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Thread: what propeller to use?

  1. #1

    what propeller to use?

    I have a large Graupner slow flier that I recently aquired from an aquaintence. I don' tknow what model it is, but it has a fiberglass fuselage with balsa and monocoat wings. Wingspan is about 65 inches. I am trying to make this airplane flyable. It has a Speed 480 BB Race 7.2V motor, an electrifly C-25 Mini ESC, and a FlightPower EVO25 LiPo battey rated at 2170mAh, 7.4V, 2s. The amperage on this set up is currently around 33 amps at one half to full power. The propeller that is on the plane is a high pitch propeller that seems to be the most likely culprit for causing the load reading on the meter. Also, we suspect the length of the prop is too long also at around 6 inches. The previous owner installed the prop, but never flew it.

    My question is, what is the most appropriate propeller to use with this airplane to bring the meter reading in line to around 25 amps?

    Thanks for any assistance.

  2. #2
    Senior Member Jay Burkart's Avatar
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    Re: what propeller to use?

    Does the motor have a gear box on it?
    Jay
    SAM Grand Champion 2004.07,10,12

  3. #3

    Re: what propeller to use?

    Hi Jay. No, it does not have a gearbox.

  4. #4
    Senior Member Jay Burkart's Avatar
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    Re: what propeller to use?

    That is a high rpm motor made for something more like a pylon racer.
    It max's out at about 18 amps and is happiest with something like a 5x5 prop.
    with a 7.4 2S lipo and pushing it up to a 6 x 5 prop draws right at 17.5 amps or so.
    To use it on a slow flyer or slower flying airplane or sport airplane generally required a gearbox.
    But you would be hard pressed to find a gearbox to fit it anymore.
    Sorry but it really is not a good slow flyer motor.
    Regards,
    Jay
    SAM Grand Champion 2004.07,10,12

  5. #5

    Re: what propeller to use?

    Thanks for the reply Jay. Could you recommend a good motor to use for this airplane, using the other components that are already in it?

  6. #6
    Senior Member Jay Burkart's Avatar
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    Re: what propeller to use?

    Can you use a brushless motor?
    It is best that you can do that. There just is not much selection in brushed motors anymore.
    Also can you use a 3S pack if you want anything like aerobatic performance.

    What is the projected flying weight and what is the wing area.
    What kind of performance do you want?
    Maybe you can look at the Graupner website and find the airplane.
    Here is their URL:
    http://www.graupner.de/en/

    Thanks,
    Jay
    SAM Grand Champion 2004.07,10,12

  7. #7

    Re: what propeller to use?

    Jay, I wouldn't have any problem installing a brushless motor. As far as a 3S battery, I'm not interested in getting aerobatic performance from this plane. I plan on lazy leisure flying with this plane, plus letting my dad fly it, so I want to keep it reasonably docile. I'm pretty sure the plane isn't designed as an aerobat anyway. It's more of a motor glider.

    I looked at the Graupner web site you referenced, but did not find the plane. I'm pretty sure it is several years old, as it was originally designed to use NiCad batteries, according to the previous owner. I can give you some particulars about the plane though. the fuselage length is 33 inches long, including rudder. The wingspan is 56", with dihedral in the center of the wing and last 7" of the wing. 43" of the wing has a constant chord of 6.5 inches, with the last 7" of wing on each side having an elliptical taper. The wing area should be about 322" It is a high-wing design with the wing sitting atop a dorsal on the fuselage. I'm lousy at guessing weights, but I would say that the flying weight would be about 2 pounds, or similar to something like a Parkzone T-28. I hope this paints a useful picture. Can you recommend a motor/propeller combination using this information? :)

  8. #8
    Senior Member Jay Burkart's Avatar
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    Re: what propeller to use?

    Here is a great economy motor that I use a lot and really like it:
    SK400XT, This motor mounts from a X bracket on the rear, make sure you can mount it.
    These are due back into stock soon.
    9 x 3.8 prop PN P09038
    Prop shaft adapter 3 mm shaft PN MJ4698
    About a 15-18 amp ESC something like a Jeti JEE018
    A 3S lipo on this one.
    If you want to use a 2S lipo then you need to go up to a 11 x 3.8.
    I like it best with a 3S it has power when you need it but can throttle back and cruise forever.

    Thanks,
    Jay
    SAM Grand Champion 2004.07,10,12

  9. #9

    Re: what propeller to use?

    Thanks very much Jay.

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