CPT 5

Cockpit Procedures Trainer FIVE

=Discuss:=

Dynamic rollover


During slope or crosswind landing and takeoff maneuvers exceeding the critical rollover angle (15°) or exceeding 10° per second will cause the helo to roll over onto its side regardless of cyclic corrections introduced by the pilot. For dynamic rollover to occur 3 essential elements must exist:

Note
 * 1. Ground pivot point
 * 2. A side force
 * 3. Lift approximately equal to weight
 * Side force is always present due to right tail rotor thrust, which is offset with left cyclic. Left cyclic tilts the lift vector to the side creating a sideward force to balance the thrust from the tail rotor.  Critical rollover angle is reduced for a right skid down condition, crosswind, lateral CG offset, and left rudder pedal inputs.

When landing or taking off, keep aircraft trimmed and do not allow aircraft roll rates to build. If roll rates begin to build recover by smoothly lowering the collective.

Note:
 * Lowering the collective will eliminate the lift vector and hence the sideward force
 * The static roll-over angle for the TH-57 is approximately 31°.

Critical rollover angle is reduced (made worse) for a right skid down condition, cross winds, lateral center-of-gravity offset, and left rudder pedal inputs.





In other words you can't do this.

Rotor blade stall
As airspeed increases the retreating blade linear flow is reduced. In order for the retreating blade to generate the same amount of lift it flaps down, decreasing induced flow. This causes the AOA on the retreating blade to increase. Eventually as airspeed increases the blade will exceed the critical AOA and stall. The effects on the helicopter are:


 * 1. 2:1 Vibration level increases
 * 2. Pitch-up of the nose (Left blade 270° stalls, due to phase lag the loss of lift is felt over the tail causing the tail to drop and the nose to pitch up)
 * 3. Rolling tendency toward the stalled side (left)

Three factors causing blade stall:
 * 1. Up collective (increased power for forward airspeed-increase blade pitch)
 * 2. Forward Cyclic (increased forward airspeed-causes retreating blade pitch angle to increase)
 * 3. Increased blade flapping due to high airspeed

Factors which increase the potential for blade stall:
 * High blade loading (i.e. high gross weights / G loading)
 * Low rotor RPM
 * Turbulent air
 * High Density Altitude
 * High airspeed

In the event of a blade stall, it will be characterized by a progressively increasing two-per-revolution vibration, terminating in a loss of longitudinal control and severe feed back in the cyclic control stick. The nose of the helicopter will oscillate up and down violently, independent of cyclic control stick position. Recovery may be accomplished by one or a combination of the following actions:


 * 1. Decrease the severity of the maneuver
 * 2. Decrease collective pitch
 * 3. Reduce airspeed
 * 4. Descend to lower altitude
 * 5. Increase rotor rpm

CAUTION
 * Entry into severe blade stall can result in structural damage to the helicopter.

Vortex ring state
Vortex ring state is an uncommanded increase in rate of descent caused by the helicopter settling into its own downwash. In this state, the flow through the rotor system is upward near the center of the rotor disk and downward in the outer portion. This results in zero net thrust from the rotor and extremely high aircraft descent rates. Vortex ring state is not restricted to high gross weights or high density altitudes. It may not be recognized and a recovery effected until considerable altitude has been lost. Helicopter rotor theory indicates that it is most likely to occur when descent rates exceed 800 feet per minute during vertical descents initiated from a hover and steep approaches at less than 40 knots.

Indications to the pilot are:
 * 1. Rapid descent rate increase
 * 2. Increase in overall vibration level
 * 3. Loss of control effectiveness

Recover by:
 * 1. Decrease collective
 * 2. Forward cyclic to gain airspeed

If impact is imminent:
 * 3. Level to conform to terrain.

WARNING Increasing collective has no effect toward recovery and will aggravate vortex ring state. During approaches at less than 40 kias, do not exceed 800 feet per minute descent rate.

