Is enough for this motor?


New member
I just started the hobby and crashed my fms red dragonfly trainer and I want to build a Ft simple scout from the leftover electronics. Can a 10x3.5 Slowfly prop work with the dragonfly's motor and a 20A esc and a 3 cell battery?


Master member
Looked up the FMS Red Dragonfly. Says it has a 2805 2720kv motor. Near as I can tell, that motor has a 100 Watt limit.
I ran the numbers for that prop and motor combination through an online calculator. A 10x3.5 prop on that motor would need be about 450 watts of power.
You'd cook that motor so fast a microwave would be jealous.


looking up down under
google is your friend

per the spec sheet attached, you need a maximum 2s lipo drawing no more than 12 amps

so the esc is fine, but the battery needs to be 8.4v max (that's 2s, not 3s)

as for the prop required at 2s - a 7 or 8" seems appropriate, but an 8x4 should be a safe bet

indeed, chatgpt says:
The appropriate pitch for an 8-inch propeller on a 2S 2805 2720KV motor would depend on the type of RC aircraft and your performance preferences. Propeller pitch is the theoretical distance in inches that a propeller would move forward in one revolution if it were moving through a soft solid like a screw.
For an 8-inch propeller, common pitch values might range from around 3 to 6 inches. However, the specific pitch that will work best for your setup depends on factors such as the type of aircraft, desired thrust, speed, and the motor's characteristics.
If you're looking for a starting point, you might consider a propeller with a pitch in the middle of the typical range, say around 4 to 5 inches. Keep in mind that you may need to experiment with different propellers to find the one that provides the desired performance for your specific application.
Always refer to the motor manufacturer's recommendations and specifications, as they often provide guidelines for suitable propeller sizes and pitches. Additionally, you can use online propeller calculators to estimate the expected performance based on your motor, battery, and aircraft specifications.

i personally used the 8043 slow fly prop on a few planes, and it is a safe choice i think - not sure a plastic prop is up to the task - you likely need to source a nylon one

and put it on the right way round for the build - the scout is a tractor, the dragonfly was a pusher


  • specs.pdf
    70 KB · Views: 0


looking up down under
unless you have a watt meter, you will have to find out the hard way as that motor clearly states 2s

but for this size plane, an 8" prop will make it fly at a scale speed and be way quieter than a screaming 3s

that said, i routinely run a small 18-112000kv on 3s for a 5x3 which is not recommended in the specs, but using the watts up! meter proves i am not exceeding its rated amps on that combo
some details on that build here
without testing using a meter, you run the risk of frying the motor, or the esc (or both)


Elite member
I'm no good at calculating so I've just learned through other's tips and testing some general brackets:

4 inch to 6 inch: 2300kv motor. A 20A ESC will serve you up to a 5x4.5 3-blade (Min 2s). It can also do 6x4 2-blade but you will want a 30A ESC for that on 3S probably.

7 to 8 inch: 1400kv motor. A 30A ESC will serve an 8X5 2-blade well and is pretty standard. It's what comes in these cheap packs I've used for my BiPlanes which are between an FT mini and a normal sized swapable.

9 to 10 inch: 1000kv motor. A 30A ESC will spin a 10x4 2-blade. A 40A ESC will spin a 9x4 3-blade. A 10x7 3-blade is too much propeller for a 1000kv motor I've found.

10 to 11 inch: 750kv motor. Getting expensive now. This is what you'll need to spin that 10x7 3-blade I mentioned. 40A ESC and 4S Batteries needed at this level.

I have a 730kv motor spinning a 12x5 slowfly wooden prop. Also running 40A ESC and a 4S Battery.