Title: The ability to maintain and control rotor RPM in the event of an engine malfunction so controlled flight may be continued to the ground.
1Autorotation
The ability to maintain and control rotor RPM in
the event of an engine malfunction so controlled
flight may be continued to the ground.
Airflow during helicopter descent provides the
necessary energy to overcome blade drag and to
turn the rotor.
The aviator gives up altitude at a controlled
rate in return for the needed energy to turn the
rotor at an RPM that provides aircraft control.
Stated another way, the helicopter has potential
energy by virtue of its altitude.
2UH OH!
POOF!
In powered flight, rotor drag is overcome with
engine power. When the engine fails, or is
otherwise disengaged from the rotor system, some
other force must sustain rotor RPM so controlled
flight can be continued to the ground.
3If a loss of power should occur with the
helicopter in this condition, RPM decay is rapid.
To prevent RPM decay, the collective must be
lowered immediately to reduce the drag and
incline the TAF vector forward toward the axis of
rotation
4Entry and Descent
Specific entry technique may vary and will be
determined by such factors as airspeed, gross
weight, density altitude and altitude above the
landing surface.
5Entry and Descent cont..
From cruise altitudes and airspeeds, the
collective must be reduced and the cyclic
adjusted to achieve an airspeed that maintains
RRPM while affording a reasonable glide distance
and rate of descent.
6Entry and Descent cont..
Once a steady state autorotation has been
achieved, any movement of the cyclic will affect
Rotor RPM.
Aft cyclic will initially increase R-RPM and
forward cyclic will reduce RRPM. R-RPM will
stabilize at some other value once cyclic inputs
are stopped.
7Maximum Glide Distance
- Best Glide Distance is determined through flight
tests - The specific speed at which a power-off glide
will cover the maximum distance - Typically 4 to 1 (4 feet forward for every 1 foot
of descent) Or One NM per 1,500AGL - Rotor RPM Approximately 90
- Airspeed Approximately 75 KIAS
8Minimum rate of descent
- For each aircraft, there is an airspeed that will
result in the minimum rate of descent. - The values for minimum rate of descent are
determined through flight tests. - For the R-22 - 53KIAS
- Values are very close to the airspeed for minimum
drag.
9Driven Region 30 of radius
Driving Region 45 of radius
Blade regions in a vertical autorotation
Stall Region 25 of radius
10Stall Region
- That area inboard of the 25 radius
- Operates above the critical angle of attack
- Contributes little vertical lift but some
rotational drag
11Stall Region
TAF
L
D
12Driving Region
- That blade region between approximately 25 and
70 radius - Operates at comparatively high angles of attack
- Resultant aerodynamic force is inclined slightly
forward of axis of rotation in the direction of
rotation - Inclination of the total aerodynamic force
provides horizontal thrust in the direction of
rotation and tends to increase RRPM
13Driving Region
TAF
L
D
14Driven Region
- The blade region outboard of the 70 radius
- Operates at slightly less angle of attack than
Driving region - Because of higher relative wind speed, provides
most of the vertical lift opposing weight - Inclination provides horizontal drag, opposite
the direction of rotation, which tends to
decrease RRPM
15Driven Region
TAF
L
D
16Forward
Autorotative regions in forward flight. Regions
incline towards the retreating side
17(No Transcript)
18The rotor disk TAF is tilted well forward
providing the necessary thrust to propel the
helicopter at the desired airspeed
However, the individual blade segment TAF is
inclined well aft of the axis of rotation. The
engine is needed to overcome the drag forces
generated by this situation.
19Requirements
The rotor system must be decoupled from the
engine(s)
This occurs if an engine malfunctions, or if the
pilot retards the throttle, as in a simulated
engine failure.
The collective must be lowered so the angle of
attack will not become so excessive that RPM will
be lost.
20Questions?