Aviation cheat sheet

Four forces

Lift and weight act in opposing vertical directions in a simple level-flight model; thrust and drag act along the direction of travel.

Steady level flight requires balanced forces, not zero forces.

Angle of attack

Angle of attack is the angle between an aerofoil’s chord line and the relative airflow. It is different from the aircraft’s pitch attitude.

Changing airflow direction can change angle of attack without the same change in pitch.

Lift model

A common aerodynamic model writes lift as L = ½ρv²SCL. Density, speed, wing area and lift coefficient all matter.

At unchanged ρ, S and CL, doubling speed multiplies modelled lift by four.

Pressure and altitude

Atmospheric pressure generally decreases with altitude. Indicated altitude depends on a pressure reference and instrument interpretation.

Distinguish geometric height from a pressure-derived indication.

Attitude and flight path

Pitch attitude describes orientation relative to the horizon; angle of attack describes the angle between a reference chord and relative airflow. They are different angles.

A diagram should show the horizon, wing reference and airflow separately.

Density and aerodynamic force

In a simplified aerodynamic model, force depends on dynamic pressure, reference area and a coefficient. The coefficient also changes with the flow and shape.

Dynamic pressure q = ½ρV²; doubling speed gives four times q at unchanged density.

Energy and power

Power is the rate of doing work. In a steady simplified model, useful propulsive power equals thrust multiplied by speed along the thrust direction.

100 N of thrust acting at 30 m/s corresponds to 3000 W of useful propulsive power.

Stability and control

Stability concerns a system’s response to a disturbance. Control concerns the ability to change its state. Static and dynamic stability describe different aspects of the response.

An initial restoring tendency does not by itself show whether oscillations will decay over time.

Worked example: lift scaling

For ρ = 1.2 kg/m³, V = 20 m/s, S = 2 m² and CL = 0.8, the model L = ½ρV²SCL gives 384 N.

State that CL and the other conditions are fixed; the calculation is a model, not a flight-performance instruction.

Common mistake: a fixed stall attitude

A stall concerns aerodynamic flow and a critical angle of attack, not one universal pitch attitude. Aircraft configuration and loading also affect the relationship between speed and lift.

Keep aerodynamic definitions separate from aircraft-specific operating procedures.

Check your understanding

At constant density and coefficient, what happens to model lift when speed doubles?

It increases by a factor of four because the lift equation contains V².

Curriculum connections

Sources