AERO2362 - Aerospace Design Project Assignment

Assignment Task

Introduction

In recent years, hybrid electric turboprop aircraft is growing as a promising technology in the aircraft industry. These aircraft are designed to provide improved efficiency, reduced fuel consumption and lower emissions compared to conventional aircraft using a combination of traditional turbine engines and electric motors [5]. The basic concept is to rely on turbine engines for cruising and other flight stages after additional power are provided using an electric motor during take-off and landing, which requires the most energy [14]. This development could progress a new 50-seat regional aircraft that meets the U.S. domestic "Scope Clause", which aims for better fuel consumption and economy than existing options [7]. This report describes the various components that make up hybrid electric turboprop aircraft, the advantages and disadvantages of the relevant technology, and the current state. This study aims to achieve at least a 20 per cent improvement over existing 50 seat area turboprops on 500nmi block fuel per seat, including a hybrid propulsion system, within the budget of building existing aircraft [12].

Background

The regional turboprop aircraft were manufactured in ATR and De Havilland Canada, owned by Longview aircraft company. In the mid-1980s, they introduced the current turboprop aircraft, while most airlines tried to replace older propeller aircraft [1]. There are ATR 72 and Dash 8 of De Havilland Canada. The two products are similar regarding mission, size, and power. As aviation companies aim to produce more efficient airliners, The ATR 72 and Dash 8 Q400 were designed to offer passengers an exceptional travel experience while being financially efficient for the company that operates them. The latest edition of the ATR 72 is known as the -600 series. This model has been designed with enhanced efficiency, which translates to lower fuel consumption and operating expenses. Due to its increased efficiency, there has been a surge in demand for this aircraft. Consequently, ATR has boosted its production capacity by introducing additional units. Due to its effectiveness, there is a great demand for the aircraft, which led ATR to restructure and add additional hangar facilities and an upgraded assembly line, resulting in increased production of up to 120 aircrafts per annum. People seeking a greater level of power and capable seatings for passengers will likely opt for the Dash 8 Q400, whereas individuals prioritising flights of shorter distances may prioritise the ATR 72 [2]. Embraer stopped production of the EMB-120 in 2001 but plans to enter the 70 to 100 seats turboprop aircraft market [2,3].

The concept of hybrid electric aircraft has been suggested before. In recent years, the development of efficient and sustainable electric batteries and motors has increased the possibility of realizing the development of electric hybrid aircraft. Electric hybrid aircraft use the traditional turboprop engine method of supplying power to the electric motor that drives the propeller after charging the battery in the generator [6]. Through NASA's X-57 project, NASA is working to make commercially viable fully electric planes a reality. The X-57 Maxwell electric aircraft successfully installed two 400-pound lithium-ion battery packs in its cabin [10]. The project's team has developed a new technology that safely packs thousands of ready-made lithium-ion cells into one light, powerful battery [8]. In addition, while the internal combustion engine's efficiency is less than 20%, all power is converted to practical work, and the efficiency is more than 90% [8,12]. When electric motors are used, the number of moving parts is reduced, requiring less maintenance, and increasing reliability [8]. It can also precisely control the propeller, increasing efficiency and reducing noise [9].

According to an analysis by the aircraft industry, the number of 70-seat turboprops has been increasing since 2010 in Australia and the Pacific islands. In addition, the global turboprop aircraft market is expected to grow to about 2,450 units in the next 20 years.

Benefits and limitations

Hybrid electric turboprop aircraft have advantages over conventional aircraft. The main benefit is that it can reduce fossil fuel dependency and use various renewable fuels such as biofuels [14]. It is also environmentally friendly because it uses electricity to produce fewer emissions and noise pollution. These hybrid electrical systems allow better fuel efficiency, reducing aircraft operating costs [9]. Electric motors also have advantages when taking off and landing because they perform better at low speeds and altitudes.

However, despite the potential advantages of hybrid electric turboprop aircraft, some challenges remain to be addressed in aircraft development. A battery that could drive a motor for an extended time shall be developed by storing sufficient energy as the driving range of an electric motor is restricted. It is also necessary to minimize the battery's weight and size to reduce the aircraft's weight as much as possible. The complexity of hybrid power systems requires careful management and integration to ensure optimal performance and stability [15]. Although challenges remain to overcome, the demand for aircraft using hybrid electric systems is expected to increase as environmental concerns grow along with technological advances.

Components

To power a typical hybrid electric turboprop aircraft, the following components are required:

• A conventional turboprop engine that generates electricity to recharge the batteries.
• A generator that converts the mechanical energy generated by the turboprop engine into electrical energy that powers the electric motors.
• Batteries that store the electrical energy generated by the generator and supply power to the electric motors.
• Electric motors convert the electrical energy stored in the batteries into mechanical energy that drives the propellers.

