Wing incidence difference?

[bret]

Setting up the wings for drilling the rear spar, after setting fuse level, wing sweep, and wings level
with the spacer, I am finding that from the top skin to the top of rear fuse spare I measure .125" difference from L to R. I know the wings are the same incidence, I measured 432 times. Is this normal?

[bret]

Never mind, I found the problem.....Note to self. Do not use cheap a$$ tools for critical measurements.

[Bob Axsom]

Do not force yourself into some mind games that are subconciously designed to "accept as is" rigging that is wrong. The canopy deck reference plane and the mutually perpendicular axis is what the wings, stabilizer and fin (vertical stabilizer) need to be rigged against. Our fuselage (quick built) was not perfectly square but that doesn't matter unless one tries to rationalize requirements other than the reference axes have to be satisfied and compromise the correct rigging. I forget the ammount I had to lift the trailing edge of the left wing but it was a lot (on the order of 1/2"). I think I measured 433 times before I drilled the rear spar holes on our RV-6A

Bob Axsom

[ChiefPilot]

Like Bob, mine was off a bit as well. Not by as much, but it was more than 1/8" for sure.

I have that same kind of level. It's as repeatable as a blue spirit level BUT it has to be oriented the same way to get the same repeatability. That means the display would be towards the wingtip on one side, and towards the fuselage on the other for example. That said, the spirit level is what I used on my wings.

ETA: ...but then again we have the old "mine the ore first" -6A models, not the snap together -7A :-)

[roee]

Originally Posted by ChiefPilot

I have that same kind of level. It's as repeatable as a blue spirit level BUT it has to be oriented the same way to get the same repeatability. That means the display would be towards the wingtip on one side, and towards the fuselage on the other for example. That said, the spirit level is what I used on my wings.

Yep, it's not so much the tool, but how you use it. A cheap level might have very poor absolute accuracy, but would still be very precise from one use to the next at a given orientation. Even with a more expensive level, you wouldn't want to rely on its absolute accuracy. You'd want to use it in ways that are governed by precision instead, a good example being what ChiefPilot suggested.

[wirejock]

Looks like that level is Tango Uniform. Husky tools are guaranteed for life. Take the pieces to Home Depot and tell them you are a railroad engineer and it got hit while measuring tracks!
Seriously though, it's great you found the problem.

[Veetail88]

Mine is a quick build and was off by a lot too! So much so that I ended up without enough edge distance on the rear spar that I had to fix!

[rzbill]

I hope everybody knows to always flip a level end for end and average the bubble position.
This eliminates the inherent error of construction of the level. It allows a bad level to be used in an accurate manner. It is good practice even with well made levels.

[bret]

A no go, I was in the sun for 4 hours setting everything up, brought everything in for lunch, came back out and the R wing incidence was . 4 deg different! Just for S... And Giggles I put my calibrated Samsung galaxy S 3 on there and sure enough they were off by .4 deg I don't know if the sun and heat made the tool read different or what, but that tool is history!

[lorne green]

Originally Posted by rzbill

I hope everybody knows to always flip a level end for end and average the bubble position.
This eliminates the inherent error of construction of the level. It allows a bad level to be used in an accurate manner. It is good practice even with well made levels.

Ah, spoken like a journeyman. Not a bad idea, even for an electronic level.
Oh, and Bret, .4 of a degree is nothing. More importantly, acording to Vans - is that both wings are equal in degrees of incidence.
Whether this measurement be .4* or 1.2*

Regards