Aerodynamic Principles

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Aerodynamic Principles

• Chapter 3
• Section C
• Aerodynamics of Maneuvering Flight

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Climbing Flight
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Climbing FlightSustained Vertical Flight

• Thrust-to-weight ratio greater than 1.1 to 1
• Wings supply no vertical lift
• Weight and drag opposed only by thrust
• F-16

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Left-turning Tendencies

• High power, low airspeed
• Torque
• Gyroscopic precession
• Asymmetrical thrust
• Spiraling slipstream

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Left-turning Tendencies Torque

• Newton For every action there is an equal and
  opposite reaction
• Propeller rotates clockwise causes torque which
  tends to rotate airplane counterclockwise about
  longitudinal axis

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Left-turning Tendencies Torque
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Left-turning Tendencies Gyroscopic Precession

• Prop has characteristics of gyroscope
• Rigidity in space
• Precession contributes to left turning tendency
• Precession is resultant reaction when force
  applied to rim of rotating disk

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Left-turning Tendencies Example Conventional
Gear Airplane
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Left-turning Tendencies Asymmetrical thrust
P-factor
Airplane flown at high power and high angle of
attack Uneven angles of attack
between ascending and descending blades Unequal
thrust causes yaw to left
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Left-turning Tendencies Design Considerations

• To counteract left-turning tendencies
• Metal tab on trailing edge of rudder
• Horizontally canted engine
• Engine turned slightly toward right

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Left-turning Tendencies Spiraling Slipstream

• Slipstream from propeller wraps around fuselage
  and hits left side of vertical fin
• Causes tail to move right nose to yaw left

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Descending Flight

• Weight has two components during descent
• perpendicular to flight path
• forward along flight path

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Descending Flight Maximum Lift-to-Drag Ratio

• Specific angle of attack that generates the
  greatest lift with least amount of drag
• Used to measure gliding efficiency of AC
• Best glide angle
• Max gliding distance

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Descending Flight Glide

• Best glide speed
• For given weight, L/Dmax corresponds to an
  airspeed
• Glide ratio
• distance aircraft will travel forward, without
  power, in relation to altitude loss
• best glide ratio available only with optimum
  angle of attack associated with L/Dmax
• Glide angle
• angle between glide path and horizon

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Descending Flight Factors Affecting Glide

• Weight
• does not affect glide ratio
• heavier aircraft needs higher airspeed
• Configuration
• landing (more total drag) vs. clean (less total
  drag)
• Wind
• strong headwind reduces glide range, increase
  airspeed
• strong tailwind increases glide range, decrease
  airspeed

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Turning Flight

• Horizontal component of lift causes airplane to
  turn
• When vertical component of lift equals weight
  aircraft will neither gain nor lose altitude

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Turning FlightAdverse Yaw

• In a turn, outside wing produces more lift
• Induced drag is a product of creation of lift so
  total drag increases
• Causes yaw toward the outside of turn
• Use rudder in coordination with ailerons to
  compensate for adverse yaw

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Turning FlightOverbanking tendency

• Additional lift on outside wing tends to roll the
  aircraft beyond the desired bank even after
  neutralizing the controls
• Use small amount of opposite aileron to maintain
  the bank desired

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Turning FlightRate and Radius of Turn

• Angle of bank and airspeed regulate both
• Rate
• Amount of time it takes to turn specific number
  of degrees
• Increase airspeed, same angle of bank rate is
  slower
• Increase angle of bank, same airspeed rate is
  faster
• Radius
• Horizontal distance used to complete a turn
• Increase airspeed, same angle of bank radius
  larger
• Increase angle of bank, same airspeed radius
  smaller

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Turning FlightRate and Radius of Turn
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Turning FlightRate and Radius of Turn
22
Load Factor

• Ratio of
• Load supported by the wings
• to
• Actual weight of the aircraft and contents
• G-forces
• Feel heavier in turns
• Pilot input or environmental

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Load FactorLoad Factor in Turns

• Load factor increases as angle of bank increases
• Compensate for apparent increase in weight and
  loss of vertical lift in turn by increasing angle
  of attack with back pressure.
• During constant altitude turns, relationship
  between load factor and bank angle is same for
  all aircraft See chart on Page 3-60

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Load FactorLoad Factor and Stall Speed

• Increasing load factor will cause and airplane to
  stall at a higher speed Chart Page 3-61
• Stalls that occur with G-forces being applied are
  accelerated stalls
• Show that the reason for stall is exceeding
  critical angle of attack, not airspeed

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Load FactorLimit Load Factor

• Amount of stress or load factor that an aircraft
  can withstand before structural failure
• Function of design
• Established by category normal, utility,
  acrobatic
• In POH

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Load FactorLimit Load Factor
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Load FactorDesign Maneuvering Speed Va
Max speed at which you can use full, abrupt
control movement without over stressing the
airframe
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Load FactorDesign Maneuvering Speed Va

• Va not normally marked on airspeed indicator
• Changes with weight
• Found in POH and/or placard
• The amount of excess load that can be imposed on
  an airframe depends on the aircrafts speed