Generate an optimal blade

Generate designs a minimum-induced-loss blade straight from your targets. You give it the size, the design point (RPM and airspeed), and a thrust or power target — it works out the optimal chord and twist, then opens the result in the editor so you can refine it by hand. You never enter an aerodynamic coefficient: you pick section shapes (airfoils) and, at most, a design lift coefficient; the solver computes the section aerodynamics for you.

The ⓘ next to any control on the Generate form links straight here.

What minimum-induced-loss means

A propeller wastes energy two ways: profile drag on the blade sections, and induced loss — the swirl and downwash left in the wake. A minimum-induced-loss (MIL) blade is shaped so the wake it leaves behind carries the least possible energy for the thrust it produces. That is the classic Betz condition (refined by Larrabee and by Adkins–Liebeck): the optimal loading puts a specific amount of circulation at each radius so no radius is working harder than it should. It is the theoretical best starting point for an efficient blade, which is exactly what Generate seeds from.

What "design point" means

A propeller is only optimal at one operating condition — a particular rotation speed and forward airspeed. That condition is the design point. Generate shapes the blade to be most efficient right there. Off the design point (a different RPM or airspeed) the blade still works, it just gives up a little efficiency. Choose the design point that matches how you will actually fly: cruise speed and cruise RPM for a fixed-wing prop, or 0 airspeed at hover RPM for a multirotor.

Getting in

Generate an optimal blade

Open the Generate route from the create-a-propeller chooser. You give it a blade count and size, a design RPM and airspeed, and a thrust or power target; it generates the optimal blade and opens it in the editor. It is one of three ways into the same editor — the others are scanning a photo and starting from a blank template.

When to use it. Reach for Generate when you know the performance you want (a thrust or a power budget at a known RPM and speed) and you want the optimal blade to hit it, rather than copying or hand-building one.

Blade & size

Blades

How many blades the propeller has. More blades share the thrust (each blade carries less, so each chord is narrower) but the blades interfere with each other more, which costs a little efficiency. Two blades is the usual choice when efficiency comes first.

Diameter

The tip-to-tip diameter of the propeller. It sets the tip radius the blade is designed over. A larger disk moves the same thrust at a lower disk loading, which usually means higher efficiency — so go as large as your airframe and clearance allow.

Hub radius

Where the working blade starts, measured out from the center. Everything inboard of the hub radius is structure, not an aerodynamic surface. It must be smaller than the tip radius (half the diameter), or there is no blade to design.

When to change it. Match it to the real hub or spinner of the prop you are designing for.

Design point

Design RPM

The rotational speed the blade is optimized for. The blade is shaped to be most efficient at exactly this RPM; running faster or slower still works but gives up a little efficiency. Pick the RPM you expect to cruise or hover at.

Airspeed

The forward flight speed the blade is designed for. 0 = static (hover, or static-thrust testing) is a valid, first-class value: the design solver handles the static limit directly, so there is no separate "static mode" to switch into. Enter your cruise speed for a fixed-wing propeller, or 0 for a hover rotor.

When to change it. Set it to the speed you will actually fly at the design RPM — that is the point the blade is tuned for.

Design target

Design target

You fix one quantity and the optimizer solves the blade to meet it. Choose Thrust to design to a thrust target (the result then reports the power it takes), or Power to design to a power budget (the result reports the thrust you get). Only one target value is ever shown — the toggle decides which one you are fixing.

When to change it. Use Thrust when you have a thrust requirement (a hover weight, a required static thrust); use Power when you have a power or battery budget and want the best thrust within it.

Design Cl distribution

The target section lift coefficient. By default the generator picks the single Cl that produces the most efficient blade for your operating point — it maximizes hover figure of merit (static) or propulsive efficiency (forward), searching at or below the airfoil's best lift-to-drag Cl. (A pure max-L/D blade is often too narrow and over-pitches under load, so the most efficient choice is usually a bit lower.) The advanced curve lets you override the radial loading on purpose — only open it if you know you want a different distribution.

When to change it. Leave it on the default unless you are deliberately trading efficiency for a different loading shape (for example, unloading the tip).

Airfoils

Airfoils

The section shape used along the blade — the same per-station airfoil picker as the editor. Pick one airfoil for the whole blade, or add radial breakpoints so the section varies from root to tip. You choose shapes only; the solver computes each section's lift and drag automatically, so there is nowhere (and no need) to type a coefficient. See the editor's per-station airfoil model for the full picker.

How Generate works

How Generate works

Generate runs in two stages, and the result is never worse than the first stage.

• Stage 1 · Betz seed. An analytic minimum-induced-loss design — the theoretically optimal circulation for your target at your design point. It is near-instant, so it flashes to a ✓ almost immediately.
• Stage 2 · Polish. A differentiable efficiency polish on the full solver, started from the seed, that streams its iterations and watches the efficiency climb.

Because the seed is already the induced-loss optimum, the polish is cheap and only ever improves on it. If the polish cannot beat the seed, Generate keeps the seed and tells you so (a non-blocking notice) — you always get a blade that is at least as good as the analytic optimum, never a worse one.

Why two stages

The analytic seed is fast and globally optimal for induced loss, but it idealizes the profile drag and the operating point. The polish runs the real, validated forward solver and refines the chord and twist for actual efficiency — catching the things the closed-form theory cannot. Seeding the polish from the analytic optimum is what makes it fast and reliable: the optimizer starts already close to the answer, so it converges quickly and cannot wander off into a worse blade.

The result

Design-point efficiency

The propulsive efficiency η of the generated blade at your design point — the useful thrust power out divided by the shaft power in. At static (airspeed 0) propulsive efficiency is zero by definition (there is no forward speed to do work), so the result reports an actuator-disk figure of merit instead, which measures how close the rotor is to the ideal hover. The free quantity — the thrust or power you did not fix — is reported next to η so you can see the full operating point at a glance.

Open in editor hands the generated chord, twist, and airfoil layout straight to the station editor, exactly as a scanned or template blade would arrive — so you can refine every station by hand from the optimal starting point. Adjust targets takes you back to the form with your inputs preserved to try another design point.