The maximum lift coefficient CLmax is directly connected to the selection of wing loading,which further affects aircraft’s mass and economy.CLmax of propeller aircraft is improved with increased slipstream intensity at powered condition,however the conventional theory trends to some conservative and smaller power-off value,hence does not utilize the full potential per-formance of aircraft.Combining the airworthiness regulations and the actual flight condition of an aircraft with four turbo-prop engines,a new concept is proposed to find the optimal CLmax based on engine standby condition.The power-on CLmax is separated into four parts:power-off CLmax , propeller thrust component,propeller normal force and lift due to slipstream,which are simula-ted,measured and corrected by power-off and multi-balance power-on wind tunnel tests.The calculation shows that the propeller aircraft with four engines has slipstream intensity in the order of 0.1 at stall flight test condition with engines standby.The slipstream effect is the major factor of lift increment even at small slipstream intensity,and the increment increases as flap angle or slipstream intensity increase.The four engines at standby condition also generate considerable thrust and normal force due to lift.The power effect of turbo-prop engine increases the CLmax of different flap configurations up to 8%~9%.The CLmax obtained by the method agrees well with flight test,and the low speed performance of the aircraft is well utilized.The research can be an important reference for propeller aircraft design.%飞机的最大升力系数 CLmax 直接影响翼载的选取，进而影响飞机的重量和经济性。螺旋桨飞机在带动力条件下 CLmax 随滑流强度增加而提高，但按照常规理论采用无动力 CLmax 数据选取的翼载偏小偏保守，没有充分发掘飞机的性能潜力。结合适航规定以及某四发螺旋桨飞机飞行实际情况，提出了一种基于发动机慢车状态确定 CLmax的概念，并将飞机带动力 CLmax 分解为无动力 CLmax 、螺旋桨拉力、螺旋桨法向力、滑流增升效应等4部分贡献，通过无动力和多天平带动力风洞实验完成了上述分量的模拟、测量和修正。计算表明某四发螺旋桨飞机在发动机慢车失速试飞条件下的滑流强度约为0．1，螺旋桨系统的动力增升作用使不同襟翼构型的 CLmax 增加8％～9％。该方法获得的 CLmax 与飞机试飞结果较为吻合，充分挖掘了飞机的低速性能潜力，并为同类螺旋桨飞机设计提供了一定的参考。
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