Conceptual Design and Optimization of Distributed Electric Propulsion General Aviation Aircraft

Jiang Wu; Feng Gao; Shengwen Li; Fengtian Yang

doi:10.3390/aerospace10050387

Wu, Jiang;Gao, Feng;Li, Shengwen;Yang, Fengtian

2023-04-22 00:00:00

aerospace Article Conceptual Design and Optimization of Distributed Electric Propulsion General Aviation Aircraft 1 , 2 1 3 1 , 2 , Jiang Wu , Feng Gao , Shengwen Li and Fengtian Yang * Liaoning General Aviation Academy, Shenyang 110136, China; wujiangnuaa@163.com (J.W.) Shenyang Aircraft Design & Research Institute, Shenyang 110035, China AVIC Aerodynamics Research Institute, Shenyang 110034, China * Correspondence: yang_ft_lgaa@163.com Abstract: The interaction between the slipstream of the propellers and the wing of an aircraft with distributed electric propulsion (DEP) could beneﬁt aerodynamics. A conceptual design and optimization are carried out in order to increase the range of an electric general aviation aircraft without affecting its takeoff and landing velocity in the same fuselage condition. Propellers are modelled using the actuator disk (AD) theory, and the aircraft is modelled using the vortex lattice method (VLM) to obtain DEP aircraft’s aerodynamics in conceptual design. The DIRECT method is used for global optimization. To concentrate on the layout of the propellers and wing, a propeller with the same chord distribution, twist distribution, and number of blades is selected. The design and optimization of DEP aircraft’s range is carried out with the objective of achieving the maximum product of the lift–drag ratio with propeller efﬁciency under force balance constrains. Additionally, to decrease the takeoff and landing distance, the DEP aircraft’s takeoff and landing performance are optimized with the objective of the smallest velocity at an angle near the tail down angle under the constrains of acceleration bigger than 0 and a Mach number at the tip of blades smaller than 0.7. The CFD simulation was used to conﬁrm the DEP aircraft’s pretty accurate aerodynamics. Compared to the reference aircraft, the improved DEP aircraft with 10 high-lift propellers on the leading edge of the wing and 2 wing-tip propellers may boost cruise performance by 6% while maintaining takeoff and landing velocity. Furthermore, it has been shown that the stall speed of DEP aircraft with smaller wings would rise proportionally when compared to conventional design aircraft, and the power need of DEP aircraft will be increased as a result of the operation of high-lift propellers. The conceptual Citation: Wu, J.; Gao, F.; Li, S.; Yang, design and optimal approach suggested in this work has some reference value for the design and F. Conceptual Design and research of the ﬁxed-wing DEP general aviation aircraft. Optimization of Distributed Electric Propulsion General Aviation Aircraft. Keywords: distributed electric propulsion; conceptual design; optimization; range Aerospace 2023, 10, 387. https:// doi.org/10.3390/aerospace10050387 Academic Editor: Dimitri Mavris 1. Introduction Received: 21 February 2023 Research and development for new energy electric aircrafts has become one of the most Revised: 3 April 2023 Accepted: 21 April 2023 important ﬁelds in green aviation because of its environmentally friendly features, such Published: 22 April 2023 as little noise and no emissions of greenhouse gases [1]. In the past ten years, a great deal of aircrafts that use electricity for either all or part of their propulsion have been built [2]. The speciﬁc energy of onboard energy storage systems, such as lithium-ion batteries, is a signiﬁcant impediment to the development of all-electric aircrafts [3]. Distributed electric Copyright: © 2023 by the authors. propulsion is currently viewed as the essential technology for electric aircrafts that become Licensee MDPI, Basel, Switzerland. more powerful and achieve greater performance, despite limits in the speciﬁc energy of This article is an open access article batteries and other issues [4]. It is even seen as a game changer in the ﬁeld of electric aircraft distributed under the terms and construction due to improvements in aerodynamic efﬁciency, ruggedness, and payload [5]. conditions of the Creative Commons The DEP aircraft, which is now the subject of extensive research, is a type of aircraft Attribution (CC BY) license (https:// driven by several electric motors in conjunction with thrust-generating apparatuses, such creativecommons.org/licenses/by/ as electrically powered fans or propellers [6]. TheX-57 is a well-known DEP aircraft 4.0/). Aerospace 2023, 10, 387. https://doi.org/10.3390/aerospace10050387 https://www.mdpi.com/journal/aerospace Aerospace 2023, 10, 387 2 of 19 that NASA is currently researching and developing as a demonstration of the leading edge asynchronous propeller technology (LEAPTech) [7]. According to projections, the X-57 will use just 20% as much energy as the original aircraft [8]. The high aerodynamic performance of the DEP aircraft could be obtained through the interaction of aerodynamics and propulsion, and the efﬁciency of the propulsion system could be increased by the use of electric motors and battery systems in X-57 [9]. Before DEP was suggested, a few academics had investigated the interaction between the slipstream of the propellers and the wing. In [10], several results were reached on the role of factors in the interaction between the slipstream of propellers and the wing. To begin, the inboard up rotation of propellers at the tip of the wing was beneﬁcial in increasing the lift–drag ratio. Second, a high position of the propellers’ rotation axis to the top surface of the wing was excellent for a large lift coefﬁcient, while a low location of the propellers’ rotation axis to the upper surface of the wing was ideal for a high propeller efﬁciency. Thirdly, although a large distance was beneﬁcial, the distance between the propellers and the leading edge of the wing had little bearing on the efﬁciency of the propellers. In a test conducted in [11], it was discovered that a layout with propellers moving inboard and up at the tip of the wing reduced the drag coefﬁcient while increasing propeller thrust. For a CFD simulation with tractor propellers modeled as an actuator disk in [12], the average accuracy in the lift coefﬁcient was 3.9% higher than the wind tunnel test, while the drag coefﬁcient was practically the same. According to [13], the interaction between the slipstream of the tractor propeller and the wing might lower the drag of the wing by around 10%. Several studies on the leading edge asynchronous propeller arrangement were carried out by NASA after the X-57’s debut. At the LEAPTech ground tests conducted on the lakebed outside NASA’s Armstrong Flight Research Mission Directorate in California in 2015, it was discovered that the lift coefﬁcient of a wing may be more than doubly boosted with the action of high-lift propellers [14]. In the high-lift conﬁguration, the performance of the X-57 was examined in FUN3D, USM3D, Kestrel, and STAR CCM+ [9], and it was discovered that the lift coefﬁcient could be enhanced by about 170% and the generated drag coefﬁcient could be lowered by about 7.5% [7]. The speciﬁcs for selecting high-lift propellers were investigated, and the mechanism for selecting the number of high-lift propellers in a system is presented in [15] for NASA’s SCEPTOR DEP ﬂying demonstrator. According to [16], high-lift propellers need to be properly built with a trade-off between the airfoil, blade planform parameters, and wing integration, such as a wing–nacelle offset for DEP aircrafts. In [17], a straightforward strategy for designing propellers that might improve wing lift considerably while producing little thrust and power was described. It was demonstrated that the propeller produced using this technique could use 15% less power and generate 11% less thrust than the one developed using the lowest induced loss method [17] for a NASA SCEPTOR ﬂying demonstrator. In addition to the X-57 research, a growing number of studies on the testing and simula- tion of DEP aircrafts’ aerodynamics have also been conducted. In [18], a type of distributed electric-propelled propeller aircraft was presented, and the ways the distributed propeller slipstream effect affected the aerodynamic properties of the aircraft were discovered. A maximum increase in an aircraft’s lift coefﬁcient of more than 65% was demonstrated in [18]. A distributed propeller electric general aviation aircraft aerodynamic arrangement was demonstrated in [19], and slip grid technology was utilized to model the slipstream of the propellers. Additionally, in [19], the aerodynamic parameters of DEP aircrafts in the cruising state, takeoff state, and landing state were obtained based on the CFD simula- tion. In [20], a series of ground test platforms for the aerodynamic propulsion system of DEP aircrafts were constructed, and the performance of the power system, aerodynamic performance, and aerodynamic-propulsion coupling relationship of DEP