1) Title of the invention
Design concept for measuring displacement at feedback end of Tail Rotor Actuator (TRA) used on helicopter
2) Field of invention
The invention is in the field of mechanical engineering design which is design of fixtures used for mounting the measuring instrument.
3) Use of invention
This invention finds application in places where ever transducer is to be mounted and displacement is to be measured on Tail Rotor Actuator. This design also finds application on horizontally installed flange mounted Tail Rotor Actuators on Tail Boom mid structure.

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4) Aim of the invention
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The primary objective of the invention is to design a attachment fixture to install the linear potentiometer between the moving Tail Rotor Actuator and fixed structure and measure the displacement of the Tail Rotor Actuator without affecting the functionality and safety of the Tail Rotor Actuator. The Fixture designed helps to fulfill the aim and in turn ensures completion of flight testing on Prototypes. It also aims in minimizing the change in Standard Of Preparation of the helicopter, since the measurement system will not be a permanent fit on helicopter and will be removed after completion of testing. The fixture, is designed in such a way that the reversion for final production Standard of Preparation can be easily accounted.
5) Summary of the present invention
Tail Rotor Actuators are used on helicopters to control the Tail Rotor Blade angles. During prototype testing of the helicopters, it is required to measure the displacement of the Tail Rotor Actuator for evaluation and certification of the Yaw control of the helicopter. Hence measurement of the linear movement of actuator is necessary for achieving required blade position to control the helicopter.
The Present invention, design of fixture for installing the potentiometer is used to measure the displacement of Tai Rotor Actuator. The Tail Rotor Actuator is a flange mounted actuator mounted horizontally on the mid of Tail boom structure. The linear displacement of Tail Rotor Actuator is measured by a special arrangement by installing linear potentiometer between one fixture end from the actuator feedback end and the other fixture from the Tail boom top structure.
6) Brief description of drawings
Figure 1(a) shows the unassembled view of the measuring system without the Tail Rotor Actuator.
Figure 1(b) and 1 (c) shows the assembled view of the measuring system with and without Tail Rotor
Actuator. The measuring system consists of 4 brackets, one linear potentiometer and securing screws
& nuts. Three brackets viz, C-clamp, L-Plate & L Angle are installed on the Tail Rotor Actuator to arrest
the rotation and any further movement of the potentiometer with respect to the Tail Rotor Actuator.
The L-Plate has a fonk to which one end of the linear potentiometer is installed. The other bracket
1 (with fork end) is installed on the tail boom top structure through inserts with the attachment point in
line with the Tail Rotor Actuator axis. Linear potentiometer is installed between these two fork ends.

7) Statement of invention
The present invention of design of fixture is unique to Tail Rotor Actuator and is used for measuring i the displacement ofi Tail Rotor Actuators. This arrangement is used only for prototype testing of
helicopters for evaluation & certifying the Yaw control of the helicopter. The safety and functionality of
the Tail Rotor Actuators are not affected by this fixture. The fail safe criteria of helicopter are aiso
considered as a vital requirement. The fixture designed is not loaded as the total aerodynamic load of
the helicopter is taken over by the Tail Rotor Actuator. This measuring system does not come in the
load path; hence the fixtures will not fail in any case, therefore ensuring the safety and functionality of
the Yaw control system.
8) Detailed description of invention
Figure 1 shows the installation, assembled and unassembled views of measuring system. Linear potentiometer is used here to measure the displacement of Tail Rotor Actuator for the given YAW control input by the pilot. The three brackets help in holding the potentiometer firmly and in-line with the Actuator axis for measuring the displacement. The space available at the feedback lever attachment area of Tail Rotor Actuator is used for installation of the brackets. C-clamp and the L-plate used for locking the linear potentiometer with the Tail Rotor Actuator. The L-angle caters for arresting the rotation of the entire assembly along Z axis with respect to the Tail Rotor Actuator. All degrees of freedom are arrested except for the X-axis as shown in figure l{a). The measurement fixture is capable of arresting all five degrees of motion. Without the L-angle installed, the measurement system will
work but the arrangement tends to rotate about Z-axis which results in inaccurate measurement. The
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L-angle has a small curvature which rests on the cylinder of the Tail Rotor Actuator which arrests the entire measurement system from rotating along the Z axis. The other end of Linear Potentiometer is attached to the fixed bracket with fork end as shown in figure 1. The fixed bracket is attached to the top surface of the Tail Boom through inserts and bolts. The bolts used are wire locked to ensure positive securing on to the structure. The fail safe criteria of helicopter are also considered as a vital requirement. The failure in the displacement measurement system will not affect the functionality of the tail rotor actuator. The failure of any of the parts or the securing screws will not affect the functionality of the Tail Rotor Actuator. This ensures that the safety of the helicopter will not get affected.