[[Media:vortexringstate.mpeg| Watch a Canadian Sea King enter Vortex Ring state from a 300 foot hover]]

Power required exceeds power available (Settling with Power)
When power required for a maneuver exceeds power available under the ambient conditions, an uncommanded rate of descent will result. Factors that can cause or aggravate this situation are: Power required exceeding power available becomes dangerous to the crew and helicopter when operating in close proximity to obstructions where the pilot may not have enough altitude / maneuvering space to recover prior to impacting an obstacle. This condition will be aggravated by rotor droop and loss of tail rotor effectiveness associated with excessive power demands. Pilots can avoid power required exceeding power available by:
 * 1. High G loading (i.e. level turn)
 * 2. High gross weight
 * 3. High density altitude
 * 4. Rapid maneuvering (i.e. quick stops)
 * 5. Spool up time from lower power settings to high power settings (i.e. power pull at the completion of a power recovery auto rotation)
 * 6. Loss of wind effect (i.e. descending below a tree line during a confined area landing)
 * 7. Change of wind direction (i.e. during lower altitude / low airspeed flight terrain following)
 * 8. Loss of ground effect (i.e. transitioning to forward flight from the deck of a ship with a heavy internal load)


 * 1. Preflight planning to calculate expected aircraft performance.
 * 2. Avoiding excess maneuvering, particularly during high hot and or high gross weight marginal power available situations.
 * 3. Avoiding high descent rates at low altitudes which will require large power inputs to arrest the helicopter’s descent.
 * 4. Avoiding downwind landings and takeoffs.
 * 5. Maintaining awareness of wind speed and direction, especially during low altitude low airspeed maneuvers.
 * 6. Maintaining awareness of the factors leading to power required exceeding power available and the associated effects on aircraft performance.

Indications to the pilot of settling with power are an uncommanded descent with torque at maximum allowable and or rotor droop and possible loss of tail rotor effectiveness.

Recover By:
 * 1. Nr	Maintain
 * 2. RPM switch	Full Incr.
 * 3. Airspeed Increase / Decrease to 50 kias (minimum power airspeed)
 * 4. Angle of bank	Level wings
 * 5. Jettison	As Required

If impact is imminent:
 * 6. Level aircraft to conform to terrain
 * 7. Cushion the landing

SPRAG CLUTCH SLIPPAGE
Sprag clutch slippage may occur following power-off maneuvers in which Nr and Nf have been split.

Indications: Procedures: If time and altitude permit:
 * Nf indications higher than Nr
 * Low torque indication
 * Ng and TOT indications lower than normal and not responsive to collective.
 * 1. Autorotate
 * 2. Twist grip	Flight Idle
 * 3. Twist grip	Smoothly rotate to full open

If Nf/Nr are married:
 * 4. Collective Increase

If sprag clutch continues to slip:
 * 5. Autorotate
 * 6. Twist grip closed.

If sprag clutch reengages;
 * 7. Land as soon as possible

CAUTION
 * After completing the autorotative landing, ensure that the twist grip is secured. Failure to do so may result in sudden reengagement of the sprag clutch, causing severe damage to the drive system.

Note
 * Multiple attempts to reengage the sprag clutch are permitted dependent on time and altitude.

SPRAG CLUTCH SEIZURE
Indications: Note Procedure:
 * Nf / Nr married during shutdown
 * Nf / Nr married above 100% during autorotative flight
 * In a normal autorotation, Nr and Nf may be matched together between 92-96% steady state.
 * 1. Ensure twist grip is full open
 * 2. Land as soon as possible

WARNING
 * If suspected during an autorotation, execute a wave-off before Nr decays below 85%.

=Review=
 * 1. FAM stage check lists
 * 2. Normal start / shutdown
 * 3. Abnormal starts
 * 4. Overspeed, high Nr
 * 5. Underspeed, low Nr
 * 6. Compressor stall
 * 7. Engine failure
 * 8. Engine restart
 * 9. Engine fire
 * 10. Electrical fire
 * 11. Smoke and fume elimination
 * 12. Suspected fuel leakage
 * 13. Main drive shaft failure
 * 14. Fuel system malfunctions
 * 15. Post shutdown fire / internal