载重与平衡飞行员手册.pdf

8-1 Compliance with the weight and balance limits of any airplane is critical to flight safety. Operating an airplane above the maximum weight limitation compromises the structural integrity of the airplane and adversely affects its performance. Operation with the center of gravity (CG) outside the approved limits may result in control difficulty. WEIGHT CONTROL Weight is the force with which gravity attracts a body toward the center of the earth. It is a product of the mass of a body and the acceleration acting on the body. Weight is a major factor in airplane construction and operation, and demands respect from all pilots. The force of gravity continually attempts to pull the air- plane down toward earth. The force of lift is the only force that counteracts weight and sustains the airplane in flight. However, the amount of lift produced by an airfoil is limited by the airfoil design, angle of attack, airspeed, and air density. Therefore, to assure that the lift generated is sufficient to counteract weight, loading the airplane beyond the manufacturer’s recommended weight must be avoided. If the weight is greater than the lift generated, the airplane may be incapable of flight. EFFECTS OF WEIGHT Any item aboard the airplane that increases the total weight is undesirable as far as performance is con- cerned. Manufacturers attempt to make the airplane as light as possible without sacrificing strength or safety. The pilot of an airplane should always be aware of the consequences of overloading. An overloaded airplane may not be able to leave the ground, or if it does become airborne, it may exhibit unexpected and unusually poor flight characteristics. If an airplane is not properly loaded, the initial indication of poor per- formance usually takes place during takeoff. Excessive weight reduces the flight performance of an airplane in almost every respect. The most important performance deficiencies of the overloaded airplane are: • Higher takeoff speed. • Longer takeoff run. • Reduced rate and angle of climb. • Lower maximum altitude. • Shorter range. • Reduced cruising speed. • Reduced maneuverability. • Higher stalling speed. • Higher approach and landing speed. • Longer landing roll. • Excessive weight on the nosewheel or tailwheel. The pilot must be knowledgeable in the effect of weight on the performance of the particular airplane being flown. Preflight planning should include a check of performance charts to determine if the airplane’s weight may contribute to hazardous flight operations. Excessive weight in itself reduces the safety margins available to the pilot, and becomes even more hazardous when other performance-reducing factors are combined with overweight. The pilot must also consider the con- sequences of an overweight airplane if an emergency CH 08.qxd 10/24/03 7:07 AM Page 8-1 8-2 condition arises. If an engine fails on takeoff or air- frame ice forms at low altitude, it is usually too late to reduce the airplane’s weight to keep it in the air. WEIGHT CHANGES The weight of the airplane can be changed by altering the fuel load. Gasoline has considerable weight—6 pounds per gallon—30 gallons may weigh more than one passenger. But it must be remembered that if weight is lowered by reducing fuel, the range of the air- plane is decreased. During flight, fuel burn is normally the only weight change that takes place. As fuel is used, the airplane becomes lighter and performance is improved. Changes of fixed equipment have a major effect upon the weight of the airplane. An airplane can be over- loaded by the installation of extra radios or instruments. Repairs or modifications may also affect the weight of the airplane. BALANCE, STABILITY, AND CENTER OF GRAVITY Balance refers to the location of the center of gravity (CG) of an airplane, and is important to airplane sta- bility and safety in flight. The center of gravity is a point at which an airplane would balance if it were suspended at that point. The prime concern of airplane balancing is the fore and aft location of the CG along the longitudinal axis. The center of gravity is not necessarily a fixed point; its location depends on the distribution of weight in the airplane. As variable load items are shifted or expended, there is a resultant shift in CG location. The pilot should realize that if the CG of an airplane is dis- placed too far forward on the longitudinal axis, a nose-heavy condition will result. Conversely, if the CG is displaced too far aft on the longitudinal axis, a tail-heavy condition will result. It is possible that an unfavorable location of the CG could produce such an unstable condition that the pilot could not control the airplane. [Figure 8-1] Location of the CG with reference to the lateral axis is also important. For each item of weight existing to the left of the fuselage centerline, there is an equal weight existing at a corresponding location on the right. This may be upset, however, by unbalanced lateral loading. Th。