RC Plane Propellers: Size, Pitch and How to Choose

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Swap a propeller and the airplane changes. A bigger or steeper prop asks more of the motor, which means more current through the ESC and the battery. A smaller one trades thrust for revs. Yet the prop is usually the last part chosen, often by copying whatever someone else flies.

This is a researched buyer's guide. The numbers come from APC's published documents, motor makers' specification pages, the AMA safety handbook and a few magazine and engineering sources, not from our own bench testing or flying. The aim is to explain what the two numbers on a prop mean, how to read the letters after them, how to check a prop against a motor's published limits, and which readily available props are worth a look. Pair it with the motors guide and the ESC guide, since the three parts are really one decision.

Quick Reference

How Diameter and Pitch Work

APC states it plainly: the two numbers stamped on the blade, separated by an X, are the diameter in inches first and the pitch in inches per revolution second. A 10x6 is a 10-inch circle with a 6-inch pitch.

Diameter sets the size of the disc the blades sweep. Area grows with the square of the diameter, so stepping from a 10-inch to an 11-inch prop gives 21 percent more swept area. That is geometry, not a thrust promise, but it explains why larger props feel stronger at low speed.

Pitch is the distance the prop would advance in one turn if it were threading through a solid. That makes it the number that ties most directly to airspeed. Model Airplane News gives the conversion as rpm x pitch (inches) / 1056 = pitch speed in mph. A 6-inch pitch spinning at 10,000 rpm works out to about 56.8 mph.

Treat that figure as a ceiling. The same source calls pitch speed the speed the model would fly if the prop never slipped, and says real models fly slower: typically 10 to 15 percent for a clean airframe and more for a draggy one. Its calculator also suggests a pitch speed of about two and a half to three times the model's stall speed, and sorts pitch speeds into bands: under 30 mph for park flyers, 30 to 60 for trainers and sport, 60 to 90 for sport aerobatic and 90 to 120 for warbirds.

Both numbers load the motor. More diameter or more pitch means more torque to turn the prop, which means more current. The best evidence is maker test data. SunnySky publishes a thrust table for its X2814 900 Kv motor, with a recommended 40 A ESC and a maximum continuous current of 40 A for 30 seconds. At full throttle on 3S (11.1 V) the table lists:

Going from 6.5 to 8 inches of pitch at the same diameter added 3 A and bought only 20 gf of bench thrust. On 4S (14.8 V) the same table shows the pattern again:

The 11x7 and 11x8 give the same bench thrust, yet the 11x8 draws 3.1 A more, a lot of it close to the motor's 40 A limit. The table also shows efficiency falling with throttle: the 13x6.5 makes 500 gf from 5 A (55.5 W) but needs 29.5 A for 1,750 gf. These are one maker's bench figures for one motor, so they show direction, not a universal rule.

Static Thrust Is Not Flight Thrust

Bench numbers are easy to collect and easy to misread. Martin Hepperle, whose propeller pages are widely used by aircraft designers, writes that the thrust of a propeller is not constant for different flight speeds, and that this is why the static thrust of a propeller "is not such a terribly important number." Static conditions are hard on a prop: the flow can be heavily distorted or partly separated, and the page says a prop reaches only 50 percent or less of its predicted ideal thrust when stationary, against 80 to 90 percent at its design point. Static results also depend on the surroundings, such as the fuselage, a crosswind and ground clearance.

The practical reading: use bench readings to check current and power against the maker's limits, since a stationary prop is a demanding condition for the motor. Do not use a stand figure or a forum thrust number to predict how an airplane will climb or cruise.

Reading Prop Codes

APC's nomenclature document explains the letters after the size. With no letters, the prop is a standard right-hand Sport prop, intended for internal combustion engines, though APC says sport props can also be used on electric motors. The type letters mark electric-only props:

Modifier letters then refine it:

Letters combine, so APC's own example is MRP, a reverse-rotation multi-rotor prop. A 13x4W, listed by Horizon as a 3D Fun Fly prop, is therefore a 13-inch, 4-inch-pitch wide-chord sport-style prop, and a 13x4EP is a thin electric pusher. Other makers use their own systems, so these codes apply to APC only.

