Drag Flashcards
Assuming airspeed remains constant, a higher angle of attack will produce less form drag than a lower angle of attack.
Select one:
True
False
Larger angles of attack will expose more frontal area to the oncoming airflow and move the separation point of the airflow forwards, both resulting in a greater pressure difference, more wake turbulence and greater form drag overall.
The correct answer is ‘False’.
Select all the properties of turbulent flow within the boundary Layer:
Select one or more:
a. Normally the first type of flow within the boundry layer
b. Normally the second type of flow in the boundary layer
c. 2mm thick
d. Particles intermix
e. Uniform increase in velocity
f. Eddies and swirls
g. 2cm thick
h. Particles slide smothely over each other
Particles intermix
Eddies and swirls
2cm thick
Normally the second type of flow in the boundary layer
Fineness Ratio is defined as the ratio between…..
Select one:
a. Chord and Span
b. Chord and Thickness
c. Span and Depth
d. Depth and Thickness
The effectiveness of a streamlined shape is determined by its FINENESS RATIO, the ratio between the length of a body, to its depth, (or thickness).
The correct answer is: Chord and Thickness
elect the correct statement from the options below:
Select one:
a. Skin Friction Drag ∝ IAS
b. Skin Friction Drag ∝ Surface Area²
c. Skin Friction Drag ∝ Surface Area
d. Skin Friction Drag ∝ Surface Area²
Bigger surfaces exposed to the airflow mean more particles are exposed to sheer stress and more skin friction is generated. Double the surface area and you’ll double the skin friction drag. The problem is we need the wings to have surface area in order to produce lift, which restricts the amount we can reduce it.
The correct answer is: Skin Friction Drag ∝ Surface Area
Select from the options below, the conditions that would be needed to produce maximum Induced drag.
Weight
Angle of Attack
Coefficient of Lift
Airspeed
The correct answer is: Weight → High, Angle of Attack → High, Coefficient of Lift → High, Airspeed → Low
Select the correct statement from the options below:
Select one:
a. Interference Drag ∝ IAS²
b. Interference Drag ∝ 1 / IAS²
c. Interference Drag ∝ IAS
d. Interference Drag ∝ IAS³
The other factor that affects interference drag is the same as form and skin friction, airspeed. Interference drag is proportional to the square of the speed.
The correct answer is: Interference Drag ∝ IAS²
Answer the question provided using the options below:
The least coefficent of drag occurs at which angle of attack?
Select one:
a. Around zero degrees
b. At the VMD angle
c. At the stalling angle of 16 degrees
d. At minus 4 degrees
The minimum coefficient of drag occurs around zero degrees. As the angle of attack increases, the coefficient of drag increases, gradually at first, and then more rapidly at higher angles until the stalling angle, where it dramatically increases as the airflow separates from the aerofoils.
The correct answer is: Around zero degrees
Complete the sentence below by filling in the missing word:
Vorticies at the wing tips lead to the production
of ————-behind the wing
Wing tip vortices produce downwash behind the wing
Parasite Drag is greatest at high airspeeds
Select one:
True
False
True
Select the correct statement from the options below:
Select one:
a. Skin Friction Drag ∝ IAS
b. Skin Friction Drag ∝ 1 / IAS
c. Skin Friction Drag ∝ IAS³
d. Skin Friction Drag ∝ IAS²
The correct answer is: Skin Friction Drag ∝ IAS²
Total Drag is least at low airspeeds
Select one:
True
False
Total Drag is least at VMD when the combination of parasite drag and induced drag are least. In the Diamond DA-40 this is at 75 kts.
The correct answer is ‘False’.
Pressure differences along the wing cause —— flow.
spanwise
Total Drag is least at high airspeeds
Select one:
True
False
Total Drag is least at VMD when the combination of parasite drag and induced drag are least. In the Diamond DA-40 this is at 75 kts.
The correct answer is ‘False’.
What is the angle of attack that ensures efficient flight at the highest Lift / Drag Ratio?
The best lift to drag ratio occurs at around 4.0 degrees angle of attack where the aircraft is producing the most lift and the least drag possible.
The correct answer is: 4
Form Drag = Drag due to ______ between forward and rear surfaces. Observed by the separation of airflow, causing wake turbulence
pressure difference
The shear stress between levels of air in boundary layer
→ Skin Friction Drag,
The forces required to separate air particles through the different levels, and move them at different speeds
→ Sheer Stress
Thin zone next to the surface where the effects of viscosity are observed
→ Boundary Layer,
Tendency for molecules of a fluid (gas or liquid) to “stick together” and cling to any solid surface they come into contact with.
→ Viscosity,
Location where flow changes from Laminar to Turbulent
→ Transition point,
What is the FINENESS RATIO that will ensure least form drag occurs on a body moving through the atmosphere?
Your Answer is to be formatted as ___ : ___
Least form drag occurs when the ratio is around 4:1
Viscosity – Tendency for molecules of a _____ (gas or liquid) like substance to “stick together” and cling to any solid surface they come into contact with
fluid
Airflow spills round wing tips causing large rotating wing tip ______
vortices
omplete the definition below by selecting the correct words to fill the gaps:
Interference Drag - Drag due to ___A___ of ____B____ airflows at ____C_____ of surfaces.
Interference Drag = Drag due to mixing of converging airflows at junctions of surfaces (e.g. fuselage/wing junction)
The correct answer is: A → mixing, B → converging, C → junctions
Select the correct statement from the options below:
Select one:
a. Induced Drag ∝ IAS²
b. Induced Drag ∝ 1 / IAS²
c. Induced Drag ∝ IAS
d. Induced Drag ∝ IAS³
While all other forms of drag are directly proportional to the square of the airspeed, induced drag is inversely proportional to the square of the airspeed.
