Chapter 11 Flashcards
(42 cards)
NATOPS CH. 11
What is ground effect? When is the MH-60R considered to be in ground effect?
When rotor disc is within one rotor diameter of the ground. The ground reduces the amount of recirculated air through the rotor disc, increasing efficiency of lift production and reducing power req.
H-60R in ground effect at 45’ on RADALT (bc its on the bottom of the aircraft)
11.1.1.1.1
NATOPS CH. 11
Describe blowback
With increasing forward airspeed, the rotor disc tilts aft.
The advancing blade experiences higher velocity relative wind than the retreating blade which creates more lift on the advancing side. phase lag causes max displacement to occur 90 after applied force so max upward flapping occurs at the 12 o’clock position and downward flapping at 6 o’clock.
11.1.1.1.3
NATOPS CH. 11
Translational Lift
As the flow of air moves through the rotor more horizontally, the rotor operates more efficiently. In forward flight, the rotor encounters undisturbed air versus recirculating vortices in a hover.
Horizontal airflow reduces induced drag which decreases induced power required. profile and parasite drag effect power requirements at higher airspeeds which means the greatest benefit of translational lift is noticed at lower airspeeds.
According to NATOPS Effective Translational Lift begins at 15 knts in 7.9.2.1
Between 17-30 knots theres a noticable vibration that occurs as the aircraft encountersits own ground vortex (11.1.1.2.2)
11.1.1.2.2
NATOPS CH. 11
Below 30 KIAS, the stabilator is at what position?
42* trailing edge down
11.1.1.2.1
NATOPS CH. 11
Explain the cause(s) of retreating blade stall. When is it most likely to occur?
As airspeed increases, the relative wind on the advancing blade increases but decreases on the retreating side.
As the in-air velocity of the retreating blade decreases with increasing forward airspeed, the AOA must be increased to equalize lift to provide stabilized flight.
Flapping aggravates the lift distribution on the retreating blade further and eventually the blade stalls. This is most likely to occur when operating at high speed, gross weight, density altitude, and power
11.1.2.1
NATOPS CH. 11
Name the methods of eliminating retreating blade stall
“PSA RAG”
“PSA RAG”
pitch (collective)
severity (decrease)
airspeed (decrease)
rotor rpm (increase)
altitude (decrease)
gross weight (decrease)
11.1.2.2
NATOPS CH.11
Tractor Tail Rotor
The tractor tail rotor provides antitorque and 2.5% of the total lift in hovering flight. This helps offset the aircrafts’ aft center of gravity and provides a lower nose attitude hover. The tail rotor is canted 20 degrees.
11.1.3.1
NATOPS CH.11
Explain Loss of Tail Rotor Authority
LTA is a power issue. The tail rotor can no longer produce enough thrust to react against the high torque and the helo will spin to the right
11.1.3.2.1
NATOPS CH.11
Define Loss of Tail Rotor Effectiveness
A wind issue - the inability of the tail rotor to provide sufficient thrust to maintain yaw controllability.
AOA Reduction: 060-120
Weathervane Instability: 120-240
Tail Rotor VRS: 210-330
MR Vortex Interference: 280-330
11.1.3.2.2
NATOPS CH.11
How can you recovery from LTE?
“CAL”
- Collective lower - reduces torque and assists in arresting right yaw
- Airspeed increase - fwd cyclic and turn in direction of rotation as req.
- Left pedal apply
11.1.3.7
NATOPS CH.11
At what roll rate and airspeed does tail rotor spar loading / damage occur?
Left roll at 30 deg. per second and 75 KIAS.
11.1.4.3
When executing high roll rate maneuvers to the left, what should you be cognizant of?
left roll rates (> 30*/sec above 75 KIAS) can combine with induced tail rotor gyroscopic and flapping loads to cause excessive tail rotor spar loading.
when executing high roll rate maneuvers to the left, collective should be lowered concurrently to control transient torque increases and reduce tail rotor spar loading
NATOPS CH. 11
What can cause main rotor flapping margins to be exceeded and droop stop pounding to occur?
Inducement of less than 1g flight by rapid application of forward cyclic
11.1.4.5
NATOPS CH. 11
Describe the phenomena associated with rolling pullouts.
The weight vector of the aircraft increases in a rolling pullout due to centrifugal acceleration (g-loading)
- Lift produced by the rotor system must be increased proportionally to the g-load to arrest descent and establish level flight.
- This can result in a situation where power required for recovery greatly exceeds total power available in the rotor system and a mushing occurs.
- During mushing the aircraft will continue to descend rapidly even with max power applied, longitudinal cyclic control will feel sluggish, increased 4 per vibes, and retreating blade stall may occur.
11.1.4.9
NATOPS CH. 11
Power Required exceeds Power Available
May occur at high DA, gross weight, or reduced power. May be unable to maintain level flight in certain regimes.
These effects are most significant when conditions exceed: 35C and 80% relative humidity at MRP or CRP.
11.1.4.11
NATOPS CH. 11
Name the four flow states of a rotor system.
Normal thrusting
Vortex ring
Autorotative
Windmill brake
11.1.5
NATOPS CH. 11
Describe vortex ring state
An aerodynamic condition where a helicopter may be in a vertical descent with max power required and little or no cyclic authority.
Tip vortices are created by air curling up from the bottom of the rotor system and rejoining the air entering the rotor from the top. They consume engine power but produce no useful lift. When the helo descends vertically, it settles into it’s own downwash, which greatly enlargens the tip vortices. VRS is a state where most of the engine power is wasted accelerating vortices around the rotor.
11.1.5.1
NATOPS CH. 11
When is the effect of VRS measurable?
At descent rates greater than 700 FPM and airspeeds between 0-20 KIAS.
Worst at descent rates of 1500 FPM and airspeeds of 5-10 KIAS.
11.1.5.1
NATOPS CH. 11
What is fully developed VRS characterized by?
An unstable condition where the helicopter experiences:
- Uncommanded pitch and roll oscillations.
- Little or no cyclic authority.
- Descent rate that may approach 6,000 FPM.
11.1.5.1
NATOPS CH. 11
How do you recover from VRS?
- Decrease collective pitch.
- Increase forward airspeed.
- Enter autorotation if altitude permits.
11.1.5.1
NATOPS CH. 11
The autorotative state can be achieved at descent velocities between approx. ________FPM and ________FPM at 19,000 lbs. gross weight.
3,125
4,450
11.1.5.2
NATOPS CH. 11
What are the regions of the rotor disc in a steady state autorotation? What % is each one?
prop - 30%
auto - 45%
stall - 25%
11.1.5.2
NATOPS CH.11
Which of the three regions of the rotor disc create lift in an autorotation?
the prop region creates usable lift
the auto region produces forward-tilting force that creates lift and pro-rotational force that overcomes blade drag and keeps the rotor spinning at a constant rpm
the stall region creates only drag
11.1.5.2
