Lightweight Aluminum Open Car Trailer(s) and Mods

Discussion in 'General' started by xcel, Feb 15, 2020.

  1. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi All:

    I have a call with an OEM about a possible event drive involving some EVs next week and I am working down some of the prelims in case it goes through.

    I spent much of the day looking over lightweight aluminum car trailers including tire selection, brake selection, various configurations, weight, and GVWRs. The top two aluminum lightweight car trailer brands appear to be Featherlite and Sundowner but a smaller concern that has been in business since 1968 captured my attention.

    The brand is called Hillsboro and not only do they offer the lightest weight 16', 18", and 20' length dual axle trailer(s) at ~ 1,300 - 1,500 lbs. with a GVWR of 7,770 lbs., they also appear to provide one of the most aerodynamic designs despite that not being a design goal. A side benefit is that they are also one of the least expensive aluminum trailer offerings in the industry with new ones on trailer lots around the country running at just over $6k with no extras. The exact way I would spec it before modifications.

    Here is one the employees highlighting the company's all-aluminum car hauler in detail. Pretty slick design ideas if I do say so myself.

    Hillsboro Aluminum Open Car Trailer


    Std. equipment includes the following:
    • 15" alloys with ST205/75R 15C Trailer tires - Stiffer sidewalls than car tires
    • 2-15/16" coupler at 16" height
    • Safety chains
    • Safety breakaway system
    • 2000 lb. rated tongue jack
    • (4) 6,000 lb. rated in-bed tie downs (2 fronts, 2 rears)
    • LED lighting all around
    • 20" load height
    • (2) 7'-6" Long x 12" Wide HD Ramps (rated at 2000 lbs. ea.) with built in anti-rattle storage compartment(s) & doors
    • Built in stabilizer jack at each rear corner
    • (2) removable aluminum fenders
    • 82-1/2" between the fenders
    The most important items were that the trailer weighs less than 1,500 lbs., provides a minimum GVWR of at least 5,000 lbs., and has at least 80" between the fenders. Other positive attributes include a flat load floor with little to no obstructions to air flow, little in the way of compartments or extrusions under or off to the side of the trailer itself, longer 7’ internally stored ramps from the rear trailer edge providing a lower breakover angle, ramps that butt up closer to the top of the platform providing a smoother transition to the load floor and again, a lower breakover angle, LED tail and side marker lights to reduce ancillary loads to the tow vehicle, and finally LED taillamps built into the rear trailing edge and not hung off some angle aluminum behind the finders like other trailer manufacturers.

    The Hillsboro 16' fits most of the bill. However, consider the underside detail in one of the advert pics below.

    [​IMG]

    See all of the exposed aluminum cross members perpendicular to the air flow? I would need to either have multiple thin aluminum or stiff plastic sheet(s) glued or welded to the entire underbody to smooth out the air flow beneath the trailer.

    Around the axles, possibly a teardrop wing shape from one side to the other clamped onto the axles themselves to smooth air flow around them?

    And finally, I would need to do something about the wheels and fenders. For the fenders, a removable side extension of some sort so that the entire wheels sides are covered down to about 3/4 of the wheel diameter on both the outside and inside. For the wheels, maybe even some mooncaps over the outside and some center cutout mooncaps for the inside of the rims. Also, (2) wheel strakes just in front of the front wheel to help guide air down underneath that front tire.

    Does anyone have any other or better ideas that I can toss around the discussion if some quick trailer mods would be necessary? I would probably approach Hillsboro directly for the customized setup to pick up and tow away from their factory in Hillsboro, Kansas if the project sees the light of day?

    [​IMG]

    I get into some the craziest damn ideas and sometimes they pan out. Other times they go flat as a balloon with no air. If it goes, you will all be some of the first to know. It may involve a Guinness World Record of consequence too. ;)

    Wayne
     
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  2. The belly pan wouldn't seem too hard to do. My Airstreams have always had a covered underside (except the axle). Aluminum panels riveted to the rails.

    [​IMG]

    A drive event with EVs needing an aerodynamic car hauler trailer. I'm envisioning an EV truck pulling something that weighs no more than 3500 pounds.
     

