Chapter 13: Stall

Question 1

Stall Reason (2)

Answer 1

Excessive AoA

Adverse pressure gradient

Question 2

Largest 3D Stall AoA: glider, fighter, commercial?

Why

Answer 2

1. Fighter bc. low aspect ratio -> high downwash -> higher induced AoA and lower effective AoA -> retards stall.
2. Commercial
3. Glider

Question 3

Tapered / Swept Wings Stall Characteristics (4)

Answer 3

No natural buffet (tip stalls first)
Wing drop (tip stalls first)
Cp moves forward (longitudinal instability)
Downwash on horizontal stabilizers (Cp moves inwards)

Question 4

Reducing Tip Stalling (6)

Answer 4

Vortillon
Wing fence (reduce spanwise flow)
Saw tooth (LE, restrict spanwise flow)
Washout
Reduce camber
Sharp LE (stall first)

Question 5

Aileron Manoeuver Near Stall

Answer 5

Aileron increases local AoA -> stall wing tip
Instead of lifting wing, wing falls
= low speed aileron reversal

Question 6

Stall, what affects it (9)

Answer 6

Mass
Landing Gear
Powered stall
Thrust on wing
CG position
Sweepback
Compressibility
Load Factor
Contaminant

Question 7

Effect on Vs
Powered stall
Thrust on Wings

Answer 7

Thurst increases lift -> Vs decreases

Thurst energises airflow -> Vs decreases

Question 8

Effect on Vs
Landing Gear
CG Forward
Mass Increase

Answer 8

LG Pitch down tendency -> more elevator downforce -> more lift -> Vs increases
CG forward -> more elevator downforce -> more lift -> Vs increases
Mass -> More lift -> Vs increases

Question 9

Effect on Vs
Straight vs Sweeback Wing
Compressibility

Answer 9

Sweepback: lower Cl max, lower AoA stall, stall region not abrupt -> Vs increases
Compressibility: TAS > 300 kn
air loses energy, Vs increases

Question 10

Effects on Vs
Load Factor
Contaminant Types (3) and Effects

Answer 10

LF increases -> Vs increases Vs = Vs1g * sqrt(LF)
Contaminants = ice, snow, water
increase mass, degrade wing performance -> Vs increases