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Aerodynamic Forces Lift and Drag
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Lift Equation Lift Coefficient of Lift, Cl Direction of Flight
Presentation Name Course Name Unit # β Lesson #.# β Lesson Name Lift Equation Lift Direction of Flight Coefficient of Lift, Cl Determined experimentally Combines several factors Shape Angle of attack πΆ π =πΆππππππππππ‘ ππ πΏπππ‘ π·=π·πππ π πΆ π = 2πΏ π΄π π£ 2 πΆ π = πΏ ππ΄ π΄=ππππ π΄πππ π 2 Rearranging the coefficient of lift equation shows that lift is increased by wing area, air density, and velocity. Velocity is a squared function, giving it a more significant impact on lift. π=π·πππ ππ‘π¦ ππ π 3 Alternate format π£=πππππππ‘π¦ ππ π 3 π=π·π¦πππππ ππππ π π’ππ ππ
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Applying the Lift Equation
Presentation Name Course Name Unit # β Lesson #.# β Lesson Name Applying the Lift Equation The Cessna 172 from Activity step #2 takes off successfully from Denver, CO during an average day in May (22 OC) with a standard pressure day (101.3 kPa). Assume that the take off speed is 55 knots (102 kmph). 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 m2 and weight is 2,328 lb (1,056 kg) Average temperature source =
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Applying the Lift Equation
Convert mass into weight Convert velocity π€=0.92ππ π€=0.92(1,056 ππ) π π 2 π€=9,531 π π= 102 πππβ π ππ πππ βπ π πππ π=28.3 π π
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Applying the Lift Equation
Calculate Air Density π= π π+273.1 π= πππ β+273.1 π=1.196 ππ π 3
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Applying the Lift Equation
Calculate coefficient of lift assuming that lift equals weight πΆ π = 2πΏ π΄π π£ 2 πΆ π = 2(9,531 π) π ππ π π π 2 πΆ π = 1.09
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Boundary Layer Fluid molecules stick to objectβs surface
Presentation Name Course Name Unit # β Lesson #.# β Lesson Name Boundary Layer Fluid molecules stick to objectβs surface Creates boundary layer of slower moving fluid Boundary layer is crucial to wing performance More information is available through the NASA Reynolds Number webpage:
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Boundary Layer and Lift
Presentation Name Course Name Unit # β Lesson #.# β Lesson Name Boundary Layer and Lift Airflow over object is slower close to object surface Air flow remains smooth until critical airflow velocity Airflow close to object becomes turbulent
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Presentation Name Course Name Unit # β Lesson #.# β Lesson Name Reynolds Number, Re Representative value to compare different fluid flow systems Object moving through fluid disturbs molecules Motion generates aerodynamic forces Airfoil1 Airfoil2 More information is available through the NASA Reynolds Number webpage: Comparable to when Re1 = Re2
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Angle of Attack (AOA) Affects Lift
Presentation Name Course Name Unit # β Lesson #.# β Lesson Name Angle of Attack (AOA) Affects Lift Lift increases with AOA up to stall angle Lift Direction of Flight Airflow Lift Direction of Flight Airflow Airflow becomes turbulent at the critical angle of attack. Airflow separates from airfoil, and lift decreases dramatically. NASA developed an applet to show how the angle of attack impacts lift. It can be accessed through this link: Stall Lift Angle of Attack
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Presentation Name Course Name Unit # β Lesson #.# β Lesson Name Reynolds Number Ratio of inertial (resistant to change) forces to viscous (sticky) forces Dimensionless number π
π = πvπ π π
π = vπ Ξ½ Ξ½= π π or π=πΏππππ‘β ππ πΉππ’ππ ππππ£ππ π π
π =π
ππ¦πππππ ππ’ππππ More information is available through the NASA Reynolds Number webpage: π=πΉππ’ππ π·πππ ππ‘π¦ ππ π 3 π=πΉππ’ππ πππ πππ ππ‘π¦ ππ π 2 v=πππππππ‘π¦ π π Ξ½=πΎππππππ‘ππ πππ πππ ππ‘π¦ π 2 π
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