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Ducted Fan Efficiency

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  • Ducted Fan Efficiency

    I am currently designing a plane that will need to be able to carry a five pound payload, but I also want to be as fast as possible when empty. I have heard some great things about jets and EDFs in the RC realm, but I need to know if there are any big drawbacks if any. The plane will most likely be a balsa and carbon-fiber composite, and I was wondering what kind of stress these types of engines put on the fuselage. Also, provided this is my best bet, what are reliable brands for purchase.

  • #2
    Re: Ducted Fan Efficiency

    Welcome Disk.

    It is difficult to truly answer your question but here is some things to be aware of. First, ducted fans produce an air flow many times greater than a prop but they also lack the thrust of a prop due to the shorted diameter of the prop/fan. For hauling cargo, this means that the plane will be slow to get up to speed and will not respond that crisply when you change throttle in the air/ground. As for stresses, there are very few that I can name. A well balanced fan unit will turn around 40K rpm but will have very little vibration. As mentioned above, the small fan diameter will create only a modest amount of torque so that should not be an issue. Ducted fans are power hungry as moving air at a high speed takes a lot of juice. Gas turbines also have this issue as the power produced by the fuel powers the turbine and creates part of the thrust, but they also drink fuel in large quantities so there that weight issue. Electric fan units need larger batteries to help supply the power needed and to allow a plane to fly longer than a few minutes.

    So, just from your questions I kind of doubt that an EDF unit is really the right choice. You state that you want to carry 5 lbs which is a lot in model terms. If you have a plane that is capable of this payload, it would likely weigh in around 10 lbs itself. You could get something closer to a 5 lb. plane but you would sacrifice strength and performance. Speed and lifting capability don't really go together well. High lift wings just aren't designed to go fast.

    Sorry for the downer but there is a reason you don't find any supersonic transport planes in the world.

    Good luck

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    • #3
      Re: Ducted Fan Efficiency

      http://lmgtfy.com/?q=Supersonic+transports
      <smiley image="smiley_ninja.gif"/>

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      • #4
        Re: Ducted Fan Efficiency

        And we all know what happened to the SST. Not a practical plane for carrying heavy loads.

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        • #5
          RE: Ducted Fan Efficiency

          Has anyone tried a EDF on a Multiplex Funjet Ultra? I want to try a 70 mm unit. Any ideas or comments? The Doctor

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