Finals-Module 6- Drag Measurement Flashcards
The four (4) forces of flight
Weight, Lift, Thrust, Drag
An airplane like all bodies have
mass, with the aircraft positioned in the
ground, it has only the force of the acceleration due to gravity. This force, called ____________ acts vertically
downwards at all times.
weight
Before an airplane can leave the
ground and fly the force “weight: must be
surpassed or balanced by a force which
acts upwards called __________
lift
To generate lift, the airplane must
be propelled forward through air by a force
called _________. Provided by its ________
thrust
engine
From the very moment the airplane
moves forward, the air pushing against the aircraft relatively resists the motion, and is
called ______
drag
the force that resists the forward motion of an object
moving through a medium.
drag
It acts parallel to and in the opposite direction of the aircraft.
drag
As an aircraft moves/travel through air, every part of it that is exposed to the airflow produces a different type of resistance to the forward motion which constitute to the __________
Total Drag.
Total Drag is sub-divided into two (2 )main types. These two main types are:
Parasite drag
Induced Drag
type of drag is comprised of all the forces that work to
slow an aircraft’s movement
Parasite
the drag that is not
associated with the production of lift
Parasite Drag
As the term parasitic implies, it is the drag that is not
associated with the production of lift. This includes the
1.the displacement of the air by the
aircraft
2.turbulence generated in the airstream,
3. a hindrance of air moving over the
surface of the aircraft and
It is an inevitable
consequence of lift and is produced by the passage
of an airfoil through the air.
Induced drag
Induced drag proves that
there is no system that does work in a mechanical
sense can be ________ efficient
100%
the induced drag is inherent in the production of lift, as whenever an airfoil is producing one, the pressure on the lower surface is ___________ than that on the upper surface.
greater
This difference in level of pressure results in air tending to flow from the high pressure area below the tip upward to the low pressure area on the upper surface, creating ____________
wing tip vortices
3 Types of Parasite Drag
Skin Friction Drag
Form Drag
Interference Drag
It is the aerodynamic
resistance due to the contact of moving air with the surface of an object, and in this particular
case that object would be an aircraft
Skin Friction Drag
As distance from the surface _________, less and less acceleration of the layers takes place
increases
This layer of air extending from the surface (in direct contact) to the point where no viscous effect is noticeable is known as the ___________
Boundary layer
At the top of the boundary layer, the molecules ___________velocity and move at the _____________ as the molecules outside the boundary layer
increase
same speed
The actual speed at which the
molecules move depends upon the:
- shape of the wing,
- the viscosity (stickiness) of the air through which the wing or airfoil is moving,
- its compressibility (how much it can be
compacted)
The boundary can exist in two forms
laminar and turbulent
The ___________rate of change in velocity at the surface in the turbulent flow, then gives more skin friction than the laminar flow
increased
____________movement of the transition point will give rise to an increase in skin friction, as this gives a _______ area of turbulent
Forward
Greater
The position of the transition point is dependent upon a number of factors. Some of the factors are:
Surface Condition and Adverse Pressure Gradient
The thin laminar layer is extremely sensitive to surface irregularities. Any roughness on the skin of a leading portion of an aircraft will cause transition to __________ at that point and the thickening, turbulent boundary layer will spread out ____________causing a marked increase in skin friction drag
turbulence
fanwise down-stream
A laminar layer cannot exist when _______________
pressure is rising in the
direction of the flow.
On a curved surface, such as an airfoil, the transition point is
usually at, or near ____________
to the point of maximum thickness.
the adverse pressure gradient existing on a curved surface the transition point will be _______________ than if the surface was flat.
further forward
generated by the aircraft due to its
shape and the airflow around it.
Form Drag
When the air has to separate to move around a moving aircraft and its components, it eventually rejoins after passing the body. How quickly and smoothly it rejoins is representative of the resistance it creates, which creates additional force to overcome.
