Receiver-hitch boat tail
 

Here is a rendering from back in 2004.
The Stowaway II offered the elongation which would allow boat-tailing,and there would be the utility of additional cargo space without resorting to a roof rack system.
Earlier European designs had retractable wheels which would allow the tail to be slipped out of the receiver and rolled away without any lifting involved.
I'd gone through an advanced composites course at ABARIS and knew that a composite structure could be extremely light,since this is an all-compound surface and benefits from 'egging'.
A thermo-formed plastic structure would also be doable.
All light-metal,likewise.
A passenger side window would be beneficial when backing,as the 'C-pillar' would be enormous.
Or a camera system as is common now.
I won't be going for a patent,so feel free to use it if it can help.:)
http://i1271.photobucket.com/albums/...ntitled1-7.jpg
http://i1271.photobucket.com/albums/...ntitled2-7.jpg
The Koenig/Kamm K-form was predicated on a 50% frontal area wake.So this would be the recommendation for a 'practical' length.
http://i1271.photobucket.com/albums/.../11x17Scan.jpg

that is very similar to how my tail worked:

it all was built on this:

http://i835.photobucket.com/albums/z...s/2e3f80f9.jpg

with top attachment to keep it tight to the car:

http://i835.photobucket.com/albums/z...s/d56c3a10.jpg

all the weight on the receiver worked very well. after 3.5 years it was going strong.

3.5-yrs
 

It's a great way to go.And for urban warfare they're easily removed for parking ease.
We'll lament the loss of your boat tail,but relish in the knowledge that we had 3.5 years of it.Thanks mucho!:D

THANK YOU for posting this :)

In regards to shape/size/length... How would one determine this for their particular vehicle? I see mention that it would be based off of 50% frontal area wake... Can a fella get a translation for this? I know you guys are wicked smart with this stuff, but I'm not so much :o

Also, I see you based it off the bottom lines of the hitch for your underside... Did you intend for there to be a rear diffuser to meet with this design? it seems that dropping below the rear bumper would create more drag/poor air flow?

I had planned on basing my design off of the aero backs on the big rigs trailers, rather than an actual boat tail. It seems that yours follows this train of thought as well?

Any feedback you or ANYBODY else can give me would be awesome! I fully intend to build something for my Mountaineer. Spare tire, recovery gear, emergency gear, all tucked away inside it.

~C

Look at my build thread (search for matrix full boat tail).

People helped me figure out design and it should help you too.

It just occurred to me that I've been focusing entirely on my car for ecomodding. THIS however, would be perfect for my wife's SUV! Ideas are starting to flow... :)

http://i1271.photobucket.com/albums/...ntitled1-7.jpg
==> Lake Oswego, OR

Did this ever progress beyond a rendering? Did you intend for it to expand and collapse, or is it more of a 'bodykit' for the commercial item?

Split tailgate.

Each side could swing open into a storage locker, with depth equal to half the tailgate width and a width equal to the length of the boattail.

I've been meaning to ask how WeatherSpotter got the plasic wing off of the top of the hatch. I dream of doing this to my SUV. Problem is I got a hitch mount bicycle carrier but not a hitch yet. I can't use the old bike carrier because its made to hang off of the top of the hatch.

Mine came off with 4 bolts, those are the holes I used to hang the tail off of.

design
 

Here's what you're up against
http://i1271.photobucket.com/albums/...ad2/Scans4.jpg
http://i1271.photobucket.com/albums/...ad2/Scans2.jpg
http://i1271.photobucket.com/albums/...ad2/Scans1.jpg
You want the tail to fill in the region occupied by the smoke (1st image),of the blue area in the other two.
You could use the 'Template' or Mair's boat tail
http://i1271.photobucket.com/albums/...ntitled324.jpg
You can do better than a 'Trailer Tail.'

That was my original thought too! I would rather the design not utilize my receiver, for a multitude of reasons. The first being, that this will hold my spare tire so I see no need for this to be removable once it is built.

Could split the weight between two hinges, allowing for a stronger structure and a heavier payload for storage of plus size tire and equipment. Would also allow for a true key lock on the split to gain access to the inside of the hatch rather than trying to reach between boat tail in truck to release the arm. BUT, my problem was I didn't know if the seam would create bad flow? Or worse yet, how would I seal it to prevent air flow into the structure and causing a "parachute" effect? It increases the number of variables, and would necessitate a more accurate design of both the structure and the shell. Of course, that's not that big of a deal. I've only started thinking about his in a serious fashion lately, it's probably far simpler than my first impression of it.

