How ThrustLab models oblique inflow

When a propeller is flying at an angle — climbing, descending, cruising forward, or mounted with tilt on a multirotor or VTOL frame — the air does not arrive straight through the disk the way it does in a simple hover test. ThrustLab's simulation engine accounts for this directly rather than treating every propeller as if it only ever hovers.

This page is a plain-language description of what the engine does with your flight condition. For the numbers behind a given release, see that release's validation report, linked from the solver-version chip on any result.

Modeling the true flight condition

Every simulated rotor now carries its actual flight condition: the vehicle's forward speed, its climb or descent rate, and each rotor's own mounting tilt relative to the airframe. Instead of assuming air always arrives straight down the rotor's axis, ThrustLab resolves the airflow the rotor genuinely experiences at that operating point.

Axial and edgewise inflow

That airflow is split into two components: the axial component, running straight through the disk along the rotor's spin axis, and the edgewise component, moving sideways across the disk. A rotor climbing straight up sees almost pure axial inflow; a rotor tilted forward in cruise, or mounted on a tilted arm, sees a mix of both. The blend of the two changes how the loading is spread across the disk and shifts the propeller's thrust, power, and efficiency from what a hover-only estimate would predict.

Both-frame thrust readout

Because a tilted rotor's thrust does not all point the way the vehicle needs it to, results are reported in both frames: the rotor's own frame (the thrust and in-plane force as the propeller itself experiences them) and the ground frame (how that same force resolves vertically and horizontally once the tilt is accounted for). This lets you see both what the propeller is doing and what the vehicle is actually getting from it — lift versus forward push — at any tilt angle.

Steep-descent advisory

In a sufficiently fast, steep descent, the air a rotor pushes down can curl back up around the disk and get drawn through again rather than flowing cleanly away — an unsteady, recirculating condition. ThrustLab detects when an operating point enters this regime and flags it, so the result there reads as an approximation rather than a precisely resolved answer. The simulation keeps running and every other result still comes through; only the flagged point should be treated as approximate. See the steep-descent flag in Warnings explained for what to do when you see it.

Accuracy

This model draws on the same propeller and motor data ThrustLab uses throughout the app — it is not a separate, less-tested code path. As with any aerodynamic model, results are most reliable in the well-behaved middle of the flight envelope and more approximate at its edges (very high tilt, very steep descent); the flags described above exist to tell you when an operating point has reached one of those edges.