# Evaluation and Comparison of Hybrid Wing VTOL UAV with Four Different Electric Propulsion Systems

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## Abstract

**:**

## 1. Introduction

## 2. Propulsion and Power System Analysis

#### 2.1. Structures of Electric Propulsion System

#### 2.2. Energy Saving Mechanism and Power Distribution

- Compared with the turboelectric propulsion system, a smaller ICE is needed to meet the power demand of cruise and charging, and the battery provides additional power such as takeoff and climb, so as to improve the load rate of ICE;
- Make ICE always work in the optimal fuel economy area;
- In cruise phase, when ICE works in the optimal fuel economy area, the excess energy charges the battery to improve the overall efficiency of the propulsion system.

#### 2.3. Mass Calculation

#### 2.3.1. Composition of UAV Mass

#### 2.3.2. Power Calculation

#### 2.3.3. Mass Estimation of Propulsion and Power System

_{prop}= 15, K

_{material}= 0.6, where D

_{prop}is the diameter of propeller/rotors, which can be expressed as [22]:

_{p}is 0.1072, 0.0995, and 0.0938 for different blade numbers 2, 3, and 4, respectively.

## 3. Initial Sizing Method

#### 3.1. Initial Sizing Process

#### 3.2. Fixed-Wing Constraint Analysis and Design Point Selection

_{p}is the current propeller efficiency. Cruise constraints can be expressed as:

## 4. Numerical Results

#### 4.1. Case Studies

#### 4.2. Sensitivity Study

#### 4.2.1. Takeoff Altitude Sensitivity

#### 4.2.2. Cruise Distance Sensitivity

#### 4.2.3. Payload Sensitivity

## 5. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## References

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**Table 1.**Technology assessment of hybrid electric systems. Data from [27].

Parameters | Min | Max |
---|---|---|

Electric Motor Efficiency | 0.86 | 0.98 |

ICE Efficiency | 0.2 | 0.4 |

Generator Efficiency | 0.86 | 0.98 |

Battery Efficiency | 0.8 | 0.99 |

Battery Power Density (kW/kg) | 0.35 | 0.8 |

Battery Energy Density (Wh/kg) | 151 | 260 |

ICE Power Density (kW/kg) | 0.25 | 3 |

Electric Motor Power Density (kW/kg) | 3 | 5 |

**Table 2.**Design optimization problem Data from [19].

Minimize | Design Variables | Constraints |
---|---|---|

MTOM, cost, fuel mass… | Maximum output power of propulsion components, wing area… | Performance, aerodynamic characteristics, mechanical characteristics, and stability… |

Performance | Value |
---|---|

Cruise speed | 30 m/s |

ROC | 3 m/s |

Service ceiling | 1000 m |

Stall speed | 12.5 m/s |

Payload | 10 kg |

Cases | Takeoff Altitude (m) | Cruise Distance (km) |
---|---|---|

Case 1 | 500 | 30 |

Case 2 | 1500 | 100 |

Case 3 | 3000 | 500 |

Types | Case 1 | Case 2 | Case 3 | |||
---|---|---|---|---|---|---|

MTOM (kg) | Fuel (kg) | MTOM (kg) | Fuel (kg) | MTOM (kg) | Fuel (kg) | |

All electric | 41.35 | 0 | / | / | / | / |

Series hybrid | 20.89 | 0.135 | 21.57 | 0.45 | 26.34 | 2.34 |

Parallel hybrid | 23.98 | 0.11 | 28.32 | 0.45 | / | / |

Turboelectric | 24.26 | 0.156 | 25.16 | 0.52 | 30.54 | 2.73 |

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**MDPI and ACS Style**

Zong, J.; Zhu, B.; Hou, Z.; Yang, X.; Zhai, J.
Evaluation and Comparison of Hybrid Wing VTOL UAV with Four Different Electric Propulsion Systems. *Aerospace* **2021**, *8*, 256.
https://doi.org/10.3390/aerospace8090256

**AMA Style**

Zong J, Zhu B, Hou Z, Yang X, Zhai J.
Evaluation and Comparison of Hybrid Wing VTOL UAV with Four Different Electric Propulsion Systems. *Aerospace*. 2021; 8(9):256.
https://doi.org/10.3390/aerospace8090256

**Chicago/Turabian Style**

Zong, Jianan, Bingjie Zhu, Zhongxi Hou, Xixiang Yang, and Jiaqi Zhai.
2021. "Evaluation and Comparison of Hybrid Wing VTOL UAV with Four Different Electric Propulsion Systems" *Aerospace* 8, no. 9: 256.
https://doi.org/10.3390/aerospace8090256