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13 Cards in this Set
- Front
- Back
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Define total drag, parasite drag, and induced drag.
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Total Drag: Dt=Dp+Di
Parasite Drag: It is all drag that is not associated with the production of lift. Induced Drag: Is the portion of total drag associated with the production of lift. |
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List the three major types of parasite drag.
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1) Form Drag
2) Friction Drag 3) Interference Drag |
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State the cause of each major type of parasite drag.
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Form: caused by airflow separation from a surface and the low pressure wake that is created by that separation. (shape of the object)
Friction: A retarding force due to viscosity. Turbulent flow creates more than laminar. (Rough surfaces) Interference: generated by the mixing of streamlines between components. |
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State the aircraft design features that reduce each major type of parasite drag.
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Form: streamline fuselage and other exposed surfaces
Friction: smoothing the exposed surfaces through painting, cleaning, waxing, or polishing. Flush rivets. Interference: Proper Fairing and Filleting |
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Describe the effects of changes in density, velocity, and equivalent parasite area
on parasite drag, using the parasite drag equation. |
Dp=1/2pV^2f=qf
They are directly related. |
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Describe the effects of upwash and downwash on the lift generated by an infinite
wing. |
Upwash: Increases lift because it increases the average angle of attack on the wing.
Downwash: decreases lift by reducing the average angle of attack on the wing. Infinite wing=upwash=downwash=no net change in lift |
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Describe the effects of upwash and downwash on the lift generated by a finite
wing. |
Downwash doubles upwash since there is now spanwise flow that flows up and around the wingtips, adding to the downwash. This gives the average relative wind a downward slant, moving the total lift vector aft. The parallel component of the total lift is induced drag.
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State the cause of induced drag.
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Induced drag is that portion of total drag associated with the production of lift.
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State the aircraft design features that reduce induced drag.
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winglets, wingtip tanks, and missile rails.
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Describe the effects of changes in lift, weight, density, and velocity on induced drag, using the induced drag equation.
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Di=(kL^2)/(pV^2b^2)=(kW^2)/(pV^2b^2)
Increases in lift and weight=increase in Di density and velocity are inversely related with Di |
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Describe the effects of changes in velocity on total drag.
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As Velocity increases, Total Drag decreases before L/Dmax, then increases after
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Define and state the purpose of the lift to drag ratio.
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To determine the efficiency of an airfoil. A high L/D ration indicates a more efficient airfoil. L/D=CL/CD
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State the importance of L/DMAX.
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L/DmaxAOA will produce the minimum total drag. Any movement away from L/Dmax will increase drag. For velocities below L/Dmax, the airplane is affected by induced drag, and above is parasite drag. L/DmaxAOA produces the greatest ratio of lift to drag. L/DmaxAOA is the most efficient AOA of the wing, not the engine. Changes in weight or altitude will increase L/Dmax airspeed, but not affect L/Dmax or L/DmaxAOA. Only a change in configuration will change it.
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