AME T101 Theory of Flight - Rotary Wing Flashcards
What do Conventional Helicopters have that identify them as “conventional”?
A Main Rotor & a Tail Rotor.
What are some typical Helictopter uses?
Name Three
1) Emergeny Transport.
2) Firefighting
3) Police Work
How does the Center of Pressure move with a Symmetrical Airfoil?
Predictably.
Why are some helicopters equipped with Asymmetrical Blades?
Mainly due to the incorporation of computer designs.
What is Lift?
Lift is the force produced by the Airfoil perpendicular to the relative wind.
It is the opposition of Gravity.
Due to the spinning rotor-head, lift occurs where?
At the Center of the blades.
Define Drag
This is the force parallel and opposite to the relative wind.
Drag is the resistance to the atmosphere to the motion of the aircraft.
It also opposes thrust.
What produces Thrust on a Heliccpter?
It is produced by the Rotor System.
Thrust is parallel to what?
The Relative Wind.
Where is the Relative Wind?
It is always on the leading edge of the main rotor blades.
The advancing blade has a lower what than the retracting blade?
Has a lower Angle of Attack.
A Helicopter will never stall due to which blade?
The Advancing Blade.
A Stall will occur at which blade first?
The Retreating Blade.
Which part of the Retreating Blade will stall first?
The tip of it.
True or False.
Retreating Blade Stall is noticeable.
True.
What indications of a stall exist?
An increase in vibration.
The Helicopter will want to tip upward.
During a stall, the pilot must do one what three things?
1) Unload the Rotor System
2) Slow Down
3) Increase Rotor Speed
Pitch Angle is the Angle created by what?
This is the Angle created by the Chord Line to a reference plane.
The Pitch Angle is changed ________ among the Rotor Blades.
Equally
How is Pitch Angle Controlled?
Through the Collective.
The Cyclic changes the pitch on how many blades?
Individual Blades.
Define Blade Droop.
This is when the Rotor Blades hang down in a stationary mannor.
Define Coning.
During Flight, the blades bend upward.
What forces cause coning?
Centrifugal Force and Lift
What is the purpose of a Helicopter’s Tail Rotor?
List Two Reasons.
To counteract torque generated by the main rotor.
To allow for Yaw.
Changing the pitch on all the blades allows for movement along which axis?
The Vertical Axis.
The Cyclic allows for what kind of control?
Directional Control.
What is Newton’s Third Law?
For every action, there is an equal and opposite reaction/
What is Translating Tendency?
This is the tendency that causes a helicopter to wander.
What three methods exist to counteract Translating Tendency?
1) Offsetting the Swashplate or the rigging of the Swashplate.
2) Offsetting the Mast
3) Offsetting the Transmission
Tandem Rotor Set-Up has two Main Rotors placed where?
One in the Front, One in the Back.
Describe the Coaxial Rotor Design.
Two Rotors are stacked. One on top of the other.
Describe the Intermeshing Rotor Design.
Thsee Rotors rotate within one another.
Why must Intermeshing Rotors be timed perfectly?
To prevent them from self destructing.
Define the Coanda Effect.
A big fan is place at the head of the tail boom to send a stream of air downward onto it.
The rushing air moves down to a small slit within the boom and rushes out again.
This air is high velocity and low pressure.
As a result, lift is generated wherever the stream is pointing.
Why would the Coanda Effect be used on a helicopter?
It is a design meant to deal with the torque generated by the Main Rotor.
List the three axis’ of motion on a Rotor-Head.
1) Feathering
2) Flapping
3) Lead-Lag
What is Feathering?
The blades pitching movement.
What controls Feathering?
The Collective.
What is the purpose of Flapping?
Meant to compensate for Dissymmetry of Lift.
What does Lead-Lag compensate for?
Compensates for Coriolis Effect.
Main Rotor Systems spin in what direction when built in North America?
Counter Clockwise.
Main Rotor Systems spin in what direction when built in Europe?
Clockwise.
Define In-Ground Effect.
Induced flow has decreased so less power is needed to fly the helicopter.
Define Out-of-Ground Effect.
Out-of-Ground Effect is when induced flow has increased and can then escape.
More what is needed when a Helicopter experiences Out-of-Ground Effect?
Power.
