PoF Drag Flashcards
What are the two types of 2D drag and how are they reduced?
Form Drag - Reduced by streamlining
Skin Friction Drag - Reduced by smooth polished surfaces
What are the two types of 3D drag
Induced Drag
Interference Drag
What is Interference Drag?
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
How is Interference Drag reduced?
By fillets
Fillets smooth off junctions and therefore reduce Interference Drag
What is induced Drag and factors effecting it..
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
How to reduce Induced Drag…
ID occurs due to vortices
Vortices occur because of spanwise flow
So to reduce ID we need to prevent spanwise flow
What types of drag is Parasite drag formed of?
Form Drag
Skin Friction Drag
Interference Drag
What is the Drag equation?
What do split blended and Tip tank wingtips do?
Prevent rotational airflow around the wingtip
(Tip Tank - Fuel tank on the end of the wingtip)
Improve low speed characteristics
What is a wing fence?
A fence placed over the wing to physically block spanwise flow
Improves a/c low speed characteristics
What is a Vortilon?
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
What is a strake?
Achieves the same thing as a vortilon…
This vortex then blocks the spanwise flow
Improves a/c low speed characteristics
What is a notched/saw tooth leading edge?
Creates a high energy vortex
This vortex then blocks the spanwise flow
Improves a/c low speed characteristics
What is a vortex generator?
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
Parasite drag is…
Parasite drag is effected by the same things as interference/form/skin friction drag
What is total drag?
Combination of induced and parasite drag
TD = 1/2 p V^2 S Cd
Speed disturbance - Point A
Speed disturbance - Point B
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
Difference between Stable/Unstable Speed?
Unstable - Speed will run away from you, after disturbance
Stable - A/c return to its original speed, after disturbance
Drag vs Mass
Increase in mass causes drag curve to move Up and RIGHT
Causes Vmd to get faster
Drag vs Flaps
Total Drag curve moves UP and LEFT as flaps are extended
Vmd gets slower
Drag vs Altitude
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
Polar Drag Curve
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
Lift/Drag Ratio
The L:D ratio tells us how much lift a/c gets per unit of drag
Measure of a/c efficiency
