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- Oct 5, 2007
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A few questions relating to rigging and some errors I am finding.
So, starting with an S2B that has been rebuilt. There had been spar compression so this has been repaired and in essence the wings are back to factory new, trammelled and all square etc.
Aircraft levelled longitudinally and laterally with 3 rigging boards made. Rigging boards tuned by getting the level on the top and bottom the same (to find the chord). The top wing is levelled with a slight bit of dihedral prior to getting the wires tight and no twist (about 1.3 degrees on the boards, give or take 0.1-0.2, although it should be 1.5 degrees).
The bottom wings are where the issue arises. Measuring the incidence near the wing / fuse attach gives about 1.2 degrees on the left and about 1.8 on the right. Is this a manufacturing tolerance that I may expect?
I've retuned the rigging boards to suit the bottom wing, same technique as the top, and needed a small adjustment.
When I measure the incidence toward the tips on both sides, even with 5 AN960-416 washers (large area washer against the spar first at all attach points of the I struts) on the bottom rear of the I strut, I can only get to about 0.7 degrees on the left and about 0.4 on the right. To get anywhere near 1.5 degrees I will need 4-6 more washers (total of nearly 10 which is crazy).
What am I doing wrong?
The I struts are up the right way but could possibly have been change from right to left accidentally.
Should I get rid of the slight dihedral in the top wing, I thought this would likely pull down a bit when tightening the flying wires (as mentioned in Doug Sowders notes).
At this stage the landing wires are just tight to get the top wing level with no twist but the flying wires are loose.
Bottom wing dihedral is pretty close to the expected 3 degrees.
Thoughts.
So, starting with an S2B that has been rebuilt. There had been spar compression so this has been repaired and in essence the wings are back to factory new, trammelled and all square etc.
Aircraft levelled longitudinally and laterally with 3 rigging boards made. Rigging boards tuned by getting the level on the top and bottom the same (to find the chord). The top wing is levelled with a slight bit of dihedral prior to getting the wires tight and no twist (about 1.3 degrees on the boards, give or take 0.1-0.2, although it should be 1.5 degrees).
The bottom wings are where the issue arises. Measuring the incidence near the wing / fuse attach gives about 1.2 degrees on the left and about 1.8 on the right. Is this a manufacturing tolerance that I may expect?
I've retuned the rigging boards to suit the bottom wing, same technique as the top, and needed a small adjustment.
When I measure the incidence toward the tips on both sides, even with 5 AN960-416 washers (large area washer against the spar first at all attach points of the I struts) on the bottom rear of the I strut, I can only get to about 0.7 degrees on the left and about 0.4 on the right. To get anywhere near 1.5 degrees I will need 4-6 more washers (total of nearly 10 which is crazy).
What am I doing wrong?
The I struts are up the right way but could possibly have been change from right to left accidentally.
Should I get rid of the slight dihedral in the top wing, I thought this would likely pull down a bit when tightening the flying wires (as mentioned in Doug Sowders notes).
At this stage the landing wires are just tight to get the top wing level with no twist but the flying wires are loose.
Bottom wing dihedral is pretty close to the expected 3 degrees.
Thoughts.
