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Old 11-22-2017, 01:31 AM   #1
billdit
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Default SA 750 aileron push rod

I have been looking over my SA 750 plans to see how some of the recommended changes could be done and noticed when I lay a rib over the plans on the mounting point for the fuselage bellcrank the push rod to the aileron bellcrank would hit the lower edge of the opening in the ribs. Do the ribs have to be notched a bit ?


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Old 11-22-2017, 02:55 AM   #2
Dave Baxter
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Bill, I do not think so, and I think the lower wing has about 1.5 degrees of dihedral, and this may be the difference. There are differences between builders, but until you trial fit the wings to the fuselage you will not know for sure. Dave


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Old 11-22-2017, 01:16 PM   #3
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Thanks Dave. I made a full scale drawing from the bellcrank to the first rib and it will just clear the rib opening. After that it progressively gets better. I also made a full size m6 rib drawing just to compare to the symmetrical rib. I don't know how accurate it is but I found a comparison on the Pitts S1S vs the S1C stall speed, 62 mph 58 mph. So maybe it would be worth the effort for my purpose. I see where the Starduster 2 has 1 degree of incidence on the lower wing. Is that so the lower wing stalls before the top wing? That 1 degree looks to be the most difficult part of a conversion. The lower wing to fuselage fittings on the AD are set up for 0 degrees.
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Old 11-22-2017, 02:02 PM   #4
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I see where the S1C has 3 degrees incidence on the upper wings and 0 on the lower. Incidence on the AD would be easier on the upper wing. I haven't built the cabanes yet anyway and would make them without the eye bolts. So custom fit. Seems like most non aerobatic biplanes have some incidence on the top wing, just wandering why the SD is opposite.
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Old 11-22-2017, 02:25 PM   #5
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I believe the C top wing has 1.5 degrees of incidence, not 3 degrees. The similar D model has 1.5 all around.
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Old 11-22-2017, 02:26 PM   #6
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My airplane had a lot of rubbing on the aileron push/pull tube, from the reverser to the outboard bell crank. I relieved all the ribs that interfered. Doesnt take much, about a 1/4 inch is all you need.

I am very interested in your M6 airfoil drawing. Did you determin that this is the SA750 airfoil?
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Old 11-22-2017, 02:44 PM   #7
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The SA750 airfoil looks more like the NACA 63012A airfoil.
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Old 11-22-2017, 03:02 PM   #8
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I have a set of plans for the S1C but the assembly manual with them is for a S1T. Couldn't find incidence listed anywhere. I got the 3 degrees from a Google search. The m6 is a lot different than the original AD symmetrical airfoil. I scaled up my S1C rib drawing just to compare. I am thinking the M6 would suit my purpose better than the symmetrical wing.
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Old 11-22-2017, 03:54 PM   #9
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I recently went through the numbers using the 1967 S-1C plans. The top wing incidence came out to 1.5.
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Old 11-22-2017, 05:40 PM   #10
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Thanks Bill. 3 degrees did seem to be a lot compared to the others that I looked at.


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