aerodinámica del helicoptero

1. LOS HALCONES
CAMILO ISIDRO GUAYAZAN MORENO
INSTRUCTOR ESPECIALIDADES TERRESTRES
HELICOPTER
AERODYNAMICS

2. Learning Objectives
 Applied and simplified
understanding of
helicopter
aerodynamic
characteristics
 Correlate relationships
between these
characteristics
CIGM

3. Rotary Wing Aerodynamic
Subject Areas
 Aerodynamic Factors
– Relative Wind
– Induced Flow Production
– Resultant Relative Wind
– Angle of Attack / Angle of Incidence
– Total Aerodynamic Force
 Lift
 Drag
 Airflow During a Hover
CIGM

4. Rotary Wing Aerodynamics
Subject Areas (Cont)
 Translating Tendency
– Mechanical and Pilot
Inputs
 Dissymmetry of Lift
– Blade Flapping
– Blade Lead and Lag
– Cyclic Feathering
CIGM

5. Rotary Wing Aerodynamic
Subject Areas (Cont)
 Retreating Blade Stall
 Compressibility
 Settling with Power
 Off Set Hinges
 Dynamic Rollover
CIGM

6. CIGM

7. Relative Wind
• Relative wind is defined
as the airflow relative to an
airfoil
• Relative wind is created
by movement of an airfoil
through the air
CIGM

8. Induced Flow Production
• This figure illustrates
how still air is changed
to a column of
descending air by rotor
blade action
CIGM

9. Resultant Relative Wind
• Angle of attack is
reduced by induced flow,
causing the airfoil to
produce less lift
• Airflow from rotation,
modified by induced flow,
produces the Resultant
Relative Wind
CIGM

10. Angle of Attack
• Angle of Attack (AOA) (4) is
the angle between the airfoil chord
line and its direction of motion
relative to the air (the Resultant
Relative Wind)

11. Angle of Incidence
• Angle of Incidence (or AOI) is
the angle between the blade chord
line and the plane of rotation of the
rotor system.

12. Total Aerodynamic Force
• A Total Aerodynamic Force (3)
is generated when a stream of air
flows over and under an airfoil that
is moving through the air
CIGM

13. Total Aerodynamic Force
 Total aerodynamic force may be divided
into two components called lift and drag
 Lift acts on the airfoil in a direction
perpendicular to the relative wind
 Drag acts on the airfoil in a direction
parallel to the relative wind and is the
force that opposes the motion of the
airfoil through the air
CIGM

14. CIGM

15. Airflow at a Hover (IGE)
• Lift needed to sustain an
IGE Hover can be produced
with a reduced angle of
attack and less power
because of the more vertical
lift vector
• This is due to the ground
interrupting the airflow under
the helicopter thereby
reducing downward velocity
of the induced flow
CIGM

16. Airflow at a Hover (OGE)
• Downward airflow alters the relative wind and
changes the angle of attack so less aerodynamic
force is produced
• Increase collective pitch is required to produce
enough aerodynamic force to sustain an OGE
Hover
CIGM

17. Rotor Tip Vortexes (IGE/OGE)
CIGM

18. Rotor Tip Vortexes Effects
 At a hover, the Rotor Tip Vortex reduces
the effectiveness of the outer blade
portions
 When operating at an IGE Hover, the
downward and outward airflow pattern
tends to restrict vortex generation
 Rotor efficiency is increased by ground
effect up to a height of about one rotor
diameter for most helicopters CIGM

19. CIGM

20. Translating Tendency
 The tendency for a
single rotor helicopter to
drift laterally, due to tail
rotor thrust
CIGM

21. CIGM

22. Dissymmetry of Lift
 Definition
 Compensation
– Blade Flapping
– Cyclic Feathering
– Blade Lead and Lag
CIGM

23. Dissymmetry of Lift Definition
Dissymmetry of Lift is the
difference in lift that exists between
the advancing half of the rotor disk
and the retreating half
CIGM

24. Blade Flapping
• Blade Flapping is the
up and down movement
of a rotor blade, which, in
conjunction with cyclic
feathering, causes
Dissymmetry of Lift to
be eliminated.
CIGM

25. Blade Flapping CIGM

26. Cyclic Feathering
• These changes
in blade pitch are
introduced either
through the blade
feathering
mechanism or
blade flapping.
• When made
with the blade
feathering
mechanism, the
changes are
called Cyclic
Feathering.
CIGM

27. Blade Lead and Lag
• Blade Lead / Lag Each rotor
blade is attached to the hub by a
vertical hinge (3) that permits each
blade, independently of the others,
to move back and forth in the
rotational plane of the rotor disk
thereby introducing cyclic feathering.
CIGM

28. CIGM

29. Retreating Blade Stall
 A tendency for the
retreating blade to stall
in forward flight is
inherent in all present
day helicopters and is
a major factor in
limiting their forward
speed

