On-board aircraft weighting and center of gravity determing apparatus and method

• US 5,521,827 A
• Filed: 09/16/1994
• Issued: 05/28/1996
• Est. Priority Date: 09/16/1994
• Status: Expired due to Term

• Current Assignee: Hydro-Aire, Inc. (Crane Company)
• Original Assignee: General Electrodynamics
• Inventors: Lindberg, George R., Thomas, Harold O.
• Primary Examiner(s): Teska, Kevin J.
• Assistant Examiner(s): Walker, Tyrone V.
• Application Number:
  US08/307,274
• Time in Patent Office: 620 Days
• Field of Search: 364/463, 364/424.1, 251/57, 177/136, 177/141, 92/65, 73/862.041, 73/65.06, 73/65.01, 73/65.05, 244/102 SS, 244/104 FP, 244/103 R
• US Class Current: 701/124
• CPC Class Codes: G01G 19/07 for weighing aircraft
• CPC Class Codes: G01M 1/125 of aircraft

Abstract

An apparatus for determining the weight and/or center of gravity of an aircraft is disclosed and includes a plurality of fittings attached to each oleo strut on the aircraft for accessing the working fluid in the oleo strut, a computer, a first, electronically-responsive valve coupled to each fitting for controlling the fluid flow through the fitting in response to control signals from the computer, a pressure transducer coupled downstream of the first valve for measuring the pressure of the working fluid therein and coupled to the computer to provide a pressure measurement signals to the computer for each strut, and an inclinometer attached to the aircraft and electronically coupled to the computer for providing incline information to the computer. A method is disclosed that includes accessing the working fluid of each oleo strut cylinder, attaching a pump to each oleo strut cylinder, cycling each oleo strut cylinder between a near fully extended position and a near fully retracted position while recording pressure measurements in the cylinder at a plurality of points between the two positions while keeping the aircraft level, and mathematically manipulating the recorded pressure measurements to arrive at an approximation of the weight on each strut. The total weight can be then found by adding the weight on each strut plus any dead weight for each strut. The center of gravity may then be determined by summing the moments for each load on each strut and dividing the total or sum of the moments by the total weight to arrive at the center of gravity.

Claims

1. An on-board system for determining the weight and center of gravity of an aircraft having a plurality oleo struts each having a strut cylinder with a working fluid, the system comprising:

a computer means for developing control signals and for receiving and storing pressure measurement signals and incline measurement signals and for performing calculations;

a display coupled to the computer for displaying visual indicia;

an inclinometer attached to the aircraft and electronically coupled to the computer, the inclinometer develop an incline measurement signal; and

a plurality of pressure measuring and adjusting subsystems, one subsystem associated with each of the plurality of oleo struts, each pressure measuring and adjusting subsystem comprising;

a fitting attached to the associated oleo strut for accessing the working fluid therein;

a first in-line, electronically-responsive valve coupled to the fitting for controlling fluid flow through the fitting and electrically coupled to the computer,

a pressure transducer coupled downstream of the first in-line valve for measuring the pressure of the working fluid, the pressure transducer coupled to the computer and providing a pressure measurement signal to the computer, and

an electronically-responsive pump downstream of the pressure transducer for adjusting the fluid pressure of the working fluid to extend or retract the strut in response to control signals from the computer;

a second in-line, electronically-responsive valve downstream of the pressure transducer and electronically coupled to the computer;

wherein the computer means is programmed to perform the following steps;

open and close the first valve of each of the plurality of subsystems;

receive the pressure measurement signals from each of the pressure transducers of each of the subsystems;

receive the incline measurement signal;

operate the pump of each of the plurality of subsystems to adjust the fluid pressure in each of the plurality of oleo struts to make the aircraft level with respect to the gravity field and to move each oleo struts;

calculate the weight on each of the plurality of oleo struts to determine a total weight from the pressure measurement signals; and

calculate the center of gravity of the aircraft based on the weight experienced by each strut and on a location of each of the plurality of oleo struts; and

wherein the computer is further programmed to raise each oleo strut of the plurality of oleo struts between a near fully extended position and a near fully retracted position and to record a plurality of pressure measurement signals for each oleo struts of the plurality of oleo struts between the near fully extended position and near fully retracted position for each strut.

