Design of Revolutionary Ultra-Quiet Propulsors for S/VTOL
Award last edited on: 10/18/2022

Sponsored Program
Awarding Agency
Total Award Amount
Award Phase
Solicitation Topic Code
Principal Investigator
Moble Benedict

Company Information

Harmony Aeronautics LLC

15605 Tiger Creek Coirt
College Station, TX 77845
   (240) 676-5023

Research Institution

Texas A&M Research Foundation

Phase I

Contract Number: FA8649-21-P-0124
Start Date: 12/5/2020    Completed: 6/5/2021
Phase I year
Phase I Amount
Recently, the aerospace industry has witnessed a surge in interest in multirotor UAM (urban air mobility) systems for short-range personnel and cargo transportation for both civilian and military applications. This has resulted in significant capital investment and the development of numerous eVTOL (electric Vertical Take-off and Landing) aircraft. Soon, skies will be filled with busy buzzing multirotor aircraft, generating a new urban and suburban soundscape that is both different and louder than ever before. This intrusion of acoustic irritants into the last quiet recesses of life must be stopped if eVTOL are to be accepted by the public. Undesirably high sound levels are particularly problematic during hover and transition to cruise when the vehicle is close to people. During this time the propeller disk loading and rotational speeds are high creating high levels of annoying tonal noise. To address this, Harmony Aeronautics LLC will design and develop adaptable ultra-quiet coaxial propulsors for today’s diverse array of emerging eVTOL aircraft which will be 8 times (18dB) quieter than existing eVTOL propellers. Several in-house acoustic and rotor aerodynamic simulation tools have been developed. The acoustic code models the primary sources of rotor and propeller noise generation: thickness, loading, and broadband noise. The aerodynamic code predicts performance characteristics based on design parameters. These programs will be combined with high-fidelity 3D CFD simulation for a comprehensive analysis of propeller performance and rotor flowfield characteristics, and will be used to develop aeroacoustically optimized modular coaxial propulsors with minimal noise disturbances. A high blade solidity coaxial rotor configuration will be used to minimize the rotor RPM, as the blade tip speed is the primary driver of tonal noise. The impulsive unsteady loading caused by rotor-rotor and rotor-airframe interactions will be further attenuated using a novel double swept blade planform shape that dephases the acoustic effect of these interactions. Harmony Aeronautics has developed a hover-optimized prototype of the quiet coaxial rotor system and incorporated it into a sub-scale 22lb drone and a full-scale 550lb personal air vehicle. This was the result of participation in the Boeing sponsored GoFly challenge, a $2 million X-prize contest to develop a quiet, compact, high-endurance eVTOL personal air vehicle. The full-scale vehicle generated ~72dBA of noise in hovering flight at 50 feet, approximately 25 dBA quieter than a light helicopter in hover, and unprecedented for an aircraft of this size. The success of this quiet coaxial rotor demonstrates a promising solution to reducing eVTOL aircraft noise. Similar quieting techniques will be used to design propellers and integrate them into single coaxial propulsor units which will be scaled according to application requirements as demonstrated in the sub-scale and full-scale vehicles.

Phase II

Contract Number: FA8649-22-P-0771
Start Date: 3/11/2022    Completed: 6/11/2023
Phase II year
Phase II Amount
The overarching objective of the Phase-II effort is to build upon Harmony’s in-house developed conceptual design tools for S/VTOL (Short/Vertical Take-Off and Landing) propulsors (both propellers and rotors) and demonstrate their effectiveness by developing and testing a full-scale propulsor with low noise and high efficiency. Phase-I computational aeroacoustic analysis clearly demonstrated the ability to quiet VTOL propulsors (8X quieter than traditional VTOL propellers) with superior aerodynamic efficiency. While sub-scale experiments in an anechoic wind-tunnel with rapid-prototyped blades demonstrated similar reductions in interaction noise, aeroelastic effects (blade deflections and flutter instabilities) caused by the novel blade planform shape deteriorated thrust and produced excessive vibration. Therefore, a focus of Phase-II will be to couple an aeroelastic analysis with an improved aeroacoustic solver to produce a tool for the preliminary design and analysis of S/VTOL propulsors. The design tool, once validated with sub-scale experiments, will be utilized to design an aeroacoustically tailored 8-ft diameter full-scale coaxial propulsor utilizing structurally stiff composite blades to minimize deflections and overall weight. The propulsor prototype will be built and its ability to generate the target thrust (1500 lbf) with a hover figure of merit (FM) > 0.7, propulsive efficiency (?prop) > 0.85 and noise level < 80 dBA at 100 ft will be demonstrated via testing.