Leveling QB fuse for gear install

[lancef53]

Hello--I am just starting on the Qb fuse of my RV 8, and the instructions say to level the fuse upside down by using the 822-1 skin. It is easy enough to level it left to right, but the bottom of the fuse us not flat enough to decide which part to level off of for fore and aft. Can I use the canopy rail mount section of the longerons for this measurement? Is level on the bottom also level on the top?

Thanks, I tried to search but couldn't find any mention of this--maybe I am overthinking

Lance

 

[DanH]

In terms of leveling for gear leg install, fore and aft leveling doesn't matter very much. If you use the "two straight edges and triangulate to the tailwheel" method, perfect side-to-side leveling doesn't matter much either.

 

[Ironflight]

Whew - I'm glad Dan answered first, because I couldn't remember taking much painstaking effort to level the fuselage (inverted) for the gear leg install!

Since the inboard (pivot) hole is already drilled, the only real adjustment that you can make on a QB when drilling the gear install holes is fore/aft movement. This will affect the parallelism of the axle attach faces, as well as if those faces are crabbed relative to the centerline - which can be fixed by triangulating to the tail wheel attach bolt.

But then again, this was probably four years ago for me now.....

Paul

 

[lancef53]

Thanks for the tips, I didn't think it was real critical, but my mind was overthinking.

It didn't seem like it was critical when I was thinking of going from the wheel landing phase to 3 point attitude, but I thought I would ask.

Thanks--Lance

 

[chris mitchell]

use "skiis" to align the landing gear...

Also, the Vans 4 plumb-bob method will drive you plumb crazy! Use some aluminum angle clamped to the ends of the gear legs - like a pair of skiis - to get the gear parallel. Then you can measure from the tail wheel attach bolt to make sure the gear legs are not crabby ie to make sure they are aligned with the centre-line of the fuselage. If you use this method then there is no need to level the fuselage at all.

Chris

 

[lancef53]

Yep, I used the straight edge method, no plumb bobs for me.

Ever wonder where the name plumb bob came from??? Hmmm

 

[scsmith]

careful - it matters

I leveled my fuselage using the inner forward skin, as described in the plans.
I found that this is NOT the same as leveling the cockpit longerons - it is a slightly different angle.

When you set up the gear so that the front edges of the two struts form a straight line (I used plumb bobs with no trouble), it defines the fore-and-aft position that the outer gear saddle rests. I found mine ended up well centered in the gear opening in the skin.

Other posts on this subject have shown pictures where the outer saddle is offset well aft of the gear opening, requiring some skin trimming - I suspect this is because of improper fore-and-aft leveling. I think if you level the cockpit longerons instead, the front edges of the two gear struts will line up straight with the gear set slightly farther aft.

On the other hand, I ended up with about one degree of toe-in on both gear, which required a shim on each side. So maybe I shouldn't have set them that far forward?

For sure in any case, be sure they are both the same distance from the tail wheel. Also be sure to observe the 3/16" dimension for the outer saddle from the edge of the longeron. If you exceed a 1/4", you will make the saddle bridge across a slope discontinuity between the longeron and the inner structure.