An aerofoil is a cross-sectional shape designed to produce lift. The textbook model relates faster airflow above the wing to lower pressure and slower airflow below it to higher pressure.
Learning Outcomes
An aerofoil produces lift perpendicular to airflow.
Pressure above the wing is lower than below it.
Lift equals pressure difference multiplied by wing area.
Bernoulli relates pressure difference to the two air speeds.
Intermediate Level
How Lift Develops
The curved wing shape produces different airflow speeds. Faster upper airflow gives lower pressure; slower lower airflow gives higher pressure. Their pressure difference produces net upward force.
Key equation
FL=(Pbelow-Pabove)A
Using Bernoulli at Equal Height
Key equation
Pbelow-Pabove=12ρ(vabove2-vbelow2)
Key equation
FL=12ρ A(vabove2-vbelow2)
Textbook Lift Assignment
Air speeds above and below a 15 m × 3 m wing are 450 m s⁻¹ and 410 m s⁻¹. Use ρ = 1.29 kg m⁻³.
1
Working
A = 15 × 3 = 45 m²
2
Step 2
ΔP = ½ρ(450² − 410²)
3
Step 3
ΔP = 22,188 Pa
4
Step 4
F = ΔP A
Final answer:F ≈ 9.98 × 10⁵ N upward
Balanced Explanation
Real aircraft lift also involves airflow deflection, angle of attack and circulation. For the FBISE textbook answer, clearly present the stated Bernoulli pressure-difference model.
Common Mistakes
Do not reverse the high-speed and low-pressure regions.
State the ideal-flow conditions before using Bernoulli reasoning.
Use consistent SI units in calculations.
Short-Question Preparation
Q. Define an aerofoil.
A. A cross-sectional shape that produces lift while moving through a fluid.
Q. Why is lift upward?
A. Pressure below the wing exceeds pressure above it, producing a net upward force.
Q. Write the lift formula.
A.FL = ΔP A.
Sticky Notes
An aerofoil produces lift perpendicular to airflow.
Pressure above the wing is lower than below it.
Lift equals pressure difference multiplied by wing area.
Bernoulli relates pressure difference to the two air speeds.
60-Second Revision
An aerofoil is a cross-sectional shape designed to produce lift. The textbook model relates faster airflow above the wing to lower pressure and slower airflow below it to higher pressure.
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Exam preparation
Exam Focus
Important points
An aerofoil produces lift perpendicular to airflow.
Pressure above the wing is lower than below it.
Lift equals pressure difference multiplied by wing area.
Bernoulli relates pressure difference to the two air speeds.
Common mistakes
Check speed, pressure and height carefully.
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.
Aerofoil and Lift
Sticky Notes · Quick Revision
1.
Key Point 1
An aerofoil produces lift perpendicular to airflow.
2.
Key Point 2
Pressure above the wing is lower than below it.
3.
Key Point 3
Lift equals pressure difference multiplied by wing area.
4.
Key Point 4
Bernoulli relates pressure difference to the two air speeds.
