Quick questions on Bernoulli's principle and aerofoils: HSC Engineering Studies Aeronautical Engineering

For a streamline of an incompressible, inviscid, steady flow, the total pressure is constant:

An aerofoil has an asymmetric or angled cross-section. As air flows around it:

$$L = \frac{1}{2} \rho v^2 S C_L$$

Aircraft adjust angle of attack to keep $C_L$ matched to the required lift at the current airspeed and density.

Air density falls with altitude (approximately 1.225 kg/m^3 at sea level, 0.74 kg/m^3 at 5000 m, 0.41 kg/m^3 at 10{,}000 m). For the same lift, an aircraft at altitude must fly faster (true airspeed). The pilot reads indicated airspeed, which already accounts for density via the pitot static system; indicated airspeed is roughly constant for a given $C_L$ regardless of altitude.

The Royal Australian Air Force PC-21 trainer aircraft and the F/A-18F Super Hornet use modern aerofoils with leading-edge devices and trailing-edge flaps to vary $C_L$ across the flight envelope. Civil airliners (Boeing 737, Airbus A320) use supercritical aerofoils that delay shock formation at high subsonic Mach numbers, raising the practical cruise speed.

Lift scales with $v^2$. Halving speed cuts lift by a factor of four.

True airspeed is the physical air speed; indicated airspeed corresponds to dynamic pressure and depends on density. The lift equation uses true airspeed unless density is already factored into the indicated airspeed in the question.

Stall is an aerodynamic phenomenon (flow separation), not a structural one. The wing can fly faster than stall speed even at higher angles of attack as long as flow remains attached. :::