Power Distribution in the Conventional Aircraft - Essay Example

The modern trends in aircraft hydraulic system Name University School Course Assignment Title Date The modern trends in aircraft Hydraulic system Introduction Traditional air crafts relied on three sources of power to run their systems and subsystems namely the hydraulic system, pneumatic system and the electrical system. These systems of power generation worked in consonance with the well-distributed system functionalities ensuring that the system functions have optimum redundancy thus securing the safety of the flight. The hydraulic systems are useful in driving the control systems of the flight as well as the aircraft’s landing gear system. These systems comprised of servo-valves, servo-actuators, power cylinders, solenoid valves, hydraulic motors, orifices as well as check valves, which have very close similarities with industrial hydraulic compositions (Zhanlin & others, 2000). The aircraft’s hydraulic system had the capacity to generate pressures of 20.7MPa until the late 1970’s when hydraulic systems generating 55.2MPa were developed. Currently, manufacturers of hydraulic products have commercialized highly pressurized hydraulic components for the air crafts. Highly maneuverable air crafts apply hydraulic systems that generate a standard 34.5MPa. Several adjustments continue to find their way to the evolving hydraulic systems with more shifting towards electrifying the aircraft system while progressively reducing the use of hydraulic systems (Cao, Mecrow, Atkinson, Bennett, & Atkinson, 2012). Power distribution in the conventional aircraft Conventional air crafts use engines to convert fuel into power a significant proportion of which propels the aircraft while the rest is converted into four forms. Pneumatic power generated from high-pressure compressors in the engine is useful in powering the Environmental Control System (ECS) while supplying hot air to de-ice the wings. Secondly, the gearbox conveys mechanical power generated by the engines to localized pumps serving the engines as well as other subsystems that rely on mechanical power, and the main generator for electricity production. Thirdly, hydraulic pump supplies hydraulic energy to the actuators for powering both the primary as well as the secondary control of the flight. Lastly, electric power produced from the main generator drives the avionics, aircraft and cabin lifting, galleys as well as other systems including entertainment systems (Cao et al., 2012) . Figure 1: Distribution of power in a conventional aircraft The need to improve the performance of the aircraft's power system, enhance reliability, and reduce the maintenance costs of air crafts birthed the concept of more electrified air crafts (MEA) with remarkable modifications from the original systems. The shift to MEA was also informed by the need to create a more efficient system that weighs less as compared to the hydraulic systems. In addition, the maintenance requirements for hydraulic systems remain high and they are more vulnerable to security risks. Reduction of weight is useful in cutting down the energy requirements for the aircraft translating to manageable user costs. The commencement of using electrically powered systems has seen the reduction of energy requirements for the air crafts by half. This is very crucial especially for the military departments that consume huge proportions of the national budget on powering their airborne systems (Emadi & Ehsani, 2000). The use of electrically computerized control systems replaced the use of mechanical signals from the pilot while controlling hydraulic servo actuators used in flight control. This allows for the conversion of electrical signals to hydraulic signals thereby amplifying power control of actuators. Upon improvement of the characteristics of electric magnets in the 1990s, direct drive valves (DDV) that rely on force motors from an electric coil began serving as hydraulic servo-valves. However, procurement of DDV is very costly thus forcing most of the large air crafts to continue relying on EHSVs as servo-actuators (Peeters, Hendricx, Debille, & Climent, 2009). Comparison between electric and hydraulic actuators Following the increase of system pressures to 34.5MPa, the reliance and maintenance of hydraulic systems for air crafts stabilized. The electrical systems of power supply contribute about 270VDC of power thus making the current reduction in electric controllers and actuators possible through the provision of high power voltages to the supply systems. The costs for producing electric actuators are tapering downwards whereas their reliability is being improved. Consequently, this led to the commencement of progressive replacement of hydraulic actuators with electric actuators for primary control of flight systems in new air crafts (Moir & Seabridge, 2011). Electric actuators have comparable performance to hydraulic actuators thus providing an option for aircraft manufacturers to consider while installing the system with considerations to costs, ease of maintenance, the weight of the systems, and source of power redundancy. On the other hand, electric actuators require constant supply of electricity in order to maintain the actuator in position with application of an aerodynamic load while in use in primary control of a flight whereas hydraulic actuators can maintain an actuator’s position under similar circumstances as long as the control valve is closed thus maintaining the cylinder’s differential pressure. Unlike electric actuators, hydraulic actuators allow an opportunity to obtain a damping effect whenever there is a system failure through the utilization of bulk amounts of hydraulic fluid as well as restricting its flow through