Chapter 11: Elevators


11parts.jpg

Alright, time to install some hardware and make some moving parts. I didn't find the elevators to be all that technically challenging, but Chapter 11 does have extensive set-up time and you have to be careful with handling the elevator cores. The foam material (like the canard cores) is really soft and fragile.

My elevator weights with the outer counterbalance weights installed are 34.6 ounces (starboard) and 35.1 ounces (port).

My lessons learned:

1.  The NC-2's won't fit into the torque tube pockets without first filing down the corners of the NC-2's to fit. I guess one could file out the corners of the torque tube pockets, but in my opinion, you would run the risk of increased stress concentrations and potential cracks at the corners (thin wall tubing!).

2.  I used hot-stuff glue "gel" from a local hobby shop. Hot-stuff glue is a brand name for super glue. The gel-type glue is great because it doesn't run all over the place.

3.  I didn't bother putting grease in the hinge pin holes. I just made sure to go easy on the epoxy around the NC-2's. The only reason for adding the grease is to ensure no excess epoxy wicks into the holes. I believe if you’re shooting for a dry layup, then you’ll have no wicking problems.

4.  Everyone seems to have problems slipping the cores onto the torque tubes without breaking the fragile edges. I simply sliced off an eighth inch from the top and bottom forward edges of the core. The tubes popped right in. Take a look at the drawings…you end up sanding these edges away anyway when feathering in the foam and torque tube prior to layups. An alternative is to slide the cores onto the torque tube, hold the cores still, then rotate the tube while applying liberal amounts of micro.

5.  I used drywall screws to hold down the cores during cure. I predrilled my table in the proper locations, then screwed in the drywalll screws from underneath the table.

6.  I glassed the tops first, bottoms last to improve cosmetics of having the micro on the bottom. The drywall screws kept the cores perfectly flat while glassing the top.

7.  I had to go back in with a dremel and clear the other slot to prevent impingement on the hinges. At first, I thought the plans only had us clear out the front slot. But I had to shave down the edge of the window cut-out. It was rubbing on the hinge.

8.  The new Lm jigs work great for floxing the hinges at the minus 15 degree travel point. But, you’ll need to reverse the order - glue down the elevators first, then attach to canard. Otherwise there will not be enough room between the jig and the canard for you to slip the elevators into place.

11_L-jigs.jpg

9.  When I first trail-fitted the MKNC-12A's, I aligned the hinge pin holes, but I noticed that the counterweight arm was pointed down from the position shown in the drawings. If I positioned the NC-12A's with the counterweight arms at the 126-degree position shown in the M-drawings, then the hinge pin holes wouldn't line up. Not wanting to worry about flutter, I chose to position the NC-12's as shown in the drawings and just take my chances that I could get the hinge pin to go into the holes. Much after the fact, I discovered that the counterbalance arms hit the canard and limit trailing edge down travel to 25 degrees instead of 30 degrees. (Whaaatt?!?) I went back and looked at the M-drawings. Sure enough, there's no way for 30-degrees rotation with the counterbalance arms positioned as shown. It's an easy fix to simply notch out a small area on the counterbalance arms. My lesson learned is just to install the MKNC’12As with the holes aligned. Don’t try to position it as shown on M-11 drawing or it will hit the bottom of the canard for full 30 degrees elevator travel.

10.  Put box sealant tape onto the J jigs to keep from bonding the foam and counterweights to the jigs.

11. This picture shows the details of the counterbalance weights and their cutouts, allen screw, and hinge pin.

11details.jpg

12. When drilling the hole into the ends of the elevator hinge pins, I sized it to the size of the allen wrench. I figured that since I'll carry the small allen wrench with me as part of my on-board tool kit, the hole might as well be large enough to stick the allen wrench into the hole and pull the hinge pin out.

13. The wingtips were fun to make and are probably the most individualistic elements on the entire airplane. Here's how mine turned out.

11tipfoam.jpg  11tipmicro.jpg  11wingtip.jpg

My first Oaf Story

To ensure exact profiles on the cores, I made two profile templates and screwed them down onto the table and put the core between them. I covered a section of pipe with sand paper and started gently sanding the cores down to contour. I noticed something wasn't right. To my disbelief, the middle of the cores were now well under profile. How could this undercut have happened? After all, I chose the straightest section of pipe I could find. Checking the pipe again, I noticed it wobbled when rolled on a flat table top. Much to my chagrin, I had picked up the wrong section of pipe. I had cut a 5-foot section off the 10-foot pipe I had bought. I chose the straightest one, put it down, had a sandwich, came back in, and picked up the wrong one. The wrong one had a big dent in one side which translated into a bend in the other side. I never noticed the dent or the bend, but it certainly resulted in bad cores.

I tried to salvage them anyway. I ended up with GREAT looking cores, great glasswork, and very light....but they didn't match the profile templates. It took all of 30 seconds with a "Nosholvka" (Russian for "hacksaw") to erase 15 hours' work. I'm glad I made the second set. I wouldn't want to be worried about flight characteristics at 12,000 feet.


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