2WHAT 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 POWERROTOR SYSTEM EFFICIENCY
3AVAILABLE ENGINE POWER Affected by:Environmental conditions (Density Altitude)Hot temperatures / High altitudes are conducive to high DA conditions.Determined by Performance PlanningUnable to be controlled in flight
4BASIC ENGINE OPERATION Engine air is taken in through the intake
5BASIC ENGINE OPERATION Compressed by the compressor
6BASIC ENGINE OPERATION Passes into the combustion chamber
7BASIC ENGINE OPERATION This energy then passes through the Gas Producer turbine
8BASIC ENGINE OPERATION Then through the Power turbine and out of the exhaust.
9BASIC ENGINE OPERATION Some engine layouts may differ, but the operating principles are the same
10Air is ingested by the engine and compressed by VOLUME
11Approximately 25% of this VOLUME is used for combustion with fuel Air is ingested by the engine and compressed by VOLUMEThe approximate MASS ratio of air / fuel is 15:1 during combustion.The other 75% is used for cooling the engine
12Approximately 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
13DENSITY ALTITUDE EFFECTS UPON AVAILABLE ENGINE POWER Power generation depends upon the MASS of fuel + air able to be combusted.This is a 15:1 ratioEngine cooling depends upon the MASS of the cooling charge.The MASS of a certain volume of air changes depending upon the Density Altitude.
14HIGH DA – Low air density LESS MASSLOW DA – High air densityMORE MASSThe MASS of air may change with DA, but the required MASS of air for engine performance does not change.
15Example: 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 HPThat 500 LBS of fuel requires a certain MASS of air with which to combustA certain MASS of air is also required to keep the engine coolThis cannot change if the engine is to provide the performance for which it was designedIf the engine cannot take in enough air to combust the necessary amount of fuel, and to cool itself, then a limitation will be encountered
16The 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.
17There 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 TGTLO DAMAX TORQUEAVAILABLE TORQUEMAX TGTHI DAMAX TORQUEAVAILABLE TORQUE
18This 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.
20INDUCED FLOWHas a direct effect on the efficiency of the rotor system.The greater the amount of induced flow present, the less efficient the rotor system
21It 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.CLRESULTANT RELATIVE WINDINDUCED FLOWROTATIONAL RELATIVE WIND
22INDUCED DRAGLIFTANGLE OF ATTACKRESULTANT RELATIVE WINDTAFDRAGINDUCED FLOW
23VECTOR DIAGRAMS CAN APPLY TO INDIVIDUAL PORTIONS OF THE ROTOR BLADES
27Both rotor systems are producing the same amount of lift, because they have the same overall angle of attackHowever; this one is using more power to do it
28A rotor system requires more engine power to produce a certain amount of lift if it is operating with an increased amount of induced flowBecause this higher induced flow creates more induced drag against which the rotor blades must work
29If the rotor system cannot overcome this drag, the result will be: RPM droop due to excessive drag slowing the rotor systemOvertorque, overtemp, or both, while the aircraft is forced to provide the needed liftIf the aircraft has TGT or torque limiting, the aircraft will continue to descend, because it just WON’T give any moreOr a combination of any of the above
30Excess 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.
31Control of induced flow: EFFECTIVE TRANSLATIONAL LIFTGROUND EFFECTROTOR INFLOW
32EFFECTIVE 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 DEGREESANGLE OF INCIDENCE = 25 DEGREESINDUCED FLOWANGLE OF ATTACK = 15 DEGREESANGLE OF INCIDENCE = 25 DEGREESINDUCED FLOW
33GROUND EFFECTWhen 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 groundNot 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.
34MINIMIZE DECELERATIVE ATTITUDES WHILE IN A TAILWIND CONDITION ROTOR INFLOWCaused 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 TAILWIND10 KNOTS INFLOW10 KNOTS FWD SPEEDMINIMIZE DECELERATIVE ATTITUDES WHILE IN A TAILWIND CONDITION
35DENSITY ALTITUDEIn 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 DAHIGH DA7000 LBS LIFTTWO FOLD: High DA reduces rotor efficiency, and reduces available engine power.
37Rotor 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
38FACTORS 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.
