I recently purchased an electric motor for my new plane based on a vendor recommendation for my specific plane.
The motor, rated as comparable to a 70cc gas motor, turned out to be inadequate for my 30lb
Plane and the claim that it's comparable to a 70cc gas motor may not be exactly accurate.
The motor is an Axi 5360HD and the vender recommends a 26/12 Fiala Prop. for it.
That's the same prop. DA shows for it's 100cc motor.
Based on what I'm learning, it seems that my 30lb plane should have at least a 5,000 watt motor in order to perform the basic scale aerobatics.
I know there are some accomplished electric motor Guru's out there and I hope you will give me some help in better understanding how these comparisons work.
Thanks for your help

Rule of thumb:
3D flying use Greater than 150Watts / Lb
Scale Flying 80-100 Watts / Lb

@ 30 lbs, yes 4500 Watts or greater

Select a motor with a KV Rating that will give you the RPM you're looking for equivalent to the size of motor for the Voltage you want to run.

Example: 70cc Plane usually uses a 24x9 or 25 x 8 Prop spinning at 6600 = 7000 rpm.

if you're using 2 x 6S in Parallel and I want to turn a 24x9 at 6600rpm, I'd be looking for a 5000 Watt Motor with 250 KV.

The math would be as follows.
Lipo Cells X voltage = Total Voltage
Target RPM / Total Voltage = KV Required

Using both formulas above

We're looking for a 5000 Watt motor that has a KV of 250 ish (Note: KV is the number of RPM / Volt)

There's more to it than that, but it can be used as a guideline.

A 70cc 30 pound build, what is it a dump truck? Most 120cc aerobatic planes come in at 27 to 30 pounds.

Originally Posted by Festivus

A 70cc 30 pound build, what is it a dump truck? Most 120cc aerobatic planes come in at 27 to 30 pounds.

And where did he say it's an aerobatics airplane? I've seen many a scale Mustang, running on G62s that are MUCH heavier than that and have great scale performance.

There's an old adage "If you don't have anything good to say, don't say anything". Since apparently you've never heard it before maybe you should google it :^)

Originally Posted by wfield0455

And where did he say it's an aerobatics airplane? I've seen many a scale Mustang, running on G62s that are MUCH heavier than that and have great scale performance.

There's an old adage "If you don't have anything good to say, don't say anything". Since apparently you've never heard it before maybe you should google it :^)

Was just poking fun, just gave the aero bat as a reference since OP gave very little information was trying to gather more information from OP. I did not intend to trigger the sjw in you. If you're not familiar with the terms maybe you can Google that.

Below an excellent quote, a step by step instruction for motor selection.
From
brushless motors Kv? - RCG

Originally Posted by scirocco

While an absolutely critical part of the system ...
... Kv is actually the item one should choose last.

1. Decide your peak power requirement based on the weight of the model and how you want to fly it:
   Magic numbers for e-flight - WFF
2. Pick a preferred cell count (voltage) and pack capacity for how to deliver the power.
3. Pick a prop that will a) fit on the model and b) fly the model how you want - often as big as will fit is a good choice, but if high speed is the goal, a smaller diameter higher pitch prop will be more appropriate.
4. Look for a size class of motors that will handle the peak power - a very conservative guide is to allow 1 gram motor weight for every 3 watts peak power.
5. Then, look for a motor in that weight range that has the Kv to achieve the power desired with the props you can use - a calculator such as eCalc allows very quick trial and error zooming in on a decent choice. For a desired power and prop, you'd need higher Kv if using a 3 cell pack compared to a 4 cell pack. Or for a desired power and cell count, you'd need higher Kv if driving a smaller diameter high speed prop compared to a larger prop for a slow model.

The reason I suggest picking Kv last, is that prop choices have bounds - the diameter that will physically fit and the minimum size that can absorb the power you want. On the other hand, combinations of voltage and Kv are much less constrained - at least before you purchase the components.

So Kv is not a figure of merit, in that higher or lower is better, it is simply a motor characteristic that you exploit to make your power system do what you want, within the constraints you have, e.g. limited prop diameter, if it's a pusher configuration, or if you already have a bunch of 3S packs and don't want to buy more, and so on.

Minor lay-out changes by RvS

Originally Posted by Flybye Steve

I recently purchased an electric motor for my new plane based on a vendor recommendation for my specific plane.
The motor, rated as comparable to a 70cc gas motor, turned out to be inadequate for my 30lb
Plane and the claim that it's comparable to a 70cc gas motor may not be exactly accurate.
The motor is an Axi 5360HD and the vender recommends a 26/12 Fiala Prop. for it.
That's the same prop. DA shows for it's 100cc motor.
Based on what I'm learning, it seems that my 30lb plane should have at least a 5,000 watt motor in order to perform the basic scale aerobatics.
I know there are some accomplished electric motor Guru's out there and I hope you will give me some help in better understanding how these comparisons work.
Thanks for your help

Steve, please tell what is the plane and which motor you have in hand since there are at least 3 versions.
The AXI 5360HD V2 is an extremely low kV high torque motor intended to spin very large props for low speed scale flying (i.e WWI birds).
Maybe you have not selected the correct motor for your application.
Ronaldo

We’re your batteries up to task? Did you measure how many amps you we’re pulling? Then you can calculate the watts.

I don’t think you will get where you want to go with that motor. I want to say my a80 hacker will pull over 200 amps when you hammer it.

Thank all of you for the feed back. It's been very informative and the comments confirm that
choosing an electric motor for your plane requires due diligence.
The plane I have is a H9 1/4 Scale Fokker. The battery pack weighs 4lbs which has the plane weighing in at about 30lbs.
The Axi Motor we're using fits the description outlined by Ronaldo. It swings a 26/12 prop and will fly the plane in horizontal flight with authority. It will climb out at 45 degrees ok but bogs down on the vertical portion of a simple loop or emmelman.
Since the vendor (for the motor) listed this motor specifically for this plane, it raises another important question which relates to what your expectations are for this plane.
The plane vendor recommended a Rimfire 65 for the plane which actually performs better than the
motor I chose. I thought the Axi would deliver more power.
I wanted and expected the plane to perform some basic maneuvers.
Looks like I'll need something like a 5,000 watt motor to fly this beautiful plane.
Thanks again for the help.
Steve

Add more cells or more pitch in the prop. The kv is so low on those motors you will need more pitch to get more umph. But you really need to measure the amps to see what it is doing before you make changes

Assuming a 26" prop is within the recommended range for the plane and also assuming you're running the power system on 12S you should get a pitch speed of a little over 60mph and almost 5000W with the Rimfire 65cc at 160rpm/V. That is a nice speed for a sport plane and maybe a bit high for a scale WWI bird.
Just manage the throttle and have fun!
Ronaldo