Aircraft Systems: Simplex, Duplex, Triplex, Quadruplex, Dual-Duplex

This report provides a comprehensive overview of several critical aircraft systems, including Simplex, Duplex, Triplex, Quadruplex, and Dual-Duplex configurations. It begins by exploring the Simplex fuel nozzle system, highlighting its use in turbine engines and its components. The report then delves into the Duplex system, explaining its application in aircraft control and communication, emphasizing its role in transmitting signals between control centers and remote aircraft components, and discussing its evolution to reduce cable complexity and improve reliability. The Triplex system is examined in the context of redundancy in hybrid actuation systems, detailing its application in electric aircraft and the importance of dissimilar redundancy. Subsequently, the Quadruplex system is analyzed, focusing on its role in safety and redundancy in flight control systems, including signal consolidation and failure mode analysis. Finally, the Dual-Duplex system is presented, highlighting its use in fly-by-wire flight control systems in helicopters. Throughout the report, diagrams and examples are provided to illustrate the concepts and applications of each system.

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AIRCRAFT SYSTEMS
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Table of Contents
Topic Page
Simplex 3
Duplex4
Triplex7
Quadruplex 8
Dual-Duplex 10
References 13

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Simplex
The term Simplex in aircraft systems has significantly been used in the turbine engine fuel
system.
Simplex fuel nozzle was one of the first types of nozzles to be used in turbine engines, and it
was later replaced in most installations with a duplex nozzle, which was giving better
atomization at idling and starting speeds. Up to date, the simplex nozzle is still applicable in
several facilities in aircrafts. All the simplex nozzles consist of the nozzle tip, a strainer
which is made up of a screen of fine-mesh, an insert and support (Atkins, 2017, p. 345).
Gas turbines systems, particularly in the cases of aircraft engines, are greatly exacting their
demands for fuel nozzles. That is due to the high velocity which is experienced in the
combustion chambers in relation to the size of the combustion apparatus. For the purpose of
promoting proper combustion very high levels of fuel, atomization must be achieved (Austin,
2013, p. 254). There are many challenges of attaining consistent good spray and atomization
of the fuel. The diagrams below explains the simplex fuel nozzle into details.
Fig 1;the siplex fuel layout source www.jetairgroup.com

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Fig 2; Simplex fuel nozzle image source www.jetairgroup
The examples where the term simplex has been used in aircraft systems.
The term simplex has been used in the turbine fuel system, where it is used to explain a type
of a fuel nozzle.
Duplex
The term duplex has been widely used in aircraft systems as discussed below:
Aircraft duplex system
Aircraft duplex system refers to a system used for actuating transmitting and feedback the
signals between the control centre and the remote portion of an aircraft by the use of standard
wires. Operating signals from electrohydraulic valve and signals from a linear varying
differential transformer which is used in the monitoring of the valve operations mostly occur
in a considerably different frequency spans and they are transferred concurrently on the
ordinary wire (Cane, 2014, p. 34). Signal discrimination is usually accomplished by the
application of capacitors and inductors which are connected in series and also by use of

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reliance on the behaviour of a given control components.
Fig 3; Aircraft Duplex system source www.comtronics-aero.com/intercoms.php
This discovery relates directly to the control systems missiles and aircrafts, and it is
commonly used in the system which is responsible for transmitting, monitoring and
controlling signals within different parts of an aircraft.
To a limited extent, it is conflicting with the considerable attention which has been directed in
recent past to the reduction in weight and size of hydraulic and electronic components. For
operating and controlling Different portions of an aircraft, that considerable attention has not
been focused on a cable system for the purpose of transferring electrical signals between
different locations. In some cases is of great bulk and weight than that of the control
components. This challenge has been of the recent past been highlighted in the inventions
which are geared towards aircrafts are much better and safer (Dalamagkidis, 2014, p. 67).

