Enabling the potential of hybrid electric propulsion through lean-burn-combustion turbofans

Hybrid-electric propulsion has emerged as a promising technology to mitigate the adverse environmental impact of civil aviation. Boosting conventional gas turbines with electric power improves mission performance and operability. In this work the impact of electrification on pollutant emissions and direct operating cost of geared turbofan configurations is evaluated for an 150-passenger aircraft. A baseline two-and-a-half-shaft geared turbofan, representative of year 2035 entry-into-service technology, is employed. Parallel hybridization is implemented through coupling a battery-powered electric motor to the engine low-speed shaft. A multi-disciplinary design space exploration framework is employed comprising modelling methods for multi-point engine design, aircraft sizing, performance and pollutant emissions, mission and economic analysis. A probabilistic approach is developed considering uncertainties in the evaluation of direct operating cost. Sensitivities to electrical power system technology levels, as well as fuel price and emissions taxation are quantified at different time-frames. The benefits of lean direct injection are explored along short-, medium-, and long-range missions, demonstrating 32% NO<italic>_x</italic> savings compared to traditional rich-burn, quick-mix, lean-burn technologies in short-range operations. The impact of electrification on the enhancement of lean direct injection benefits is investigated. For hybrid-electric powerplants, the take-off-to-cruise turbine entry temperature ratio is 2.5% lower than the baseline, extending the corresponding NO<italic>_x</italic> reductions to the level of 46% in short-range missions. This work sheds light on the environmental and economic potential and limitations of a hybrid-electric propulsion concept towards a greener and sustainable civil aviation.

Wing Thickness Optimization for Box Wing Aircraft

Background: In the interest of improving aircraft performance, studies have highlighted the benefits of Box wing configurations over conventional cantilever aircraft configuration. Generally, the greater an aircraft's average thickness to chord ratio (τ), the lower the structural weight as well as volumetric capacity for fuel. On the other hand, the lower the ., the greater the drag reduction. A review of patents related to the Box-wing aircraft was carried out. While methodologies for optimizing wing thickness of conventional aircrafts have been studied extensively, limited research work exist on the methodology for optimizing the wing thickness to chord ratio of the Box wing aircraft configurations. Methods: To address this gap, in this work, a two stage optimization methodology based on gradient search algorithm and regression analysis was implemented for the optimization of Box wing aircrafts wing thickness to chord ratio. The first stage involved optimizing the All Up Mass (AUM), Direct Operating Cost (DOC) and Zero Lift Drag Coefficients (CDO), with respect to the aft and fore sweep angle for some selected τ values. At the second stage, a suitability function (γ) was optimized with respect to the aft and fore sweep angle for some selected τ values. A comparative study was further carried out using the proposed methodology on similar size cantilever wing aircraft. Results: From the result, an optimal τ value was reached. Also the τ value for the cantilever aircraft found based on the proposed methodology was similar to the true τ value of the adopted aircraft, thereby validating the methodology. Conclusion: Based on the optimal τ value reached from this work, the Box wing aircraft are suitable for thin airfoils.

Towards a methodology for new technologies assessment in aircraft operating cost

The need for a greener and competitive aircraft is leading to the use of new technologies. A thorough assessment of these technologies is mandatory from the initial phases of aircraft design to understand their feasibility and to select the most promising one both in terms of performances and in terms of costs. This paper proposes a methodology to assess the operating cost of innovative technologies for regional aircraft. In particular, two NASA studies have been adopted to determine the impact onto costs of MEA and AEA technologies and advanced ECS solutions for two innovative regional aircraft concepts developed during the European Clean Sky 2 research. The proposed methodology is able to assess the effect of on-board systems electrification level in terms of fuel and maintenance costs savings. The methodology, which allows to evaluate the effect of specific technological improvements onto costs, is applied exploiting the results provided by a reliable cost model and gives the opportunity to quantify operating cost savings for different regional aircraft. Applying the modified cost model to the reference aircraft under study, savings ranging from 1.6 to 3.1% of direct operating cost are estimated for MEA and AEA technologies. Greater savings are estimated for the individual cost items involved. More specifically, a reduction of fuel cost ranging from 6 to 14.5% is envisaged as a consequence of the lower SFC associated to innovative ECS technologies.