APC's rpm limits

APC publishes recommended maximum rpm for each prop family as a number divided by the diameter in inches (Rev 5, March 2022):

APC's example: a 10x6 glow prop should be limited to 19,000 rpm. For an 11-inch Thin Electric the limit is 150,000 / 11, or about 13,636 rpm; for an 8-inch Slow Flyer it is 8,125 rpm. Check the limit against your motor's Kv and voltage. A 1000 Kv motor on 3S spins an unloaded 11,100 rpm, and a loaded prop turns slower. Model Airplane News's calculator uses 85 percent of Kv x volts as a typical loaded figure, which here is about 9,435 rpm. Slow Flyer props have a low ceiling, so they are not for a fast, high-Kv setup.

Tip speed is the other ceiling. It equals pi x diameter x rpm, which works out as diameter (in) x rpm x pi / 720 in feet per second. An 11-inch prop at 11,000 rpm has a tip speed near 528 ft/s, comfortably under the roughly 780 ft/s where Model Airplane News says noise rises and efficiency falls.

Materials: What the Makers Say

Many prop-material claims online are lore. These are the ones makers actually state:

• APC props are listed as plastic by Horizon, with a carbon option defined by APC as 40 percent carbon and 60 percent nylon by weight, and a D (durable) material modifier.
• Master Airscrew's nylon/glass line is described by Horizon as "Made of Glass-filled Nylon for strength & durability."
• Xoar makes beechwood, laminated, carbon fiber and composite props for gas, electric and glow engines. Its lines include PJA sport props in beech, a laminated version, PJE for 3D, PJN electric beech, and warbird-style props (PJWWI and PJWWII). Xoar says its props suit gas engines from 34cc to 240cc and glow engines from .049 to 3.00 cu in.
• Folding props are an APC type (F) and are electric only. Horizon sells an APC 11x8 folding prop and folding hubs in three sizes, 35, 45 and 50 mm.

How those materials fail in a crash, or how they feel on the throttle, is mostly forum talk. This guide does not rank them on that basis, except to repeat the AMA's firm line in the safety section below.

Matching a Prop to a Motor and ESC

Start from the maker's numbers, not from habit. Motor makers publish a recommended prop range, an ESC size and current ratings:

• E-flite Power 15 (950 Kv). Horizon recommends 10x6 to 13x6.5 props and a 40 A to 45 A brushless ESC, for sport and scale airplanes weighing 36 to 56 oz (1020 to 1590 g) or models needing up to 575 W.
• E-flite Power 25 (1000 Kv). Horizon lists 11.1 to 14.8 V input, 43 A maximum continuous current, 54 A burst and a recommended 60 A brushless ESC. The recommended props are a 14x8 folding on 3S and a 12x8 folding on 4S. Note the ESC is larger than the motor's continuous rating.
• Spektrum Avian 4250 (800 Kv). Horizon lists 12x6 to 13x8 electric props on 3S to 4S, with 925 W maximum continuous power.
• SunnySky X2814 (900 Kv). Maker props are APC 13x6.5, 13x8, 11x8, 11x5.5 and 11x7 with a 40 A ESC and 40 A for 30 seconds maximum continuous current.

A workable procedure, built from those sources:

1. Pick a prop inside the motor maker's recommended range for your pack voltage.
2. Check the rpm against the prop family's limit (APC formulas above).
3. Check pitch speed against the airplane's stall speed and class, using the Model Airplane News bands.
4. Put a watt meter in line and read the current at full throttle. Pat Tritle's Model Airplane News article says a test needs only a watt meter, a tachometer and a calculator, and warns against simply moving to larger diameter or higher pitch without knowing how close the system already is to its limits.
5. Keep that reading under the motor's maximum continuous current and inside the ESC's rating. If it is too high, a steep prop drops current faster in the SunnySky data than a smaller diameter does at the same thrust.
6. Fly, then judge the behavior in the air, not on the stand.

The LiPo battery guide covers the other half of the current equation, because a pack that cannot deliver the current sags and trips low-voltage cutoffs. If the setup cuts out or feels weak, the underpowered fix guide and the motor cutting out guide walk through the usual causes.

