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Method and apparatus for the linear real time estimation of an aircraft center of gravity
| Details |
Inventors: Wu, Tzong-Hsiu B.;
Assignee: The Boeing Company (Seattle, WA)
Primary Examiner: Oda; Christine K.
Assistant Examiner:
Attorney, Agent or Firm: Christensen O'Connor Johnson & Kindness PLLC
A method and apparatus for the real time estimation of the location of the center of gravity in an aircraft using a linear estimation technique. The center of gravity estimate is used in the aircraft's flight control system (12) to implement flight control laws that depend on the aircraft's center of gravity. The center of gravity is initially estimated based on signals indicative of the aircraft angle of attack, flap setting, elevator position, and stabilizer position. The initial approximation is then refined by multiplying or dividing the center of gravity estimate by additional factors including the weight of the aircraft, the expected load factor on the aircraft, the dynamic pressure on the aircraft, and the reference wing area of the aircraft. The resulting center of gravity estimate is measured as a percentage of the mean aerodynamic chord (MAC) of the aircraft. |
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DETAILED DESCRIPTION The present invention provides an improved method and apparatus for estimating the position of an aircraft's center of gravity while the aircraft is in flight, and for executing a maneuver procedure that at least in part depends upon the aircraft's center of gravity.
Initially, the following three signals are added to arrive at a center of gravity approximation for the aircraft: (1) a signal representing a constant K.
sub.
1 ; (2) a signal indicative of the aircraft angle of attack that is multiplied by a constant K.
sub.
2 ; and (3) a signal indicative of an adjusted stabilizer position that is multiplied by a constant K.
sub.
3.
After approximating the center of gravity based on the stabilizer position and the angle of attack, several additional factors are multiplied or divided into the approximation to arrive at a center of gravity estimate.
The additional factors include the weight of the aircraft, the expected load factor on the aircraft, the dynamic pressure on the aircraft, and the reference wing area of the aircraft.
The resulting signal provides a real time estimate of the aircraft center of gravity as the aircraft is landing.
In a preferred embodiment of the invention, the center of gravity is measured as a percentage of the mean aerodynamic chord (MAC).
In accordance with one aspect of the invention, the constants used to estimate the center of gravity depend on the flap setting of the aircraft.
During landing, the aircraft flaps will typically be set at either 20 or 30.
When the flap setting is 20, a first set of values for constants K.
sub.
1, K.
sub.
2, and K.
sub.
3 is selected.
When the flap setting is 30, a second set of values for constants K.
sub.
1, K.
sub.
2, and K.
sub.
3 is selected.
The method disclosed herein therefore adapts the center of gravity calculation based on the control surface settings of the aircraft during landing.
In accordance with another aspect of the invention, the center of gravity estimate is input to a limiter.
The limiter bounds the values that the center of gravity estimate can assume to a minimum and maximum value, preventing erroneous estimates of the center of gravity due to invalid input signals
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Navigation and GPS 