technology were evaluated using ground test and numerical modeling. A rapid aerodynamic performance evaluation software was developed in [21] using the vortex grid methodology with viscos- ity correction and linear non-viscous aerodynamic coupling calculation methods. When compared to the CFD ﬁndings, the greatest error from the evaluation of the lift coefﬁcient Aerospace 2023, 10, 387 3 of 19 and drag coefﬁcient of single wing and single propeller/wing in [21] was less than 8.2%. In [22], an optimization approach for the distributed propeller layout design under the slipstream effects was given; a conﬁguration with an optimized propeller layout had a lift coefﬁcient gain of around 5.6% and a drag coefﬁcient decrease of about 13.9%. In [23], opti- mization methods for conceptual and early design stages were reviewed, and the strategy for a propulsion number optimization was investigated to maximize overall efﬁciency in cruise. In [24], a low-cost aero-propulsive approach to study DEP aircrafts was created and utilized to assess the aero-propulsive effectiveness of DEP aircrafts in pusher and tractor propeller conﬁgurations. In [24], the wing was modeled using the vortex lattice technique, with the wake modeled using the VLM method with boundary corrections, and the pro- peller was modeled using the blade element method, with the slipstream represented using the vortex ring method. In [25], the aerodynamic performance of the DEP system was evaluated using wind tunnel experiments and computer simulations, and it was discovered that the stall of the DEP conﬁguration could be delayed and the lift–drag ratio could drop before the stall when compared to an isolated wing. In [26], an aerodynamic analysis tool was created by adding a viscous correction to OpenVSP using a Python wrapper, and it was discovered that the lift and drag coefﬁcients of the tool and those from the CFD solver were in excellent agreement. A low-order method to forecast the overall lift and lift distribution of a wing was presented in [27], and the method’s outcomes were rather accurate when compared to those from the CFD simulation and testing before the stall. A multidisciplinary design optimization framework for a general aviation aircraft wing design that took into account the impact of a wing-mounted propeller was given in [28], and it demonstrated that superior designs could be obtained by taking this interaction into account. In [29], a strategy for improving the wing lift–drag ratio was developed by optimizing the propeller slipstream, and it was demonstrated that applying this method might enhance the wing lift–drag ratio at the expense of propeller efﬁciency. A program based on the vortex particle approach was created in [30–32] to study the interaction of the slipstream from several rotors. Based on the simulation outcomes of speciﬁc multirotor conﬁgurations, it was shown that the code might be used as a mid-ﬁdelity modeling tool for the early design of distributed propulsion electric aircrafts. As previously indicated, the possible beneﬁts of the DEP design have been extensively researched. However, with the exception of the X-57, little research has been conducted on how to design a ﬁxed-wing DEP aircraft that can proﬁt from the interaction between the propeller ’s slipstream and the wing. In this study, a method for designing a ﬁxed-wing DEP general aviation aircraft in the conceptual stage is proposed. The ﬁxed-wing DEP aircraft under study here has a similar conﬁguration to the X-57, which has tractor propellers installed on the leading edge of the wing and wingtip. The low-order analysis tool selected here is OpenVSP, in which the wings and aircraft are represented using the vortex lattice method and the propellers are treated as actuator disks. In Python, an optimization code is created using the DIRECT global optimization method. To precisely optimize the cruise performance of DEP aircrafts, the restrictions of force balancing are initially presented. In accordance with the method, the cruise, takeoff, and landing performance of DEP aircrafts is optimized. The design scheme of the DEP airplane is further examined in STAR CCM+ once concept design is complete. The performance of the aircraft is then determined accordingly to conﬁrm the viability of the suggested strategy. 2. The Aerodynamic Interaction of the Wing and Tractor Propeller Slipstream 2.1. Effects of the Wing on the Propeller Wings create an upstream effect by changing the inﬂow at the propeller disk owing to in-plane and out-of-plane generated velocities [33]. The in-plane velocities are primarily inﬂuenced by the wing’s tail vortex system and bound vortex. The out-of-plane-induced velocity is a combination of the wing blockage and the velocity produced by the wing bound vortex [33]. Figure 1 depicts how the propeller and wing interact. Aerospace 2023, 10, 387 4 of 20 Aerospace 2023, 10, 387 4 of 20 2. The Aerodynamic Interaction of the Wing and Tractor Propeller Slipstream 2. The Aerodynamic Interaction of the Wing and Tractor Propeller Slipstream 2.1. Eﬀects of the Wing on the Propeller 2.1. Eﬀects of the Wing on the Propeller Wings create an upstream eﬀect by changing the inﬂow at the propeller disk owing to in-plane and out-of-plane generated velocities [33]. The in-plane velocities are primarily Wings create an upstream eﬀect by changing the inﬂow at the propeller disk owing inﬂuenced by the wing’s tail vortex system and bound vortex. The out-of-plane-induced to in-plane and out-of-plane generated velocities [33]. The in-plane velocities are primarily velocity is a combination of the wing blockage and the velocity produced by the wing inﬂuenced by the wing’s tail vortex system and bound vortex. The out-of-plane-induced Aerospace 2023, 10, 387 4 of 19 bound vortex [33]. Figure 1 depicts how the propeller and wing interact. velocity is a combination of the wing blockage and the velocity produced by the wing bound vortex [33]. Figure 1 depicts how the propeller and wing interact. Figure 1. Propeller–wing interaction diagram [33]. Figure 1. Propeller–wing interaction diagram [33]. Figure 1. Propeller–wing interaction diagram [33]. 2.2. Eﬀects of the Propeller’s Slipstream on the Wing 2.2. Effects of the Propeller’s Slipstream on the Wing 2.2. Eﬀects of the Propeller’s Slipstream on the Wing The propeller has a downstream impact on the wing by altering the inﬂow over it. The propeller has a downstream impact on the wing by altering the inﬂow over it. The axial and swirl velocity created by the propeller have a distinct inﬂuence on the ﬂow The propeller has a downstream impact on the wing by altering the inﬂow over it. The axial and swirl velocity created by the propeller have a distinct inﬂuence on the ﬂow over the wing. The axial velocity has a signiﬁcant impact on the local forces because it The axial and swirl velocity created by the propeller have a distinct inﬂuence on the ﬂow over the wing. The axial velocity has a signiﬁcant impact on the local forces because it increases the dynamic pressure over the wing [10]. The swirl velocity changes the angle over the wing. The axial velocity has a signiﬁcant impact on the local forces because it increases the dynamic pressure over the wing [10]. The swirl velocity changes the angle of of att ack in diﬀerent parts of the wing. The upward blade raises the local wing angle of increases the dynamic pressure over the wing [10]. The swirl velocity changes the angle attack in different parts of the wing. The upward blade raises the local wing angle of attack, att ack, while the downward blade reduces it [10]. When the wing is at a positive angle of of att ack in diﬀerent parts of the wing. The upward blade raises the local wing angle of while the downward blade reduces it [10]. When the wing is at a positive angle of attack, it att ack, it produces positive lift, resulting in higher lift on the upward blade side and de- att ack, while the downward blade reduces it [10]. When the wing is at a positive angle of produces positive lift, resulting in higher lift on the upward blade side and decreased lift creased lift on the downward blade side [10]. Figure 2 depicts the impact of the propeller att ack, it produces positive lift, resulting in higher lift on the upward blade side and de- on the downward blade side [10]. Figure 2 depicts the impact of the propeller slipstream slipstream on the wing. creased lift on the downward blade side [10]. Figure 2 depicts the impact of the propeller on the wing. slipstream on the wing. Figure 2. Figure 2.LLift ift distribu distribution tion in in wing wing sections sectionsinﬂuenced inﬂuenced by propeller-sl by propeller-slipstr ips eam-pr tream-produ oducedced v velocity eloc[i10 ty ]. [10]. Figure 2. Lift distribution in wing sections inﬂuenced by propeller-slipstream-produced velocity The position of the propeller in relation to the wing is a factor that signiﬁcantly [10]. inﬂuences the interaction. According to the ﬁndings indicated in the introduction, the The position of the propeller in relation to the wing is a factor that signiﬁcantly inﬂu- stream-wise propeller position to the wing leading edge is set to a 1.0 radius of the pro- ences the interaction. According to the ﬁndings indicated in the introduction, the stream- The position of the propeller in relation to the wing is a factor that signiﬁcantly inﬂu- peller, and the vertical propeller position is set to a 0.6 radius of the propeller for high-lift wise propeller position to the wing leading edge is set to a 1.0 radius of the propeller, and ences the interaction. According to the ﬁndings indicated in the introduction, the stream- propellers. the vertical propeller position is set to a 0.6 radius of the propeller for high-lift propellers. wise propeller position to the wing leading edge is set to a 1.0 radius of the propeller, and the vertical propeller position is set to a 0.6 radius of the propeller for high-lift propellers. 