Props?

Discussion in 'Electronics' started by Funnyfoot, Oct 3, 2015.

  1. Funnyfoot

    Funnyfoot Airman

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    Ok so I wanna know what the different kind of props are and what the difference is? APC? Some have an E on the end? 5x4 or 6x3 (not counting 6 x 4). Thanks!
     
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  2. Thelic

    Thelic Ace Pilot

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    Crash course time!

    The first number represents the diameter of the prop in inches, as I'm sure you've figured out.

    The second number represents the pitch of the prop in terms of how far it wants to advance in a single rotation. So a 6x4 prop wants to advance 4" per revolution.

    Consider the following setup:
    6x4 Prop
    2200Kv Motor
    11.1V 3S LiPo

    The Kv of the motor says it will want to spin at 2200 RPM/Volt applied.

    2200 * 11.1 = 24,420 RPM!

    Now we know the RPM so we can determine the speed that the prop wants to screw through the air.

    24,420 RPM * 4" = 97680inches/minute = 148.8km/h

    Now obviously your plane isn't going to go 148.8km/h, nor is the air going through the prop, there will be some losses. Quite a bit in fact.

    The best way to think of the second number in a prop designation is its "gear". Lower gear props will spin up faster and give you more "torque" for acceleration. They are also easier on electric motors as they will draw less current to spin. Similar to a car, you could try to start in 4th gear, and you may even be able to, but its going to be hard on things and its going to work the crap out of your engine. Planes are the same way, but consider 1st gear to be a 6x3 prop, 2nd to be a 6x4, etc.

    Also remember that larger props are designed to spin at lower RPMs, this means they need a higher pitch number to cover the same ground as a smaller one. For example you probably won't be able to find a 8x3 prop as its simply too low of "gear" to be useful. I believe the lowest common one in 8" size is a 8x3.8 which is considered a "slow fly" prop.

    Real aircraft use variable pitch props and are able to change the pitch with airspeed. For small RC stuff we're basically locked into a pitch and have to make the best of it, which is why a 6x4 "2nd gear" prop is advised. It gives us a balance of airspeed and enough acceleration to keep us out of trouble. Similarly if you only could have one gear in a car you would likely choose second.

    Lastly the "E" means its a high RPM electric prop. It can run the same RPM on an electric motor as a similar size prop would run on a glow engine. Contrast this with the "SF" for "Slow Fly" where it wants to be ran about 1/2 the RPM. SF props deform under high RPM and may be dangerous if ran at high RPM.

    DO NOT USE AN E or SF PROP ON A GLOW ENGINE, GLOW ENGINE PROPS ARE MUCH HEAVIER BUILT!
     
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  3. Funnyfoot

    Funnyfoot Airman

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    Ok thanks so much! This helps a lot. So is this a suitable 6x4 prop for the profile F16 MK2? http://www.valuehobby.com/6-x-4-electric-prop.html
     
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  4. Thelic

    Thelic Ace Pilot

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    Yes, that looks good.
     
  5. Funnyfoot

    Funnyfoot Airman

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    Thanks! I'll order 4. Haha
     
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  6. Thelic

    Thelic Ace Pilot

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    Yes, don't be shy with buying a number of props. They do break!
     
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  7. CRMERC

    CRMERC Ace Pilot

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    I just went out and bought two of what ever props I could find in 6 inch by what ever. I have 6x3 , 6x4 and 6x5 in pitch. I even found a few 3 blade props. So far the 6x4 and 6x5 work best but I have not run the three blade.
     
  8. Fz1Fazer

    Fz1Fazer Ace Pilot

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    I love the EMP 6x3E, the EMPs are a bit larger than the number says and the shape is a bit different, in a pusher config like our midmounts they can give you more trust with the same motor than an APC 6x4E.
    I use it for example with my profile Mig-29 v1 with a D2822-2600kv 38 gram and it's better than the APC 6x4E @2s and 3s only the topspeed is a little better with the APC caused by its higher pitch.
    I think you should try one at your F-16 MkII ;)
     
  9. F1wanabe

    F1wanabe Administrator

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    Funnyfoot, some motors do better on emp than they do on apc. The higher kv motors like the 2550 kv smjv2, 2600 kv zoom 370 and fp 2700 kv get a little bogged down on apc props and all the thrust on these small motors comes from high rpms. I'd compare that to an F1 engine-they make max power at 20,000 rpms. If anything limits the rpms (like a prop with more pitch) then the thrust suffers. The added rpms that you get from emp props is due to the more gradual pitch on them whereas the apc props have a big 'bite' section towards the middle. The 6x4 emp is good, but those motors really shine on a 6x3 emp prop! The good news is that they have been notoriously out of balance right out of the package and I would spend 10 min per prop sanding the heavy blade little by little until balanced. However, I just opened up a new package today from heads up rc and the 6x3 emp prop was almost totally balanced! This is a big deal since they cost half that of the apc. I'll post a picture of the two side by side so you can see. Apc is grey, emp is black...
    [​IMG]
    [​IMG]

    Our Website :www.frcfoamies.com
    My youtube :www.youtube.com/user/gstrysky
     
  10. Baufritz96

    Baufritz96 Ace Pilot

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    Props to you, sir.
     
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  11. Funnyfoot

    Funnyfoot Airman

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    Please tell me that was an intentional pun. I found it hilarious.
     
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  12. Baufritz96

    Baufritz96 Ace Pilot

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    It was :p
     
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