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Help! Old Piper Cub Revamp

#1
I am trying to fix up a very old Piper J3 given to my son by a members of my local flying club. It is at least 20 years old and is a 71" wingspan balsa plane that may well have been a scratch build. It had a very old electric motor and esc that I could not get to work. The nose/cowling was carved from a solid piece of balsa and was set up for a off-set-geared, brushed motor. It has an 11x7 wooden prop.

I have decided on an 80 Amp Esc with a Turnigy Aerodrive SK3 - 4250-500KV Brushless Outrunner Motor. I decided on the motor based on a weight-to-power ratio chart I found online.

Can anyone tell me if that seems to be about the correct size/power motor for this plane?

The old motor said "Turbo '10' Plus" and "War Emergency Power Series" on the can. It was made by Model Electronics, Inc. of Seattle, Washington.

I plan to use a 6s battery with it.

Thanks for any help,

Scott "Kobur" Stevens
 

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#3
It sounds good. How much will your plane weight when it is ready to fly?
I beleieve it was about 6-7 pounds? I’ve lost the sheet I wrote the weight down on. Had to measure the wings and fuse separately. Also added the battery and motor.
 

quorneng

Well-known member
#4
According to HK this motor is only rated for 5s.
It appears the motor gets particularly hot when run close, or at, its maximum rating of 57A.
Are you planning on using the 11x7 prop? This is on the small size for this motor so it will not reach full power (only 850W?) but should at least eliminate any issues on a 6s battery.
I trust you have a Watt meter so you can check what is really happening. ;)
 
#5
According to HK this motor is only rated for 5s.
It appears the motor gets particularly hot when run close, or at, its maximum rating of 57A.
Are you planning on using the 11x7 prop? This is on the small size for this motor so it will not reach full power (only 850W?) but should at least eliminate any issues on a 6s battery.
I trust you have a Watt meter so you can check what is really happening. ;)
Must have missed the 5S max or read the 5 as a 6. Wonder if I can get it working on 4s. Not sure I’ve ever actually seen a 5S battery. Always seems to jump from 4S to 6S or even 8s. Don’t recall any odd numbers above 4, but the battery itself has markings like they do make them. Has options on the label for 5, 7 and 9 as well as even numbers of cells up to 10.

As for the prop, any suggestions?

I do have a watt meter, but use it rarely, not having any other behemoths like this one. I’ll need to dig it out of the toolbox and dusty it off.:)
 

rockyboy

Skill Collector
Mentor
#6
If you're still open to other motor suggestions, I like to use Heads Up Hobby because they publish real-world performance testing for almost all of their motors with different batteries and props.

So if you want to use the same prop as the plane has now, the following motor will put out this power on a 4s battery

4-Cell 14.8v APC 11 x 7E 88 oz. 47 amps 740 watts

http://www.headsuphobby.com/Power-Up-32-Sport-800kv-Outrunner-Brushless-Motor_p_1602.html

That should be very reasonable on a cub in the 6 to 7 pound range.

Or if you want some more power options, this motor will handle an 10x7 on 6s and crank out 960 watts for crazy vertical performance

http://www.headsuphobby.com/Power-Up-46-Sport-620kv-Outrunner-Brushless-Motor_p_723.html