2408-21 Outrunner Brushless Electric Motor

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2408-21 Outrunner Brushless Electric Motor

The very popular 2408-21, also known as the BP21, is a direct drive outrunner brushless motor designed for medium to high speed park flyers. Best performance is obtained with the GWS EP8040 prop and a 3 cell Lipo battery rated for at least 14 amps. This combination is often used on the GWS Formosa, Mustang, Zero, Spitfire, and many sport planes weighing up to about 30 ounces. Producing up to 22 ounces of thrust, it far outclasses the 300 to 400 speed brushed motors it replaces. It is both lighter and more powerful than the typical 400 speed brushed motor. And with the included stick mount, it is often a simple drop in replacement.

The 2408-21 works quite well with 2 cell Lipo batteries as well. It will provide up to 15 ounces of thrust with the GWS EP1060 prop, and it is sometimes used in Combat plane competitions with the GWS EP9070 prop.

The 2408-21 works well on many models weighing between 10 and 30 ounces.

A firewall mount and aluminum stick mount with heat sink are included, along with two prop nuts and a washer. Always check the tightness of  all motor set screws and motor mount screws when installing motors. The motor set screws require a 1.5mm Allen wrench.

Some experienced flyers who post on the 'Wattflyer' forums suggest using a little 'JB Weld for metal' to secure the aluminum stick mount to the motor tube. This prevents it from working loose and spinning in the mount. Be very careful not to get any on the shaft and bearing though.

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Please check out my Motor Guide and FAQ section further down the page for help in choosing the right motor for your plane.

Propeller data for 3 cell Lipo batteries:

GWS props fit the 3mm shaft on this motor perfectly - no adapter needed. APC and Master Airscrew props require a prop adapter or prop saver for a 3mm shaft (available in my store).

The GWS EP8040 is the most commonly used prop with this motor. It will produce about 22 ounces of thrust at 14 amps with a pitch speed of 43 mph. This motor is only rated for 13 amps, so you need to provide for plenty of airflow over the motor and use full throttle sparingly until your Lipo has discharged somewhat.

The APC 8x4E produces 22 ounces of thrust at 14 amps with a pitch speed of 39 mph. The same caution must be used as with the GWS EP8040.

I do not recommend using any other 8 inch props with this motor when using a 3-cell Lipo.

The APC 7x5E produces 20 ounces of thrust at 14 amps with a pitch speed of 54 mph. The same caution must be used as with the GWS EP8040.

The GWS EP7035 produces 16 ounces of thrust at 9 amps with a pitch speed of 47 mph.

The APC 6x5.5E produces 11 ounces of thrust at 10 amps with a pitch speed of 65 mph.

The Master Airscrew 7x4 3-blade produces 15 ounces of thrust at 12.5 amps with a pitch speed of 43 mph.

The Master Airscrew 6x4 3-blade produces 11 ounces of thrust at 9.5 amps with a pitch speed of 48 mph.

Recommended props for 2 cell Lipo batteries:

The GWS EP1060 prop produces about 15 ounces of thrust at 11.5 amps with a pitch speed of 33 mph.

The GWS EP1047 prop produces about 15 ounces of thrust at 12.5 amps with a pitch speed of 24 mph.

The APC 9x3.8SF prop produces about 16 ounces of thrust at 11.5 amps with a pitch speed of 24 mph.

The GWS EP9047 prop produces about 14 ounces of thrust at 10.5 amps with a pitch speed of 27 mph.

The GWS EP9050 prop produces about 14 ounces of thrust at 10 amps with a pitch speed of 32 mph.

The GWS EP9070 prop produces about 13 ounces of thrust at 12.5 amps with a pitch speed of 35 mph.

The GWS EP8040 prop produces about 12 ounces of thrust at 7.5 amps with a pitch speed of 32 mph.

The GWS EP8043 prop produces about 12.5 ounces of thrust at 8 amps with a pitch speed of 31 mph.

The GWS EP8060 prop produces about 13 ounces of thrust at 10 amps with a pitch speed of  39 mph.

The GWS HD8060 prop produces about 12 ounces of thrust at 9 amps with a pitch speed of  41 mph.

The above data is a result of my own testing using fully charged Lipo batteries.

2408-21 Specifications:

Weight = 1.6 ounces (46 grams)

Diameter = 1.2 inch (31mm)

Total Length = 2.4 inches (62mm)

Shaft Length = 1.2 inches (31mm)

Shaft Diameter = 3mm (GWS Props fit nicely)

Voltage = 7.2 to 12.6   

KV = 1750

Current = 13 amp max.

Heads Up RC Brushless Motor Guide

When choosing a brushless motor for your plane, keep in mind that you will usually get better efficiency with larger propellers. Please see the individual motor listings for more information and suggested uses. All data presented is with the use of 3-cell Lipo batteries.