Induced Flow has what kind of effect on Angle of Attack?
A Negative Effect.
Why is Washout built into Rotor Blades?
Provides equal lift along the entire length of the blade.
If you add the Speed of the Aircraft to the Blade Tip Speed you get the total speed of what?
You get the Total Speed of the Advancing Blade.
Subtracting the Blade Tip Speed from the Total Speed of the Advancing Blade you get the Speed of what?
The Retreating Blade.
The Retreating Blade gets less lift than the Advancing Blade causing what phenonmenon?
Dissymmetry of Lift.
Dissymmetry of Lift is the difference between what two things due to airspeed?
The amount of lift on the Advancing and Retreating Blades of the Rotor System due to Airspeed.
How would one compensate for Dissymmetry of Lift?
Flap up or Flap Down
Retreating Blade: Flap Down (Increases Angle of Attack)
Advancing Blade: Flap Up (Decreases Angle of Attack)
Why would you Flap the Rotor Blades when experiencing Dissymmetry of Lift?
This Flapping motion equalizes lift throughout the rotor system.
Coriolis Effect is necessary to maintain what?
To maintain the same momentum from both the Advancing and Retreating Blades.
How is Coriolis Effect compensated for?
With Lead-Lag.
What is a Drag Hinge?
A Hinge attached from Blade to Rotor Hub.
What is the purpose of the Drag Hinge?
To allow for Lead-Lag.
What would happen if no Drag Hinge were present?
The Blade would be required to physically bend.
List three types of Rotor Heads.
1) Rigid
2) Semi-Rigid
3) Fully Articulated
Which axis of motion does a Rigid Rotor-Head allow?
The Feathering Axis. (Pitch)
What is the advantage of a Rigid Rotor-Head?
Its Maneuverability.
Which Rotor-Head is simple and robust?
The Rigid Rotor-Head.
Which Rotor-Head type is the most common?
The Semi-Rigid Rotor-Head.
Which axis of motion does the Semi-Rigid Rotor-Head allow?
Feathering and Flapping
Which Rotor-Head design is considered a workhorse?
The Semi-Rigid Rotor-Head.
What axis does the Fully Aritculated Rotor-Head possess?
Feathering
Flapping
Lead-Lag
Which Rotor-Head has a Shock Absorber built into its design?
The Fully Articulated Rotor-Head.
On the Fully Articulated Rotor-Head, what does the Shock Absorber allow for?
What does the Shock Absorber control?
Allows for Lead-Lag.
Controls the Speed and Intensity of Lead-Lag’s occurrence.
What is another name for the Fully Articulated Rotor-Head’s Shock Absorber?
The Lead-Lag Damper.
The swashplate transfers movement of the Cyclic & Collective controls to convert it from a ________ push-pull movement to a ________ push-pull movement.
Blank #1) Linear
Blank #2) Rotating
What is the purpose of the swashplate?
To convert linear movement to rotating movement.
What are the two swashplates inputs?
Cyclic and Collective
What is the phenomenon that causes an action to occur nintey degrees after a force has been applied?
Gyroscopic precession.
Explain Gyroscopic Precession
It is the phenomenon that causes an action to occur ninety degrees from where it was initially applied.
On a helicopter, what compensates for Gyroscopic precession?
The swashplate.
What happens when a helicopter blade goes “out of phase?”
It causes a vibration to go through the system.
What phenomenon can out of phase blades cause?
Ground Resonance.
What can Ground Resonance potentially cause a helicopter to do?
Shake it pieces.
What is Translational Lift?
An increase in lift as the rotor enters linear flight.
An increase in lift as the rotor enters linear flight is known as what phenomenon?
Translational lift.
Induced Flow increases / decreases in the transition from a hover to a linear movement?
Increases / decreases angle of attack in a linear movement?
Increases in the transition from a hover to a linear movement.
Decreases the angle of attack in a linear movement.
Tranverse Flow Effect is also known as what?
Inflow Roll
Inflow Roll is also known as what?
Transverse Flow Effect.
What is Transverse Flow Effect?
It is a roll that occurs on take-off.
What is Inflow Roll?
A roll that occurs on take-off.
Inflow Roll:
The direction of this depends on what?
Which way the rotor turns.
