Aeronautics and astronautics – Aircraft – heavier-than-air – Helicopter or auto-rotating wing sustained – i.e. – gyroplanes
Reexamination Certificate
2003-03-20
2004-11-30
Dinh, Tien (Department: 3644)
Aeronautics and astronautics
Aircraft, heavier-than-air
Helicopter or auto-rotating wing sustained, i.e., gyroplanes
C244S017270, C244S00700B
Reexamination Certificate
active
06824096
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a device for controlling the pitch of the blades of a convertible aircraft rotor of the known type supporting at least two wings, generally fixed, and at least one tilting rotor.
A particularly advantageous application of the pitch control device according to the invention consists in fitting it to constant velocity drive tilting rotors for convertible aircraft, particularly of the type known and described in U.S. Pat. Nos. 6,276,633, 6,260,793 and 6,607,161 to which reference may advantageously be made for further details.
Briefly, such a convertible aircraft with tilting rotors generally comprises, as shown schematically in
FIG. 1
, a fuselage
1
, of the aircraft fuselage type, supporting two fixed wings
2
, for example high wings, raised with respect to the fuselage
1
, each wing
2
itself supporting a power pod
3
, housing a power unit driving in rotation a rotor
4
, represented schematically by the plane of rotation of the rotor blades, via a transmission (not shown in FIG.
1
), a rear reduction gear unit of which is directly driven by the power unit and housed like the latter in the stationary rear part
5
of the power pod
3
. The front part
6
of the power pod, housing a rotor mast and a rotor hub, as well as a front reduction gear unit driving the rotor mast in rotation, is mounted so as to pivot with the rotor
4
, so that it can pivot from an aeroplane configuration, in which the rotor
4
operates as a propeller at the front of an engine pod
5
-
6
facing into the relative wind, to a helicopter configuration, in which the rotor
4
′ operates as a helicopter main lifting rotor at the upper end of the front pivoting part of the pod in the upright position
6
′ above the corresponding wing
2
, this latter configuration being used for take-off and landing of the convertible aircraft which, after transition from the helicopter configuration to the aeroplane configuration, is able to move in forward flight like an aircraft. As a variant, the pods
3
may pivot totally with the rotor
4
with respect to the fixed wings
2
.
BACKGROUND TO THE INVENTION
The tilting rotors of convertible aircrafts differ from the rotors, particularly main rotors, of helicopters by the following characteristics. The range of control of the blades of these rotors in collective pitch is very large, due to the fact that the aircraft must be able to fly not only as a helicopter but also as an aeroplane; the power for controlling them must remain low, which necessitates a very small flapping eccentricity (i.e. the distance between the flapping axis of the blades and the axis of rotation of the rotor); the rotors, and their hubs in particular, must have high rigidity in the plane of the rotor, in order to obtain a high drag mode, to avoid the dangers of ground resonance; and they have a high level of cyclic flapping.
To meet these different requirements, it has already been proposed that such convertible aircrafts be equipped with tilting rotors of the gimbal type, with zero flapping eccentricity, on which the hub is driven in rotation by the mast and connected to the latter by tilting means, allowing the hub, and therefore the rotor, to tilt as a whole about a flapping axis passing through the axis of the mast and perpendicular to the latter, and being able to occupy any position extending in any direction about the axis of the mast. On such rotors, the absolute requirement that the pitch-flap coupling, commonly referred to as the delta-3 relation, should have a slightly negative value for the control of such a tilting rotor, has led the designers of such rotors to adopt three-bladed rotors, so that a conventional pitch control device is retained, similar to those fitted to helicopter main rotors, with a swashplate mechanism, in which the oscillations of a rotating star control the movements, substantially along the axis of rotation of the rotor mast, of pitch control rods, each of which is hinged to the end of a pitch change lever integral in rotation with the root of a corresponding blade about the longitudinal pitch change axis of this blade, the pitch change lever projecting on the leading edge or trailing edge side of this blade, in order that the distance between the flapping axis and the centre of the pitch change lever hinge to the corresponding pitch control rod is short.
In actual practice, this condition of a short distance between the flapping axis and the centre of the pitch change lever hinge to the control rod can be met on a three-bladed rotor with conventional pitch change levers, i.e. levers placed substantially in the plane of the rotor disc, since the space available between successive blade roots is generally sufficient to accommodate such pitch change levers.
On the other hand, on a rotor equipped with at least four blades, the flapping axis of a blade corresponds substantially with the longitudinal axis of the following blade, so that for reasons of geometry and interference the pitch change levers cannot be positioned to satisfy the above conditions.
SUMMARY OF THE INVENTION
The problem addressed by the present invention is to propose a device for controlling the pitch of the blades of a gimbal-type rotor as defined above, preferably rigid in plane, and which may comprise at least three blades, but preferably four blades or more, while meeting the strict requirement for a slightly negative delta-3 value.
To this end, there is provided a device for controlling the pitch of blades of a convertible aircraft tilting rotor, for a rotor comprising:
a rotor mast having a base and a longitudinal axis, the rotor mast being capable of being driven in rotation by said base about said longitudinal axis,
a hub, driven in rotation by the mast, and connected to the masse by a tilting arrangement, allowing the hub as a whole to tilt about any flapping axis passing through the axis of the mast and perpendicular to the axis of the mast, and
at least two blades, each of which is linked to the hub by a coupling retaining and hingeing said blade in pitch about a longitudinal pitch change axis of said blade, which pitch change axis extends in a plane of rotation of the rotor,
wherein the pitch control device is external to the hub and comprises for each blade of the rotor:
a pitch change lever, integral in rotation with a root of said blade about said pitch change axis, and projecting on a side of a plane of rotation of the rotor which faces towards the base of the mast,
a pitch control rod which is movable in a direction substantially parallel to the longitudinal axis of rotation of the mast,
a bellcrank mounted so as to pivot about a pivot axis substantially contained in a radial plane relative to the longitudinal axis of rotation of the mast, on a fixed point of a drive plate, integral in, rotation with the mast, said pitch control rod being hinged to said bellcrank, at least so as to pivot about an axis substantially parallel to the pivot axis of the bellcrank on the drive plate, and at a point offset radially outwardly of said pivot axis relative to the longitudinal axis of rotation of the mast, and
a link rod, hinged at least so as to pivot at one end to said pitch change lever, about an axis substantially parallel to said pitch change axis and, at an other end of said link rod to the bellcrank, at a fixed point on the bellcrank located between said plane of rotation of the rotor and the point of hingeing of the bellcrank to the drive plate, so that said link rod is slightly inclined to any radial plane relative to the longitudinal axis of rotation of the mast, and that the bellcrank converts any movement of said pitch control rod into movement of said link rod in a direction substantially transverse to the direction of the longitudinal axis of the mast.
An essential advantage of this pitch control device is that an angle of inclination of said link rod to any radial plane (perpendicular to the axis of the mast) may be chosen to correspond to a desired pitch-flap relation (delta-3) for the corresponding blade.
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