DISCUSS
a. Dynamic rollover
b. Rotor blade stall
c. Vortex ring state
d. Power required exceeds power available
e. Sprag clutch malfunction
REVIEW
a. FAM stage checklists
b. Normal start/shutdown
c. Abnormal starts
d. Overspeed, high Nr
e. Underspeed, low Nf
f. Compressor stall
g. Engine failure
h. Engine restart
i. Engine fire
j. Electrical fire
k. Smoke and fume elimination
l. Suspected fuel leakage
m. Main drive shaft failure
n. Fuel system malfunctions
o. Post shutdown fire/internal
DISCUSS
a. Dynamic rollover - An accelerated roll about a ground pivot point (landing gear/skids). When AOB or side drift during takeoff or landings occur, lateral cyclic control becomes sluggish and less effective. If AOB passes 15 degrees, the helo will enter a roll which can not be stopped with cyclic. Without lateral trim, aircraft may exceed angle in less than 2 sec.
To avoid entering roll, pilot should
1) Maintain
trim
2) Not allow
aircraft rates from becoming large
3) Not allow
aircraft bank angle from becoming too large
4) Fly smoothly
To recover, pilot should use a smooth, moderate collective
reduction less than 40% (full up to down in 2 sec). Lowering collective
too quickly may cause mast bumping or dynamic roll in the opposite direction.
During slope landings
1) Descend
slowly, placing upslope skid down first
2) Lateral
cyclic into slope to maintain level TPP
3) Set cyclic to neutral
position once assured helo will remain stable
4) Do not
land on a slope greater than 7.5 degrees
5) If helo
rolls upslope side (5 to 8 degrees of level), collective down
In crosswind maneuvers, hold cyclic into wind and land/takeoff downwind skid first until firmly on ground.
Static rollover (if aircraft were pushed with no thrust from blades) is 31 degrees.
Warning - With one skid on the ground and thrust
approx. equal to weight, if the lateral control becomes sluggish or ineffectual,
contacts the lateral stop, or if bank angle or roll rates become excessive
(15 degrees or 10 degrees/sec) the aircraft may roll over on its side.
Reduce the collective to stop the roll and correct the bank angle to level.
Warning - When landing or
taking off, with thrust approx. equal to the weight and one skid on the
ground, keep the aircraft trimmed and do not allow aircraft roll rates
to build up. Fly the aircraft smoothly off (or onto) the ground, carefully
maintaining trim.
Note - Do not attempt to
level the skids prior to takeoff/landing as this will aggravate the side
drift and possibly lead to dynamic rollover [NATOPS
11.8, AERO 5-8]
b. Rotor blade stall - All helicopters have a tendency to have their retreating blade stall in forward flight, which limits their forward speed. The airspeed of the retreating blade slows down as forward airspeed increases. To equal the lift of the advancing blade, the retreating blade must have an increased AOA, which will cause stall earlier than the advancing blade. Stall angle is considered to be 14 degrees for this rotor system. Upon entry into blade stall, a two-to-one vibration will begin, loss of longitudinal control will occur, and severe cyclic feedback will result. Also, the nose will pitch up as loss of lift at 270 position is felt at tail.
Factors which affect stall include:
1. Airspeed
2. Gross Weight
3. Density
Altitude
4. G loads
5. Nr.
If blade stall is encountered the pilot
should:
