Analysis of Helicopter Flying Control Systems and Subsystems

This report provides a detailed overview of helicopter flying control systems, encompassing both primary and secondary systems, also known as subsystems. It delves into the functions and components of various control systems, including the stabilator, ailerons, and rudder, as well as subsystems such as leading-edge devices, trim systems, propellers, and spoilers. The report examines the fuselage, main rotor system, and the three major controls: collective pitch control, cyclic pitch control, and anti-torque pedals. It explains how each control affects helicopter flight, including changes in pitch angle, rotor speed, and aircraft direction. Furthermore, the report highlights the mechanical components, such as ailerons, elevators, and rudders, that enable precise and reliable aircraft control. The report also explores the Health and Usage Monitoring System (HUMS), emphasizing its role in recording system conditions for proactive maintenance and safety improvements. The conclusion stresses the significance of fault detection in aircraft control systems, especially in military helicopters, using physical and analytical redundancy for enhanced safety and operational efficiency. The report is supported by several academic references.

HELICOPTER FLYING CONTROLS SYSTEMS AND ASSOCIATED
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Describe the operation of the Flying control Systems or sub system and the function of
its components within a helicopter and associated components.
Introduction
Helicopter control system is normally made of secondary and primary systems. The secondary
systems are also called subsystems. The control systems constitute stabilator or elevator,
ailerons, and rudder. The subsystems are made up of the leading edge devices, trim systems,
propellers and spoilers. These systems are meant to improve the performance properties of the
helicopter as well as relieving the pilot of the excessive forces for the control(Khoshlahjeh and
Gandhi 2014). This particular paper seeks to highlight some of the control systems and relevant
components of the helicopter
Fuselage
This is the outer core of the airframe main body which functions to house the cabin that is
responsible for holding the crew, cargo, and passengers. The cabins of the helicopters have a
variety of the sitting arrangement with the majority having pilots seated on the right side.
Main rotor system
The rotating parts of the helicopter are called the rotor system. The rotor system is responsible
for the generation of the lift that is required by the aircraft. The rotor system is made up of rotor
blades, mast, and hub. The mast is actually a hollow cylindrical component that usually extends
upwards. There is an attachment at the top of the mast called hub. The blades of the rotor are
then attached to the hub by the use of different techniques.

Figure 1: Components of the helicopter rotor system(Khoshlahjeh and Gandhi 2014)
In the helicopter, there are usually three major controls that the pilot must put into use during the
flight. They include ant torque pedal, cyclic pitch control and finally collective pitch control.
Collective pitch control
This kind of control system is located on the left-hand side of the captain or pilot's seat. Its
operation is usually done by the left hand. This kind of control system is used to introduce
changes in the pitch angle of the primary rotor blades. Such operation is carried out
simultaneously(Rotaru 2013). When the collective pitch control is raised the pitch angle
increases for all the rotor blades. The reverse happens when it is lowered. When the pitch angle
is changed, the angle of incidence also changes to affect the drag and this the rpm is altered. As
the pitch angle increases there is a subsequent increase in the angle of incidence and finally the
drag increases. This lowers the rpm(Tan, and Wang 2013)
In order to effectively have a constant rotor rpm as required by the helicopter operations, there
will be a requirement of a proportionate change in power so as to compensate for the drag. This
compensation is achieved by the use of a subsystem like the governor.

Figure 3: Use of collective pitch control (Khoshlahjeh and Gandhi 2014)
Cyclic pitch control
This is usually projected upwards from the floor of the cockpit. This flight control system allows
the pilot to have the helicopter flow to any direction of travel. The function of the cyclic pitch
control is to assist in the tilting of the tip-path plane in the desired horizontal direction. It controls
the thrust of the rotor disc against the horizontal influence thus allowing the pilot to control the
direction of the travel.
Figure 4: Cyclic pitch control system(Khoshlahjeh and Gandhi 2014)

Anti-torque Pedals
These are located at the floor of the cabin at the feet of the pilot. The Anti-torque Pedals allows
for the change of the pitch angle of the tail rotor blades which will eventually put the aircraft in
the longitudinal trim. At the hover scenarios, the pilot can turn the plane to 360 degrees.
Figure 5: Anti-torque pedal(Khoshlahjeh and Gandhi 2014)
A control system is basically a collection of electronic equipment and mechanical components
which allow the aircraft to be flown with the exceptional reliability and precision. The control
system is made up of sensors, cockpit controls, and actuators. The mechanical systems of control
are made of aileron, rudder, and elevator as the main components. The ailerons are used in the
control of rolling of the aircraft. They control the roll angle(Khoshlahjeh and Gandhi 2014).

