AAE 556 Aeroelasticity Control effectivenesspart 2 9252020 Copyright

AAE 556 Aeroelasticity Control effectiveness-part 2 9/25/2020 Copyright 2008 -Purdue University AAE 556 – Spring 2008 - 8 1

Summary • Control surfaces generate less lift because the control deflection creates a nose-down pitching moment as it generates lift. • At a special dynamic pressure (a combination of airspeed and altitude) the deflection of an aileron creates more downward lift due to nose-down deflection than upward lift 9/25/2020 Copyright 2008 -Purdue University AAE 556 – Spring 2008 - 8 2

Two different ways to compute the pressure distribution resultants 9/25/2020 Copyright 2008 -Purdue University AAE 556 – Spring 2008 - 8 3

Force equivalence definition producing the same effect with different models Solve for the distance d from the AC A lift force at d produces the same result as a lift force and moment at the AC 9/25/2020 =d e Copyright 2008 -Purdue University AAE 556 – Spring 2008 - 8 Ld d 0 4

mid-chord small flap big flap Distance aft of 1/4 chord Resultant lift position AC Flap to chord ratio 9/25/2020 Copyright 2008 -Purdue University AAE 556 – Spring 2008 - 8 5

Reversal in terms of divergence parameters 9/25/2020 Copyright 2008 -Purdue University AAE 556 – Spring 2008 - 8 6

lift effectiveness expression when divergence dynamic pressure is less than reversal <1 9/25/2020 Copyright 2008 -Purdue University AAE 556 – Spring 2008 - 8 7

Plots of aileron effectiveness as functions of reversal q when R<1 9/25/2020 Copyright 2008 -Purdue University AAE 556 – Spring 2008 - 8 8

Aileron effectiveness when R>1 9/25/2020 Copyright 2008 -Purdue University AAE 556 – Spring 2008 - 8 9

Summary aileron deflection creates. . . • (a shift in zero lift line due to "camber" created by control surface deflection) • twisting downward if lift vector due control deflection is behind section shear center downward 9/25/2020 Copyright 2008 -Purdue University AAE 556 – Spring 2008 - 8 10

Torsional divergence a classical model Idealizations 9/25/2020 Copyright 2008 -Purdue University AAE 556 – Spring 2008 - 8 11

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Divergence 9/25/2020 Copyright 2008 -Purdue University AAE 556 – Spring 2008 - 8 17

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