Hybrid Aircraft Research Articles

Assessing the Impact of Hybrid Propulsion Systems on the Range and Efficiency of Aircraft

The demand for aviation continues to grow, posing issues in terms of fuel consumption, environmental effect, and operational efficiency. In addition, the COVID-19 pandemic has also highlighted the need for sustainable solutions in the aviation sector. To address these issues, hybrid electric propulsion systems have emerged as a potential option. Hybrid electric propulsion systems have the potential to improve airplane performance while reducing environmental impact. This article looks into the effects of hybrid electric propulsion technologies on optimal aircraft range. The study looks at aviation's environmental impact, several hybrid aircraft prototypes, and battery capacity and density challenges. Fuel usage increases in proportion to the weight of the aircraft. As a result, the range is shorter. In modern technology, along with to the added weight of batteries used as energy storage in hybrid propulsion systems, there are low battery densities and capacities. When the researches were reviewed, it was discovered that overcoming these limitations was easier for small aircraft and more difficult for large aircraft. As a consequence of the studies and research conducted, the development of light and reliable batteries with high energy density and capacity would expand the range of hybrid aircraft and allow them to be used more efficiently over long distances.

Porous activated carbon integrated carbon nitride nanosheets as functionalized separators for the efficient polysulfide entrapment in Li[sbnd]S batteries

Electrification of vehicles, hybrid aircraft and the advancement of portable electronics are exacting the deployment of high energy-dense batteries. The high theoretical capacity of sulfur (1675 mAh g−1), cost-effectiveness and environmental benignity of the lithium‑sulfur batteries (LSBs) are propitious for electrochemical energy storage beyond Li-ion battery technology. In this work, we described a simple, scalable preparation and electrochemical performance of porous activated carbon (PC)-infused graphitic carbon nitride (GCN) nanosheets with various ratios (PC@GCN 11, PC@GCN 12 and PC@GCN 21) as a polysulfide anchoring functionalized separator for LSBs. The high specific area (822 m2/g), hetero porosity, conductive carbon framework, surface functionalities and enriched N-doping of the PC@GCN synergistically induce mitigation of polysulfides via chemical and physical adsorption pathways in LSBs. The PC@GCN 21 modified separator demonstrates a high initial discharge capacity of 1389 mAh g−1 at a 0.1C rate and exhibits better capacity retention over 500 cycles at a 1C rate (655 mAh g−1) with sulfur loading of 3.8 mg/cm2 accompanied by high coulombic efficiency (94 %). The assembled cell with high S-loading (5.12 mg/cm2) shows a high initial discharge capacity of 712 mAh g−1 at 0.1C rate conditions. High Li-ion transference number (0.714), stable shuttle current, minimal coulombic efficiency loss (0.84 %), low shuttle factor and negligible self-discharge behaviour support the superior performance of the PC@GCN 21 coated cells. This report demonstrates that combining the high surface area, non-polar porous carbon with polar graphitic carbon nitride is a practical approach for designing metal-free functionalized separators for energy-dense LSBs.

Biofuel–Electric Hybrid Aircraft Application—A Way to Reduce Carbon Emissions in Aviation

As global warming intensifies, the world is increasingly concerned about carbon emissions. As an important industry that affects carbon emissions, the air transportation industry takes on the important task of energy saving and emission reduction. For this reason, major airlines have designed or will design different kinds of new-energy aircraft; however, each aircraft has a different scope of application according to its energy source. Biofuels have an obvious carbon emission reduction effect in the whole life cycle, which can offset the drawback of the high pollutant emission of traditional fossil fuels in the preparation and combustion stages. At the same time, a battery has zero emissions in the operating condition, while the low energy density also makes it more applicable to short-range navigation in small aircraft. In this paper, the development direction of a biofuel–electric hybrid aircraft is proposed based on the current development of green aviation, combining the characteristics of biofuel and electric aircraft.

Aircraft electric power plants

The paper presents a review of electrification of the existing propulsion systems and creating new hybrid propulsion systems based on the concept of more electric aircraft and all-electric aircraft in Russia and abroad. New promising directions of electrification of the existing aircraft propulsion systems and creating new hybrid aircraft propulsion systems are specified on the basis of the review.

