Aerodynamics Block 15 Flashcards
Which goes up when laminar flow turns into turbulent flow at the boundary layer?
Parasite Drag, particularly Form Drag
What form of drag goes down when vortex generators are put ON?
Form Drag goes down
What is pressure drag? What is another name for pressure drag?
Pressure drag is the difference in leading pressure, and the aft edge.
Pressure drag is known as FORM DRAG
What do wingtip vortices create by definition?
INDUCED DRAG
What are the two types of turbulent flow?
Burbling
Vortex Tubes
Dt is constant/not constant
Not Constant
Pressure Drag/Form Drag may aid in recovery of what?
Pressure/Form drag help recovery in a spin (ex . F-16)
Parasite drag is ________due to _______
Powerplant cooling
Air Conditioning
Leakage through access gaps
Poor construction
Skin Friction Drag AKA _________ is ?
.
High aspect ratio for induced drag changes the airflow
Minimal / Maximum
Therefore
High Aspect ratio = ____________
High aspect ratio for induced drag changes airflow minimally.
Therefore high aspect ratio = low induced drag.
REMEMBER THE SPHERE OF INFLUENCE
Induced Drag is influence mainly by (3)
- Lift
- Altitude
- Speed
When lift is double what happens to drag?
At a flight from 1 to 5 Gs then induced drag is ___?
If everything else is held constant induced drag varies as the _____ of _____
Di=L2
As lift is doubled, induced drag is 4 times as great.
At 1 g changed to 5 g’s induced drag is 25 times as great.
INDUCED DRAG AS SQUARE OF LIFT IF ALL ELSE CONSTANT IS IMPORTANT
What’s interesting about total drag?
ITS NOT CONSTANT
Induced drag In regard to ALTITUDE:
What has to happen to the less dense, thinner air at higher altitudes?
At 39,000 feet air is ___ the density of sea level, requiring ____ times the lift.
Thinner air must be deflected FURTHER to create the same lift.
At 39,000 feet - air is 1/4 the density at sea level, requiring 4 times the lift.
(des not increase Di by 4^2 due to increase in air density.
Induced drag in regard to SPEED -
Di varies ___ as the ____ of _____.
Low airspeeds mean ________
Double the airspeed means?
Cut airspeed in half and what happens?
As average relative wind changes, induced _____ changes and _______ change.
Di varies inversely as the square of airspeed.
Low airspeeds mean high Cl
Double the airspeed means 1/4 of the Di
Airspeed in half = 4 times the Di
As average relative wind changes, induced AOA
changes and lift vectors change.
Induced Drag Speed:
Slow an airplane from 300 - 150, dp is now 1/4 at ____the speed. This forces the airflow to be deflected ____ times greater.
Slow an airplane from 300 - 150, dp is now 1/4 at 1/2 the speed. This forces the airflow to be deflected 4 times greater.
What is a Boundary Layer?
A layer of air over the surface which shows local retardation due to viscosity.
In regards to drag what is viscosity?
Viscosity is resistance to shear.
Turbulent air transfers heat better/worse?
What happens aft of the separation point in turbulent air?
Better.
It helps locate the separation point.
Frost, oil, water are removed faster AFT of the separation point.
Turbulent air holds less _______ energy.
Turbulent air holds less KINETIC energy.
Boundary Layer Sections
What are they and what happens?
Laminar - Fluid particles do not intermingle
Transition - laminar flow is disturbed
Turbulent - cross-streamline flow
During adverse pressure gradient.
Flow does what?
Once reversed what happens?
Adverse pressure gradient _______ -_______ energy.
PRESSURE DRAG is caused by ______
Flow slows to the point of reversing.
Once reversed, boundary layer separates from the surface!
Adverse pressure gradient reduces KINETIC energy
Pressure drag is caused by the separation.
Characteristics of
Laminar
Turbulent
Laminar
- thin flow layer
- low viscous drag
Turbulent
-thick layer flow
Equation for Parasite drag is the same as ____ except instead of ____ it’s _____
Two characteristics of parasite drag
Nearly the same as lift, except instead of Cl it’s Cdp.
Drag
- resistance to flow
- retards forward motion
Types of Parasite Drag (6)
Form Drag / Pressure Drag Skin Friction Drag Profile Drag Interference Drag Cooling Drag Leakage
Parasite drag is any loss of momentum int he air stream due to: (4)
- power plant cooling
- air conditioning
- leakage through access gaps
- poor construction
SKIN FRICTION DRAG
What is it?
Where does it happen?
What’s the fineness ratio.
Viscous drag over the boundary layer.
Happens in the wetted area
Fineness Ratio 3:1
FORM DRAG
What’s another name for it?
How is it caused?
What does it do to the laminar boundary layer?
Turbulent (vortex) boundary layer does what?
Streamlining helps ___ to stay _____.
(_______wake)
Pressure Drag
Caused by pressure difference between forward and aft surfaces.
Laminar boundary layer separates easily
Turbulent vortex boundary layer stays attached.
Streamlining helps flow to stay attached.
(smaller wake)
PROFILE DRAG
What is it?
Combines both skin friction drag and form drag
(surface irregularities)
COOLING DRAG
What is it?
FORM DRAG
LEAKAGE DRAG
What is it?
Leaked air from pressurized airplanes
What is Parasite Drag?
Parasitic drag is drag that results when an object is moved through a fluid medium.
INTERFERENCE DRAG
What is it? What is it caused by ? Where is it worst? What happens as angle increases? Total interference drag is \_\_\_\_\_ than the sum of all individual drags. Reduced by?
Where is it most dangerous?
Where is it more critical and why?
Drag at the intersection of two bodies.
Caused by intersection of boundary layers.
Worst at acute angles
Drag increases as angle increases.
Total interference drag is greater than the sum of all individual drags.
Reduce with fairings.
Close to stall conditions most dangerous.
More critical on the upper portion of wing due to increased flow speeds.
Underside of high wing aircraft not faired for this reason.
Factors affecting total drag
The Object (Size and shape) The Motion (velocity and inclination to the flow) The Air (mass, viscosity, compressibility)
Parasite drag (ALL TYPES OF DRAG EXCEPT?)
All except induced.
Parasite drag _____ with the square of velocity.
Induced drag _____ . with square of velocity
Parasite drag increases
Induced drag decreases
Total Drag Elements:
THE OBJECT
What determines form drag?
What determines induced drag?
What determines skin friction?
Size and shape determine form drag
Lift determines induced drag
Surface roughness determines skin friction.
Total Drag Elements:
THE MOTION
_____ increases as the square of
_____ decreases with the square of velocity
_______ determines the varying shape.
_______ create additional drag known as “_______ “drag
_______________ = Viscous Drag
Dp increases
Di decreases
Inclination determines the varying shape.
SHOCK WAVES create additional drag known as WAVE DRAG
Boundary Layer = Viscous Drag
Total Drag Elements:
THE AIR
Elements of?
The density of air - Thick or Thin
Viscosity or stickiness - humid or dry
Compressibility
Change in Total Drag?
Altitude
Configuration
Weight
