ORIGINAL: HarryC
Oc -22.5 (this says the flap will be half down when the servo is at centre, this is the crucial bit that was missing before, a value of 0 says flap is horizontal when servo is at centre, so flap will travel up and down from horizontal, whereas we want up and down from half-way down!)
And now the diagram is exactly what we expect to see.
Harry
Thank you for your input Harry. That is one trigonometric tip that I didn't see. Great idea...