X Title of the invention

Design of Flight Control Linkages of Helicopter in Transmission Deck

2 Field of invention

The present invention relates to flight control system's mechanical linkage which controls the helicopter motion in Pitch, Roll and Collective. The flight control linkage in transmission deck area of the helicopter is designed in such a way that:

1. Main Gear Box vibrations do not affect the functioning of flight controls.

2. There is negligible geometric inter axis cross coupling among the control axes e.g. Pitch, Roll and Collective.

3. Lesser length main rotor actuators can be accommodated which is good for their load bearing capacity.

3 Background of Invention

Helicopter includes main rotor, main gear box, flight controls, hydraulic actuators and structure. In helicopters, a very common phenomenon is that, the vibrations due to the rotating systems like rotor and main gear box gets transferred to flight controls, actuators and the structure causing unintentional input to controls resulting in undesirable change in helicopter response. To reduce these un-intentional inputs to flight controls the vibration isolation systems are introduced in the helicopters which is an additional system that increases inventory of helicopter parts, complexity, weight and cost. However, during initial stages of design, if flight control architecture is planned judiciously the effect of un-intentional inputs to controls can be avoided to a greater extent.

In the present invention, the flight controls in transmission deck area are architectured in such a way that there is negligible effect of un-intentional inputs to the flight controls due to main gear box movements/vibrations.
Also, the present invention ensures negligible inter-axis geometrical cross couplings and enables the use of a shorter length hydraulic actuator which can have higher load bearing capacity.

3.1 Prior Art

US 2010/0308178 A1 dated Dec 9,2010: invention relates to a crank having a variable ratio transmission in a manual flight control that acts on a linkage Suitable for giving rise to flight attitude changes in a rotary wing aircraft.

The purpose of present invention is entirely different from the prior art. It reduces the effect of un-intentional inputs due to MGB vibrations on flight controls, minimizes the inter axis geometrical cross couplings among the control axes and facilitates the installation of simple, short length actuator having higher load bearing capability. In the present invention, no variable ratio transmission is used in manual flight control linkages which is mentioned in the prior art.

US 2009/0242691 A1, Oct. 1,2009: includes: a rotational system; a multiple of servos operable to articulate the rotational system; a kinematics model of the rotational system; and a module which performs a servo rate limiting algorithm in response to the kinematics model to transform a non-rate limited servo position command into a rate limited servo position command to drive each of the multiple of servos through a proportional rate reduction of all of the multiple of servos to reduce off-axis coupling in the rotational system.

A method of controlling a rotary-wing aircraft according to an exemplary aspect includes transforming a non-rate limited servo position command into a rate limited servo position command; and driving each of a multiple of main rotor servos through a respective rate limited servo position command having a proportional rate reduction of all of the multiple of main rotor servos to reduce off-axis coupling in a Swashplate articulatable by the multiple of main rotor servos to reduce off-axis coupling in the Swashplate.
In the present invention the inter axis coupling is minimized by installing the control linkages in a particular manner whereas in the prior art mentioned the off-axis coupling is reduced by a servo rate limiting algorithm.

US 2011/0 155841 A1 dated jun30,2011: The present invention relates to mechanisms for damping vibration induced by aeroelastic instabilities resulting from coupling between modes of vibration of the carrier structure and modes of vibration of the rotor. The invention provides such a mechanism and a flying machine provided with such a mechanism.

The present invention reduces the effect of un-intentional inputs due MGB vibrations, on flight controls and this is achieved without using any damper in the flight control linkages and it does not use any damping mechanism such as masses and dampers as mentioned in the prior art.

4 Summary of the present invention

It was observed that, the vibrations due to the rotating systems like Rotor and main gear box gets transferred to flight controls, actuators and the structure causing un-intentional input to controls resulting in undesirable change in helicopter response.

The present invention discloses the flight controls architecture in transmission deck area is in such a way that there is negligible effect of unintentional inputs to the flight controls due to MGB movements. Also, the present invention ensures negligible inter-axis geometrical cross couplings and enables the use of a shorter length hydraulic actuator which can have higher load bearing capacity.
5 Brief description of drawings

Figure-1: shaded part on the helicopter HC indicates the flight controls linkages, main rotor actuators and MGB installation (100) in the top deck area of helicopter.
Figure-2: shows the flight controls linkages (200), main rotor actuators (300) and main gear box (400).

