Wing twist & grease zerks?

[Barry]

Everyone, I have mounted my right wing in the jig and have been checking the level and twist and squaring everything up. I have a plumb bob from the main spar to the rear spar mounting holes. Everything is perfect EXCEPT that when I check the level from the main spar down to the rear spar (1 1/2" spacer block taped to the one end of the level) I am showing 1/4" of twist in the wing from the root to the tip? Not sure what to do, any suggestions? I also ordered my flap supports and aileron supports from Avipro and there are no grease zerks in them, is it necessary or can I just lube them up good during assembly and call it good to go?

Thanks,
Barry

[N3UW]

Barry, I am not sure I understand. Where are you seeing the twist?

[Barry]

John,

It is very hard to describe. It is when I am checking the vertical level between the main spar and rear spar. Both spars are mounted in the jig perfectly level horizontally, it is the vertical I am having issues with. I may need to post my first video to the group!

Barry

[alaskabearhawk]

What are you trying to grease? The bearings are slipped into the mounts.

[Barry]

The flap supports for the flap torque tube have no bearings.

[Mark Goldberg]

You can weld a zerk fitting on the bottom of the wing root flap support. Then make a hole in the skin to access it. However, not really required. I use LPS2 with a long "straw" and get the lubricant and straw close (not that easy) and give it a squirt or two. Then move the flap a bit and re squirt. Something I do at annuals.

My BH ended up with a slight twist of less than 1/8 but is present on both sides. No issues. If you had this twist (wash in or wash out) equal on both sides there would never be any problem. One side might require some rigging adjustments but I suspect very minor. Perhaps a question for Bob. Mark

[dedgemon]

Barry,
You have to look at the plans pretty hard, BUT....

the line between the main spar attachment hole and the rear spar attachment hole does NOT run parallel to the wing chordline.
So if you drop a plumb bob between these holes the tip end should end up at a slight angle.

For a straight wing the angle of the main spar and rear spar are the same from root to tip.
What I do is attach a spacer to a 4' level (like you are doing) so that when held against the bottoms of the 2 spars it reads vertical. Then I can quickly check that it is the same all along the wing.

Good luck

[KyBearhawk]

Oh mercy...here we go with the plumb bob alignment thing again...LOL...

Maybe I am not following you but it sounds to me like to just need to move one of the spars at the tip end to make it level vertically the full length of the wing. Am I missing something? Also on the zerk fittings... I wish I did not put them on now. Do what Mark said.

Also dedgemon is correct they do not line up with a plumb bob if you follow the plans...but most people do it this way from what I have noticed and they are flying.

[KyBearhawk]

http://www.mykitlog.com/users/display_log.php?user=wlmassey&project=221&category=2763&log=36225&row=38

This is a great explanation by Wayne Massey.

[N3UW]

I would have to agree. I went back to drawing #4 and marked the center line of the main spar and rear spar and marked the 1-1/2" up to represent the main spar attach point and 1-1/8" up on the rear spar. The cord line of the rib should be parallel to any plumb line. From the drawings there would be a 1/2" offset from the main spar hole to the rear spar hole. Without hat offset you would have a twist I the wing from the root to the tip. Here are some photos of drawing #4 and my measurements. This offset would make the tip match the root

[SC Patrol 253]

Yet another proof of the 1/2 inch offset! We have to get Bob to change page 19 to refer to the 1/2 in offset from front to rear attach hole.

[Barry]

Everyone, thanks for all the help and suggestions. I have been called out of town for work. I will post my findings in a few weeks.

[Wayne Massey]

I talked to Bob about this several years ago and his advice was, “Build the wing to match the drawing and everything will work out just right.”

If you are building your wings in a vertical jig and you want to build the wings to match the drawing precisely then you need to offset the rear spar and main spar attach holes per the drawing. Everything fits better when you build it squared and aligned correctly. If you build the wings with the holes lined up then you are building an out of jig spar box. It’s been proven that the airplane will fly that way but that is not how the wing is drawn or designed. If you build with the holes lined up you’d actually be positioning your top spar and bottom spar out of alinement. In carpenter terms it would be the same as building a wall with the top plate and bottom plate offset by 3/4 inch resulting in a slightly leaning wall. It will still work that way but you wouldn’t normally intentionally do that.

[Barry]

Everyone, thanks for the help and replies. I did as Wayne and Jon suggested, offset the attach holes by 1/2" and the twist went away. Everything is now plumb and level and ribs fit tight and square. I also will NOT be using grease fittings.

[Bradrock]

Could you clarify that the grease zerks you're mentioning are the ones that Eric explains in his manual?

[Barry]

Bradrock, the zerks I am referring to are the ones in Eric's manual.