Example of load capabilities on split swing bumpers, they're used a lot on trail rigs and overland vehicles:
http://i.imgur.com/QcU0kJRl.jpg

And the latching mechanism that could be extended via metal subframe to the rear of the boat tail (this could be hidden behind a locked hatch). I would probably secure one side to the bumper, an then lock the opposite to it... Like you do with double door in a house:
http://i.imgur.com/7qy69N4l.jpg

As far as mounting to a factory bumper goes, it's a bad idea... Very few are meant to handle the weight and even fewer are designed in a manner that you can weld the hinge to it. But you can weld a subframe that hides behind the stock bumper. Here is an example of one, I found it here Gray Goose Build Thread - JeepForum.com , but pretty much no information other than to show the following pics. I was kind of bummed there weren't more pics or a proper write up on it :(

He unbolted the factory hitch, and welded a cross beam that goes in the bumper and two runner welded to the arms which bolt to the frame. Pretty clean/simple once you determine correct placement.

http://i.imgur.com/rILfeMXl.jpg

http://i.imgur.com/JuuXrJ6l.jpg

his simple description:
"It's an A to Z hinge (off road fab company), 3/4" bolt with a "t" welded to it to latch the carrier"

And the amazing "factory" look he was able to achieve with this design (even color matched the swing away arm):

http://i.imgur.com/WAy17Rcl.jpg

http://i.imgur.com/oGbw1Kyl.jpg

I would imagine this wouldn't be cheap... But cost would probably be far cheaper when comparing what you get. The hinges are $52, add $25 for a larger HD version. So on a split version, you have $100 to $150 in the hinges (Tire Carrier Swingout Heavy Duty Hinge Kit) . Latches can be purchased in various sizes and costs, and metal costs would be determined by type and source. But considering the high cost of thule slide aways, and hitch mount versions, I think it would be worth it. Plus it would allow peace of mind knowing it can handle ANYTHING you would build onto it. It might be overkill for some or even most of you guys, but I spend a lot of time driving forest service roads in the mountain... Two weekends ago I spent a few hours trying to pull a 150' downed tree out of the roadway :eek::cool: And I have a plus size spare that won't fit under the truck anymore, got's to have somewhere for it to go. I don't like having it inside, since it becomes an unsecured mass in the case of an accident... "Death by spare" doesn't appeal to me :D

As soon as I can get a decent photo of my truck, I'll start drawing/designing the tail structure to mount on my contraption. I really wanna make this happen, just a matter of time and resources haha

~C

But isn't your original post very similar in design to a "trailer tail"?

your posted design:
Trailer tail:
http://i.imgur.com/zZAH1KHl.jpg

Would this not net me FE gains on the back of an SUV? Or are you simply saying that I should try to do better because I can?


~C

How about for a rough shape 2 pieces of coroplast held together with a piano hinge with torque springs to hold outward tension as you pull sides plush with the SUV sides. Make a box frame for them to mount to. The piano hinge is the point of the backwards boat bow shape.

Sounds like you've thought about it more than I had. :thumbup: Split like this, two ways, the height of the storage would be cut in half.

http://upload.wikimedia.org/wikipedi...x-WikiHVan.jpg

You could have something like the tailgate area above pushed back to mimic the trailer tail. The bottom half could swing 225° to put the shelving on the corners when it's open. That would put the hinges in the new construction.

Insofar as the Trailer Tail—it is a box cavity (for stowability). A flat truncation (flat, concave or convex but with a sharp separation) will perform better, though not as well as a 'later' truncation or full boattail.

simply saying
 

AT Dynamics' Trailer Tail is designed for collapsability and minimum displacement when nested against the trailer.It's way out ahead of nothing,aerodynamically,but is intentionally compromised for operator ease of operation and also DOT length limitations.
My rendering comprises the most complicated geometric structures as far as fabrication goes.There's not a flat surface anywhere and the subtle curvilinear contours needed for boundary layer protection are everywhere.
Kamm's last project has this complex form
http://i1271.photobucket.com/albums/...ntitled7-2.jpg
Tou can see how NASA went gently into the 'slopes'
http://i1271.photobucket.com/albums/...Untitled36.jpg
I took advantage of VW's existing curvature when I did my Transporter
http://i1271.photobucket.com/albums/...ntitled319.jpg
These curves are very important to the boundary layer.