Figure-3 & 4: shows forward pitch actuator (300a), roll actuator (300b), rear pitch actuator (300c) and the detailed flight controls assembly (200) which contains bell crank levers (1,2,3,13,16 & 17) and levers (7,8,9) which are connected using control rods (4,5,6,10,11,12). Actuator’s input lever ends are connected through link rods (14,17 & 18) and piston ends of actuators are connected up to non-rotating swash plate (25) using levers (19,20,21) & non rotating control rods (22,23,24). Bell crank levers and other levers are mounted on brackets (26,27,28,29,30) using fasteners and bearings.

Figure-5 & 6: shows the mounting points of actuators (300a,300b & 300c), installation of last bell cranks (13,15 & 16) of flight control system at main gear box (400), link rods (14,17,18) and the long length control rods (10,11 & 12).

Figure-7: shows linkages between actuator and non-rotating swash plate this includes levers (19,20 & 21), Bracket (30) and non-rotating control rods (22,23 & 24)

6 Detailed description of invention

The flight control linkage (200) as shown in figure-3 & 4, installed in top deck is common for Pitch, Roll and Collective controls. When Collective control input is given by the Pilot, three bell cranks (1,2,3) moves together and gives input to three control rods (4,5,6) which further transmits the motion to levers (7,8,9), the levers further give input to three control rods (10,11,12) which transmits the motion to the bell cranks (13,15,16) mounted on the main gear box. Further, the bell cranks (13,15,16) mounted on main gear box moves the input levers of hydraulic actuators via link rods (14,17,18). Finally, pistons of all the three actuators moves simultaneously by equal displacement and transmits this motion to levers (19,20,21) installed on main gear box which further moves the non-rotating control Rods (NRCR)
(22,23,24) and thus the swash plate assembly (25) moves up or down which in turn changes the pitch of all four blades simultaneously resulting in generation of the lift of the helicopter.

When a pitch input is given by the pilot, two bell cranks (1,3) moves in opposite direction by equal amount of displacement. This input is further transmitted till forward pitch actuator (300a) and rear pitch actuator (300b) by the linkage which includes control rods (4,6,10,12), Levers (7,9,13,15) and link rods (14,17). Finally, the pistons of forward and rear pitch actuators (300a,300c) move in opposite direction by equal amount of displacement, this displacement further enables the tilt of non-rotating swash plate (NRSP) (25) by means of NRCRs (22,23,24) resulting in change of pitch of main rotor blades in cyclic manner which enables the helicopter pitching motion.

When the roll input is given by the Pilot, Bell Crank (2) moves and transmits this motion till roll actuator input lever through the Control Rod (5,11), levers (8,16) and link rod (18). Thus, the Piston of input lever moves up / down and transmits this motion to lever (20) and NRCR (23) which enables the tilt of swash plate assembly resulting in change of pitch of main rotor blades in cyclic manner and thereby the rolling motion of helicopter is attained.

The un-intentional input to the controls due to main gear box (MGB) vibrations are reduced to almost negligible by:

• Installing the hydraulic actuators (300a,300b,300c) vertically around the main gear box keeping both the mounting points on the main gear box (MGB) as shown in Figure-5 & 6.

• Installing the last bell cranks (13,15,16) of flight controls on the main gear box (MGB) as shown in Figure-5 & 6.

• (Having longer length last three control rods (10,11,12) as shown in Figure-5 & 6

The inter axis geometric cross coupling means whenever a control input is given to a specific axis e.g., collective then it should not affect the other
control axes e g., Pitch and / or Roll. So, if Pilot has given the collective input to the controls, then there should not be any cyclic input to the actuators. Alternatively, if the cyclic input is given by the pilot, then there should not be any Collective input to the actuators.

The negligible inter axis geometric cross coupling is achieved in the present invention by:

• having symmetrical installation of bell cranks (13,15,16) on the left and right side of the main gear box (MGB) and same length of link rods (14,17,18) as shown in figures 5 & 6.

• maintaining the angles between control rods, link rods and levers as 90 degrees in the neutral position of the controls as shown in Figures 3 & 4.

The linkage (19,20,21,22,23,24,30) between actuators (300a,300b,300c) and non-rotating swash plate (25) shown in figure-7, facilitated the installation of short length actuator which has advantage of a simple design with higher load bearing capability.

The particulars disclosed in this article are exemplary representations of the invention, it is also possible that the invention may be modified and practiced in equivalent but different ways or arrangements by one who is skilled in the art with the help of the details described in this manuscript. Therefore, all such variations are to be considered within the scope and spirit of the invention disclosed in this article. Accordingly, the protection is sought.