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- Aug 5, 2008
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My lower wings are installed on the fuselage with 1 deg. dihedral and 1.5 deg. incidence. I've also installed the lower ailerons and bellcrank on both sides. Because other builders have reported interference problems with these push/pull tubes and other components I wanted to make sure everything moved freely through the full range of motion, plus and minus 23 degrees, of the ailerons. I had not drilled the rear spar for the idler bracket located in the first bay outboard of the wing walk. My idler centers the rod end bearing 1-3/16 inch below the wing chord line. I wanted to investigate small up/down movements of the idler bracket before drilling the spar to see if this would help or hurt clearances in any location. I knew that there was very little clearance between the push/pull tube from the torque tube to the idler and the lower fuselage longeron. I knew some early builders actually had to bend the push/pull tube(s) to get clearance. I thought the idler arms were going to solve this problem, but I also believed lowering the dihedral per the Hale revision might reduce clearance with the longeron. The first photo is of the idler assembly hanging on the rear spar while I investigated the best location.
Here's what I found starting at the aileron and working inboard. I used 25 deg. plus and minus aileron deflection as my starting point. This equated to about 4 inches up and down movement at the trailing edge. I put the 5 deg. bend in the 1/2 inch tube per plans and also had to notch the filler strip under the spar to relieve interference as others have noted. I added four AN960 washers between the bellcrank and the forward RE bearing in this link to gain desired clearance through full motion of the aileron. The forward arm of the bellcrank is close to the anti-drag wire in this bay. On final installation I will use an AN24 clevis bolt if needed for additional clearance between the wire and the bolt head. With my setup there was no interference between the push/pull tube from the bellcrank to the idler through the full range of motion, about 1-1/4 inch of lateral movement in each direction.
There were significant problems with the push/pull tube that goes from the idler to the torque tube. This tube has approximately 5/32 inch movement downward from neutral in the vicinity of the lower longeron and lower wing butt rib because of the arc of the torque tube. Left and right aileron/stick deflection will causes the same movement. Because of the arc of the idler arm, this tube also moves to the rear about 1/8 inch with full stick/aileron deflection. The down movement (left and right aileron) caused contact with the lower longeron. Raising the idler bracket to try to relieve the interference caused contact with the anti-drag wire that is located close above under the wing walk. This interference was on the left side only. I can only conclude slight differences between lower longeron location on the left and right sides of my fuselage. And this underscores the caution that others have made that all of this final fitting should be done on the actual airplane. As much as I would like to avoid it, I may have to put a slight, perhaps 1/8 inch step down with two small bends, in this tube on the left side only. After final installation of the idler and fabrication of all other linkage, I will decide what and how much is needed to make this right.
The final problem I had to solve was where and what size hole to drill through the butt rib to route this push/pull tube from the torque tube to the idler. My second photo shows that my first guess for this hole was far from what was needed. Even worse by the time I got the hole where it was needed the compression strut had been notched about 5/16 inch. After I knew where the push/pull tube should pass through the butt rib and how much it was going to move with the ailerons I designed and installed the fix pictured in the third photo. The fitting is milled from 1/2 inch 6061-T651 plate. It is 1-7/8 inches high by 2-1/4 inches wide. The hole is 1-1/8 inch in diameter. The oversize hole in the rib was patched with a balsa core and ply sheet both sides.
Happy Thanksgiving Everybody--Ed T
Here's what I found starting at the aileron and working inboard. I used 25 deg. plus and minus aileron deflection as my starting point. This equated to about 4 inches up and down movement at the trailing edge. I put the 5 deg. bend in the 1/2 inch tube per plans and also had to notch the filler strip under the spar to relieve interference as others have noted. I added four AN960 washers between the bellcrank and the forward RE bearing in this link to gain desired clearance through full motion of the aileron. The forward arm of the bellcrank is close to the anti-drag wire in this bay. On final installation I will use an AN24 clevis bolt if needed for additional clearance between the wire and the bolt head. With my setup there was no interference between the push/pull tube from the bellcrank to the idler through the full range of motion, about 1-1/4 inch of lateral movement in each direction.
There were significant problems with the push/pull tube that goes from the idler to the torque tube. This tube has approximately 5/32 inch movement downward from neutral in the vicinity of the lower longeron and lower wing butt rib because of the arc of the torque tube. Left and right aileron/stick deflection will causes the same movement. Because of the arc of the idler arm, this tube also moves to the rear about 1/8 inch with full stick/aileron deflection. The down movement (left and right aileron) caused contact with the lower longeron. Raising the idler bracket to try to relieve the interference caused contact with the anti-drag wire that is located close above under the wing walk. This interference was on the left side only. I can only conclude slight differences between lower longeron location on the left and right sides of my fuselage. And this underscores the caution that others have made that all of this final fitting should be done on the actual airplane. As much as I would like to avoid it, I may have to put a slight, perhaps 1/8 inch step down with two small bends, in this tube on the left side only. After final installation of the idler and fabrication of all other linkage, I will decide what and how much is needed to make this right.
The final problem I had to solve was where and what size hole to drill through the butt rib to route this push/pull tube from the torque tube to the idler. My second photo shows that my first guess for this hole was far from what was needed. Even worse by the time I got the hole where it was needed the compression strut had been notched about 5/16 inch. After I knew where the push/pull tube should pass through the butt rib and how much it was going to move with the ailerons I designed and installed the fix pictured in the third photo. The fitting is milled from 1/2 inch 6061-T651 plate. It is 1-7/8 inches high by 2-1/4 inches wide. The hole is 1-1/8 inch in diameter. The oversize hole in the rib was patched with a balsa core and ply sheet both sides.
Happy Thanksgiving Everybody--Ed T