Improving the calculation module for estimating pollutant emission from conventional and hybrid regional aircraft

For the aviation sector, it is extremely important to devise revolutionary solutions in the field of technology to restrain the potential impact of civil aviation on the environment to the level of the established strategic goals of ACARE (FlightPath2050). The introduction of innovative technologies (improvement of the combustion chamber, the introduction of electric hybrid power plants on airplanes, and the use of alternative aviation fuel) will ensure the sustainable growth of air transportation. To assess the effectiveness of advanced technologies, it is extremely important to have a model for calculating global/local emissions that takes into account the parameters of the flight path of conventional and hybrid aircraft, operational characteristics of the aircraft engine and hybrid powerplant, and the features of sustainable fuel. The improved module for calculating emission indices by combining the module for calculating the parameters of the flight path and the results of calculating the thermogas-dynamic calculation of the aircraft engine makes it possible to detect the influence of fuel consumption (engine thrust) on the values of the emission indices. This feature is representative for evaluating the efficiency of hybrid powerplants because the electrification of the aircraft fleet is primarily aimed at reducing fuel consumption. The analysis of simulation results reveals that the fuel consumption and EINOx are significantly reduced (for the climb stage – 25 %; for the descent stage – 30 %) for the hybrid AN26 compared to the conventional AN26. The specified operational measure, in the part of the low-pitch descend, significantly reduces EICO for the hybrid AN26 by an average of 50 % compared to the descend stage for the conventional trajectory. The results of calculations for the entire flight path demonstrate that the use of a hybrid power plant for An26 contributes to an average reduction of fuel consumption by 10 %, NOx emissions by 25 %, water vapor emissions by 10 %, and CO2 by 10 %.

Applications of the TL-Based Fault Diagnostic System for the Capacitor in Hybrid Aircraft

The article concerns the problem of capacitor diagnosis in a hybrid aircraft. Capacitors are one of the most commonly damaged components of electrical vehicle drive systems. The result of these failures is an increase in voltage ripple. Most known analytical methods are based on frequency spectrum analysis, which is time-consuming and computationally complex. The use of deep neural networks (DNNs) allows for the direct use of the measurement signal, which reduces the operating time of the overall diagnostic system. However, the problem with these networks is the long training process. Therefore, this article uses transfer learning (TL), which allows for the secondary use of previously learnt DNNs. To collect data to learn the network, a test bench with the ability to simulate a capacitor failure was constructed, and a model based on it was made in the MATLAB/Simulink environment. A convolutional neural network (CNN) structure was developed and trained by the TL method to estimate the capacitance of the capacitor based on signals from the Simulink-designed model. The proposed fault diagnostic method is characterised by a nearly 100% efficiency in determining capacitance, with an operating time of about 10 ms, regardless of load and supply voltage.

A New Range Equation for Hybrid Aircraft Design

A new Range Equation for a hybrid-electric propeller-driven aircraft was formulated by an original derivation based on the comparison of Virtual Electrical Aircraft (VEA) and Virtual Thermal Aircraft (VTA) range equations. The new formulation makes it possible to study the range of a hybrid aircraft with pre-established values of electric motor usage rate. The fuel and battery mass are defined "a priori", and do not depend on the power split, so even the aircraft’s total mass is constant. The comparison with the typical range formulas available for hybrid aircraft was made on the basis of a reference composite VLA category aircraft manufactured by the CFM Air company. The analysis carried out shows that there is an optimum hybridization level as a function of the pre-set specific energy of the batteries system.

A Review of Powertrain Electrification for Greener Aircraft

This review proposes an overview of hybrid electric and full electric powertrains dedicated to greener aircraft in the “sky decarbonization” context. After having situated the state of the art and context of energy hybridization in the aviation sector, we propose the visit of several architectures for powertrain electrification, situating the potential benefits but also the main challenges to be faced to takeoff these new solutions. Then, as a first example, we consider the EU project “HASTECS” (Hybrid Aircraft: reSearch on Thermal and Electric Components and Systems) in the framework of Clean Sky 2. It relates to a series hybrid chain integrated into a regional aircraft. This energy system integrates especially power electronics and electric machines with a high degree of integration, which raises the “thermal challenge” and the need to integrate cooling devices. Through the snowball effects typical of the aviation sector, this example emphasizes how important it is to “hunt for kilos”, an alternative solution consisting of eliminating the power electronics within the powertrain. This is why we propose a second example, which concerns an AC power channel without power electronics that only integrates synchronous magnet machines (generator and motor) directly coupled on an AC bus. This last architecture nevertheless raises questions in terms of stability, with one solution being to insert an auxiliary hybridization branch via battery storage. Theoretical analyses and experiments at a reduced power scale show the viability of this concept. Finally, some recommendations for future research with potential technological breakthroughs complete that review.

