This is a very nice down push block gun you can build in stage 13:
The right push blocks push the gun across the screen. The down push block is blocked by the slide block. The generator block copies and shoots the down block.
Since the character is moving on a wheel, it is only possible to move on ground. When you are in the air, you are not on ground, so the wheel cannot change your direction/momentum/whatever in midair. Therefore, changing speed or direction in midair is impossible.