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  3. litesong

    litesong litesong

    Aerodynamic applications only added to the most obvious & seeable trailer aspects are no aerodynamic considerations at all. Adding stuff to make up for their lack of aerodynamic forethought is crippling the whole idea of aerodynamic efficiency. There are no other companies with "from the ground up" aero ingenuity.... maybe even access to a wind tunnel?
    In America, I may already have the answer to my question.
     
    Last edited: Feb 16, 2020
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  4. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi James:

    Thanks for the underbody pic of an Airstream! I was hoping you would see this as you have towed plenty for hundreds of thousands of miles with more miles of towing experience than possibly the rest of the membership combined.

    2020 Hillsboro Aluminum Open Car Trailer

    [​IMG]
    Notice how the ramps align to the top of the load floor vs others where there is as much as a 1" to 1.5" step.​

    I have some concerns with trailer flex distorting a series of welded on underbody aluminum sheet panels but what if they were slid into welded on channel brackets and then somewhat flexible automotive sealant applied? They could flex with the trailer without breaking a weld or bending/creasing the sheet, it should prove to be a non-noise junction if the channels are designed properly, and would solve the underbody air flow problem. Just thinking out loud because I do not have any experience with trailer builds. A car uses tabbed plastic aero covers into sub frame or exterior sheet metal but a trailer only has the structure mounting points and drilling into them would cause all kinds of rigidity and structural failure points. That is why I was thinking of an automotive adhesive of some sort. The steel to steel automotive adhesive is stronger than a weld but is not flexible. The type of sealant used over the roof to body seam for example is far more pliable but still extremely tough. Also, would thin aluminum sheet slid into a channel not screech and groan?

    Moving onto the fender extensions, at least on the outside seems pretty straight forward as they bend and weld the aluminum sheet at the plant. I would just need the fender jig to be opened up for that exterior extension. The backside however could be a problem as it appears the removable fenders are brackets to fit within recesses to the front and rear sides locking it in. I am not sure what Hillsboro could do to bring an extension around while securely fastening it down for long term durability?

    I have other ideas for the steps and the short diamond plate extrusions off the front and rear of the fender skirts. They sure do look like they would generate vortices. I am thinking along the lines of an F-18 Super Hornet with the extended aero strakes that actually hold more fuel. The cut could come from the front of the trailer and work its way back to the fenders. The longer the cord length the better for reducing drag. The same idea on the back of the fenders with a longer trailing taper to the rear edge of the trailer. Instead of the diamond plate, I would use sheet but with black anti-slip tape. That would surely be well under the boundary layer creating no separation vs Diamond plate that would be tall enough to see airflow interrupted.

    The full-length tie down rail may be a strong design but that is a lot of open gap causing a mess with regards to clean air. I could close that up with simple duct tape top and bottom along the entire length of the trailer. The Four 6,000 lb. in-bed tie downs would be how I strap the vehicle to the trailer in this application.

    I would also revise the tongue design so that it would keep the fully covered A-box section but the platform would be raised to the trailer load floor so there would be no step. I would lose the spare tire section just below the load floor but it would surely improve the trailers aero. One of the Featherlite open car trailer models (3182) was designed and built similar to what I would like to see and I thought it was a really good idea.

    Featherlite Model 3182 Open Car Trailer

    [​IMG]
    Notice the enclosed A-Box section and how it aligns almost to the top of the load floor itself.​

    I have no idea what the air flow off the back of the tow vehicle into the gap between the rear hatch and trailer would look like so maybe the last paragraph above would be moot? A cleaner trailer no matter where it is in relation to the tow vehicle has to improve drag buy a few points?

    All questions I will ask Hillsboro if the project receives the greenlight.

    Given it is a Guinness World Record, I wonder if Hillsboro would be interested in comping out a trailer with the aero mods and possibly even upgrade their lineup with a new "Aero" model like I have in mind? What is a short drive from Southern CA to Kansas and back in the name of science anyway? Road trip!!! ;)

    Wayne
     
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  5. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi James:

    Another question for you. Is there a decent off the shelf TPMS monitor with the ability to see individual tire pressures available within the industry? I do not need it incorporated into the tow vehicles displays - I am sure Ford, GM, or RAM have figured that out already - but a simple dash top electronic display that communicates with each wheels TPMS sensor and displays the individual tire pressures? I can have TPMS sensors installed at any Discount Tire. I am just hoping to hear of an off -the-shelf box that can communicate with the industry std. TPMS sensor and learn which wheel it is actually displaying.

