PoF Drag

Question 1

What are the two types of 2D drag and how are they reduced?

Answer 1

Form Drag - Reduced by streamlining

Skin Friction Drag - Reduced by smooth polished surfaces

Question 2

What are the two types of 3D drag

Answer 2

Induced Drag

Interference Drag

Question 3

What is Interference Drag?

Answer 3

At junctions between different a/c surfaces, airflows travelling in different directions meet and form vortices

At sharper angles, the vortex will be stronger and cause more drag

Question 4

How is Interference Drag reduced?

Answer 4

By fillets

Fillets smooth off junctions and therefore reduce Interference Drag

Question 5

What is induced Drag and factors effecting it..

Answer 5

The by-product of lift

Factors effecting:
~Anything that makes the wing work harder
~Low speeds
~Banking
~Pitching up
~Load factor increase
~A/c weight

Question 6

How to reduce Induced Drag…

Answer 6

ID occurs due to vortices

Vortices occur because of spanwise flow

So to reduce ID we need to prevent spanwise flow

Question 7

What types of drag is Parasite drag formed of?

Answer 7

Form Drag

Skin Friction Drag

Interference Drag

Question 8

What is the Drag equation?

Answer 8

Question 9

Answer 9

Question 10

What do split blended and Tip tank wingtips do?

Answer 10

Prevent rotational airflow around the wingtip

(Tip Tank - Fuel tank on the end of the wingtip)

Improve low speed characteristics

Question 11

What is a wing fence?

Answer 11

A fence placed over the wing to physically block spanwise flow

Improves a/c low speed characteristics

Question 12

What is a Vortilon?

Answer 12

Tin strips added to the leading edge, it creates a high energy vortex back over the wing

This vortex then blocks the spanwise flow

Improves a/c low speed characteristics

Question 13

What is a strake?

Answer 13

Achieves the same thing as a vortilon…

This vortex then blocks the spanwise flow

Improves a/c low speed characteristics

Question 14

What is a notched/saw tooth leading edge?

Answer 14

Creates a high energy vortex

This vortex then blocks the spanwise flow

Improves a/c low speed characteristics

Question 15

What is a vortex generator?

Answer 15

Draw in air from the free stream airflow into the boundary layer (Re energises the boundary layer, delaying separation)

Delays slow speed stall

Helps maintain control effectiveness during high speed stall

DOES NOT REDUCE INDUCED DRAG

Question 16

Parasite drag is…

Answer 16

Parasite drag is effected by the same things as interference/form/skin friction drag

Question 17

What is total drag?

Answer 17

Combination of induced and parasite drag

TD = 1/2 p V^2 S Cd

Question 18

Speed disturbance - Point A

Speed disturbance - Point B

Answer 18

Gust of wind slows a/c down
~ Thrust is bigger than drag
~T>D
~A/c will speed back up to original speed

Gust of wind slows a/c down
~Increased drag
~T<D
~A/c slows and continues to slow until stall

Question 19

Difference between Stable/Unstable Speed?

Answer 19

Unstable - Speed will run away from you, after disturbance

Stable - A/c return to its original speed, after disturbance

Question 20

Drag vs Mass

Answer 20

Increase in mass causes drag curve to move Up and RIGHT

Causes Vmd to get faster

Question 21

Drag vs Flaps

Answer 21

Total Drag curve moves UP and LEFT as flaps are extended

Vmd gets slower

Question 22

Drag vs Altitude

Answer 22

Drag and IAS are based on the same thing, hence, as an IAS, drag is the same at all alt

As a TAS, total drag curve moves RIGHT as alt incrases

Question 23

Polar Drag Curve

Answer 23

A = Vy(JET), 1.32Vmd

B = Vmd, CL/CD x MAX, L/D MAX (Max glide range, Vx (JET)

C = Amp, Minimum Sink Rate, Max glide endurance

D = CL MAX, Vs

Question 24

Lift/Drag Ratio

Answer 24

The L:D ratio tells us how much lift a/c gets per unit of drag

Measure of a/c efficiency