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Aerodynamic Drag Force

Aerodynamic Drag Force. Air resistance (fluid resistance) motion of the air flowing past projectile equal to projectile’s velocity BUT in the opposite direction of projectile’s motion. Headwind Tailwind. V drag + V headwind  flow velocity acting on body body v = 20mps

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Aerodynamic Drag Force

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  1. Aerodynamic Drag Force • Air resistance (fluid resistance) • motion of the air flowing past projectile • equal to projectile’s velocity BUT in the opposite direction of projectile’s motion

  2. Headwind Tailwind • Vdrag+ Vheadwind •  flow velocity acting on body • body v = 20mps • Vheadwind= 5mps • Vres= ------------- • Vdrag - Vtailwind •  flow velocity acting on body • body v = 20mps • Vtailwind= 5mps • Vres= ------------

  3. Skin Friction Profile Drag • most noticed @ low v • rubbing of layers of air adjacent to projectile •  with: flow v, surface size, surface roughness • secondary concern •  with area exposed to approaching air flow •  with projectile v • lead side =  pressure • trail side =  pressure • main source of Drag

  4. STREAMLINING • Achieved by: 1. decreasing size of area facing oncoming airflow 2. tapering leading side - air is not abruptly moved • Streamlining results in: A. more laminar flow past body with less “wake” B. less turbulence behind bodyless difference in pressure zones between front and tail of body

  5. Mass of Projectile and Drag Effect • a =Fm • a in this case stands for deceleration [negative a] • deceleration =Fm • deceleration inversely proportional to projectile m

  6. Drag Factors FDrag = ½ CD Aρv² • Skin Friction and Profile Drag • CDcoefficient of drag, indicates how streamlined a projectile is (low number = very streamlined) • A is the frontal area of projectile facing the flow • ρ (rho) is the air density(density less in warm air and at higher altitude) • v² means if v doubles, drag quadruples

  7. Profile Drag increases froma to c as more AREA is exposed to oncoming airflow AREAa: ----------b: ----------c: ---------- FIG K.10 pg 424

  8. FLUID LIFT FORCE • FL (Lift Force) always perpendicular to direction of the oncoming air flow • Lift can be upward, downward, lateral • FL due to difference in pressure zones on opposite sides of projectile • Bernoulli’s Principle: • high flow velocity creates ------- pressure zone • low flow velocity creates -------- pressure zone

  9.  flow v on top p zone on top p zone on bottom upward Flift flow v on top p zone on top p zone on bottom downward Flift

  10. 8-May-2001National Post from“New Scientist”David Anderson disputesDaniel Bernouilli’s Principle

  11. LIFT : DRAG • Maximize LIFT FORCE by creating an optimal angle of attack or shaping projectile like an airfoil • Minimize DRAG FORCE with a moderate ATTACK  • FL = ½ CL Aρv²CL (lift coefficient) A (area of pressure)ρ(air density) v² (air flow velocity)

  12. FIG K.9 page 424

  13. http://www.grc.nasa.gov/WWW/K-12/airplane/incline.html LIFT and DRAG: Effects of Inclination of an AIRFOIL

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