Off-Design Performance Analysis of a Parallel Hybrid Electric Regional Turboprop Aircraft

Hybrid electric propulsion is one of the alternative solutions for reducing fuel burn and lower emissions while keeping a reasonable battery mass for regional turboprop aircraft operating on short routes. Most studies reporting fuel burn reductions evaluate the aircraft on the design mission, although regional transport aircraft rarely operate under these conditions. Therefore, considering its off-design performance is essential for providing a more complete understanding of aircraft capabilities under various operating conditions. Under these flight conditions, the multi-energy management aspect of hybrid propulsion and the fixed size of the batteries could have a significant impact on the system robustness in off-design operation. In this study, the off-design performance of an existing regional turboprop aircraft retrofitted with a parallel hybrid electric powertrain is assessed. Fuel burn benefits are evaluated on the payload–range diagram for an initial hybrid design and compared to the baseline aircraft. Then, using a novel sizing approach, considering a typical mission operation, this study shows an average improvement of percentage point on fuel burn benefits relative to the initial hybrid aircraft, creating a more robust design.

Analysis of the immersion cooling of electric motors for hybrid aircraft

The focus of this paper is to investigate the practicality of incorporating immersion cooling methods to mitigate the temperature elevation of motors utilized in hybrid aircraft. Air cooling, oil jacket cooling, slot-channel oil cooling and immersion cooling techniques are each applied to a permanent magnet synchronous motor. When a hybrid aircraft is operating, the amount of fuel it carries is limited and decreases over time. In this case, the normal operating time of the motor is investigated in this paper. The study shows that for the motors in this paper, immersion cooling is the most effective with a limited amount of coolant and takes the longest time to reach the upper temperature limit, which can be improved by 5.6 times compared to slot-channel cooling. This paper serves as a reference for the design of motors for hybrid aircraft utilizing immersion cooling technology.

A high‐efficiency magnetic‐geared double‐rotor machine with the coreless stator for hybrid aircraft propulsion

AbstractMagnetic‐geared double‐rotor machines are recognized as a promising power‐splitting component in hybrid electric aircrafts (HEAs). However, the high fuel efficiency speed of the turbine engine in HEAs is about 10,000 rpm, whereas conventional topologies suffer from low efficiency at high speed due to its specific operation principle—the magnetic field modulating principle. A coreless stator magnetic‐geared double‐rotor machine (CS‐MGDRM) is proposed to enhance high‐speed efficiency and thus comply with the operation condition of HEAs. First, the machine structure and hybrid propulsion system configuration are introduced, and power‐flow analysis of three basic operation modes is presented. Second, the operation principle of the machine is illustrated, and investigation of electromagnetic performances is carried out by finite element analysis. Third, an analytical model of the machine is developed, based on which the design optimization towards the maximum torque capacity is investigated. Furthermore, the loss distribution law and transmission efficiency are analysed and compared with conventional scheme, and the power factor characteristic is investigated as well. Finally, the overall performance of the proposed machine is evaluated.

Comprehensive technical analyses of a solid oxide fuel cell turbine-less hybrid aircraft propulsion system using ammonia and methane as alternative fuels

This paper presents a novel hybrid aircraft propulsion system that combines a turbojet engine with an ammonia decomposition reactor and a solid oxide fuel cell system, where the compressor is driven by a solid oxide fuel cell instead of a turbine. Ammonia and methane are selected as alternative fuels to replace kerosene. Technical analyses, including energy and exergy analyses, and comprehensive parametric studies, including engine, flight, fuel cell, and decomposition parameters, are performed, together with quantification of global warming potential (GWP). The results show that the solid oxide fuel cell has a power of 316.68 kW and an electrical efficiency of 42.09%. The hybrid aircraft propulsion system has a thrust of 851.82 N, a specific fuel consumption of 49.93 g/(kN·s) and an exergy efficiency of 22.27%. Compared to a kerosene-fueled turbojet, the hybrid aircraft propulsion system can decease 80.37% of GWP. The optimum choice of engine parameters is a low fuel ratio, a medium pressure ratio and a high air ratio. The best choice of flight parameters is a high Mach number and a medium altitude. Fuel cell parameters cannot achieve high thrusts and low fuel consumptions at the same time. The decomposition temperature should be as high as possible.

