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Old Mar 22, 2010, 04:47 PM
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The 'Wack, BC, Canada
Joined Oct 2002
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Whatever motor and prop you use you'll want to prop it to draw around 70 to 80 watts per lb to achieve a more or less period correct style of flying. Actually that would be more power than the original .15 would have provided even at 80 watts per lb. The more generally accepted modern amount is 100 watts per lb but that gives darn near vertical climb ability. Not really something in keeping with this sort of model.

So you will need a motor that provides something near 75 x 3.5 = 260 watts. On a 3S pack that would mean 260 / 11 = 24 amps. So both of your motors are pretty much overkill in that area. Keep in mind that when they suggest these things to replace an "X" size glow engine they are typically expecting you to put then into a 3D stunt model.

And you'll want to manage to get this with an 8 or 9 inch prop. With 10 inch being about as much as I'd want to use. If nothing else but for the sake of the landing gear providing the clearance needed for grass takeoffs. Also an 11 or larger prop with high power will definetly begin to show signs of torque effects if you jam it on at slower speeds.

With that in mind of your two options I'd opt for the second one. But perhaps find a similar power motor but with a slightly higher Kv value so it's more in tune with a 3cell pack and getting the current to the right level with a 10 inch or smaller prop option. Even the second motor shows the smallest prop as the 10x6 which means they are intending it for use with 4 or more cells in series since it is the smallest prop they list.

If it were me I'd look for one of their motors that is rated for a max 350'ish watts so you'll still be running nice and cool at th 260 you'll be using. And I'd go for a Kv value of around 1100 so it will work with props in the 9 to 10 inch range with 3 cells so you cause the motor to draw the desired amperage. Remember that it's the motor and load on it that determines the max draw. Prop big to pull more current and small to reduce current at full throttle. But to allow this to work you need to have a motor that will work well with a specific range of prop sizes. That's where the Kv value comes in along with looking at their range of props and considering the range of cell count they list.
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