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Here goes... I am trying to attach photos of what I have done so far.
In regards to the measurements... The trim tabs are 14.5 inches in span, measured from the pivot rod/root rib intersection straight out to the tip.
The root chord INCLUDING the extra aluminum bend-able adjustment strip is 12 inches, and the tip chord WITH the aluminum bend strip is 5.5 inches.
The trailing edge is parallel with the pivot rod, i. e. 90 degrees to the major axis of the fuselage.
The pivot rod is 6 inches forward of the trailing edge (including the aluminum bend strip).
The root rib is not 90 degrees to the trailing edge, because of the taper of the rear fuselage.
The Birch wood "spar" starts off as 1 x 1 x 9 and 3/8 inches, with a 3/8" hole through the center for the pivot rod. Because I didn't have a long enough drill or machinery to "gun-drill" it, I made each birch spar out of two pieces of wood that had been routed with a half-round groove along one edge, then epoxied together as shown in one of the photos. This spar is tapered and shaped and carved so it is flush with the airfoil, which makes it look kind of twisted and oddly tapered if you look at it by itself.
This spar piece is glued into a slot cut in the foam core, a balsa leading edge added to the core and shaped to match the airfoil, and then the core is "sheeted" with 1/64" plywood glued to the spar as well as the cores. After initial test flights, I added an aluminum bend strip to fine tune the aerodynamics of the trim tabs. this strip was put on with very very high grade double stick tape.
One photo shows the old trim tab sitting on top of the new one. My guess is that the new ones are 33-40% larger. One photo shows the blue foam "core" with the balsa leading edge taped in place while the epoxy cures. On the first photo you can see the aluminum bend strip on the back of the trim tab.
The overly modern shape of the tab was dictated by the need for aerodynamic balance and the location of the lower stabilizer brace wire. I much rather would have made a larger tab the same shape as the original but it would not have worked well.
Based on my experience only HALFWAY through the testing, if I were to do it again I would probably use a 23012 airfoil like the rest of the airplane, and incorporate the aluminum bend strip frm the start to fine tune the tabs to the particular airplane. I also would be able to make the shape of the tabs SLIGHTLY more similar to the stabilizer/elevator than they are. But it was proven to me immediately that the aerodynamic balance is critical, so the brace wire will determine the general outline.
I would also make certain changes to how they were built to save some time.
Here are the photos.............
In regards to the measurements... The trim tabs are 14.5 inches in span, measured from the pivot rod/root rib intersection straight out to the tip.
The root chord INCLUDING the extra aluminum bend-able adjustment strip is 12 inches, and the tip chord WITH the aluminum bend strip is 5.5 inches.
The trailing edge is parallel with the pivot rod, i. e. 90 degrees to the major axis of the fuselage.
The pivot rod is 6 inches forward of the trailing edge (including the aluminum bend strip).
The root rib is not 90 degrees to the trailing edge, because of the taper of the rear fuselage.
The Birch wood "spar" starts off as 1 x 1 x 9 and 3/8 inches, with a 3/8" hole through the center for the pivot rod. Because I didn't have a long enough drill or machinery to "gun-drill" it, I made each birch spar out of two pieces of wood that had been routed with a half-round groove along one edge, then epoxied together as shown in one of the photos. This spar is tapered and shaped and carved so it is flush with the airfoil, which makes it look kind of twisted and oddly tapered if you look at it by itself.
This spar piece is glued into a slot cut in the foam core, a balsa leading edge added to the core and shaped to match the airfoil, and then the core is "sheeted" with 1/64" plywood glued to the spar as well as the cores. After initial test flights, I added an aluminum bend strip to fine tune the aerodynamics of the trim tabs. this strip was put on with very very high grade double stick tape.
One photo shows the old trim tab sitting on top of the new one. My guess is that the new ones are 33-40% larger. One photo shows the blue foam "core" with the balsa leading edge taped in place while the epoxy cures. On the first photo you can see the aluminum bend strip on the back of the trim tab.
The overly modern shape of the tab was dictated by the need for aerodynamic balance and the location of the lower stabilizer brace wire. I much rather would have made a larger tab the same shape as the original but it would not have worked well.
Based on my experience only HALFWAY through the testing, if I were to do it again I would probably use a 23012 airfoil like the rest of the airplane, and incorporate the aluminum bend strip frm the start to fine tune the tabs to the particular airplane. I also would be able to make the shape of the tabs SLIGHTLY more similar to the stabilizer/elevator than they are. But it was proven to me immediately that the aerodynamic balance is critical, so the brace wire will determine the general outline.
I would also make certain changes to how they were built to save some time.
Here are the photos.............
Attached Files
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