A basic study on braking and regenerative braking torques for an axial gap type eddy current brake

Because of growing demand in the aircraft industry, research is being conducted around the world to reduce CO2 emissions by electrifying aircraft. The authors are studying a non-contact hybrid aircraft brake that combines an eddy current brake and a magnetorheological fluid brake. This paper presents a basic study of braking and regenerative torque using an axial gap type eddy current brake. The result as that a maximum braking torque of 51.3 mNm was obtained with a three-phase AC power supply when the speed of the conductor disc was 2,000 rpm, the current was 3 A, and the frequency was 10 Hz in the CW direction. The maximum regenerative torque was 48 mNm when the speed of the conductor disc was 2,000 rpm, the current was 3 A, and the frequency was 10 Hz in the CCW direction.

On the Transition to Green Aviation

To solve the problem of harmful emissions into the atmosphere, the principles of “green aviation” have been developed, which are based on optimizing flight schedules, changing the aircraft design, using lightweight composite materials, changing the engine operation principle and design, and the fuel used. The staff of the National Research Center Zhukovsky Institute, working jointly with other institutes, develops the principles of “green aviation”. Over the past few years, specialists of the Zhukovsky Institute have developed a number of powerful switching voltage converters as part of power plants for electric and hybrid aircrafts, in particular, for charging aircraft on-board storage batteries. Owing to the use of modern solid-state electronic components and an ergonomic design, the power plant specific capacity has been brought to a level from units to tens of kW/kg. In the field of low-temperature plasma physics, work is also underway on electrohydrodynamic flow control systems for aircraft, which is of primary importance for increasing aerodynamic and energy efficiency, thus helping solve the environmental problem of reducing harmful emissions, including carbon and nitrogen oxides, and achieve significant fuel saving.

Optimization of a hydrogen-based hybrid propulsion system under aircraft performance constraints

This paper addresses the topic of the conceptual design of a regional aircraft with hybrid electric propulsion based on hydrogen fuel cells. It aims at providing an optimization-based method to design a hybrid propulsive system comprising two power sources (jet fuel and hydrogen) for the generation of the required propulsive power and at studying the impact of fuel cell technologies on the aircraft performances. Indeed, by performing optimizations for two hybrid propulsive systems using either low temperature or high temperature proton-exchange membrane fuel cells, this study provides a preliminary assessment of the impact of the fuel cell operating temperature on the system design and the overall aircraft performance. First, this paper gives a description of the baseline turboprop regional aircraft with a focus on its high speed and low speed flight performances which will serve as requirements for the design of the hybrid aircraft. Then, the hybrid electric architecture and the sizing models of the propulsion system are presented. Finally, optimizations are performed to design two parallel hybrid propulsive systems based on different fuel cells technologies and aimed at minimizing the block fuel per passenger over a mission of 200 n mile. Results show how the proposed methodology and models lead to design two propulsive systems capable of reducing the fuel consumption per passenger by more than 30 % compared to the baseline aircraft. The study also shows that the choice of fuel cell operating temperature has a first-order impact on the total mass of the propulsive system due to the higher cooling requirement of the low temperature fuel cells.

