1. Power Management
1-212th Aviation Regiment

2. WHAT IS POWER MANAGEMENT?
Operating a helicopter with an awareness of the limitations of that helicopters’ engine and rotor system.
This allows a pilot to avoid an unintended descent which results in unwanted contact with the ground or other obstacles.
Two broad categories:
AVAILABLE ENGINE POWER
ROTOR SYSTEM EFFICIENCY

3. AVAILABLE ENGINE POWER
Affected by:
Environmental conditions (Density Altitude)
Hot temperatures / High altitudes are conducive to high DA conditions.
Determined by Performance Planning
Unable to be controlled in flight

4. BASIC ENGINE OPERATION
Engine air is taken in through the intake

5. BASIC ENGINE OPERATION
Compressed by the compressor

6. BASIC ENGINE OPERATION
Passes into the combustion chamber

7. BASIC ENGINE OPERATION
This energy then passes through the Gas Producer turbine

8. BASIC ENGINE OPERATION
Then through the Power turbine and out of the exhaust.

9. BASIC ENGINE OPERATION
Some engine layouts may differ, but the operating principles are the same

10. Air is ingested by the engine and compressed by VOLUME

11. Approximately 25% of this VOLUME is used for combustion with fuel
Air is ingested by the engine and compressed by VOLUME
The approximate MASS ratio of air / fuel is 15:1 during combustion.
The other 75% is used for cooling the engine

12. Approximately 25% of this VOLUME is used for combustion with fuel
The approximate MASS ratio of air / fuel is 15:1 during combustion.
The other 75% is used for cooling the engine

13. DENSITY ALTITUDE EFFECTS UPON AVAILABLE ENGINE POWER
Power generation depends upon the MASS of fuel + air able to be combusted.
This is a 15:1 ratio
Engine cooling depends upon the MASS of the cooling charge.
The MASS of a certain volume of air changes depending upon the Density Altitude.

14. HIGH DA – Low air density
LESS MASS
LOW DA – High air density
MORE MASS
The MASS of air may change with DA, but the required MASS of air for engine performance does not change.

15. Example: 500 LBS per HOUR = 800 HP
All other variables being equal, two different engines burning the same amount of fuel per hour will create the same amount of power.
Example: 500 LBS per HOUR = 800 HP
That 500 LBS of fuel requires a certain MASS of air with which to combust
A certain MASS of air is also required to keep the engine cool
This cannot change if the engine is to provide the performance for which it was designed
If the engine cannot take in enough air to combust the necessary amount of fuel, and to cool itself, then a limitation will be encountered

16. The question that is answered during Performance Planning is:
While burning the amount of fuel and air necessary to make 800 HP, is there enough air MASS left over from that to sufficiently cool the engine?
YES – Maximum power is available.
NO – Then you cannot use that much air to burn that much fuel.

17. There must be a tradeoff.
During HI DA conditions, the amount of air burned with fuel must be reduced, so that this air may be used for cooling.
The combustion charge within the engine will be smaller.
This will result in decreased torque available.
MAX TGT
LO DA
MAX TORQUE
AVAILABLE TORQUE
MAX TGT
HI DA
MAX TORQUE
AVAILABLE TORQUE

18. This relationship is calculated during performance planning.
PPC LIMITATIONS:
BASED UPON STATIC, CONSTANT CONDITIONS WITH NO WIND.
DOES NOT TAKE INTO ACCOUNT TRANSIENT, IN FLIGHT CHANGES, SUCH AS WEIGHT INCREASES DUE TO “G” FORCES.

19. VARIABLES AFFECTING ROTOR EFFICIENCY
INDUCED FLOW EFFECTS
EFFECTIVE TRANSLATIONAL LIFT
GROUND EFFECT
ROTOR INFLOW
DENSITY ALTITUDE
BLADE CONING
VORTEX RING STATE
TRANSIENT TORQUE

20. INDUCED FLOW
Has a direct effect on the efficiency of the rotor system.
The greater the amount of induced flow present, the less efficient the rotor system

21. It is the downward component of air movement across an airfoil.
WHAT IS INDUCED FLOW?
It is the downward component of air movement across an airfoil. CL
RESULTANT RELATIVE WIND
INDUCED FLOW
ROTATIONAL RELATIVE WIND

22. INDUCED DRAG
LIFT
ANGLE OF ATTACK
RESULTANT RELATIVE WIND
TAF
DRAG
INDUCED FLOW

23. VECTOR DIAGRAMS CAN APPLY TO INDIVIDUAL PORTIONS OF THE ROTOR BLADES

26. OR TO THE ENTIRE ROTOR SYSTEM

27. Both rotor systems are producing the same amount of lift, because they have the same overall angle of attack
However; this one is using more power to do it

