Aerodynamics for engineering students - part 2

Nó cho thấy sự trỗi dậy được tạo ra bởi một chiếc Cessna Citation VI đã bay ngay lập tức trên các ngân hàng sương mù trên hồ Tahoe tại khoảng 313 km / h. Một độ cao rrf về icat 122 m trên mặt hồ, và khối lượng của nó khoảng 8400 kg. Downwash gây ra các xoáy dấu để đi xuống trong lớp sương mù và làm phiền nó để làm cho dòng chảy. lĩnh vực trong bối cảnh có thể nhìn thấy. | Basic concepts and definitions 45 Fig. Typical lift curves for sections of moderate thickness and various cambers zero camber it is seen to consist of a straight line passing through the origin curving over at the higher values of Cl reaching a maximum value of Crnm at an incidence of as known as the stalling point. After the stalling point the lift coefficient decreases tending to level off at some lower value for higher incidences. The slope of the straight portion of the curve is called the two-dimensional lift-curve slope dCi da or ữoc. Its theoretical value for a thin section strictly a curved or flat plate is 2tt per radian see Section . For a section of finite thickness in air a more accurate empirical value is The value of Cl is a very important characteristic of the aerofoil since it determines the minimum speed at which an aeroplane can fly. A typical value for the type of aerofoil section mentioned is about . The corresponding value of as would be around 18 . Curves b and c in Fig. are for sections that have the same thickness distribution but that are cambered c being more cambered than b . The effect of camber is merely to reduce the incidence at which a given lift coefficient is produced . to shift the whole lift curve somewhat to the left with negligible change in the value of the lift-curve slope or in the shape of the curve. This shift of the curve is measured by the incidence at which the lift coefficient is zero. This is the no-lift incidence denoted by ao and a typical value is 3 . The same reduction occurs in as. Thus a cambered section has the same value of Cl as does its thickness distribution but this occurs at a smaller incidence. Modern thin sharp-nosed sections display a slightly different characteristic to the above as shown in Fig. . In this case the lift curve has two approximately straight portions of different slopes. The slope of the lower portion is almost the same as that for a thicker section but at

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