So it's not that they aren't appropriate design, they are just to "simple" with straight lines and flat panels... Got it.

I got out my protractor and a pic of my Beast, it appears that I have about a 30 degree departure angle with my hitch. I would need to maintain that steep angle for my non-paved adventures... I routinely drag my hitch, so a lower angle would probably be a quick trip to catastrophe with a boat tail. I know the steepest angle on the "teardrop" aero template is 22 degrees, so how screwed am I with my need for 30 degrees? I'd hate to build this thing and then see no improvements due to my design limitations :( Could maintaining correct angle/curve on the sides and top be good enough? Could I do some sort of rear belly pan/diffuser that would assist in directing air up along the bottom of the tail?

-C

On the Aerocivic, I've had to compromise on the bottom angle to keep from dragging on a steep driveway entry. As long as you keep the top and side angles correct you be ahead of the game. Having a smooth underbelly transitioning to a diffuser on the underside of the boattail will help at reducing the drag increase of too sharp of an angle under the boattail.

http://ecomodder.com/forum/member-fr...1273951782.jpg

Compare C and D. The inverted fins are called 'skegs'. If they were retractable, with a hinge at the front and skateboard wheels at the tips, that would preserve your departure angle. And it could be combined with F, similar to the Trailer Tail.

Sweet, Game on :thumbup:

I want to take advantage of no longer having a spare hanging behind the rear axle! I'll hopefully get under there in the next week or two and figure out what I'm working with.

True! I guess you could even have the fins spring loaded and retractable upon pressure being applied... Have them go up into a slit in the boat tail? That's got some serious potential for experimentation if I ever get this thing built.

Would this have the potential to cause lift under the tail? Or would this actually create down force the way a diffuser works?

~C

Exactly the way a difusser works, or the endplates on a wing; by imposing order on the air which would just do whatever it wants otherwise.

30-degrees
 

GM's Aero 2000 'Epcot' car had an active rear valance/diffuser.In the video at Epcot Center,in the GM exhibit,you can see the rear panel lower to a more favorable angle when on the highway.
GM's the only company to my knowledge to do it so far.
It's worth knowing,as you get your 'RUBICON' drivabilty,and also some slick open road performance.
Here's a link
1982 GM Aero 2000 Concept Boldride.com - Pictures, Wallpapers

Thanks for the link, that's awesome! Think how many folks could utilize that on SUV's and trucks that wander off the beaten path on the regular! Or for cars that encounter steep drive ways for that matter.

Quick question, on your design for the hitch mount... How did you secure it to the rear of the vehicle? Or did you simply intend to design it's footprint slightly smaller than the back of the vehicle so that air would "jump" any gap between vehicle and structure?

~C

to secure
 

The premise of the design is that it integrates directly to the host vehicle as if it were an OEM organic extension.There's no gap.
The receiver carries the vertical load in cantilever,checks vertical displacement, while upper tension straps inhibit any longitudinal movement or 'roll.'
The tail on my CRX was built on the car and fit like a glove.It would be the same for SUVs,just a larger structure.
http://i1271.photobucket.com/albums/...ntitled310.jpg
http://i1271.photobucket.com/albums/...d2/Scan102.jpg
http://i1271.photobucket.com/albums/...d2/Scan2-2.jpg
http://i1271.photobucket.com/albums/...d2/Scan101.jpg

My parents used to silk-screen magnetic stick-on car door signs. Cut sheets of the blank material into strips and use flush rivets to attach to the boattail. With some marginal grip around the whole perimeter it would help affix the tail to the vehicle. There might be ~1/8" step at the edge, a router should be able to chamfer that.

It might be tedious to peel and tape back each piece to release the -tail, but why would you want to do that?

So this is an old thread but I am probably getting a Honda CR-V or something like that and the thought struck me:

A typical hitch rack can be surrounded with a box to make it a detached box cavity/spoiler-like object that doesn't require any body modification.

