Airplane performance is the capability of the airplane, if operated within its limitations, to accomplish maneuvers which serve a specific purpose. For example, most present-day airplanes are designed clean and sleek, which results in greater range, speed, payload, and increased efficiency. This type of airplane is preferred for cross-country flights. Airplanes used for short flights and carrying heavy loads, such as those used in certain agricultural operations, are designed differently, but still exhibit good performance for their purpose. Some of the factors which represent good performance are short takeoff and landing distance, increased climb capability, and greater speeds using less fuel.
Because of its effect on performance, airplane weight and balance information is included in this chapter. Also included is an introduction to determining takeoff, cruise, and landing performance. For information relating to weight and balance, takeoff, cruise, and landing performance for a specific make and model of airplane, reference should be made to that Airplane’s Flight Manual or Pilot’s Operating Handbook.
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 problem in airplane construction and operation, and demands respect from all pilots.
The force of gravity continually attempts to pull the airplane 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, altitude cannot be maintained.
Effects of Weight
Any item aboard the airplane which increases the total weight significantly is undesirable as far as performance is concerned. 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 performance 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 landing speed.
• Longer landing roll.
• Excessive weight on the nosewheel.
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 consequences of an overweight airplane if an emergency condition arises. If an engine fails on takeoff or ice forms at low altitude, it is usually too late to reduce the airplane’s weight to keep it in the air.
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 airplane 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 overloaded by the installation of extra radios or instruments. Repairs or modifications usually affect the weight of the airplane.