Ch. 11 - Flight Characteristics Flashcards
Blade tips move at ________.
725 ft/sec
The MH-60R is considered to be in ground effect below what altitude?
45 ft
Flapping fixes _____________. By reducing lift on the _________ blade and increasing it on the ___________ blade by flapping _________.
Asymmetrical distribution of lift
Advancing
Retreating
Flapping down
Phase lag is felt ______ degrees from where the inputs are put in.
90*
Blowback
In a windless hover lift is symmetrical.
In headwind hover advancing blade flaps up (reducing AOA) retreating flaps down (increasing AOA)
Realized 90* later due to phase lag tilting disk aft.
Short term: SAS 2 (Gust alleviation)
Long Term: Pilot input (Transition to forward flight)
Translational lift is at approximately what?
17kts
Stab begins programming at what?
30 kias
Methods to eliminate Blade Stall?
5 Decrease and 1 Increase
Decrease Severity of maneuver
Decrease Collective Pitch
Decrease Airspeed
Decrease Altitude
Decrease Gross Weight
Increase rotor RPM
Blade Stall happens when
The retreating blade has increased is AOA so much that it has stalled.
The blade tip is traveling at rotational speed minus forward airspeed of helicopter.
Weather vaning is what?
And occurs when?
120* to 240*
Winds push on the tail and cause the helicopter to rotate into the wind.
What is tail rotor vortex ring state?
What region does it occur in?
210* to 330*
The tail rotor operates in its own airflow. Causing unpredictable yaw rates
Main rotor disc vortex interaction is what?
Occurs in What region?
280* to 330* and possibly 030* to 080*
Main rotor vortex is directed onto the rotor changing the AOA on the tail rotor.
How can you recover from LTE?
Lowering collective
Forward cyclic
In a hover, applying full left pedal.
Vortex ring state occurs when?
When are they worst?
Descent rates greater than 700 fpm and 0 - 20 kias
Descent rates of 1500 fpm and 5 - 10 kias
How do you recover from vortex ring state?
Decrease collective pitch
Increase forward airspeed
Enter autorotation if altitude permits.
Regions of prop during autorotative state?
Prop region- 30%
Autorotative-45%
Stall region - 25%
Prop region creates _______.
Usable lift
The autorotative region creates __________________.
Lift and rotational forces
Stall region creates only ___________.
Drag forces
When does static Rollover occur?
28*
Critical rollover occurs at?
12*
How does aircraft respond to rotor blade Stall?
Increased vibs
Pitch up
Roll left
Ground Effect
45’ Rad Alt
Transition to forward flight w/ tail wind
In a hover the disk does not care which direction the wind is coming from.
Transitioning forward will require increase in coll. as rel wind initially decreases before gaining forward airspeed.
M/R 1 Per Rev Vibrations
Main Rotor Blades out of track
feels like a lateral oscilatory roll to the pilot
1.44 per rev
Caused by an initial aerodynamic upset amplified by SAS and Pilot insuced oscilations.
Four per rev
Due to asymetrical blade loading
At low airspeeds blades traversing doenwash of preceding blades
At higher speeds can be due to worn out vibrabration absorbers, m/r pressure plates, dampers, loose stab etc.
Adjusting the RPM will adjust the 4 per vib
Ground Resonance
Self excited mechanical vibration when the lead-lag motion is out of phase and not controlled by the dampers.
Rotor system forces become unaligned and feed back into the rotor hub.
1 per tail rotor
Due to tail rotor imbalance. Can be hard to distinguish since its very close to M/R 4 per vibrations.
