Drag Veronica, Patrick, Jimmy, Garrett
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Drag
Veronica, Patrick, Jimmy, Garrett
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Simplistic View
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Wingtip Vortices Revisited
http://www.capelaction.com/Source/38496_GOOBJ.jpg
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•Lift generated from differences in pressure above the airfoil and below
•Air flow moves from high pressure to low pressure with freedom along tips
•Produces circular motion affects the air, clockwise of the left and counter-clockwise
on the right
http://www.centennialofflight.gov/essay/Theories_of_Flight/Vortex/TH15G1.jpg
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Airflow varies
Less effect due to induced flow More effect due to induced flow
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Induced Drag
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Induced Drag
• Vortices reduce the
wings’ ability to
generate lift
• As a result of thesevortices, the local angle
of attack is increased.
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Efficiency Factor
• Elliptical distribution
has the lowest induced
drag
• e=1• Other wing shapes: e<1
• Therefore, more
induced drag
http://3.bp.blogspot.com/_1fXv2yds-Xs/TMGvkAJMHtI/AAAAAAAABW8/8z5mzN2rgl0/s1600/spitfire.jpg
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Minimizing Induced Drag
Twisted Wings:Less angle of attack at the
tips and higher angle of
attack on the inner wing
Curved Trailing Edges:
Wright Brothers used
curved trailing edges-
attempted to minimize
induced drag of
rectangular wings
http://i.telegraph.co.uk/multimedia/archive/01691/boeing767_1691451c.jpg
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Winglets
• Minimizing the wingtip to a
fraction of total wing area• Weaken the vortices
20% less induced drag
http://www.flightglobal.com/blogs/flightblogger/assets_c/2008/12/48289-224-thumb-560x373.jpg
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Minimizing Induced Drag
• Long and thin wingspan
leads to lowered
induced drag
• However, this designdoes not minimize
parasitic or form drag
well
http://1.bp.blogspot.com/_NSJHITf-yrc/SgrSXdyfljI/AAAAAAAAAuE/BUOB865IInc/s1600/glider.jpg
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Viscosity
• Air has relatively low viscosity, however,
it still does have viscosity that creates
“internal friction”
• Air rubs against the surface of an
airplane, generating the force thatopposes movement
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Boundary Layer
• A very thin
layer of air
flowing
around thesurface of an
object
• Friction dragoccurs here
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Boundary Layer
- Ludwig Prandtl
introduced the conceptin the early 1900s
- Revolutionized fluid
dynamics
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Reduce drag
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Laminar Design
• Less friction drag
• More stability
•
Better fueleconomy
• Better looking
(personal
reference)
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WAVE DRAG
Veronica Rico
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What is Wave Drag?
• Force retarding an airplane,
especially in supersonic and
transonic flight, as a
consequence of theformation of shock waves
• a sudden and very powerful
form of drag that appears
on aircraft flying at high-subsonic speeds
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So powerful that for some time, it was thought that engines
would not be able to provide enough power to easily
overcome the effect, which led to the concept of :
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• New techniques
developed during
WWII that
reducedmagnitude of
problem
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Reduction of Wave Drag
• Development of ‘perfect’ shapes to reduce
wave drag as much as possible: Sears-Haack
body
• Swept Wing
• Whitcomb Area Rule
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Sears-Haack Body
•
Cross-sectional areadistribution along the body
determines wave drag
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Swept Wing
• Figure shows data confirming that a swept
wing reduces the wave drag Credits - NASA
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Other High Speed Wing Designs
X-29: Forward Swept Wing NASA AD-1: Oblique Wing
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Form Drag
• Drag due to flow separation
• As velocity increases, boundary layer
separation moves toward the leading edge of
the object
• This results in a larger pressure at the leading
edge than the trailing edge causing a large
drag force on the body
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Examples of Form Drag
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More Examples
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Why Golf Balls have Dimples
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Methods of Reducing Drag
• Important to reduce drag because it allows for
faster, more efficient travel
CAD Model of ORCA Flyer
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Airfoil Selection
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Fuselage Design
ORCA Flyer Fuselage Design
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Winglets