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Thread: Razor Back Option

  1. #1
    dginok's Avatar
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    Default Razor Back Option

    I'm trying to decide whether I should install this on my Super Sport. Does anyone have an opinion regarding this feature, whether it is useful/desirable?
    Doug
    Super Sport
    912ULS
    Constant Speed IVOProp


  2. #2
    Senior Member
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    Default Re: Razor Back Option

    From pure asethics it looks good, is not hard to install. Don't know if it helps increase anything or not (haven't flown my SS yet).

    Dick B

  3. #3
    dginok's Avatar
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    Default Re: Razor Back Option

    Thanks Dick!
    Doug
    Super Sport
    912ULS
    Constant Speed IVOProp


  4. #4
    Senior Member MotReklaw's Avatar
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    Default Re: Razor Back Option

    I like it too, but no experience with how it performs.
    Tommy Walker in Alabama

  5. #5
    Senior Member jtpitkin06's Avatar
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    Default Re: Razor Back Option

    The razorback option applies to the model 7 SS. It is a 3 inch high dorsal fin extension to the vertical stab reaching forward and tapering to zero height at the rear of the baggage compartment.

    According to the supplement in the builder's manual it "does add to the yaw stability of the aircraft."

    The option is made from a 5 foot long piece of aluminum tube and a plywood rib. The parts weigh about 7 ounces. The increase in fabric is negligible.

    This photo shows the razorback tubing and the plywood support. It is bonded in place with Hysol at the rear. The front end of the tube slips over a weldment and is bonded to a fuselage cross member.

    John Pitkin
    Greenville, TX
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  6. #6
    Senior Member Geowitz's Avatar
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    Default Re: Razor Back Option

    Ahh yes, I just always called it a dorsal fin. Thanks.

  7. #7
    Senior Member HighWing's Avatar
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    Default Re: Razor Back Option

    I know of guys that are incorporating this idea on the earlier models as well. I have been told that it simplifies the fabric covering in that area. One thing on the IV, there is usually antenna mounting plates on the top surface of the fusalage, and extending the dorsal fin to the turtle deck will eliminate the use of these mounting plates. If going all the way forward, I would suggest cutting them out for weight savings. I terminated mine just aft of the forward plate as I still wanted the com antenna to be mounted there. For weight savings I also eliminated the wood rib most guys are using as I sort of thought that it was a bit of overkill as the linear length of the shrinkable fabric on each side of the tube is less than a foot and shrink pressure on the aluminum stringer would be minimal. I glued a couple of aluminum stand-offs under the rib similar to the stand offs on the side stringer - no wood there and longer runs between standoffs.

    Keep in mind that for the IV, it is not a kit option, but a builder design option and I am trying to work toward simple and light.

    Lowell
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  8. #8

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    Ma
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    Default Re: Razor Back Option

    I added one to my model 4 when I rebuilt it. I used a piece of 3/8" 4130 molly tubing and bent it and welded it in place. I dont know if it added any yaw stability or other benefits. I did it for aesthetics. There are photos in my profile.
    Good Luck~Cain B

  9. #9
    Senior Member dholly's Avatar
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    Default Re: Razor Back Option

    I did something similar on my Avid Mk-IV. A word of caution to any Avid builders considering this... the Avid flaperon counter balance weights are positioned on the flaperons so as to fit into this area with the wings folded... ie., watch your clearances... don't ask me how I know this.
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  10. #10

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    Default Re: Razor Back Option

    The dorsal came standard on my Super Sport. It might be a good idea to install one so that your plane looks as up to date as possible (helps with resale).

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