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Old May 20, 2003, 10:54 PM
Forgot how to fly
Mike Parsons's Avatar
Atlanta, Georgia
Joined Oct 2002
10,201 Posts
Help with what prop for this motor and GB

Ok, I need help with what size prop to swing. This is going in Kyosho Cessna 180 (3.5 lbs). It has a stock 550 motor in it and...well, yeah right. So here is what is going in it to substitute. However, I dont know what size prop to swing with it. Do I stick with the 8X6 or can I step up a size or two for better thrust? Thanks to everyone in advance.

MEC Superbox 6.0:1
Endoplasma
Castle Creations Griffen 55 amp esc.

Mike
www.atlantaeflyers.com
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Old May 20, 2003, 10:55 PM
Forgot how to fly
Mike Parsons's Avatar
Atlanta, Georgia
Joined Oct 2002
10,201 Posts
The plane

The plane
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Old May 20, 2003, 10:56 PM
Forgot how to fly
Mike Parsons's Avatar
Atlanta, Georgia
Joined Oct 2002
10,201 Posts
The motor

motor
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Old May 20, 2003, 11:36 PM
RIP Ric
Andy W's Avatar
Marietta, GA
Joined Jun 1999
43,312 Posts
What battery did you have in mind? That little model won't carry more than 8 sub C's, I'd think, but on 8 cells with a 6:1 box, an 8x6 will draw about 5A! A 14x9.5 would be a better bet, or 10 cells (perhaps CP1700 to keep the weight down), 12x8 prop. Do you have the ground clearance, however?
..a
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Old May 20, 2003, 11:43 PM
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ScottS's Avatar
Houston,TX
Joined Mar 2000
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How many cells are you using?
With the 6:1 ratio you will need a prop much bigger than 8x6!
With 10 cells on that ratio a 12x8 would be about the smallest prop I would use, you could go up to about 14" but would want to use the throttle or brush life would be short. With fewer cells the prop size gets bigger.

If you aren't using 10 cells you might want to consider getting a different pinion to change the ratio and make the prop smaller if you are planning to use the wheels - unless it has enough ground clearance (doesn't look like it).

The 12x8 should pull around 25-26A on 10 cells per Ecalc.
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Old May 21, 2003, 07:58 AM
Forgot how to fly
Mike Parsons's Avatar
Atlanta, Georgia
Joined Oct 2002
10,201 Posts
Thanks Andy and Scott,
I was thinking of 8C 5/4 1800 MAH Hecells. They are rated at 26 amps. I also have some 8c 1100 mah Hecells and 10c 1100 mah Hecells rated for 16 amps. Would it be better to direct drive instead of using the gearbox? I can put new gear on it to swing a bigger prop. Another pilot in the group has a magnetic mayhem swinging the 8x6 DD in his. I was not sure how this would compare though. Thanks again guys.

Mike.
www.atlantaeflyers.com
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Old May 21, 2003, 08:17 AM
RIP Ric
Andy W's Avatar
Marietta, GA
Joined Jun 1999
43,312 Posts
Quote:
Originally posted by Andy W
..with a 6:1 box, an 8x6 will draw about 5A! A 14x9.5 would be a better bet, or 10 cells (perhaps CP1700 to keep the weight down), 12x8 prop..
Quote:
Originally posted by ScottS
..With the 6:1 ratio you will need a prop much bigger than 8x6!
With 10 cells on that ratio a 12x8 would be about the smallest prop..
He he.. great minds and all that.

Mike,
the Endo is no good for DD unless you have a fan (EDF) or a pylon (i.e. Kwik-E on 6 cells). That setup you have is perfect for a 3-4lb aerobatic model like an E3D or similar, but not for a sport flyer. A Magnetic Mayhem direct drive would work just fine with an 8x6, or you could drop a lower-ration gearbox on the Endo (3:1 or so) and swing a 'more appropriate' prop on 8 cells with the model you have.
..a
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Old May 21, 2003, 08:25 AM
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Dr Kiwi's Avatar
Chattanooga, Tennessee, United States
Joined May 2003
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8X6 v 12x8

Hi Foamflyer,

I don't think DD with a standard 550 will cut it. You'd have to run the numbers through MotoCalc to see what your current draw might be, but assuming you'll need about 28oz thrust for your 56oz plane, the LCRC calculator suggests you'd have to have your 8x6 spinning at around 12,000rpm! With a gearbox, a 12x8 spinning at only 5300 will give you the same amount (28oz) of thrust. To get over the ground clearance problem your best bet might be to look at about 3:1 with a 10x7 - provided your motor is capable of spinning that size prop at around 9000rpm. Otherwise get an AXI or Phasor!

Cheers, Phil
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Old May 21, 2003, 08:52 AM
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Chattanooga, Tennessee, United States
Joined May 2003
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Calculation

Sorry, I forgot you were substituting an Endoplasma! However, the gearbox/prop size argument still holds true. Using this motor calculator: http://brantuas.com/ezcalc/dma.asp [which I feel, tends to be a bit too optimistic as far as thrust output goes] it seems that DD would require at least 30amps to get the 10000-12000rpm prop speed with the 8x6. The 10x7 on 3:1 apparently might only require about 12-15amps to get the 7000-9000rpm you'd need for 28oz thrust.

Good luck, Phil
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