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3D Prop Selection

Old 06-15-2017, 01:49 AM
  #1  
dereckbc
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Default 3D Prop Selection

OK I have a basic idea on how to size a prop, but not quite sure of some of the trade-offs. To be specific I have a Extreme Flight 48-inch Edge 540 with a T2814T-820 motor using 3S 2600 mah battery and Castle 50 Amp ESC. The book only recommends using 4S 12 x 6 prop. Somewhere I picked up if using 3S to use a 13 x 6.5 prop. I do have Drive Calc program and know what props should work.

I also know the basic rules of half square like 12 x 6, 13 x 6.5, and 14 x 7. I can use all 3 prop sizes without over loading the motor or ESC. Obviously the 14 x 7 produces the most thrust, but does that make it the best for a 3D plane.

Hard to find information on what props to use on electric 3D planes. My gut tells me I want as wide of diameter as I can get, bur real life tells me that may introduce significant P factor in post stall maneuvers.

Anyone have links that explains the trade-offs? Example what props are best for Post Stall vs Extreme Maneuvers.
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Old 06-15-2017, 07:23 AM
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solentlife
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It really comes down to trial and error. Personally I hate SF props even though some swear by them.

As you already know .... diameter will give thrust .... pitch will give speed.

Verticals need diameter ..... flicks need pitch.

The balance of both is always a trade off .... but luckily with electric we have an advantage over wet fuel. Electrics can run slower and even stop ....
So that high pitch prop is less problem with electrics.

Example ...

My Zlin with wet fuel needs a 15x4 --- otherwise she just has too much low speed idle pull. The 15 is needed for vertical / hanging .... but 4 to tame the idle grunt and speed.
My electric Zlin runs a 15x10 ..... because I can stop / run slower than the wet fuel but get same manouevres etc.

I always aim for large diameter with reasonable pitch. Because you are using 3s instead of 4s .... you need to have greater diameter and pitch to compensate. I use a really rough and ready formula for this :

S x KV x pitch x diameter .... EF say 4S on the 800kv with 12x6 .... which gives 4 x 800 x 12 x 6 : 230400

Now you are using 3s on that motor .... so we play with numbers to get similar final result.

Let's say we take the 230400 and reduce it down ... 230400 /800 /3 : 96

96 is our prop factor .... and a 12" prop in that would be 8" pitch.

I would suggest a 13x7 for slow speed and control or a 12x8 for general.

Nigel
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Old 06-15-2017, 07:25 AM
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solentlife
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As to links .... I find eCalc good .... and the results it gives are actually less than real - so a safe factor.

Nigel
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Old 06-15-2017, 04:22 PM
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JetPlaneFlyer
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I've flown this plane with this same motor in various setups. It will be quite marginal for 3D work with a 3S battery and a 13x6.5 prop, it will be much better on the 14x7 but this will work a 45A ESC pretty hard. But better yet, run it on 4S as this gives much more speed for faster 3D 'stick banging' manoeuvres.

At the risk of slightly over-simplifying; diameter gives you thrust and pitch gives you speed. A larger diameter prop is also more efficient in terms of thrust generated for watt of power consumed. The 14x7 is better in all respects vs. the 13x6.5 so there are no downsides other than working the motor and ESC harder.

Last edited by JetPlaneFlyer; 06-15-2017 at 05:11 PM.
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Old 06-15-2017, 08:50 PM
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dereckbc
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Originally Posted by JetPlaneFlyer View Post
I've flown this plane with this same motor in various setups. It will be quite marginal for 3D work with a 3S battery and a 13x6.5 prop, it will be much better on the 14x7 but this will work a 45A ESC pretty hard. But better yet, run it on 4S
I do run 14 x 7 on 3S. My ESC is a Castle Lite 50 and meter pegs at 46 amps on a 14 x 7 prop.

I do have a couple of 4S batteries but that will require a 12 x 6 prop which reflects what the manual says.. On Drive Calc, with a 4S battery, the largest Prop the motor can handle is 13 x 4 APCE, and that produces the most thrust at 2495 grams @ 41 amps. With a 12 x 6 works out to 2662 grams of thrust @ 45.2 amps.

