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Royal P-38 Electric Question

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Royal P-38 Electric Question

Old 07-10-2011, 09:22 AM
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Default Royal P-38 Electric Question

I am thinking about building a Royal P-38 this fall, and would like to try electric motors. After a few hours of browsing, and trying to understand the various parts of an electric power system, I am a little confused.

I picked a motor and battery, and reviewed their specs to see if I could make sense of all the information avaible. I'm hoping I can get some answers.

If I look at an AXI 282610 outrunner, the followin information is supplied.
Kv = 920
Volt Range 11.1V to 19.2V
Max Amps 40A
Suggest battery 3-5s

For a battery, I looked at a Prolite V2 4 cell 2600 mah, 14.8V
C = 20
Continuous current = 52A
Max current = 104A

Motor rpm is calculated by multiplying 14.8 x 920 to get 13,616 rpm

Here is where I get a little confused

Motor volt range is 11.1 to 19.2
Why is there a range?
Will an battery over 19.2 damage to motor?

Max motor amps is 40A
Will a battery feeding more than 40A damage the motor?
What is the difference between continuous and max amps?
The max battery current is listed at 104A which 2.5 times greater than the listed motor current of 40A
How do you calucalte the power in watts of this system (V*A) but I don't know which numbers to use.

I just chose these two items in an attempt to understand the math. I may have made a bad coice.
Would this battery kill the motor?
would two these power a 12 pound p-38.

I would appreciate any answers or suggestions. I'm a litte confused about all the numbers that turn up.

Thanks, Keith
Old 07-12-2011, 04:15 PM
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Default RE: Royal P-38 Electric Question

The bad choice is electric.......
Old 07-15-2011, 09:19 PM
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Default RE: Royal P-38 Electric Question

Hi Kelsey B

I have a Royal P38 that I built and first flew with Magnum Pro 45 glow engines in 2001. It flew very well at about 9.5 lbs dry with Romair retracts I had trouble getting both motors to transition throttle evenly and switched to lightweight plain bearing OS LA46s about 4 years ago. Better but I am tired of cleaning oil so am in the process of switching over to 32 size electric motors and Eflite retracts. The flying weight will be about 10. 5 lbs with 5000 mah 4s packs. I first saw a Royal P38 fly beautifully in the early 70s that weighed 14lbs with Merco 61s and fixed gear.

Royal kits have a weight problem based on their 60's construction methods. It is truly a lumberyard of carved blocks reminiscent of old control line models. For electric or glow it requires modification to build reasonably light. The first thing I did when starting mine (for glow power) was to get a Forstner bit set and cut holes in every former, doubler and rib in the kit. I hollowed blocks and wing tips. For reference I saved the cutouts in a milk carton and had about 1.25 lbs of throwaways before even starting assembly. This is the only way to go if you are thinking electric.

For electric you will need motors that run 4s Lipos producing about 600 watts each at full throttle. This will give you about 100 watts per lb on a 12 lb airplane. The H9 Twin Otter is a comparable size and weight. The Eflite Power 32s used on the H9 Twin Otter are the perfect size. I run 3 blade MAS 13 x 8 props.(1 pusher- one tractor) as per the full size P38. I am using a Power 32 knockoff from HobbyPartz/ NitroPlanes called a Monster Power 32 with a 60 amp ESC. I use a 5000 mah 4s pack in each nacelle and 2 recievers rather than long y leads. I have test flown this ESC-Motor-Prop combo on a Sig Kadet. Flight times are about 8 minutes at 2/3 throttle. 52 amps max on the ground which unloads to 45 in the air. I wouldn't go less than 4500 mah[img][/img].

It is a major undertaking but will produce an excellent flying; great looking airplane.

Break a leg

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Old 07-26-2011, 06:38 PM
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Default RE: Royal P-38 Electric Question

hmmm so this is whats been going on!

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