System Malfunctions (Part Four)

Main Drive Shaft or Clutch Failure The main drive shaft, located between the engine and the main rotor gearbox, transmits engine power to the main rotor gearbox. In some helicopters, particularly those with piston engines, a drive belt is used instead of a drive shaft. A failure of the drive shaft clutch or belt has […]

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System Malfunctions (Part Three)

Main Rotor Disk Interference (285–315°) Refer to Figure 11-11. Winds at velocities of 10–30 knots from the left front cause the main rotor vortex to be blown into the tail rotor by the relative wind. This main rotor disk vortex causes the tail rotor to operate in an extremely turbulent environment. During a right turn, […]

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System Malfunctions (Part Two)

Loss of Tail Rotor Effectiveness (LTE) Loss of tail rotor effectiveness (LTE) or an unanticipated yaw is defined as an uncommanded, rapid yaw towards the advancing blade which does not subside of its own accord. It can result in the loss of the aircraft if left unchecked. It is very important for pilots to understand […]

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System Malfunctions (Part One)

The reliability and dependability record of modern helicopters is very impressive. By following the manufacturer’s recommendations regarding operating limits and procedures and periodic maintenance and inspections, most systems and equipment failures can be eliminated. Most malfunctions or failures can be traced to some error on the part of the pilot; therefore, most emergencies can be […]

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Low Rotor RPM and Blade Stall

As mentioned earlier, low rotor rpm during an autorotation might result in a less than successful maneuver. However, if rotor rpm decays to the point at which all the rotor blades stall, the result is usually fatal, especially when it occurs at altitude. It can occur in a number of ways, such as simply rolling […]

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Low-G Conditions and Mast Bumping

Low acceleration of gravity (low-G or weightless) maneuvers create specific hazards for helicopters, especially those with semirigid main rotor systems because helicopters are primarily designed to be suspended from the main rotor in normal flight with only small variations for positive G load maneuvers. Since a helicopter low-G maneuver departs from normal flight conditions, it […]

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Dynamic Rollover (Part Two)

Cyclic Trim When maneuvering with one skid or wheel on the ground, care must be taken to keep the helicopter cyclic control carefully adjusted. For example, if a slow takeoff is attempted and the cyclic is not positioned and adjusted to account for translating tendency, the critical recovery angle may be exceeded in less than […]

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Dynamic Rollover (Part One)

A helicopter is susceptible to a lateral rolling tendency, called dynamic rollover, when the helicopter is in contact with the surface during takeoffs or landings. For dynamic rollover to occur, some factor must first cause the helicopter to roll or pivot around a skid or landing gear wheel, until its critical rollover angle is reached. […]

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Ground Resonance

Helicopters with articulating rotors (usually designs with three or more main rotor blades) are subject to ground resonance, a destructive vibration phenomenon that occurs at certain rotor speeds when the helicopter is on the ground. Ground resonance is a mechanical design issue that results from the helicopter’s airframe having a natural frequency that can be […]

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Retreating Blade Stall

In forward flight, the relative airflow through the main rotor disk is different on the advancing and retreating side. The relative airflow over the advancing side is higher due to the forward speed of the helicopter, while the relative airflow on the retreating side is lower. This dissymmetry of lift increases as forward speed increases. […]

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Settling With Power (Vortex Ring State)

Vortex ring state describes an aerodynamic condition in which a helicopter may be in a vertical descent with 20 percent up to maximum power applied, and little or no climb performance. The term “settling with power” comes from the fact that the helicopter keeps settling even though full engine power is applied. In a normal […]

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