by Jonathan M. Stern
The second element in weight and balance calculations is the balance of the airplane along its longitudinal axis. Distribution of the load in different parts of the airplane affects the location of the airplane's center of gravity. Center of gravity, in turn, must be within manufacturer-defined limits to ensure that the airplane is capable of safe flight within the published performance envelope.
The manufacturer of the airplane, through calculations and testing, determines an approved loading envelope for the airplane. For any given allowable weight, a range of centers of gravity is acceptable.
Just as safety and performance may be affected by overloading an airplane, unbalanced loading, even within weight limitations, can have a catastrophic effect on a flight. Distribution of weight from fore to aft should be calculated before each flight. Lateral distribution (from side-to-side) is not normally calculated but should be considered. An out of balance situation exists when the airplane's center of gravity is aft of the aft-most allowable center of gravity or forward of the most forward allowable center of gravity.
If the airplane is flown with the center of gravity forward of the most forward allowable center of gravity (nose-heavy), it may be difficult or impossible to raise the nose for takeoff or to flare during landing. Alternatively, if the airplane is flown with the center of gravity aft of the aft-most allowable position (tail-heavy), it may be difficult or impossible to recover from stalls. Moreover, elevator control forces become very light, which could lead to inadvertent overstress of the airplane.
Flight Simulator provides little control over loading of the simulated airplanes. I assumed, for the purpose of flight planning, that the airplane is at maximum gross weight when the fuel tanks are filled. The only aspect of loading over which you have control is the fuel loading. Nonetheless, the flight characteristics of the simulated airplanes are noticeably different when you go from full tanks to near empty tanks.
The Cessna 182RG holds approximately 88 gallons of usable fuel. At six pounds per gallon, the fuel weight with full tanks is 528 pounds, not an insignificant number when you consider that the maximum takeoff and landing weight of the airplane is 3,100 pounds.