Common Questions with APC Propellers

Written by Jay Smith
APC Propellers’ Annie Torres shares her knowledge about propellers
As seen in the March2021 issue of Model Aviation.

Common Questions

Glow propellers vs. electric: Propellers for glow- or gas-powered, internal-combustion engines are made stronger to withstand the high acceleration forces that result with each piston stroke. These propellers can also be used on electric motors.

Electric propellers, however, should only be used with electric motors because they do not have the higher strength needed for glow engines. If you are unsure about how to identify glow or electric propellers, please visit the APC website for more information about our propeller nomenclature.

Propeller Balance

APC propellers come factory balanced, but it is always a good idea to check the balance of your propeller. To properly do this, a good-quality, high-point balancer with cones should be used. The tapered portion of one cone should go in the center hole on the back side of the propeller hub. The at part of the other cone should be used against the front face of the hub, similar to the way the propeller is clamped to the motor.

A washer might be needed for larger propeller hubs. A magnetic balancer should only be used for small propellers—those less than 5 inches in diameter. Magnetic balancers are too sensitive for larger propellers and repeatability becomes difficult. More details about propeller balancing can be found on the APC website.

Propeller Pitch

Pitch is similar to the gears in your car. A high pitch allows for higher top speeds but at the expense of takeoff and climb performance. For better acceleration and low-speed performance, a lower-pitch propeller should be used. For high-speed applications, a propeller with a similar pitch-to-diameter ratio (pitch ratio) is needed (such as a 9 × 9). For aerobatics and hovering, a propeller with a lower pitch ratio (such as a 13 × 4) is ideal.

Painting APC Propellers

APC propellers are made out of nylon. As a result, they can be painted or dyed. When painting, scuff the blade with a scratch pad and be sure to check the balance after painting. We recommend Rit dye when dyeing propellers. Dark colors work best and no rebalancing is needed.

Properly Orienting a Propeller

To properly orient any fixed-pitch propeller on your aircraft, the leading edge (LE) of the propeller blade should always point toward the direction of flight and in the direction of motor rotation. The LE of the blade is the thicker, rounded edge. In the case of multicopter applications, the direction of flight is up.

Custom Propellers

APC makes custom propellers. We can either design a propeller for your specific application or take your design and manufacture it. When ordering small quantities, we charge for tooling materials, machining, and setup.

For more information, please contact us at the email address in "Sources."

Propeller Performance Data

The performance data for all APC propellers is listed on the company’s website. The data is based on analytical simulations using vortex theory and is formatted based on rpm and airspeeds. The data is a great resource for comparing one propeller with another, or for finding new propellers for a specific application. Please see the link in "Sources."

Good Rules of Thumb

Two-blade, three-blade, and four-blade equivalents: Assuming that the the blade shape and pitch are unchanged, a three-blade propeller is 90% of a twoblade diameter. A four-blade propeller is 84% of a two-blade diameter.

Pitch vs. diameter: Increasing the diameter by 1 inch is roughly equivalent to decreasing the pitch by 1 inch per revolution (e.g., the load from a 12 × 6 propeller is approximately equal to the load of an 11 × 7 propeller).

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