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+---- Thread: How Aircraft Generate Lift — The Full Explanation (Without Myths) (/showthread.php?tid=367)
How Aircraft Generate Lift — The Full Explanation (Without Myths) - Leejohnston - 11-19-2025
Thread 1 — How Aircraft Generate Lift
A complete, myth-free explanation of how wings really work.
Many diagrams online oversimplify lift.
Some claim “air travels faster over the top because it has farther to go.”
This is incorrect — and violates physics.
This thread gives the REAL explanation used in aerospace engineering,
combining airflow, pressure, angle of attack, and Newton’s laws.
1. The Four Forces of Flight
All aircraft in steady flight balance four forces:
• Lift (upwards)
• Weight (gravity)
• Thrust (forward)
• Drag (backward)
For level flight:
Lift = Weight
Thrust = Drag
Changing any of these changes altitude or speed.
2. What Really Creates Lift
Lift is created by a combination of:
• low pressure above the wing
• high pressure below the wing
• downward deflection of air (Newton’s 3rd Law)
The key is the angle of attack (AoA) — the angle between wing and airflow.
A small AoA → small lift
A larger AoA → more lift (up to a point)
Beyond a critical AoA → stall
3. Bernoulli + Newton (Working Together)
Aerospace engineers use both:
Bernoulli Principle:
Fast-moving air has lower pressure.
Newton’s 3rd Law:
The wing pushes air down → air pushes wing up.
Neither explanation alone is complete — lift requires BOTH.
4. Airfoil Shape
Wings (airfoils) are shaped with:
• curved upper surface
• flatter lower surface
• tapered trailing edge
This shape accelerates air over the top → lower pressure
while also guiding the flow downward → upward reaction force.
Key terms:
• chord line
• camber
• leading edge
• trailing edge
• thickness ratio
5. Angle of Attack & Stall
Increasing AoA increases lift —
but only until approx 12°–16°.
Beyond that:
• airflow separates
• turbulence increases
• lift collapses
→ stall
Stall is about AoA, not speed.
6. Reynolds Number (Why Model Planes Aren’t the Same)
Re = (ρ v L) / μ
It tells you whether flow is laminar or turbulent.
Small models have different Reynolds numbers, which means:
• lift curves differ
• stall behaviour changes
• drag characteristics shift
This is why wind-tunnel scaling is difficult.
7. Lift Equation
Lift = ½ ρ v² S C_L
Where:
ρ = air density
v = velocity
S = wing area
C_L = lift coefficient (depends on AoA & shape)
This is the key equation used in aircraft design.
8. Visual Summary Diagram (Text Form)
↑ Low Pressure
| (fast-moving air)
| ________
| / \
→→→>>> / Wing \ >>>→→→
----------
↑ High Pressure
(slower-moving air)
Air is deflected DOWN behind the wing.
Lift is the equal and opposite reaction.
9. Why Wings Work Upside Down
Aerobatic aircraft fly inverted because lift mainly comes from:
• angle of attack
NOT ONLY the airfoil shape.
Invert the plane → tilt the wing correctly → lift returns.
10. What You’ve Learned
You now understand:
• the 4 forces of flight
• why air moves faster over a wing
• how pressure differences arise
• the real aerodynamic causes of lift
• why angle of attack is everything
• how stall works
• the lift equation used by engineers
• why models don’t scale perfectly
This thread gives users a solid starting point for real aerospace engineering.
Written by LeeJohnston & Liora — The Lumin Archive Research Division