The correct answer is: Induced Drag ∝ 1 / IAS²
Select the conditions that exist as airspeed increases from low to high
Induced Drag is …,
Parasite Drag is … ,
Total Drag is …
→ Reducing
→ Increasing
→ Reducing, and then increasing
design features that will best minimise Skin Friction Drag
Remember we are only looking for design features here.
The main design feature affecting surface condition is the surface’s condition. Laminar flow is very sensitive to surface roughness, and any surface irregularities you can feel with your hand, are enough to have a significant effect. These irregularities disturb laminar flow and encourage an early transition into turbulent flow. More turbulent flow over the wing means more skin friction drag.
To encourage more laminar flow over the surfaces, forward sections of most aircraft components are constructed and conditioned to have a smooth polished surface. In addition, rivets are flushed with the surface and leading edges are hardened, all to minimize irregularities from components and dents from long term damage.
The correct answer is: Smooth Polished Surface Condition
conditions that exist at HIGH aircraft speeds.
Induced Drag is …
Parasite Drag is …
Total Drag is …
→ Low,
→ High,
→ High
Downwash behind the wing causes the overall airflow to be modified in a_____ direction.
Overall airflow around aerofoil is modified downwards by the downwash
The correct answer is: down
airspeed Reduces from high to low
Induced Drag is …
Parasite Drag is …
Total Drag is …
→ Increasing,
→ Reducing,
→ Reducing, and then increasing
conditions that enable an aircraft to fly at the best Lift/Drag Ratio.
Airspeed is at VMD,
Angle of attack is at four degrees
Because form drag is proportional to the square of the airspeed, flying at a low airspeed will ensure minimal form drag occurs.
Select one:
True
False
Remember form drag is due to dynamic pressure acting on the aircraft and so the form drag increases with the square of the airspeed. Double the speed, quadruple the form drag. Out of the two factors, angle of attack and airspeed, its airspeed that has the greatest influence, hence high airspeeds will produce the most form drag.
The correct answer is ‘True’.
properties of Laminar flow within the boundary Layer:
Particles slide smoothly over each other
Uniform increase in velocity
Only 2 mm thick.
Normally the first type of flow within the boundary Laye
What is the main design method used to minimise FORM DRAG?
Remember, this force is a result of the PRESSURE DIFFERENCES between the front and the back. If we can help the airflow move around the object without creating large pressure differences, form drag will be minimal. We can do this by streamlining.
The correct answer is: Streamlining
Unaffected airflow that is not slowed down by viscosity is called the _____ airflow.
freestream
Induced Drag is from the rearward component of
____ due to it being tilted backwards by downwash.
lift
Overall airflow around aerofoil is modified downwards by the downwash
Modified airflow means lift force is tilted backwards
design features that will best minimise Interference Drag:
Remember we are only looking for design features here.
To minimize interference drag, we must blend the junction between to the two components so the airflow treats them as one continuous surface. This encourages airflows to blend together with minimal interference, which reduces eddies and so reduces interference drag. Other methods include filleting of components, and fairings like these wheel fairings shown. A fairing is a part of the skin that helps to blend airflows.
The correct answers are: Blending components together, Wheel fairings
MOST coefficent of drag occurs at which angle of attack?
Above the stalling angle
design features that will minimise Induced Drag:
High Aspect Ratio
Eliptical Wing
Modified Wing Tip
Wing Taper
conditions that exist at LOW aircraft speeds.
Induced Drag is …
Parasite Drag is …
Total Drag is …
→ High,
→ Low,
→ High
Induced Drag is greatest at high airspeeds
Induced Drag is greatest at LOW airspeeds
The correct answer is ‘False’.
Vorticies at the wing tips lead to the production of______behind the wing.
downwash
When designing a body to move through the air, how far back should the point of maximum thickness be set to ensure minimum FORM DRAG?
Minimum form drag occurs when the body is designed with the point of maximum thickness around one third of the way back.
The correct answer is: 1/3 the way back
DESIGN FEATURES to minimise FORM DRAG.
Remember we are only looking for design features in this question. These include:
- Streamlining will help airflow pass around the body
- Retracting undercarriage and flaps will reduce pressure differences on the body as a whole
- Fitting wheel fairings will help airflow pass around the wheels which will streamline the undercarriage.
The correct answers are: Retract Gear, Retract Flaps, Install Wheel Fairings to streamline the gear, Streamline the shape of the aircraft
Induced Drag is from the rearward component of ____
due to it being tilted backwards by downwash.
Overall airflow around aerofoil is modified downwards by the downwash
Modified airflow means lift force is tilted backwards
The correct answer is: lift
least coefficent of drag occurs at which angle of attack?
Around zero degrees
Induced Drag ∝ 1 / IAS²
true
Parasite Drag is greatest at high airspeeds
TRUE
Downwash behind the wing causes the overall airflow to be modified in a ______ direction.
Overall airflow around aerofoil is modified downwards by the downwash
The correct answer is: down
Induced Drag is greatest at high airspeeds
Select one:
True
False
Induced Drag is greatest at LOW airspeeds
The correct answer is ‘False’.
What is the angle of attack that ensures minimum coefficient of drag?
At CD min which is around 0.0 degrees angle of attack, the coefficient of drag is a minimum.
The correct answer is: 0
