Aerodynamic Drag Force

1
Aerodynamic Drag Force

• Air resistance (fluid resistance)
• motion of the air flowing past projectile
• equal to projectiles velocity BUT in the
  opposite direction of projectiles motion

2
Headwind Tailwind

• Vdrag - Vtailwind
• ? flow velocity acting on body
• body v 20mps
• Vtailwind 5mps
• Vres ------------

• Vdrag Vheadwind
• ? flow velocity acting on body
• body v 20mps
• Vheadwind 5mps
• Vres -------------

3
Skin Friction Profile Drag

• ? with area exposed to approaching air flow
• ? with projectile v
• lead side ? pressure
• trail side ? pressure
• main source of Drag

• most noticed _at_ low v
• rubbing of layers of air adjacent to projectile
• ? with flow v, surface size, surface roughness
• secondary concern

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 F m
• a in this case stands for deceleration negative
  a
• deceleration F m
• deceleration inversely proportional to projectile
  m

6
Drag Factors FDrag ½ CD A ? v²

• Skin Friction and Profile Drag
• CD coefficient of drag, indicates how streamlined
  a projectile is (low number very streamlined)
• A is the frontal area of projectile facing the
  flow
• ? (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
• Bernoullis 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 fromNew
ScientistDavid Anderson disputesDaniel
Bernouillis 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 A ? v²CL (lift coefficient) A
  (area of pressure) ? ( air density)
  v² (air flow velocity)

12
FIG K.9 page 424
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(No Transcript)
14
http//www.grc.nasa.gov/WWW/K-12/airplane/incline.
html
LIFT and DRAG Effects of Inclination of an
AIRFOIL