Analyze a propeller

The Analyze tab inside the propeller editor runs the blade you are editing through an aerodynamic analysis and shows you how it performs — its thrust, power, efficiency, and how those are distributed along the blade. It reads whatever the editor currently holds, so you can shape a blade on the Geometry tab, switch to Analyze, and see the result without any save or export step. The ⓘ next to any control on the panel links straight here.

This is an aerodynamics tool, not a full performance simulation. It tells you what the blade does in the air; it does not pick a motor or a battery for you. When you want current draw, temperatures, and flight time, run a full simulation instead.

If you are new, the fastest path is: leave the operating point at its defaults, keep the mode on Single point, and press Analyze. You will get the blade's radial distribution at a sensible static operating point. From there, sweep across speeds or solve for a thrust target.

What this panel does

Aero-only analysis

This panel runs the blade in isolation — just the propeller spinning in air, with no motor, ESC, or battery in the loop. It tells you the blade's thrust, power, and efficiency at an operating point, and how the aerodynamics vary from the hub to the tip. That makes it the right tool for blade design: you can compare two planforms, or check where a blade stalls, without committing to a powertrain.

For powertrain results — current draw, motor and battery temperatures, sag, and flight time — run a full simulation instead. A full simulation couples this same blade aerodynamics to your chosen motor, ESC, and battery; the Analyze panel deliberately leaves all of that out so you can iterate on the blade alone. A persistent note at the top of the panel reminds you of this so the scope is never a surprise.

When to use it. Reach for Analyze while you are still shaping the blade; reach for a full simulation once the blade is settled and you want to size the rest of the drivetrain.

Choosing what to run

Analysis mode

Picks what kind of analysis to run.

• Single point gives the full radial distribution along the blade at one operating condition — one RPM, one airspeed, one air density.
• Advance-ratio sweep traces CT, CP, and efficiency across a range of speeds, producing the blade's performance curves.
• Solve to target fixes a thrust or power goal and finds the RPM that meets it.

When to change it. Start at Single point to understand a blade; switch to a sweep to see its full operating envelope; use Solve to target when you know the thrust or power you need and want the RPM.

The operating point

Every mode shares the same operating point: how fast the blade spins, how fast air flows into it, and how thick that air is. Press Analyze to run — nothing runs as you type, so you can set up the whole operating point before committing.

RPM

How fast the propeller spins, in revolutions per minute. Faster spin makes more thrust but draws more power. In Solve to target mode you don't enter this — it's the value the solver finds for you, shown read-only once it converges.

When to change it. Set the rotational speed you want to evaluate, or hand it to the solver in Solve-to-target mode.

Airspeed

How fast air is flowing into the propeller — your forward flight speed. Zero means static (a hover or a bench test). Higher airspeed unloads the blade and shifts where it works most efficiently. The value is shown in your unit system (m/s, mph, or kt).

When to change it. Set it to your cruise speed to see the blade in forward flight, or leave it at zero for static thrust.

Air density

How thick the air is — denser air makes more thrust and more drag for the same RPM. You can type a density directly, or switch the field to Altitude and we derive the density for you from a standard atmosphere model. The default is standard sea-level air (ISA, 15 °C, 1.225 kg/m³), a sensible baseline.

When to change it. Enter your field elevation (as altitude) or a measured density when you care about hot-and-high performance.

Sweeping across speeds

Advance-ratio range

The span of advance ratios (J) to sweep across, set by a from value, a to value, and a number of steps. Advance ratio is how far the prop moves forward per revolution relative to its size; sweeping it traces the performance curves. You can enter an RPM range instead — at a fixed airspeed and diameter the two are interchangeable.

When to change it. Widen the range to see the whole envelope, or narrow it and add steps to resolve a region (for example, around the efficiency peak) in more detail. The range must go from a lower value to a higher value with at least two steps.

Solving for a target

Solve target

Whether to solve for a thrust goal or a power goal. Pick Match thrust to find the RPM that produces a target thrust, or Match power to find the RPM that draws a target power. The solver brackets and bisects on RPM until it hits the target, at the airspeed and air density you set.

When to change it. Choose the quantity you actually have a requirement for — a thrust you need to hover, or a power budget you must stay under.

Solve convergence

Whether the solver actually found an RPM that meets your target. Converged means it did: the panel shows that RPM plus the blade's full state there. Non-converged means the target is outside what this blade can produce at this airspeed — the solver tells you clearly and shows no result, rather than silently reporting a wrong operating point. When that happens, try a lower target, a different airspeed, or a different blade.

