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Blade Feathering and Blade Flapping

Blade feathering is the term for changing blade angle (pitch), and influences the blade's angle of attack. A blade feathers along its longitudinal axis, and a bearing is usually used to support this. The blade angle is set by the control rod, which is connected to the swashplate. Changing the blade pitch will result in a change in blade flapping behaviour.

The place where the control rods connect to the blade, and the position of the flapping axis (for example, the position of the flapping hinge), both influence feathering and, therefore, blade angle. Take a look at the figure below. In this example, when a blade flaps up the blade angle will be reduced and vice versa. This causes additional blade flapping damping (which leads to a lower blade flapping amplitude). This configuration is also referred to as a 'delta 3 configuration'. Blade flapping doesn't interfere with pitch angle when the control rod connecting joint lies at the flapping axis, as in the second figure below.

Note that blade flapping is also dampened by aerodynamic forces. See Blade Flapping.

The designer of a rotorhead has another way of reducing the flapping amplitude (creating more damping). This is achieved by utilising a construction in which the flapping hinge axis is positioned as set out in the next figure. In this configuration, when the blade flaps up, the angle of attack will decrease by construction. When the blade flaps down, the reverse will happen. This design is also referred to as a Delta 3 Hinge, and is often seen in tail rotorheads. 

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Cyclic & Collective

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Art of the Helicopter (Hardback)

  • Well structured text that covers many technical aspects. It starts with an introduction to helicopters, followed by a treatment of the technical background needed when studying them. Thereafter, dynamics, rotor systems, engines and transmission are explained in detail. The book concludes with a section on performance and other types of rotorcraft. Its main asset is that the text is technically and theoretically very accurate, and rather than mathematics, its focus is always on enabling the reader to achieve an understanding of helicopters from a technical or engineering point of view. The more technically orientated reader will love this work.
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Principles of Helicopter Flight (Paperback)

  • If you are wondering how a helicopter flies, and really want to comprehend the process, you have no choice but to delve into aerodynamics. This means not only understanding which forces play a role and the laws of physics, but also being able to put it all together and apply your knowledge to a rotating system consisting of a number of rotor blades. This is a demanding task and requires some very hard work. It is, undoubtedly, worth the effort though, and will help you to become a better pilot. There are many books out there to help you with this task of exploring the principles of helicopter flight, but they tend to fall into two camps: populist and taking a rather simplistic approach, or highly technical and assuming the reader has a degree in mathematics. This book is different, because it clearly explains the principles of flight in a step by step way that is easy for most readers to follow. Further benefits are that a lot of attention is paid to flight manoeuvres and operations, and every chapter concludes with questions as a study aid.
  • 320 pages
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