P1 / Aerodynamics Flashcards
What are the 3 conditions required for a dynamic roll over ?
- pivot point
- rolling motion
- Exceeded critical angle
What is ETL - from T/O ?
airspeed - what happens - consequence on a/c - pilot input)
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
Pilot input because of ETL when landing
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
What does the pilot experience as a result of transverse flow effect ?
Rotor vibrations and right roll
Define transverse flow
The differential of lift, drag and induced flow that exist between the forward and rear half of the rortor disc
Why does transverse flow effect cause vibrations ?
Due to the difference in drag between forward and aft part of the rotor disc.
Why does right roll occur when experiencing transverse flow effect ?
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
What is pilot input in regard to transverse flow ?
left cyclic
Dynamic roll over causes
Tie down laying over skid
Skid contact
Slope operations
Rough surface conditions (mud)
Cyclic at limits T/O (slope)
What are the human factors that can lead to dynamic rollover
Human: I-I-F-I-L
(Inattention, inexperience, failure to take timely corrective action, inappropriate control inputs, loss of visual ref.)
What’s translating tendency ?
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
How do we compensate for translating tendency ?
Riging (flight controls, transmission)
Computer
Pilot gives left cyclic
What’s dissymmetry of lift ?
Helicopter moves though air:
The advancing blade move quicker than the retrieving blade. Therefore it creates more lift.
Equation for lift
Define “Transverse flow”
Airspeed occurance ?
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
What are the regions in the rotor system during autorotation ?
- Stall
- Driving
- Driven
Which conditions can cause settling with power ?
Maskin/unmasking
Downwind approach
Steep approach (>30 deg)
Formation approach
OGE
Hovering above max hover ceiling
Define settling with power
A condition of powered flight in which the helicopter settles in its own downwash.
Vortex ring state
Settling with power conditions
Near vertical / veritcal descent >300 fpm
Low airspeed < ETL
20-100% power to rotor (insufficient power to arrest descent)
Settling with power recovery
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
What the recovery from retreating blade stall
abbreviation
DIRRR
Descent to lower atitude (if possible)
Increase RPM
Reduce collective
Reduce airspeed
REduce severity of maneuver
Definition: Dynamic rollover
The susceptibility of a helicopter to a lateral-rolling tendency
When can dynamic rollover occur
Level ground, Slope and crosswind T/O and landing
An increase in induced flow will have what effect on AOA ?
Higher IF = Smaller AOA
What happens to induced flow & AOA when going through ETL ?
Induced flow decreases and AOA increases
What happens at airspeeds above “Best rate of climb Vy” that results in decreased climb performance ?
Lower efficiency due to increased parasite drag
At what airspeeds does the follow occur:
1. Transverse flow effect
2. Effective translational lift
3. Settling with power
4. Retreading blade stall
- 10-20 kts
- 16.24 kts
- IAS < ETL
- Excessive airspeed
What causes blowback ?
Dissymmetry of lift
How is dissymmetry of lift corrected for ?
Blade flapping (aerodynamic) and cyclic feathering (mechanical)
What happens when blade flaps up ?
Upflap (advancing blade) increases induced flow which decreases AOA
What does blade flapping and cyclic feathring do to correct for dissymmetry of lift ?
Blade flapping - changes induced flow
Cyclic feathering - Changes AOI
Forward movement of cyclic will ____ AOI over the ____blade and cause a ____ in AOA
decrease AOI
advancing blade
decrease AOA
What happens when HOGE in comparenson to HIGE
( requires —- to Maintain —- this due to —— )
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
What can prevent dynamic rollover ?
( action When dynamic Rollover is about to occur )
Smooth, moderate collective input
What’s the critical rollover angle ?
The angle a which if exceeded makes recovery impossible.
Why does retreating balde stall occur at high airspeeds?
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.
What will the pilot experience during retreating blade stall ?
Rotor vibrations, left roll, nose pitch up
What conditions is likely to cause retreating blade stall ?
Low rotor RPM (rotor droop)
Turbulent air
Loads (high blade loading/high GW)
Altitude ( high DA)
High G maneuvers
What are the physical factors that can lead to dynamic rollover
Thrust (tail rotor)
Thrust (Main rotor)
Cross wind
CG
Slopes
Surface