    The working goal is close to 5k pounds but not exceed it. With this ~ 1,350 lb. trailer and a just over 3,500 lb. car, it meets the target mass.

    Wayne
     
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  6. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi Litesong:

    While there are few actual trailers that have been wind tunnel tested, there are minor design upgrades that go along ways to eliminating points of drag. The minor mods like what I have described above are pretty easy. All of them in fact may actually enhance the beauty of the trailer which is already great looking due to the bright all-aluminum structure and load floor. If I had the time, I would also attack the wheels from the axle and bearings to the tires to reduce rotational friction and the tires RRc. Today's latest vehicles include some very interesting friction reducing metallurgy and design in this realm but the trailer manufacturers have never been tasked toward the same outcome. They will soon but just not to the level we are experiencing in our vehicles today. Not yet anyway?

    The Cd of the towed vehicle will be in the .23 to .25 range. The tow vehicle is in the 0.27 to 0.28 range. Those are some very low Cd vehicles to begin with. Why screw it up with a trailer that is not up to the task other than looking pretty? I hope some of my ideas help solve that underbody air flow problem in particular.

    Wayne
     
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  7. BillLin

    BillLin PV solar, geothermal HVAC, hybrids and electrics

    Hi Wayne. Looks like an interesting project and potential world record.

    I was wondering if there was any need for the air to pass between the trailer and the car being carried. You already have the bottom and sides of the trailer being taking care of aerodynamically. The trailered car's top and sides take care of much of the rest of the aero envelope. I was thinking maybe something like gaitors for the car could bridge the space between the trailer load surface and trailered car. It could be something rigid that sits around the front and sides of the car, but atop the open trailer. Something like an upside down front air dam but big enough to give room for the trailered vehicle not to touch.

    Those 6000 lb straps and other fastening hardware would not even feel the air this way... It could also afford a tiny amount of protection for the trailered vehicle.
     
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  8. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi Bill:

    Big rigs pull the trailers as close to the cab as possible to reduce the drag induced by an ever-larger gap between trailer and cab. I wish I had some leeway with a gator type solution too but when you turn, that gap has to be flexible. A Big Rig is sitting on a fifth wheel and the manufacturers of the rig have an adjustable fore and aft fifth wheel in order to allow the swing of the trailer not to interfere as the tractor trailer combination is turning sharply.

    The same problem arises with a bumper/frame/chassis mount Class V hitch. When turning sharply, the trailer needs room between the hitch and rear of the tow vehicle to not interfere and cause major damage. If a gator system were designed to let out on the outside of the turn and pull in on the inside, your design would actually work pretty slick! A solid sheet for air guidance however would cause a lot of problems in the turns and thus why I have never seen one on the open road.

    I seem to remember seeing something like what you described in an old Popular Mechanics magazine from the 1930s or 40s. It did not go anywhere way back when. :(

    Wayne
     
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  9. BillLin

    BillLin PV solar, geothermal HVAC, hybrids and electrics

    I think you took my proposed solution further forward than I had intended. Think of the reverse air dam within the confines of the existing rectangle of the carrying surface.

    For the turning problem and an air diverter further up, I've seen trailers with V shaped plow fronts to split the front air. That might help in this usage.
     
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  10. BillLin

    BillLin PV solar, geothermal HVAC, hybrids and electrics

    Coincidentally, I just got a set of valve cap replacement style TPMS sensors with a display unit for use on the dash. Works well. Pressure and temperature is reported for each tire. USB rechargeable but supplemented by a built in solar panel. This was $40 on Amzn when I bought it a couple weeks ago. Not the cheapest available. The concept works and I did not feel any tire bouncing from being out of balance. You can look through similar devices and find one for the intended use/expected tire pressure range. Transmission distance seems pretty good. I've tested well beyond the distance between trailer wheel to tow vehicle dash.

    The reason I got this set is because the TPMS sensors on my winter tires have run out of juice. Yes, the tires are getting older now. I bought the wheel/tire combo originally for the 2012 PIP.
     
