Research on Electric Propulsion Systems for Powered-Lift Aircraft [Electric Drive System Conference]

On June 21, at the 2025 SMM (4th) Electric Drive System Conference & Drive Motor Industry Forum - eVTOL Electric Drive System Forum jointly hosted by SMM Information & Technology Co., Ltd., Hunan Hongwang New Material Technology Co., Ltd., Louxing District People's Government, and the National-level Loudi Economic and Technological Development Zone, Dr. Jie Gao, an associate professor from the Electric Propulsion System Safety and Airworthiness Technology Research Laboratory at Civil Aviation University of China, shared insights on "Research on Electric Propulsion Systems for Electric Aircraft."

Technical Characteristics of Electric Propulsion Systems

►Main Types of Key Technologies in Electric Propulsion Systems

Axial Flux Motors vs. Radial Flux Motors; Internal Rotor vs. External Rotor; Direct Drive vs. Gearbox Drive; Air Cooling vs. Liquid Cooling vs. Hybrid Cooling; Propellers: Variable Pitch, Reversible Pitch, Feathering Pitch, etc.

►Research Starting Points

Analysis of Existing Regulations Domestically and Overseas

A brief analysis of regulations on electric propulsion systems, including FAA: Type Certification - Powered Lift, EASA, EHPS Certification Guidelines, Type Certificate-Pipistrel E-811, Type Certificate-Safran ENGINeUS100B1, and Special Conditions by the Civil Aviation Administration, etc.

The speaker also elaborated on the development of group standards.

General Requirements for Electric Propulsion Systems

Compliance Verification

XX.3327 Overspeed

(a) As defined in paragraph (g)(2) of XX.3375, rotor overspeed must not result in rotor burst, deformation, or damage that could lead to hazardous electric engine consequences. Compliance with this clause must be demonstrated through testing, valid analysis, or a combination of both. The set speed for overspeed must be declared and its rationale explained.

(b) The rotor must have sufficient strength and adequate burst margin under conditions exceeding certified operating conditions and failure conditions that could lead to rotor overspeed. The burst margin must be demonstrated through testing, valid analysis, or a combination of both.

(c) The electric engine must not exceed speed limits that could affect the structural integrity of the rotor.

XX.3519 Durability

Original Clause: Each part of the propeller must be designed and constructed to minimize any unsafe conditions occurring between overhauls.

Clause Interpretation: From the aspects of design, manufacturing, testing, use, and maintenance, it must be ensured that each part of the propeller will not fail in a way that affects propeller safety during its overhaul period, guaranteeing the propeller's ability to operate safely between overhauls. The key points can be broken down as follows:

a) Design: This involves considering the operating environment, stress levels, and material selection for propeller components. It also encompasses structural, strength, stiffness, deformation, and fatigue performance. Fatigue tests need to be designed to ensure that the propeller does not fail due to fatigue between overhaul intervals, and to determine these intervals.

b) Testing and Analysis: Conduct analysis based on test results from static tests, fatigue tests, durability tests, functional tests, and other tests (such as bird strike, lightning strike, overspeed and over-torque, propeller control system components, hydraulic components, etc.).

c) Usage and Maintenance: Use and maintain the propeller in accordance with the manual.

In addition, it also elaborates on the test outline, test reports, etc.

Review Practice for Standard Application

Certification of Electric Propulsion Systems for Electric Aircraft

The current certification method for electric propulsion systems is still case-by-case certification.

Risk-Based Review - Aircraft Level; Supplementary Requirements for Electric Aircraft Power Plants in Chapter CCAR-23-R4H; Guide for Developing Special Conditions for Electric Propulsion Systems - Advisory Circular; Special Condition.

It also introduces the release of four group standards for electric propulsion systems and the continuous development of civil aviation standards in the future.

》Click to view the special report on the 2025SMM (4th) Electric Drive System Conference & Drive Motor Industry Forum