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Old Aug 06, 2011, 04:19 PM
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What Motor

Hi All I'm building a glow plane that I'm converting to E flight..The plans called for a 40-46 4 stroke..Plane weight 3 1/2 lbs.What E motors will be equal to the 40/46 4 stroke??

Thanks Dan
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Old Aug 06, 2011, 04:29 PM
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Ken Myers's Avatar
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How about an E-Flite Power 46 or Monster Power 46?
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Old Aug 06, 2011, 04:46 PM
Jack
USA, ME, Ellsworth
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Note: I missed the "four stroke" thing in spite of it being clearly stated. The numbes below are not right for four stroke motors.

The rule thumb is that displacement in cu. in x 2000 = equivalent power in watts.

.40 x 2000 = 800 Watts

.46 x 2000 = 920 Watts

If you know the prop size and battery voltage you want to use, you can use that to figure out the Kv you want.

If it is a common plane you may be able to find some other conversions that have already been done on it in the Glow to Electric Conversions forum:

http://www.rcgroups.com/glow-to-elec...nversions-247/

Jack
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Old Aug 06, 2011, 05:55 PM
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.46 four-stroke.... not a glow or diesel... therefore the cubic inches x 2000 is excessive. For a 3.5lb plane 350W-400W should be enough.

http://www.horizonhobby.com/Products...odID=EFLM4025A.... should be plenty.
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Old Aug 06, 2011, 05:55 PM
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Jack,

I know you know this, but the 'rule' you stated is for 2-stroke engines, and is actually a bit above the 'normal' two stroke output in shaft horsepower (shp).
Shaft horsepower equates to watts out.

An O.S. 46 LA 2-stroke in FlyRC, July 2010 using an APC 11x6 sport prop and 5% nitro had a shp of 0.60 which is equivalent to about 446 watts out and with a 75% efficient power system about 600 watts in. That would be multiplying only by 1300, not 2000. That LA is a low power 2-stroke, so it is not too surprising. 1500 may be more typical than 2000, but ya pays your money and takes your choice.

Even an O.S. 95AX on 10% nitro has multiplier of only about 1500 for watts in when using a 15x8 prop.

I have data on some larger 4-strokes, including a Saito .82 and .72 that show a multiplier of 1100 for watts in might be about right. Again, these engines are not know as 'power houses'.

I've collected data and calculated shp for several 2-stroke and 4-stroke glow engines. One 4-stroke gas and a couple of gas engines.
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Old Aug 06, 2011, 06:09 PM
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Another important thing to keep in mind

From my friend Tom Hunt:

Electro-Active by Tom Hunt, Fly RC, August 2011, p52 – p56
Glow to electric conversion tips – Part 1, Theory

p. 52 Unlike a glow engine, a motor doesn’t not have a narrow operating range. When you buy and ordinary .40 cu.in. glow engine, you generally put a 10x6 prop on the shaft and it turns around 12,000 rpm. If you are lucky, it develops about one horsepower. The first thing we should be leaning when flying e-powered models is that if we are swinging a “glow size” prop at “typical glow” rpm on our models we are doing something wrong.

The biggest advantage to electric flight is to choose a motor/prop combination that swings a larger prop that better matches not only the way you want to fly, but the ability of the model to fly in the manner intended. Calling a motor a “46” and using it on a 40 glow size model may work well for a sport model that, because of the design, cannot swing a much larger prop. However, it would not be the “best” answer for a lumbering 40 glow trainer with lots of room for prop growth. That “46” motor can be run on three LiPo cells effectively with a large prop and fly a light-weight (but large) model and it can be run on 5-6 LiPo cells on a fast moving sport model with a much smaller prop. The eclectic motor is capable of running effectively at 1/3hp as well as it is at one horsepower! This is why we should not give the motor a “glow” equivalent designation. It makes things easier for the marketing manager, but not for the modeler.
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Old Aug 09, 2011, 06:46 AM
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What Motor?

Hi All
Soo then I'm going to NEED a 25 size motor, or 350 watts..

Thanks Dan
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Old Aug 09, 2011, 07:54 AM
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What you should get is a motor rated for 450W and run it at only 350W!

http://2dogrc.com/product/dualsky-xm...-450w-21-speed

maybe even the 3548.
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Old Aug 09, 2011, 10:25 AM
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DBono

You asked the wrong question in post 1.

Much better to give details of the model and the style of flying. Then the answers could suggest.... the motor Kv & voltage..........and a matching propeller.......in addition to the motor size.
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Old Aug 09, 2011, 12:48 PM
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Motor

Quote:
Originally Posted by DBono99 View Post
Hi All I'm building a glow plane that I'm converting to E flight..The plans called for a 40-46 4 stroke..Plane weight 3 1/2 lbs.What E motors will be equal to the 40/46 4 stroke??

Thanks Dan
Try here: http://www.bphobbies.com/view.asp?id...1&pid=B3915415 Bob
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Old Aug 09, 2011, 06:01 PM
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What Motor

You asked the wrong question in post 1.

"Much better to give details of the model and the style of flying. Then the answers could suggest.... the motor Kv & voltage..........and a matching propeller.......in addition to the motor size."

1.The "model" is a sport/pattern plane( 58" WS/wing area 540 Sq. In./Weight 3 1/2 lbs.Just want A nice relaxing type of plane to fly..
I will be using 3 cells Lipo's, so I'm probably going to need a motor that can handle 40 amp..If need 450 watts

Thanks Dan
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Old Aug 09, 2011, 06:59 PM
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How does this look then: http://2dogrc.com/product/dualsky-xm...t-450w-32-size
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Old Aug 10, 2011, 08:41 AM
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Motor

Hi All Was looking at this motor, with Apc E 11x 5.5 on 3's??
http://www.headsuprc.com/servlet/the...5-Sport/Detail
Thanks Dan
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Old Aug 10, 2011, 09:21 AM
Jack
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And as they point out, there is another motor there at Head's Up that is nearly identical in every respect:

http://www.headsuprc.com/servlet/the...lectric/Detail

Good reports have been seen on both of those motors, I don't have any experience with either one. I guess maybe my choice would come down to the colors (red and black or gold and silver) that best matches the colors on my plane?

Jack
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Old Aug 10, 2011, 12:23 PM
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Also as they point out, both motors are near their max amps (to be used for only 60 sec) on any prop larger than a 10x5.

Larry
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