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Thread: Please Need Help with Finger Skirt Design

  1. #1
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    Default Please Need Help with Finger Skirt Design

    Hi all

    I am bulding a hovercraft model, and it is the first time for me to deal with finger skirts.
    I saw a picture of the finger pattern and i dont know the design procedures, i tried to figure it out on my own but i couldnt.
    I have a PDF which gives only a simple drawing with some angles and doesnt go through the exact steps.
    can anyone please help me on how to get to the final pattern of the finger skirt

  2. #2
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    Default Re: Please Need Help with Finger Skirt Design

    Depending on the scale of your model the fingers are probably going to be tiny, so I don't envy you - sewing them will be a real challenge. Are you looking for a segmented skirt design, or is your model of a commercial hovercraft with a loop & finger skirt - like a tube around the perimeter with little fingers underneath?

    For a segmented skirt there are design principles contained in the "Constructors Guide" which results in the traditional curved shape segment. There is a simpler segment design which is more square in appearance - see the attached design guide. If this is the sort of thing you want, it is pretty straightforward. If you need any help with this sort of design please get in touch through the PM system.

    SKIRT DESIGN.pdf

    Good luck with the model build.

    Kevin

  3. #3
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    Default Re: Please Need Help with Finger Skirt Design

    i am not buiding a small scale hovercraft, it is about 70 cm * 50 cm, and i am buiding this to only test the segmented skirt because i didnt deal with it befor and idont know any thing about it, and after i reach the proper design i will build a real one .
    The PDF i ve got mentioned two types : extended and byconical, and you will see that the segment is not standing on its edge, there is a curve in the pattern to make the edge trimmed to reduce wear,
    but it doeaent say how to get this pattern.

    I dont know how to get the constructors guide.

    thank you for your quick repond and waiting for you
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  4. #4
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    Default Re: Please Need Help with Finger Skirt Design

    Your ratio of length to width is rather more square than most small hovercraft designs. Most practical single seat hovercraft are in the region of 3.0m long x 1.8m wide, so your model is about 1/4 scale - this means that segments would be about 35 to 38mm wide when scaled down.

    The Constructors Guide is published by the HCGB and available for purchase through the on-line shop - it describes the design of the extended type segment in your diagrams. I can't say I've ever seen the bi-conical type of segment although it has similarities with the skirt design I attached earlier. The sketches you've been given are very indicative and do not reflect current practice. The lower skirt attachment point would normally be about 100mm up from the junction of the planing surface and the floor. The contact point of the skirt to the ground can be calculated when the weight of the craft and the dimensions of the craft are known, but as a rule of thumb I use 125mm on typical single seaters. Any skirt material to the right of line BC on the sketches is wasted - it does nothing, its not under tension when the skirt is inflated so the large curve shown on the developed drawing is unneccessary. All that extra contact area is just adding friction, a well designed skirt should sit up on its tips.

    Hope this helps

    Kevin

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    Default Re: Please Need Help with Finger Skirt Design

    Quote Originally Posted by foster2958 View Post
    The lower skirt attachment point would normally be about 100mm up from the junction of the planing surface and the floor.
    i am sorry i dont understand this one.

    and one thing else, in the PDF you attached i tried to draw the main panel but i dont know angles AQP & QAS and their relation with the side view angles.
    QP in the mail panel is equal to QP in the side view right, but i dont know AS in the main panel and PS in the main panel should be equal to PS in the side view right.

    please could you help me with this.

  6. #6
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    Default Re: Please Need Help with Finger Skirt Design

    The lower skirt attachment point is point S on my section drawing - it is about 100mm from the bottom corner where the planing surface meets the floor.

    The easiest way to develop the main panel is to draw everything full scale and measure the edges including the diagonals; AP and SQ, and the distance AQ. These will then allow you to draw up the main panel. If you measure all the lengths on the section and transfer these to the main panel drawing you shouldn't go wrong.

    Once you've worked eveything out if you post your sketches/drawings on here I'll gladly check them for you.

    Kevin

  7. #7
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    Default Re: Please Need Help with Finger Skirt Design

    yes i will do this thank you

    but you didnt tell me the angles AQP and QAS, it is a major obstacle for me now....

  8. #8
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    Default Re: Please Need Help with Finger Skirt Design

    The angles will depend on many factors, the width of the skirt segment, the hover height, the angle of your planing surfaces etc. If you follow the instructions, draw it up in section full size and then measure all the sides and diagonals you will have enough to draw up the pattern. You don't need to know the angles. Think of it as a series of triangles. With the length of all three sides known you can construct a triangle correctly every time.

    Have a look at the attached drawings showing a section through the plenum/side view of the skirt and compare with the developed plan of the segment - this is taken from a design by the students on a course I'm running at the moment.

    SKIRT CONSTRUCTION LAYOUT.pdf
    skirt section.pdf

    Kevin

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