What is the time-frame in which Transverse Flow Effect impacts the aircraft?
It happens and disappears very quickly.
On what kind of rotorhead does Ground Resonance effect?
Fully articulated Rotor-Heads.
What is needed for Ground Resonance to occur?
Two Things
1) A fully articulated rotor-head.
2) Wheeled Landing Gear could aggravate an out-of-phase blade.
What could aggravate an out-of-phase rotor blade?
Wheeled Landing Gear.
How would one prevent Ground Resonance?
(The Pilot does this).
Why would they do this?
Take-off immediately.
Reason: Neutralizes Ground Resonance.
What is Dynamic Rollover?
A helicopter drifts and one of the skids hits the ground. It causes the helicopter to essentially flop over.
What causes Dynamic Rollover?
The pilot making a mistake.
Attempting to take off on a hill could also cause this to happen.
What are the two kinds of vibrations that may occur in a rotor system?
1) Lateral Vibration
2) Vertical Vibration
Lateral Vibration means that the rotor is what?
What does it mean if the rotor system is experiencing Vertical Vibrations?
1) Rotor is Out of Balance
2) Rotor is Out of Track.
The rotor system is out of balance…
what does this mean?
The center of mass is rotating outside of the center of gravity.
The rotor system is out of track…
what does this mean?
The blades are not following the same paths.
What are the three general frequencies of Vibrations?
1) High Frequency
2) Medium Frequency
3) Low Frequency
High Frequency Vibration run at 2000 RPM and above.
What are three components that fall into this category?
1) Tail Rotors
2) Some Engine Components
3) Drive Trains
High Frequency Vibrations run at what RPM?
2000 RPM and above.
Medium Frequency Vibrations run at 200 to 500 RPM.
What are some components that fall into this category?
Cooling Fans.
On Reciprocating Engines
Out of the three general Vibration categories, which two the most difficult to differentiate?
Medium and High Frequency vibrations.
Low Frequency Vibrations run from 0 to 500 RPM.
What are some components that fall into this category?
Main Rotor Heads.
How do low frequency vibrations manifest in a main rotor system?
It sounds like a “beat.”
What phenomenon is the product of multiple blades within a rotor system?
Multiple Rotor Vibrations.
Multiple Rotor Vibrations is the result of what?
Multiple Blades within a rotor system.
Why is alignment paramount in a rotor system?
If this is done incorrectly, the helicopter may be uncontrollable.
What are the two methods of aligning Helicopter Blades?
String and Mirrors Method.
Rifle Scoping.
Describe the String and Mirrors method of aligning Helicopter Blades.
1) Stick a rotor head onto a stand.
2) Attach a sawhorse below the blades and mirror them
3) Support the blades using skates.
4) Place a string between them.
1) Stick a rotor head onto a stand.
2) Attach a sawhorse below the blades and mirror them
3) Support the blades using skates.
4) Place a string between them.
These are the steps to accomplish what task?
Align the blades on a rotor head.
What type of Helicopter must you NEVER place a skate beneath its’ blades?
Bell Medium.
Why wouldn’t you place skates beneath a Bell Medium’s Rotor Blades?
Because it could be incredibly unsafe.
What is Flag Tracking?
Taking a steel frame and placeing it withing the the range of the spinning rotor system.
What is the overall process of reducing vibrations or eliminating vibrations in a rotor system?
(Three general steps)
1) Alignment
2) Static Balancing
3) Dynamic Balancing
When attempting to limit the vibrations of a rotor system, what is the acceptable range?
Anything below 0.1 IPS.
IPS: Inches per Second
What is IPS?
Inches per Second
What is the purpose of a Blade Belt?
To add / subtract weight from the rotor system.
When Autorotating:
What is the force responsible for lifting the rotor as the aircraft descends?
It is driven by the action of the air moving through he blades.
Autorotation:
When the engine fails, relative wind shifts ________ causing lift to shift ________.
1st Blank: Downward
2nd Blank: Upward
When Autorotating what needs to happen when landing?
A final flare.
What is Dead Man’s Curve?
The area of the Height Velocity Chart where very bad things occur.
What kinds of Engines have clutches?
Reciprocating Engines
Fixed Shaft Turbine Engines.
What are two kinds of clutches?