3. Methods 3.1. Frame for the Conceptual Design and Optimization of DEP Aircrafts A wing with outstanding cruising performance is required for the design of DEP aircrafts [13]. Hence, the wing is initially created. Then, the DEP aircraft’s wing area is reduced in comparison to the reference aircraft. Next, a CFD analysis of the performance of the small-wing aircraft in the cruise state is performed. If the performance of the new aircraft is inferior to that of the reference aircraft, a new wing design is created. The optimal design of the DEP in cruise is then carried out following the veriﬁcation of the performance enhancement of the new aircraft. The DEP aircraft, designated as DEP_TP in Aerospace 2023, 10, 387 5 of 20 3. Methods 3.1. Frame for the Conceptual Design and Optimization of DEP Aircrafts A wing with outstanding cruising performance is required for the design of DEP air- crafts [13]. Hence, the wing is initially created. Then, the DEP aircraft’s wing area is re- duced in comparison to the reference aircraft. Next, a CFD analysis of the performance of the small-wing aircraft in the cruise state is performed. If the performance of the new air- craft is inferior to that of the reference aircraft, a new wing design is created. The optimal Aerospace 2023, 10, 387 5 of 19 design of the DEP in cruise is then carried out following the veriﬁcation of the perfor- mance enhancement of the new aircraft. The DEP aircraft, designated as DEP_TP in cruise, is equipped with two wing-tip propellers. Following the completion of the optimal design cruise, is equipped with two wing-tip propellers. Following the completion of the optimal of DEP_TP, a CFD study of the DEP_TP is performed. DEP_TP will be the optimal conﬁg- design of DEP_TP, a CFD study of the DEP_TP is performed. DEP_TP will be the optimal uration if its performance is superior to that of the reference aircraft throughout cruising, conﬁguration if its performance is superior to that of the reference aircraft throughout takeoﬀ, and landing. The choice is based on the ﬁndings of [34], which show that pylons cruising, takeoff, and landing. The choice is based on the ﬁndings of [34], which show that or nacelles reduce the lift–drag ratio in cruise. If DEP_TP cannot outperform the reference pylons or nacelles reduce the lift–drag ratio in cruise. If DEP_TP cannot outperform the aircraft in overall cruising, takeoﬀ, and landing performance, a further optimal design will reference aircraft in overall cruising, takeoff, and landing performance, a further optimal be conducted with a high-lift propeller arrangement on the leading edge of the wing. The design will be conducted with a high-lift propeller arrangement on the leading edge of new conﬁguration may be deﬁned as DEP_HP. Following optimization, a further CFD the wing. The new conﬁguration may be deﬁned as DEP_HP. Following optimization, a analysis of DEP_HP will be carried out, and the performance of the DEP_HP will be ob- further CFD analysis of DEP_HP will be carried out, and the performance of the DEP_HP tained accordingly. The conclusion might be drawn by comparing the results to the per- will be obtained accordingly. The conclusion might be drawn by comparing the results to formance of the reference aircraft. As a result, Figure 3 depicts the roadmap for the design the performance of the reference aircraft. As a result, Figure 3 depicts the roadmap for the of DEP aircraft. design of DEP aircraft. Figure 3. Roadmap for the design of DEP aircraft. Figure 3. Roadmap for the design of DEP aircraft. Figure 4 depicts the process of optimal design. Python Wrapper is used to conceptually create and optimize DEP settings. The method for balancing local and global search is DIRECT (Dividing Rectangles), which can be used easily as a global optimizer in Python programming [35]. After providing DIRECT with the design variables and the correspond- ing interval range, the optimizer will search as its strategy, and a candidate design scheme will be entered into the Python code. Using the script generated by this code, the wing or DEP aircraft will be represented in the OpenVSP as vortex lattices and propellers as actuator disks. Then, with VSPAERO called in script, the aerodynamic performance, such as lift coefﬁcient, drag coefﬁcient of wing or aircraft, and thrust coefﬁcient, power coefﬁcient, and Aerospace 2023, 10, 387 6 of 20 Figure 4 depicts the process of optimal design. Python Wrapper is used to conceptu- ally create and optimize DEP sett ings. The method for balancing local and global search is DIRECT (Dividing Rectangles), which can be used easily as a global optimizer in Python programming [35]. After providing DIRECT with the design variables and the corre- sponding interval range, the optimizer will search as its strategy, and a candidate design scheme will be entered into the Python code. Using the script generated by this code, the Aerospace 2023, 10, 387 6 of 19 wing or DEP aircraft will be represented in the OpenVSP as vortex latt ices and propellers as actuator disks. Then, with VSPAERO called in script, the aerodynamic performance, such as lift coeﬃcient, drag coeﬃcient of wing or aircraft, and thrust coeﬃcient, power coeﬃcient, and propeller eﬃciency, are obtained. In the case of constraints, the candidate propeller efﬁciency, are obtained. In the case of constraints, the candidate design scheme is design scheme is evaluated in code, and the workable plans are kept in a database. The evaluated in code, and the workable plans are kept in a database. The optimum solution is optimum solution is established after the code quits. established after the code quits. Figure 4. Process of optimum design. Figure 4. Process of optimum design. Despite the low-order tool’s neglect for the effect of viscosity, the aerodynamic per- formance of DEP aircrafts could be precisely predicted before stalling. The correctness of low-order tools in the interaction between the slipstream of propellers and the wing was already conﬁrmed in [36,37] and other publications. 3.2. Validation of the Effectiveness of Low-Order and CFD Simulation for DEP Setup As previously stated, OpenVSP and VSPAERO are the low-order analytic tools selected for this paper. The interaction between the slipstream of the propellers and the wing may Aerospace 2023, 10, 387 7 of 20 Aerospace 2023, 10, 387 7 of 20 Despite the low-order tool’s neglect for the eﬀect of viscosity, the aerodynamic per- Despite the low-order tool’s neglect for the eﬀect of viscosity, the aerodynamic per- formance of DEP aircrafts could be precisely predicted before stalling. The correctness of formance of DEP aircrafts could be precisely predicted before stalling. The correctness of low-order tools in the interaction between the slipstream of propellers and the wing was low-order tools in the interaction between the slipstream of propellers and the wing was already conﬁrmed in [36,37] and other publications. already conﬁrmed in [36,37] and other publications. 