Power Management 1-212th Aviation Regiment

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

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

BASIC ENGINE OPERATION Engine air is taken in through the intake

BASIC ENGINE OPERATION Compressed by the compressor

BASIC ENGINE OPERATION Passes into the combustion chamber

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

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

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

Air is ingested by the engine and compressed by VOLUME

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

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

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.

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.

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

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.

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

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.

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

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

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

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

VECTOR DIAGRAMS CAN APPLY TO INDIVIDUAL PORTIONS OF THE ROTOR BLADES

OR TO THE ENTIRE ROTOR SYSTEM

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

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

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

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.

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

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

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.

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

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.

BLADE CONING

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

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.

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

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

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

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

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

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

Effects of a tailwind on an approach EFFECTIVE ANGLE APPROACH ANGLE

Effects of a tailwind on an approach EFFECTIVE ANGLE APPROACH ANGLE

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

EXAMPLE OF A POORLY EXECUTED TAILWIND APPROACH

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%

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%

? 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%

? 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%

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

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

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

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

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

FACTORS THAT ARE CONDUCIVE TO THE VORTEX RING STATE 20 - 100% 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.

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

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

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

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

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)

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

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.

AIRCRAFT MANEUVERING CONSIDERATIONS

Turning into a tailwind condition

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.

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

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

BUCKET SPEED MOST AVAILABLE POWER LEAST DRAG

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

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.

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

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

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.

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

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.

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.

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.

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.

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

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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