Ch. 11 - Flight Characteristics

Question 1

Blade tips move at ________.

Answer 1

725 ft/sec

Question 2

The MH-60R is considered to be in ground effect below what altitude?

Answer 2

45 ft

Question 3

Flapping fixes _____________. By reducing lift on the _________ blade and increasing it on the ___________ blade by flapping _________.

Answer 3

Asymmetrical distribution of lift

Advancing

Retreating

Flapping down

Question 4

Phase lag is felt ______ degrees from where the inputs are put in.

Answer 4

90*

Question 5

Blowback

Answer 5

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)

Question 6

Translational lift is at approximately what?

Answer 6

17kts

Question 7

Stab begins programming at what?

Answer 7

30 kias

Question 8

Methods to eliminate Blade Stall?

5 Decrease and 1 Increase

Answer 8

Decrease Severity of maneuver
Decrease Collective Pitch
Decrease Airspeed
Decrease Altitude
Decrease Gross Weight
Increase rotor RPM

Question 9

Blade Stall happens when

Answer 9

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.

Question 10

Weather vaning is what?

And occurs when?

Answer 10

120* to 240*

Winds push on the tail and cause the helicopter to rotate into the wind.

Question 11

What is tail rotor vortex ring state?

What region does it occur in?

Answer 11

210* to 330*

The tail rotor operates in its own airflow. Causing unpredictable yaw rates

Question 12

Main rotor disc vortex interaction is what?

Occurs in What region?

Answer 12

280* to 330* and possibly 030* to 080*

Main rotor vortex is directed onto the rotor changing the AOA on the tail rotor.

Question 13

How can you recover from LTE?

Answer 13

Lowering collective

Forward cyclic

In a hover, applying full left pedal.

Question 14

Vortex ring state occurs when?

When are they worst?

Answer 14

Descent rates greater than 700 fpm and 0 - 20 kias

Descent rates of 1500 fpm and 5 - 10 kias

Question 15

How do you recover from vortex ring state?

Answer 15

Decrease collective pitch

Increase forward airspeed

Enter autorotation if altitude permits.

Question 16

Regions of prop during autorotative state?

Answer 16

Prop region- 30%
Autorotative-45%
Stall region - 25%

Question 17

Prop region creates _______.

Answer 17

Usable lift

Question 18

The autorotative region creates __________________.

Answer 18

Lift and rotational forces

Question 19

Stall region creates only ___________.

Answer 19

Drag forces

Question 20

When does static Rollover occur?

Answer 20

28*

Question 21

Critical rollover occurs at?

Answer 21

12*

Question 22

How does aircraft respond to rotor blade Stall?

Answer 22

Increased vibs

Pitch up

Roll left

Question 23

Ground Effect

Answer 23

45’ Rad Alt

Question 24

Transition to forward flight w/ tail wind

Answer 24

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.

Question 25

M/R 1 Per Rev Vibrations

Answer 25

Main Rotor Blades out of track

feels like a lateral oscilatory roll to the pilot

Question 26

1.44 per rev

Answer 26

Caused by an initial aerodynamic upset amplified by SAS and Pilot insuced oscilations.

Question 27

Four per rev

Answer 27

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

Question 28

Ground Resonance

Answer 28

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.

Question 29

1 per tail rotor

Answer 29

Due to tail rotor imbalance. Can be hard to distinguish since its very close to M/R 4 per vibrations.