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The main objective is achieving economy of operations.
Fig 4 ; Duplex connection layout source
www.comtronics-aero.com/intercoms.php
Further a lot of wiring which is encountered in aircrafts introduces a very complex problem
regarding the reliability of the aircraft. It is unquestionable that the bigger the number of
connecting terminal and connecting lines in a given installation, the more significant are the
chances of encountering faults. In a closed loop servo system, this is of great importance
since it is considered to be possible (Dillingham, 2012, p. 128). In the case of failure of the
response loop, for instance, that an uncontrollable or hard over conditions will be
significantly affected. It would be of great importance to have a system with components
which are controlled by a remote.
Fig 5 ;Control of duplex aircraft system source www.comtronics-aero.com/intercoms.php
The aircraft duplex system was invented with the main objectives of reducing the additional
number of cables within an aircraft installation. That can be achieved by utilizing the

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common lines mainly for the purpose of transferring signals to and from different control
components.
The aircraft duplex system is used as an object to give a system of wiring mainly for the
control system which in most cases is reliable than the initial systems which were used. It
also provides an economy of bulk and weight.
The duplex system provides an improved version for interconnecting a servo system with a
closed loop which comprises a linear variable differential transformer and an electrohydraulic
valve which are located at the aircraft electronic bay and the control station (Kempinski,
2015, p. 124). The aircraft duplex system comprises many features which are used in the
transmitting of signals from one point of the aircraft to another.
Example where applicable in the aircraft systems.
The term duplex has been used in the control and communication systems of the aircraft. The
term has been used in a system to transmit the signals between the control system and the
remote area.
Triplex
The term triplex has been widely used in the simulation and modelling of redundancy hybrid
auctions system. This triplex system conforms to the future development trends in the electric
aircrafts. Triplex redundant hybrid actuation comprises of the traditional servo which is a
valve controlled hydraulic actuator, electro-mechanical actuator and an electro-hydrostatic
actuator. The operating principles and structure of this system are represented as a
mathematical simulation model.
The requirements of reliability and safety are much higher than the ones which were observed
initially. To meet the needs of security and safety increasing the number of redundancy is not
enough. Dissimilarity in all the redundant is required which is known as hybrid actuation is
highly required. In most cases the power-by –wire is the best. Below is a schematic diagram
showing the triplex Redundant Hybrid Actuation system.
Fig 4 ; triplex Redundant Hybrid Actuation system source www.jetairgroup.com

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During the modelling of the system, the following are determined to enable come up with a
system which works efficiently without any challenge.
The equation for electromotive, torque balance, back electromotive force, load torque, flow
control and flow continuity equations (Krieger, 2016, p. 82). For the purpose of reflecting the
actual feedback of the system, it is compulsory that the whole system is built in the LMS .in
figure 2 the various modes of operation are simulated and analysed.
Fig 5 ; TRHA system layout source www.jetairgroup.com
As a result of physical principles which were much different from the actuators which are in
most cases used in the triplex redundant hybrid actuation and the various loads which are in
most cases characterised with the uniqueness in the load driving.
Examples where the term duplex has been used in the aircraft system.
The term duplex is used in many aircraft systems such as the aircraft flight control system,
fuel and turbine system. In the Aircraft flight control system, the term is used when
explaining the fly-by-wire control system which is used in the control of flying aircrafts and
helicopters (Langton, 2016, p. 342). In the case of the turbine and fuel system, the term is
used to explain a type of fuel nozzle.
Quadruplex
The term Quadruplex in aircrafts and Helicopters has significantly been used in the safety and
redundancy system. The systems quadruplexed that is four different channels are used to
prevent the loss of a signal where there is a failure of either one or two channels.
Increasing the number of redundancy to be four separate lanes of aircraft flight control
system would be compulsory if the logic voting was applied and persistent augmentation

