Theory of Flight Flashcards
Provide an example of inertia
(1) Requires more torque to accelerate to 100% RPM than to maintain 100% RPM.
(2) Straight and level flight.
Provide an example of acceleration
(1) Rate of acceleration to 100% RPM from Engine Idle dependent upon amount of force applied through introduction of fuel and oxygen.
(2) Power required to accelerate heavy A/C versus light A/C.
Provide an example of action/reaction
Torque effect. Main rotor turns counterclockwise forcing nose of helicopter to turn clockwise. T/R thrust is used to compensate for this action.
Main rotors left, nose yaws right
Newton’s First Law
First law–inertia. Definition. A body at rest will remain at rest, and a body in motion will remain in motion at the same speed and in the same direction unless acted upon by some external force.
Newton’s Second Law
Second law–acceleration. A change in velocity with respect to time. A=F/M (Acceleration = Force/Mass)
Newton’s Third Law
Third law–action and reaction.
(a) Definition. For every action, there is an equal and opposite reaction.
How is chord measured? What can be determined from this?
The chord is measured from the leading edge to trailing edge of the airfoil. It provides longitudinal dimension and is self contained in the airfoil section
Why is center of pressure important?
the most important part of the air foil because all aerodynamic forces are considered to act
With an increase in speed of air over a surface what happens to dynamic pressure?
Higher dynamic pressure
What happens to static pressure?
With an increase in the speed of air over a surface, there will be a decrease in static pressure; conversely, with a decrease in speed, there will be an increase in static pressure.
What kind of lower camber does a nonsymmetrical airfoil have?
lower straight camber
What are the advantages of a symmetrical airfoil?
constant center of pressure
ease of construction
lower cost
Chord Line
It is an imaginary line which extends through the leading edge of which all angles and winds are measured
Blade Span
physical measurement of one blade from root to tip
Define resultant relative wind.
Rotational relative wind modified by induced flow.
Define angle of incidence.
What control moves it?
The angle between the chord of an airfoil and the plane of rotation (tip path plane.
It is a mechanical angle rather than an aerodynamic angle.
Collective
Which control changes the angle of incidence on all blades simultaneously?
Angle of incidence is changed on all blades simultaneously by collective pitch control.
Define angle of attack.
The angle between the chord of an airfoil and the resultant relative wind. Angle of Attack is an aerodynamic angle.
Can the angle of attack change with no change in angle of incidence?
Yes
How is angle of incidence measured?
from the chord line to the rotational relative wind
How is angle of attack measured?
from the chord line to the resultant relative wind
What is the relationship of lift to resultant relative wind?
Perpendicular to the resultant relative wind.
What is the relationship of drag to resultant relative wind?
Parallel to and in the same direction of the resultant relative wind.
What are the 4 types of drag?
Induced, Profile, Parasite, Total
What is Total Drag?
sum of induced, profile, and parasite
How does the rotor system compensate for dissymmetry of lift?
Flapping
What is another way to compensate for dissymmetry of lift?
cyclic feathering
If the velocity of the relative wind increases, will the airfoil produce more or less lift?
more
Induced Drag
results from producing lift. Decreases with increase in speed
major source of drag at a hover, but decreases with forward airspeed.
Profile Drag
caused by the frictional resistance of the rotor blades passing through the air. “main rotor blades”
remains relatively constant at low airspeed, but increases slightly at higher airspeed ranges.
Parasite Drag
drag created by the fuselage; i.e., strut, skin friction, interference, etc. (any non lifting components).
Everything else on the aircraft except the main rotors.
lowest point at a hover, but increases with airspeed. The major source of drag at higher airspeeds
Dissymmetry of Lift
Differential (unequal) lift between advancing and retreating halves of the rotor disk caused by the different wind flow velocity (directional flight, i.e., forward flight) across each half.
Blades must _____ and _____.
flap, cone
What temperature, pressure, and humidity will produce the most lift?
29.92”Hg, 15 degrees C
Semi-rigid rotor disc tilts in reference to what point on the aircraft?
The Mast
Articulated/rigid rotor disc tilts in reference to what point on the aircraft?
The Hub
What is centrifugal force?
the outward force produced whenever a body moves in a curved path.
Centrifugal force is proportional to
rotational velocity
Rotor blade coning is a compromise between what two forces?
The amount a blade will cone is a compromise between lift and centrifugal force.
Excessive stress forces on the blade could result in what conditions?
Excessive stress forces in the rotor could lead to blade cracking or blade separation from the rotor system.
Loss of disc area results in what effect?
Excessive Coning
Precession occurs what number of degrees after application?
The phenomenon of precession occurs in rotating bodies that manifest an applied force 90° after an application in the direction of rotation.
How is precession overcome?
The effects of precession are overcome by offsetting the linkage in the cyclic pitch control system to create an input 90 ahead of the desired action.
Why is blade twisting necessary?
Blade twisting is necessary to distribute the lifting force more evenly along the blade.
How is the blade twisted along the span of the rotor blade?
(1) Higher pitch angle at the root of
the blade.
(2) Lower pitch angle at the tip of the blade.
What direction does the main rotor turn?
Counter Clockwise
With an increase in power, the nose of the helicopter will turn in what direction?
Greater power being delivered to the rotor system results in a yaw to the right.
Identify the force that causes the fuselage to rotate in the opposite direction of the main rotor rotation?
Newton’s third law of motion states that for every action there is an equal and opposite reaction.
How do you counter torque?
Tail Rotor
In order to make the nose of the aircraft turn left, which pedal do I need to apply?
