Performance · longitudinal geometry

Forces & angles in the longitudinal plane

In symmetric flight the velocity, the weight and the aerodynamic forces all lie in the aircraft's vertical longitudinal plane. Three angles tie the picture together: theflight-path angle γ of the velocity above the horizon (positive in a climb), the pitch angle θ of the body axis, and the angle of attack α between them — related by the fundamental identity θ = γ + α. Drag the sliders to fly a climb, a glide or level flight, and switch between the exact 2D side-view and a 3D view of the same geometry.

What you're looking at

V points along the flight path at γ above the horizon. Lift L is perpendicular to V (rotate V by +90°), dragD opposes V, and weight W always points straight down. Thrust T acts along the body axis x_b, which sits at θ above the horizon — that is, α above the velocity vector.
Set γ = 5°, α = 10° and the body axis leads the velocity vector by α = 10°, giving θ = 15°. Push γ negative for a glide: the velocity vector drops below the horizon while α (and so the lift direction) is still measured from the flight path.
The 2D side-view is exactly the projection of the 3D scene onto the highlighted vertical longitudinal plane. In 3D the Spitfire is pitched to θ using the same Rust/WebAssembly attitude code as the Euler demo; orbit to confirm every vector stays in that one plane.