GU Canard Offset Torque Tube
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I wanted to document the construction of my GU Canard Offset Torque Tubes (TT). They were easily made with a lathe and a TIG welder with no jigs or special tooling.. Instead of trying to write the process up I thought I would just show the pictures I took while building (worth 1000 of my words) to help clarify the process. The TT's only took about 5 hrs to construct, and it ended up the closure and repainting of the fuselage sides took the most time and effort.
The easiest way to make them is by fabricating them on your existing canard. This will ensure the alignment of all the pivot points are perfectly aligned. I think they can be pre-manufactured, but this may mean removal of the hinge supports (CS-3's) closest to the fuselage. This can be done by heating them up and pulling them out of the flox. You will re-aligning them by reinserting the hinges in fresh flox.
The starting point...
Using a stick and clamps to align the trailing edge when necessary.
Mark a straight line along the edge of the elevator. This line represents the clearance necessary for the side plates of the TT to the fuselage. As long as the TT assembly does not go beyond this line reinstallation of the canard will not be a problem.
Measure the length from the support to the pencil line and do the necessary calculation for the thickness of the side plates to determine the length of the 3/4" sidewall penetration tube. In my case it was about 1.770"
This is the basic layout of the tube parts. Overall you are just building a joggle in the Al TT around a rotation point (in this case it is hinge support). Later we will be putting a small bearing in the hinge support.
There are 9 parts to the TT offsets.
For lack of a better way to describe the parts, I will call them:
-3 ea short side plates (left part of the drawing) 4130, .090"
-1 ea of the long side plate (right side of the drawing former CS-12) with the bottom part removed 4130, .090" thick
-2 ea sidewall penetration tubes 3/4" 4130
-3 ea short tube rings, 1" long, 4130 1.25 dia .095" wall thickness machined down to just slip into the Al TT's.
-2 ea oil-lite bearings.
This is important general construction detail.... when you cut to length of the penetration tubes OR the tube rings, be sure to face off both ends on the lathe to ensure squareness of the tube. This way when you clamp and weld them to the flat plates, the will always be perfectly perpendicular to the center of rotation. No Jigs!
Clamp the penetration tube on to the large side plate and weld it up. No need to be exact.
Chuck the penetration tube in the lathe and center drill, and then tap the hole for a 10-32 screw. You have now insured an accurate center point of hinge rotation.
Machine the 3 tube rings about 1" long.
Weld up 2 of the side plates assembles (short side plates and ring tubes) You'll notice in my work I did not accurately cut the side plates. I just welded the assemblies up, then used a bench grinder to clean up the plates. EZ!
The last assembly will be welded up later.
Cut your existing AL elevator TT and push the short slide plate assembly into the elevator TT. Place a straight edge along the side of the elevator edge. As long as the side plate assembly clears the edge of the elevator (remember the pencil line you drew), you will not have a clearance issue when you later reinstall the canard in the plane.
If your measurements were accurate when you cut the fuselage tube, then there is no need for adjustment.
Reinstall the elevator, and bolt everything together (just like it would be installed in the plane. Align the trailing edges of both elevators as shown previously.
You can now clamp and tack weld the elevator side plate to the fuselage penetration tube. Disassemble the canard and complete the welding. Grind off the excess steel and your first tube is done. Drill the CS-3 and install the bearing for the attachment bolt.
Determine where you want to drill a hole in the tube rings for permanent installation to the elevator. Once done, assemble the elevator, align the trailing edges, carefully remove the elevators, and drill the hole though the Al TT through the tube rings holes. Hollow out a pocket in the foam of the elevator for the nut, and glass one layer of bid over the foam. Insert the AN3 bolts and test the assembly.
Now we will complete the offset second TT. Measure the distance from the support point to the edge of the elevator pencil line to calculate the length of the second fuselage penetration tube. Weld the penetration tube on to the shore side plate that does not have the tube ring welded on (the one you saved). Put the assembly into the lathe and center drill and 10-32 tap the hole as you did with the long side plate..
Cut the elevator AL TT off to insert the last short side plate assembly. Keep trimming the AL tube until the penetration tube has the proper clearances (clears the edge of the elevator pencil line). Make sure the side plates are aligned, clamp and tack weld the penetration tube to the side plate assembly. Disassemble and weld the tubes together. Clean up the side plates with the grinder....
Reclamp the tube ring in the lathe make center drill mark. This will represent the center of the last tube ring to weld on. This method will ensure the alignment of the original TT from the elevator to the center transition piece of TT.
Use a compass and draw circle to help you position the last tube ring. When you have it positioned it by eye, just weld it on.
Reassemble and you are done with the metal work!
Reassemble everything together, check to ensure movement. Clamp the align the trailing edges of the elevator as you did previously, mark the position of elevator. Disassemble and drill and install the bolt which connect the elevator to the offset TT. Reassemble everything together and repeat the process for the other side of the offset TT.
Here you can see were I drilled a hole in the elevator support and inserted a oil-lite bushing. Since the bolts which connect into the new offset provide a pivot point, I wanted to ensure they were not rubbing on the Al support.
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