- Introduction
Following the endless consumption of natural resources (such as petrol) and sustained damages to the natural environment (such as ozone layer loss, air pollution and noises), the energy-saving concepts and environmental awareness are arising around the world. A number of eco-friendly and energy-saving measures and strategy has therefore been developed. For example, the green living environment policy promoted by the Environmental Protection Agency (EPA), the United States; and the greenhouse gas reduction measures promoted by Environmental Protection Agency (EPA), Executive Yuan proved that the world trend is to realize the energy-saving and environmental protection concepts. This trend is also followed by the transportation industry (such as aviation and railway industry), where the governmental, industrial and academic circles have further developed or ameliorated the carrier design, manipulations or driving technology to save energy and protect our environment (for example, establishment and analysis of the energy-saving measures and strategy of Taiwan High Speed Rail [1]; or the green energy flight measures promoted on the China Airlines’ environmental protection website [2]). As for the flight energy saving measures, as the discussion focuses on the technology and methods of effectively saving the fuel, this article will outline some of the practices of flying energy-saving operations.
- Types of Energy-Saving Flight
In recent years, environmental issues, such as air pollution and energy risk, have become more serious. The increase of CO2, on the other hand, leads to the greenhouse gas effect, which has further interfered with seasonal changes and regulations and resulted in frequent natural disasters and losses of crops. Besides, the sustained consumption of petroleum energy also pushed worldwide countries to develop and promote relevant environmental protection, energy saving and carbon reduction measures and policies. Therefore, to follow the green environmental trend and to effectively reduce the flight transportation cost, civil air industry has studied and developed the new aircraft design (including the aircraft); upgraded the performance and design of aircraft (including the aircraft); and ameliorated flight manipulation details. This article has outlined the flight energy-saving strategy (that is, how to reduce the fuel consumption) and the aircraft energy saving technology and methods to introduce relevant and applicable methods.
- Aircraft design and improvements
Concerning the overall flight cost of civil air transportation industry, the aircraft flight costs are quite impressive. To effectively improve the fuel consumption and enhance the flight efficiency, the aircraft manufacturing industry has carried out a series of research and developments that are related to the flight resistance and aircraft loading; new aircraft models; new wing profile design; control of the aerodynamic flow field; a lighter aircraft structure using composite materials; development of the low-noise and low-pollution engine; or ameliorated power system [3]. The objectives are to effectively reduce the resistance of aircraft during the flight; enhance the flight speed; improve the flow field and lifting power of airflow; increase the flight stability; enhance the engine operating efficiency with an expectation to reach the advanced design goals rapidly and comfortably while saving energy consumption, reducing the noises and pollution. Regarding design details that are related to the aircraft performance, please refer to relevant academic and practical researches and literature; no citation herein.
- Energy-saving measures for each stage
- Taxi: when the twin-engine aircraft slides to the runway and gets ready to take off, plan the most ideal and shortest taxi route and, if possible, provide all necessary power using only one engine (shall refer to the airport’s actual runway environment and conditions; the performance of the aircraft engine and other machines; aviation control policy and so on) [4] with an expectation to save energy by reducing the fuel consumption.
- Climbing: when the aircraft climbs up, the faster the aircraft climbs up to the cruise level, the longer the climbing distance will be (flatter climbing slope) and the more fuel will be consumed. Therefore, try to shorten the climbing distance if it can be done based on the aircraft performance and there is no safety concern (increase the slope gradient if the aircraft will not be made to stall). In the meantime, slow down the climbing rate in order to consume less oil. Nevertheless, as the energy-saving (less fuel consumption) efficiency may be affected by ATC airspace isolation policy and/or the high flight intensity within the airspace, steep climbing will be replaced practically. That is, the aircraft will climb up to 18000 to 20000 feet first and then to the cruise attitude step-by-step. This strategy will comply with the air traffic control policy and save fuel consumption [5].
