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Aerodynamic Aerodynamic

Aerodynamic - PowerPoint Presentation

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Aerodynamic - PPT Presentation

Forces Lift and Drag Lift Equation Coefficient of Lift C l Determined experimentally Combines several factors Shape Angle of attack Lift Direction of Flight             Alternate format ID: 161343

drag lift number applying lift drag applying number reynolds equation calculate coefficient air wing www layer airflow object aeronautics

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Presentation Transcript

Slide1

Aerodynamic Forces

Lift and DragSlide2

Lift EquationCoefficient of Lift, ClDetermined experimentally

Combines several factors

Shape

Angle of attack

Lift

Direction of Flight

 

 

 

 

 

 

Alternate format

 Slide3

Applying the Lift Equation The Cessna 172 from Activity 1.2.2 step #2 takes off successfully from Denver, CO during an average day in May (22 OC) with a standard pressure

(

101.3

kPa). Assume that the

take-off speed is 55 knots (102 kph

). What is the minimum coefficient of lift needed at the point where the aircraft just lifts off the ground? The Cessna wing area is 18.2 m

2 and weight is 2,328 lb (1,056 kg). Slide4

Applying the Lift EquationConvert mass into weightConvert velocity

 

 

 

 

 Slide5

Applying the Lift EquationCalculate Air Density

 

 

 Slide6

Applying the Lift Equation Calculate coefficient of lift assuming that lift equals weight

 

 

 Slide7

Boundary LayerFluid molecules stick to object’s surfaceCreates boundary layer of slower moving fluidBoundary layer is crucial to wing performanceSlide8

Boundary Layer and LiftAirflow over object is slower close to object surfaceAir flow remains smooth until critical airflow velocityAirflow close to object becomes turbulentSlide9

Reynolds Number, ReRepresentative value to compare different fluid flow systemsObject moving through fluid disturbs moleculesMotion generates aerodynamic forces

=

Re

1

Re

2

Comparable

to

Airfoil

1

Airfoil2whenSlide10

Angle of Attack (AOA) Affects LiftLift increases with AOA up to stall angle

Lift

Direction of Flight

Airflow

Lift

Direction of Flight

Airflow

Lift

Angle of Attack

StallSlide11

Reynolds NumberRatio of inertial (resistant to change) forces to viscous (sticky) forcesDimensionless number

 

 

 

o

r

 

 

 

 

 

 Slide12

Applying Reynolds Number A P-3 Orion is cruising at 820 kph (509 mph) at an altitude of 4,023 m (13,198 ft). Assume a

fluid viscosity

c

oefficient of 1.65x10-5

N(s)/m3. What is the average Reynolds Number along a wing cross section measuring 1.1 m (3.6

ft) from leading edge to trailing edge? Need components to calculate Re

 Slide13

Applying Reynolds NumberCalculate Air TemperatureCalculate Air

Pressure

 

 

 

 

 Slide14

Applying Reynolds NumberCalculate Air Density

 

 

 Slide15

Applying Reynolds NumberConvert Velocity

 

 Slide16

Applying Reynolds NumberCalculate Re

 

 

 Slide17

Drag EquationCoefficient of drag, CdDetermined experimentally

Combines several factors

Shape

Angle of attack

Drag

Direction of Flight

 

 

 

 

 

 

Alternate format

 Slide18

Coefficient of Drag (Cd)Object shape affects C

dSlide19

Applying the Drag Equation The same Cessna 172 from Activity 1.2.2 step #2 takes off under the same conditions as described earlier in this presentation. How much drag is produced when the wing is configured such that the coefficient of drag is 0.05?Slide20

Applying the Drag EquationCalculate drag

 

 

 

 Slide21

Downwash and Wingtip VorticesPressure difference at wing tipsAir to spill over wingtip perpendicular to main airflowAir flows both upward and rearward, forming a vortexDecreases lift

Increases dragSlide22

Wingtip VorticesAir flows both upward and rearward, forming a vortexWinglets are vertical airfoils that limit vortices and improve fuel efficiencySlide23

ReferenceNational Aeronautics and Space Administration (2011).

Aerodynamic forces

. Retrieved from http://www.grc.nasa.gov/WWW/K-12/airplane/presar.html

National Aeronautics and Space Administration (2011).

Reynolds number

. Retrieved from http://www.grc.nasa.gov/WWW/BGH/reynolds.html

National Aeronautics and Space Administration (2011). Winglets. Retrieved from http://www.nasa.gov/centers/dryden/about/Organizations/Technology/Facts/TF-2004-15-DFRC.html

Raymer, P. (2006). Aircraft design: A conceptual approach. Reston, VA: American Institute of Aeronautics and Astronautics

.