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RV-8 MLG alignment

N804RV

Well Known Member
Any tail draggers wanna share their secrets and pictures for main landing gear alignment?

This is a new build. Haven't drilled the holes through the lower longerons yet. I'm installing the SkyDesigns gear. So, I've already trimmed the Z bracket. But, I kinda feel like I'm playing whack-a-mole, trying to get the leading edges of the gear legs to line up with the wear plates correctly positioned.
 
Last edited:
No pictures but...

Any tail draggers wanna share their secrets and pictures for main landing gear alignment?

This is a new build. Haven't drilled the holes through the lower longerons yet. I'm installing the SkyDesigns gear. So, I've already trimmed the Z bracket. But, I kinda feel like I'm playing whack-a-mole, trying to get the leading edges of the gear legs to line up with the wear plates correctly positioned.

I don’t have any pictures, but I did this before drilling the outboard gear holes:

After securing the inboard part of the gear legs with the large fasteners I installed the axles the used ratchet straps attached to the outboard end of the axles and run across the top side of the fuselage (now the side closest to the floor while upside down) and pulled the gear legs down (towards the floor) so that the outboard portions were pulled flat against the outboard wear plates, before I did the final alignment and hole drilling.

What I found was that when the gear legs are initially set on the fuselage and aligned, the outboard part of the mounting area doesn’t necessarily sit flat against the outboard wear plates. If you align and drill them in this condition, the legs will twist slightly in the fuselage area, shifting their alignment when the bracket fasteners are torqued. By pulling them down with the straps, you help ensure that they will remain properly aligned once drilled and the outboard brackets are bolted in place. Also be sure to follow the plans and instructions regarding bolt torque and ensuring you have at least 1/32” inch clearance between the brackets the the wear plates.

Skylor
 
I also have the SkyDesigns gear. I purchased two aluminum angles from Lowes 1 1/2 x 1/8 x 8 ft and clamped each to the outside face of each gear leg to align with the fuselage centerline. Drew a centerline reference on the floor with fuselage leveled laterally inverted. Placed two lines parallel to the centerline that are the width of the outside face of the gear with clamped aluminum angles. Used plumb bobs to align aluminum angles with reference lines on floor. When both legs are lined up, clamp the two angles to each other front and back (I used a couple of 3/4 in aluminum angles long enough to reach) so they cannot move and double check that they are parallel to each other and the fuselage reference line. Snug the 7/16 inboard gear bolts of each leg so they won’t move. When everything was set up, I double checked everything again. I step drilled the longerons using a bushing I made to start with a 1/8 in drill. I put a bolt in each hole as it was final drilled to prevent any movement. The holes came out exactly where they were supposed to. I also planned all holes drilled undersized and finished with a correctly sized reammer. Take your time, I spent a couple of days aligning, checking and double checking before I was comfortable drilling the first hole. Good luck!
 
I made a jig out of a 2X6 and a few pieces of 2X4. Used two chalk lines lengthwise set apart the diameter of the axel and screwed the 2X4s on either side to make a saddle where the axles go, then clamped the axels in. I measured from end of the axles to the aft most bulkhead to get them even.
 
Gear Alignmnet Front Side 1.JPGGear Alignment Rear.JPGWheel Alignment 2.jpg

Aligned gear with plumb bobs down to 6" channels (these were hinged and were my heavy duty trailing edge brake). It's been a while but I must have squared the "brake" to the fuselage centreline, probably triangulated to the tail as well.

Final aligned the wheels with 6ft 2x2 tubes bolted to the wheel rims. The wheels were on mating plates with grease between them. Did this with the tail up in wheel landing configuration. Added shims on the axle to get alignment just right. I'm happy with the handling in the end.

I've got a lot more pictures if you need something specific but these tell my overall method.
 
I used two six foot harbor freight box levels clamped to the gear legs for the toe-in/out check. Nice and straight. $20 a piece and are useful for other stuff.
 
Make sure the holes you drill go through the longron with sufficient edge distance. You can always shimmy the axils you can’t get lost strength back from lack of proper edge distance.

Oliver
 
Well, its a done deal! With the inboard AN7 bolt in place, and the outboard wear plates drilled onto the lower longerons, the main landing gear are pretty much locked in place.

I did use the 2 four foot levels (purchased from Harbor Freight) clamped to the outboard faces of the bottom of each MLG, where the axles mount. I adjusted the legs fore and aft until the distance between each end of the levels was the same, and the distance from the outboard plumb bobs to the one on the tail post was the same. Then, I re checked to insure I had the outboard edge of the outboard wear plates 3/16" from the vertex of the lower longerons. And, I just kept going back and forth till I could consistently get the same dimensions without making any adjustments.

The funny thing was that it was so exact. The lateral distance between the ends of the levels clamped to the lower leg outboard faces was exactly 67" forward and aft. And, the distance from each outboard plumb bob to the aft plumb bob (on the center line of the aft bulkhead) was exactly 114 and 1/8th inches on each side. Exactly!

I had to trim the aft Z-bracket outboard corners quite a bit, making the outboard most rivet hole unusable. But, I'll have to remove that much of the belly skin anyway. So, I'll just add another rivet just inboard.

The kicker is, I dropped 2 more plumb bobs on the inboard leading edges of each gear leg (ala, Van's instructions). And, all 4 plumb bobs attached to the leading edges of the gear legs line up, exactly!
 
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