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Old 09-10-2017, 09:11 PM
dr cooper dr cooper is offline
Join Date: Aug 2006
Posts: 41
Unhappy Setting incidence

Help, please

When trying to level the longitudinal axis, I can not get it exactly the same on both sides.

I can only get one side level with the other one showing 'nose high' by 20+ th along the top of the longeron. I'm holding the level as close to the outer edges of the longeron as I can.

To measure the incidence, I'm using the level measuring from the root at 21", 71" and 125".

I can get the bubble centered at the 21" mark on the left wing. Then as I measure outwards from there, the bubble moves forward approximately 20 th at the tip, indicating that the nose is up.

On the right wing, using the same measurements, the trailing edge is high at the tip by more than 20 th.

I'm using a block for leveling that is 4 5/64".
My level is a 6" machinist's level on a 4' carpenter's level.

Cliff Jones, RV9-A incidence
Pritchard, BC
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Old 09-11-2017, 03:55 AM
KRviator's Avatar
KRviator KRviator is offline
Join Date: Oct 2009
Location: Sydney, Aust.
Posts: 694

By '20th', I'm guessing you mean "20 thousandth of an inch" difference from "right on" to "T/E up (or down)"? I've tried to think of a way to calculate the angular error trigonometrically and have struck out. Anyone smarter than me out there?

Without running a digital level over it, that small amount is not likely to be a factor overall, and I would suggest anything you do do is likely to be absorbed by the elasticity of the wing structure. You could try to put a stand with a shim under the outboard trailing edge and re-measuring it, but as soon as you remove the stand, I venture you'll be back where you started for no significant benefit.

I used a digital level with mine with the pointy spar incidence tool and gave it away at a 0.05*difference. Working under an Australian summer sun to get exactly 0* is not worth it, and my -9 flies well enough.
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