Authors: KARAN KAUSHIK

HITESH MOHAN TRIVEDI T VISHWANATH

MANOJ KUMAR SINGH

AIRCRAFT RESEARCH AND DESIGN CENTER HINDUSTAN AERONAUTICS LIMITED

Modeling and Simulating

Physical System – Pilot Control stick circuit

Virtual System – MATLAB model using

Simulink

SimMechanics

Identifying undesirable conditions and their points of origin.

Reducing time involved in rectification.

A two-seater, tandem cockpit, fly-by-wire aircraft has its front and rear cockpit Pilot control sticks mechanically interconnected.

The interconnection between the two cockpits is done using

mechanical link rods, levers, and torque tubes.

Separate linkage connections or ‘circuits’ are made for the pitch

and roll controls.

Positional sensors detect the control stick movement and

generate corresponding electrical signals.

The signals are transmitted to the flight computer, which

depending on the aircraft’s control law, sends suitable signals to

electro-hydraulic actuators, which move the aircraft’s control

surfaces.

The system is designed in such a way that the movement of the control stick in either cockpit will provide same movement in the other cockpit.

To prevent injudicious usage of the control stick by the Pilot, an Artificial Feel Unit (AFU) is used in each circuit (i.e. Roll and Pitch).

It consists of a spring-damper system which provides an

artificial force/feel to the pilot as he deflects the control stick.

AFU is also used to keep the control stick in a defined neutral

position, when no force is applied. To prevent unwanted vibrations, the AFU design ensures

that the natural frequency and damping ratio of the system are in a certain range.

Spring

Damping fluid

Stops

Piston

Fluid orifice

Damping is achieved by the fluid flowing from one chamber to another through the orifice

Artificial force/feel is achieved by compression of spring as the piston moves up/down

A model was designed, representing the interconnection between the two cockpits and of the AFU.

The model should simulate the behavior of

the mechanical system.

Based on the 3-D CAD model of the control circuit, a SimMechanics model for Pitch and Roll circuits were created.

The models consist of multiple part bodies

representing the various mechanical link rods, levers, and torque tubes that are used on the aircraft.

Dimensions and mass of the part bodies were same

as of the designed parts.

Roll Circuit SimMechanics Model

Rear Cockpit Stick

Front Cockpit Stick

AFU

Lever Rod

Spring

Damping fluid

Stops

Piston

Fluid orifice By giving an initial displacement to a body (AFU Piston), the actuators function so as to bring the body to its neutral position, within a time limit.

The movement of the body is sensed and used to calculate the natural frequency and damping ratio of the system, using MATLAB code.

Due to the physical functioning requirement of the spring in the AFU, no available spring-damper blocks could be used.

So, the functionality of the spring-damper

system in the AFU was modeled using Simulink blocks.

AFU Simulink Model

Stick moved to a position Piston moves, spring compressed

Stick Released Spring – Damper Force Equations

Piston (Stick) moves Piston positions sensed,

Max Overshoot and Rise time calculated

Using this data Damping Ratio and Natural Frequency calculated

using MATLAB code

1. Displacement Measurement Displacements in both cockpits were measured and found to be same. Leverage from Control Stick to AFU is as per design.

Neutral Position

Extreme Position

2. Load Measurement Loads were measured at different points of the circuit and were comparable with expected values. 3. Dynamic Behavior Natural frequency and damping ratio of the system were obtained from the code and found within limits: Natural frequency > 4 Hz, Damping ratio: 0.3 to 0.7

Identification of undesirable conditions and their points of origin.

Reduction in time involved in rectifying

issues. Basis for modeling complete linkage circuit

from cockpit controls to control surfaces, for aircrafts with mechanical flight controls.