I know for a rudder pull-pull set up that the ideal location for the control horn pivot is the center of the hinge line. Is this the best location for the Ailerons & elevators for the best geometry? Most of the photos I have seen on this forum lately have the pivot somewhat rearward of the hinge line. Is it better to have the pivot closer to the center of the 8-32 control horn bolt?
WW2 Ace

The best arrangement will always be at the center line. As for the ailerons and elevators, since both locations can be individually adjusted via the travel adjust/EPA function of a transmitter, many don't worry about things being as perfect as they could be. I'm guilty of it, too

Pat

Pat, If you look at the photos you will see the reason I asked. Attached are photos of my WH 28% Edge 540 wing panel. When the pivot point is lined up with the hinge line and the aileron is deflected in the down direction the horn arm will hit the bottom of the wing. This actually prevents full down travel. If I shorten the arm about 3/8" it should clear.

The other problem I just noticed can be seen in the other photos. If I connect the push rod at 1.25" on the servo arm the push rod is no longer perpendicular to the hinge line. I believe this condition will cause binding as the aileron travels up and down. The right wing panel is not as bad but it has the same problem. As you can see in the photos the only time the push rod is perpendicular to the hinge line is if the rod is less than 1/2" out from the center of the servo, and 1/2" on the servo arm will not provide enough throw for 3D. I hope Tom will chime in on this and let me know how I can fix this.

What you are encountering is one of the reasons I don't usually bother with Dubro horns. Plus they have a tendency to rotate on the shaft while they are in use. Counter that problem with the application of green Locktite on the threads after installation.

You've got the good servo arms to make an excellent installation, but a change for the linkage hardware could be made to either the JR 4-40 ball links and horn or the Nelson Hobbies RCL 70 linkage. I prefer the Nelson and have stayed with it for a long time now.

For a very positive 3D installation, using the equipment noted above, install a ball link on the servo arm at a distance of 1-1/8" from the servo output shaft. Next install the clevis for the aileron or elevator screw a distance of 1-1/8" or more from the center of the hinge line. Installing the clevis at a distance less than the distance from that used at the servo gives a leverage advantage to the flight surface, which is a bad thing.

Another option, using what you already have, would be to shorten the length of the plastic tab coming from the aileron or elevator, and adjust the travels the same as you would with the Nelson or JR linkage, with the transmitter. It will do no harm.

Pat

I forgot to put the next part in.

The angle of the rod will be closest to perpendicular when the servo arm will be at full 3D deflection. That's not a bad thing at all. I have had five planes set up that way using the Nelson linkage and haven't worn one out yet. They DO get flown very hard.

It's ok to shorten the horns for more deflection, but it's totally unnecessary. You will never need that much throw, if you deflect the aileron enough for the horn to hit the bottom of the wing the plane will be rolling so fast it will be impossible to see it.

The angle of the pushrod to the hinge line is not super-critical. As you can see it's impossible to be square at all deflection angles. If it's square at some point in its trave you are close enough and it will work fine.

TF

Tom

Regarding the pushrod angle. What you have implemented on the Edge works out really well. It's better if the push rod is more in line with the attach points when it's at full deflection, rather than at neutral.

Pat

Some linkage views. Some are from an Ultimate. The pull/pull is from a Giles. The principle is the same for all the W/H planes if you decide to use the RCL70 linkage or an SWB arm and adjusters.

Pat