I did some rough calculations last night with a wing tip in the hangar for our RV-6A. The wing tip is a homemade racing tip for when I'm racing with the extra tanks installed (long story - I have many wingtip sets). It is reasonably stable but if I decide to go ahead with this mod I am thinking of I will redo this with one of my metal tip tanks as a pattern.
I traced the airfoil on my 4'x8' workbench top with the leading edge and the trailing edge the same distance from the edge of the surface for general alignment. I drew a straight line (chord line) from the most forward point of the leading edge to the trailing edge of the airfoil drawing and I measured from the trailing edge to locate the point specified in the manual for rigging the wing incidence when setting up to drill the rear spar attach hole (~11.5" - I don't have the measured number with me at the moment but it was 11 3/8" or 11 5/8"). I drew a perpendicular line from the chord line at that point and marked it with a rigging reference point 3 1/32" above the surface of the airfoil. Then I drew a measurement reference line from that point tangent to the high point of the airfoil. Then I measured the vertical distance from the chord line intersection of the nose of the airfoil to the measurement reference line as 4.5" (4 16/32"). Then I measured the vertical distance from the chord line at the rigging reference station to the measurement reference line and found it to be 4 25/32" (4.78125") for a difference of 0.28125" (9/32"). The distance between the two points on the measurement reference line is 47" so the sine of the angle is .28125/47= 0.005984043 and the arc sin = 0.342862429 degrees. Since the semetrical airfoil horizontal stabilizer (assumption) is rigged at 0.0 degrees with respect to the same leveled canopy deck reference plane then the decalage is ~ 0.34 degrees + or - the deformation errors of the wingtip for the airfoil pattern.
I'm interested in speed and I have a friend with an RV-4 that has shimmed his stabilizer leading edge up at the forward mounting point by 1/8". I haven't pulled my tail fairing and started measurement work in there yet but off the top of my head it seems like that would take me past zero-zero on my airplane. In an RV-6 the fuel and the passengers are sitting very close to the CG and a smaller design decalage may be tolerable for pitch stability.
Just out of idle curiosity what is the decalage on an RV-4?
Bob Axsom
I traced the airfoil on my 4'x8' workbench top with the leading edge and the trailing edge the same distance from the edge of the surface for general alignment. I drew a straight line (chord line) from the most forward point of the leading edge to the trailing edge of the airfoil drawing and I measured from the trailing edge to locate the point specified in the manual for rigging the wing incidence when setting up to drill the rear spar attach hole (~11.5" - I don't have the measured number with me at the moment but it was 11 3/8" or 11 5/8"). I drew a perpendicular line from the chord line at that point and marked it with a rigging reference point 3 1/32" above the surface of the airfoil. Then I drew a measurement reference line from that point tangent to the high point of the airfoil. Then I measured the vertical distance from the chord line intersection of the nose of the airfoil to the measurement reference line as 4.5" (4 16/32"). Then I measured the vertical distance from the chord line at the rigging reference station to the measurement reference line and found it to be 4 25/32" (4.78125") for a difference of 0.28125" (9/32"). The distance between the two points on the measurement reference line is 47" so the sine of the angle is .28125/47= 0.005984043 and the arc sin = 0.342862429 degrees. Since the semetrical airfoil horizontal stabilizer (assumption) is rigged at 0.0 degrees with respect to the same leveled canopy deck reference plane then the decalage is ~ 0.34 degrees + or - the deformation errors of the wingtip for the airfoil pattern.
I'm interested in speed and I have a friend with an RV-4 that has shimmed his stabilizer leading edge up at the forward mounting point by 1/8". I haven't pulled my tail fairing and started measurement work in there yet but off the top of my head it seems like that would take me past zero-zero on my airplane. In an RV-6 the fuel and the passengers are sitting very close to the CG and a smaller design decalage may be tolerable for pitch stability.
Just out of idle curiosity what is the decalage on an RV-4?
Bob Axsom
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