the orifices (Bu & Yao, 2000). Advancements in hydraulic systems The control systems for modern flights are highly pressurized and made more electrical with the conversion of electrical commands to hydraulic commands using motors. Significant progress has been made in the research for materials that can directly convert electrical signals to mechanical signals. These active materials have the potential for serving as actuators in shutoff valves, small-sized hydraulic pumps, and servo valves. They include electrostrictive elements and piezoelectric elements, which give an optimal response at higher frequencies. Application of these materials to hydraulic systems confers several benefits in improving the functionalities of the systems. In this case, electromagnetic coils are applied on the superior part thus allowing the production and conveyance of magnetic currents initially propelling the flapper (Goharrizi & Sepehri, 2010). Secondly, the movement of the flapper consequently alters the pressure fields on both sides of the valve thus amplifying the control pressures moving the servo valve's main control valve. The possibility of applying active materials on this portion is made possible by the fact that the electrical magnet mildly displaces the base of the flapper. Piezoelectric stacks are the most preferred for use in electro-hydraulic servo valves (EHSV) because the response frequency of EHSV falls between 10-200 Hz and that the electromagnetic part controlling the EHSV should be as small as possible (Márton, Fodor, & Sepehri, 2011). Piezoelectric elements produce sufficient force and displacement for stabilizing operations. However, their vulnerability to forces of tension hence can cause stacks' avulsion in the force of extreme tension. The use of piezoelectric elements in combination with compression forces reduces this unwanted effect, which has no known effect on the deflection properties of piezoelectric elements. The current trend involves designing the piezoelectric stacks with compressive forces to enhance the durability of the stacks and the system at large. The use of piezoelectric stacks in the aircraft’s hydraulic systems requires more evaluation of the power consumed, and the environmental requirements as well as their durability (Cao et al., 2012). Lightening the system for reduced consumption of energy Reduction in the weight of the aircraft is useful in lessening its energy consumption hence lower user costs. The American Airlines made savings of up to $1.2 million on fuel expenditures by using an iPad instead of the traditional paper manual. Electric actuators only convert energy once as opposed to the hydraulic actuators that use two energy conversions hence the weight of the former excludes that of the components required in the second energy conversion. Analyzes by Boeing clearly show the weight reductions associated with electrified technologies translating to reduced fuel consumptions (Jelali & Kroll, 2012). Military and defense are at the forefront of fuel saving initiatives for reduced operational costs and recently, electric actuators are finding their way to vehicles used in ground combat. Electric systems possess low weight compared to hydraulic systems because they are not piped, lack hydraulic fluid and power units. In addition, the system only runs when in use, unlike hydraulic systems that need the pump to run continuously (Goharrizi & Sepehri, 2010). Increasing the efficacy and reliability of the system for performance improvement In the traditional aircraft, hydraulic and pneumatic systems drive the non-propelling systems, a function being progressively eliminated by electric actuators. Magnetic materials with high performance, power electronics as well as gear technology have given electric actuators more competitive advantage than hydraulic actuators. Original equipment manufacturers (OEMs) for air crafts in collaboration with suppliers have shifted their operations to designing frameworks for air crafts that are more electric (Márton et al., 2011). The majority of the new air crafts rely on electric actuators as spoilers, flight control system as well as flaps thus replacing the previously used hydraulic systems. Boeing 787 is amongst the initial air crafts using the "more electric aircraft" concept that completely eliminated pneumatic systems resulting in improved efficiency by eliminating the need shaft to pneumatic engine power conversion. The engine serves as the source of electric power for the aircraft thus allowing an efficient mechanism for de-icing wings, secondary control of flight actuators, pressurizing the cabin system, operating the brakes of the aircraft as well as the engine starter system (Jelali & Kroll, 2012). The electrically driven system provides a wealth of real-time data via motor controllers as opposed to the hydraulic systems that only infer feedback via a hydraulic signal. It is easier to link electrically powered systems to remotely located diagnostic systems, which provide simplified diagnostic information on any faults established on the flight system. Essentially, using electric actuators has significantly improved the efficiency, efficacy, and lifespan of the systems and provided a more flexible platform for design modification that translates to reduced operational costs for the air crafts (Cao et al., 2012). Design simplification for reduced maintenance costs The new electric actuators allow for more accuracy in controls as well as gear repeatability coupled with a quicker reaction time. They have improved the reliability of the system by eradicating the functions of the solenoids, hydraulic power unit, hydraulic couplings, valves for directional control, pressure sensors, filters, accumulators as well as any moving