ORIGINAL: HarryC
Very useful article, thank you Olivier. I have a question for you. Ys and Yc are distances from the ''chord line''. What is the chord line? If in a wing do you mean literally the wing section's chord line? The diagrams of the linkages suggest that the chord line is a reference line tht passes through the centre of the servo output shaft, and the hinge line of the control surface but if that is the case then Ys must by definition always be zero so why include it as a variable? So what exactly is the ''chord line'', is it simply any reference line that the user chooses?
Harry
Hi Harry,
The chord line is a line that passes across the airfoil section from the leading edge to the trailing edge ( flight control surface set at zero degrees ). It is the white measurement line in the graph below:
Here are the definitions again:
Xs: servo distance forward of the hinge line
Ys: servo distance above/below chord line
Xc: control horn distance aft of the hinge line
Yc: control horn distance above/below chord line
To compute Ys, I make am approximation here: I measure the wing/surface thickness ( skin to skin ) at the servo axis location and divide it by 2. I assume that the chord line passes by at this distance. I then check the distance of the servo axis from one side of the skin and deduct Xs. There will be a few mm mistake in case of a non symmetrical profile, but this is non critical.
Yc: The program assumes that the chord line and the hinge line are superposing. This is not always the case ( live hinged surface on a thick wing for example ). In that case you need to take the
control horn distance above/below the hinge line. Of course, this distance is the measure from the
used control horn hole to the hinge line.
In the example above, the distance from the chord line ( white dot ) to the control horn hole differs greatly from the distance from the hinge line ( green dot ) to the control horn hole