30. Retreating Blade Stall
Lift at a Hover

31. Retreating Blade Stall
Lift at Cruise

32. Retreating Blade Stall
Lift at Stall Airspeed
CIGM

33. Retreating Blade Stall
Causes
 When operating at high forward airspeeds,
the following conditions are most likely to
produce blade stall:
– High Blade Loading (high gross weight)
– Low Rotor RPM
– High Density Altitude
– Steep or Abrupt Turns
– Turbulent Air
CIGM

34. Retreating Blade Stall
Indications
 The major warnings of approaching
retreating blade stall conditions are:
– Abnormal Vibration
– Nose Pitch-up
– The Helicopter Will Roll Into The Stalled Side
CIGM

35. Retreating Blade Stall
Corrective Actions
 When the pilot suspects blade stall, he can
possibly prevent it from occurring by
sequentially:
– Reducing Power (collective pitch)
– Reducing Airspeed
– Reducing "G" Loads During Maneuvering
– Increasing Rotor RPM to Max Allowable Limit
– Checking Pedal Trim
CIGM

36. CIGM

37. Compressibility
CIGM

38. Compressibility
What Happens?
 Rotor blades moving through the air below
approximately Mach 0.7 cause the air in front of
the blade to move away before compression can
take place.
 Above speeds of approximately Mach 0.7 the air
flowing over the blade accelerates above the
speed of sound, causing a shock wave (also
known as a sonic boom) as the blade compresses
air molecules faster than they can move away
from the blade.
 The danger of this shock wave (Compressibility)
is its effect on aircraft control and fragile rotor
blade membranes. CIGM

39. Compressibility
Causes
 Conditions conducive to Compressibility
– High Airspeed
– High Rotor RPM
– High Gross Weight
– High Density Altitude
– Low Temperature
– Turbulent Air
CIGM

40. Compressibility
Indications
 As Compressibility
approaches:
– Power Required
Increase as Lift
Decreases and
Drag Increases
– Vibrations Become
More Severe
– Shock Wave Forms
(Sonic Boom)
– Nose Pitches Down
CIGM

41. Compressibility
Corrective Actions
 When the pilot suspects Compressibility, he
can possibly prevent it from occurring by:
– Slowing Down the Aircraft
– Decreasing Pitch Angle (Reduce Collective)
– Minimizing G Loading
– Decreasing Rotor RPM
CIGM

42. CIGM

43. Settling with Power
 Settling With Power is a condition of powered
flight where the helicopter settles into its own
downwash.
 It is also known as Vortex Ring State
CIGM

44. Settling with Power
Cause
 Increase in induced flow results in reduction of angle of
attack and increase in drag
 This creates a demand for excessive power and creates
greater sink rate
 Where the demand for power meets power available the
aircraft will no longer sustain flight and will descend
CIGM

45. Settling With Power
Conditions
 Conditions required for Settling with power
are:
– 300-1000 FPM Rate of Descent
– Power Applied (> than 20% Available Power)
– Near Zero Airspeed (Loss of ETL)
 Can occur during:
– Downwind Approaches.
– Formation Approaches and Takeoffs.
– Steep Approaches.
– NOE Flight.
– Mask/Unmask Operations.
– Hover OGE. CIGM

46. Settling With Power
Indications
 Symptoms of Settling with Power:
– A high rate of descent
– High power consumption
– Loss of collective pitch effectiveness
– Vibrations
CIGM

47. Settling With Power
Corrective Actions
 When Settling with
Power is suspected:
– Establish directional
flight.
– Lower collective
pitch.
– Increase RPM if
decayed.
– Apply right pedal.
CIGM

48. CIGM

49. Off Set Hinges
 The Offset Hinge is
located outboard from the
hub and uses centrifugal
force to produce
substantial forces that act
on the hub itself.
 One important advantage
of offset hinges is the
presence of control
regardless of lift condition,
since centrifugal force is
independent of lift.
CIGM

50. CIGM

51. Dynamic Rollover
 With a rolling
moment and a pivot
point if the helicopter
exceeds a critical
angle it will roll over.
CIGM

52. Dynamic Rollover
 The critical rollover
angle is further
reduced under the
following conditions:
– Right Side Skid Down
Condition
– Crosswinds
– Lateral Center Of
Gravity (CG) Offset
– Main Rotor Thrust
Almost Equal to Weight
– Left Yaw Inputs
CIGM

53. Dynamic Rollover
 Pilot Technique
When landing or taking off,
with thrust (lift) approximately
equal to the weight (light on
the skids or wheels), the pilot
should keep the helicopter
cyclic trimmed (force
trim/gradient) and prevent
excessive helicopter pitch and
roll movement rates. The pilot
should fly the helicopter
smoothly off (or onto) the
ground, vertically, carefully
maintaining proper cyclic trim.
CIGM
CIGM

54. Summary
 Websites containing additional and more
detailed information on Helicopter
Aerodynamics:
– http://www.dynamicflight.com/aerodynamics/
– http://www.copters.com/helo_aero.html
– http://www.helicopterpage.com/html/forces.html
CIGM

55. QUIZ
Click on the link below to access the
Aerodynamics Quiz
http://ang.quizstarpro.com
Log-in and Click “Search” Tab
Class Name = Aerodynamics
CIGM