Newbie question about trimming an aircraft

[Flyboy666]

I've watched several videos on trimming, and I’ve also read up a bit, including my Aeroscout manual. I understand the concept of trimming a plane and why you do it, but I am still a bit confused about one aspect of the process.
In my AeroScout manual, it explains how to trim the aircraft in flight, using the trim control buttons on the transmitter. I understand that. But then it says, "After the aircraft is trimmed in flight, land the aircraft and proceed to the Manually Adjusting Trim section to re-center the servos and set the trim mechanically. Carefully move the linkage forward or rearward, depending upon which direction control surface requires trim adjustment."
My point of confusion is this: Let's say you adjust the elevator trim in flight so the elevators are slightly upward, in order to keep the flight horizontally stable. Now you land the plane and manually adjust the elevator servo arm back to a neutral (horizontal vis a vis the fuselage) position. It seems that you have now removed the trim that you just put in while flying. Which means that next time you fly, you are going to have adjust the elevator trim buttons to put in the trim again.
See two pictures to explain what I am asking. One is the current position of my elevator and rudder servo arms. (Focus on the elevator arm for this question.) You can see that they are offset; not perfectly horizonal to the fuselage. This is how they came from the factory; without any trim adjustments made so far. So, once I adjust the trim of the elevator in flight, I assume the elevator servo arm will still be offset a bit from a “horizontal” position.
The other attached graphic is the verbiage and picture from the manual. It seems to be saying that the pictures are how you should manually position the servo arms after trimming it in flight.
My basic question: Is the manual telling me that once I get the elevator trim properly adjusted in flight, I should then adjust the respective servo arm to be in a horizontal (vis a vis the fuselage) position instead of it being tilted a bit? And if so, why?
Is it because using the trim button on the transmitter somehow moves the centerpoint range of motion of the elevator stick and limits it somehow?
Hope this question makes sense. Thanks

 

[WickedFog]

I think the only reason you would want to do the manual adjustment is so you can then reset your Tx trims back to, or close to zero. Just guessing. So after trimming in the Tx, land the plane. Loose the linkage rod screws, then set trim to zero so the servos move without disturbing the rods, then retighten.

 

[tudordewolf]

Is it because using the trim button on the transmitter somehow moves the centerpoint range of motion of the elevator stick and limits it somehow?

That's exactly why.

The servos can do +/- 60° of motion. To trim it, you're giving up some amount of travel in that direction, basically, always applying a little bit of stick.

 

[WickedFog]

That's exactly why.

The servos can do +/- 60° of motion. To trim it, you're giving up some amount of travel in that direction, basically, always applying a little bit of stick.

That makes a lot of sense.

 

[MrBeanCar]

The procedure is:
1) Fly the plane, use trim button to adjust a surface so that it flies correctly
2) Land
3) Do not turn off transmitter, or disconnect the battery
4) Note "EXACTLY" where that control surface is, relative to something fixed. If aileron, maybe the fixed part of the wing on either side of the aileron
5) Return the trim setting to neutral
6) Now, adjust the aileron position to return to that "EXACT" position you noted, in step 4 above

The end result of this is, the trim setting for that surface is neutral (0), and yet the control surface is at the position where it will fly correctly.

Note on the word "EXACT": Ok, it does not have to be exact. That's why I put it in quotes. You need to get it as close as you can. When you fly it again, you may find it's not flying exactly the way you want it, you still need to dial in some trim. But, hopefully, it's a lot less than the first time

A little bit of trim is ok, no problem. You just don't want to have a lot, as it consumes possible range of control. Even that is not the end of the world, either

 

[Flyboy666]

OK thanks, good explanation, makes sense. Just to be clear: On Step 6, I will adjust the control surface to that "exact" position (Step 4) by setting the control surface into that position by adjusting the linkage, right? (Not via the transmitter, which would seem to undo what I've you've done in Steps 1-5.)

Am I correct?

 

[MrBeanCar]

Yes, that is it.

One other consideration:
Take a look at the image of the servo arms, from the manual, and the foto of your servo arms.
Your left one (rudder plus front wheel) is rotated a bit counter clockwise. The right one, for elevator, is rotated a bit clockwise. This is hopefully/probably due to having to trim those surfaces in order for the plane to fly straight/level. What I call, the airplanes "happy place".

When you've made the adjustments, what you would like to see is an orientation like the one in the manual.

Does not have to be "exact", close would be good enough.

At this point, knowing why this is so is interesting but not essential, however if you are curious let me know.

 

[Flyboy666]

Thanks. Yeah, I did notice that my servo arms are not "straight" (parallel to each other), but that is the way it came, if I recall correctly. In any case, if I follow your procedure for trimming the plane, won't they end up off-center anyway once I adjust the respective servo arm?

And yes, I am curious why they should be parallel, other than giving you more range of motion in each direction if you need it.

Thanks again. Your procedure was MUCH clearer than the manual.

 

[MrBeanCar]

When the arms are perpendicular to the body of the servo, and the servo moves counter clockwise, lets say 15%, it is going to move the surface, lets say, X inches, millimeters, degrees.
When it rotates clockwise that same amount (15%), it is going to move in the opposite direction that SAME amount.

When the arm is NOT perpendicular, this is NOT the case. A CCW rotation of 15% will result in Y movement, a CW rotation will result in something NOT EQUAL to Y.

There are times when you actually want to do this, it would be referred to as "differential". Most times that you want differential, it is with your ailerons. Many people accomplish this not with this servo arm offset, but by having a dedicated servo for each aileron. Much easier to configure exactly how you want it.

Completely unneccesaray with the Aeroscout, a fantastic plane to learn on BTW

 

[Flyboy666]

OK, I figured that was the reason. (You said it better than I did above). As far as I know, I am getting the full range of motion for my control surfaces as-is, so I will leave well enough alone until I trim the plan per your procedure.

Thanks again