Cruise Flight Performance Optimization for Minimizing Green Direct Operating Cost

To cope with the environmental impact of aviation and pollution problems in the future, airlines need to assess environmental impacts and offer countermeasures in advance. In order to measure the influence of environment on the airlines’ operational costs, this paper establishes an aircraft green direct operating cost (GDOC) model to quantify adverse environmental effects, such as air pollution and greenhouse effects, into the direct operating cost (DOC). Furthermore, fuel consumption, flight time, and distance in the cruising stage account for about 80% of the entire flight mission, and optimizing cruise flight performance can contribute greatly to reduce GDOC. Therefore, this paper sets up an optimal control model to minimize GDOC, establishes a discrete time dynamic system for optimizing the cruise altitude and speed profiles, and searches the optimal results by using dynamic programming. Besides, as meteorological conditions affect aircraft aerodynamics, fuel flow rate, contrail formation, and so on, this paper analyzes meteorological uncertainty by using historic meteorological data. Finally, a route is selected as an example, and the rationality of the optimal results is proven by comparing GDOC with DOC. The results and discussion of the numerical test also show that environmental effects on aircraft operation can be reduced significantly by adopting GDOC as the optimization objective, especially the contrail cost, and the step-climb cruise mode can further reduce GDOC effectively.

Flight operation and airframe design for tradeoff between cost and environmental impact

Besides the influence of aircraft noise and emissions on the local air quality, the impact of greenhouse gas emissions on the global climate achieves more and more attention recently. The engine is very important for the noise and emission reductions, whereas the airframe and flight conditions have great effect on these items as well. This paper aims to study the effect of the airframe parameters and the flight conditions on the emissions during standardized landing and takeoff cycle, the total emitted greenhouse gas, the noise during approach, and the cost with the multidisciplinary analysis framework. The analysis displays that the cruise and the climb stages have the main effect on global warming potential with about 95%, and reducing the cruise altitude may result in a decrease of the global warming impact but an increase of direct operating cost. The flap with fewer gaps is better to be employed for the noise reduction. Meanwhile, a larger wing area is needed to make up for a loss of aerodynamic effect. The steeper approach could reduce both of the noise during approach and the emissions during landing and takeoff-cycle. Two types of configuration are achieved after optimization.

Optimization of small aircraft parameters in the initial phase of the project

Conceptual and preliminary designs of future aircraft have become increasingly complex due to the enlargement of the basic criteria for evaluating emerging solutions. In the past, the basic performance characteristics of an airplane were the only selection criteria. Today, more and more emphasis is placed on factors such as impact on the environment, cost-effectiveness, or comfort of travel. The method for optimization of the key parameters of a small aircraft for use in the initial phase of a project is presented in this paper. It takes into account the requirements of aviation safety imposed by the European Union certification specifications CS-23 and requirements of aircraft competitiveness. Requirements and design assumptions were formulated based on the concept of the Small Air Transport system (SATs). The method is based on the multidisciplinary design optimization and covers the basic areas related to the design of aircraft: aerodynamics, aircraft structure, performance and expected operating costs. The objective function is defined as the value of the direct operating cost per passenger-kilometre. An evolutionary algorithm was applied to solve the optimization problem. As an example of the use of this method, the optimization of design parameters of the two classes of aircraft, 9-seater and 19-seater was carried out. The results were compared with the parameters of aircraft, which are in service. Sensitivity analysis of the objective function with respect to selected parameters of the aircraft was also made. The analysis allowed to select the most important parameters responsible for the operational costs.