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Handling qualities of fixed-pitch, variable-speed multicopters for urban air mobility

Published online by Cambridge University Press:  17 December 2021

M. Bahr Open the ORCID record for M. Bahr [Opens in a new window] ,
M. McKay ,
R. Niemiec Open the ORCID record for R. Niemiec [Opens in a new window]  and
F. Gandhi
M. Bahr*
Affiliation:
Rensselaer Polytechnic Institute, Center for Mobility with Vertical Lift, Troy, NY, United States of America
M. McKay
Affiliation:
Rensselaer Polytechnic Institute, Center for Mobility with Vertical Lift, Troy, NY, United States of America
R. Niemiec
Affiliation:
Rensselaer Polytechnic Institute, Center for Mobility with Vertical Lift, Troy, NY, United States of America
F. Gandhi
Affiliation:
Rensselaer Polytechnic Institute, Center for Mobility with Vertical Lift, Troy, NY, United States of America
*
E-mail: [email protected]
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Abstract

Optimisation-based control design techniques are applied to multicopters with variable-RPM rotors. The handling qualities and motor current requirements of a quadcopter, hexacopter and octocopter with equal gross weights (5,360N) and total disk areas (producing a 287N/m $^2$ disk loading) are compared in hover. For axes that rely on the rotor thrust (all except yaw), the increased inertia of the larger rotors on the quadcopter increase the current requirement, relative to vehicles with fewer, smaller rotors. Both the quadcopter and hexacopter have maximum current margin requirements (relative to hover) during a step command in longitudinal velocity. In yaw, rotor inertia is irrelevant, as the reaction torque of the motor is the same whether the rotor is accelerating or overcoming drag. This, combined with the octocopter’s greater inertia as well as the fact that it requires 30% less current to drive its motors in hover, results in the octocopter requiring the greatest current margin, relative to hover conditions. To meet handling qualities requirements, the total weight of the motors of the octocopter and hexacopter is comparable at 13.5% weight fraction, but the quadcopter’s motors are heavier, requiring 16% weight fraction. If the longitudinal and lateral axes were flown in ACAH mode, rather than TRC mode, the total motor weight of all configurations would be nearly identical, requiring about 13.5% weight fraction for motors (compared to 7–9% weight fraction from hover torque requirements).

Keywords

Multicoptershandling qualitiesUrban Air MobilityeVTOL
Type
Research Article
Information
The Aeronautical Journal , Volume 126 , Issue 1300 , June 2022 , pp. 952 - 972
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Copyright
© The Author(s), 2021. Published by Cambridge University Press on behalf of Royal Aeronautical Society

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