Furthermore, you can add the straps that come with trunk mount bike racks as anchors for a plastic sheet spoiler extension from the roof.

detach
 

The new tail for SPIRIT mounts to a C-frame, which itself pivots from a JEEP Wrangler-esque bumper-mount spare-tire, swing-away fixture.
I used clamps from 50-caliber ammo boxes to snug the tail to the rear.
Once released, the whole tail swings away, and to the passenger side curb, exposing the storage 'trunk,' as some cargo aircraft do.
I believe that it will be relatively painless to live with on the road.
Since the shell is all compound curves, it's extremely thin for it's strength. Triple-biased, pre-preg, carbon -fiber epoxy, vacuum-bagged in an autoclave, as we did at ABARIS, would render a tail of just a few pounds all-up weight; as a commercial unit.
If vehicle aft-body architecture were rationalized among weight classes, you wouldn't need to own one. You could just lease one for holiday vacation, at the edge of town, and return it when you return home from the road trip. Let the things work 52-weeks out of each year.
Okay, brain-vomit ends now.

Pics or it didn't happen.

pics
 

I photo-documented the build up to where I got to in 2017. They're on a memory stick.
I'll need to be tutored on how to post them. COVID closed off all access to learning. I'd been totally reliant on Photo-Bucket. What a disaster that became!

I'm one to talk, I don't even have a functional camera.

You need to conjoin the memory stick and the Ecomodder website. Details vary. :)

....on some kind of computer, if you can see the [presumably USB] device on the desktop and have an open browser you're almost there.

Then you just go to an album under your Profile and Upload.

Tell us how it works out.

ever progress?
 

Only now, with AeroStealth's Chevy BOLT, do I have access to a 'SUV' as a candidate. We've run some numbers.
The BOLT's belly is like the IONIQ hybrid. It must have rear skirts, must be paneled in, with the addition of a diffuser.
He'll get a receiver hitch installed and wired then.
When the all-aluminum cargo carrier at Harbor Freight goes on sale, we'll snag one. And begin.
John's already seen over 300-miles on a charge, bone stock.

how would a rear diffuser even be attached for an ioniq hybrid and how would it stay stiff and stable?

attached, stiff, stable
 

1) Any existing holes can be re-purposed for attachment points.
2) 1/4- 20 all-thread can be cut, bent into a 'J' on one end, and slung over an existing rigid structure to create a tension member to 'hang' a subframe, skinned, and stiffened with aluminum angle extrusion, box-section, square tubing, etc.., 'pinched' against double-nutted fasteners, locked at the desired elevation for the panel.
Welded, brazed, spot-welded, bolted, self-tapping screwed, riveted, epoxy-bonded, etc..
You have exhaust heat issues, so that's got to be addressed either with custom heat-shielding, or the use of sheet metal.
10mm, fluted Coroplast would be stiff enough for non-heated locations. Throw metal at problem heat areas.
Spread compressive loads of attachment over wide fender washers, so as not to 'crush' the panel. Nyloc nuts cannot vibrate themselves loose.
Dzus fasteners are great! it your budget allows.

Strips of magnetic stick-on car door sign material to bridge the gap, fastened permanently to one edge.

was thinking about underbody being abs sheet and then cut out the sections that are near the muffler and use aluminum there

bolting diffuser on would be easy with the attachment points underneath. just would need to keep it stiff and stable at higher speeds so it doesnt flop around

That's why I don't like receiver mount boxes/tails. They can move on three axes.

ecomodder.com/forum/showthread.php/project-ecofamily-civic-its-aero-hitch-box-boat-...

Compare a single wheel trailer, with two attachment points. It can only move on one axis.

ecomodder.com/forum/showthread.php/boat-tail-project-based-single-wheel-trailer

I proposed a 'wheel-less single-wheel' design held up by internal air pressure

https://ecomodder.com/forum/member-f...pe-ii-boat.jpg

ABS sheet
 

There would be some center-to-center distance between reinforcements where the sheet material would act like a diaphragm. You'd have to figure that out, and respect that spacing, otherwise aeroelastic deformation could be induced at the speeds you're going to operate at. You don't live in Australia.

Polymetal would be stiffer.

Maybe just a full aluminum under try with with steel reinforcement beams and structure support is a good way?

Polymetal claims stiffness equal to 5/8" plywood. One could compare the weight per sq ft.

And cost.