HELICOPTERWEIGHTANDBALANCE HELICOPTER WEIGHT AND BALANCE

The weight and balance principles and procedures that have been described apply generally to helicopters.

Each model helicopter is certificated for a specific maximum gross weight. However, it cannot be operated at this maximum weight under all conditions. Combinations of high altitude, high temperature, and high humidity determine the density altitude at a particular location. This, in turn, critically affects the hovering, takeoff, climb, autorotation, and landing performance of a helicopter. A heavily loaded helicopter has less ability to withstand shocks and additional loads caused by turbulent air. The heavier the load, the less the margin of safety for the supporting structures, such as the main rotor, fuselage, landing gear, etc.

Most helicopters have a much more restricted CG range than do airplanes. In some cases this range is less than 3 inches. The exact location and length of the CG range is specified for each helicopter and usually extends a short distance fore and aft of the main rotor mast or the centroid of a dual rotor system. Ideally, the helicopter should have such perfect balance that the fuselage remains horizontal while in a hover, and the only cyclic adjustment required should be that made necessary by the wind. The fuselage acts as a pendulum suspended from the rotor. Any change in the center of gravity changes the angle at which it hangs from this point of support. More recently designed helicopters have loading compartments and fuel tanks located at or near the balance point. If the helicopter is not loaded properly and the CG is not very near the balance point, the fuselage does not hang horizontally in a hover. If the CG is too far aft, the nose tilts up, and excessive forward cyclic control is required to maintain a stationary hover. Conversely, if the CG is too far forward, the nose tilts down and excessive aft cyclic control is required. In extreme out of balance conditions, full fore or aft cyclic control may be insufficient to maintain control. Similar lateral balance problems may be encountered if external loads are carried.

Upon delivery by the manufacturer, the empty weight, empty weight CG, and the useful load are noted on the weight and balance data sheet in the helicopter flight manual. If, after delivery, additional fixed equipment is added or removed, or if a major repair or alteration is made, which may affect the empty weight, empty weight CG, or useful load, the weight and balance data must be revised. All weight and balance changes should be entered in the appropriate aircraft record.