Rotorhead Types
There are 2 categories of rotorhead designs: fully articulated and hingeless. The
former
uses 3 hinges for each blade; one for the feathering axis, one to support flapping
up and down, and one to support lead and lag blade movements. On the other
hand, a hingeless rotorhead (sometimes known as rigid, which is not a very accurate description) uses materials
that are both strong and, to some degree, flexible. Moreover, the blades are also designed to incorporate some form of flexibility.
Both designs have their advantages and disadvantages:
Fully articulated
-
No moment transmitted to rotorhead. The rotorhead doesn't have to be very strong,
and so can be lighter.
-
Blade movements, for example due to turbulence, are, to some degree, not transmitted
to the rotorshaft and hull.
-
A lot of hinges also require a lot of maintenance.
-
Because moments are not transmitted to the rotorhead, the hull will not follow the
rotordisc attitude. The rotorsystems have less control power.
Hingless
-
Unlike a fully articulated system, moments are transmitted to the rotorhead, which
must be able to cope with these forces.
-
Because (to some degree) moments are transmitted to the rotorhead, the attitude
of the hull will try to follow the rotordisc's attitude. This rotorsystem has a
high degree of control power.
-
Because there are no hinges, less maintenance is required.
Teetering rotorhead
Of course, in between these 2 solutions, other designs also exist, an important example
being the 2 bladed, semi rigid, rotorhead which uses feathering hinges for pitch
control. Its 2 (opposite) blades are mounted in one, teetering, hinge. So,
if one
blade flaps up, the other has to flap down. In this design, the blades are mounted
(fixed) in the rotorhead at the average
coning angle, in order to prevent blade stress. By using a gimballed teetering head, the rotordisc
can tilt in any direction. In this way, the Hookes' joint effect is absent, so there
is no need
for lead and lag hinges. These are also un-necessary if an underslung rotor design
is used. This 2 bladed teetering rotorhead system has already been in operation
for many years, ever since
the famous designs from Hiller and Bell.
Next topic > Pitch Control
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Cyclic & Collective
- The title of this book leads me to wonder what more it will teach me in addition to its content about these two, most frequently used, helicopter input controls. As it turns out, the answer is: a lot more. Of course, all of the obligatory subjects like basic physics, rotor aerodynamics and helicopter performance are dealt with as well, as are piston engine and basic helicopter manoeuvres. Yet the scope of this book is actually much wider than one might initially think.
Firstly, it is divided into a 'beginners’ and an 'advanced’ section. This means that the book can treat more complex concepts in depth, even though the focus in the first section is directed more towards newcomers to the field.
Secondly, subjects like turbine engines, multi-engine helicopters and autopilots are also examined. This is particularly helpful, since these topics are not usually covered in the majority of helicopter books aimed at this target audience.
Thirdly, the book deals with many things that you will not normally find in a text book: helicopter related experiences and a great deal of interesting detail. This is the sort of information that can only be provided if you have flown a lot of different helicopters and have been working in this industry for some time. What’s more, this tone is amplified by the consistently narrative style of the book.
- 536 pages
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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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