1. Reduce airspeed (reduces pwr req, reducing pitch/AOA)
2. Decrease collective pitch (reduces AOA)
3. Descend to a lower altitude (decreases pwr req.)
4. Decrease the severity of the maneuver (reduces G loading)
5. Increase rotor rpm (increases rotational velocity)
Caution - Entry into severe blade stall can result
in structural damage to the helicopter. [NATOPS 11.9, AERO 5-3]
c. Vortex Ring State - The uncontrolled rate of descent caused by the helicopter rotor encountering disturbed air as it settles into its own downwash, also known as power settling. This condition may occur in powered descending flight at low airspeeds while out of ground effect, when rate of descent approaches or equals the induced flow rate. At 300 - 600 ft/min descent, vortex ring state may begin and will not clear until exceeding 1500-3000 ft/min. Glide slope of 70 degrees (nearly vertical) seem increase the possibility of settling. When these conditions are met, the rotor pumps air into a large bubble underneath it, which then bursts, disturbing air flow and blade thrust. [AERO 5-6] Because approach angles less than 50 degrees and airspeeds of 15-30 kts allow enough new air to enter the rotor system, the TH-57 is limited to descent rates less than 800 ft/min, with airspeeds greater than 40 KIAS, and approach angles less than 45 degrees. [AERO 4-2]
VORTEX RING STATE (POWER SETTLING) [NATOPS 11.6]
INDICATIONS:
Rapid descent rate increase
Increase in overall vibration level
Loss of control effectiveness
PROCEDURES:
1. Forward cyclic to gain airspeed
2. Decrease collective
If impact
is imminent:
3. Level aircraft to conform to terrain
Warning - Increase collective has no effect toward
recovery and will aggravate vortex ring state. During approaches at less
than 40 KIAS, do not exceed 800 feet/min descent rate.
d. Power required exceeds power available -
May be caused or aggravated by:
1. High G loading
2. High gross weight
3. Rapid maneuvering
4. Engine spool up time from low to high pwr
5. Loss of wind effect
6. Change of wind direction
7. Loss of ground effect
Pilots can avoid situation by:
1. Preflight planning to calculate expected a/c performance
2. Avoiding excessive maneuvering, esp. during high/hot and or high gross
weight/marginal pwr avail. situations
3. Avoiding high descent rates at low altitudes which will require large
power inputs to arrest helicopter's descent
4. Avoid downwind landings and takeoffs
5. Maintaining awareness of windspeed and direction, especially during
low altitude/low airspeed maneuvers
6. Maintaining awareness of the factors leading to pwr req. exceeding pwr
available and the effects on a/c and perf
POWER REQUIRED EXCEEDS POWER AVAILABLE [NATOPS 11.7, AERO 5-7]
INDICATIONS:
Uncommanded descent with associated maximum torque
Rotor rpm droop
Possible loss of tail rotor effectiveness
PROCEDURES:
1. Nr Maintain
2. RPM switch FULL INCREASE
3. Airspeed 50 KIAS (min pwr req.)
4. Angle of bank Level Wings
5. Jettison stores As Req.
If impact is imminent:
6. Level aircraft to conform to terrain
7. Cushion the landing
e. Sprag clutch malfunctions - The sprag clutch assembly is the main component of the freewheeling unit and provides et means to disconnect the power train from a failed or secured engine. The sprags are held in a cage assembly and rotation of the outer race {Nf} by the engine jams the sprag between the inner {Nr} and outer races {Nf}. If the outer races stops because of engine failure/shutdown, the inner race is free to turn because of sprags. [SYSTEMS 4-8]
SPRAG CLUTCH SLIPPAGE [NATOPS
14.3]
Sprag clutch slippage may occur following power-off maneuvers
in which Nr and Nf have been split.
When the twist grip is full open the pilot may experience:
INDICATIONS:
Nf indication higher than Nr
Low torque indication
Ng and TOT indications lower than normal and not responsive to collective
PROCEDURES:
*1. Autorotate
*2. Twist grip FLIGHT IDLE
If time and altitude permit:
*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 the sprag clutch reengages:
*7. Land as soon as possible
Caution - After completing the autorotative landing,
ensure 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 [NATOPS 14.4]
INDICATIONS:
Nf/Nr married during shutdown
Nf/Nr married above 100% during autorotational flight
PROCEDURES:
*1. Ensure twist grip is full open
*2. Land as soon as possible
Warning - If suspected during
an autorotation, execute a waveoff before Nr decays below 85%.
Note - In a normal autorotation, Nr and Nf may
be matched together between 92-96% steady state.
REVIEW
a. FAM stage checklists - CPT1
b. Normal start/shutdown - CPT1
c. Abnormal starts - CPT1
d. Overspeed, high Nr - CPT4
e. Underspeed, low Nf - CPT4
f. Compressor stall - CPT4
g. Engine failure - CPT4
h. Engine restart - CPT4
i. Engine fire - CPT3
j. Electrical fire - CPT4
k. Smoke and fume elimination - CPT2
l. Suspected fuel leakage - CPT2
m. Main drive shaft failure - CPT4
n. Fuel system malfunctions - CPT3
o. Post shutdown fire/internal - CPT1