is turned on, the corona wire becomes charged with high voltage, usually between 20 and 50 kV. When the corona wire reaches approximately 30 kV, it causes the air molecules nearby to become ionised by stripping their electrons from them. As this happens, the ions are repelled from the anode and attracted towards the collector, causing the majority of the ions to accelerate toward the collector. These ions travel at a constant average velocity termed the drift velocity. Such velocity depends on the mean free path between collisions, the strength of the external electric field, and the mass of ions and neutral air molecules. The fact that the current is carried by a corona discharge (and not a tightly-confined arc) means that the moving particles diffuse into an expanding ion cloud, and collide frequently with neutral air molecules. It is these collisions that create thrust. The momentum of the ion cloud is partially imparted onto the neutral air molecules that it collides with, which, because they are neutral, do not migrate back to the second electrode. Instead they continue to travel in the same direction, creating a neutral wind. As these neutral molecules are ejected from the ionocraft, there are, in agreement with Newton's Third Law of Motion, equal and opposite forces, so the ionocraft moves in the opposite direction with an equal force. The force exerted is comparable to a gentle breeze. The resulting thrust depends on other external factors including air pressure and temperature, gas composition, voltage, humidity, and air gap distance. The air mass in the gap between the electrodes is impacted repeatedly by excited particles moving at high drift velocity. This creates electrical resistance, which must be overcome. The end result of the neutral air caught in the process is to effectively cause an exchange in momentum and thus generate thrust. The heavier and denser the air, the higher the resulting thrust. Aircraft configuration As with conventional reaction thrust, EAD thrust may be directed either horizontally to power a fixed-wing airplane or vertically to support a powered lift craft, sometimes referred to as a "lifter". Design The thrust generating components of an ion propulsion system consist of three parts; a corona or emitter wire, an air gap and a collector wire or strip downstream from the emitter. A lightweight insulating frame supports the arrangement. The emitter and collector should be as close to each other as