Main Gear Leg

Attaching the main gear leg proved to be a difficult task, as other builders have reported. I experienced a lot of the same difficulties, resulting in the need to file the legs in a few spots, both spread it and squeeze it, and then finally I was able to obtain a fit to allow me to thread the 10 x 170mm retaining bolts. It took me quite a few hours over the course of 3 evenings to get the leg mounted, about 7 hours total.

My first task was to reorient my work table to give me access to the gear channel. I had already built a tail stand when I joined the rear fuselage to the main fuselage, so all I had to do was turn the work table. I used my work stool as a temporary lifting surface.

Using a stool to temporarily lift the front of the fuselage
Work table rotated to expose the main gear channel
Rear of the fuselage supported by a tail stand

After the fuselage was again resting on the work table, I used the stool to maneuver the gear leg beneath the fuselage. I’m glad I used a rolling stool, because I had to move the gear leg in and out about a dozen times to make fit adjustments.

Stool used to roll and lift the leg into place

The first fit problem I encountered was that the leg wouldn’t fit into the channel. The rivets shown in the next photo were sticking out too far, so I gently filed the tails down a little – just enough to gain about 1mm clearance without compromising the strength of the rivets.

Rivet tails sticking out too far
After grinding the rivet heads a little bit

From here on, all the fit adjustments related to aligning the holes for the 170mm-long bolts. On my first attempt, I couldn’t get any of the bolts through the holes. I noticed that the leg was bottoming out on the thick metal reinforcement plates at each end of the gear channel (this plate is visible in the two previous photos). I had to file down a groove on both sides of the leg to accommodate the reinforcement plate.

Groove filed into the leg to clear the reinforcements at each end of the gear channel

The next fit challenge were the rivet nuts sticking down into the gear channel. The leg was bottoming out on the ends of the rivet nuts. I stuck a pencil down through each of the rivet nuts to mark their location on the leg, then used a Dremel with a burr bit to grind out little semicircle notches for the rivnuts, about 4mm deep.

Notches for rivnuts
Another view of the notches

Finally, I was getting the holes mostly lined up, but it still was too tight a fit / misaligned to allow the bolts to fit through. The manual states that the legs may be unlevel due to the composite process; indeed I found this to be true, resulting in some misalignment of the bolt shafts on the legs with their mating holes on the gear channel. I had to do a few things to correct the misalignment:

  • Filing the Bolt Ends: As suggested in the last page of the undercarriage manual, I filed the ends of the bolts with a Scotchbrite wheel to give them a beveled edge, making them easier to push through the holes.
  • Spreading: I used a 2×4 piece of lumber (cut to 64″ length) along with a car jack to spread apart the legs about 4″; this caused the outer holes to line up correctly. This tip was first suggested by Bob Z for his Sling 2 build, and later used by Craig M and others. The trick worked well for the outer holes, but spreading the legs made the inner holes misaligned and impossible to push bolts through, so the next step was…
  • Squeezing: I removed the jack and 2×4 to relax the legs back to their original shape, and I found that this improved the clearance of the inner bolt holes, but they still weren’t lined up correctly. Both of the inner holes were out of alignment in the vertical plane, but otherwise OK. So, to correct this I squeezed the legs together a few inches (2-3″ or so) using a ratcheting strap. This worked perfectly, and I was able to push the bolts through the inner holes with just finger pressure; no hammering or prying required.
Using a ratcheting strap to squeeze the legs together for the inner bolt fit
Inner bolts easily pushed into place this far with just finger pressure. They had to be threaded the rest of the way through.
Creep marks on the heads and nuts after tightening to a hefty 24 Nm / 18 ft-lbs. There was about 5 ft-lbs of drag due to the locknut and tight fit of the bolt, so I tightened until my torque wrench indicated just under 25 ft-lbs.
Leg fully attached!

Next I will build and attach the main wheel assemblies – a task for another night.

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