An aircraft is said to be in balance, or balanced, when all weight items in, on, or of the aircraft are distributed so that the longitudinal center of gravity (cg) of the aircraft lies within a predetermined cg range. This range is defined by the most forward and aft permissible cg locations, which are called the forward and aft cg limits, respectively. To determine if an aircraft is balanced, the aircraft cg must be calculated and compared to the forward and aft cg limits for that particular configuration and gross weight. 

Learning

Objective: Recognize the different types of slings and the hoisting requirements for naval aircraft.

There are three main conditions that might require you to hoist an aircraft or its components. They are aircraft mechanical problems, ship mechanical problems, and aircraft mishap afloat or ashore. Aircraft lifting slings are specialized items of support equipment whose function is to aid in the hoisting of aircraft and aircraft components. Each airframe has structural lifting points for the attachment of a sling designed to lift that aircraft or aircraft subassembly. Slings are used to hoist aircraft from the pier to carrier deck, clear crash-damaged aircraft, and to remove and install engines and other components during maintenance operations. In general, slings are hand portable and attach to a single suspension hook of a crane or other hoisting equipment.

Aircraft lifting slings are constructed in accordance with Military Specification MIL-S-5944, and can be classified under four types of construction or combinations of type. The four types are the wire rope, the fabric or webbing type, the structural steel or aluminum type, and the chain.

Slings of this type employ wire rope or cable. The wire rope sling is the most common type, and it combines high strength, ease of manufacture, and a great deal of flexibility for compact storage. There are two basic types of wire rope slings. The simplest is a multi-legged wire rope sling with an apex lifting link. The other is one built with structural steel or aluminum in combination with wire rope supports. See figure 3-20.

Fabric or webbing type slings are generally reserved for lifting lightweight objects, or applications where contact between wire rope and the component being lifted could result in damage.