2. The system of claim 1 wherein the computer is further programmed to average the plurality of pressure measurement signals for each oleo strut of the plurality of struts and thereby determine an average pressure for each oleo strut.

3. The System of claim 2 wherein the computer is further programmed:

to multiply the average pressure of each oleo strut by the surface area of a strut cylinder of each oleo strut to determine an average pressure force on each oleo strut of the plurality of oleo struts;

to add to the pressure force for each oleo strut a dead weight amount for each strut to arrive at a total strut weight for each oleo strut; and

to sum the total strut weight for each oleo strut to determine a total weight of the aircraft.

4. The System of claim 3 wherein the computer is further programmed:

to multiply the total strut weight for each of the plurality of oleo struts by the corresponding strut'"'"'s distance from a datum to produce a moment value for each strut;

to sum the moment value for each strut; and

to divide the total moment value by the total weight to produce a center gravity value with respect to the datum.

5. The System of claim 4 wherein the computer is further programmed to convert the center of gravity value in terms of distance to the datum to a center of gravity value in terms of percentage mean aerodynamic chord (MAC).

6. A weight and balance system for use with aircraft having a nose wheel oleo strut, a port main oleo strut, and a starboard main oleo strut, each strut having a strut cylinder containing a working fluid, a strut piston, and an orifice plate, the system comprising:

a microprocessor having a storage device coupled thereto for holding instructions and data;

a first fitting coupled to the nose oleo strut for accessing the working working fluid therein;

a first electronically-responsive, in-line, shutoff valve downstream associated with the first fitting and coupled in fluid communication thereto, the shutoff valve for controlling the fluid flow therethrough in response to a first control signal from the microprocessor;

a first pressure transducer downstream of the first valve and coupled in fluid communication with the first shutoff valve and electronically coupled to the microprocessor, the first pressure transducer operable to produce a first pressure measurement signal;

a first electronically-responsive pump coupled in fluid communication with the nose strut cylinder for adjusting the nose gear strut between an extended position and a retracted position in response to a second control signal from the microprocessor;

a second fitting coupled to the port main oleo strut for accessing the working working fluid therein;

a second electronically-responsive, in-line, shutoff valve downstream associated with the second fitting and coupled in fluid communication thereto and operable to control the fluid flow therethrough in response to a third control signal from the microprocessor;

a second pressure transducer downstream of the second valve and coupled in fluid communication with the second shutoff valve and electronically coupled to the microprocessor, the second pressure transducer operable to produce a second pressure measurement signal;

a second electronically-responsive pump coupled in fluid communication with the port main strut cylinder for adjusting the port main gear strut between an extended position and a retracted position in response to a fourth control signal from the microprocessor;

a third fitting coupled to the starboard main oleo strut for accessing the working fluid therein;

a third fitting coupled to the starboard main oleo strut for accessing the working working fluid therein;

a third electronically-responsive, in-line, shutoff valve downstream associated the third fitting and coupled in fluid communication thereto in response to a third control signal from the microprocessor;

a third pressure transducer downstream of the third valve and coupled in fluid communication with the third shutoff valve and electronically coupled to the microprocessor, the third pressure transducer operable to produce a third pressure measurement signal;

a third electronically-responsive pump coupled in fluid communication with the starboard main strut cylinder for adjusting the port main gear strut between an extended position and a retracted position in response to a sixth control signal from the microprocessor;

an inclinometer attached to the airplane and electrically coupled to the microprocessor for delivering an incline measurement signal thereto; and

the microprocessor and storage device programmed to perform the following steps;

determine the airplane'"'"'s pitch attitude based on the incline measurement signal,

level the airplane if the pitch attitude is not zero,

while maintaining the aircraft substantially level, cycle the nose, port main, and starboard main struts between a near fully extended position and near fully retracted position,

receive and store the first, second, and third pressure measurement signals for a plurality of positions of each strut during the cycle between the near fully extended position of the struts and near fully retracted position to produce a first, second, and third plurality of pressure measurement signals,

mathematically manipulate the first, second, and third plurality of pressure measurements to determine the approximate weight experienced by the nose, port, and starboard strut,

find the nose moment value, port main moment value, and the starboard main moment value by multiplying the approximate weight experienced by the nose, port, and starboard strut by its respective distance from the datum,

sum the nose, port, and starboard moments to produce a total moment value, and

divide the total moment by the total weight to the find the center gravity.