Form Drag
Easiest type of drag to reduce when designing an aircraft.
Form Drag
Solution for Form Drag
Streamlining
Each part of an aircraft (exposed) will
be subject to form drag. To reduce form
drag, it is necessary to _______________________
delay the separation as close to the trailing edge as possible.
It increases the ratio between the
length and depth of the body, reducing the curvature of the surfaces and thus the adverse pressure gradient
Streamlining
it is the measurement of streamlining
fitness ratio
What is fitness ratio
ratio of length to depth of an airfoil
the combination of skin friction and form drag.
Profile drag
It can be considered that
these drags result from the “profile” of the aircraft presented to the relative airflow
Profile drag
When considering a complete aircraft, parasite drag will always be __________ than the sum of its parts that is because of the additional drag resulting from the boundary layer created at the ____________
greater
junctions of the aircraft
The most interference drag is observed when two surfaces meet at ______________angles.
perpendicular
_____________ are used to reduce interference drag
Fairings
Parasite Drag Formula
Dp= (1/2)(density)(Velocity)^2(Area)(Parasite Drag Coeffiecient)
Factors Affecting Parasite Drag
- Indicated Air Speed
- Configuration
- Airframe Contamination
Parasite drag varies with the ____________ of the Indicated Air Speed
(IAS).
square
If the Indicated Air Speed is doubled the parasite drag will be__________ greater, however if it is halved, the value of parasite drag will be __________
of its previous value.
four times
one quarter
Parasite drag varies _____________________ to the frontal area presented to the airflow, also known as the ____________
directly in proportion
Parasite Area
Contamination by ice, frost, snow, mud or slush will increase the __________, and in the case of severe airframe icing, the area
parasite drag coefficient
Methods in reducing contamination is by ______________ on these prone areas.
employing de-icing and anti-icing devices
_________ is an inherent component, a rather undesirable by-product of
lift.
Induced drag
They modify upwash and downwash in the vicinity of the wing which produces a rearward component to the lift vector known as the “induced drag”
Wing Tip Vortices
Wing tip vortices modify _________ and _________in the vicinity of the wing which produces a __________component to the lift vector known as the ___________
upwash
downwash
rearward
Induced drag
When an airfoil is flown at a positive AOA, a pressure differential
exists between __________________________________________________________________
the upper and lower surfaces of the airfoil.
The pressure above the wing is
less than ___________ and the pressure below the wing is equal to or greater than __________
atmospheric pressure
The pressure above the wing is
___________ atmospheric pressure and the pressure below the wing is _____________atmospheric pressure
less than
equal to or greater than
Movement of air relative to pressure
air always moves from high pressure toward low pressure
Since air always moves from high pressure toward low pressure, and
the path of least resistance is toward the airfoil’s tips, there is a __________ of air from the __________ from____________
spanwise movement
bottom of the airfoil outward
the fuselage around the tips.
This flow of air results in “spillage” over the tips, thereby setting up a whirlpool of air called a ____________.
vortex
Wing tip vortices create certain __________ velocity components in the
airflow in the vicinity of the wing, both in front of and behind it
vertical
These vertical velocities created by wing tip vortices strengthen ________________________________ which reduces the_______________
upwash and downwash
effective angle of attack
Relationship of Vortices and Effecitve angle of attack
The stronger the vortices, the greater the reduction in the effective angle.
Relationship of Effective angle of attack and overall lift if there no was spanwise pressure differential
Due to the localised reduction in effective angle of attack, the overall lift generated by a
wing will be below the value that would be generated if there were no spanwise pressure
differential
To replace the lift lost by the
increased upwash and downwash the
wing must be flown at a ____________
higher angle of attack,
To replace the lift lost by the
increased upwash and downwash the
wing must be flown at a higher angle of
attack, than would otherwise be
necessary. This increases drag. This
extra drag is called ___________
induced drag
Relationship of IAS, AOA ,vortices, and induce drag
The lower the Indicated Air Speed
(IAS), the higher the Angle of Attack (α
- the stronger the vortices- the greater the induced drag
Factors that affect induced Drag
- Size of the lift force
- Speed of the aircraft
- Aspect Ratio of the wing
Relationship of lift and induced drag
the greater the lift, the greater will be the induced drag
Relationship of induced drag and weight of an aircraft.
