Chapter 6 terms Weight & Balance Flashcards
Datum
The datum is an imaginary vertical plane from which all horizontal measurements are taken for balance purposes, with the aircraft in level flight attitude.
Arm
The arm is the horizontal distance from the datum to any point within the aircraft. The arm’s distance is always measured in inches, and it is preceded by the algebraic sign for positive (+) or negative (), except for a location which might be exactly on the datum. The positive sign indicates an item is located aft of the datum, and the negative sign indicates an item is located forward of the datum
Moment
Force that causes or tries to cause an object to rotate
The word moment is the product of a force or weight times a distance.
To calculate a moment, a force (or weight) and a distance must be known. The weight is multiplied by the distance from the datum and the result is the moment, which is expressed in inch-pounds (in-lb), a point through which the force acts
Center of gravity (CG)
The CG is the point at which all the weight of the aircraft is concentrated and balanced; therefore, the aircraft can be supported at that point (the CG).
Maximum Weight
The maximum weight is the maximum authorized weight of the aircraft and its contents, and is indicated in the Aircraft Specifications or TCDS
Maximum Ramp Weight
The heaviest weight to which an aircraft can be loaded while it is sitting on the ground. This is sometimes referred to as the maximum taxi weight.
Maximum Takeoff Weight
the heaviest weight an aircraft can be when it starts the takeoff roll. The difference between this weight and the maximum ramp weight would equal the weight of the fuel that would be consumed prior to takeoff.
Maximum Landing Weight
The heaviest weight an aircraft can be when it lands. For large, wide body commercial airplanes, it can be 100,000 lb less than maximum takeoff weight, or even more.
Maximum Zero Fuel Weight
The heaviest weight an aircraft can be loaded to without having any usable fuel in the fuel tanks. Any weight loaded above this value must be in the form of fuel.
Empty Weight
The empty weight of an aircraft includes all operating equipment that has a fixed location and is actually installed in the aircraft
Empty Weight Center of Gravity (EWCG)
The EWCG for an aircraft is the point at which it balances when it is in an empty weight condition.
Useful Load
Anything not a part of the empty weight
subtract the empty weight from the maximum allowable gross weight.
Example: Crew member, luggage’s, fuel, passengers, pilot, copilot
Minimum Fuel
Indicates that an aircraft’s fuel supply has reached a state where, upon reaching the destination, it can accept little or no delay.
Minimum fuel is the amount needed for 30 minutes of flight at cruise power.
Tare Weight
The weight of the plane without any luggage, crew, or passengers. However, this weight would include any useful weight, such as fuel.
Examples: Wheel clocks, places on scales and ground locks left in place on retractable landing gear
Weight and Balance Data
The weighing of the aircraft, the maintaining of the weight and balance records, and the proper loading of the aircraft.
Scales
A device that uses load cells, designed to measure force or weight, to accurately determine the weight of an aircraft.
Top of jack load cells, as the name implies, can be used on top of the current wing jacks or can be used under axle for larger jets.
Spirit Level
A leveling instrument placed on or against a specified place on the aircraft
Spirit levels consist of a vial full of liquid, except for a small air bubble.
Plumb Bob
A heavy metal object, cylinder- or cone- shaped, with a sharp point at one end that is suspended by a string to produce a vertical reference line useful in aircraft measurements
Oil System
The engine oil system performs several important functions: Lubrication of the engine’s moving parts. Cooling of the engine by reducing friction. Removing heat from the cylinders. Providing a seal between the cylinder walls and pistons
Hydrometer
A device used for measuring the specific gravity of liquids
When an aircraft is weighed with full fuel in the tanks, the weight of the fuel must be accounted for by mathematically subtracting it from the scale readings. To subtract it, its weight, arm, and moment must be known.
Miscellaneous Fluids
The hydraulic fluid reservoir and all other reservoirs containing fluids required for normal operation of the aircraft should be full. Fluids not considered to be part of the empty weight of the aircraft are potable (drinkable) water, lavatory precharge water, and water for injection into the engines.
Flight Controls
The position of such items as spoilers, slats, flaps, and helicopter rotor systems is an important factor when weighing an aircraft. Always refer to the manufacturer’s instructions for the proper position of these items.
Weighing Points
When an aircraft is being weighed, the arms must be known for the points where the weight of the aircraft is being transferred to the scales
Jacking the aircraft
Jacking of aircraft is done in order to perform maintenance and inspection.
Leveling the aircraft
When an aircraft is weighed, it must be in its level flight attitude so that all the components are at the correct distance from the datum. This attitude is determined by information in the TCDS. Some aircraft require a plumb line to be dropped from a specified location so that the point of the weight, the bob, hangs directly above an identifiable point.
CG Range
The distance between the forward and aft CG limits indicated on pertinent aircraft specifications
Empty Weight Center of Gravity (EWCG) Range
Use of Ballast:
Ballast is used in an aircraft to attain the desired CG balance, when the CG is not within limits or is not at the location desired by the operator. It is usually located as far aft or as far forward as possible to bring the CG within limits, while using a minimum amount of weight.
Temporary Ballast
Weights that can be carried in a cargo compartment of an aircraft to move the location of CG for a specific flight condition
Permanent Ballast
A weight permanently installed in an aircraft to bring its center of gravity into allowable limits
Helicopter Weighing
When a helicopter is being weighed, the location of both longitudinal and lateral weighing points must be known to determine its empty weight and EWCG. This is because helicopters have longitudinal and lateral CG limits
As with the airplane, the longitudinal arms are measured from the datum, with locations behind the datum being positive arms and locations in front of the datum being negative arms.
TCDS (Type Certificate Data Sheet)
Where the Datums location can be identified
Aircraft with TCDS has a separate Equipment list
The Aircraft Specifications
Another way where the Datums location can be Identified
The Aircraft Equipment list is included in this one
MAC (Mean Aerodynamic Chord)
the average chord length of a tapered, swept wing.