28. A rotor system requires more engine power to produce a certain amount of lift if it is operating with an increased amount of induced flow
Because this higher induced flow creates more induced drag against which the rotor blades must work

29. If the rotor system cannot overcome this drag, the result will be:
RPM droop due to excessive drag slowing the rotor system
Overtorque, overtemp, or both, while the aircraft is forced to provide the needed lift
If the aircraft has TGT or torque limiting, the aircraft will continue to descend, because it just WON’T give any more
Or a combination of any of the above

30. Excess engine power allows the rotor to produce the needed angle of attack, and in turn, required lift during conditions of very high induced flow and drag.
While excess power gives the aviator higher margins for error, it does not make one invincible.
10,000 HP may sound like a lot, but it does no good if the rotor system is unable to use it.

31. Control of induced flow:
EFFECTIVE TRANSLATIONAL LIFT
GROUND EFFECT
ROTOR INFLOW

32. EFFECTIVE TRANSLATIONAL LIFT
When the aircraft is above ETL, the rotor system produces more lift for a given power setting than during speeds below ETL.
ANGLE OF ATTACK = 5 DEGREES
ANGLE OF INCIDENCE = 25 DEGREES
INDUCED FLOW
ANGLE OF ATTACK = 15 DEGREES
ANGLE OF INCIDENCE = 25 DEGREES
INDUCED FLOW

33. GROUND EFFECT
When the aircraft is IGE, it’s rotor system operates more efficiently than when it is out of ground effect.
OGE begins at 1 to 1.25 rotor diameters above the ground
Not a linear relationship with altitude. Most of the efficiency of ground effect is found within ½ rotor diameters above the ground, with small decreases in efficiency until the aircraft is OGE.

34. MINIMIZE DECELERATIVE ATTITUDES WHILE IN A TAILWIND CONDITION
ROTOR INFLOW
Caused when wind is blown down into the top of the rotor system.
Causes an increase in overall induced flow and drag in the rotor system.
Increases the need for power.
20 KNOT TAILWIND
10 KNOTS INFLOW
10 KNOTS FWD SPEED
MINIMIZE DECELERATIVE ATTITUDES WHILE IN A TAILWIND CONDITION

35. DENSITY ALTITUDE
In high DA conditions, a higher VOLUME of air must be displaced downward in order to displace the same MASS of air that it would during conditions of low air density.
LOW DA
HIGH DA
7000 LBS LIFT
TWO FOLD: High DA reduces rotor efficiency, and reduces available engine power.

36. BLADE CONING

37. Rotor blades are designed to produce optimum lift with a certain degree of coning
Excessive blade coning results in loss of rotor efficiency and lift, because it actually affects the design properties of the blades themselves

38. FACTORS THAT CONTRIBUTE TO BLADE CONING
Low rotor RPM - When the rotor system is operating, the blades maintain their rigidity due to centrifugal force. Loss of this force with collective pitch applied allows a higher degree of blade coning.
Power droop - Causes low rotor RPM, which causes excessive blade coning.
** The danger from this can be two fold. If the application of power causes a droop, the aircraft could descend from having insufficient power available. Excessive coning in addition to this will cause an even greater loss of lift.

39. FACTORS THAT CONTRIBUTE TO BLADE CONING
High gross weight - Increases lift requirements, which causes more blade coning.
Increased “G” loading - Causes a momentary increase of the gross weight of the aircraft

40. THINGS THE PILOT CAN CONTROL WHILE IN FLIGHT
IN or OUT of Ground Effect
ABOVE or BELOW ETL
Transient weight changes
Blade coning
Rotor inflow
Deceleration rates and attitudes

41. Example of “G” forces and rotor inflow effects:
AIRCRAFT WEIGHT 10,000
MAX AVAIL POWER 100%
OGE HOVER POWER 100%
MAX TORQUE AVAILABLE
OGE HOVER
10,000 LBS

42. Example of “G” forces and rotor inflow effects:
AIRCRAFT WEIGHT 10,000
MAX AVAIL POWER 100%
OGE HOVER POWER 100%
1.2 “G” DECELERATION
BELOW ETL
12,000 LBS
MAX TORQUE AVAILABLE
OGE HOVER
10,000 LBS

43. Example of “G” forces and rotor inflow effects:
AIRCRAFT WEIGHT 10,000
MAX AVAIL POWER 100%
OGE HOVER POWER 100%
1.2 “G” DECELERATION
BELOW ETL
12,000 LBS
10 KNOTS INFLOW
MAX TORQUE AVAILABLE
OGE HOVER
10,000 LBS

