Inverted flight, though not a routine maneuver for an airplane, is in fact possible. Stunt pilots and those flying high performance fighter planes commonly do fly upside down. However, commercial aviation has no room for inverted flying, since it would compromise both efficient flight and passenger safety.
Angle of Attack: Rightside Up vs Upside Down
When flying upright, the wing of an aircraft meets the airflow at a certain angle, commonly known as the angle of attack.
This angle of attack, the angle between the chord line of an aerofoil and relative airflow, has to be kept within a range that supports flight, with the upper limit at about 16 degrees.
For flying upside down, the primary requirement is that the angle of attack of the wings remains within the flyable range of angles of attack. Wings designed specifically for upright flight have a curved upper section of the wing (cambered wings) and are only efficient in upright flight. Nonetheless, cambered wings too can support inverted flight.
Aerobatic aircraft have wings that are symmetrical (having identical curvature on the upper and the underside of the wings). This allows the wing to produce an equal amount of lift, whether flying upright or upside down.
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Requirements for Inverted Flight
In addition to considerable amounts of practice, a pilot should keep a few different areas in mind before deciding to attempt inverted flight.
- Typical gravity-fed fuel systems are a complete failure when flying upside down. Specialized fuel systems that maintain fuel pressure through the lines regardless of the flight attitude are required to fly upside down. Otherwise, the engine will choke and go silent due to fuel starvation in an inverted flight attitude. Similarly, the oil system of the engines must also be adaptable to the change of gravity in inverted flight.
- An airplane flying upside down also has its controls reversed. To raise the nose of the aircraft (with respect to the ground) the pilot would have to push the nose down and vice versa. Similarly, in order to turn right, the pilot would have to bank left.