Step 4: Fabrication and Installation of Aileron Pushrods
For the aileron geometry to work properly the CS132R aileron cranks and the CS128 bellcranks must form 90 degree angles to the CS129 push-tubes when the ailerons are in their neutral positions. The plans call this out in the drawings on page 19-15 and 19-16. Pay close attention to this. I was a few degrees off on the starboard CS132R and it threw the geometry off. I had a harder time rigging the ailerons through their ranges of motion.
I used this process for getting the 90 degree angles and for determining the custom lengths for the CS129 push-tubes. Having done this twice, I really feel it's best to start from the ailerons and work my way to the firewall. This process assumed I had NOT YET DRILLED the hole through the CS132R aileron crank and the CS152 steel insert that goes through the wing root bearing.
Setting the 90-degree Angle for the CS132R Aileron Crank
1. Block out the ailerons to their zero positions. I did this by clamping the ailerons to the wing trailing edge using mixing sticks and clamps.
2. Slide the CS132 aileron crank over the CS152 steel insert that goes through the wing root bearing.
3. In order to set the position of CS132R aileron crank, I had to partially install the CS129 tube so I could use it as a reference for determining the required 90-degree angle. Assemble one end of the CS129 by inserting a CS1A rod end fitting and match drilling the holes for the rivets. (I cut my CS129 push-tube longer than needed, and I assumed the CS1A rod end fittings are inserted fully into the tubes.) Insert the rivets to hold the CS1A in place and wrap the rivets with black electrical tape. Insert an MM-4 rod end bearing and set the jam nut to be at 10 turns out. At the other end , take the other MM-4 rod end bearing and screw it all the way into another CS1A rod end fitting. Slip the fitting into the end of the tube. I did NOT DRILL or RIVET that end at this time. Temporarily install the CS129 by attaching the drilled end to the CS128 bellcrank and attaching the free end to the CS132R aileron crank. (Again, all I'm doing at this time is using this CS129 mockup as a reference for setting the CS132R aileron crank to 90 degrees. The length of the CS129 tube is determined in a later step.)
4. Make a 90-degree jig as shown in this picture. I made mine from a shim that is screwed onto a small piece of pine stringer. It doesn't have to be fancy, but it must lay flush along the top of the CS129 tube. I made a small notch in the pine stringer so it could sit flush over the rivet heads. The shim is be positioned so that its vertical edge is 90 degrees to the horizontal surface of the stringer. Now, with the aileron blocked off as per Step 1, rotate the CS132R crank fore and aft until it is precisely at 90 degrees to the CS129. It helps to draw a reference line on the CS132R. Make a few index marks on the ends of the CS132R and the CS152 steel insert.
5. Remove the aileron from the wing and remove the CS152 steel insert. (Confession: I wasn't brave enough to drill the hole through the CS132R and the steel insert with them still installed in the wing root.) At the drill press, slide the CS132R crank onto the CS152 insert and carefully match up the index marks. Clamp the two in place so the insert won't move around. Drill the hole through the CS132R and the steel insert.
6. Re-assemble everything and put the aileron back onto the wing. Reconnect the mocked-up CS129 tube. Verify the CS132R aileron crank is at 90 degrees to the CS129. (Mine was! Alleluia.)
Determining the Final Length of the CS129 Push-Tube
7. Make a similar jig to measure the 90 degree angle between the CS129 and the CS128 bellcrank. As shown in this picture, I used a piece of rigid foam and screwed it onto the same pine stringer used above. I made sure the angle of the jig was exactly 90 degrees. Caution: The only way to determine a proper 90 degrees at the bellcrank is to measure across the bolts protruding out the end of the MM-4 and the bolt protruding out the center of the bellcrank bearing. Do not measure by using the side of the bearing arm itself. This will give a false indication.
8. With the ailerons still blocked out as in Step 1, move the CS128 bellcrank in and out until the angle is 90 degrees. (The CS1A rod end fitting at the free end should slide in and out of the CS129 tube. If it is too tight a fit and won't slide, then unbolt the tube at the CS132R aileron crank. Rotate the tube and/or turn the MM-4 rod end bearing to adjust the length of the tube until the 90-degree position is achieved.) Measure the eye-to-eye distance required for the CS129 tube. Subtract the lengths of the rod end bearings to yield the length required for the tube. Cut the tube to length, install the other CS1A rod end fitting, drill the rivet holes, and insert the rivets. Set the MM-4s for 10 turns out. Re-install the CS129 and verify that the CS132R aileron crank and the CS128 bellcrank remain at 90 degree angles.