7. The System of claim 6 further comprising a display for presenting visual indicia.

8. A method for determining the weight on an oleo strut having a strut cylinder with a working fluid therein and strut piston, the method comprising the steps:

moving the strut between a near fully extended position and a near fully retracted position;

storing pressure measurements for the working fluid in the cylinder at a plurality of points between the near fully extended position and the near fully retracted position to produce a plurality of pressure measurements; and

approximating the actual weight on the strut from the plurality of pressure measurements.

9. The method of claim 8 wherein the step of approximating the actual weight comprises averaging the plurality of pressure measurements.

10. The method of claim 8 wherein the step of approximating the actual weight comprises determining the mean for the plurality of pressure measurements.

11. The method of claim 8 wherein the step of approximating the actual weight comprises discarding a predetermined number of the highest pressure measurements and a predetermined number of the lowest measurements from the plurality of pressure measurements and then averaging the remaining plurality of pressure measurements.

12. A method of manufacturing a system for determining weight information of an aircraft having a plurality of oleo struts, each oleo strut having a piston and strut cylinder with a working fluid in the cylinder, the method comprising the steps of:

providing a digital computer;

mounting a fitting on each of the plurality of oleo struts that provides fluid communication with the working fluid from outside each strut;

placing an electronically-responsive, in-line, shutoff valve downstream of each fitting in fluid communication with the working fluid and electrically coupling each valve to the digital computer;

placing a pressure transducer operable to produce pressure measurement signals downstream of the valve and in fluid communication with the working fluid of strut cylinder for each strut and electronically coupling the pressure transducer to the digital computer;

placing an electronically-responsive pump in fluid communication with the cylinder of each strut and electronically coupling each pump to the digital computer;

attaching an inclinometer to the aircraft to produce incline measurement signals and electrically coupling the inclinometer to the digital computer;

programming software for the digital computer to perform the following steps;

(a) receive incline measurement signals;

(b) determine from the incline measurement signals whether a nose of the aircraft is high or the tail of the aircraft is high;

(b) produce pump control signals to be delivered to one or more pumps to retract or extend the struts as desired to level the aircraft;

(c) produce pump control signals to be delivered to the pumps to move each strut to a near fully extended position;

(d) receive a pressure measurement signal from each cylinder and store the pressure measurement signal for each cylinder in the digital computer;

(e) produce pump control signals for delivery to each pump to move each strut a predetermined amount toward the near fully retracted position;

(f) repeat step (d);

(g) repeat steps (e) and (f) until the near fully retracted position is reached for one of the plurality of struts to produce an array of pressure measurement signals for each strut;

(h) approximate the weight on each strut from the array of pressure measurement signals; and

(i) total the weight of each strut as determined at step (h) to arrive a total weight.

13. The method of claim 12 further comprising the step of programming software for the digital computer to perform the following steps:

(j) multiply the weight of each strut determined in step (h) by a distance from a datum corresponding to each strut to produce a plurality of moment values;

(k) sum the moment values; and

(l) divide the summed moment values by the total weight to arrive at the center of gravity of the aircraft in terms of distance from the datum.

14. The method of claim 13 further comprising the steps of:

attaching a display to the digital computer; and

displaying the total weight and center of gravity of the aircraft.

15. The method of claim 13 further comprising the step of programming the computer to carry out the step of (m) converting the center of gravity in terms of distance from the datum to the center of gravity in terms of percentage of the mean aerodynamic chord.