Forces in Level Flight

Question 1

Through where does Lift act?

Answer 1

Centre of pressure

Question 2

Through where does weight act?

Answer 2

Centre of gravity

Question 3

Through where does wing drag act?

Answer 3

Through CP

Question 4

However, where does total drag act? Like the fuselage and tail?

Answer 4

It may act along a different line

Question 5

Around where does the aircraft move in pitch, roll or yaw?

Answer 5

Around its CG

Question 6

Where does the couple Lift/Weight make the aircraft pitch?

Answer 6

Nose down

Question 7

Where does the couple Thrust/Drag make the aircraft pitch?

Answer 7

Nose up

Question 8

How is trim drag created? What are the implications of having trim drag?

Answer 8

When CP is aft of CG → Tail creates a down force to oppose the wing’s nose down pitching moment as the couple Thrust/Drag is not large enough do this on its own → TRIM DRAG → ↑lift to balance that down force → ↑ fuel consumption

Question 9

How can you reduce trim drag?

Answer 9

• Longer fuselage → ↑moment arm → smaller forces need to be generated
  o This also produces ↑weight and ↑drag
  o Fuselage less stiff → bengin under the tail loads
• Variable incidence tails and slab tails → give the least trim drag