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  11. I've never used them, but here is one from Amazon


    A friend had one from camping world and like it. Maybe this:
    https://www.campingworld.com/tiremi...hNzcQSstS29zVKerEYkaAn5uEALw_wcB&gclsrc=aw.ds
     
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  12. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi Bill:

    Is this what you are speaking of?

    [​IMG]

    These are the std. air dams from Hillsboro (top), Featherlite (lower left), and Sundowner (lower right).

    It sounds like you may have the TPMS model that James linked? I have not done any research on that yet. I would like to purchase the internal TPMS sensors and have them communicate with an outside box.

    Wayne
     
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  13. BillLin

    BillLin PV solar, geothermal HVAC, hybrids and electrics

    They're all much taller than I was thinking, but the Sundowner is closest. I would also include more along the sides, like a tall curb level.

    Here's what I meant by the V front. This one is still taller than I had imagined, and I still think side skirts along the sides of the trailered car can help. Lets say about 6 inchest to 1 foot tall running from the bottom of the tapered front down to at least the trailer fender leading edge. Yes, it would interfere with getting in and out of the vehicle. :)

    sundowner tapered front.jpg
     
  14. BillLin

    BillLin PV solar, geothermal HVAC, hybrids and electrics

    I hear you... internal TPMS would of course be a more elegant solution. I hadn't looked for that kind since it wasn't what I wanted. :)

    Here's a picture of the one I got.
    rocboc.jpg
     
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  15. BillLin

    BillLin PV solar, geothermal HVAC, hybrids and electrics

    Here's an internal TPMS system.



    internal TPMS.jpg
     
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  16. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi Bill:

    I discarded any of the air dam addons and the open trailers all offer them.

    Think of placing an airplane fuselage on a trailer. A Cd of maybe 0.15 and a frontal area of 3.14 * r**2.

    Now place an air dam covering the entire width of the trailer and 3/4 the height of the same fuselage. A Cd of maybe .45 and a frontal area of 7 ft X 4 ft.

    The naked fuselage has a far lower drag than any air dam. The target vehicles have a Cd of between 0.23 and 0.25 plus straps and a frontal area less 2/3 that of a trailer air dam.

    I also rejected any framing or stops as options above the load floor for the same reason.

    I am just not sure what kind of airflow separation occurs behind the tow vehicle with a towed vehicle on a trailer behind it. Is the air dam close enough that its Cd * frontal area (drag) is negligible?

    Thanks for the TPMS links! Those could be quite useful going forward.

    Wayne
     
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  17. A few tests on Youtube but haven't found any with a pickup and trailer yet.



     
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  18. BillLin

    BillLin PV solar, geothermal HVAC, hybrids and electrics

    I hear all that and it makes sense to me. The underlying question I have is if you take the low Cd car and put it in the wind tunnel, then compare that with the same vehicle with no airflow going underneath it, which is more aerodynamic? Intellectually, I know there would be more frontal area, but would the Cd be lower making up enough to lower the overall drag? So *if* a lowered air dam on the car can lower overall drag, I was looking for ways to implement that on the trailer bed without modifying the trailered vehicle. The side part of the idea was to deal with real world air flows that would likely still go under the car with a simple front air dam.

    I like your ideas to modify the trailer fenders.

    Beyond all the thoughts around a loaded trailer's air flow, it would probably matter what the speeds you'll be driving and what kind of vehicle is doing the towing and how dirty the air will be at the leading edge of the trailer. If you're going for records, are you looking for a high speed towing efficiency record or an overall efficiency of car/truck plus trailer/load totaling maybe 5-6 tons being moved a certain distance at Wayne Gerdes speeds? Don't know your vehicle doing the towing so allowing for maybe 5000 lbs towing another 5000 lbs. A Grand Cherokee ecodiesel would pull a nice load. :)

    I wasn't really looking for improvements to a flat trailer, but you started talking about tractor to trailer gaps and turning issues, so I got side tracked. :) That's my story and I'm sticking to it. :D
     
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  19. BillLin

    BillLin PV solar, geothermal HVAC, hybrids and electrics

    I really enjoyed the pickup truck video.
     
