In this paper we revisit the modeling framework used to derive the Betz limit of power extraction from the wind based on linear momentum theory. One of our contributions is to suggest that the Betz limit of 16/27≈59%$16/27\approx 59\text{\%}$ should in fact hold true for any device that harvests power through drag or torque in a horizontal-axis rotational motion perpendicular to the wind field, which is not only the case of conventional wind turbines but also of Loyd's drag power Airborne Wind Energy (AWE) systems. Another contribution is to show that Loyd's lift power AWE devices during the reel-out phase can harvest up to 4/27≈15%$4/27\approx 15\text{\%}$ of usable power available in the wind, i.e. exactly 1/4$1/4$ of the theoretical limit of the horizontal-axis turbines and AWE drag power systems with ideal airfoils. Moreover, in order to operate at such limit, AWE lift power systems must also extract from the wind an amount of drag power that is equal to the reel-out power. These claims are supported by physical principles and mathematical formulations.

在本文中，我们将重新研究基于线性动量理论用于从风中提取功率的Betz极限的建模框架。我们的贡献之一是建议贝兹极限为16 /27≈59％$16/27\approx 59\text{％}$实际上，对于在垂直于风场的水平轴旋转运动中通过阻力或扭矩来获取动力的任何设备而言，这都应适用，不仅是常规风力涡轮机，而且是Loyd阻力的机载风能（AWE）系统。另一个贡献是表明，在收卷阶段，Loyd的提升功率AWE设备可以收获高达4 /27≈15％的能量。$4/27\approx 15\text{％}$风中可用的可用功率的百分之一，即精确地为1/4$\mathrm{1个}/4$具有理想机翼的水平轴涡轮机和AWE拖动动力系统的理论极限。而且，为了在这样的极限下运行，AWE提升动力系统还必须从风中提取与卷取动力相等的牵引力。这些主张得到了物理原理和数学公式的支持。