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There are 2 categories of rotorhead designs: fully articulated and hingeless. The
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:
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.
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.
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,
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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