3.2. Validation of the Eﬀectiveness of Low-Order and CFD Simulation for DEP Setup 3.2. Validation of the Eﬀectiveness of Low-Order and CFD Simulation for DEP Setup Aerospace 2023, 10, 387 7 of 19 As previously stated, OpenVSP and VSPAERO are the low-order analytic tools se- As previously stated, OpenVSP and VSPAERO are the low-order analytic tools se- lected for this paper. The interaction between the slipstream of the propellers and the wing lected for this paper. The interaction between the slipstream of the propellers and the wing may be quickly and reasonably precisely achieved in this tool by modeling DEP aircrafts may be quickly and reasonably precisely achieved in this tool by modeling DEP aircrafts in VLM and propellers in AD. The CFD tool here is STAR CCM+, which allows for an be quickly and reasonably precisely achieved in this tool by modeling DEP aircrafts in VLM in VLM and propellers in AD. The CFD tool here is STAR CCM+, which allows for an accurate examination of the aerodynamic performance of an aircraft. A propeller is repre- and propellers in AD. The CFD tool here is STAR CCM+, which allows for an accurate accurate examination of the aerodynamic performance of an aircraft. A propeller is repre- sented as a virtual disk in STAR CCM+. examination of the aerodynamic performance of an aircraft. A propeller is represented as a sented as a virtual disk in STAR CCM+. Here, simulations are performed to determine whether the tools mentioned above virtual disk in STAR CCM+. Here, simulations are performed to determine whether the tools mentioned above are eﬃcient. Figure 5 depicts the simulation model, which comes from [10]. Moreover, the Here, simulations are performed to determine whether the tools mentioned above are eﬃcient. Figure 5 depicts the simulation model, which comes from [10]. Moreover, the information from the wind tunnel test in [10] is also displayed in the tables below to eval- are efﬁcient. Figure 5 depicts the simulation model, which comes from [10]. Moreover, information from the wind tunnel test in [10] is also displayed in the tables below to eval- uate the outcomes of the simulations. the information from the wind tunnel test in [10] is also displayed in the tables below to uate the outcomes of the simulations. evaluate the outcomes of the simulations. Figure 5. Model for calculation [10]. Figure 5. Model for calculation [10]. Figure 5. Model for calculation [10]. The simulation model in OpenVSP is displayed in Figure 6. The simulation’s relevant The simulation model in OpenVSP is displayed in Figure 6. The simulation’s relevant The simulation model in OpenVSP is displayed in Figure 6. The simulation’s relevant inputs are V = 50 m/s, λ = 0.85, and RPS = 249 Hz. V stands for inﬂow velocity, λ for pro- inputs are V = 50 m/s, = 0.85, and RPS = 249 Hz. V stands for inﬂow velocity, inputs are V = 50 m/s, λ = 0.85, and RPS = 249 Hz. V stands for inﬂow velocity, λ for pro- peller advance ratio, RPS for propeller rotation speed, and BEM (blade element momen- for propeller advance ratio, RPS for propeller rotation speed, and BEM (blade element peller advance ratio, RPS for propeller rotation speed, and BEM (blade element momen- tum) is used to calculate propeller thrust. momentum) is used to calculate propeller thrust. tum) is used to calculate propeller thrust. Figure 6. Model in OpenVSP. Figure 6. Model in OpenVSP. Figure 6. Model in OpenVSP. Table 1 displays the outcomes from VSPAERO. It is obvious that the VSPAERO results Table 1 displays the outcomes from VSPAERO. It is obvious that the VSPAERO re- are quite close to the data from the wind tunnel tests. The low-order tool could be utilized Table 1 displays the outcomes from VSPAERO. It is obvious that the VSPAERO re- sults are quite close to the data from the wind tunnel tests. The low-order tool could be for the analysis of the interaction between a wing and a propeller ’s slipstream because the sults are quite close to the data from the wind tunnel tests. The low-order tool could be utilized for the analysis of the interaction between a wing and a propeller’s slipstream results are rather precise for such a small wing that is sensitive to factors. utilized for the analysis of the interaction between a wing and a propeller’s slipstream because the results are rather precise for such a small wing that is sensitive to factors. because the results are rather precise for such a small wing that is sensitive to factors. Table 1. Results from VSPAERO. Method C C L D ( ) Test 0.0055 0.0986 VSPAERO 0.0028 0.0998 Test 0.3135 0.0916 VSPAERO 0.3026 0.0873 Aerospace 2023, 10, 387 8 of 20 Table 1. Results from VSPAERO. Method CL CD (°) Test 0.0055 −0.0986 VSPAERO −0.0028 −0.0998 Test 0.3135 −0.0916 Aerospace 2023, 10, 387 8 of 19 VSPAERO 0.3026 −0.0873 The virtual disk and k-ε turbulence model are used in STARCCM+ to create a steady The virtual disk and k-" turbulence model are used in STARCCM+ to create a steady simulation. Figure 7 depicts the model. More than 1.2 million cells make up the grid, and simulation. Figure 7 depicts the model. More than 1.2 million cells make up the grid, and they are polyhedral cells. The model’s border is conﬁgured as a smooth wall with no slide, they are polyhedral cells. The model’s border is conﬁgured as a smooth wall with no slide, and the y plus at the wall is conﬁgured as 100. Table 2 displays the results from the CFD and the y plus at the wall is conﬁgured as 100. Table 2 displays the results from the CFD simulation. simulation. (a) (b) Figure 7. Model in STAR CCM+: (a) Region model in STAR CCM+; (b) Model of wing and Figure 7. Model in STAR CCM+: (a) Region model in STAR CCM+; (b) Model of wing and virtual virtual disk of propeller in STAR CCM+. disk of propeller in STAR CCM+. Table 2. Results from CFD. Table 2. Results from CFD. Method CL CD Method C C L D (°) ( ) Test 0.0055 −0.0986 Test 0.0055 0.0986 CFD −0.0070 −0.0948 CFD 0.0070 0.0948 Test 0.3135 0.0916 Test 0.3135 −0.0916 CFD 0.3096 0.0862 CFD 0.3096 −0.0862 For such a F parameter or such a -sensitive parameter- small sens wing, itive the smal CFD l wirng esults , the CFD resu have good agr lts ha eement ve good ag with reement with the wind tunnel test; therefore, the steady simulation in CFD might be used for con- the wind tunnel test; therefore, the steady simulation in CFD might be used for concept design scheme cept desi evaluation. gn scheme ev It should alua betinoted on. It shoul that the d be noted tha C in Tables 1t the C and 2 D is in the Ta combined bles 1 and 2 is the effect of prcombined e opeller thrustﬀec and t of pr aer opel odynamics, ler thrushence t and a its ero value dynamay mics,be henegative. nce its value may be negative. 4. Design and Optimization of DEP Aircraft 4. Design and Optimization of DEP Aircraft 4.1. Reference Aircraft 4.1. Reference Aircraft The four-seat full electric general aircraft known as RX4E in the Liaoning General The four-seat full electric general aircraft known as RX4E in the Liaoning General Aviation Academy served as the reference aircraft for the construction of a DEP ﬁxed-wing Aviation Academy served as the reference aircraft for the construction of a DEP ﬁxed- aircraft. In Figure 8, the airplane is depicted. The DEP aircraft’s fuselage shares the same Aerospace 2023, 10, 387 9 of 20 wing aircraft. In Figure 8, the airplane is depicted. The DEP aircraft’s fuselage shares the dimensions as the RX4E fuselage to simplify the design. Moreover, the DEP aircraft shares same dimensions as the RX4E fuselage to simplify the design. Moreover, the DEP aircraft an aerodynamic design with the X-57 (in Figure 9). shares an aerodynamic design with the X-57 (in Figure 9). Figure 8. RX4E in LGAA. Figure 8. RX4E in LGAA. Figure 9. X-57. 4.2. Conceptual Design and Optimization of DEP Aircraft 4.2.1. Design and Optimization of Wing The wing is designed and optimized using the process depicted in Figure 4. The wing is deﬁned by the following variables: wing root chord, wing tip chord, half of wing span, wing geometric twist angle, wing incidence angle, and wing dihedral angle. Table 3 shows the variable interval range. Except for the wing variables, the sweep angle in 1/4 chord of the wing is set to zero, and the airfoil of the wing is the same as RX4E. The objective of wing optimization is to maximize its lift–drag ratio at a 0°att ack angle. Table 3. Variables of wing. Variables Minimum Maximum Wing root chord 1.20 1.50 (m) Wing tip chord 0.45 0.60 (m) Half of wing span 5.50 7.00 (m) Wing geometric twist angle −3.00 0.00 (°) Wing incidence angle 0.00 3.00 (°) Aerospace 2023, 10, 387 9 of 20 Aerospace 2023, 10, 387 9 of 19 Figure 8. RX4E in LGAA. Figure 9. X-57. Figure 9. X-57. 4.2. Conceptual Design and Optimization of DEP Aircraft 4.2. Conceptual Design and Optimization of DEP Aircraft 4.2.1. Design and Optimization of Wing 4.2.1. Design and Optimization of Wing The wing is designed and optimized using the process depicted in Figure 4. The wing The wing is designed and optimized using the process depicted in Figure 4. The wing is deﬁned by the following variables: wing root chord, wing tip chord, half of wing span, is deﬁned by the following variables: wing root chord, wing tip chord, half of wing span, wing geometric twist angle, wing incidence angle, and wing dihedral angle. Table 3 shows wing geometric twist angle, wing incidence angle, and wing dihedral angle. Table 3 shows the variable interval range. Except for the wing variables, the sweep angle in 1/4 chord the variable interval range. Except for the wing variables, the sweep angle in 1/4 chord of of the wing is set to zero, and the airfoil of the wing is the same as RX4E. The objective of the wing is set to zero, and the airfoil of the wing is the same as RX4E. The objective of wing optimization is to maximize its lift–drag ratio at a 0 attack angle. wing optimization is to maximize its lift–drag ratio at a 0°att ack angle. Table 3. Variables of wing. Table 3. Variables of wing. Variables Minimum Maximum Variables Minimum Maximum Wing root chord Wing root chord 1.20 1.50 (m) 1.20 1.50 (m) Wing tip chord 0.45 0.60 Wing tip chord (m) 0.45 0.60 Half of wing span (m) 5.50 7.00 (m) Half of wing span Wing