Think I might try a 13 x 4 with a 4S battery. Will not go real fast but should be excellent at Post Stall maneuvers, easy to control throttle, and not stress the ESC or motor.
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Old 06-16-2017, 12:55 AM
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birdDog
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13x4 grabs a lot of air. You will like the throttle response. Just fitted a 14x4 to a 2820 870 motrolfly on 4s in my 48 Yak. 55 amps is right where Ken says should be my limit. Blucore foam baffles all around to focus the airflow coming into that dinner plate looking cowl Should be an interesting next flight...

I forget if the Edge ships with baffles but when you start getting close to motor limits, it never hurts to focus the air on the motor a bit.

Last edited by birdDog; 06-16-2017 at 01:14 AM.
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Old 06-16-2017, 03:52 AM
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dereckbc
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Originally Posted by birdDog View Post
13x4 grabs a lot of air. You will like the throttle response. Just fitted a 14x4 to a 2820 870 motrolfly on 4s in my 48 Yak. 55 amps is right where Ken says should be my limit. .
Honestly I do not think a 13 x 4 is any problem with 4S on the motor or ESC. 41 amps. Less than a 12 x 6 @ 45 amps.
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Old 06-17-2017, 11:52 AM
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JetPlaneFlyer
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Yeah, a 13x4 on 4s should be great for slow work but will lack a bit of speed. I guess it depends what sort of flying you like to do but I'd recommend at least trying the recommended 12x6 on 4S as it's a pretty good setup all round.

If you want to really make the thing rip use a 14x7 on 4s with a Motrolfly DM-3615 750kv, this is my EF laser but the Edge performs just the same:
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Old 06-18-2017, 09:10 PM
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dereckbc
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Originally Posted by JetPlaneFlyer View Post
If you want to really make the thing rip use a 14x7 on 4s with a Motrolfly DM-3615 750kv, this is my EF laser but the Edge performs just the same:
Perhaps some day. Right now have factory stock motor and it cannot handle the 14 x 7 on 4S.
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Old 06-20-2017, 06:02 AM
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JetPlaneFlyer
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Originally Posted by dereckbc View Post
Right now have factory stock motor and it cannot handle the 14 x 7 on 4S.
Correct, the magic smoke would be released if you tried! The stock motor on 4S with a 12x6 has plenty of power and is a good all round balance, so nothing wrong with that.
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Old 06-21-2017, 12:47 AM
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dereckbc
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Originally Posted by JetPlaneFlyer View Post
Correct, the magic smoke would be released if you tried! The stock motor on 4S with a 12x6 has plenty of power and is a good all round balance, so nothing wrong with that.
Yes I am more than happy with the factory motor.. I spent a lot of time doing homework on this model before selecting all the bits and pieces.

I upgraded the servos to digitals with metal gears and higher operating voltage. Factory recommended Hitec HS-70MG, I used Hitec HS-5070MG. I upgraded the ESC to a Castle Creations Phoenix Lite 50 which gives me a little more current cushion on the motor, significantly more SBEC current, and the ability to run 8 volts to the servos and RX, I also upgraded the hinges to a Dubro pin hinges.

Lastly I consulted with a user that goes by the name Doc Austin. He convinced me to go with the 48 inch 540T Edge EXP because I have so many 3S 2200 mah batteries. With a 13 x 6.5 and 14 x 7 props is really more than enough power. When I do get comfortable with the plane, I do have a few new 4S 2500 mah batteries and a few 12 x 6 props when I think I am ready for the added speed. Right now I have all the control surfaces limited to 45 degree deflection. Since I used upgraded control arms,, control horns, and digital servos going to 80 degree deflection is just a matter of programming the servos for the extra range. Right now they only rotate roughly 100 degrees, and they can go to 180 degrees. I spent a lot of time getting the geometry right from the start.

Well that is I plan to try 4S in the future if I do not turn it into toothpicks first. I will say it is a fairly easy plane to fly. Not as easy as my Addiction X, but not a huge step up in skill to handle. Just faster landing speeds. Hell the Addiction X is super easy to fly and can land at 0 ground speed easily with throttle control.
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