Induced drag will be greater at
higher aircraft weights
Relationship of lift to weight ratio
load factor
Why does induced drag increase during a steady turn compared to straight and level flight?
Induced drag increases during a steady turn because the lift generated by the aircraft must be greater than its weight
Relationship of load factor and induced drag
induced drag also increases as the load factor increases
Relationship of induced drag coefficient and lift coeffiecient
the induced drag increases as the square of the lift coefficient.
Relationship of induced drag and speed of an aircraft
Induced drag decreases with increasing speed.
Why does induced drag decrease with increasing speed?
Induced drag decreases with increasing speed because the downwash from the tip vortices becomes less significant, reducing the rearward inclination of the lift and thereby lowering induced drag.
Relationship of speed and dynamic pressure
As speed increases, dynamic pressure increases with the square of the speed.
Relationship of Aspect Ratio and Induced Drag.
Induced drag therefore decreases as aspect ratio increases
(for a given lift force)
How does increasing the aspect ratio affect the wing angle of attack needed to produce a given lift coefficient?
Increasing the aspect ratio decreases the wing angle of attack needed to produce a given lift coefficient.
How do higher aspect ratio wings affect the sensitivity to changes in angle of attack and the angle required to reach maximum lift?
Higher aspect ratio wings are more sensitive to changes in angle of attack, but they require a smaller angle of attack to reach maximum lift compared to lower aspect ratio wings.
What happens to induced drag at high lift coefficients (low indicated airspeed)?
At high lift coefficients (low indicated airspeed), induced drag becomes very high and increases rapidly as the lift coefficient increases.
Factors to consider if one decides to continue the increase of Aspect
Ratio
- Excessive wing bending
- reduced roll of rate
- reduced Ground Clearance in roll during take-off and landing
How can excessive wing bending moments be reduced?
Excessive wing bending moments can be reduced by carrying fuel in the wings and mounting the engines in pods beneath the wing
What causes a reduced rate of roll in an aircraft?
A reduced rate of roll is caused by the down-going wing experiencing an increased effective angle of attack
Methods of Reducing Induced Drag
- Wing end-plates
- Tip tanks
- winglets
- Wing tip shape
What effect do wing end-plates have on aircraft performance?
Wing end-plates restrict tip vortices, similar to increasing aspect ratio, without adding extra bending loads.
However, they generate parasite drag, and at higher speeds, the overall drag reduction may not be significant.
How do tip tanks affect induced drag and wing bending moments?
Tip tanks reduce induced drag by limiting tip vortices, similar to wing end-plates, and also help reduce wing bending moments.
How do winglets reduce induced drag?
Winglets reduce induced drag by blocking the airflow from the bottom to the top surface of the wing, weakening the tip vortex. Additionally, the vortex generated by the winglets interacts with and further weakens the main wingtip vortex.
designs of wing tip
turned down and turned up
How does wing tip shape affect induced drag?
The shape of the wing tip affects the strength of the tip vortices
The __________ of an aircraft in flight is the sum of its induced drag and parasite drag
total drag
The _______________ is a number that aerodynamicists use to model all of the complex dependencies of shape, inclination, and flow conditions on aircraft drag.
drag coefficient
The total drag coefficient Cd is equal to the _____________ plus the _________________
drag coefficient at zero lift
induced drag coefficient
Factors that affect the type of flow in the Boundary Layer:
- Flow Quality
- Shape
- Texture
- Pressure Gradient
- Reynolds Number
- Heating of the fluid
