Roll trim servo/pitch AP servo: rigging question.

[John Courte]

My plan was to assemble the wings to the fuse when I got to the airport. Now, it appears that may be in doubt. Since I don't have the wings rigged and the ailerons locked in neutral, how do I know where exactly to mount the roll trim servo on the seat rib? Is there a foolproof way to make sure the sticks themselves are neutral so I can mount the servo independent of having the wings on?

While we're on the subject, is there a foolproof way to set stick-neutral for pitch? I have the same issue with the AP roll servo.

thanks,
-John

 

[Rupester]

Neutral pitch ...

The guys at Vans told me the stick is intended to incline 5 degrees forward in the neutral position. As I recall, when you look at the factory bend in the stick, 5 degrees forward incline above the pivot makes the bottom almost vertical.

 

[roee]

Wrong questions

John, in both cases I think you're trying to use the wrong reference points.

Roll trim servo mounting & rigging:

Mounting: You don't need the wings on for this at all. See drawing OP-19, which is provided with the aileron trim kit. The "SERVO MOTOR & F-6124 ATTACHMENT DETAIL" view shows what the neutral position of the WD-756 arm is supposed to be with the servo at mid-travel. That's how you should determine the exact mounting location of the servo. No reason why you can't do that now.

Final rigging: With the servo already mounted, only later will you do the rigging of the springs and wires to connect the servo mechanism to the stick bases. In principle you could even do that without the wings on, just setting the tension so that the sticks are centered at neutral trim. Then by virtue of the correct rigging of the ailerons to the sticks, everything should come out right. But I would actually suggest that you wait on connecting the trim mechanism to the stick bases, not only until you have the wings on, but until you've actually flown the airplane first without even connecting the aileron trim to the stick bases. That way you can detect and correct any primary rigging issues (i.e. the dreaded "heavy wing") without having the aileron trim in there to muddy the waters.

A/P pitch servo mounting & rigging:

You didn't mention which autopilot you're installing. If it is TruTrak and you're going with the standard servo installation behind the elevator bellcrank, then you should rig the servo to the elevator bellcrank with the elevator bellcrank vertical as the reference for the neutral position. See TruTrak servo installation drawings. The sticks don't enter the equation at all at that point. You will rig the sticks to the elevator bellcrank independently of the A/P servo, which you can do at a later time.