Left
Does left pedal require more or less power?
More power
What aerodynamic principle causes the aircraft to drift laterally to the right?
Translating Tendency
How is translating tendency overcome?
(1) Rigging of the flight control system
(2) Tilting the mast slightly
(3) Programmed mechanical inputs/automatic flight-control systems/stabilization augmentation systems
(4) Left cyclic input by the pilot
Why is centrifugal force the most dominant?
It provides rigidity
Why is hunting necessary in the articulated/rigid rotor system?
Relieves the stress forces on the blade caused by flapping
How is hunting corrected for in a rigid/articulated system?
articulated - drag dampers
rigid - bending of the rotor blades
What is the vertical component of total force?
lift
What is the horizontal component of total force?
thrust
What are the two conditions of flight?
balanced - opposing forces are equal (Newtons first Law - inertia)
unbalanced - opposing forces are not equal (Newton’s second law - acceleration)
Newton’s Law of Inertia applies to which condition of flight?
Balanced
Why is more power required to hover OGE rather than IGE?
increased induced flow velocity and larger rotor tip vortices
You are in ground effect up to what altitude?
one rotor-disc diameter from the rotor disc to the surface
Effective translational lift occurs at what airspeed?
at approximately 16 – 24 KTS
the rotor completely outruns the recirculation of old vortices and begins to work in relatively undisturbed air
What causes the nose of the helicopter to pitch up and how do you control the pitching up?
Flapping increases with forward airspeed causing the nose to pitch up
Additional forward cyclic pressure (feathering) is necessary at this point
Transverse flow effect is noticeable at what airspeed?
10 to 20 knots
Which portion of the disc creates the most lift?
forward half
What are the two components of the TAF?
Lift and Drag
What does rotation create?
Rotational relative wind
What does hunting provide to the rotor system?
Relieves the stress forces on the blade caused by flapping
total force
single force which is emitted through the center of rotation
Tip Path Plane
or
Plane of rotation
measurement of all the blades from tip to tip
the line across the rotor diameter
how does total force act to the tip path plane?
Total force acts perpendicular to the tip path plane.
What are the two components for total force?
a horizontal force acting as lift and a vertical force acting as thrust
What are the two ways to obtain ETL?
Horizontal flight or hovering in a headwind
FAA test
What is a shutter or vibration felt along the ground roll?
Transverse Flow Effect
Newtons Law
Torque effect
Action and Reaction
Newtons Law
More power is needed to obtain a desired RPM than is need to maintain the RPM
Inertia
Newtons Law
Greater load, less acceleration
Acceleration
If the airflow atop the airfoil increases, static pressure will ______________ and dynamic pressure will
decrease, increase
Define Center of Pressure
the point along the chord line which all aerodynamic forces are considered to act
Define airfoil
A surfaced body or structure designed to produce lift or thrust when subjected to airflow
List two basic types of airfoils.
Symmetrical and Nonsymmetrical
Define rotational relative wind as applied to an airfoil.
The flow of air parallel and opposite to the flight path of an airfoil
Define Induced Flow
Downward flow of air through the rotor blades
Which flight control changes the angle of incidence differentially around the rotor system?
Cyclic Pitch Control
With an increase in the speed of air over a surface, what happens to dynamic and static pressure?
Dynamic pressure increases and static pressure decreases
Which portion of the disc creates the most lift?
The blade tip
What are the simultaneous conditions for settling with power?
A vertical or near vertical descent of at least 300 fpm
the engine must be using 20% to 100% of available engine power
Slow forward airspeed - less than effective transitional lift
What are the corrective actions for settling with power?
Increase airspeed with cyclic
Reduce collective pitch as altitude permits.
During autorotation, no _______________ ___________________ is supplied and the main rotor is driven only by the action of ___________________ _____________.
engine power, relative wind
How does the pilot prevent a rotor RPM over-speed during autorotation with turn?
Collective control
If you observe an overspeed trip, you must raise the collective creating more drag on the rotor system to stop the escaping RPMs
If you observe an under speed trip, you must lower the collective freeing up the blades to stop decaying decaying RPMs.
What conditions must be present for the onset dynamic rollover to occur?
Three conditions are required for dynamic rollover: establish pivot point, initiate rolling motion, and exceeding the critical angle.
Dynamic rollover occurs due to a combination of what two factors?
Physical (helicopter and environment) and human factors (pilot error)
What is the primary factor of a retreating blade stall?
excessive airspeed
What is the recommended action at the onset of dynamic rollover?
On level ground, a smooth moderate collective reduction is recommended if the onset of dynamic rollover is encountered.
What is the recommended action at the onset of a dynamic rollover?
smooth moderate collective reduction
What are the characteristics of stall airflow?
What are the two procedures to recover the aircraft during a retreating blade stall?
Reduce collective pitch.
Regain control of aircraft.
What are the symptoms of retreating blade stall?
Pitch-up of the nose.
Tendency to roll toward the stalled (left) side.
What is settling with power?
Can be described as settling in your own downwash.
What is the cause for most stalls?
exceeding the critical angle of attack
What are the contributing factors to retreating blade stall?
High gross weight High DA High “G” maneuvers Low rotor RPM Turbulence
What are the 4 causes of excessive coning?
Low RPM - less centrifugal force
High gross weight - more lift needed
High “g” maneuvers - more lift needed
Turbulent air
Blade flapping up at the ___ position.
Describe what is happening to induced flow
Induced flow - increasing
AOA - decreasing
less lift produced
What is the most dominant force?
centrifugal force
