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Prop recomendation, Rimfire 55 ?

Discussion in 'Electric Motors, ESC's, Batteries, and Chargers' started by js-rc, Jun 16, 2016.

  1. js-rc

    js-rc 70cc twin V2

    I built this electric Yak a couple yrs. ago for another guy & he just gave it back to me cause it immediately zooms off to the left as soon as it get airborn. I've tried everything with the rudder & throttle & it always does it. It flies great after you get it straightened out ! I'm thinking if I drop down in size & pitch or either one or the other it may not have so much toque on takeoff ? It's a 6 cell battery & Rimfire 55 & I have an APC 15 x 8 on it now.
    What size would be good to drop down to ? ! Any suggestions are much appreciated !!
    Thanks, John !
    49dimes likes this.
  2. 49dimes

    49dimes Damn I'm hungry

    How is the thrust line on the plane? Can you "shim" in right and down thrust by adding washers to the motor x mount?

    I just maiden my MXS. It has a similar size motor (5055 SK3 Aero Drive 485kv). 15x6 carbon but has the "APC" shape. Works well but I think a 16x8 would be better. 900watts and 39 amps WOT with 15x6 and 6S pack.. 16x8 should put me at around 1100watts and 45 amps WOT. Motor makes 1750watts max @70amps.
    Any thing smaller than your 15x8 is wasting watts. You could try a 14x10-12. But again I think you loose to much and don't think it will fix your problem. Try a bigger and not smaller prop and double check your motor thrust line.
    js-rc and stangflyer like this.
  3. stangflyer

    stangflyer I like 'em "BIG"!

    Have to agree with this. Any design of power plant hanging from the front of our planes will pull hard left if thrust angle is not correct. It is just a natural occurance of torque and rotation. Also, sudden and full throttle will also cause this. Typically, if thrust angle is correct a plane will still have a tendency to pull a little to the left. Hence the right rudder input on take off. However the closer we approach the actual flying speed of the aircraft, the need for right rudder input becomes less. I would do as Kelly suggests. Shim down and right on the motor. You may find you will have to move the motor to the left of the firewall to keep the crankshaft centered of where it needs to be.
    49dimes and js-rc like this.
  4. js-rc

    js-rc 70cc twin V2

    Thanks Guys !! I did drop down to a smaller size prop & it worked great !! I had a perfect take-off & it was flying great but not as much power as with the old prop, but then I got in a little trouble & was turning to bring the plane back & it kind of spiraled into the ground. I broke a rertact & knocked the cowl around a little bit but the plane is in good shape otherwise. I just for some reason can't fly these electrics very well !!
    Thanks again Rob & Kelly !!
    49dimes and stangflyer like this.
  5. stangflyer

    stangflyer I like 'em "BIG"!

    Ugh...that sucks. Glad it survived. {Mostly} You are very welcome. Don't feel alone on the 'lectric plane blues. If it don't make noise, I can't fly it. LOL
    js-rc and 49dimes like this.

  6. 49dimes

    49dimes Damn I'm hungry

    Some smaller planes just cant handle all that power! lol Glad a smaller prop worked but it sounds it was short lived for now. Get it fixed up and try a 16x8 and gradually/gently apply power during the take off roll. Of course 2 to 4 degrees of right thrust should help considerably! Performance electrics have some of the most HUGE power to weight ratios there are! Also the speed control may help you also if you can program in "soft start" or even dial in some expo or a throttle curve as to tame the torque down a bit.
    js-rc and stangflyer like this.
  7. js-rc

    js-rc 70cc twin V2

    Oh, now that's a good idea on programming the speed control !! It has a 65 amp one from Buddy RC but we traded this plane arounf & now now nobody has the instructions for it. Maybe it's on the webb somewhere though so I'll look for it !!
    Thanks Kelley !!
    49dimes likes this.

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