How much space do you need between props?

Discussion in 'Cinestar Misc' started by Dave King, Feb 21, 2014.

  1. Dave King

    Dave King Well-Known Member

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    When I had 500mm booms and 15 inch props my cinestar fit inside the trunk of my altma just fine. It actually had a little bit of room to clear. Now with the 550mm booms and the 16 inch props I can't fit it in their with the props on. The question I have is how much space do you need between the props? Currently I have about 1 7/8" inch between adjacent props and I was wondering if I cut the booms down slightly if it would give me the needed clearance. My question is how much space do I really need to keep? Can I take them down to 1" space between them? Is there any adjacent prop wash that will be worst if I narrow the space between props? I don't want to affect the flying characterics.
     
  2. Michael McVay

    Michael McVay Active Member

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    Well, the stock CS8 with 450mm booms and 14 inch props has 1/2 inch or less between the tips. I always thought this is what gave it the "frisbee effect" in the wind - lots of upward loft in the wind without altitude hold on. After flying an X8 and even a CS6 with 14 inch props I am convinced that they fly better with more space between the props. Certainly someone on the forum will have a more technical explanation, but that has been my experience.

    Having said that, for someone who does a lot of flying, taking the props on and off between each job would be a real pain and certainly increases the chances of making a mistake at some point.

    Overall size and wind stability are two of the reasons I went in the X8 direction with my last build.

    Good luck with the test flight of the new props! Hoping they really help for you...
     
  3. Dave King

    Dave King Well-Known Member

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    Hi Michael

    The copter flew very well with the 500 booms and the Xoar props. I wish I knew the spacing between props with that setup. Does anyone else have any input as far as how the spacing between the props can affect in flight performance?
     
  4. Tim Joy

    Tim Joy Active Member

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    Can you just push the booms into the center a little bit so you don't have to cut them? I was considering doing this so I could have 550 and 500 adjustability on the same build, but I don't think they have that much room before they will touch, but it might be enough for your purposes.
     
  5. Michael McVay

    Michael McVay Active Member

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    I'm sure there are a number of people here with 500mm booms and 15 inch props that could get you the measurement of the space between the prop tips. If you end up without a number, I have a spare CS8 center hub and some 500mm booms I could put together and mount a couple motors and props to measure for you.

    ...Or, you could always slide 2 of your motor mounts in 50mm and put your old 15 inch props on to measure. That might be quick and easy for you too.
     
  6. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Dave:
    I'm pretty sure that the props will be generating prop tip vortices, however, these, in my experience will be projected downwards not laterally. So I don't think there is likely to be much lateral interaction between the prop blade tips of two adjacent motors -- there might be some -- e.g. compression/rarefaction effects, but it's not immediately obvious to me what practical effect this might have on the amount of thrust the props produce or their ability to respond to speed change commands. Also, two adjacent motors are going to be changing speed continually, so the blade tips won't be that close most of the time.

    As to how close the blade tips can be -- well, let's put it this way, if you put them too close, they will automatically self-adjust to a length where they will not be too close together any more. It will only take about half a revolution, depending on the rotational relationship between the two props. That's a complicated way of saying you'll hear a very distinctive crunching sound as the props self-adjust. ;)

    Andy.
     
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  7. Gary Haynes

    Gary Haynes Administrator
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    Self adjusting props. :D Someone should patent that idea. Would mean you only need to manufacture one length, say 28" in case you want to run a mongo copter...
     
  8. Steve Maller

    Steve Maller UAV Grief Counselor

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    If you made them out of wood, they could adjust in both directions. It just might take a little while for the wood to grow back.
     
  9. Dave King

    Dave King Well-Known Member

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    I can to test but I can't push them with the wires running through because they aren't long enough.
     
  10. Janne Hoglund

    Janne Hoglund Member

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    On my ¨small¨ std Mikrokopter Okto2 I use 11 Inch props.
    To be able to do that every second prop is raised 20 mm because the props overlap by 10-15 mm, and this copter does fly very well indeed!!
     
  11. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    You forget my day job, gentlemen.
    Bearing in mind that a patent claim must clearly and specifically describe the invention and be expressed in the form of a single sentence:

    Claim 1: An aeronautical propeller wherein the blades are manufactured with built-in lines of reduced strength, where said lines traverse the blade from the leading edge to the trailing edge, running through then entire structure of the blade, where said reduced strength lines are placed at predetermine distances along, and at 90 degrees to, the long axis of said blades for the purpose of failing under impact and thus permitting said blades to automatically adjust their length without damaging the aerodynamic properties of the surviving innermost part of said blade.​

    Claim 2: The invention of claim 1 wherein the propeller may be made of material incapable of growth such as ABS plastic or of living material such as wood and thus be capable of longitudinal growth to re-adjust out to a precise maximal length which may be between said lines of reduced strength.​

    You read it here first. ;)

    Andy.
     
  12. Janne Hoglund

    Janne Hoglund Member

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    For easier mounting and asembling I have adopted Tabs idea of having my Cinestar motor cables on top of the booms instead of inside.
    At first it may not look as nice but you soon get used to the new look ;-)
     
  13. Dave King

    Dave King Well-Known Member

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    Thanks Andy. I have a couple 500 booms left over and I'll measure that tip to tip and see how that measures. I think if I have 3/4 of an inch clearance it should be enough. I hope :eek:
     
  14. Dave King

    Dave King Well-Known Member

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    I pushed the booms in as far as I could go before they were hitting each other. I was able to get the booms i about 3/4 to 7/8 of an inch inside the hub. I then put the props back and on and remeasured. Theres about 3/4 of an inch of space between the props. I then rechecked my measurements and I was able to fit it in (barely).

    Anyone think 3/4 of an inch space between props is going to cause a problem?
     
  15. Michael McVay

    Michael McVay Active Member

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    I think you will be OK. I just measured a stock CS8 and they are a little under 1/2 an inch apart. I don't prefer them that close (I think it makes it float a little more in the wind - however, a stock CS8 is also much lighter), but I would also not want to take the props on and off every time I had to put it in the car.
     
  16. Dave King

    Dave King Well-Known Member

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