Aerodynamics of Flight Chapter 2 Part 3

1
Aerodynamicsof Flight Chapter 2 Part 3

• Aerodynamics in Flight Maneuvers
• Basic Propeller Principles

2
Turns
2
Turning Force Vel /Radius
In a coordinated turn
Lift
Weight
3
Coordinated Turns
Aircraft bank is just enough so that
Coordinated Turn
2
Horiz comp of lift Velocity / Radius of Turn
Result of Coordinated Turn
Heading changes at the same
rate as direction of flight changes
4
Skidding Turn
What Trying to turn with not enough bank for
the speed
Causes

Symptoms of Skidding Turn
-Not enough bank

-Too much rudder in direction of turn
-Heading changes faster than direction of flight
changes, plane yaws through turn
Correction

-Feels like you're being thrown to outside of
-Increase bank
turn
-Reduce rudder if holding inside rudder
-Ball goes to outside of turn
Lift
Vert Comp of Lift
Skid
Centrifical force -Centripetal force
Horizontal
component of lift
2
Velocity /Radius of Turn
Radius of turn over ground
NOT equal

Radius of turn about vertical axis
opposite to lift
Weight
5
Slipping Turn
What Trying to turn with too much bank for the
speed
Symptoms of Slipping Turn
Causes

-Too much bank for airspeed
-Heading changes slower than direction of
-Holding rudder opposite to the direction
flight changes, (heading can be constant)
of turn
-Feels like you're falling towards inside of turn
Correction

-Ball goes to inside of turn
-Decrease bank
-Reduce rudder if holding outside rudder
Lift
Vert Comp of Lift
Slip
Centrifical force -Centripetal force
Horizontal
component of lift
2
Velocity /Radius of Turn
n
r
u
t

f
o

s
NOT equal
u
i
d
a
R


d
e
r
i
s
opposite to lift
e
D
Actual
Radius of
Turn
Weight
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Lift in a level, coordinated Turn

• Vertical component of lift must equal weight
• As weight increases, AOA must increase for same
  bank airspeed
• As bank increases, AOA must increase for same
  weight airspeed
• Increasing AOA moves you closer to critical AOA
  without changing airspeed
• Hence, plane stalls at a higher airspeed than
  level flight

7
Climbs and Descents

• During the climb or descent entry, the forces
  initially become imbalanced. Initializing a
  climb, upward forces exceed downward forces.
  Initializing a descent, downward forces exceed
  upward forces.
• Once the climb or descent is established, the
  forces are again in balance.

8
Initializing a climb
Jeppesen, ICM
9
Once climb is established
10
Forces pulling out of dive

• Component of Weight is trying to keep plane from
  leveling off
• Lift must be large enough to cancel component of
  lift PLUS provide FV2/R to curve flight path to
  level
• Trying to pull out too quickly, means small R,
  big F, can overstress wings

• Pitching the plane about CG without changing
  flight path can cause accelerated stall

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Airspeed in ClimbWhat wrong with this picture?
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Stalls

• An airplane can stall at any airspeed and in any
  attitude
• Cause of Stalls
• Direct cause is always excessive angle of attack
• Any time critical angle of attack is exceeded
• Critical angle of attack is fixed, and does not
  vary with
• Airspeed, weight, density altitude, load factor,
  or CG location
• Indirect causes are
• getting too slow,
• pulling too many Gs
• suddenly pitching aircraft before flight path can
  catch up

13
Stall Progression

• Angle of Attack vs.
• Coefficient of Lift

14
Stall Speed/Load Factor
15
Effects of Flaps on Stall Speed
16
Basic Propeller Principles

• Propeller is a big screw a sideways airfoil
• Blade angle of attack, a, is the vector sum of
  rotational velocity and forward velocity
• Blade angle angle between chord and plane of
  rotation
• For a fixed-pitch prop, as airspeed increases, a,
  decreases (for a given RPM)
• Design pitch usually based
• on cruise speed,
• Can install a climb prop instead
• Wont get max RPM
• on takeoff or climbs

17
Fixed-Pitch versus Constant-Speed

• Fixed-pitch propeller has
• constant pitch, a varies with RPM and airspeed
• Adjustable-pitch prop
• Pilot can manually select between several pitches
  
• Constant Speed propeller
• More accurately called a variable-pitch propeller
• Pitch changes automatically to optimize a for
  given RPM and airspeed

18
Propeller Pitch

• Can be given as angle between plane of rotation
  and face of blade (14o)
• Can be given as the distance the blade would
  screw through the air in 1 revolution
• Geometric Pitch ideal distance the blade would
  screw through the air in 1 revolution
• Effective Pitch actual distance the blade would
  screw through the air in 1 revolution

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Why a controllable-pitch prop

• Pitch of blade varies to always have optimum
  blade angle of attack

Fixed Pitch Prop
Variable-Pitch Prop
20
Propeller Efficiency

• Horsepower from engine is called Brake horsepower
• Horsepower actually turned into thrust is thrust
  horsepower
• Always less than brake horsepower
• Propeller Efficiency ratio of thrust horsepower
  to brake horsepower
• For fixed-pitch prop, best efficiency is a
  specific airspeed and RPM
• For variable pitch, best efficiency is over a
  range

21
Propeller Twist

• Twist allows the angle of attack to be relatively
  constant over the length of the blade in cruise
  flight