geometric twist angle 5.50 7.00 3.00 0.00 (m) ( ) Wing geometric twist angle Wing incidence angle −3.00 0 0.00 3.00.00 ( ) (°) Wing dihedral angle Wing incidence angle 0.00 2.50 ( ) 0.00 3.00 (°) The optimal solution is selected from more than 4000 options once Python’s optimum code terminates. Table 4 displays the optimal solution. The highest lift–drag value from the code is around 26.69. Table 4. Optimal solution of wing. Variables Optimal Solution Wing root chord 1.21 (m) Wing tip chord 0.45 (m) Half of wing span 6.33 (m) Aerospace 2023, 10, 387 10 of 20 Wing dihedral angle 0.00 2.50 (°) The optimal solution is selected from more than 4000 options once Python’s optimum code terminates. Table 4 displays the optimal solution. The highest lift–drag value from the code is around 26.69. Table 4. Optimal solution of wing. Variables Optimal Solution Wing root chord 1.21 (m) Wing tip chord Aerospace 2023, 10, 387 10 of 19 0.45 (m) Half of wing span 6.33 (m) Table 4. Cont. Wing geometric twist angle −1.75 Variables (°) Optimal Solution Wing incidence angle Wing geometric twist angle 1.752.60 ( ) (°) Wing incidence angle Wing dihedral angle 2.60 ( ) 2.10 (°) Wing dihedral angle 2.10 ( ) Naturally, as the wing area changes, so will the parameters, such as the root chord, tip chord, and wing span. However, the wing form is determined relative to the predeter- Naturally, as the wing area changes, so will the parameters, such as the root chord, tip mined values of the wing aspect ratio, wing taper ratio, wing geometric twist angle, wing chord, and wing span. However, the wing form is determined relative to the predetermined incidence angle, wing dihedral angle, and wing sweep angle in the 1/4 chord. values of the wing aspect ratio, wing taper ratio, wing geometric twist angle, wing incidence angle, wing dihedral angle, and wing sweep angle in the 1/4 chord. 4.2.2. Aircraft with the Optimal Wing The DEP aircraft will have a smaller wing area than the reference aircraft for the pur- 4.2.2. Aircraft with the Optimal Wing pose of the DEP conﬁguration study. Given the need for structural strength, the wing area The DEP aircraft will have a smaller wing area than the reference aircraft for the ratio of the DEP design to the reference aircraft in this study was established at roughly purpose of the DEP conﬁguration study. Given the need for structural strength, the wing 0.85. A simulation was ran in STAR CCM+ to evaluate the new aircraft’s lift–drag perfor- area ratio of the DEP design to the reference aircraft in this study was established at mance. Figure 10 displays the new airplane in STAR CCM+. roughly 0.85. A simulation was ran in STAR CCM+ to evaluate the new aircraft’s lift–drag performance. Figure 10 displays the new airplane in STAR CCM+. Figure 10. Surface grid of aircraft with the optimal wing. Figure 10. Surface grid of aircraft with the optimal wing. The new aircraft’s lift coefﬁcient, drag coefﬁcient, and lift–drag ratio in cruise condition The new aircraft’s lift coeﬃcient, drag coeﬃcient, and lift–drag ratio in cruise condi- is 0.4768, 0.0224, and 21.29, respectively. This new aircraft might serve as the basis for the tion is 0.4768, 0.0224, and 21.29, respectively. This new aircraft might serve as the basis for DEP conﬁguration since it has a lift–drag ratio that is 1.10 times that of the RX4E in cruise. the DEP conﬁguration since it has a lift–drag ratio that is 1.10 times that of the RX4E in cruise. 4.2.3. Design and Optimization of DEP_TP The layout of the propellers on the wing is the subject of the DEP conﬁguration design 4.2.3. Design and Optimization of DEP_TP and optimization. The diameter and advance ratio of the propeller are chosen as variables for the optimal design of DEP_TP. Table 5 shows the design variable interval ranges. A three-blade propeller with a certain performance is chosen in order to lessen the impact of the propellers’ performance. Figure 11 depicts its performance. According to the similarity theory for propellers, a propeller ’s performance is fundamentally ﬁxed, and its performance is directly connected to its advance ratio in certain Re and Mach ranges. Yet, the propeller ’s size and working condition may be modiﬁed according to the demands of the design. Moreover, all propellers rotate inboard and up. Table 5. Variables for DEP_TP. Variables Minimum Maximum Diameter of propeller 0.70 1.50 (m) Advance ratio of propeller 0.63 0.96 Aerospace 2023, 10, 387 11 of 20 The layout of the propellers on the wing is the subject of the DEP conﬁguration de- sign and optimization. The diameter and advance ratio of the propeller are chosen as var- iables for the optimal design of DEP_TP. Table 5 shows the design variable interval ranges. A three-blade propeller with a certain performance is chosen in order to lessen the impact of the propellers’ performance. Figure 11 depicts its performance. According to the simi- larity theory for propellers, a propeller’s performance is fundamentally ﬁxed, and its per- Aerospace 2023, 10, 387 11 of 19 formance is directly connected to its advance ratio in certain Re and Mach ranges. Yet, the propeller’s size and working condition may be modiﬁed according to the demands of the design. Moreover, all propellers rotate inboard and up. The highest lift–drag product with propeller efﬁciency at an attack angle of 0 degree is set as the optimal objective of DEP_TP in Formula (1). The optimal objective is a Table 5. Variables for DEP_TP. comprehensive result of aerodynamics and propulsion, and it is reasonable for evaluating the interaction between the slipstream of the propellers and the wing. In a sense, the Variables Minimum Maximum optimum objective is an indicator of the DEP aircraft range because it is directly related Diameter of propeller 0.70 1.50 to the power consumption of the DEP aircraft in cruise. The identical parameter used (m) in this paper ’s optimum objective was used in the performance evaluation of a tractor Advance ratio of propeller 0.63 0.96 propeller–wing system and a UAV in [13,38]. (a) (b) Figure 11. Performance of propeller: (a) CT and CP with λ; (b) η with λ. Figure 11. Performance of propeller: (a) C and C with ; (b) with . T P The highest lift–drag product with propeller eﬃciency at an att ack angle of 0 degree Force balance is the constraint condition during the optimum, and it is employed is set as the optimal objective of DEP_TP in formula (1). The optimal objective is a com- in Formulas (2) and (3) to calculate the propeller ’s advance ratio and cruising velocity. prehensive result of aerodynamics and propulsion, and it is reasonable for evaluating the Without the restriction, the aerodynamic gain can be overestimated since the propeller ’s advance interactio ratio n betw direen the ectly affects slipstrea the m lift–drag of the prop ratio eland lers the andef the wi ﬁciency ng. In a of the sepr ns opeller e, the opti . mum objective is an indicator of the DEP aircraft range because it is directly related to the power The lift coefﬁcient and drag coefﬁcient of an aircraft should depend on the propellers’ diameter consumpt and ion of t advanc he DE e ratio, P aircr accor aft in ding cruto ise. The the discussion identical p ofathe ramet impact er use of d in pr t opeller his paper slip- ’s str optimum objectiv eam on wing ine w Section as used in the performanc 2.2. The cruising speed e ev ofal an uaair tion of craft a might tractor propell be obtained er–fr wi om ng Formula (2) in Formulas (4) and (5). Additionally, Formulas (6)–(10) clariﬁes the relation- system and a UAV in [13] and [38]. ship between the characteristics of the propellers and the drag coefﬁcient and wing area of Force balance is the constraint condition during the optimum, and it is employed in the Form air ul craft as (2 based ), and on (3) t Formula o calculat (3). e th As e p aro result, peller’ the s adv optimal ance ra objective tio and crui of sing the DEP veloc air ity craft . Witin h- cruise in Formula (1) is to match the optimal propeller characteristics to the aircraft. out the restriction, the aerodynamic gain can be overestimated since the propeller’s ad- vance ratio directly aﬀects the lift–drag ratio and the eﬃciency of the propeller. h = h (1) The lift coeﬃcient and drag coeﬃcient T of an aircraft should depend on the propellers’ diameter and advance ratio, according to the discussion of the impact of propeller slip- stream on wing in Section 2.2. The cruising speed of an aircraft might be obtained from L = W (2) Formula (2) in Formulas (4), and (5). Additionally, Formula (6)–(10) clariﬁes the relation- ship between the characteristics of the propellers and the drag coeﬃcient and wing area of the aircraft based on Formula (3). As a result, the optimal objective of the DEP aircraft T = D (3) in cruise in Formula (1) is to match the optimal propeller characteristics to the aircraft. L = C rV S = W (4) 𝜂 =𝜂 (1) 2W V = (5) C rS = (6) n D s p C = (7) rV S 2 Aerospace 2023, 10, 387 12 of 19 C = (8) 2 4 rn D s p V 1 2 4 2 2 2C rn D = 2C r D = C rV S (9) T s p T p D l 