Whole aircraft drag

Question 1

What is induced drag

Answer 1

Caused by vortices which occur whenever lift is produced.

Question 2

What is total drag

Answer 2

Total drag is the sum of all drag
Subdivided into Induced drag(lift)
and parasite drag which occurs regardless of lift.

Question 3

What is interference drag

Answer 3

Aircraft surface presented at differing angles to relative airflow. Direction of flow differs over theses components. Where these meet different flow velocities meet and local airflow loses energy.

Question 4

What can form by interference drag

Answer 4

Some junctions boundary layer gets thicker and slows causing separation while at others vortices can for due to high energy air flows meeting at an angle.

Question 5

What factors affect form drag.

Answer 5

Greater the airspeed greater the form drag. Pressure on front surfaces greater than rear surfaces resulting in greater net force acting backwards on the object.

Question 6

What affects form drag

Answer 6

Kinetic energy of boundary layer.

Amount of streamlining aft of point of thickness.

Question 7

What are the influencing factors on skin friction drag

Answer 7

Speed-high shear forces leading to greater skin friction drag.
Surface area- larger surface area means S more skin friction drag.
Boundary layer-turbulent boundary layer more skin friction drag
Surface roughness-turbulent boundary layer.

Question 8

Does parasite drag change

Answer 8

Once design of plane is complete many elements of parasite drag become fixed.

Question 9

Relationship between speed and parasite drag

Answer 9

Parasite drag increases as the square of speed. Eg is speed doubles parasite drag increase fourfold

Question 10

Influence of flaps on parasite drag

Answer 10

Increasing frontal are increases parasite drag. When flaps or landing gear is deployed parasite drag curve becomes steeper

Question 11

Parasite drag Equation

Answer 11

0.5x rho xV2 x S xCdp
Parasite drag is proportional to air speed squared
Aircrafts surface area
Coefficient of parasite drag.

Question 12

What is the coefficient of parasite drag determined by

Answer 12

Aircrafts shape and amount of streamlining.
Surface roughness.
Presence and effectiveness of fillets.

Question 13

What influences induced drag

Answer 13

Vortices and downwash are primary cause of induced drag.

Anything that affects intensity of vortices affects amount of drag.

Question 14

Relationship between speed and induced drag

Answer 14

Induced drag is inverse to speed squared.

Question 15

Relationship between airspeed and weight

Answer 15

Heavier aircraft requires more lift to counterbalance weight force.

Question 16

Relationship between planform and induced drag

Answer 16

A wing planform that produces more lift at tips generates more drag

Question 17

Relationship between manoeuvring and induced drag

Answer 17

Aircraft manoeuvres by generating more lift force to overcome weight force.. induced drag increases during manoeuvres.

Question 18

Is induced drag proportional or inversely proportional to aspect ratio

Answer 18

Inverse Induced drag=1/aspect ratio.

Question 19

What is the coefficient of drag and what are its relationships

Answer 19

Cdi is a measure of the downwash or induced AOA.

Cdi is inversely proportional to aspect ratio and directly proportional to lift squared.

Question 20

Equation of induced drag

Answer 20

0.5x rho x v2 xS xCdi

Question 21

How can induced drag be reduced

Answer 21

Reduced length of tip chord by using high aspect ratio.
Physically restrict movement of air around wing tip i.e winglets
Decrease camber or angle of incidence close to tip.