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# spl8c - to note that EDA= for the case of a simple...

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Equivalent Dihedral Angle Some multi-panel wings have polyhedral , which is a spanwise-varying dihedral angle Υ( y ). In order to apply stability and control criteria to such a wing, it is necessary to determine its Equivalent Dihedral Angle , or EDA, in terms of Υ( y ). This EDA then takes the place of the constant Υ which appears in stability and control criteria. Using the convenient normalized spanwise coordinate η 2 y/b , the EDA is computed as a weighted average of Υ( η ). Assuming the spanwise loading is approximately elliptical, the appropriate weight function is the ellipse (1 η 2 ) 1 / 2 times the roll moment arm η . 1 EDA = 0 Υ (1 η 2 ) 1 / 2 η dη = 3 1 Υ 1 η 2 1 / 2 η dη (1) 1 0 (1 η 2 ) 1 / 2 η dη 0 This is still gives good results for more general wings with non-elliptical loading. It’s useful to note that EDA= Υ for the case of
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Unformatted text preview: to note that EDA= for the case of a simple V-dihedral wing with constant ( ). By introducing the cubed-ellipse function f = 1 2 3 / 2 (2) df = 3 1 2 1 / 2 d (3) equation (1) can be rewritten as follows. 0 EDA = df (4) 1 For the usual case where the wing consists of at panels, is piecewise constant, with values 1 , 2 . . . in between the dihedral-break stations , 1 , 2 . . . . The integral (4) can then be written as a sum over the individual panels. The 2-panel case is shown in Figure 1. EDA = 1 ( f 0 f 1 ) + 2 ( f 1 f 2 ) + . . . (5) f 1 f 1 f 2 f f 1 0 1 2 1 2 = 0 1 2 = 1 1 2 Figure 1: Quantities used for calculating the EDA of a 2-panel polyhedral wing....
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