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Thread: Glider Tow Hook

  1. #1
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    Question Glider Tow Hook

    Hello,


    I want to use a PA-18A-150 as a Glider tow hook, looking for STCīs the Schweizwer STC itīs no longer available, i dont know if the wings unlimited STCSA220SO can be used for this kind of operation.


    Do you know another STC that can i install for Glider tow hook operations

  2. #2
    Administrator Jon Delamarter's Avatar
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    Default Re: Glider Tow Hook

    Christhian,

    Our factory service center has a PA18 glider towhook for sale. Please call Vera at (509)248-1025.
    Jon Delamarter, A&P/IA
    Customer Support Manager
    Cub Crafters, Inc.
    jond@cubcrafters.com
    Office (509)367-5200
    Cell (509)833-6993

  3. #3
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    Default Re: Glider Tow Hook

    Quote Originally Posted by Jon Delamarter View Post
    Christhian,

    Our factory service center has a PA18 glider towhook for sale. Please call Vera at (509)248-1025.

    Jon,

    the Schweizer tow hook? i wrote to Vera some days ago looking for a STC but Cub crafters doesnt have not.

  4. #4
    Administrator Jon Delamarter's Avatar
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    Default Re: Glider Tow Hook

    I just spoke with Vera. She's going to have Stan take a look at the towhook they have in stock and find out what brand it is.

    Quote Originally Posted by Cristhian View Post
    Jon,

    the Schweizer tow hook? i wrote to Vera some days ago looking for a STC but Cub crafters doesnt have not.
    Jon Delamarter, A&P/IA
    Customer Support Manager
    Cub Crafters, Inc.
    jond@cubcrafters.com
    Office (509)367-5200
    Cell (509)833-6993

  5. #5
    Administrator Jon Delamarter's Avatar
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    Default Re: Glider Tow Hook

    Quote Originally Posted by Jon Delamarter View Post
    I just spoke with Vera. She's going to have Stan take a look at the towhook they have in stock and find out what brand it is.
    Vera says they have a Schweizer tow hook for sale for $1000, but no STC paperwork.
    Jon Delamarter, A&P/IA
    Customer Support Manager
    Cub Crafters, Inc.
    jond@cubcrafters.com
    Office (509)367-5200
    Cell (509)833-6993

  6. #6
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    Default Re: Glider Tow Hook

    The Schweizer tow hook is related in the PA-18 IPC as an Optional kit, i dont know if i can install this as a kit

  7. #7
    Administrator Jon Delamarter's Avatar
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    Default Re: Glider Tow Hook

    The Schweitzer tow hook does not appear in my copy of the PA18 Parts Manual. However, it is rumored to be in the flight manual.

    Click HERE to read a discussion over on supercub.org that may answer your questions.

    Also, you may consider the Tost tow hook.
    Jon Delamarter, A&P/IA
    Customer Support Manager
    Cub Crafters, Inc.
    jond@cubcrafters.com
    Office (509)367-5200
    Cell (509)833-6993

  8. #8
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    Default Re: Glider Tow Hook

    A couple of additional thoughts from someone who ran a full time soaring school for about 20 years.

    It would be interesting to test the release forces necessary with the rope pulling at 90 degrees at the maximum down force available on the horizontal tail surfaces at 75mph. We had close to 100,000 flights and never had a situation where the release did not function. The only scenario I can think of would be if the release lever surface had become "notched" from vibration and wear over time.

    In severe "out of position" situations where the tow pilot did not respond quickly by releasing his end, the tow rope would always fail before the tow plane reached an extreme attitude. I have heard the above story many times over the years, but have serious doubts that the force required to activate the release was too high to execute.

    The PA-18 STC hitch is welded so that it will remain oriented with the centerline of the aircraft. I have seen cases where bolt on hitches were simply added to the tailwheel mounting bolt. In these cases, sideways forces could rotate the tow hitch so that the release cable was pulling the release lever sideways so that no amount of force would trigger the release.

    Things can happen quickly, and the likelihood of pilots not pulling the release when things are going rapidly wrong is high. Instinct is telling them to regain control first and if the rope is not released by the pilot as step one, the aircraft can be lost.

    There are a number of considerations to take into account.

    Tow pilots can experience many thousands of flights without ever having to use the release, so, it is vital that the tow pilot is trained and drilled to reflexively pull the release in _any_ situation where loss of control is a factor. It has to be a reflex action... there is no time to think about it. The tow rope is cheap and the glider has the ability to recover safely from a rope failure at any altitude. Part of every preflight control check should include pulling the release without looking for it.

    The release cable must be steel and routed directly from the hitch to the handle. A release cable in a tube must be routed straight from handle to hook since a curved routing can result in sufficient cable length slack for the handle to be fully pulled and the release lever on the hook to remain closed. A rope or cord, especially nylon, can stretch with the same results. If you have concerns with using a release lever, using the European approach of pulling down on an anchored release cable running over the pilot's head offers simplicity plus the additional force generated by pulling an anchored cable 90 degrees to it's length.

    A properly "weak linked" rope will almost always snap when abnormal forces are encountered on tow or the towrope snags on something... in almost all cases, the pilot will not feel much when the rope breaks.

    The exceptions are when force is applied to the tow rope gradually. Examples of this are snagging a sagging power line or if the rope ends up in water. Especially critical is making a low turn over water. The rope will gradually increase it's pull as more ends up in the water, and, in a turn, the rope will gradually pull the tail down and to the inside of the turn until the aircraft stalls under full power with full down elevator and rudder into the turn.

    You can see that in the last scenario, the last thing on the pilot's mind would be the tow rope... he only knows that the aircraft is not responding to his/her control inputs even with full power applied to recover... hence, train constantly to pull the release as part of any control difficulties... even if there is no tow rope attached.

    Hope that this information is of value,
    Beverly Howard

  9. #9
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    Default Re: Glider Tow Hook

    One more thing...

    I looked and I have the PA-18 STC paperwork and STC drawings for the PA-18 tow hook assembly.

    I also have Cessna parts list pages showing the Schweizer tow hook installation using the tail tie down bolt on a tricycle gear Cessna.

    Ironically, the Cessna documents show using a rope release cord running outside the fuselage, through the pilot's door window and secured to the handle on the door post ;-)

    If there is interest, I can make copies of these documents and post them.

    Beverly Howard

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