2 C C S T D D = (10) l 4 The optimal solution is obtained from more than 1700 solutions after the optimal code terminates. Table 6 shows the optimal solution. According to the analysis results in Python code, the lift–drag ratio advantage is around 1.05 times more than that of the aircraft in Figure 10, and the efﬁciency gain is roughly 1.19 times greater than that of the RX4E. Table 6. Optimal solution of DEP_TP. Variables Optimal Solution Diameter of propeller 1.067 (m) Advance of propeller 0.895 Additionally, a CFD simulation is ran, as shown in Figure 12. A motor nacelle is added to the new layout based on Figure 10. The cruise lift–drag ratio from CFD for a comparable arrangement in Figure 12 without propeller but with nacelle is 20.82 at a speed of around 62 m/s. The cruise lift–drag ratio from CFD is 21.66 at 61 m/s, with a propeller advance ratio of 0.90 for the setup shown in Figure 12. As a consequence, according to the CFD simulation, the lift–drag advantage for the conﬁguration in Figure 12 is around 1.7% bigger than that for Figure 10, and the efﬁciency gain for Figure 12 is nearly 19% higher than that for RX4E. It should be mentioned that the aerodynamic advantage of the 1.017 times Aerospace 2023, 10, 387 13 of 20 lift–drag ratio may be divided into two parts: 0.978 from the extra nacelle and 1.040 from the propeller ’s slip-stream. Figure 12. Figure 12. DEP DEP_TP’s _TP’s m model odel in in ST ST AR C AR CCM+. CM+. In addition to the performance in cruise, the performances in takeoff and landing are In addition to the performance in cruise, the performances in takeoﬀ and landing are also obtained from two further CFD simulations. The takeoff speed is around 33.0 m/s also obtained from two further CFD simulations. The takeoﬀ speed is around 33.0 m/s with a ﬂap deﬂection of 10 and an attack angle of 8 , which is somewhat less than the tail with a ﬂap deﬂection of 10° and an att ack angle of 8°, which is somewhat less than the tail down angle. The landing speed is around 32.3 m/s, with a ﬂap deﬂection of 25 and an down angle. The landing speed is around 32.3 m/s, with a ﬂap deﬂection of 25° and an attack angle of 8 . According to a CFD simulation, the RX4E’s takeoff and landing velocities att ack angle of 8°. According to a CFD simulation, the RX4E’s takeoﬀ and landing veloci- are 31.45 m/s and 29.52 m/s, respectively. In comparison to RX4E, DEP_TP’s takeoff and ties are 31.45 m/s and 29.52 m/s, respectively. In comparison to RX4E, DEP_TP’s takeoﬀ landing speeds are a little higher. So, in a sense, the DEP_TP’s ground run distance during and landing speeds are a litt le higher. So, in a sense, the DEP_TP’s ground run distance takeoff and landing should be greater than that of RX4E. It is necessary to lay out high-lift during takeoﬀ and landing should be greater than that of RX4E. It is necessary to lay out propellers in order to improve DEP_TP’s takeoff and landing performance. high-lift propellers in order to improve DEP_TP’s takeoﬀ and landing performance. 4.2.4. Design and Optimization of DEP_HP The optimum purpose of DEP_HP is to maximize the lift coeﬃcient during takeoﬀ and landing by minimizing the takeoﬀ and landing velocity. The propellers used to create DEP_HP are the same as those used to design DEP_TP. The propeller diameter and ad- vance ratio are further design variables. Table 7 speciﬁes the interval ranges for the design variables. Section 2.2 speciﬁes the streamwise and vertical positions of high-lift propellers. The axis of propeller rotation is parallel to the aircraft’s longitudinal axis. All the propel- lers rotate inboard and up. The parameters are the same for every high-lift propeller. The state of ﬂight is set at an att ack angle of 8 ° but without a deﬂection of ﬂaps. Hence, CL may be accurately approximated without turbulence separation’s inﬂuence. The length of the span remaining after deducting the diameter of the wing-tip pro- peller and the fuselage width is one constraint. Another constraint is the Mach number of the blade tip, which is used to present noise restriction. The range of the advance ratio of the propeller is then calculated using the noise constraint. Table 7. Variables for DEP_HP. Variables Minimum Maximum Diameter of high-lift propeller 0.40 1.00 (m) Advance of high-lift propeller 0.46 0.96 Advance of wing-tip propeller 0.46 0.96 The highest lift coeﬃcient to diameter of high-lift propellers is depicted in Figure 13 based on the code. Figure 14 depicts the lift coeﬃcient to advance ratio of high-lift propel- lers and wing-tip propellers in a setup with a high-lift propeller diameter of 0.967 m. Aerospace 2023, 10, 387 13 of 19 4.2.4. Design and Optimization of DEP_HP The optimum purpose of DEP_HP is to maximize the lift coefﬁcient during takeoff and landing by minimizing the takeoff and landing velocity. The propellers used to create DEP_HP are the same as those used to design DEP_TP. The propeller diameter and advance ratio are further design variables. Table 7 speciﬁes the interval ranges for the design variables. Section 2.2 speciﬁes the streamwise and vertical positions of high-lift propellers. The axis of propeller rotation is parallel to the aircraft’s longitudinal axis. All the propellers rotate inboard and up. The parameters are the same for every high-lift propeller. The state of ﬂight is set at an attack angle of 8 but without a deﬂection of ﬂaps. Hence, C may be accurately approximated without turbulence separation’s inﬂuence. Table 7. Variables for DEP_HP. Variables Minimum Maximum Diameter of high-lift propeller 0.40 1.00 (m) Advance of high-lift propeller 0.46 0.96 Advance of wing-tip propeller 0.46 0.96 The length of the span remaining after deducting the diameter of the wing-tip propeller and the fuselage width is one constraint. Another constraint is the Mach number of the blade tip, which is used to present noise restriction. The range of the advance ratio of the propeller is then calculated using the noise constraint. The highest lift coefﬁcient to diameter of high-lift propellers is depicted in Figure 13 Aerospace 2023, 10, 387 14 of 20 based on the code. Figure 14 depicts the lift coefﬁcient to advance ratio of high-lift propellers and wing-tip propellers in a setup with a high-lift propeller diameter of 0.967 m. Figure 13. The maximum C with diameter of high-lift propeller. Figure 13. The maximum CL with diameter of high-lift propeller. From Figure 13, it can be concluded that the diameter of high-lift propellers has little effect on the maximal lift coefﬁcient of DEP_HP. Nevertheless, it should be emphasized that the drag coefﬁcient would invariably be underestimated since C related to the pylons of D0 high-lift propulsions will be reduced because their impact on the wing was disregarded in VSPAERO. With pylons on the wing, the lift–drag ratio will decrease signiﬁcantly compared to [33]. Thus, as the number of pylons increases, the diameter of the high-lift propeller will have a signiﬁcant impact on the DEP’s cruise performance. Figure 15 depicts the results of two CFD simulations with various numbers of high-lift propellers. It reveals that the cruise lift–drag ratio is 10.7 for the 24 high-lift propellers conﬁguration with a wing-tip propeller advance ratio of 0.85, and 17.08 for the 10 high-lift propeller conﬁguration, with a wing-tip propeller advance ratio of 0.88. Figure 14. CL with λ_tp and λ_hp. From Figure 13, it can be concluded that the diameter of high-lift propellers has litt le eﬀect on the maximal lift coeﬃcient of DEP_HP. Nevertheless, it should be emphasized that the drag coeﬃcient would invariably be underestimated since CD0 related to the py- lons of high-lift propulsions will be reduced because their impact on the wing was disre- garded in VSPAERO. With pylons on the wing, the lift–drag ratio will decrease signiﬁ- cantly compared to [33]. Thus, as the number of pylons increases, the diameter of the high- lift propeller will have a signiﬁcant impact on the DEP’s cruise performance. Figure 15 depicts the results of two CFD simulations with various numbers of high-lift propellers. It reveals that the cruise lift–drag ratio is 10.7 for the 24 high-lift propellers conﬁguration with a wing-tip propeller advance ratio of 0.85, and 17.08 for the 10 high-lift propeller conﬁguration, with a wing-tip propeller advance ratio of 0.88. Aerospace 2023, 10, 387 14 of 20 Aerospace 2023, 10, 387 14 of 19 Figure 13. The maximum CL with diameter of high-lift propeller. Aerospace 2023, 10, 387 15 of 20 Aerospace 2023, 10, 387 15 of 20 Figure 14. C with _ and _ . Figure 14. CL with λ_tp tp and λ_hp. L hp (a) (b) From Figure 13, it can be concluded that the diameter of high-lift propellers has litt le Figure 15. Diﬀerent conﬁgurations of DEP_HP: (a) Cruise conﬁguration with 24 high-lift pro- eﬀect on the maximal lift coeﬃcient of DEP_HP. Nevertheless, it should be emphasized pellers pylons; (b) Cruise conﬁguration with 10 high-lift propellers pylons. that the drag coeﬃcient would invariably be underestimated since CD0 related to the py- lons