Choosing by Airplane

There is no universal table of prop sizes by airplane, so use examples from makers:

• Trainers and park flyers. The best trainer planes guide shows makers' own numbers: the AeroScout S 2 uses a 5 x 4.5 pusher prop, and the Arrows Pioneer a 5 x 2.75 two-blade. Slow Flyer props such as the APC 8 x 4.7SF suit low-rpm, low-Kv setups where the family's 65,000 / diameter ceiling is not an issue. The beginners guide covers ready-built options.
• Gliders. Electric gliders use folding props so the blades fold back when the motor stops. The E-flite Conscendo Evolution 1.5m BNF uses a 9.5 x 7.5 folding prop, and the Volantex Phoenix V2 and ASW28 use 10x6 folding props. The glider guide covers the airframes.
• Warbirds. Scale models sometimes use three or four blades. Horizon's P-47 Razorback 1.2m uses a four-blade 10.5 x 8, and Dynam's Bf-109 V2 uses a three-blade 1373. The warbird guide covers these models. On blade count, Hepperle notes that for high static thrust a smaller number of blades seems better because they have wider chord, which is a reason not to assume more blades means more thrust.
• Pushers. Use a pusher-rotation prop (APC's P modifier or an EP code), and check that its hand matches your motor direction.

Safety

The AMA Member Safety Program Handbook (March 2023) is short and firm on propellers:

• Cracked, nicked, or unbalanced propellers or rotor blades should be replaced and not reused.
• Stay clear of the propeller arc while starting or running any engine or motor.
• Do not stop engines by throwing rags or other objects in the propeller.
• Painting the tips a bright color helps you see the arc during rotation.
• Check the propeller and spinner for tightness before each operation.
• For wooden propellers, check the grain patterns for strength at high rpm.

Xoar adds that a final balance check is suggested before flight, because temperature and handling in transit can change a prop's balance. Du-Bro's Tru-Spin balancer is a common tool for this; Horizon describes its aluminum wheels as turning virtually friction free.

Props Worth a Look

These are real, current listings, and all were in stock at Horizon Hobby when checked in October 2026. Stock changes quickly, and the list is a starting point rather than a recommendation for every airplane.

APC 11 x 7E Electric. A common thin electric size, comfortably inside the maker ranges listed above for 3S setups. Under APC's formula its ceiling is about 13,636 rpm.

APC 13 x 4 Sport. A sport prop for combustion engines that APC says can also run on electric motors. On an electric motor it falls under the Sport-on-electric limit of 225,000 divided by diameter. The thin electric version (13 x 4E) and the pusher (13 x 4EP) were also in stock.

Master Airscrew 8 x 4 Nylon/Glass. Made of glass-filled nylon, per Horizon, in a small size for park flyers and small sport models.

APC 8 x 4.7 Slow Flyer. Designed for slow, low-rpm setups, with the 65,000 / diameter ceiling: about 8,125 rpm.

APC 11 x 8 Folding. For electric gliders, with a 120,000 / diameter ceiling. Folding hubs in 35, 45 and 50 mm were also in stock, so check the hub fits your motor and spinner.

Xoar beechwood props. For gas, glow or electric scale models where a wooden prop is wanted. Xoar's catalog is organized by line (PJA, PJN, PJWWII and others), so choose the line first and then confirm the size against your engine or motor.

Tools. The Du-Bro Tru-Spin Prop Balancer and a tachometer such as the Hangar 9 Micro Digital Tachometer, which Horizon says measures props with two, three or four blades up to 32,000 rpm, make the checks above possible.

Common Mistakes

• Choosing by the motor alone. Two airframes can share a motor yet want different props. Start from the maker's range, then tune for the airplane.
• Treating bench thrust as flight performance. Hepperle's analysis says static thrust is a poor guide.
• Ignoring the rpm limit. APC publishes limits for each family; running above them with a high-Kv motor is outside the maker's recommendation.
• Skipping the watt meter. Current is the number that protects the ESC and motor, and the SunnySky table shows how a small pitch step can add several amps.
• Reusing a damaged prop. The AMA says cracked, nicked or unbalanced props should be replaced and not reused.

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