44. Transient weight increase
PERFORMANCE PLANNING DID NOT ACCOUNT FOR:
Transient weight increase
Rotor inflow

45. Effects of a tailwind on an approach
EFFECTIVE ANGLE
APPROACH ANGLE

46. Effects of a tailwind on an approach
EFFECTIVE ANGLE
APPROACH ANGLE

47. Effects of a tailwind on an approach
COMPOUNDED BY LOWER ROTOR EFFICIENCY DUE TO INFLOW
INFLOW
MUCH STEEPER ANGLE

48. EXAMPLE OF A POORLY EXECUTED TAILWIND APPROACH

49. 87% AIRCRAFT WEIGHT- 12,000 LBS MAX POWER AVAIL- 100%
Speed of the aircraft falls below ETL while still at an OGE altitude
MAX POWER AVAIL- 100%
This requires at least 87% torque according to Performance Planning data
IGE HOVER PWR- 75%
OGE HOVER PWR- 87%
OGE
IGE
10 KNOT TAILWIND
BELOW ETL
OGE
87%

50. 87% AIRCRAFT WEIGHT- 12,000 LBS MAX POWER AVAIL- 100%
Pilot is late to apply power
MAX POWER AVAIL- 100%
1.25 G’s of deceleration will increase the aircrafts weight to 15,000 lbs
IGE HOVER PWR- 75%
OGE HOVER PWR- 87%
OGE
IGE
10 KNOT TAILWIND
BELOW ETL
WEIGHT INCREASE
OGE
87%

51. ? 87% AIRCRAFT WEIGHT- 12,000 LBS MAX POWER AVAIL- 100%
Rotor inflow will reduce the lift produced by the rotor system even more
MAX POWER AVAIL- 100%
IGE HOVER PWR- 75%
OGE HOVER PWR- 87%
OGE
IGE
10 KNOT TAILWIND
BELOW ETL
WEIGHT INCREASE
ROTOR INFLOW ?
OGE
87%

52. ? 87% AIRCRAFT WEIGHT- 12,000 LBS MAX POWER AVAIL- 100%
Rotor inflow will reduce the lift produced by the rotor system even more
MAX POWER AVAIL- 100%
IGE HOVER PWR- 75%
OGE HOVER PWR- 87%
OGE
IGE
EXCESSIVE BLADE CONING AND / OR A POWER DROOP WILL ONLY WORSEN THE SITUATION
10 KNOT TAILWIND
BELOW ETL
WEIGHT INCREASE
ROTOR INFLOW ?
OGE
87%

53. Only two of the four factors involved here were accounted for during performance planning
BELOW ETL
WEIGHT INCREASE
ROTOR INFLOW ?
OGE
87%
These need to be planned for while flying

54. MINIMUM PITCH ATTITUDE
Decelerate early, while still above ETL
Give yourself more room in which to decelerate
OGE
IGE
Each of the factors that would cause an increased power demand is countered by a condition that reflects greater rotor system efficiency.
10 KNOT TAILWIND
WEIGHT INCREASE
BELOW ETL
ROTOR INFLOW
HIGH POWER CONDITION
OGE
MINIMUM PITCH ATTITUDE
ABOVE ETL
ABOVE ETL
COUNTERING FACTOR
IGE

55. TERRAIN FLIGHT DECELERATION
Get most of the deceleration out of the way early, before losing ETL
ETL
TAILWIND

56. Don’t stack the variables against yourself MINIMUM PITCH ATTITUDE
Remember the times when your rotor is more efficient, and use those times to make demands from the engine(s).
Don’t stack the variables against yourself
WEIGHT INCREASE
BELOW ETL
ROTOR INFLOW
HIGH POWER CONDITION
OGE
MINIMUM PITCH ATTITUDE
ABOVE ETL
COUNTERING FACTOR
ABOVE ETL
IGE

57. VORTEX RING STATE
A condition in which the helicopter settles into it’s own downwash.
When the helicopter’s descent matches the descent of the rotor systems vortices and downwash, it is subject to this phenomena.
It is a transient state that occurs between normal powered flight and autorotation

58. FACTORS THAT ARE CONDUCIVE TO THE VORTEX RING STATE
% of available power applied - With power applied, vortices and downwash are generated from the rotor system.
Low forward airspeeds below ETL - At these speeds, the vortices and downwash descend from the helicopter in a vertical or near vertical fashion.
300 feet per minute or greater rate of descent - This is the range where the descent of the helicopter matches the descent of the vortices and downwash.

