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  1. #1

    Join Date
    Nov 2003
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    MURRIETA, CA
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    Viper /Great Planes

    I have my first nelson engine and its spinning over 18,000 RPM. I also have a great planes
    Viper and was wondering if the frame would hold up to that kind of speed. Of course the
    engine will turn more however, what I tach today was enough for me.

  2. #2

    Join Date
    Jun 2003
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    houston, TX
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    RE: Viper /Great Planes

    it will with several of the fuse mods
    wrap 2 oz fiberglass 2" width around top to bottom and side to side on the nose 4 inches from the nose
    re inforce wing hold downs
    fiberglass/carbonfiber prefered on sides of fues at the le of vtail
    re inforce landing gear platform

    do a search in this forum for my pics of what i have done

    MAKE SURE wing has no twists and that elevator is on thrust line.

    i have 7 vipers with nelsons and jett engines. mike helsel has flown one of mine at 174 on the gun out of turn 1. my best was 163

    i have a jett q500 that dub setup and exceeds 19500 with a 8.8x8w on the ground.

    this plane may come out a little heavy but is a lot of fun to fly.

  3. #3

    Join Date
    Dec 2001
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    RE: Viper /Great Planes

    Do you know if it is a Short Stroke, or Long Stroke Nelson? What prop are you running? 18,000 sounds low and should not be run there.
    Dave Norman
    29w

  4. #4

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    RE: Viper /Great Planes

    I have no idea if it is a long or shortstroke but I suspect its a short stroke
    on the crankcase there is the letter "N" and no other mark

  5. #5

    Join Date
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    RE: Viper /Great Planes

    An LS normall has "LS" inscribed on the muffler near where it meets the motor.

    What prop were you using?

    I would suggest 8.8" x 8.75 and if it won't peak over 19,000 use a smaller prop. It needs to peak over 19k on the ground or it just won't unload like it should.
    Dave Norman
    29w

  6. #6

    Join Date
    Dec 2001
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    Upplands Vasby, SWEDEN
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    RE: Viper /Great Planes

    Hi!
    It seems the weak spot on the Viper is the area just in front of the stabilizer. My second Viper nearly crasched due to a crack just there (se picture below) and I have seen other Vipers go down because of the stabilizer leaving the fuselage just there. It's just the 3mm balsa sides that's supports the stabilizer, which isn't enough when the you use a Nelson or Jett engine.
    The remedy is to support the fuselage inside with thin 0,4mm plywood or some more 3mm balsa and hard balsa stringers or something like that and /or adding 25g glassfiber/laminating epoxy on the out side.
    I did both when I repared mine.

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    Jan Karlsson - Supplier MVVS Products


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