Welcome: Why AOA?
It’s all about measuring lift.
Because takeoff and landing operations are critical, commercial airliners, military aircraft (especially Navy), and even the space shuttle require Angle of Attack systems for safety. The RiteAngle Angle of Attack instrument, accurately measures angle of attack using a vane. The resultant signal is then converted and displayed for the pilot using green, amber, and red LED’s. The RiteAngle display module is designed in accordance with FAA recommendations; green indicating safe, yellow caution, and red for danger.
Airspeed is of less value to the pilot than angle of attack due to its inherent errors. All STOL (Short Take Off and Landing) operations require the aircraft to be able to operate with precision for maximum performance. The indicated airspeed during these maneuvers will vary due to weight, load factor and other errors, however the AOA will be correct, ask any Navy Carrier pilot!
The angle of attack:
The Angle Of Attack (AOA) is the angle that is formed by the chord line of the airfoil and the direction of the air that strikes the airfoil which is known as the relative wind. As the angle of attack changes, the lift and drag also change during flight as the pilot changes the attitude of the aircraft. The increase in angle of attack increases lift up to a point. Too high of an angle of attack results in a loss of lift and can cause an aircraft to stall, which is also known as exceeding the critical AOA. The critical Angle of Attack will remain constant for the airfoil, however it will vary with any change in the airfoil, including lowering of flaps or modifying the airfoil in any way.
The critical angle of attack:
The Critical Angle of Attack is the angle of attack at which the air no longer flows sufficiently and smoothly over the upper surface of the airfoil. At this point, the wing will no longer support the aircraft in level flight and is said to be in a stall. A fixed-wing aircraft always stalls at the same Critical Angle of Attack, rather than at the same airspeed. The airspeed at which the aircraft stalls is variable, depending on the weight of the aircraft, the load factor at the time and the thrust from the engine. Flaps change the lift of an airfoil when extended, so the AOA must be corrected for it. . Our systems for aircraft with flaps automatically correct for this change in lift. The Critical Angle of Attack will vary on every airplane depending on the design of the wing.