59. Normally, vortices and downwash descend from a hovering helicopter at 300 to 500 FPM

60. As the aircraft descends, a region of upflow is created at the center of the rotor disk

61. When the rate of descent matches the rate at which the downwash and vortices descend from the rotor system, the aircraft will experience:
Loss of rotor system lift production
Increased rate of descent

62. The aircraft is now in the vortex ring state
Rotor is unstable at this point.
Increasing power will only increase the rate of descent.

63. If the aircraft is at a high enough altitude, and if allowed to continue, the aircraft will enter an autorotative state, and may continue into a windmill brake state (overspeeding rotor)

64. NORMAL THRUSTING STATE
VORTEX RING STATE
300 – 500 FPM
WINDMILL BRAKE STATE
(AUTOROTATIVE)

65. RECOVERY:
If sufficient power is available, then it should be used EARLY.
If there is sufficient time and altitude, the aircraft may also be flown out of these conditions with forward or lateral cyclic input.
At low altitudes, the early stages of this phenomena are the most likely to be encountered.

67. AIRCRAFT MANEUVERING CONSIDERATIONS

68. Turning into a tailwind condition

69. AIRCRAFT BANKING
Sustaining a bank requires more engine power
A 45 bank angle requires 1.4 times the power required for straight and level flight.
A 60 degree bank requires twice the power.

70. Bank Angle vs. Power Req.
If adequate excess engine power is available, increasing collective pitch will enable continued flight while maintaining airspeed and altitude.

71. If you do not have the power available, then something must be traded off, either airspeed or altitude.

72. BUCKET SPEED
MOST AVAILABLE POWER
LEAST DRAG

73. BUCKET SPEED Best maneuvering airspeed Max endurance airspeed
Minimum rate of descent airspeed (autorotations)

74. Transient Torque
This is seen in the cockpit as a momentary increase in torque when the cyclic is displaced left of center. Conversely, as right cyclic is applied, a reduction in pitch on the advancing blade results in a reduction of induced drag that tends to increase Nr and a corresponding transient torque decrease.

75. Transient Torque
The amount of total drag within the rotor system is subject to changes during left and right rolls.
During flight, the types of drag that are affected are:
Advancing Blade – Induced Drag
Retreating Blade – Profile Drag

76. During a left roll, this induced flow is increased even more.
Advancing Blade – Normally, the advancing blade flaps upward during flight, creating higher induced flow.
During a left roll, this induced flow is increased even more.
This increases the amount of induced drag on the advancing blade
DIRECTION OF FLIGHT

77. During a left roll, this profile drag is increased even more.
DIRECTION OF FLIGHT
During a left roll, this profile drag is increased even more.
Retreating blade – Normally, the retreating blade flaps downward during flight, giving it higher profile drag.

78. During a right roll, the total drag within the rotor system decreases
During a left roll, the total drag within the rotor system increases

80. Conservation of Angular Momentum
A rotating body will rotate at the same velocity until some external force is applied to change the speed of rotation.

81. To minimize transient rotor droop, avoid situations which
UH60 Performance Characteristics
TRANSIENT ROTOR DROOP -
To minimize transient rotor droop, avoid situations which
result in rapid rotor loading from low Ng SPEED and
% TRQ conditions. Initiate maneuvers with collective inputs leading or simultaneous to cyclic inputs. During approach and landing, maintain at least 15% - 20% TRQ and transient droop will be minimal as hover power is applied.

82. Mushing
Mushing results during High G maneuvers when at high forward airspeeds aft cyclic is abruptly applied. This results in a change in the airflow pattern on the rotor, exacerbated by total lift area reduction as a result of rotor disc coning.

83. Combat Maneuver Do’s and Don’ts
Every aviator that employs these techniques at the wrong place and time endangers our ability to continue this critical training.
Only train maneuvers that have a combat application.
Taking unnecessary risks when carrying a load of combat equipped infantry soldiers can be equated to a Commercial Airline pilot showing off when carrying athletes to the Olympics.
There is no excuse. Do what the mission requires.

84. Pilot controls while in flight:
SUMMARY
Pilot controls while in flight:
IN or OUT of Ground Effect
ABOVE or BELOW ETL
Deceleration rates and attitudes
Do not forget about:
Vortex Ring State
Transient Torque

85. ????????????????????????????????????????????????????????

86. 3000 Series Tasks for Maneuvering Flight
3005 Demonstrate / Perform Flight Characteristics at Vh-IAS
3006 Perform Maximum Bank Angle
3007 Perform Maximum Pitch Angle
3008 Perform Decelerating Turn