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  20. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi Bill:

    Excellent points! I have a watched a lot of Aero vids today and of course they all go off into the tractor trailer rig side of it. A few Electric Vehicle owners doing tow tests on tear drops and such as well. I have found little to nothing related to towing a open air trailer with a car strapped on top of it unfortunately. The Big Rig OEMs - an interesting vid from Volvo trucks on this topic was fascinating - are stating that as a rule of thumb, a 10 percent decrease in drag equates to a 5 percent decrease in fuel consumption.


    Considering all of that, if we separate the two towed items, the trailer and the car, the trailer without a vehicle on top has a cross section of ~ 6" x 8' for the bed (4 sq. ft.) and 32" x 8" for the (2) fender/tire combinations (3.5 sq. ft.) or ~ 7.5 sq. ft. total frontal area. This is about 1/4 to 1/5 that of a std. car. With the flat load surface at ~ 16' in length and redesigned detachable fenders, air is probably going to smooth out over that cord length and exiting off a 6" height Kammback is going to add minimal drag. The tire/fender drag is going to be significant but at least it is a small frontal area.

    Air flowing underneath the tow vehicle and towed trailer will be somewhat disturbed off the bottom of the tow vehicle but with smooth trailer underbody surfaces, it may even stay connected which would be pretty slick. Instead of the flat face aluminum, maybe a rounded cone shape welded to the leading edge of the trailer floor to reduce drag further.

    I am also thinking of sheathing the safety chains to reduce drag from those too. ;)

    Together, the tow vehicle and 1,350 to 1,450 lb. empty trailer, the drag is almost to the point of possibly not feeling it although there will probably be a 5 to 7% hit to tow vehicle efficiency with the empty trailers extra mass on climbs and the small drag increase. Is it even worth considering adding aero enhancements to the trailer since its frontal area is so small vs the towing or towed vehicle?

    I am unfortunately probably adding a lot of aluminum to this trailer to clean it up - more aluminum or plastic sheets underneath is going to weigh quite a bit, doubling the fender mass with extended side skirts on the inside and outside of the tire wells, additional mass with the strakes from the trailers leading edge to the front edge of the fender and trailing edge of the fender to the rear of the load floor, a rounded leading edge attached to the front of the trailer load floor, and plastic or aluminum moon caps on the wheels themselves. If the two trailer axles are round, there would be little to gain by adding a tear drop shape over them. If they are square however, well then maybe... All in search of lower drag and it all should pay off in spades despite increasing the mass of the trailer by maybe 75 to 100 lbs.? How thin aluminum sheet can you use underneath before it begins to oscillate and create a whole new set of aerodynamic challenges is also a consideration? The trailer underbody treatment is where a plastic/pvc/coroplast/foamboard sheet(s) may be much more cost and mass effective plus being infinitely more flexible than welded aluminum? That is if there are enough angled stays welded to the aluminum crossmembers to attach the sheets with screws or using adhesive and attaching directly to the cross members to keep vibration to almost non-existent at any speed?

    Now what happens when we add a very low Cd car and extremely low Cd trailer to that separated dirty air just after the tow vehicle with its own Cd of 0.27 to 0.28? Maybe the low Cd towed car and low Cd trailer's drag is not simply additive but increases exponentially far faster than the tow vehicle alone as speed increases? The towed vehicle with its low 0.23 to 0.25 Cd will still have air going under, over and around while on the trailer, just that it will be very disturbed air off the back of the tow vehicle impinging on the front fascia and windscreen.

    Without a Super Computer and an exact model of the towing vehicle, trailer and towed vehicle using CFD, we know we can decrease drag and increase efficiency of the trailer with what has been proposed. However, would drag of the "system" be reduced significantly enough to make up for the additional mass of the trailer mods or a full air dams is the real question? My thoughts are to reduce the trailer drag as much as possible with simple aero mods, add the lowest Cd vehicle on the load floor creating a very low trailer and towed vehicle "towed system" Cd that will have much lower drag then the trailer with an air dam attached and the low Cd car sitting behind it.

    If there were a way to connect the towing and towed vehicles with any number of "contraptions", the entire "systems" drag could actually be reduced in a very significant fashion. The long cord length and smooth air flow from the towing vehicles roof to a tapered rear at the end of the trailer – towed vehicle completely covered – would lower Cd of the system significantly. There is no way we are going to do that but it would be a damn cool super mod for another experiment. ;)

    Wayne
     
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