7/28/2019 Theory of Weight and Balance

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THEORY OF WEIGHT AND BALANCEThe theory of weight and balance is extremely simple. It is that of the familiar lever that is inequilibrium or balance when it rests on the fulcrum in a level position. The influence ofweight is directly dependent upon its distance from the fulcrum. To balance the lever theweight must be distributed so that the turning effect is the same on one side of the fulcrumas on the other. In general, a lighter weight far out on the lever has the same effect as a

heavy weight near the fulcrum. The distance of any object from the fulcrum is called thelever arm. The lever arm multiplied by the weight of the object is its turning effect about thefulcrum. This turning effect is known as the moment.

Weight is the forcegenerated by the gravitational attraction of the earth ontheairplane. We are more familiar with weight than with the other forces acting on anairplane, because each of us have our own weight which we can measure every morning onthe bathroom scale. We know when one thing is heavy and when another thing is light. Butweight, the gravitational force, is fundamentally different from the aerodynamicforces,lift and drag.Aerodynamic forces are mechanical forces and the airplane has to be inphysical contact with the the air which generates the force. The gravitational force is a fieldforce; the source of the force does not have to be in physical contact with the object togenerate a pull on the object.

The Maximum Takeoff Weight (MTOW) or Maximum Takeoff Mass of an aircraft isthe maximum weight at which the pilot of the aircraft is allowed to attempt to take off, dueto structural or other limits. The analogous term for rockets is Gross Lift-Off Mass, or GLOW.MTOW is usually specified in units ofkilograms or pounds, but some aircraft manufacturersalso use kilogram-force (kgf) orpound-force (lbF)

[1].MTOW is the heaviest weight at which the aircraft has been shown to meet alltheairworthiness requirements applicable to it. MTOW of an aircraft is fixed, and does notvary with altitude or air temperature or the length of the runway to be used for takeoff orlanding. A different weight the "maximum permissible takeoff weight", or "regulated takeoffweight", varies according to flap setting, altitude, air temperature, length of runway andother factors. It is different from one takeoff to the next, but can never be higher than theMTOW.

TheMaximum Ramp Weight (MRW)(also known as theMaximum TaxiWeight (MTW)) is the maximum weight authorised for manoeuvring (taxiing ortowing) an aircraft on the ground as limited by aircraft strength and airworthinessrequirements. It includes the weight of taxi and run-up fuel for the engines and theAPU.It is greater than the maximum takeoff weight due to the fuel that will be burnedduring the taxi and runup operations.

The difference between the maximum taxi/ramp weight and the maximum take-offweight (maximum taxi fuel allowance) depends on the size of the aircraft, thenumber of engines, APU operation, and engines/APU fuel consumption, and istypically assumed for 10 to 15 minutes allowance of taxi and run-up operations.

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