Weight and Balance

the fuselage centerline, there is an equal weight existing at The forward CG limit is often established at a location that a corresponding location on the right. This may be upset is determined by the landing characteristics of an aircraft. by unbalanced lateral loading. The position of the lateral During landing, one of the most critical phases of flight, CG is not computed in all aircraft, but the pilot must be exceeding the forward CG limit may result in excessive loads aware that adverse effects arise as a result of a laterally on the nosewheel, a tendency to nose over on tailwheel type unbalanced condition. In an airplane, lateral unbalance occurs airplanes, decreased performance, higher stalling speeds, and if the fuel load is mismanaged by supplying the engine(s) higher control forces. unevenly from tanks on one side of the airplane. The pilot can compensate for the resulting wing-heavy condition by Control adjusting the trim or by holding a constant control pressure. In extreme cases, a CG location that is beyond the forward This action places the aircraft controls in an out-of-streamline limit may result in nose heaviness, making it difficult or condition, increases drag, and results in decreased operating impossible to flare for landing. Manufacturers purposely efficiency. Since lateral balance is addressed when needed in place the forward CG limit as far rearward as possible to the aircraft flight manual (AFM) and longitudinal balance is aid pilots in avoiding damage when landing. In addition to more critical, further reference to balance in this handbook decreased static and dynamic longitudinal stability, other means longitudinal location of the CG. undesirable effects caused by a CG location aft of the allowable range may include extreme control difficulty, Flying an aircraft that is out of balance can produce increased violent stall characteristics, and very light control forces pilot fatigue with obvious effects on the safety and efficiency which make it easy to overstress an aircraft inadvertently. of flight. The pilot’s natural correction for longitudinal unbalance is a change of trim to remove the excessive control A restricted forward CG limit is also specified to assure pressure. Excessive trim, however, has the effect of reducing that sufficient elevator/control deflection is available at not only aerodynamic efficiency but also primary control minimum airspeed. When structural limitations do not limit travel distance in the direction the trim is applied. the forward CG position, it is located at the position where full-up elevator/control deflection is required to obtain a high Effects of Adverse Balance AOA for landing. Adverse balance conditions affect flight characteristics in much the same manner as those mentioned for an excess The aft CG limit is the most rearward position at which the weight condition. It is vital to comply with weight and CG can be located for the most critical maneuver or operation. balance limits established for all aircraft. Operating above As the CG moves aft, a less stable condition occurs, which the maximum weight limitation compromises the structural decreases the ability of the aircraft to right itself after integrity of the aircraft and can adversely affect performance. maneuvering or turbulence. Stability and control are also affected by improper balance. For some aircraft, both fore and aft CG limits may be Stability specified to vary as gross weight changes. They may also Loading in a nose-heavy condition causes problems in be changed for certain operations, such as acrobatic flight, controlling and raising the nose, especially during takeoff retraction of the landing gear, or the installation of special and landing. Loading in a tail heavy condition has a serious loads and devices that change the flight characteristics. effect upon longitudinal stability, and reduces the capability to recover from stalls and spins. Tail heavy loading also The actual location of the CG can be altered by many variable produces very light control forces, another undesirable factors and is usually controlled by the pilot. Placement of characteristic. This makes it easy for the pilot to inadvertently baggage and cargo items determines the CG location. The overstress an aircraft. assignment of seats to passengers can also be used as a means of obtaining a favorable balance. If an aircraft is tail heavy, Stability and Center of Gravity it is only logical to place heavy passengers in forward seats. Limits for the location of the CG are established by the Fuel burn can also affect the CG based on the location of the manufacturer. These are the fore and aft limits beyond fuel tanks. For example, most small aircraft carry fuel in the which the CG should not be located for flight. These limits wings very near the CG and burning off fuel has little effect are published for each aircraft in the Type Certificate Data on the loaded CG. Sheet (TCDS), or aircraft specification and the AFM or pilot’s operating handbook (POH). If the CG is not within the allowable limits after loading, it will be necessary to relocate some items before flight is attempted. 10-3