Figure 6: Cyclic in the roll angle control(Khoshlahjeh and Gandhi 2014)
The elevator component is used in the control of the pitch angle. In order to climb, the pilot will
pull the control stick back.This will result in the deflection of the elevators. Also, this causes the
airflow to push the tail down and the nose up hence the pitch angle is increased. In order to dive
the pilot will push the stick forward so that the elevator can deflect downwards(Punjabi and
Abbeel 2015). This makes the airflow to lift the tail while pushing down the nose hence lowering
the pitch angle.
Figure 7: Demonstration of collective in pitch angle control(Khoshlahjeh and Gandhi 2014)

The rudder is used in the turning of the aircraft right or left a process called yawing. In order to
yaw to the right or to the left, the pedals of the rudder swivel on the tail but in the direction of the
specific turn.
Figure 8: Yaw angle control(Hu, Du and Zhang 2016)
Health and Usage Monitoring System(HUMS)
A Health and Usage Monitoring System(HUMS) functions to record the conditions of the critical
systems as well as components on the helicopters. By so doing, it is possible for the rectification
to be achieved before adverse effects are reflected on the operation safety. The equipment that is
on board stores data on a special card of PCMCIA. A typical type of HUMS has sensors that are
distributed throughout the airframe as well as its components which are connected or linked to
the central computer with system of data recording and storage. The monitoring trend of the
computer the computer allows for the determination of aircraft possible faulty areas for
rectification processes((Hu, Du and Zhang 2016).

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Conclusion
The operation of any aircraft is initiated at the control system. The control system of the aircraft
is thus regarded as the “brain” of the aircraft. Considering the advances in the technology and
the need for complex operating systems, the fault detection becomes each time more important in
the aircraft control systems. If the fault can be detected, the safety levels will be better. This is
because one the causes of the fault are detected the corrections can be done quicker thus
preventing the occurrence of the incorrect system operations.
Most of the accidents o of the aircraft can be controlled. In the case of the military helicopters,
the first step that is used in the fault detection is based on the physical redundancy that involves
installation of multiple sensors(Vu, Lee and Shu 2013).
These sensors are meant to be used in the measurement of the same physical quantity. Any
significant discrepancy between the measurements is an indicator of the sensor fault. The
analytical redundancy which takes the measurement from the sensors is compared with the
signals originating from the models of the system. This will launch a system of alarm as a result
of the signal residue hence allowing for the corrective measures to be taken.

References
Hu, Y., Du, F. and Zhang, H.L., 2016. Investigation of unsteady aerodynamics effects in
cycloidal rotor using RANS solver. The Aeronautical Journal, 120(1228), pp.956-970.
Khoshlahjeh, M. and Gandhi, F., 2014. Extendable chord rotors for helicopter envelope
expansion and performance improvement. Journal of the American Helicopter Society, 59(1),
pp.1-10.
Punjabi, A. and Abbeel, P., 2015, May. Deep learning helicopter dynamics models. In 2015
IEEE International Conference on Robotics and Automation (ICRA) (pp. 3223-3230). IEEE.
Rotaru, C., 2013. Nonlinear characteristics of helicopter rotor blade airfoils: an analytical
evaluation. Mathematical Problems in Engineering, 2013.

Tan, J.F. and Wang, H.W., 2013. Simulating unsteady aerodynamics of helicopter rotor with
panel/viscous vortex particle method. Aerospace Science and Technology, 30(1), pp.255-268.
Vu, N.A., Lee, J.W. and Shu, J.I., 2013. Aerodynamic design optimization of helicopter rotor
blades including airfoil shape for hover performance. Chinese Journal of Aeronautics, 26(1),
pp.1-8.