of high-lift propulsions will be reduced because their impact on the wing was disre- The decrease in the advance ratio of high-lift propellers has a signiﬁcant impact on garded in VSPAERO. With pylons on the wing, the lift–drag ratio will decrease signiﬁ- the DEP aircraft’s lift coeﬃcient, according to Figure 14. This makes sense since, for a given cantly compared to [33]. Thus, as the number of pylons increases, the diameter of the high- inﬂow velocity, an increase in the spinning speed of a propeller’s slipstream will result in lift propeller will have a signiﬁcant impact on the DEP’s cruise performance. Figure 15 a greater axis velocity. depicts the results of two CFD simulations with various numbers of high-lift propellers. Ultimately, a DEP HP conﬁguration is obtained, as seen in Figure 16. On the leading It reveals that the cruise lift–drag ratio is 10.7 for the 24 high-lift propellers conﬁguration edge of the wing, there are 10 high-lift propellers with a 0.944 m diameter. with a wing-tip propeller advance ratio of 0.85, and 17.08 for the 10 high-lift propeller Two further CFD simulations are conducted to evaluate the takeoﬀ and landing per- conﬁguration, with a wing-tip propeller advance ratio of 0.88. formances of DEP_ (a) ( HP. Figure 17 depicts the rise in axial velocity cab used by ) the propeller’s action, and Figure 18 depicts the local change in the att ack angle caused by the propeller’s Figure 15. Diﬀerent conﬁgurations of DEP_HP: (a) Cruise conﬁguration with 24 high-lift pro- Figure 15. Different conﬁgurations of DEP_HP: (a) Cruise conﬁguration with 24 high-lift propellers spin. The lift coeﬃcient of DEP_HP in takeoﬀ is 2.404, according to the CFD simulation pellers pylons; (b) Cruise conﬁguration with 10 high-lift propellers pylons. pylons; (b) Cruise conﬁguration with 10 high-lift propellers pylons. with a high-lift propeller advance ratio of 0.5 and a wing-tip propeller advance ratio of 0.88. Moreover, the other CFD simulation with the identical propeller operating condi- The decrease in the advance ratio of high-lift propellers has a signiﬁcant impact on the The decrease in the advance ratio of high-lift propellers has a signiﬁcant impact on tions yielded a lift coeﬃcient of 2.838 for DEP_HP during landing. For takeoﬀ and land- DEP aircraft’s lift coefﬁcient, according to Figure 14. This makes sense since, for a given the DEP aircraft’s lift coeﬃcient, according to Figure 14. This makes sense since, for a given 2 2 ing, the acceleration is 2.83 m/s and 1.97 m/s , respectively. The speed of takeoﬀ is ap- inﬂow velocity, an increase in the spinning speed of a propeller ’s slipstream will result in a inﬂow velocity, an increase in the spinning speed of a propeller’s slipstream will result in proximately 27.6 m/s, while the speed of landing is around 25.4 m/s. As mentioned in greater axis velocity. a greater axis velocity. Section 4.2.3, the RX4E’s takeoﬀ and landing velocities are 31.45 m/s and 29.52 m/s, re- Ultimately, a DEP HP conﬁguration is obtained, as seen in Figure 16. On the leading Ultimately, a DEP HP conﬁguration is obtained, as seen in Figure 16. On the leading spectively. Thus, DEP HP’s takeoﬀ and landing are superior to RX4E’s. edge of the wing, there are 10 high-lift propellers with a 0.944 m diameter. edge of the wing, there are 10 high-lift propellers with a 0.944 m diameter. Two further CFD simulations are conducted to evaluate the takeoﬀ and landing per- formances of DEP_HP. Figure 17 depicts the rise in axial velocity caused by the propeller’s action, and Figure 18 depicts the local change in the att ack angle caused by the propeller’s spin. The lift coeﬃcient of DEP_HP in takeoﬀ is 2.404, according to the CFD simulation with a high-lift propeller advance ratio of 0.5 and a wing-tip propeller advance ratio of 0.88. Moreover, the other CFD simulation with the identical propeller operating condi- tions yielded a lift coeﬃcient of 2.838 for DEP_HP during landing. For takeoﬀ and land- 2 2 ing, the acceleration is 2.83 m/s and 1.97 m/s , respectively. The speed of takeoﬀ is ap- proximately 27.6 m/s, while the speed of landing is around 25.4 m/s. As mentioned in Section 4.2.3, the RX4E’s takeoﬀ and landing velocities are 31.45 m/s and 29.52 m/s, re- spectively. Thus, DEP HP’s takeoﬀ and landing are superior to RX4E’s. Figure 16. DEP_HP’s model in STAR CCM+. Figure 16. DEP_HP’s model in STAR CCM+. Figure 16. DEP_HP’s model in STAR CCM+. Aerospace 2023, 10, 387 15 of 19 Two further CFD simulations are conducted to evaluate the takeoff and landing per- formances of DEP_HP. Figure 17 depicts the rise in axial velocity caused by the propeller ’s action, and Figure 18 depicts the local change in the attack angle caused by the propeller ’s spin. The lift coefﬁcient of DEP_HP in takeoff is 2.404, according to the CFD simulation with a high-lift propeller advance ratio of 0.5 and a wing-tip propeller advance ratio of 0.88. Moreover, the other CFD simulation with the identical propeller operating conditions yielded a lift coefﬁcient of 2.838 for DEP_HP during landing. For takeoff and landing, the 2 2 acceleration is 2.83 m/s and 1.97 m/s , respectively. The speed of takeoff is approximately 27.6 m/s, while the speed of landing is around 25.4 m/s. As mentioned in Section 4.2.3, the Aerospace 2023, 10, 387 16 of 20 RX4E’s takeoff and landing velocities are 31.45 m/s and 29.52 m/s, respectively. Thus, DEP Aerospace 2023, 10, 387 16 of 20 HP’s takeoff and landing are superior to RX4E’s. Figure 17. The rise in total pressure in the region of the propeller’s activity in STAR CCM+. Figure 17. The rise in total pressure in the region of the propeller ’s activity in STAR CCM+. Figure 17. The rise in total pressure in the region of the propeller’s activity in STAR CCM+. Figure 18. Change in angle of att ack in the area of propeller motion in STAR CCM+. Figure 18. Change in angle of att ack in the area of propeller motion in STAR CCM+. Figure 18. Change in angle of attack in the area of propeller motion in STAR CCM+. Hence, it can be concluded that DEP_HP’s 𝜂 in cruise will be about 1.06 times that Hence, it can be concluded that DEP_HP’s 𝜂 in cruise will be about 1.06 times that of RX Hence, 4E without a it can degra be concluded dation inthat the t DEP_HP’s akeoﬀ and h lanin ding perform cruise will be ancabout e compared 1.06 times to RX that 4E. of RX4E without a degradation in the takeoﬀ and landing performance compared to RX4E. of RX4E without a degradation in the takeoff and landing performance compared to The cruise performance gain in DEP_HP is achievable for 0.89 times the variance in aero- The cruise performance gain in DEP_HP is achievable for 0.89 times the variance in aero- RX4E. The cruise performance gain in DEP_HP is achievable for 0.89 times the variance in dynamics and 1.19 times the beneﬁt in propulsion eﬃciency. dynamics and 1.19 times the beneﬁt in propulsion eﬃciency. aerodynamics and 1.19 times the beneﬁt in propulsion efﬁciency. 5. Further Evaluation of DEP Aircraft 5. Further Evaluation of DEP Aircraft 5.1. Investigation of Stall Characteristics for DEP Aircraft 5.1. Investigation of Stall Characteristics for DEP Aircraft The stall characteristic is another important performance indicator for airplanes. As The stall characteristic is another important performance indicator for airplanes. As a result, the stall characteristic of DEP aircrafts must be obtained. According to CCAR-23- a result, the stall characteristic of DEP aircrafts must be obtained. According to CCAR-23- R4, the stall speed of an aircraft must be achieved with the propulsion systems’ power set R4, the stall speed of an aircraft must be achieved with the propulsion systems’ power set at idle or zero thrust. The advance ratio of the propellers for the wing-tip propellers in at idle or zero thrust. The advance ratio of the propellers for the wing-tip propellers in DEP_TP and DEP_HP should be adjusted to 1.07 for zero thrust. The VS1, in which ﬂap DEP_TP and DEP_HP should be adjusted to 1.07 for zero thrust. The VS1, in which ﬂap deﬂection does not occur, is selected to assess the stall characteristics of various aircrafts deﬂection does not occur, is selected to assess the stall characteristics of various aircrafts since it is diﬃcult to properly simulate the lift coeﬃcient and drag coeﬃcient for the take- since it is diﬃcult to properly simulate the lift coeﬃcient and drag coeﬃcient for the take- oﬀ and landing conﬁguration with a large ﬂap deﬂection. Furthermore, it should be noted oﬀ and landing conﬁguration with a large ﬂap deﬂection. Furthermore, it should be noted that during the simulation of VS1, all of the high-lift propellers in DEP_HP are folded up that during the simulation of VS1, all of the high-lift propellers in DEP_HP are folded up similar to how they are in the X-57’s cruising state. Figure 19 depicts the CL together with similar to how they are in the X-57’s cruising state. Figure 19 depicts the CL together with Aerospace 2023, 10, 387 16 of 19 5. Further Evaluation of DEP Aircraft 5.1. Investigation