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Fluid Power Generation in Aircraft

Discuss about the Foundations of Professional Airmanship.

There is three major power generation in the aircraft which aid in the effective movements and operations of the aircraft.  These methods of power generation include the electrical power generation, mechanical power generation and lastly mechanical power generation.  In this section, we shall focus on the different properties of each one which makes it realize its generation quality. These three methods of power generations cannot be substituted by either since the power they generated are not the same. For example, electrical generation gives the power which can be used in lighting, mechanical gives the power which can exclusively apply in rotating moving part. The methods above of power generation can be used in conjunction to form one big generation system but most cases there are used differently.

In aircraft, fluid is highly applied to help generate power which is used in the plane for a different function. The fluid power is used when the plane is landing and also during the movement of the aircraft. The below are some of the characteristics of power generated by fluid, or hydraulic, the fluid used in the aircraft is usually brake fluid, water-glycol mixture or water soluble oil[1]. Hydraulic is supplied to the motor which is then converted into a mechanical output used to perform a specific duty of work on load or even to rotate the turbine for some cases which are used to rotate the rotor part. The fluid power system is more flexible than the other due methods of power generation, and it can create more than such system of the [i]equivalent size.  This method of power generation also give a rapid and accurate responses to the controls. For this reason, fluid power systems are extensively used in present aircraft.

However, electrical power generation is lighter because of the lighter cables used but still in fluid the ratio of the power to weight for an electrical power system is much lower than fluid actuators[2]. Some special types of actuators known as the conventional linear Actuators (CLA) and some smart fluid sensing actuators which help in sensing and controlling the fluid valve to improve the performance.  The efficacy of pump applied in the fluid is very high since it is only driven when the actuation is needed Electro Hydraulic Actuator are in a range of aircraft which comprises the flight control operation surface actuation[3].  Electro Mechanical Actuators also provides the aptitude to stimulate onto the electrical bus, though it is not presently permitted.

Electrical Method of Power Generation

So in the methods above of power generation used in the aircraft, fluid power generation employs mostly the use of flowing liquid to help rotate parts including the turbine which helps to create power.  This makes the backbone characteristic of fluid power generation and fundamental of the operation of the fluid power generation. This method of generation system employs a lot of pressure pump which helps to push the fluid to the required destination. For the fluid generations, the path by which the fluid will flow is made very narrow to make the fluid flow at a high rate hence the speed will also increase. The fluid power in aircraft is applied in many parts in the aircraft like in fuels systems and breaking systems. These characteristics are very clear and highlighted as below;

The actuators are what do the final work of the fluid power; the system components are grippers, rotary actuators, and cylinder. Pumping machine that is a pumping device or an air compressor which is responsible for providing the fluid power into the entire fluid system. Sustain mechanisms that guarantee the fluid power is effectively used; the different components are the reservoirs, filters, and heat exchangers. Valves which manages the movement of the pressure and fluid flow in the whole system. The fluid powering system is mainly composed of the fluid which moves in the system and the valves and the pumps which pump the fluid through the pipes. The system also operates at a higher pressure to ensure that the fluid is effectively moving to reduce the obstacles like the gravity.

Electrical power in the aircraft is due to many parameters which make it true and fully realized in its generation.  It generation becomes a reality because of the inventions of the Michael Faraday which also has a law of the cutting of the magnetic flux with a conductor or vice versa. When either magnetic flux is cut using conductors the electricity is induced and also if the conductor cuts the magnetic flux the voltage is induced. This voltage can either be stepped up or down.  From the basic operation of electricity, we can thus get the nature of the electrical power which help in the comparison with others.

The generation is by the alternators or generators which give an AC, but this form of electricity can be as well be converted to a DC by the help of a diode. 

Mechanical Power Generation

The alternating or generators generates electrical power for performing the operations in the aircraft avionics equipment. This generator can use the mechanical power from the rotating rotors, slip rods, armature to help generate electrical power which will be applied in the aircraft for different operations like lighting, avionics among others. Some of the conspicuous characteristics of the electrical power include the following;

  1. Electrical power include the voltage controlling parts which may include the transistors like the MOSFET, BJT
  2. AC power is generated from a generator which has a rotor consisting of the moving parts of the generator like the armature and the stator which consist of the immobile parts like the field windings which develops an electromagnet which is also temporary magnet
  • The alternating current generators have the rotor or the generator field which primarily functions as a rotating magnetic field thereby providing some constant polarity.
  1. The electrical power generated will be operating at a specific frequency depending on how the production took place (nature of the generator like the number of poles used during the generation of electricity).
  2. The alternating current generators also control the voltage by regulating the strength of the magnetic field during production. The strength of the magnet is made possible by varying the flux which is proportional to the field current. And once the field current is varied then the voltage produced is also varied. 
  3. The AC electrical power generated is also stepped up or down depending on what is required. The stepping up and down is done by the help of a transformer.
  • Electrical power is always produced in AC form for the aircraft but not that in all situations the power is used in this format. Some case it is used in DC form, so the power is rectified by the help of diode. These diodes can build it make either a full wave rectifier or a single wave rectifier.

