Coaxial rotor hover power reduction using dissimilarity between upper and lower rotor design

Authors
Wicha, Jan
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Other Contributors
Gandhi, Farhan
Koratkar, Nikhil A. A.
Mishra, Sandipan
Issue Date
2015-08
Keywords
Aeronautical engineering
Degree
MS
Terms of Use
Attribution-NonCommercial-NoDerivs 3.0 United States
This electronic version is a licensed copy owned by Rensselaer Polytechnic Institute, Troy, NY. Copyright of original work retained by author.
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Abstract
The present work investigates the power reductions that can be achieved through the use of dissimilar rotors in a coaxial rotor system. The aerodynamic interactions of the coaxial system are modeled using an adapted Blade Element Momentum Theory (BEMT). A representative model of the Sikorsky XH-59A technology demonstrator is used as a baseline helicopter model to examine the benefits of dissimilarity in a rotor system that is intended for full-scale flight.
A formal optimization study was then performed to explore the power reductions that can be achieved if multiple design variables are considered for each rotor. When all variables are considered, a power reduction of 15\% is achieved. At the optimal design, the thrust share between the upper and lower rotor is 60\% and 40\%, respectively. A similar sharing of power is also observed indicating that at the optimum state the rotors operate at close to equivalent power loading. Out of the variables considered it has been shown that the optimized coaxial system is least sensitive to twist distributions and similar power reductions can be achieved if only rotor radii, RPM, and chord distributions are considered.
Initially, parametric studies are conducted to explore the effects of differential radii, RPM, twist and chord distributions. It was shown that the coaxial system can indeed benefit if a unique design is used for the upper and lower rotor. The parametric studies revealed that the largest power reduction is achieved through the use of differential radii. By using a smaller radius for the upper rotor and a larger radius for the lower rotor while maintaining total rotor area, a 5.5\% power reduction is achieved.
Description
August 2015
School of Engineering
Department
Dept. of Mechanical, Aerospace, and Nuclear Engineering
Publisher
Rensselaer Polytechnic Institute, Troy, NY
Relationships
Rensselaer Theses and Dissertations Online Collection
Access
CC BY-NC-ND. Users may download and share copies with attribution in accordance with a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License. No commercial use or derivatives are permitted without the explicit approval of the author.