of Stall Characteristics for DEP Aircraft The stall characteristic is another important performance indicator for airplanes. As a result, the stall characteristic of DEP aircrafts must be obtained. According to CCAR-23-R4, the stall speed of an aircraft must be achieved with the propulsion systems’ power set at idle or zero thrust. The advance ratio of the propellers for the wing-tip propellers in DEP_TP and DEP_HP should be adjusted to 1.07 for zero thrust. The V , in which ﬂap S1 deﬂection does not occur, is selected to assess the stall characteristics of various aircrafts Aerospace 2023, 10, 387 17 of 20 since it is difﬁcult to properly simulate the lift coefﬁcient and drag coefﬁcient for the takeoff and landing conﬁguration with a large ﬂap deﬂection. Furthermore, it should be noted that during the simulation of V , all of the high-lift propellers in DEP_HP are folded up S1 similar to how they are in the X-57’s cruising state. Figure 19 depicts the C together with the att ack angle for various aircrafts. According to Figure 19, the stall att ack angle for the DEP the a attack ircraft angle is a lifor tt le b various it smalair ler t crafts. han th Accor at of RX ding 4E. to Addit Figurie on 19 a,l c the alcu stall lation attack s sho angle w that for th the e stDEP all sp air eed craft s ofis Da EP little _TPbit and DE smaller P_HP than arthat e alm ofoRX4E. st equa Additional l and are ro calculations ughly 1.1 tim show es ththat ose o the f stall speeds of DEP_TP and DEP_HP are almost equal and are roughly 1.1 times those of RX4E. RX4E. Figure 19. Stall characteristics of different aircrafts. Figure 19. Stall characteristics of diﬀerent aircrafts. 5.2. Assessment of the Power Needs for DEP Aircraft 5.2. Assessment of the Power Needs for DEP Aircraft The power requirements for the DEP_HP during takeoff and landing were also deter- The power requirements for the DEP_HP during takeoﬀ and landing were also de- mined by the CFD simulation. At the takeoff condition, the power need is at its highest and termined by the CFD simulation. At the takeoﬀ condition, the power need is at its highest is around twice that of RX4E. The weight of propulsion in DEP_HP will rise signiﬁcantly and is around twice that of RX4E. The weight of propulsion in DEP_HP will rise signiﬁ- for the same power–weight ratio. Nonetheless, DEP aircrafts would be viable if propulsion cantly for the same power–weight ratio. Nonetheless, DEP aircrafts would be viable if with a power–weight ratio greater than 2 kW/kg was used because the power–weight propulsion with a power–weight ratio greater than 2 kW/kg was used because the power– ratio of an electric motor today can range from 1 to 5 kW/kg [39], and the RX4E has weight ratio of an electric motor today can range from 1 to 5 kW/kg [39], and the RX4E a power–weight ratio of roughly 1 kW/kg. For the DEP aircraft, a high power–weight has a power–weight ratio of roughly 1 kW/kg. For the DEP aircraft, a high power–weight propulsion is essential. propulsion is essential. 6. Conclusions and Discussion 6. Conclusions and Discussions This paper provided a conceptual design and optimization approach for DEP aircrafts. This paper provided a conceptual design and optimization approach for DEP air- Based on the CFD simulation of the optimal DEP aircraft, it was established that the cruise crafts. Based on the CFD simulation of the optimal DEP aircraft, it was established that lift–drag ratio of the DEP aircraft could not be increased by adding high-lift propulsion the cruise lift–drag ratio of the DEP aircraft could not be increased by adding high-lift system nacelles on the wing, but the efﬁciency of the DEP could be enhanced owing to the propulsion system nacelles on the wing, but the eﬃciency of the DEP could be enhanced high-efﬁciency propeller and the strategy used in the optimal design process to capture the owing to the high-eﬃciency propeller and the strategy used in the optimal design process high-efﬁciency operating point of the propeller. to capture the hi Based on the gh- CFD eﬃcien simulation cy operating of the point of the p optimal DEPrair opelle craft r. in cruise, takeoff and landing, Based on the CFD simulation of the optimal DEP aircraft in cruise, takeoﬀ and land- the following conclusions were drawn: ing, the following conclusions were drawn: • Under the restrictions of force balance, the increase in the cruise lift–drag ratio that results from the use of the wing-tip propellers that spin inboard and up is ﬁnite. It barely amounts to 1.7%, which is far less than the 5–10% discovered in the research of reference [8]; • Due to the use of high-lift propellers, the lift coeﬃcient of the DEP aircraft during takeoﬀ and landing could be satisfactorily enhanced. However, compared to conven- tional airplanes, DEP aircrafts would use nearly twice as much power; • A DEP aircraft with a small wing area will have a greater stall speed than a conven- tional aircraft. Because the stall speed could only be att ained with the propulsion systems’ power set to zero thrust or idle. Aerospace 2023, 10, 387 17 of 19 Under the restrictions of force balance, the increase in the cruise lift–drag ratio that results from the use of the wing-tip propellers that spin inboard and up is ﬁnite. It barely amounts to 1.7%, which is far less than the 5–10% discovered in the research of reference [8]; Due to the use of high-lift propellers, the lift coefﬁcient of the DEP aircraft during take- off and landing could be satisfactorily enhanced. However, compared to conventional airplanes, DEP aircrafts would use nearly twice as much power; A DEP aircraft with a small wing area will have a greater stall speed than a conven- tional aircraft. Because the stall speed could only be attained with the propulsion systems’ power set to zero thrust or idle. The method described in this study may be utilized to enhance the cruise performance of a DEP aircraft in contrast to an aircraft with a conventional conﬁguration. There could be an electric aircraft type with reduced cruise power consumption in the general aviation industry soon. Nonetheless, there are a few issues that need be addressed in the subsequent study: When optimizing wings, the airfoil is ignored in favor of the wings’ planar shape. This can make it more difﬁcult to choose the superior wing with outstanding cruising performance; Due to the low speed of a general aviation aircraft and the little variations in propeller size, the effects of the Reynolds number and Mach number on the performance of the propeller are disregarded in this study. The propeller performance could be overstated; The energy loss due to propeller thrust variability with time is neglected in the steady CFD simulation. Hence, the lift–drag ratio and propeller efﬁciency may be exagger- ated; The lift–drag ratio of DEP aircrafts is sensitive to the size of the motor, and the lift–drag ratio of the DEP aircraft here is based on the popular motor size of 9-12 inches. Hence, for the alternative DEP arrangement with various size motors, the lift–drag ratio may be somewhat altered. Author Contributions: J.W. presented the concepts, created the methodology, created the software, carried out validation, put together the models, did formal analysis, carried out the study, and completed data curation. F.G. took part in the methodology’s creation. S.L. conducted the inquiry and assisted with the validation. F.Y. speciﬁed the conception, gave permission for the formal analysis, assisted with the investigation, and supplied the research’s resources. The ﬁrst draft of the text was prepared with input from all writers. The paper was reviewed and edited by J.W. and F.Y. F.Y. performed the supervision and supplied the ﬁnancing acquisition for the project, and all writers took part in its visualization. The management of the project was done by J.W. and F.Y. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Institutional Review Board Statement: Not applicable. 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Conceptual Design and Optimization of Distributed Electric Propulsion General Aviation Aircraft

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ISSN: 2226-4310
DOI: 10.3390/aerospace10050387
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Abstract

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Aerospace – Multidisciplinary Digital Publishing Institute

Published: Apr 22, 2023

Keywords: distributed electric propulsion; conceptual design; optimization; range

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Conceptual Design and Optimization of Distributed Electric Propulsion General Aviation Aircraft

Conceptual Design and Optimization of Distributed Electric Propulsion General Aviation Aircraft

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Conceptual Design and Optimization of Distributed Electric Propulsion General Aviation Aircraft

Conceptual Design and Optimization of Distributed Electric Propulsion General Aviation Aircraft

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