Performance of a small-scale helicopter rotor for martian applications
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abstract
2015 by the American Helicopter Society International, Inc. All rights reserved. The present study is in response to the great interest from NASA in assessing the feasibility of a small-scale autonomous helicopter (gross weight < 1 Kg) for Martian exploration. An autonomous rotorcraft may be ideally suited for such an application because of its unique advantages, which include the ability to take off vertically and land from harsh terrain, greater speed, range, and field of view, when compared to a traditional surface rover. The atmospheric conditions on Mars present a unique set of design challenges. Even though the Martian gravity is only about 38% of Earth's gravity, the Martian average atmospheric density is about 70 times lower than Earth's atmospheric density. Therefore, the rotors would be operating at extremely low Reynolds numbers, even lower than 5,000 for a small-scale helicopter. However, the Mach number will be significantly higher (M>0.4) because of the higher tip speed required (due to lower density) and because of the fact that the speed of sound on Mars is only about 72% of the speed of sound on Earth. This low Reynolds number, high Mach number flow conditions on the blade imposes severe constraints on the rotor design. The solution proposed in the present study involves scaling up the rotor size to produce the required thrust at acceptable Mach and Reynolds numbers. The hover performance of a full-scale rotor for a 200 gram Martian coaxial helicopter was experimentally evaluated in an evacuation chamber, where the exact Martian air density was simulated. The maximum figure of merit obtained for the baseline rotor was less than 0.4 at an operating Reynolds number of 3,300 and Mach number of 0.34. Increasing the Reynolds number at a constant Mach number by changing the air density, increased FM of the same rotor to over 0.6 at a Re of 35,000. As the Reynolds numbers was decreased to ultra-low values (Re<5000), the blade collective pitch angle for maximum FM increased even up to 30.
American Helicopter Society International - 6th AHS International Specialists' Meeting on Unmanned Rotorcraft System 2015: Platform Design, Autonomy, Operator Workload Reduction and Network Centric Operations
author list (cited authors)
Shrestha, R., Benedict, M., Hrishikeshavan, V., & Chopra, I.
complete list of authors
Shrestha, R||Benedict, M||Hrishikeshavan, V||Chopra, I
