The Department of Defense, specifically the Army, is seeking innovative solutions through the Small Business Innovation Research (SBIR) program for the development of high power and torque electric motors suitable for direct-drive rotorcraft applications. The objective is to design an electric motor architecture that can deliver approximately 400-700+ horsepower at low rotational speeds (250-400 RPM) while maintaining high torque densities (20-30+ ft-lb/lb) to enhance the efficiency and performance of electric Vertical Takeoff and Landing (eVTOL) systems. This initiative is critical for advancing electric aviation technologies, particularly for unmanned aircraft systems and logistics applications, with the potential to simplify designs by eliminating mechanical drive systems. The solicitation is currently closed, with the application due date set for July 30, 2024. For more information, interested parties can visit the official SBIR website at https://www.dodsbirsttr.mil/topics-app/.

## Description

Electrification and hybridization are rapidly enabling new rotorcraft design options. Electric Vertical Takeoff and Landing (eVTOL) research efforts within the U.S. Army continue to expand (Reference 1) . However, current electric motor technologies tend to limit configuration options. Current high power output motors are heavy and tend to operate at high rotational speeds (RPMs) on the order of 2,000+ RPM. This means configurations are often driven towards the use of multiple, lower-power motors operating at high RPMs and/or towards coupling the electric motor with a mechanical drive system to reduce RPM. As noted in Reference 2 , given current technology limitations, direct drive is not a weight efficient design option compared to a high-speed motor coupled with a mechanical transmission. There is a need for weight-efficient electric motors capable of providing direct-drive options for rotorcraft applications, particularly for hover-efficient, low-diskloading platforms. This means that novel electric motor designs are needed to provide high output power (~400-700+ Horsepower) at low rotational speeds (~250-400 RPM), and thus high torque (~5,000 &ndash; 15,000+ ft-lb). Further, Government historical weight trends (Reference 3) indicate electric motors at these levels of power and torque may be extremely heavy. In order to be viable for aerospace applications, motors that meet these torque and speed ranges also need to be highly weight efficient as characterized by torque densities (torque per pound of weight) in the range of 20-30+ ft-lb/lb. In addition, these motors need to exhibit high torque densities in both continuous and short-term hover operations applicable to current rotorcraft duty cycles. Motors with these combinations of capabilities would allow an electric motor to directly drive a rotor, eliminating the weight, complexity, and reliability/maintainability issues of a mechanical drive system. Advancements in electric motor technology is critical to the future of electric aviation (Reference 4). These motors would have immediate application for light rotary-wing new-start designs as well as retrofit activities. In particular, the area of eVTOL unmanned aircraft systems (UAS) would benefit from the opportunities to reduce weight and complexity while also leveraging larger diameter rotors for efficient lift capacity and compact folding/transport. These benefits have the potential to enhance UAS application to the area of logistics (resupply) where lift-to-weight ratio and cost efficiency are key enablers. Potential commercial applications for Advanced Air Mobility (Reference 5) and distributed logistics are also significant.This SBIR effort will define a novel electric motor architecture that exhibits the power and torque density needed for direct-drive rotorcraft applications. It must include the analytic effort to describe the underlying physics and associated benefits or limitations in the approach, including physical scale and thermal management. It will then mature this motor architecture via a detailed design for application to a relevant rotorcraft use case. Phase III application includes the construction and demonstration of this prototype motor to substantiate performance.

## Objective

Identify and design an electric motor architecture enabling high power and torque output at motor rotational speeds and system weights suitable for direct-drive rotorcraft applications such as single main rotor helicopters. Build and demonstrate a prototype motor to substantiate weight and performance projections.

## Phase I

The Phase I effort will establish the technical feasibility of the proposed motor architecture via conceptual design analysis. It will focus on system definition and analytic modeling. Estimates of system performance and weight should be generated through physics-based modeling of the motor. This modeling should include other system attributes, such as thermal characteristics, that are critical to document the suitability of the motor for practical aerospace applications.Phase I will also define a relevant rotorcraft use case for the proposed electric motor, such as use in a new or existing eVTOL platform or potential retrofit to existing aircraft. This use case will guide development of the motor design and illustrate the advantages/challenges of the proposed approach compared to more conventional solutions. The Government will provide feedback and support on use case definitions, particularly for offerors without a targeted application in mind.

## Phase II

The Phase II effort will leverage the analytic modeling of Phase I and extend into design application. This will culminate in the design of a functional electric motor for the use case defined in Phase I. The Phase II effort should include the following key elements:<ol><li> Identification of key design parameters: Identify the motor size, weight, torque, and operating speed design targets suitable for application to the use case. System weight should include any accessories or sub-systems needed to allow continuous operation of the motor in its design environment. Projected performance against these targets should be tracked throughout the design process. These parameters also represent key evaluation parameters for Phase III demonstration.</li><li> Detailed design: Leveraging the analytic modeling from Phase I, perform a detailed design of a full-scale electric motor against the key design parameters. The detailed design should be sufficient to evaluate integration into the use case. It should also be at sufficient detail to substantiate readiness to proceed to potential Phase III build and test activities.</li><li> (As needed) Sub-component/assembly proof-of-concept testing: Only where required to support detailed design, perform proof-of-concept demonstrations on sub-components or sub-assemblies. These may be done at any scale that supports maturation of the detailed design and would be considered very limited in scope and depth.</li></ol>

## Phase III: Dual Use Applications

Phase III activities will leverage the motor design from Phase II in a relevant aerospace application. Phase III includes the manufacture or procurement of components, assembly, and testing of the new electric motor. Testing will evaluate the motor&rsquo;s performance against the key design parameters established in Phase II. Ideally, this application is direct use within the use case identified in Phase I. However, it is likely such a demonstration may not be feasible or cost effective due to insufficient maturity or availability of the targeted air platform. As such, the use of the motor in an applied Systems Integration Lab (SIL) or &ldquo;Copper Bird&rdquo; integration will be considered sufficient. The use of existing Advanced Technology Demonstration (ATD) activities will be explored, particularly the Hybrid-Electric ATD planned within DEVCOM AvMC TDD.

High Power and Torque Electric Motors for Direct-Drive Rotorcraft Applications

SBIR Opportunity Analysis

SBIR Documents

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