Warnings explained

When a result is flagged in red or amber, the ⓘ next to that flag links here. Each warning below explains the threshold it tripped, why it matters, and — most importantly — what to do about it. None of these stop the simulation from running; they tell you the result is at the edge of safe operation or at the edge of what the solver can model accurately.

A warning is not a crash. It is the tool pointing at the one thing on this operating point you should look at before you build or fly.

Irreversible magnet warning

Threshold: the hottest motor magnet has exceeded about 120 °C (T_mag > 120 °C).

Why it matters. Above roughly 120 °C the permanent-magnet material in the motor begins to demagnetise permanently — it does not recover when it cools. A motor that has been cooked this way has a lower velocity constant (Kv) and makes less thrust forever, not just for this flight. This is the most serious thermal warning because the damage is irreversible.

What to do.

Reduce the sustained throttle — a brief burst is far safer than a long climb at the same throttle.
Fit a larger or higher-quality motor with more thermal headroom.
Improve cooling: more airflow over the motor (a faster slipstream, a cowling, or forced air) lowers the thermal resistance and drops the magnet temperature.
Use a lower-Cp propeller so the motor draws less current at the same RPM.

Convergence warning

Threshold: the propeller's inner aerodynamic loop did not fully converge — frac_converged dropped below about 0.99 (under ~99% of the blade stations settled to a steady answer).

Why it matters. The solver works the blade in stations from root to tip. When some stations do not converge (often the heavily loaded or stalled tips), the thrust and power reported for that rotor are less reliable — they are the solver's best unsettled estimate rather than a pinned-down answer. The closer frac_converged is to 1, the more you can trust the numbers.

What to do.

Treat that rotor's thrust, power and efficiency as approximate, not exact.
Move to a less extreme operating point — very high disk loading, very high RPM, or a heavily stalled prop are the usual culprits.
Check the per-rotor solver quality table on the Diagnostics tab to see how many stations were affected; a frac_converged of 0.98 is a minor edge case, 0.5 is not.

Steep-descent flag

Threshold: the rotor is descending fast enough that the airflow through the disk stops flowing cleanly through and starts to recirculate — an unsteady regime the steady model is not validated inside.

Why it matters. In a fast, steep descent the air the rotor pushes down can curl back up around the disk and get drawn through again, so the flow becomes unsteady and recirculating. The model bridges through this band to keep the run going, but it cannot resolve the numbers precisely there. This is a flag, not an error: the simulation still completes and every other result is produced — the thrust, power and efficiency at the flagged point are just approximate.

What to do.

Treat the thrust, power and efficiency at that operating point as approximate rather than exact.
Reduce the descent rate — a gentler descent moves the rotor back into the validated range.
Add forward speed — flying forward while descending keeps clean air moving across the disk and avoids the recirculating regime.

Related: Vert force · H-force

Compressibility warning

Threshold: more than about a tenth of the blade stations are running above the drag-divergence Mach number — frac_above_Mdd > 0.10 (more than 10% of the stations). The blade tips are fast enough that air compressibility (the same effect that limits a propeller-driven aircraft) is adding sharp drag.

Why it matters. Near the speed of sound the air no longer behaves as an incompressible fluid; drag rises steeply and the propeller's thrust and efficiency suffer. Just as importantly, the aerodynamic model is operating near the edge of its valid range, so the numbers for that rotor are less trustworthy when this is flagged.

What to do.

Lower the propeller tip speed — the direct levers are a lower RPM or a smaller-diameter propeller.
A smaller, slower-spinning prop or a larger, lower-RPM prop both reduce the Mach tip.
Treat the thrust and efficiency for that rotor as unreliable while this warning is active.

Pack thermal warning

Threshold: the battery pack's coupled thermal model flags that cells are running hot — the pack-thermal threshold is about 60 °C at the cell core.

Why it matters. Hot cells age faster, sag more under load, and in the worst case become unsafe. The pack-thermal warning means the current draw is generating more heat than the pack can shed at this operating point, so the cell cores are climbing into a zone that shortens battery life and erodes the safety margin.

What to do.

Lower the current draw — a less aggressive throttle, or spreading the load across more rotors.
Use a higher-capacity pack (more cells share the heat) or a higher-C-rating pack (lower internal resistance, so less resistive heating).
Improve battery cooling: airflow or slipstream over the pack lowers the cell temperatures.
Check the per-cell core-temperature heatmap to see whether one weak cell is driving the warning.