Conceptual design -Hybrid-electric system

According to IATA in 2019, hybrid-electric propulsion (HEP) is viewed as a viable replacement for traditional short and medium-range planes, and companies such as Boeing, Airbus, Rolls-Royce, and Siemens are making significant investments in this technology. IATA (2019) has categorized hybrid-electric propulsion (HEP) architectures into five different types: series hybrid, parallel hybrid, series/parallel hybrid, turbo-electric hybrid, and all-electric [16]. Figure 1 provides an overview of where the components of the hybrid electric propulsion system are located within the aircraft.

Figure 1. Overview of hybrid electric system in aircraft

• Series hybrid architecture

The internal combustion engine (ICE) propels an electric generator, which, in turn, powers the motor or charges the batteries with the assistance of PECs. During flight phases that necessitate minimal propulsive exertion, such as the cruise phase, the energy produced by the generator may also recharge the batteries [5]. The main advantage of the series structure is that ICE is not mechanically coupled to the generation of thrust, so it can be continuously operated with the best operating power and speed and can easily control the propulsion [17]. According to Donateo et al. (2018), the series configuration is appropriate for applications that require high torque at low speeds, but it is not as efficient as the parallel configuration. Additionally, it necessitates bigger batteries and electrical machines, resulting in an increase in the mass and volume of the powertrain [22]. The series hybrid structure is illustrated in Figure 2 below.

Two propulsion shafts, which run parallel to each other and are mechanically linked, are driven by a combination of combustion and electric power sources. The electric motor (EM) and internal combustion engine (ICE) shafts, both powered by batteries, are connected to a common shaft that drives a fan or propeller, allowing either or both to be used for propulsion, according to the National Academies of Sciences, Engineering, and Medicine in 2016 [18]. As there is no electric generator on the shaft of the internal combustion engine (ICE), the machines can be smaller in size, and weight can be reduced since the power for propulsion is supplied by both sources [19]. Table 3 outlines the key features of series and parallel configurations and provides a side-by-side comparison of the two.

Figure 4. Series/parallel hybrid architecture

The architecture described is a hybrid of the two previously mentioned designs. Figure 3 illustrates that the internal combustion engine (ICE), electric motor (EM), electric generator, and propeller are all mechanically linked through a coupling. Some concepts are propelled solely by electric motors (EMs), which are powered either by a battery pack or by an electrical generator driven by the ICE,

Figure 5. Turbo-electric hybrid architecture

This design is comparable to the series configuration but does not rely on batteries for propulsion energy. Several hybrid electric propulsion (HEP) concepts use this design due to the current low battery energy density (BED) [5]. The source of all the power is the fuel, and there are no other energy storage devices utilized [20]. Partial turbo-electric is a variation in which electric motors (EMs) generate a portion of the propulsive power, while the remainder is produced by a turbofan that is mechanically driven by ICE-driven turbofans. This results in smaller-sized electrical components, thereby reducing weight, as noted by Welstead and Felder (2016) [18], the National Academies of Sciences, Engineering, and Medicine (2016), and IATA (2019) [16]. One benefit of this design is the potential to employ environmentally-friendly fuels, such as hydrogen.

Figure 6. All electric hybrid architecture

The all-electric configuration utilizes batteries as the sole source of power for aircraft propulsion [16]. The benefits of this design include the higher energy conversion efficiency of electric motors (EMs) and power electronics controllers (PECs) in comparison to internal combustion engines (ICEs) and the less complex control strategies needed for managing a single power source. However, the primary drawback is the low battery energy density (BED) of current technologies, rendering it impractical for most aircraft [5]. Figure 6 provides an overview of where the components of the hybrid electric propulsion system are located within the aircraft.

Design challenges

In order to fully utilize the capabilities of hybrid electric propulsion systems, design issues need to be resolved. It is important to develop the capability to resize the hybrid electric propulsion system's architecture and select the most efficient components. Furthermore, there should be a program in place to objectively compare the performance of the designed propulsion system to the existing system. Key Performance Indicators (KPIs) are not chosen correctly, it may lead to the selection of propulsion architecture designs for the vehicle that cannot realistically enhance performance, requiring a complex and relevant system evaluation.

Concepts development

The design shall define point-performance sizing flight conditions (FCs), modules to be called and structural relationships to each other, and all input parameters required for these modules. An unknown parameter is defined by the module using a continuous step-repeating process. Off-design tasks can complete a variety of analytical activities, including point performance, such as parameter sweeps, maximum measurement assessments, and time integrated mission simulations.

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