Learning Objective: Recognize the construction features of the rotary-wing aircraft (helicopter) and identify the fundamental differences as compared to fixed-wing aircraft.

The history of rotary-wing development embraces 500-year-old efforts to produce a workable direct-lift-type flying machine. Aircraft designers early experiments in the helicopter field were fruitless. It is only within the last 30 years that encouraging progress has been made. It is within the past 20 years that production line helicopters have become a reality. Today, helicopters are found throughout the world. They perform countless tasks especially suited to their unique capabilities. Helicopters are the modern-day version of the dream envisioned centuries ago by Leonardo da Vinci.

Early in the development of rotary-wing aircraft, a need arose for a new word to designate this direct-lift flying device. A resourceful Frenchman chose the two words-heliko, which means screw or spiral, and pteron, which means wing. The word helicopter is the combination of these two words.

A helicopter employs one or more power-driven horizontal airscrews, or rotors, from which it derives lift and propulsion. If a single rotor is used, it is necessary to employ a means to counteract torque. If more than one rotor is used, torque is eliminated by turning the rotors in opposite directions.

The fundamental advantage the helicopter has over conventional aircraft is that lift and control are independent of forward speed. A helicopter can fly forward, backward, or sideways, or it can remain in stationary flight (hover) above the ground. No runway is required for a helicopter to take off or land. The roof of an office building is an adequate landing area. The helicopter is considered a safe aircraft because the takeoff and landing speed is zero.

Like the fuselage in fixed-wing aircraft, helicopter fuselages may be welded truss or some form of monocoque construction. Many Navy helicopters are of the monocoque design.

Figure 1-17.-Rotary-wing blade.

A typical Navy helicopter, the H-3, is shown in figure 1-16. A flying boat-type hull provides this helicopter with water-operational capabilities for emergencies only. The fuselage consists of the entire airframe, sometimes known as the body group. The body group is of all-metal semimonocoque construction, consisting of an aluminum and titanium skin over a reinforced aluminum frame.