- Cruise: after reaching the cruise altitude, the aircraft will enter the cruise mode. Besides, all aircrafts and engines have their respective ideal cruise altitude and speed. Theoretically (without considering the amendments to thrust), aircrafts that desire to have the best and farthest cruise distance shall timely keep and adjust their angle of attack in order to fly at the max range cruise speed all the way through [6]. If the engine performance has been taken into the consideration (for example, amendments to the thrust and weight that can change according to the air density), the aircraft should fly at the optimal flight value with timely adjustment. In order to do so, the weight of aircraft will be reduced during the flight due to fuel consumption. However, if the air density is decreased in order to increase the weight correction factor value, it is a must to continuously increase the flight height. However, under the consideration of flight safety, it is practically impossible to increase the height without limitations. To overcome the limitations, it is suggested that he aircraft shall be maintained at the aforesaid max range cruise in order to timely and properly save the energy.
- Descent: after the cruise phase and before the aircraft lands on the ground, the aircraft will enter the descending phase. By taking the fixed-wing airplane ATR-72 as an example [5], its standard descending procedure is to adjust the thrust and gradually descends on the ground with a drop-off rate of 3 degrees. In regard to the energy-saving results, it can be done with the stepping-down mechanism while extending and keeping its cruise height. Besides, when it reaches specific reference point, it is a must to adopt the drop-off rate that is steeper than the standard (about 4 degrees) while maintaining the minimum thrust. Although this can increase the fuel consumption in the cruise phase, the fuel consumption in the descending phase has obviously reduced.
- Approach: when using the instrument landing system (ILS) to approach the landing site, its fuel consumption will be higher than that of visual landing due to continuous operations; corrections to the aircraft’s flight altitude or the course, altitude and sliding angle indicated in the instrument. Furthermore, as the approach distance is relatively longer and consumes more fuel comparing with visual landing, the aircraft may contact with the competent authority to carry out a visual landing, if the conditions allow and if the weather or visibility is acceptable.
- Other approaches: in regard to the flight route planning, try to plan the most economical voyage and route according to the aircraft performance, with an expectation to lower the fuel consumption of this route. As for the air space control, invite players from the air transport industry to jointly carry out the negotiations; improve airspace separation; conduct an evacuation control when the density of taking off/landing flight is high (time coordination); implement hovering and/or other measures. It is expected to consume less fuel while optimizing the efficiency of take-off and landing aircraft.
- Conclusions
Following the progress of industrial technology, the world now suffers from environmental pollution and “global warning”. Besides, continuous energy consumption will put us in the risk of energy shortage; energy shortage will result in an increase in the cost of use. Following by the increase of environmental pollution costs and the costs for acquiring and using the energy, we urge the world to pay attention to this issue and, relying on the force of academic, governmental and academic research, discuss every industry energy-saving response measures and technology. The aviation industry has now become even more proactive in changing the aircraft performance; developing new models and energy-saving technology; conducting flight control measures; and planning the flight route in order to comprehensively save energy and reduce carbon emission. Therefore, to follow the world’s environmental protection, energy-saving and carbon reduction trends with an expectation of reducing environmental pollution and the costs thereof, all industrial, governmental and academic circles shall draw up or set relevant strategy, measures, technology and equipment comprehensively.
Author: Li Yu-Hsi
Reference:
[1] Li Yu-His (2011), Establishment and analysis of energy-saving measures and strategy of Taiwan High Speed Rail, Department of Aeronautics and Astronautics, National Cheng Kung University [NCKU].
[2] China Airlines’ environmental protection website (2012), Green Energy Flight Measures: Optimal Flight Operations. No. 3 of the third volume of The Journal of Aeronautics, Astronautics and Aviation
[3]Ilan Kroo entitled, (2013), Future Technology and Aircraft Types, http://adg.stanford.edu/aa241/intro/futureac.html.
[4]Jonathan A. Lovegren and R. John Hansman, ESTIMATION OF POTENTIAL AIRCRAFT FUEL BURN REDUCTION IN CRUISE VIA SPEED AND ALTITUDEOPTIMIZATION STRATEGIES, MIT International Center for Air Transportation (ICAT) Department of Aeronautics & Astronautics Massachusetts Institute of Technology, 2011.
[5] ATR,FUEL SAVING, An Alenia Aeronautica and EADS Joint Venture,2011.
[6] Hwa Keng, Cruising Analysis for Transportation Airplanes, 民航季刊第三卷第三期,2001.