I am about to get a Hanger 9 S Bach.
When I start the initial set up I will set controls at the suggested travel. However, the starting point may be a problem, if it is anything like my last models.
My question is :- Do I line the bottom surface of the wing with bottom surface of the aileron or do I line the top surface of wing with the top of the aileron or do I split the difference?

Thanks

More than likely with the answer is yes. The top and bottom should line up with the associated surface, if not then split the diff.

Most of the time there is a portion of the wing in the center the ailes line up with. If not then yes center them.

David

At the wing tip, and the base near the fuse, there is wood that lines it up for you and center the aileron.
The fun part is lining up the servo to match.

No, always line up the aileron with the bottom of the wing. On many planes, that means the top will wind up reflexed a bit, and that's ok. If you set the ailerons with some down angle they will act as flaps in flight. That means your stall characteristics become snappier and you'll need more airspeed to have solid aileron control. It also will cause the plane to have pitch changes with speed changes, which will make precision flight trimming a real pain. It's even helpful on some planes to have them up just a little, but probably not on yours.

Here's the reason. On the bottom of the wing, you have this smooth flowing, slow moving high pressure air that stays stuck very well to the wing surface. The angle of your trailing edge has a big impact on how that air comes off the wing surface and rejoins the air on the top. The top has this fast moving, turbulent, low pressure air going over it. Really, because of the turbulence, an aileron that follows the wing taper isn't in the real airflow much at all. In a non stalled condition, the aileron affects the air on the bottom a lot and the top a bit less. That's why you get adverse yaw; an aileron has to move up a ways to actually interact with the airflow, but any down movement has a big effect. And that situation gets even more extreme in a stalled condition. That's why some planes actually fly better with their ailerons angled up a bit compared to the wing bottom. For planes that are stall prone, (heavily loaded warbirds come to mind) just that simple change can turn a snappy plane into a gentle flyer.

Line up the ailerons with the trailing edge at the root. This is an aerobatic model with a symmetrical airfoil and you want to keep it symmetrical. Angling them either up or down is just going to screw things up.

Thanks
That makes simple sense & seems obvious when I read it but being fairly new to the hobby it needed explaining
Two of my models have no root or tip guides & thinking about it they do what you say

To be clear, if there is a bit of wing area at the root do line up the aileron with it. If that's there for you to use, it will be in line with the bottom of the wing anyway.