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Parasite DragMathematics

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Additional resources toRead:

! ANA:

! Friction Effects 52-59

!

Parasite Drag 87-92

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Overview! Equivalent parasite area, f sq ft

! DP vs. Configuration

!

DP vs. Velocity! DP vs. Altitude

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Equivalent Parasite Area! D = cd S q

! Dp= cdpSq

!

Dp = lbs of forcenecessary (thrust) to"push" the a/c through airand overcome all types ofDp.

! How big would a flat plateor barn door have to be torequire the same force topush it through the air asthe Dp for a given a/c?

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Barn Door drag! Equivalent parasite area or equivalent flat plate

area. f = cdp S in sf

! Then Dp = f q

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Dp and configuration! DP1 = parasite drag

corresponding to someoriginal parasite area, f1.DP2 = parasite dragcorresponding to somenew parasite area, f2. (V, S,and are constant.)

! Lowering landing gear andflaps may increase f and

Dp by 80%.

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Dp and Velocity! Double the V, quadruple

the Dp. Half the V, quarterthe Dp.

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Dp and Altitude!

The general effect ofaltitude on parasite drag ata constant KTAS isexpressed by:

!

DP1 = parasite dragcorresponding to someoriginal altitude densityratio,1.

!

DP2 = parasite dragcorresponding to somenew altitude density ratio,2.

!

(f, VKTAS, and S areconstant)