But remember, one of the HBs arguments is that the footage was filmed at normal speed then slowed down to look like it was filmed on the moon. So that 5-10 mph (8 -16 kph) is really something more like 30-50 mph (46-80 kph). I think at that point, the air flow would definately keep the flap in the same position. Unless of course, the footage was filmed inside some giant vacuum chamber (tens of square miles or square kilometers).