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Thread: why the preference for graupner e-props?

  1. #1
    What's ATTI? stgdz's Avatar
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    why the preference for graupner e-props?

    This one has bugged me for a bit since I've looked into multi rotors but why are graupner e-props so sought after? In all my research and testing I've seen


    APC' are the most efficient in watts per amp
    Xoars produce the most thrust but at the cost of 10% amps over a comparable APC.
    Graupners produce about as much thrust as an APC but the same amp load as a xoar.


    So what is the draw with them? Most of the APCs require just a small amount of balancing and are no different than xoars when it comes to balancing. At ten bucks a prop a xoar prop strike really stings. APCs can take a hit without breaking.

  2. #2
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    One thing I have noticed is that with the graupners I need to keep a higher RPM. Since a multi-rotor's control surfaces are the props... the higher the RPM the more control I have over the aircraft. Thus, with the graupners I have more control. Also with the style of flying I like to do with FPV, APC props provide too much force. If I was using a heavy lifting aerial photography aircraft then I would use APC, but with FPV I find that the graupners give a better 'feel' with the higher rpms.
    I may be way off base here, but those are my thoughts..

  3. #3
    Banana Drone Flying Monkey's Avatar
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    Based on my tests the graupners under perform in max thrust AND efficiency (except for 14x8 it seems). A 10" graupner produces as much thrust as a 9x4.7 apc sf

    There's two reasons why they're good for multirotors...
    1. They come fairly balanced, better than most others. Require very little balancing.
    2. The shape of the blades... Cuts through the air better when the prop is run "sideways" Ie: APC slowflys were never meant to fly sideways, as we use them on multirotors. Their normal E-props have the shape common to graupners but at a much greater weight penalty. The graupners are lightweight and very stiff, so the multirotor is responsive and smooth, and when flown at high speed, the difference is realized.

    Hope this helps!

  4. #4
    Cor blimey, guv'nor!
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    I've never tried Xoars or APC props on my tri-copter before, but both GWS and Gemfly have exploded on me mid-flight, hence why I switched to Graupners. Graupners still need balancing though (just like every other manufacturer)

    Do APC do 10x5 CW and CCW props?

  5. #5
    FPV ROO speedstep's Avatar
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    Quote Originally Posted by stgdz View Post
    This one has bugged me for a bit since I've looked into multi rotors but why are graupner e-props so sought after? In all my research and testing I've seen


    APC' are the most efficient in watts per amp
    Xoars produce the most thrust but at the cost of 10% amps over a comparable APC.
    Graupners produce about as much thrust as an APC but the same amp load as a xoar.


    So what is the draw with them? Most of the APCs require just a small amount of balancing and are no different than xoars when it comes to balancing. At ten bucks a prop a xoar prop strike really stings. APCs can take a hit without breaking.
    The APC are efficient, but for taking video the little flex doesn't help the video.
    The APC are great for flying around trees and just for fun flying, because cheap as well

    The Graupners are great for taking video because they are stiff (no vibrations), but not as efficient , also light...

    And the reason why the Xoars are not that popular is because they are not listed in that many shops.
    Also I read the hubs of Xoars can be out of balance, but I reckon with wood you got more odds ( humidity etc.)
    Last edited by speedstep; 24th January 2013 at 12:28 PM.
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  6. #6
    FPV ROO speedstep's Avatar
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    Quote Originally Posted by Flying Monkey View Post
    Based on my tests the graupners under perform in max thrust AND efficiency (except for 14x8 it seems). A 10" graupner produces as much thrust as a 9x4.7 apc sf

    There's two reasons why they're good for multirotors...
    1. They come fairly balanced, better than most others. Require very little balancing.
    2. The shape of the blades... Cuts through the air better when the prop is run "sideways" Ie: APC slowflys were never meant to fly sideways, as we use them on multirotors. Their normal E-props have the shape common to graupners but at a much greater weight penalty. The graupners are lightweight and very stiff, so the multirotor is responsive and smooth, and when flown at high speed, the difference is realized.

    Hope this helps!

    Good thoughts! Remember we are all flying multicopters with plane props. I reckon the next big thing after "flashed" out of the Box BSC for multi rotors. Will be props specifically designed for multi rotors. More efficient and better to cut through air "sideways".
    And then variable pitch etc..

    Ultralight planes start to have variable pitch and the gas engine is designed to run efficient on 3500rpm and the prop just changes pitch to have the desired thrust.
    www.youtube.com/user/speedstep23

    Nothing Yaws like a Disco

  7. #7
    AMA 7082 Ham KG5BBE jerry.k's Avatar
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    "2. The shape of the blades... Cuts through the air better when the prop is run "sideways"

    "More efficient and better to cut through air "sideways".


    Props don't know they are running sideways! They also do not know we talk behind their back.

    They only know how to pull and pull harder when spun faste.r

  8. #8
    Banana Drone Flying Monkey's Avatar
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    Quote Originally Posted by jerry.k View Post
    "2. The shape of the blades... Cuts through the air better when the prop is run "sideways"

    "More efficient and better to cut through air "sideways".


    Props don't know they are running sideways! They also do not know we talk behind their back.

    They only know how to pull and pull harder when spun faste.r
    Incorrect. Have you flown multirotors before? Do you know anything about aerodynamics?

    What you are saying is that all WINGS are equal... no matter their chord, airfoil, twist or planform. Propellers act differently when flying sideways... Multirotors are even more complicated (and something that hasn't even been fully studied in a wind tunnel or with CFD - Computation Fluid Dynamics)... on a quad you have two props following the in the wake of the two front props. When transitioning from a 20 degree nose down pitch forward flight to a 0 degree level flight (while still moving forward) the rear props become fully immersed in the prop wash of the front props. Tricopters are dead smooth in this maneuver because the two front props are further out, and the rear prop is dead center, and does not get into the prop wash as much (depending on the lengths of the arms).

    A slowfly prop has a large chord and a lot of surface area... normal e-props like the graupner have a much narrower chord and a straight leading edge, and straight trailing edge. There's a lot less "wing area" to get dragged through the air. The props may not "know" or even care that they're being flown sideways but the MULTIROTOR sure does!! This is called Flight Dynamics... it tends to get a little dynamic...

    How about when a multirotor is pitched nose down 10 degrees for a slow forward flight... and how the air must make a 80 degree turn into the spinning blade and then downward? On a quad, a lot of air is "eaten" by the front props, and the rear props are a bit starved. Before changes were made to the PID firmware on the KK board you noticed this effect quite a bit... if you pitched forward, as soon as you built up some speed it would try to pitch back and level out... why? Because the front rotors are producing more thrust than the rear props.

    We could get into the theory and practical effects of blades advancing and retreating in airflow as well?
    Last edited by Flying Monkey; 24th January 2013 at 02:47 PM.

  9. #9
    Banana Drone Flying Monkey's Avatar
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    Btw, the RcTimer Carbon Fiber slowfly props are testing really well! More thrust and higher efficiency than any prop I've tested, but I haven't flight tested them yet... its raining here now

    They're expensive but about the same as graupners, and they're VERY stiff, but don't run them into anything, they'll shatter!! Oh, and be careful picking up carbon fiber shards, they can be really really sharp!

  10. #10
    Banana Drone Flying Monkey's Avatar
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    Edited post #8 to be more thorough.

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