Fabricating and Installing the CS126 Push-Tubes
9. To determine the eye-to-eye length required for the CS126 push-tubes, I first set the CS122 firewall cranks to their neutral positions. Best I can tell per the plans, the firewall cranks are neutral when all four holes are aligned horizontally. This happens when the inboard sides of the cranks are vertical. I used a pine board to hold the cranks in their vertical positions. As per the directions in the plans, I bent the crank arms (the flat plated steel) until they were parallel to the firewall. It was easy to check this because the cranks would lay flat against the pine stringer.
The plans do not give a spec for how far to set the cranks away from the firewall, but I inferred the distance from "View K-K" shown on Chapter 16, page 5. I inferred it to be just over 3/4th-inches, and the pine board is about the right thickness for setting that distance. Just know that the plans have us slip in the AN-4 bolts through the crank holes as shown in "View G-G". These bolts are LONGER than 3/4th-inch. Following my process, this was easy to do at this point because I had not yet bolted the CS121 and CS122 tubes together. I was able to slide the firewall cranks out a bit, put the bolts in, and push the cranks back toward the firewall. If you decided to follow the plans, then you already know that the only way to get these bolts in or out is to unbolt the CS121 and CS122 tubes (rear seat area), pull out the firewall cranks a bit, slide in the bolts, and bolt the tubes back together. I can't really tell if it's that way on purpose (so the bolts don't slide out on their own if the nuts inexplicably fall off) or if it's just one of those design gotchas.
13. I decided to make my CS 126 tubes as single tubes. I saw no reason to use the quick disconnects. With the ailerons still blocked out and the firewall cranks pinned in their vertical positions, measure the eye-to-eye distances required between the CS128 bell cranks and the outboard holes in the firewall cranks. Subtract the lengths of the rod end bearings to yield the length required for the tube. Cut the tube(s) to length, install the CS1A rod end fittings, drill the rivet holes, and insert the rivets. Set the MM-4s for 10 turns out. Remove the pine board jig and install the the CS-126 push-tube(s).
Fabricating and Installing the CS125 Tie-Rod
14. With the ailerons blocked out, measure the eye-to-eye distance for the CS125 tie-rod and fabricate it using the hopefully-by-now-all-too-familiar-measure-cut-drill-install process.
If all goes well, the plans say we're supposed to have at least 20 degrees up travel for each aileron. (The plans then tell us to add a stop bolt to the CS128 bellcrank to limit the travel to 20 degrees maximum. It's virtually impossible to drill this hole through the brackets when the assembly is still mounted in the wing roots. So I will do this the next time I pull the wings.) If the rigging checks out okay, now is the time to jump back a few paragraphs and do the final drilling of the CS121 and CS122 tubes.
But I had a few issues to resolve.
First, I was perplexed to find out I only had 16 degrees up travel. Why? Because the last two inches on the outboard ends of the aileron counterweights were hitting the last two inches inside the spar cut-out area. The down-traveling aileron was keeping the up-traveling aileron from reaching its full-up travel. I guess my overlapping plies near the corners of the spar cutout area just got a little too thick? Anyway, I had to grind away those two inches of glass (including some foam) in the spar cut-out to remove the interferences. I had to be extremely careful when grinding that area because of the rudder cable conduit. I didn't want to slice through it. I will re-glass that area next time the wings are removed.
Second, I was perplexed as to why the ailerons traveled downward more than they go up. With the port aileron up 20 degrees, the starboard aileron goes down 24.2 degrees. With the starboard aileron up 20 degrees, the port aileron goes down 22.6 degrees. My hoard of respected canard experts said, "There's supposed to be more down travel than up travel. That's just the way the geometry works."
Okay, but now I'm dumbfounded as to why I have differing amounts of down travel for the same amount of up travel. What tubes do I lengthen/shorten to equalize the down travel without affecting the up travel? When asked, the same hoard of experts said, "Close enough. You'll never sense that in flight."
Okay, so I tossed the perplexed thoughts into the "not-gonna-worry-about-it-anymore" drawer, and I jumped back a few paragraphs and did the final drilling of the CS121 and CS122 tubes.