ASTM F3338-21 - Standard Specification for Design of Electric Engines for General Aviation Aircraft

1.1 This specification covers minimum requirements for the design of electric engines.

1.2 Distributed propulsion is not excluded; however, additional requirements will be needed to address the additional issues that distributed propulsion can create. Some of those issues may include: use of a common motor controller/inverter, segregated electric harnesses, cooling systems, electric power supplies, and others.

1.3 This specification does not address all of the requirements that may be necessary for possible hybrid configurations where an electric engine and a combustion engine drive a common thruster. This specification may be used for the electric engine aspects with supplemental requirements for the thruster and the combustion engine.

1.4 Although this specification does not include specific requirements for electric engines that include gearboxes, thrusters, or any energy storage systems, it also does not preclude such capabilities. This specification may be used for the base electric engine aspects of the design, with supplemental requirements for any additional features prepared by the manufacturer and submitted to the Civil Airworthiness Authority for acceptance. This version of this ASTM specification also does not address all of the requirements necessary for configurations of motor driven ducted-fans. It is anticipated that the fan would be subject to parts of 14 CFR 33 or CS-E and/or 14 CFR 35 or CS-P, or equivalent, in particular blade-off and bird strike. These would be conducted on the fan as a unit (including motor) rather than on motor or fan alone.

1.5 The applicant for a design approval should seek the individual guidance of their respective civil aviation authority (CAA) body concerning the use of this specification as part of a certification plan. For information on which CAA regulatory bodies have accepted this specification (in whole or in part) as a means of compliance to their general aviation aircraft airworthiness regulations (hereinafter referred to as “the Rules”), refer to ASTM Committee F39 webpage (www.ASTM.org/COMITTEE/F39.htm), which includes CAA website links.

1.6 When applicable, this specification may be used for electric engines with a fixed-pitch propeller or fan. These configurations may be type-certificated as an electric engine including a thruster. There may be additional requirements not currently included in this specification for this type configuration. In addition, 5.25 is included as a test requirement for the electric engine. That section recognizes that when the electric engine does not have an integral thruster it will need to be tested with a representative load on the drive shaft to ensure the engine’s ability to operate properly with static and dynamic loads.

1.7 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.

1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.9 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.