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Helicopter Weight and Balance
The following section of the aircraft.cfg file defines the primary weight and balance of the aircraft:
[WEIGHT_AND_BALANCE]
max_gross_weight = 3200 // (pounds)
empty_weight = 1760 // (pounds)
reference_datum_position = 0.0, 0.0, 0.0 // (feet) distance from FlightSim Reference position: (1/4 chord, centerline, waterline)
empty_weight_CG_position = 0.0, 0.0, 0.0 // (feet) longitudinal, lateral, vertical distance from specified datum
1. max_gross_weight is primarily used for display purposes in the aircraft fuel and payload menu. It helps to notify the user that they may be exceeding the aircraft's maximum weight limits after loading fuel, passengers, etc.
2. empty_weight is an important parameter in that this it the value that flight simulator will use to set the basic empty weight of the aircraft in the physics engine. All other weight, such as station loads, fuel, etc. will be added to this weight. Changes to the value of this parameter will have a DIRECT affect on the flight dynamics of the aircraft in flight simulator.
3. reference_datum_position is used to align the mathematical flight model with the visual 3d model of the aircraft. For many aircraft the 0,0,0 of the visual model will be the same for the datum position. However, occasionally you will encounter an aircraft that has this number modified to ensure that the visual model is properly aligned with the "logical model" used for calculating physics and other measurements by the simulator. Most other items in the aircraft.cfg will based on distances from this datum position.
4. empty_weight_cg_position is used to set the center of gravity before the physics engine adds additional weights for fuel, station loads, etc. As such, this number is particular important for flight dynamics and ground handling. Often, setting everything to zeroes is a good place to start. However, many helicopters benefit from having a slight amount of forward center of gravity (.03 for example) or a slight amount of negative vertical position in the CG. This changes can help add stability in flight, and help improve the ground handling of skidded helicopters as they slide to a stop. Helicopters with skids, under normal circumstances, should be able to slide to a stop without flipping over. This parameter, in addition to properly positioned fuel, station loads, etc. is helpful for achieving this normal behavior.
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