In the publication, “Mars Helicopter Technology Demonstrator”, Balaram (2018) described the features of the rotor system of the Ingenuity.
The Ingenuity is equipped with a 1.21 m diameter coaxial counter-rotating rotor to minimize its size and constraints of its host aircraft. The rotor itself is designed with a rigid rotor to reduce flapping; that is the out-of-plane deflection the blades do when a force is applied. The rigid rotor design is due to the thin Martian atmosphere which causes poor aerodynamic damping. Which can cause the aircraft to oscillate during its flight phase. To address the poor damping and at the same time allow some degree of flapping. The blades are unusually stiff, with a rotating flap frequency of about 80–90 Hz. The blades are able to flap at the outboard portion of the blades via elastic deformation. The Martian atmosphere also requires the blades to spin at a maximum rotation of up to 2800 rpm. The bearings and swashplates are enclosed with seals and soft boots to prevent dust build up.
The Ingenuity's rotor system has 2 important design decisions to address the thin Martian atmosphere that ultimately lead to the first successful flight on Mars.
The Ingenuity is designed with a rigid rotor to address the thin Martian atmospheres effect of reducing aerodynamic damping (Balaram, 2018). Aerodynamic damping is the natural tendency for the air in the atmosphere to oppose an aircraft's movement. In this poorly damped environment, any input from the control system can amplify the resonance of the aircraft and leading to instability (Grip, 2019). Hence to reduce as much excess motion as possible within the rotor, a rigid rotor is used.
Too further ensure the stability of the Ingenuity, Blades with frequencies of 86 Hz are chosen (Balaram, 2018). The blades are to ensure that the resonance of the aircraft is higher than the resonance caused by the inputs from the control system. The high frequency blades help move the poor damped resonance to a high frequency that does not interfere with the control system (Grip, 2019).
The rigid rotor however is a direct contrast to Earthen helicopters that often have hinged rotor assemblies. This hinges allow the blades to deflect out of its plane when a force is applied rather than absorb it. Making it particularly important to prevent large longitudinal and lateral moments along the blades from destabilizing the helicopter (Bramwell, 2020).
Addressing the thinner Martian atmosphere and the poor damping dynamics. The rigid rotor with high blade frequencies have helped achieve stable flight and thus allowed multiple successful flight on Mars.
References
Balaram, J., Canham, T., Duncan, C., Golombek, M., Grip, H., Johnson, W., Maki, J., Quon, A., Stern, R., & Zhu, D. (2018). Mars Helicopter Technology Demonstrator https://rotorcraft.arc.nasa.gov/Publications/files/Balaram_AIAA2018_0023.pdf
Bramwell, A.R.S., Done G., Balmford D. (2000). Bramwell's Helicopter Dynamics.
https://www.sciencedirect.com/book/9780750650755/bramwells-helicopter-dynamics
Grip H., Johnson W., Malpica C., Scharf D., Mandić M., Young L., Allan B., Mettler B., Martin M. and Lam J. (2019). Modeling and Identification of Hover Flight Dynamics for NASA’s Mars Helicopter.
https://arc.aiaa.org.singaporetech.remotexs.co/doi/full/10.2514/1.G004228
Comments
Post a Comment