The Basics of an RC Propeller

Speaking in very broad terms, a propeller is an airplane wing traveling in a circle. If you were to slice a propeller’s blade in half, you would find that it looks like the cross-section of an airplane wing.

Taking that same wing and twisting it as it extends farther from a center point, gives the wing a positive angle of attack or the ability to ‘bite’ into the air and pull itself forward. At its basics, this is a propeller.

Rc airplane propellers are usually given a two number value which values are related to Diameter and Pitch. Diameter is the measurement, usually in inches, of the propeller from tip to tip. Pitch is the amount of ‘twist’ the propeller has and is roughly defined as the distance the propeller advances per a single revolution of the blade.

For example, a propeller labeled 9×6 describes a diameter of 9 inches and a pitch of 6 inches, which means a forward movement of 6 inches per revolution.

Another thing to note about rc airplane propeller is that a large diameter and low-pitch propeller (11 x 7) will give you greater pull at lower air speeds. Conversely, a smaller diameter and higher-pitch propeller (10×7) will give you less pull but allow for a higher maximum-airspeed.

Converting from a 2-blade to a 3-blade propeller

To convert from 2-blades to 3-blades you want to decrease the total blade area and increase your pitch. The general rule is to DECREASE propeller diameter by 1-2”,  and INCREASE by 1-2” the propeller pitch.  It is all right to keep the same pitch when you go from a 2-blade propeller to a 3-blade propeller, however don’t decrease pitch.

Why switch over to a 3-blade propeller?

From a beginners perspective the only reason to switch from a 2-blade prop to a 3-blade prop in rc aircraft is for looks. When you add another blade to your prop (i.e. going from 2-blades to 3-blades) technically you’re adding more drag and this extra drag decreases your props ability to pull and/or ‘bite’ into the air.

Unless you are flying giant sized aircraft a 3-blade propeller will not give you much increase in performance. But we admit it will look good when on the ground.

RC Prop Chart

The charts below are only to be used as a guide for choosing a correct 2-blade propeller for your airplane engine. Please refer to your engine manual for more detailed information on which propeller is best suited for your specific rc airplane engine.

2-Stroke Engines
Engine Size	Recommended Prop Size(s)	Starting Prop
.049 – .051	5.5×4, 5.5×4.5, 6×3, 6×3.5, 6×4	6×3
.09 – .10	7×3, 7×4, 7×5, 7×6	7×4
.15	7×6, 8×3, 8×4, 8×5, 8×6, 8×7	8×4
.20 – .25	8×6, 8×7, 9×4, 9×5	9×4
.29 – .35	9×6, 9×7, 9×8, 9.5×6, 10×4, 10×5, 10×6	9×5
.40	9.5×6, 10×4, 10×5, 10×6, 10×7, 10×8, 10×9	10×6
.45 – .50	10×7, 10×8, 11×4, 11×5, 11×6, 11×7, 11×7.5	10×7
.60	11×5, 11×6, 11×7, 11×7.5, 11×8, 11×9, 11×10	11×7
.71 – .80	12×6, 12×8, 13×6, 13×8, 13×10, 14×8	12×6
.90	13×6, 13×8, 13×10, 14×6, 14×8	14×6
1.08	14×8, 15×8, 16×6	16×6
1.20	14×8, 15×8, 16×6	16×8
1.50	16×8, 16×10, 18×6, 18×8	18×6
1.8	18×8, 18×10, 20×6, 20×8	18×8
2.1	20×8, 20×10	20×8
2.7 – 3.5	22×8, 22×10, 22×12, 24×8, 24×10, 24×12	22×12

4-Stroke Engines
Engine Size	Recommended Prop Size(s)	Starting Prop
.20 – .21	9×5,10×5	9×6
.40	10×6,10×7,11×4,11×5.11×7,11×7.5,12×4,12×5	11×6
.45-.48	10×6,10×7,10×8,11×7,11×7.5,12×4,12×5,12×6	11×6
.60-.65	11×7.5,11×7.75,11×8,12×8,13×5,13×6,14×5,14×6	12×6
.80	12×8,13×8,14×4,14×6	13×6
.90	13×6,14×8,15×6,16×6	14×6
1.20	14×8,15×6,15×8,16×8,17×6,18×5,18×6	16×6
1.60	15×6,15×8,16×8,18×6,18×8,20×6	18×6
2.40	18×12,20×8,20×10	18×10
2.70	18×10,18×12,20×10	20×8
3.00	18×12,20×10	20×10