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succeeding two failures was considered essential (Langton, 2011, p. 397).
Fig 6 ; quadruplexed system channels source www.jetairgroup.com
The Quadruplex system may be small than expected that is due to the complex mechanicals
which is involved in this redundancy level, in particular, that is because the rotorcraft does
not have many ways of generating regulating moments and forces about a specific axis. A
Quadruplex digital aircraft flight control systems which have self-monitoring will only be
fitted in aircrafts which have catastrophic failure modes. Based on the MTBF component of
1000 hours, it would be seen that the theoretical probability of total failure will be 7.1X 10
per hour (Valavanis, 2017, p. 45).
Signal consolidation
All the systems of the aircrafts consist of split lanes of aircraft flight control systems, and
they are joined at the central servo jack. Different architecture arranges all the sensor signals
to move to all the computers, and the computers are programmed to drive all the actuators.
This works to ensure that the system availability is improved that is due to the lane with a
failed component can go on to operate by application of signals which are obtained from the
surviving components in the remaining lanes (Piegl, 2015, p. 623). Even though the
reliability is not altered in any way. Indeed there will be a significant improvement this is
because the frequent failures which occur or the frequent failures which are not the same in
different lanes will be considered very essential the integrity of the ATCS is questioned
(Seabridge, 2012, p. 54).
Fig 7 ; quadruplexed Signal consolidation diagram source www.jetairgroup.com

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Failure modes, criticality analysis and effects
The Quadruplex system has been greatly simplified and has been made to ignore the
hydraulic/electrical supplies and free sensor package to each line. The actual systems usually
are very complicated with the accurate system architecture which varies with the type of an
aircraft or the type of AFCS manufacturer formerly a Quadruplex system can still give
augmentation following a wide range of many failures but all at a degraded level which is
within reduced flight envelope (Rigby, 2013, p. 453). In addition to that optional sensors can
be used to in a provision of a synthetical signal when the primary sensor fails.
To assess the aircraft flight control system detailed knowledge for the intended mode of
operation and the system architecture is required. Failure modes evaluation and critical
analysis are usually carried out to investigate the likely impact of all the possible failures to
ensure the soundness of any degraded assessment modes which are typically conducted as
flight test program (Moir, 2015, p. 65). Because of the short time which is usually available
only the cases which have a more significant possibility of happening will undergo a flight
assessment. Many failures can lead to loss of primary sensor in a Quadruplex system such as
the vertical gyro.
Fig 8; The Quadruplex Brushless motor layout source www.sciencedirect.com
The example where applicable in the aircraft system.
The term Quadruplex has been mainly used in the flight control system of aircrafts. The
Quadruplex Brushless DC motor which is based on a position servo system. The Quadruplex
brushless motor which is used in the aircraft control system can offer high power to the
motion velocities and weight ratio. The Quadruplex BLDC motor usually provides very high
redundancy for the actuator (Piegl, 2015, p. 56).
Dual-Duplex
The term Dual-Duplex in aircraft systems is used t in the fly-by-wire flight control in the
main rotor of a helicopter.
Currently, the fly-by-wire control system is widely used in the primary and secondary control
of flights of wing aircrafts for the case of rotary aircrafts they make use of dual-duplex
electrohydraulic systems in the fly-by-wire flight control system (Mirot, 2017, p. 45).
The Dual-Duplex fly-by-fly wire system.
This system is based on two systems of hydraulics and also four electrical lanes with the two
electrical lanes relating to one hydraulic system. As shown below in concept block diagram.

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Fig 9; The Dual-Duplex fly-by-fly wire system. Source www.sciencedirect.com
Each of the four FCCs is tasked to perform closed loop control of the position of the actuator
that is achieved by comparing the input command which is established by aircraft control
system with the actuator position (Lombardo, 2016, p. 432). The control system of the fly-by-
wire electrohydraulic system is clear explained by the block diagram below.

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Fig 9; control system of fly-by-wire system. Source www.sciencedirect.com
Examples where the term dual-duplex.
The term dual-duplex has been used in many aircraft systems such as the aircraft flight
control system. In this case, the term is used to explain how the two hydraulic systems relate
to the four electrical lines.