All components in mechanical power generation are a solid state which just rotates hence their power efficiency is relatively high because power losses are reduced. Electrical power exclusively uses electrical devices like inductors, diodes and some case we can use thyristors- Diac and Triac which are used in power electronic in the generation and transmission of electric power in the aircraft.  In all the above methods of power generation, it is the movement of particles is common, in the fluid it is the fluid which moves at high speed to create a high pressure required in the aircraft.  In electrical power generation, the movement involves the movement of electrons which help creates the flow of electric current. While in mechanical power the movement involves the movement of the rotating machines and the reciprocating movement in parts like in the cylinder.

The main components of mechanical power generation include the power transmission which is done by the help of drives, gear belts, pulleys, chains among other ways of transmitting power. The mechanical power at different torque can be used to produce electrical energy like turbines used to generate electricity. Sometimes the mechanical generation of power can just generate motion which is used to operate some moving parts.  Mechanical power generation is very important since the generated by this method is very great and can perform very heavy duties. Sometimes flywheel which is mechanical is used to operate when the electrical power is switched of just because of the momentum.

In the design of the hydraulic power there are some factors which must be considered.

In the tube sizing we have three different forms return lines, pressure line, and pump suction line. The power generated is a factor of the pressure and the size of the tube. This is higher controlled by the Bernoulli’s principle. And when the pressure is so high a thick tube is required to ensure that the tube does not burst, this provides a great safety during the operation of the aircraft. 

The selection of tubing size for return line and pressure highly depends on high analysis which is pegged on energy loss on energy loss against cost and the weight of the components as well.  Larger tubes will transmit fluid at a low pressure while smaller tube will transmit fluid at a higher pressure and the tubes must be very thick (weigh more) hence they are costly. Generally, tubes must be relatively large in all design considerations. With relatively large tubes harmful dynamic pressures due to high fluid velocities are avoided. The below figure shows a prototype of hydraulic system pressure cycle.

Design Factors for Hydraulic Power

During the operation of actuator loads, rate and aircraft, the temperature must be defined in the design. Allowable pressure losses at different pressure losses and the working temperature of the system must be determined as well. The tube lengths for installation and tube size needed in the aircraft must thus be calculated from the above requirements. The specification and calculation in this design is done mainly by considering the usage of the below Darcy-Weisbach equation;

This formula can be reduced to these different forms;


F= friction factor (no dimension)

L= length of the tube given in feet.

Q=Fluid flow rate (gallon per min).

S= Fluid specific gravity

ΔP= pressure loss (pound per square inch)

The value of f changes as the function 0of Reynold number 

The below equations shows the relationship between Reynold number and friction factor for both turbulent and laminar flow.

For laminar flow 

For turbulent flow:

Reynold number NR is a dimensionless which can be as well expressed as below;

When the rate of fluid flow (Q) is substituted for velocity (v)   and specific gravity ( s) for mass density, the outcome is the following equations.

For a straight tubing , laminar flow will be predominant for values of NR of about 1400 and then becomes fully turbulent beyond 3600. In normal operation temperatures, high flow will require aircraft hydraulic system which will result in turbulent flow. The friction factors of turbulent and laminar flow can be obtained from the below equations.

The following equations can be employed to calculate the change in the size of tubing diameters which are needed to convert an existing fluid system for use with a CITE fluid.

From the above equations, we can obtain the hydraulic power; these equation analyses help us to know the friction losses in each pipe which convey the fluid. After determining these parameters, we will hence pass the fluid to the turbine which will be used to rotate the turbine and generate the motion. The size of the turbine will depend on the load to driven and the fluid pressure from the pipes containing the fluid.  The turbines must be fully be constructed in an enclosed system with a highly thick and strong structure to ensure that there is no bursting of the pipes or breakage of the system which may cause an accident during the operation in the generation of hydraulic power.

