Propeller size to get the maximum output from the Lipos I have

Hi all. looking for some advice please. I have an electric motor capable of 900+ watts. With a 13 x 6.5 prop and a 4s Lipo. I am getting about 650 watts output. Amp rating as about 45A on an 80A speed controller, so well within limits. Without having to buy 5s, s6,7s lipos can I achieve more watts/power by using a larger prop? If so, what would you recommend? All help much appreciated.

p.s. My Extra foamee met it's demise on Monday after trying to be too clever!!

Its not just about getting more power out of the motor...you also have to match this to the airframe.
For example, you could bolt a (balanced) wooden spoon the the front and have your motor draw 800 watts, but that's no use at all!
Back to reality, if you want your model to fly faster you need more pitch. If you want it to have more thrust (better verticals) you need more diameter. You might need to try a few props to find the one that suits your airframe the best.

Denis Murphy wrote: p.s. My Extra foamee met it's demise on Monday after trying to be too clever!!

Strange! John B was spotted it flying today, Friday....:lol:

Denis, what is the KV of your motor? That will help with looking for the size/pitch range of props.

Thanks for your input Mike. I've not yet flown the model, just tested with a watt meter. I'll probably have to try a few props as you say (if the model lasts long enough!).

The specs of the motor Phil are 980 watts 800KV. The recommended prop sizes are: Minimum Propeller Size 13 x 10 (with 7S LiPo)
Maximum Propeller Size 15 x 8 (with 3S LiPo). I'm using a 4S lipo so maybe something around 14 x 8?

I smacked the Extra foamee earlier in the week and gave it to John B as I have enough models in my garage. It was repairable and John was able to fly it so all good.

Denis Murphy wrote: The specs of the motor Phil are 980 watts 800KV. The recommended prop sizes are: Minimum Propeller Size 13 x 10 (with 7S LiPo)
Maximum Propeller Size 15 x 8 (with 3S LiPo). I'm using a 4S lipo so maybe something around 14 x 8?

You don't say what size motor you have but I assume it maybe around armature size 35mm to 42 mm for that KV? 4 cells on 14 x 8 a good start. you can always try another pitch too. As Mike said it depends on the type of aircraft, thrust versus top speed and something in between. Don't rely on all maker specs, they do tend to overrate their motors. Anyway if something requires "7 cells" then to me it means pick the next size motor up for 6 cells in my humble opinion.

Example: Overlander Thumper T4250 7T KV 710. 700 watts. 3-4 cells 12 -14 prop

Phillip Ford wrote: Don't rely on all maker specs, they do tend to overrate their motors.

I've been an electric motor (and speed controller) abuser for over 30 years now and would say that most manufacturers UNDER rate their motors. They play safe so that they can walk away from warrantee claims. HobbyKing certainly under rate all of their motors. For example the Turnigy Aerodrive SK3 5045/660kv is rated as a 4-5 cell motor, 60A max and 1410W. I use this motor in my Atlas on 6 cells at over 80A and over 1900W

Mike Seale wrote:

Phillip Ford wrote: Don't rely on all maker specs, they do tend to overrate their motors.

For example the Turnigy Aerodrive SK3 5045/660kv is rated as a 4-5 cell motor, 60A max and 1410W. I use this motor in my Atlas on 6 cells at over 80A and over 1900W

I will agree to that Mike. My Curare, PC21, and long ago Angel , and recently a crashed Wing (got one SK3 5045 spare now) all used the above. Although when I said "overrate" I meant that generally. After all SK3s are a least half the price of an equivalent Hacker, etc so you get what you pay for in some respect but SK3 did up the game compared to Turnigy. I don't know what I would have done without SK3s. Maybe stuck with glow! :lol:

Simon O put a 5045 500Kv in a 30e size recently. :whistle:

It flies ok!

Simon Osborne wrote: It flies ok!

An understatement.