39FACTORS 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
40THINGS THE PILOT CAN CONTROL WHILE IN FLIGHT IN or OUT of Ground EffectABOVE or BELOW ETLTransient weight changesBlade coningRotor inflowDeceleration rates and attitudes
41Example of “G” forces and rotor inflow effects: AIRCRAFT WEIGHT 10,000MAX AVAIL POWER 100%OGE HOVER POWER 100%MAX TORQUE AVAILABLEOGE HOVER10,000 LBS
42Example of “G” forces and rotor inflow effects: AIRCRAFT WEIGHT 10,000MAX AVAIL POWER 100%OGE HOVER POWER 100%1.2 “G” DECELERATIONBELOW ETL12,000 LBSMAX TORQUE AVAILABLEOGE HOVER10,000 LBS
43Example of “G” forces and rotor inflow effects: AIRCRAFT WEIGHT 10,000MAX AVAIL POWER 100%OGE HOVER POWER 100%1.2 “G” DECELERATIONBELOW ETL12,000 LBS10 KNOTS INFLOWMAX TORQUE AVAILABLEOGE HOVER10,000 LBS
44Transient weight increase PERFORMANCE PLANNING DID NOT ACCOUNT FOR:Transient weight increaseRotor inflow
45Effects of a tailwind on an approach EFFECTIVE ANGLEAPPROACH ANGLE
46Effects of a tailwind on an approach EFFECTIVE ANGLEAPPROACH ANGLE
47Effects of a tailwind on an approach COMPOUNDED BY LOWER ROTOR EFFICIENCY DUE TO INFLOWINFLOWMUCH STEEPER ANGLE
4987% AIRCRAFT WEIGHT- 12,000 LBS MAX POWER AVAIL- 100% Speed of the aircraft falls below ETL while still at an OGE altitudeMAX POWER AVAIL- 100%This requires at least 87% torque according to Performance Planning dataIGE HOVER PWR- 75%OGE HOVER PWR- 87%OGEIGE10 KNOT TAILWINDBELOW ETLOGE87%
5087% AIRCRAFT WEIGHT- 12,000 LBS MAX POWER AVAIL- 100% Pilot is late to apply powerMAX POWER AVAIL- 100%1.25 G’s of deceleration will increase the aircrafts weight to 15,000 lbsIGE HOVER PWR- 75%OGE HOVER PWR- 87%OGEIGE10 KNOT TAILWINDBELOW ETLWEIGHT INCREASEOGE87%
51? 87% AIRCRAFT WEIGHT- 12,000 LBS MAX POWER AVAIL- 100% Rotor inflow will reduce the lift produced by the rotor system even moreMAX POWER AVAIL- 100%IGE HOVER PWR- 75%OGE HOVER PWR- 87%OGEIGE10 KNOT TAILWINDBELOW ETLWEIGHT INCREASEROTOR INFLOW?OGE87%
52? 87% AIRCRAFT WEIGHT- 12,000 LBS MAX POWER AVAIL- 100% Rotor inflow will reduce the lift produced by the rotor system even moreMAX POWER AVAIL- 100%IGE HOVER PWR- 75%OGE HOVER PWR- 87%OGEIGEEXCESSIVE BLADE CONING AND / OR A POWER DROOP WILL ONLY WORSEN THE SITUATION10 KNOT TAILWINDBELOW ETLWEIGHT INCREASEROTOR INFLOW?OGE87%
53Only two of the four factors involved here were accounted for during performance planning BELOW ETLWEIGHT INCREASEROTOR INFLOW?OGE87%These need to be planned for while flying
54MINIMUM PITCH ATTITUDE Decelerate early, while still above ETLGive yourself more room in which to decelerateOGEIGEEach of the factors that would cause an increased power demand is countered by a condition that reflects greater rotor system efficiency.10 KNOT TAILWINDWEIGHT INCREASEBELOW ETLROTOR INFLOWHIGH POWER CONDITIONOGEMINIMUM PITCH ATTITUDEABOVE ETLABOVE ETLCOUNTERING FACTORIGE
55TERRAIN FLIGHT DECELERATION Get most of the deceleration out of the way early, before losing ETLETLTAILWIND
56Don’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 yourselfWEIGHT INCREASEBELOW ETLROTOR INFLOWHIGH POWER CONDITIONOGEMINIMUM PITCH ATTITUDEABOVE ETLCOUNTERING FACTORABOVE ETLIGE
57VORTEX RING STATEA 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
58FACTORS 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.
59Normally, vortices and downwash descend from a hovering helicopter at 300 to 500 FPM
60As the aircraft descends, a region of upflow is created at the center of the rotor disk
61When 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 productionIncreased rate of descent
62The aircraft is now in the vortex ring state Rotor is unstable at this point.Increasing power will only increase the rate of descent.
63If 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)
64NORMAL THRUSTING STATE VORTEX RING STATE300 – 500 FPMWINDMILL BRAKE STATE(AUTOROTATIVE)
65RECOVERY: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.
73BUCKET SPEED Best maneuvering airspeed Max endurance airspeed Minimum rate of descent airspeed (autorotations)
74Transient TorqueThis 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.
75Transient TorqueThe 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 DragRetreating Blade – Profile Drag
76During 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 bladeDIRECTION OF FLIGHT
77During a left roll, this profile drag is increased even more. DIRECTION OF FLIGHTDuring 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.
78During a right roll, the total drag within the rotor system decreases During a left roll, the total drag within the rotor system increases
80Conservation of Angular Momentum A rotating body will rotate at the same velocity until some external force is applied to change the speed of rotation.
81To minimize transient rotor droop, avoid situations which UH60 Performance CharacteristicsTRANSIENT ROTOR DROOP -To minimize transient rotor droop, avoid situations whichresult 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.
82MushingMushing 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.
83Combat 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.
84Pilot controls while in flight: SUMMARYPilot controls while in flight:IN or OUT of Ground EffectABOVE or BELOW ETLDeceleration rates and attitudesDo not forget about:Vortex Ring StateTransient Torque