parts in the control systems. They have a simplified design ensuring the system hardly experiences any downtime and do not require the replacement or disposal of hydraulic fluids (Jelali & Kroll, 2012). Consequently, the chances of mechanical failure are minimized by the simplified electrical systems. Moreover, the electric actuators are more reliable putting a lesser burden on the personnel involved in their maintenance. The installation of the actuators has been simplified requiring less time and their use does not vary with pressure changes as the case is with hydraulic actuators (Zhanlin & others, 2000). Electric motors allow for a design that is compact, quiet and has a high density through the integration of frameless electric motors in the valves. The frameless motors encompass distinct stator and rotor, housings as well as feedback devices integrated directly into the aircraft's design. These components help in getting rid of components that are noisy and require high costs to maintain such as couplings and gearboxes. Designing the device as part of the machine allows the system to function akin to a closed loop servo. Running of the motor and management of the feedback devices is made possible by an electronic amplifier. The reduced noise production afforded by the frameless motors confers many benefits while in the enclosed spaces within the aircraft (Jelali & Kroll, 2012). Reducing risks for improved safety of the air crafts Electric actuators eradicated the pumping system in hydraulic actuators thus fewer maintenance requirements, less susceptibility to leakages, and do not require any fluid disposal. Hydraulic fluids are potential sources of health risks arising from possible inhalation, ingestion, contact with eyes as well as the skin. The fact that electric actuators cannot leak at any time due to the absence of any form of tubing and fluids further reinforces their reliability for use in air crafts. This promotes the safety of the aircraft crew and any passengers on board due to minimal exposures. Moreover, electric energy is clean and environmentally friendly unlike the power generated from the hydraulic systems with significant amounts of air pollutants which adversely affect climate change (Zeng & Sepehri, 2008). Conclusion Traditional air crafts purely depended on hydraulic and pneumatic power sources to drive their systems. Modifications in the hydraulic actuators involved commencing the use of piezoelectric elements for improved functionalities. However, the introduction of electric actuators has led to the progressive departure from hydraulic systems coupled with several benefits particularly relating to fuel cost savings, improved efficiency, and improved safety. Less costly designs for the actuators have been the subject of several research studies that continuously generate more affordable electric actuators. Boeing 787 became the first aircraft to totally embrace the new concept of a more electric aircraft by eliminating the pneumatic systems from the drive controls. The electric actuators provide reliable real-time data on the status of the aircraft’s systems and require fewer maintenance costs. The electric actuators weigh less, occupy lesser space, are non-dependant on pressure variations and allow for remote control of the aircraft's systems with a great deal of safety as opposed to the hydraulic actuators. Due to the innumerable benefits of electric actuators, the modern trends in aerodynamics have entailed the shift from hydraulic actuators by adopting and implementing the concept of a "more electric aircraft." References Bu, F., & Yao, B. (2000). Nonlinear adaptive robust control of hydraulic actuators regulated by proportional directional control valves with the dead band and nonlinear flow gains. In American Control Conference, 2000. Proceedings of the 2000 (Vol. 6, pp. 4129–4133). IEEE. Retrieved from http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=876998 Cao, W., Mecrow, B. C., Atkinson, G. J., Bennett, J. W., & Atkinson, D. J. (2012). Overview of electric motor technologies used for more electric aircraft (MEA). Industrial Electronics, IEEE Transactions on, 59(9), 3523–3531. Emadi, A., & Ehsani, M. (2000). Aircraft power systems: technology, the state of the art, and future trends. Aerospace and Electronic Systems Magazine, IEEE, 15(1), 28–32. Goharrizi, A. Y., & Sepehri, N. (2010). A wavelet-based approach to internal seal damage diagnosis in hydraulic actuators. Industrial Electronics, IEEE Transactions on, 57(5), 1755–1763. Jelali, M., & Kroll, A. (2012). Hydraulic servo-systems: modeling, identification, and control. Springer Science & Business Media. Retrieved from https://books.google.com/books?hl=en&lr=&id=AukHCAAAQBAJ&oi=fnd&pg=PR21&dq=Advancements+in+hydraulic+systems&ots=d2yAnUJcMq&sig=WM4GlCoxTrruDLhRnVljXu5db14 Márton, L., Fodor, S., & Sepehri, N. (2011). A practical method for friction identification in hydraulic actuators. Mechatronics, 21(1), 350–356. Moir, I., & Seabridge, A. (2011). Aircraft systems: mechanical, electrical and avionics subsystems integration (Vol. 52). John Wiley & Sons. Retrieved from https://books.google.com/books?hl=en&lr=&id=Hcgh8SturJQC&oi=fnd&pg=PT12&dq=The+modern+trends+in+aircraft+Hydraulic+system&ots=x2zUm5w-fm&sig=Gi5oHg4L8iyqfDsi_uYYoo4VTns Peeters, B., Hendricx, W., Debille, J., & Climent, H. (2009). Modern solutions for ground vibration testing of large aircraft. Sound and Vibration, 43(1), 8. Zeng, H., & Sepehri, N. (2008). Tracking control of hydraulic actuators using a LuGre friction model compensation. Journal of Dynamic Systems, Measurement, and Control, 130(1), 14502. Zhanlin, W., & others. (2000). Trends of Future Aircraft Hydraulic System [J]. HYDRAULICS PNEUMATICS & SEALS, 1, 3.  Read More