the crummiest looking jig you could imagine to get the angle of the two pieces right, but it worked out just fine for my purposes.

I didn't get a good picture of it, but I cut slots right next to each of the wooden stringers in both panels, then used that same 3/32 plywood to make biscuits to fit in them to really strengthen the joint. Once I had them all prepped and trial-fitted, I mixed up my epoxy and went to work. Obviously no pictures of the process, but it was messy and the epoxy gets hot in the cup pretty quick when it's 80 degree weather. No misadventures, however, and with a carefully calibrated weight on top, and carefully calibrated heat lamps in place, the curing process could begin. Tomorrow I hope to begin laying my carbon fiber and start making this look more like a fancy seat for a composite aircraft (and less like I have no idea what I'm doing.)
Continued in Seats (Part 2)