You can find several proofs that explain why a truly flat shot will be always flat, no matter what racquet will you use. And thank god!!I would be quite disappointed if I would get spin from nohere while doing a flat shot
If you take a racquet and put it on a floor perfectly in plane and you let bounce a ball without any angle on the racquet, you will see it bouncing vertically without any spin - this is a flat shot(instead of moving the racquet you re moving the ball). No spin is added when stringbed is hit perpendicular.
Let's try to explain with other words. If you make a swing path low-to-high, you have main strings moving down and suddenly moving up, giving the ball top-spin.
If you make a backhand slice, you will make a swing path high-to-low, so your main strings will move up and then suddenly down, giving the ball a backspin.
If you hit TRULY flat, a full horizontal motion, where should the mains string move?Down or up?should the racquet give top or back spin?
Obviously, they will not go in any direction beside orizontal pushing, and this is because there is no force pushing them in a normal direction(normal direction in this case is the direction perpendicular to the stringbed plane).
It is just about physics, and a very easy physics one.
The point is: a lot of player are not aware that they are still using some spin on their semi-flat shots. In that case an additional spin, even if little as 100 rpm, can have not-negligible effect.Wilson said that, for every 100 rpm of top-spin rotation, your ball will land 1 feet shorter in average. So a very wide open pattern could help even those people that hit a semi-flat stroke.
But when you gain something, you lose something
in this case, less strings in the stringbed= less accuracy. And for a flat hitter or a semi-flat hitter, accuracy is the most important thing.
So, at the end, I would recommend open pattern racquet only to people with a good spin stroke. They are less concerned about accuracy: their shots will not land inside the court because pin-point precision, but because of their high topspin, that will make every shot land suddenly.