How to read it. A green converged chip means the solved RPM is trustworthy. A warning banner means the target is unreachable for this blade and condition — adjust the target or the operating point.

Reading the results

Coefficient convention

ThrustLab reports performance with the conventional propeller coefficients used by UIUC and most propeller catalogs, defined on rotational speed n (revolutions per second): J = V/nD, CT = T/ρn²D⁴, CP = P/ρn³D⁵, and η = CT·J/CP.

Heads-up if you come from QPROP: QPROP defines its thrust and power coefficients on angular speed ω (radians per second), so its CT and CP numbers differ from these by constant factors. It is the same physics, just a different normalization — read the curves and values here as n-based. This matters whenever you cross-check ThrustLab against a QPROP run: compare J and η directly (η is convention-independent), but expect the raw CT and CP magnitudes to differ.

Why it matters. If you compare these coefficients against a tool that uses the ω-based convention without accounting for the factor, the numbers will look wrong even when the blade is identical.

Radial quantity

In single-point mode, this chooses which per-station quantity to plot along the blade — against r/R, the fraction of tip radius (0 at the hub, 1 at the tip). The options cover:

• Geometry — chord and twist (β) at each station.
• Section aerodynamics — lift coefficient Cl, drag coefficient Cd, Reynolds number Re, and Mach number.
• Loading — thrust per unit radius (dT/dr) and torque per unit radius (dQ/dr), which show where along the blade the work is being done.
• Induced flow — the axial and swirl velocities the blade adds to the air passing through it.
• Local efficiency — the efficiency η at each station.

How to read it. A blade-loading curve (dT/dr) that spikes near the tip warns of a tip-heavy design; a Cl curve that climbs past the section's stall limit near the root flags a station that is stalled. Step through the quantities to find where a blade is and isn't working.

Performance curves

In sweep mode, the panel plots CT, CP, and efficiency η against advance ratio J — the blade's signature card. CT (thrust coefficient) and CP (power coefficient) start high near hover and fall as the blade unloads at speed; η peaks at the advance ratio where the blade is working most efficiently, then drops off on either side. η rides its own right-hand axis so the small CT and CP coefficients stay readable. The convention note beneath the chart is a reminder that these are n-based coefficients.

How to read it. Find the J where η peaks — that is the advance ratio this blade is happiest at. Match it against your cruise condition (J = V/nD at your speed and RPM) to see whether the blade is well-suited to how you fly it.

Concepts

What advance ratio is

Advance ratio, written J, is a single dimensionless number that captures how a propeller is operating, independent of its size or speed. It is the distance the prop travels forward in one revolution divided by its diameter: J = V/(nD), where V is airspeed, n is revolutions per second, and D is diameter. J = 0 is static (hover, no forward speed); a higher J means the blade is moving forward faster relative to how fast it spins, which unloads it.

Why it is useful: two different propellers at the same J behave similarly in non-dimensional terms, so plotting performance against J — rather than against raw RPM or speed — lets you compare blades fairly and read off the operating point where a blade is most efficient.

Why aero-only is decoupled from the full simulation

The Analyze panel solves only the blade aerodynamics: given a geometry and an operating point, it computes the forces and the flow. It does not model the motor, the ESC, or the battery. That separation is deliberate. When you are designing a blade, the powertrain is a moving target — you have not picked it yet — and mixing it in would couple every blade tweak to a motor choice you are not ready to make.

Keeping the analysis aero-only also makes it fast and synchronous: there is no electrical solve to converge, so the result comes back immediately on the warm solver. Once the blade is settled, a full simulation re-uses this exact aerodynamics and adds the powertrain, giving you current, temperature, and endurance. Think of Analyze as the blade workbench and the full simulation as the whole-vehicle test.

How to read radial distributions

A radial distribution plots one quantity along the length of the blade, from the hub (r/R near 0) to the tip (r/R = 1). It answers where on the blade something is happening, not just the total. A few things to look for:

• Loading (dT/dr, dQ/dr) shows where the blade produces its thrust and absorbs its torque. A smooth curve that tapers to zero at the tip is the ideal; a sharp spike near the tip means the tip is overloaded.
• Cl along the blade tells you how hard each section is working. A section whose Cl exceeds its stall value is stalled — usually a root problem at low speed.
• Induced velocities show how much the blade is accelerating and swirling the air; large swirl means energy lost to rotation rather than thrust.

Read these together: a blade that looks fine on its total thrust can still have a stalled root or an overloaded tip that a radial plot reveals at a glance.