Cobra motor understanding.

[Paul Taylor]

Guys I need to make sure I am understanding this correctly.

Plane is a  F-Twister.

Looking at the suggested Cobra motors for this size plane, Cobra 2820/12 and 2820/14. The 2820/12 will not turn a prop for a Twister using a 4S battery. ( I have to use a battery that is 105mm long due to space limitation) I found a 4S that fits that space.

So I am thinking I need to order the Cobra 2820/14. Am I understanding this correctly?

See the attached prop charts for both motors.
Thanks

[William DeMauro]

You can probably use either but if I were setting up that plane I would use the 2820/12 as it is gives more head room with the props that you will most likely be using on your twister

[Paul Taylor]

Thanks for the input William. I would think a 10 or 11 in prop would be the size needed for the Twister. The 2820/12 will not turn props in that size @ 14.8.
What am I missing?

[William DeMauro]

You are right on with your prop size. That motor will spin those props without issue. We are turning those props at an rpm that keep those motors within load limits. I have flown banshees and twister with similar setups so I know it works.

[Fred Underwood]

The charts are based on "full throttle" for their recommendations.  If you need to run full power, you will not run long enough and overheat if you don't stay close to their recommendations.  There isn't a great chart for how we use the motors, just great fellow modelers experience.  Similar to WD post.

[Paul Taylor]

Totally agree on experience.
I’m just trying to understand how this all works and understand how components are selected.
So maybe what I’m missing is RPM. If you run the 2820/12 at a slower RPM then you can swing the correct prop?

Thoughts?

[Ken Culbertson]

Guys I need to make sure I am understanding this correctly.

Plane is a  F-Twister.

Looking at the suggested Cobra motors for this size plane, Cobra 2820/12 and 2820/14. The 2820/12 will not turn a prop for a Twister using a 4S battery. ( I have to use a battery that is 105mm long due to space limitation) I found a 4S that fits that space.

So I am thinking I need to order the Cobra 2820/14. Am I understanding this correctly?

See the attached prop charts for both motors.
Thanks

The 2820/12 is a perfect fit for the F-Twister.  The 2820/14 is more powerful but it will use more battery.
 I had about 200 flights on mine when it burned.  11 x 5 or 6 APC props both directions.  In 3 blade, the 10 x 6 and the MAS 11 x 5 Wood.  The charts are for high RPM RC and are only useful for comparison.  We are different.  I used several 4s batteries from 2200 to 2700mah.

This is one that I used early on:
https://www.amazon.com/HRB-2200mAh-Airplane-Helicopter-Quadcopter/dp/B0711MT5FX/ref=sr_1_4?crid=2QOXPNEL6DUYD&keywords=battery+2200mah+4s+20c&qid=1648410518&sprefix=battery+2200mah+4s+20c%2Caps%2C83&sr=8-4

Thunder Power would be a better choice.  If your weight is over 50oz try a 2600 mah.  With the 2200's I only had about 18-20% headroom.  I like 30%.  Keep the "C" value between 25 and 35, we actually use around 20 and we don't have the "slam it to the firewall, zoom across the sky" boosts that you have in RC.

OR, you could just cough up the extra $10 and get a BadAss 2820-780 instead of the Cobra.

Curious how your nose got so cramped.  Most of my fights were using the Zippy 2700 4s 25c which is 134mm.

Ken

[Brent Williams]

The Cobra 2820/12 (970KV) with a APC 11x5.5e is a pretty solid, well tested 4s combo. 
Definitely more than adequate power and headroom for a Twister.  How heavy is your airframe?
I ran that combo in a 45oz'ish Gieske Nobler and it was very nice. 

[Paul Taylor]

Thanks for all the input guys. I really appreciate it.

I will go with the -12.

[Motorman]

Eflite Power 15 is a good motor for that too.

[Paul Taylor]

Curious how your nose got so cramped.  Most of my fights were using the Zippy 2700 4s 25c which is 134mm.

Ken

I put in a 3D printed motor mount. That might be the culprit.

[Ken Culbertson]

I put in a 3D printed motor mount. That might be the culprit.

That will do it!

ken