Decision mechanism between fuel cell types: A case study for small aircraft

Research has focused on green energy alternatives that can be used instead of fossil fuels to reduce aviation-related emissions and achieve zero-emission targets. One of the most promising alternatives is hydrogen-based fuel cells. Determining the fuel cell type closest to the hydrogen side solution to the airplane emission problem will help guide the researchers working on this issue. Multi-criteria decision-making methods were used for the first time in applying fuel cells to aircraft. The study will pioneer the use of MCDM methods in determining the usability of fuel cells in other areas and vehicles. This study proposes a decision mechanism to evaluate the most suitable fuel cell type integrated into a normal class small aircraft hybrid powertrain. Accordingly, the decision problem was transformed into a hierarchical structure by determining five fuel cell alternatives and twelve criteria in consultation with expert decision-makers. The decision problem has been solved with the Analytic Hierarchy Process, one of the multi-criteria decision-making methods in accordance with its structure. The results showed that PEM fuel cells are best suited for integration into hybrid aircraft, with in power-related criteria such as Specific power, Power density, and Power capacity. Also, our results cast a new light on the properties of fuel cells to be considered for use in aircraft.

Observer-Based Optimal Control of a Quadplane with Active Wind Disturbance and Actuator Fault Rejection.

Hybrid aircraft configurations with combined cruise and vertical flight capabilities are increasingly being considered for unmanned aircraft and urban air mobility missions. To ensure the safety and autonomy of such missions, control challenges including fault tolerance and windy conditions must be addressed. This paper presents an observer-based optimal control approach for the active combined fault and wind disturbance rejection, with application to a quadplane unmanned aerial vehicle. The quadplane model is linearised for the longitudinal plane, vertical takeoff and landing and transition modes. Wind gusts are modelled using a Dryden turbulence model. An unknown input observer is first developed for the estimation of wind disturbance by defining an auxiliary variable that emulates body referenced accelerations. The approach is then extended to simultaneous rejection of intermittent elevator faults and wind disturbance velocities. Estimation error is mathematically proven to converge to zero, assuming a piecewise constant disturbance. A numerical simulation analysis demonstrates that for a typical quadplane flight profile at 100 m altitude, the observer-based wind gust and fault correction significantly enhances trajectory tracking accuracy compared to a linear quadratic regulator and to a H-infinity controller, which are both taken, without loss of generality, as benchmark controllers to be enhanced. This is done by adding wind and fault compensation terms to the controller with admissible control effort. The proposed observer is also shown to enhance accuracy and observer-based rejection of disturbances and faults compared to three alternative observers, based on output error integration, acceleration feedback and a sliding mode observer, respectively. The proposed approach is particularly efficient for the active rejection of actuator faults under windy conditions.

A review analysis of tilt rotor unmanned aerial vehicles

TRUAVs (Tilt Rotor Unmanned Aerial Vehicles) are a new technology that is becoming more and more popular in today's modern world for a range of uses, including agricultural, civil engineering, target tracking, search and salvage operations, and surveillance. Such aerial vehicles were created as a solution to a number of issues, such as the lack of runways in remote and heavily forested areas. The TRUAV is a hybrid aircraft that presents the advantages of both conventional aero plane and helicopter technology in a single aircraft. This review article is largely concerned with the design and analysis of Tilt Rotor Unmanned Aerial Vehicles (TRUAV). The flight control legislation we developed has a straightforward design and excellent technical dependability.

Assessment of different more-electric and hybrid-electric configurations for long-range multi-engine aircraft

In this study, the characteristics, penalties, gains, and challenges in the electrification and hybridization process for long-range aircraft were investigated. A system and mission analysis was conducted on thermodynamics and cost. A reference aircraft was compared with other more-electric and hybrid-electric versions of the same type. These latter versions may carry batteries to supply the aircraft system and/or engine. A state-of-the-art propulsion and system architecture were also implemented in these innovative aircraft. A full factorial analysis was conducted to vary the battery energy density and the hybridization ratio for the hybrid configurations. A typical mission profile was developed to match the boundary conditions in all cases. The hybrid powertrains were confirmed in our results as exhibiting superior behavior compared to those of the other cases. The least efficient hybrid configuration, which employed an intermediate battery choice, reduced fuel consumption by 10.7% in the conventional aircraft and by 1% in the battery-powered more-electric type. Moreover, both baseline models were surpassed by the worst intermediate-battery hybrid aircraft by 3.6% and 1% in terms of overall mission exergy efficiency. Considering the actual low density of batteries available on the market, long-range hybrid-electric aircraft will require substantial time to become viable.

Two-phase heat transfer devices for passive cooling of electric and hybrid aircraft onboard equipment

Two-phase heat transfer devices for passive cooling of electric and hybrid aircraft onboard equipment