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UH 72 > P1 / Aerodynamics > Flashcards

P1 / Aerodynamics Flashcards

1
Q

What are the 3 conditions required for a dynamic roll over ?

A
  1. pivot point
  2. rolling motion
  3. Exceeded critical angle
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2
Q

What is ETL - from T/O ?

airspeed - what happens - consequence on a/c - pilot input)

A

Effective translational lift
16-24 kts

A/c outruns vorticies and gets more efficient

Nose wanna pitch up because of dyssymmetry of lift (blowback) pilot input is forward cyclic

More right pedals as we go to ETL because tail strukture gets more efficient and less antitorque input is needed to maintain heading

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3
Q

Pilot input because of ETL when landing

A

When going below 16-24 kts
more main and tail rotor thrust is needed

pilot input: Raise collective + left pedal
to maintain HDG and ALT

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4
Q

What does the pilot experience as a result of transverse flow effect ?

A

Rotor vibrations and right roll

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5
Q

Define transverse flow

A

The differential of lift, drag and induced flow that exist between the forward and rear half of the rortor disc

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6
Q

Why does transverse flow effect cause vibrations ?

A

Due to the difference in drag between forward and aft part of the rotor disc.

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7
Q

Why does right roll occur when experiencing transverse flow effect ?

A

More lift on the forward part of the rotor disc due to more horizontal airflow = less induced flow = higher AOA = more lift.

the lift is manifested 90 degreese later due to gyroscopic persession = right roll

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8
Q

What is pilot input in regard to transverse flow ?

A

left cyclic

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9
Q

Dynamic roll over causes

A

Tie down laying over skid
Skid contact
Slope operations
Rough surface conditions (mud)
Cyclic at limits T/O (slope)

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10
Q

What are the human factors that can lead to dynamic rollover

A

Human: I-I-F-I-L
(Inattention, inexperience, failure to take timely corrective action, inappropriate control inputs, loss of visual ref.)

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11
Q

What’s translating tendency ?

A

Nose of the a/c wanting to turn to the right because of main rotor torque and tailrotor thrust. The counteractions manifests as drifting to the right

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12
Q

How do we compensate for translating tendency ?

A

Riging (flight controls, transmission)
Computer
Pilot gives left cyclic

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13
Q

What’s dissymmetry of lift ?

A

Helicopter moves though air:
The advancing blade move quicker than the retrieving blade. Therefore it creates more lift.

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14
Q

Equation for lift

A
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15
Q

Define “Transverse flow”

Airspeed occurance ?

A

The forward half of the disk operates in a more horizontal flow of air which increases lift. The rear part of the disk operates in a higher induced flow (vertical air flow).
This causes a difference in lift, drag and vibrations that causes buffering + right rolling motion due to gyroscopic pers.

10-20 kts

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16
Q

What are the regions in the rotor system during autorotation ?

A
  1. Stall
  2. Driving
  3. Driven
17
Q

Which conditions can cause settling with power ?

A

Maskin/unmasking
Downwind approach
Steep approach (>30 deg)
Formation approach
OGE
Hovering above max hover ceiling

18
Q

Define settling with power

A

A condition of powered flight in which the helicopter settles in its own downwash.

Vortex ring state

19
Q

Settling with power conditions

A

Near vertical / veritcal descent >300 fpm
Low airspeed < ETL
20-100% power to rotor (insufficient power to arrest descent)

20
Q

Settling with power recovery

A

Early stage - increase collective to arrest descent (may increase sink rate if too late )

If enough power is not avaiable - Apply cyclic in safe diretion to fly out of the column of air.
A decrease of collective may also help if altitude permits

21
Q

What the recovery from retreating blade stall

abbreviation

A

DIRRR
Descent to lower atitude (if possible)
Increase RPM
Reduce collective
Reduce airspeed
REduce severity of maneuver

22
Q

Definition: Dynamic rollover

A

The susceptibility of a helicopter to a lateral-rolling tendency

23
Q

When can dynamic rollover occur

A

Level ground, Slope and crosswind T/O and landing

24
Q

An increase in induced flow will have what effect on AOA ?

A

Higher IF = Smaller AOA

25
Q

What happens to induced flow & AOA when going through ETL ?

A

Induced flow decreases and AOA increases

26
Q

What happens at airspeeds above “Best rate of climb Vy” that results in decreased climb performance ?

A

Lower efficiency due to increased parasite drag

27
Q

At what airspeeds does the follow occur:
1. Transverse flow effect
2. Effective translational lift
3. Settling with power
4. Retreading blade stall

A
  1. 10-20 kts
  2. 16.24 kts
  3. IAS < ETL
  4. Excessive airspeed
28
Q

What causes blowback ?

A

Dissymmetry of lift

29
Q

How is dissymmetry of lift corrected for ?

A

Blade flapping (aerodynamic) and cyclic feathering (mechanical)

30
Q

What happens when blade flaps up ?

A

Upflap (advancing blade) increases induced flow which decreases AOA

31
Q

What does blade flapping and cyclic feathring do to correct for dissymmetry of lift ?

A

Blade flapping - changes induced flow
Cyclic feathering - Changes AOI

32
Q

Forward movement of cyclic will ____ AOI over the ____blade and cause a ____ in AOA

A

decrease AOI
advancing blade
decrease AOA

33
Q

What happens when HOGE in comparenson to HIGE
( requires —- to Maintain —- this due to —— )

A

HOGE requires more power (higher AOI) to maintain the same AOA and lift as IGE. This due to the increase in induced flow velocity and tip vorticies

34
Q

What can prevent dynamic rollover ?
( action When dynamic Rollover is about to occur )

A

Smooth, moderate collective input

35
Q

What’s the critical rollover angle ?

A

The angle a which if exceeded makes recovery impossible.

36
Q

Why does retreating balde stall occur at high airspeeds?

A

Because of the higher AOA needed to compensate for the advance stage of dissymmetry of lift

the increase in forward velocity, decreases the velocity of the retreating blade. A higher AOA is needed to create same amount of lift as the advancing. The no lift area wil start moving outboard as the CAOA is exceeded.

37
Q

What will the pilot experience during retreating blade stall ?

A

Rotor vibrations, left roll, nose pitch up

38
Q

What conditions is likely to cause retreating blade stall ?

A

Low rotor RPM (rotor droop)
Turbulent air
Loads (high blade loading/high GW)
Altitude ( high DA)
High G maneuvers

39
Q

What are the physical factors that can lead to dynamic rollover

A

Thrust (tail rotor)
Thrust (Main rotor)
Cross wind
CG
Slopes
Surface

UH 72 (42 decks)

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