Lift Augmentation

Question 1

What are the positives of lift augmentation devices

Answer 1

Slower flying speeds / greater weights for takeoff and landing

Reduce AOA near minimum flying speed

Increase drag on approach

Question 2

How does a training edge flap affect cl

Answer 2

Cl max increases
Due to increases camber

Stalling AOA decreases due to change in chord line

Question 3

Why does the stalling AOA decrease with training edge flap

Answer 3

Centre of pressure moves aft

Pressure gradient doesn’t have to travel as far to create same lift loss from separation

Question 4

How does training edge flaps affect wing tip vortices

Answer 4

Vortices reduce as larger proportion of lift is created at root

Question 5

What are the characteristics of a split flap

Answer 5

High drag

Allows a higher AOA

Higher cl

Requires high power setting due to drag

Question 6

What do Leading edge flaps do

Answer 6

Increase the leading edge radius encourages flow to stay attached for longer

Question 7

What is a Kruger flap and how does it help

Answer 7

Like a leading edge flap except it folds outward from the underside of the wing

Creates sharp leading edge which encourages the root to stall before the tips

Question 8

What is a droop nose

Answer 8

Like a leading edge flap except the entire leading edge drops

Question 9

What is a fowler flap and how does it help

Answer 9

Increases surface area

Increases cl due to camber change

Slides out of wing (extends out) before extending downwards

Question 10

What does a slat or slot do

Answer 10

It’s a gap between leading edge and wing
Re energises the air meaning it is less likely to separate from the wing

Also appears in fowler flaps

Question 11

How does leading edge slat affect the stalling AOA

Answer 11

Allow you to reach a much higher stalling AOA

Question 12

What happens to cl/cd when flaps are used

Answer 12

Lift to drag ratio reduces

Question 13

What effects does flaps have on the horizontal stabiliser

Answer 13

Flaps create increased downwash = initially pitch up

However drag will take over soon and return to pitch down

Question 14

What are vortex generators used for

Answer 14

Re energise air

Which creates a vortices

Which creates physical barrier to reduce spanwise flow

Question 15

How much increase in cl do you get for the first 50% of flap

Answer 15

Usually increases by over 50% of the total lift increase

Question 16

For the second 50 % of flap how much does drag usually increase by

Answer 16

Over 50% of the total drag increase