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Watt"s up

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  • Watt"s up

    I have a ARF Sig 54 electric airplane that weights 5.5 .lbs with a 4s/5000 lipo included. I'm running a Eflite 46 with a Avian 80amp speed controller. I started off with a xora 13x8 prop and initially thought that it flew great(getting back into hobby after ten years) But now she seems a bit slow,so after reading and reading I bought a watt meter. The results I'm not so sure about so would some one with knowledge about these things help interrupt my finding. Thanks in advance for your help. The 46 mfg says that the motor will go up to 800 watts.I did get that with the 14x10 prop but she swings real close to the ground maybe one inch clearance . I do not have a 13x10 yet but tested a 12x8,13x8 & 14x10. Also one of the props was a wood Xoar which drew more watts than the APC prop of the same size.Click image for larger version

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  • #2
    Hello flyguysc1 and welcome to the Squawk.

    There is various sources on the WWW about power requirements for electric RC fixed wing aircraft but for general information here is a good rule of thumb to go by.
    Trainer > 75-100 watts/lb
    Sport > 100-125 watts/lb
    Warbird > 125-200 watts/lb
    Aerobatic/3D > 200+ watts/lb

    You're Sig 4 Star 54 is considered a sport airframe which puts it into the 100-125 watts per pound power requirement range.
    You indicated that it is a 5.5lb airframe which indicates that it will require in the range of 550-687 watts of power to fly satisfactorily.
    According SIG's product page for this model the specs say to use a 500-800 watt motor for an airframe that weighs between 5-5.5 lbs.

    So to interpret your power readings, here are my recommendations.
    First, your motor and ESC selection is satisfactory. The 80A ESC has plenty of overhead which is good.
    The motor having a 670kV on 4S will be turning a prop in the 9916 rpm range which is approx. the area of 10K in RPM's used as a target which will be good.

    The 12x8 prop is just too lacking for power.
    The 13x8 Zoar is the better choice of the two 13 inchers if you are concerned with ground clearance.
    The 14x10 is way more power than you need but could be used if you decide later to up the performance into mild 3D.
    I personally run scale warbird props with only 1 ground clearance and the 14 inch prop wouldn't cause me any concern on this airframe.
    Hope ya find this info helpful.
    Best regards,
    Warbird Charlie
    HSD Skyraider; FlightLine: OV-10, Sea Fury; FMS 1400: P-40B, P-51, F4U, F6F, T-28, P-40E, 1700 F4U & F7F, FOX glider; Freewing: A-6, P-51; VQ: P-39; Dynam: ME-262, FW-190, Waco; ASM A-26; ESM F7F-3; LX PBJ-1 EFL CZ T-28, C-150

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    • #3
      Ended up with a 13x10 pushing 800 watts at 57amp Thanks for your help.

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