Choosing the correct servo/actuator system for good working of large aircraft control surfaces. Actuators system performs an important role in the control of flight surfaces in aircraft because of their workings assurances the safety of the aircraft and all the passengers on the flight. Safety is very important in the aircraft (john, 2014).  The actuators convert electrical signals into mechanical motions of various aircraft parts. The Actuators systems are applied to the landing gear, flaps or the weapon systems for military aircraft, among others.

System Pressure and Return Lines

In large aircraft which would possibly contain so many passengers or goods, selecting the best choose the best actuators to ensure that the control for such big and heavy aircraft is fully controlled by that actuator (Russell, 2001). The actuator must consider the below parameters like small size thus diminishing the aircraft's weight and bulk which make sit light hence it will become very easy to control by the help of the actuators. It should resist high vibrations while getting high dynamic forces. Furthermore, the actuator system must contain valves that are mostly vital during the time of emergencies as they interrupt the smooth flow of the fluid. Lastly, the system develops a minor inertia at a high acceleration of the aircraft

There are several of actuators which consist the hydraulic actuators and electric actuators with the hydrostatic transmission of power; hydraulic actuators uses the fluid which electrical uses electricity for the control (Sheehan, 2016). A good actuator system for the landing gear is a twofold actuator that combines both the type above (electric actuator and the hydraulic actuator). This is true since there will ensure redundancy. The application of the two aforementioned are in most cases used as a combination, but when electric actuators are used alone, they lack the valves thus it may not quite be very effective during emergencies.

For big aircraft airspeeds during landing must be maintained notwithstanding the wings being not designed to allow this, so there is a quick need for better actuators the need for a good actuator system. The wings of large aircraft are always unable to develop a suitable amount of lift to make the aircraft balances in the air before landing. Therefore, the forgone actuator to counter applies to retractable flap actuators. The actuators in the most scenario are placed outside the aircraft around the wings, but for a few, they are put inside around the wings.

The servo valves have some of features like; lands and port number – this can either be a three port or a two port, but in this article, I have chosen to use a three port, these valves also have valve sleeves. These sleeves must be correctly fitted with a well-matched pressure inside and outside the pipe.Servo valves also have dynamic pressure feedback is applicable as at low frequencies it works as position feedback.

 There are some parameters which always define a working of actuators in most systems. These parameters may judge if an actuator is effective or not, and these parameters are what make them be advantageous actuator some of these parameters include the following:

  1. Ultra low power consumption – Electro-hydraulic actuator contains fitting of a low power position controller. This makes the actuator to work effectively on a low power consumption.
  2. High operating speed- The electro-hydraulic actuators have a great speed of moving a heavy load within a very short time, for example, these actuators can move a thrust of about 900kg within a distance of 60 mm in a very short period of just forty-five  millisecond. This high-speed make these EHA more effective than electro mechanical actuators.
  • Precision: EHA is more accurate since most of the fluid used are incompressible, so the loss is highly reduced. They work up to about 5 microns. This gives more accurate operations than the electro mechanical where losses are many due to frictions.

But still, this actuator faces some drawbacks which make it not to reach hundred percentage effective operation. These drawbacks include allowable tolerance which will lead to higher cost of hydraulic components used in the construction of the system another drawback is that with the use of hydraulic fluid, there is a upper-temperature limit imposed. This temperature limit must be kept since if it is exceeded, then the system will not work effectively.


In conclusion, there are three major methods of power generation in aircraft, all these help in the provision of power used in different parts, these methods like electrical are always used to power the engine of the aircraft and also to provide the lighting in the aircraft.  The fluid method uses mainly fluid and the pump which makes it move in a very narrow pipes to help increase the pressure of the fluid. The power in the fluid is majorly used in the braking system and fueling (A., 2012).

The electrohydraulic systems have high efficiency. The efficiency is applicable in the conversion of electrical energy into useful work[4]. The conversion is done to become a linear thrust output or a torque output with high flexibility. The electro-hydraulic systems can be made from a huge range of components evident for actuator formation. Therefore a range of equipment easily meet the standard needed and the special applications.

The design of the power distribution in aircraft is very strategic and is treated with great care to ensure that any fault which may result in an accident which may be fatal is avoided at the source. The operation of the electro-hydraulic actuators gives the best working system of a high-speed, more accurate. And these are realized because of the nature of the fluid is in most cases used in the operations.


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Machado, R. (2015). Rod Machado's Instrument Pilot's Handbook. London: Aviation Speakers Bureau.

Mchapakuni, T. (2011). Flight Discipline. London: McGraw-Hill Professional.

Nagel, D. C. (2015). Human Factors in Aviation. Beijing: Gulf Professional Publishing.

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