Bede BD-4C Construction: Day 2

Steve and Rob are slave drivers and, I have to admit, I like it that way. With two of them, a whole airplane in front of us, and only a couple of days of my time to spend at Bede Corp., they have kept me more than busy. Yesterday was for big stuff, assembling the ribs onto the spar of the left wing. Today was for little jobs.

Post revised 9/24/11 to include photos.

Rob started my day with my first sheet metal fabrication job: bending 24 2″x2″ squares of aluminum 90° to make gussets for fastening the rear spar to the ribs of the left wing. (These are the ribs that we installed yesterday.) This was also my first exposure to a sheet metal brake.

After finishing the gussets, I moved on to preparing the 4′ wide skin section for the innermost end of the right wing. This section covers the first four bays, which includes one empty bay and then the three bays which comprise the fuel tank. Rob started by draping the skin over the ribs. We then carefully aligned it with the ribs and used the wing clamps to hold it in position. Rob then handled the “highly technical” job of drawing reference lines on the upper and lower skin along the trailing edges of the rear spar.

We removed the skin from the wing and took it over to the sheet metal sheer and cut it to length, i.e., about ¼” beyond the reference lines. I was very happy to let Rob position and clamp the skin in position. I did not want my first time operating a shear to be on such a large and expensive piece of metal (approximately 9’x4′ of 2024-T3 0.020″ aluminum).

Next stop was the workbench where Rob coached me through using my spiffy new caliper to measure the width of the rear spar, halve that dimension, and translate that distance into a line drawn on the skin. I then used an adjustable rivet spacer to drill holes for the rivets which will hold the skin to the rear spar. The rest of the skin is bonded in place with ProSeal. Other than at the rear spar, there are no rivets.

While all this measuring and drilling and deburring was going on, Steve was working on the fuel sender for the right wing. It came as a straight rod that had to be bent into roughly the shape of the number 7 and then cut to length. Finally, it needed a small hole ground into the bend at the top so that fuel could flow freely through the tube. I watched and learned, being otherwise busy with the wing skin.

Rob and I then put the skin back onto the ribs and we used the holes that I had previously drilled in the skin as guides for drilling into the rear spar. Drill… cleco… drill… cleco… all the way down the line. When I was done, the skin lay tight and straight on the wing.

Rob had had me use a 1/8″ bit for the first batch of holes. I removed half of the copper 1/8″ clecoes, upsized the holes with a #10 drill bit, which is the right size for the rivets, and inserted brass 3/16″ clecoes. I then removed the remainder of the copper clecoes and upsized the remainder of the holes.

Steve then grabbed me and put me to work cutting the landing gear box to length with a Dremel tool and a tiny cut-off wheel. By the time I made it through all of that 0.063″ aluminum, the wheel was even tinier, believe me.

 

Next up, and my last significant task for the day, a truly glamorous job: scuffing the inner surface of the wing skin and the edges of the ribs with Scotch-Brite so that the ProSeal will bond better. This brought back “fond” memories of a part time job that I had in high school for a while, helping to prep an airplane for painting.

Steve and I spent quite a bit of time talking about protecting the BD-4C’s fuselage from corrosion. Bede Corp used Alodine on their BD-4C and I am tempted to do the same for mine. The thought of using a bazillion spray cans of zinc-chromate primer bothers me, since I do not have a paint booth and do not really want to dump that many aerosol cans into the trash.

I was in watch-and-learn mode, again, at the end of the day as Steve and Rob hurried through the process of prepping the fuel “fin” which is the low point in the tank. Rob cut the hold in the skin for the fin and, even more so than with the shear, I was happy to let him cut on that huge sheet of aluminum. Steve very carefully tapped the threads into the bottom of the relatively thin fiberglass and threaded the fuel drain into it. Rob fashioned the fuel pickup line to the right length and drilled the 24 holes in the end, fashioning the first, coarse, fuel filter in the system. I double checked the drawing for the fuel pick-up later in the afternoon and noted that it needs to be about an inch shorter than it is now so I will shorten and redrill it in the morning.

I wrapped up the day with a conversation with Steve about how I might fabricate a real luggage compartment, where the door might go, and how I might build a floor that would still allow access to the control cables beneath.

All in all, a very satisfying day #2. Tomorrow: bonding the first section of skin onto the right wing.