Ok, this is how you get consistently out the window. It's kind of a cheat...kind of.
First you have to understand that the game can only read your mouse's position when your mouse is *over* the game. When your mouse leaves the game, the game thinks your mouse is at the last point it read.
Second you need to know that the game tells how fast you are throwing and in what direction by reading the difference between the last point read, and the current point read.
So - drag the plane to the very top left corner.
Now slide the mouse directly left out of the game window.
Carefully move the mouse AROUND the outside of the game window to the far side of the game
Look closely at the right hand side and you should see little stripes of grey in different shades on the edge of the game above the baseboard on the wall.
Bring the mouse back onto the game about 6 or 7 of those little stripes up from the baseboard.
ZOOOOM. The distance between last read and current is HUGE and slightly down, so off the plane goes.
ENjoy.