- Belt Tightener
- Centrifugal Clutch
What is Engine De-Rating?
This is when the torque gauge is marked at 100% at less power than the engine can produce.
What are the two types of freewheels?
- Ramp and Roller
- Sprag
Which clutch is the most common?
- Ramp and Roller
- Sprag
Spag are more common.
Give three key aspects of the Sprag Clutch.
1) Have more surface area.
2) Are oil lubricated.
3) Develope less problems.
What are some self lubricated components?
Engine Transmission
Main Gearbox
What does Blade Inertia allow?
Allows the pilot time to set up the aircraft into an autorotation.
Why would the pilot want to utilize Blade Inertia?
It sets up the aircraft for autorotation.
What does Blade Inertia enable?
It is used to stop an aircraft upon landing.
Vortex Ring State / Settling with Power:
What does this mean?
It is a condition of powered flight where the helicopter settles.
What is another name for a state of powered flight where the helicopter settles?
Vortex Ring State or Settling with Power.
What are some ways of avoiding Vortex Ring State / Settling with Power?
(There are three).
1) Descending on flight paths that are shallower than thirty degrees.
2) Sttep approaches should be faster or slower than an area of severe turbulence and thrust ventricles.
3) Lower the collectie (pitch) and increase the aircrafts’ powered air speed.
Of the three ways to avoid Vortex Ring State / Settling with Power, what is needed to accomplish them?
Altitude.
Loss of Tail Rotor Effectiveness:
This can occur through any maneuver which…
(There are three).
1) Requires high power.
2) Within an environment of low airspeed.
3) Any unanticipated right or left yaw occurence.
What is Tail Rotor Vortex Ring State?
It is a version of Weather Cocking.
The left crosswind counters left thrust.
This sets up an unsteady flow over the tail rotor.
(Occurs at high power).
What natural phenomenon can cause Loss of Tail Rotor Effectiveness?
Winds coming at the tail rotor in certain directions.
Loss of Translational Lift is caused by what?
The pilot runs out of pedal.
Loss of Translational Lift:
What happens when the pilot runs out of pedal?
Causes loss of translational lift in the main rotor.
Robs power from the tail rotor.
What are some different kinds of tail rotors?
Fenstrom
Notar
Traditional Design
What is the purpose of the Teetering Hinge?
Used to counter Dissymmetry of Lift.
What are strakes purpose?
The pilot has less need for the tail rotor.
Drive trains are powered by what?
Piston Engines
Jet Engines
What is the main job of the Driveshaft?
Transfers power from the engine to the transmission.
What physical property must possess?
It must be capable of flexing.
Why must the driveshaft be able to flex?
It must accomadate being connected to a fixed and moving system.
K-Flex shafts are flexible but non __________.
They are non-greaseable.
Torque effects what component?
The Tail Boom.
What does the vertical fin do?
Assists the tail rotor in forward flight.
In general, what does the Horizontal Stabilizer do for the aircraft?
Adjusts Aircraft Altitude.
In forward flight, what is the purpose of the Horizontal Stabilizer?
(Three things).
It holds the nose up.
Helps to control the cyclic movement.
Reduces Drag.
How is direction changed on a Tandem Rotor Helicopter?
By tipping each rotor in different directions.
Define Static Stability.
Movement returns to its original position.
Define Static Instability.
Movement occurs and it does not return to its original position.
What are the causes of Dynamic instability?
The rotor disc follows the fuselage.
A change in the aircrafts airspeed causes the rotor to tilt.
What are some ways to stabilize a helicopter?
Add Stabilizer Bars.
Why does adding stabilizer bars help to stabilize a helicopter?
Pilot’s input goes to the stabilizer bars and moves to hydraulic dampeners and the movement then transfers into the blades.
Aside from the obvious, what is the purpose of the stablizer bar?
Controls the speed of input to keep control of the aircraft.
What is the purpose of having friction between the swashplate and the cyclic?
To stabilize the helicopter and controls the speed of input to keep control of the aircraft.
What is mast bump caused by?
It is caused by a negative G maneuver.
Describe mast bump.
The weight of the fuselage unloads causing it to roll. The rotor head then contacts the mast.
Why is mast bump such an infamous phenomenon?
Because it can knock the rotor head right off.
