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Thread: need cg help


  1. #1

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    need cg help

    Hey racers,
    A friend of mine has an old viper Q500. It has full length ailerons, T tail and the engine mounts upright , yet the crank is no where near the thrust line center of the fuse. My question is whats the CG?
    I started at 3.38". I have since remover 1 1/4 oz from the tail ( a little at a time). It flew like crap at first, flew like crap when I took off 1/2 oz and still flies like crap with the rest off.
    When he got it, it had almost 2 ozs at the tail. My maiden was a total handfull and definately tail heavey, hence a removal process of that dead weight. I have 4 flights on it, and it still porpuses, so Im still taking throw rates down, but its next to nothing no (maybe 1/8" at most)
    The ailerons act like there is slop (cant trim) but the hinges and controls are tight?
    Any ideas here?

    For what its worth, Ive flown lots of quickys and other race type planes. Never have I had one this bad.
    Race101
    YS Engines
    Team JR AMERICAS
    Waymire Decaling

  2. #2

    RE: need cg help

    Marty
    I would set it to 2.625 to 2.75" That is what I fly the Viper Dog at. It has a viper wing on it.
    Kevin Matney 2 wrongs don't make a right But 2 Wrights make an Airplane
    www.Matneymodels.com

  3. #3

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    RE: need cg help

    Thx Kevin, is the dog using the old old viper wing?
    In fact I bet that I am close to 2 5/8 already. Has anyone heard of the crank of the engine being well below the fuse center line?
    Race101
    YS Engines
    Team JR AMERICAS
    Waymire Decaling

  4. #4

    RE: need cg help

    I got them from tower as a replacement wings
    Kevin Matney 2 wrongs don't make a right But 2 Wrights make an Airplane
    www.Matneymodels.com

  5. #5
    diggs_74's Avatar
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    RE: need cg help

    I guess I would start looking at the incidence on the firewall, wing and tail.. The center line of the engine doesn't have to be the center line of the fuse as long as it's straight.. Assuming the firewall is only 2.25" square, it can't be that far off anyway..
    Lee LaValley
    NMPRA# 33w
    www.ncplracing.org

    \"To finish first, one must first finish.....\"

  6. #6

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    RE: need cg help

    Hey Lee,

    we did discuss the incidence points. I will set the CG for sure , slow the throws. It just flies like something is wrong.
    Thx again guys
    Race101
    YS Engines
    Team JR AMERICAS
    Waymire Decaling

  7. #7
    diggs_74's Avatar
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    RE: need cg help

    The worst flying quickie I ever flew had a positive wing and negative tail.. It didn't matter what I did I couldn't get it to fly right.. It wasn't mine but the guy that owned it told me to take it and fix it or trash it.. I cut off the tail and reset the wing making sure everything was at zero.. Set the CG and it flew pretty well.. Then, promptly midaired with the guy who gave it to me the week before.. Carma I guess..
    Lee LaValley
    NMPRA# 33w
    www.ncplracing.org

    \"To finish first, one must first finish.....\"

  8. #8

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    RE: need cg help

    This is the old Hobbico Viper low wing I believe? They never did fly very good, at least I didn't think so and most were heavy pigs.

    The 2 5/8 - 2 3/4 sounds about right to me, could you possibly have a sloppy servo in there that is not centering properly? I'd swap out the elevator servo and see if that helps.
    Dave Norman
    29w

  9. #9

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    RE: need cg help

    Took another 1/4 oz off tail, reduced throws and it flew much better. I would never race it as it isnt 130 ish, yet flies good for this beginner just thinking of racing. We had to shim the L/G forward to accept the reduce aft CG. Then it seemed fine. i got 4 more set up flights on it today. Turns like a lead sled (heavy model). It is now flying with 1 1/2 oz of less tail weight. Cant believe it even flew with all that originally on it.
    Thx for the input guys.
    Race101
    YS Engines
    Team JR AMERICAS
    Waymire Decaling

  10. #10

    RE: need cg help

    The Viper Dog is set too 0,0,0
    Kevin Matney 2 wrongs don't make a right But 2 Wrights make an Airplane
    www.Matneymodels.com


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