The ability to maintain and control rotor RPM in the The ability to maintain and control rotor RPM in the event of an engine malfunction so controlled flight event of an engine malfunction so controlled flight may be continued to the ground. may be continued to the ground.

AutorotationAutorotation

Airflow during helicopter descent provides the Airflow during helicopter descent provides the necessary energy to overcome blade drag and to turn necessary energy to overcome blade drag and to turn the rotor.the rotor.

The aviator gives up altitude at a controlled rate in The aviator gives up altitude at a controlled rate in return for the needed energy to turn the rotor at an return for the needed energy to turn the rotor at an RPM that provides aircraft control. Stated another RPM that provides aircraft control. Stated another way, the helicopter has potential energy by virtue of way, the helicopter has potential energy by virtue of its altitude.its altitude.

In powered flight, rotor drag is overcome with engine In powered flight, rotor drag is overcome with engine power. When the engine fails, or is otherwise power. When the engine fails, or is otherwise disengaged from the rotor system, some other force disengaged from the rotor system, some other force must sustain rotor RPM so controlled flight can be must sustain rotor RPM so controlled flight can be continued to the ground.continued to the ground.

POOF!POOF!

UH OH!UH OH!

If a loss of power should occur If a loss of power should occur with the helicopter in this with the helicopter in this condition, RPM decay is rapid. condition, RPM decay is rapid.

To prevent RPM decay, the To prevent RPM decay, the collective must be lowered collective must be lowered immediately to reduce the drag and immediately to reduce the drag and incline the TAF vector forward incline the TAF vector forward toward the axis of rotationtoward the axis of rotation

Entry and DescentEntry and Descent

Specific entry technique may vary Specific entry technique may vary and will be determined by such and will be determined by such factors as airspeed, gross weight, factors as airspeed, gross weight, density altitude and altitude above density altitude and altitude above the landing surface.the landing surface.

From cruise altitudes and airspeeds, the From cruise altitudes and airspeeds, the collective must be reduced and the cyclic collective must be reduced and the cyclic adjusted to achieve an airspeed that adjusted to achieve an airspeed that maintains RRPM while affording a maintains RRPM while affording a reasonable glide distance and rate of reasonable glide distance and rate of descent. descent.

Entry and Descent cont..Entry and Descent cont..

Once a steady state autorotation has been Once a steady state autorotation has been achieved, any movement of the cyclic will affect achieved, any movement of the cyclic will affect Rotor RPM. Rotor RPM.

Entry and Descent cont..Entry and Descent cont..

Aft cyclic will initially increase R-RPM and Aft cyclic will initially increase R-RPM and forward cyclic will reduce RRPM. R-RPM will forward cyclic will reduce RRPM. R-RPM will stabilize at some other value once cyclic inputs stabilize at some other value once cyclic inputs are stopped. are stopped.

Maximum Glide DistanceMaximum Glide Distance

•Best Glide Distance is determined through flight Best Glide Distance is determined through flight tests tests •The specific speed at which a power-off glide will The specific speed at which a power-off glide will cover the maximum distancecover the maximum distance•Typically 4 to 1 (4 feet forward for every 1 foot of Typically 4 to 1 (4 feet forward for every 1 foot of descent) Or One NM per 1,500’AGLdescent) Or One NM per 1,500’AGL•Rotor RPM Approximately 90%Rotor RPM Approximately 90%•Airspeed Approximately 75 KIASAirspeed Approximately 75 KIAS

•For each aircraft, there is an airspeed that For each aircraft, there is an airspeed that will result in the minimum rate of descent.will result in the minimum rate of descent.•The values for minimum rate of descent are The values for minimum rate of descent are determined through flight tests.determined through flight tests.•For the R-22 - 53KIASFor the R-22 - 53KIAS•Values are very close to the airspeed for Values are very close to the airspeed for minimum drag.minimum drag.

Minimum rate of descentMinimum rate of descent

Driven Region Driven Region 30% of radius30% of radius

Driving RegionDriving Region45% of radius45% of radius

Stall RegionStall Region25% of radius25% of radius

Blade regions in a Blade regions in a vertical autorotationvertical autorotation

Stall RegionStall Region

•That area inboard of the 25% radiusThat area inboard of the 25% radius

•Operates above the critical angle of attack Operates above the critical angle of attack •Contributes little vertical lift but some Contributes little vertical lift but some

rotational dragrotational drag

TAFTAF

LLDD

Stall RegionStall Region

Driving RegionDriving Region

•That blade region between approximately 25% and That blade region between approximately 25% and 70% radius70% radius•Operates at comparatively high angles of attackOperates at comparatively high angles of attack•Resultant aerodynamic force is inclined slightly Resultant aerodynamic force is inclined slightly forward of axis of rotation in the direction of rotationforward of axis of rotation in the direction of rotation•Inclination of the total aerodynamic force provides Inclination of the total aerodynamic force provides horizontal thrust in the direction of rotation and tends horizontal thrust in the direction of rotation and tends to increase RRPMto increase RRPM

TAFTAFLL

DD

Driving RegionDriving Region

Driven RegionDriven Region

•The blade region outboard of the 70% radiusThe blade region outboard of the 70% radius•Operates at slightly less angle of attack than Operates at slightly less angle of attack than Driving Driving regionregion•Because of higher relative wind speed, provides Because of higher relative wind speed, provides most of the vertical lift opposing weightmost of the vertical lift opposing weight•Inclination provides horizontal drag, opposite the Inclination provides horizontal drag, opposite the direction of rotation, which tends to decrease RRPMdirection of rotation, which tends to decrease RRPM

TAFTAFLL

DD

Driven RegionDriven Region

Autorotative regionsAutorotative regionsin forward flight. in forward flight. Regions incline Regions incline towards the retreating towards the retreating sideside

ForwardForward

DrivenDriven

DrivingDrivingStallStall

AA

BB

CC

DD

EE

AA

DrivenDrivenRegionRegion

CC

Driving Driving RegionRegion

B,B, DD

Point ofPoint ofEquilibriumEquilibrium

Point ofPoint ofEquilibriumEquilibrium

EEStallStall

RegionRegion

The rotor disk TAF is tilted The rotor disk TAF is tilted well forward providing the well forward providing the necessary thrust to propel necessary thrust to propel the helicopter at the desired the helicopter at the desired airspeedairspeed

However, the individual blade However, the individual blade segment TAF is inclined wellsegment TAF is inclined wellaft of the axis of rotation. aft of the axis of rotation. The engine is needed to The engine is needed to overcome the drag forces overcome the drag forces generated by this situation. generated by this situation.

RequirementsRequirementsThe rotor system must be decoupled from The rotor system must be decoupled from the engine(s)the engine(s)

The collective must be lowered so the angle The collective must be lowered so the angle of attack will not become so excessive that of attack will not become so excessive that RPM will be lost.RPM will be lost.

This occurs if an engine malfunctions, or if the This occurs if an engine malfunctions, or if the pilot retards the throttle, as in a simulated pilot retards the throttle, as in a simulated engine failure.engine failure.

Questions?Questions?