Aerodynamics - Trailers?

Discussion in 'Hydrodynamics and Aerodynamics' started by Dhutch, Aug 14, 2012.

  1. Dhutch
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    Dhutch Junior Member

    Fair enough, sounds like its creeping in then! Its basic but cheap and very low maintainance way of getting a variable rate spring and a bit of damping.

    Didnt manage to upload any photos last night but will have a dig and see if I can get anything up while at work.


    Daniel
     
  2. Dhutch
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    Dhutch Junior Member

    Its a photo of a photo, and not a great one at that, but it gives some idea beyond a line drawing. Makes it look shorter than it is, but dimensions are as per the opening post.
    [​IMG]

    Daniel
     
  3. TeddyDiver
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    TeddyDiver Gollywobbler

    A bit oftopic but what's on the left in that picture? Looks there's McPhearson suspension lurking or smth :)
     
  4. FAST FRED
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    FAST FRED Senior Member

  5. Dhutch
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    Dhutch Junior Member

    Will send you a PM to keep it off the thread, but thats the kitcar mentioned above.
     
  6. Petros
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    Petros Senior Member

    Pulling that must feel like pulling a drag chute, you can do much better. A quick and dirty test will tell you a lot. Get a bunch of heavy cardboard boxes and several rolls of duct tape, make a nice swoopy fairing for the front the trailer, the fenders and the light panel (or better, relocate the light panel to mount on the rear doors), and than take it for a drive. Try and duplicate the shape of modern cars on the front, smooth rounded shape.

    or try the coast down test I mentioned later. You will notice a difference. than you have a basis for making a permanent one. A rounded front end on the trailer could also be used as a storage compartment for light weight irregular shaped items.
     
  7. Dhutch
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    Dhutch Junior Member

    In a work. YES!

    This is a model ive just thrown together at work. The plan would be to add the profile onto the front of the trailer, keeping weight down as low as possable, with the purple section hinging up and over to provide assess.

    As its a one off I would proberbly be fabricating it (steel frame clad with 0.8m steel or similar) rather than producting it from GRP so smooth compound curves might be a bit of a no-no although and the middle corners might end up looking more like the mitred top corners, altough I could have a go a getting a little creative with the tin-snips and seal it all up from behind with pu sealant...

    [​IMG]
    Click to enlarge


    Daniel
     
  8. DCockey
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    DCockey Senior Member

    The design you posted looks very good. Mitering the corners would have a negligable detrimental effect on drag.
     
  9. DCockey
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    DCockey Senior Member

    It is very easy to increase drag rather than decrease drag with add-on vortex generators. Various forms of vortex generators have been around for a long time, at least thirty years.

    From the website Fast Fred cited:
    Airtab® has undergone NASA wind tunnel tests in the United States and extensive road trials in North America, Australia, and Europe. Road trials have delivered direct fuel savings of up to 2.8% with Airtab®s installed on trailers only and over 4% savings on tractor-trailer combinations.
    Interesting that nothing is said about the results of wind tunnel tests.
     
  10. SamSam
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    SamSam Senior Member

    Google this "aerodynamic trailers" .

    These two sites show a back end remedy.
    http://www.ats-green.com/
    http://www.atdynamics.com/

    This site shows (page 6) the drag coefficient of simple shapes.
    http://www.dieselmidatlantic.org/diesel/frieght/conferencecalls/9_27_06/MADCAeroOvw2.pdf

    If you could somehow make a big bulb shape and put it on the front, it would help a lot. If you took a sheet of something and bent it into a big U shape and attached that to the front of your trailer, that would help a lot even if the top was still flat (looking at it from the side). Three or four pieces of rounded plywood attached to the front of the trailer like shelves, could be a form. Some sheet metal or a fiberglass flat panel could be attached to the side of the trailer, bent around the form and attached to the other side.

    Depending on how the trailer is made and how involved you want to get, you might be able to remove the front flat piece and slanted piece, replace it with a curved front and end up with a trailer with more inside space that also tows easier.
     
  11. Petros
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    Petros Senior Member

    I would not use vortext generator to try and reduce drag. the idea is by energizing the air with little foils (that create an attached vortex on the surface), it helps keep the flow attached and reduces drag. It only works on certain shapes, and to me as a former aerodynamics engineer, it means the design was a mistake from the beginning.

    I would not use metal at all, but either foam strips or light wood strips to form a compound shaped front end fairing, and than glass it. Just like you do with strip built hulls, you can do the same with foam strips over a temp cardboard or wood mold.

    I would make much larger rounded shape, like the front of aircraft, the front half of a tear drop shape. If you are going to glass it anyway, why not take the time to form it up properly. Take heavy card board and cut a series of profiles that you tape on the front of the trailer, support them with cross bracing tapped between the profile shapes, and than hot glue 1/4" thick foam strips over the front. fill the gaps and sand it smooth, than glass it. pull off the fairing and remove the cardboard form, than screw the fairing to the front of the trailer with flush screws and sealant. Or you could make a light frame and hinge it on the top edge to allow access.
     
  12. Dhutch
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    Dhutch Junior Member

    Yes, but there is a limit to how much space there is between the car and the trailer, as the trailer is six foot wide and only three feet from the back of the there isnt really room while maintain access to the hitch/brake/etc.
    - Furthermore being that close, means there must be a fair effect from its following the car. And also, as said, three dimensional curves are a no-no as im not planning to get the fiberglass out.


    Daniel
     
  13. SamSam
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    SamSam Senior Member

    Get a van.
     
  14. Dhutch
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    Dhutch Junior Member


  15. Petros
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    Petros Senior Member

    how about a skin-on-frame fairing? attach wood or aluminum (or plastic?) stringers on the top and sides of the trailer at the leading edge. Pull them together at the front, and attach them to the leading edge of the trailer, stretch nylon or polyester fabric over it and paint with 4-5 coats of latex paint. I could make such a fairing for about $40 and in about 2-3 hours.
     
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