ORIGINAL: opjose
ORIGINAL: Ed_Moorman
Another thing that has not been mentioned is the trailing edge of all control surfaces need to have sharp corners.
That's interesting. I didn't know that.
Why is this ( for my own edification I ask, not that I doubt that you are correct )?
I would normally expect that the squared off edges would cause mini vortexes at the edge, as the sharp "break" typically creates a low pressure area that the higher pressure flowing air gets sucked into.
With the rounded corners I would have expected that there would be some tendancy for the airflow to adhere to the contours, leading to a slightly smoother flow.
The rounded TE doesn't give the airflow a specific location to "hang on to". So the airflow can more easily fluctuate, side to side and up and down around and along the TE.
But most often a defined line of change will help to reattach separated airflow. Trip strips near the abscission line of a wing will often reattach airflow that has separated from the wing. They also help to hold flows that are about to break away. The energy that is building in that flow and would contribute to it's separation is disrupted by the disturbance in that flow.
One of the best profiles for an aileron is to taper it to follow the line of the profile, but have a definite "top" and "bottom" edge to the TE. The taper reduces the weight of the structure, yet you still have the square TE. The heavier the surface, the more prone to flutter.
The abscission line is the location along the span where the laminar airflow from the LE of the wing separates from the surface. The abscission layer is that air after it has gone from laminar to turbulent. It can reattach, but it won't go back to being laminar. There can and will be laminar layers above the abscission layer. The abscission layer can change in thickness and often will as a function of the pressure it experiences and the addition of more air going turbulent. The changes in those pressures are one of the suggested triggers for surface flutter.