Interest in the exploration of other planets has led to the success of Ingenuity (Mars helicopter)'s first flight in the Martian atmosphere. Despite this achievement, the flight of aircraft under ultra-low air density, such as Mars, is still limited. A flapping-wing aircraft that mimics nature's flyers can provide an alternative solution to conventional aircraft. Successful flapping flight on Mars, where the air density is very thin, requires an understanding of aerodynamics, and prediction of the dynamic changes of the flapping wing under very-low air density. In this paper, we constructed a simple dynamic model that can predict the changes in aerodynamics and dynamic behavior under various low air densities. The predicted changes were compared with the measured ones in a chamber that could simulate the low air density with a modified flapping-wing system based on our flapping-wing micro-air-vehicle (FW−MAV) models, the KUBeetle. Both prediction and measurement showed that when the air density decreased, the flapping frequency tended to increase due to drag reduction, even without consuming additional power. The model reasonably predicted a large decrease in the lift for the 10 % air density, where the flapping frequency increased by 10 %. Under the 50 % and 25 % low air densities, the measured lift coefficients did not change much. However, under the 10 % air density, the lift coefficient decreased by about 16 % due to less wing rotation and wing twist. While the aerodynamic power was predicted to decrease significantly due to the large decrease in aerodynamic forces under low air density, an increase in the angular velocity and peak angular acceleration caused an increase in the inertial power. Therefore, the amount of reduction in the measured mechanical power consumption under the 10 % air density was relatively small, compared to that under the 100 % air density. This work may provide insights into the design of an FW−MAV for the ultra-thin air density, such as Mars.

中文翻译：

---

低空气密度下扑翼气动及动力特性


对探索其他行星的兴趣导致了Ingenuity（火星直升机）首次在火星大气层中的飞行获得成功。尽管取得了这一成就，但飞机在火星等超低空气密度下的飞行仍然受到限制。模仿自然界飞行物的扑翼飞机可以为传统飞机提供替代解决方案。在空气密度非常稀薄的火星上成功扑动飞行需要了解空气动力学，并预测极低空气密度下扑翼的动态变化。在本文中，我们构建了一个简单的动力学模型，可以预测各种低空气密度下空气动力学和动力学行为的变化。将预测的变化与室内测量的变化进行比较，该室内可以使用基于我们的扑翼微型飞行器（FW−MAV）模型 KUBeetle 的改进扑翼系统来模拟低空气密度。预测和测量都表明，当空气密度降低时，即使不消耗额外的功率，扑动频率也会因阻力减少而趋于增加。该模型合理地预测，空气密度为 10% 时，升力会大幅下降，而扑动频率则增加 10%。在50%和25%低空气密度下，测得的升力系数变化不大。然而，在10%的空气密度下，由于机翼旋转和机翼扭转较少，升力系数下降了约16%。虽然由于低空气密度下气动力大幅下降，预计空气动力会显着下降，但角速度和峰值角加速度的增加会导致惯性功率增加。 因此，与100%空气密度下相比，在10%空气密度下测得的机械功耗的降低量相对较小。这项工作可以为超薄空气密度（例如火星）的 FW−MAV 设计提供见解。