Wake field of pickup
 

I've been following several discussions that touch on this area but I thought it should have it's own thread. I'd like to focus this discussion to pickup trucks.

Several members have fabbed some very nice aero caps for their trucks. There may not be 100% agreement on which is truly best, nor what "best" means from one person to the next. There does seem to be consensus opinion backed by MPG numbers showing improvement over an open stock bed. (Contrast that with great confusion about which produces least drag: tailgate up, tailgate down, tonneau cover, cab-matching toppers provide.)

I have read considerable discussion about side view profile as a design tool (starting point) for aero caps, but very little about top view profile by comparison. So I see that as one area of improvement in our knowledge base.

I would like to suggest some ideas to help quantify and compare designs and applications. Every truck creates a wake in the field of air molecules it plows through. That wake is effected by shape and speed of the truck. I think it could help to stick some numbers to that shape. For example, how far behind would a tailgater benefit appreciably? Call it draft zone.

I have other discussion points but I'll stop here for now.

Cheers
KB

Good Idea for a thread KamperBob.
 

Here is a link to a thesis published by a Naval Officer who used CFD study to determine an optimum aerodynamic shape for an aerocap. I had posted this link some time ago here on ecomodder and many found it informative.

It is interesting to read what this report says about a conventional camper shell. It is also interesting what fuel efficiency percentages were realized by the author, who built his own aerocap for this study.

Hope you find the report informative.

Bondo

http://www.dtic.mil/cgi-bin/GetTRDoc...c=GetTRDoc.pdf

quantify
 

KB,historically,drag coefficient has been the 'language' of aerodynamics.All elements of aero drag are represented within this number.
In 1963,researchers at GM published an SAE Paper which quantified the direct relationship between drag coefficient(Cd) and mpg,for City,Highway,Combined.
Since Cd is the most recognized indicator of shape-efficiency,we might be wise to respect it's use rather than attempt to re-invent the wheel by creating a new 'language.'
Tail-gating,in addition to being illegal in all states,would endanger all attempting to quantify it's affects.That would be better left to a test track as Myth-Busters used.
In the Seminar sticky,there is a complete discussion of the role of Cd to mpg.
As to "plan-taper" of the aeroshell.If one follows the template design tool,for a long-bed pickup you could expect a little over 21% drag reduction and 13% mpg improvement at 70-mph.

I'm surprised they went with the plaster...I think the expanding foam would make a more reasonable lightweight material to shape with. I just might experiment with replacing my current cab high fiberglass topper with an expanding foam based one... :D

Thanks for replying but you misunderstood. I did not encourage anyone to tailgate! (sigh)

Fact is, others WILL tailgate behind you whether you want them to or not. Try to "drive smart" (ie, light foot) and you too might find your efforts hampered by tailgaters. It seems like 9 times out of 10 the person tailgating me is not intentionally drafting just paying more attention to a conversation with someone via the cell phone. Why they don't just pass I do not know. I have developed strategies to discourage them. Slow down, temporarily use hazards, even take the unoccupied passing lane (in which case they invariably resume the speed with which they overtook me and proceed on their merry way).

Regardless of why they fall in behind and stay there, or how exactly you get rid of them, meanwhile they draft you. Knowing the length of your tractor beam could be a useful tool for dealing with tailgaters.

As an engineer and scientist I am hopelessly addicted to data and analysis. I would also point out that history is full of innovators who either ignored or (heaven forbid) dared to challenge conventional thinking. Low and behold some accomplished things their predecessors knew was not possible. Being tolerant of creativity and enthusiasm need not be an annoyance or threat; it could be an opportunity. :)

Cheers
KB

Bondo, that looks like some tasty reading.

Thanks a bunch!
KB

The only thing I feel I should note is that tail gaters usually decrease the aerodynamic load of the lead vehicle, which is beneficial, or this is at least the way I understand it.

Unless the shape is somewhat streamlined to begin with, of course. There is obviously, as with everything, an equilibrium point, where it could either be a moot point for them to tailgate, or even possibly have a negative effect on the drag of the leading vehicle.

Bondo, do you have any idea how many hours you cost me since yesterday? (wink)

This research went a great distance towards answering some of my questions. It also created some new ones. For example, I'm trying to puzzle out the elevation at which the horizontal slice planes were taken.

Anybody know what's up with the blunt triangular protrusion in front of the tailgate in figures 54, 55, 66 and 67? Not the underbody; I know they slice the axles. I gather they are somewhere between the top and bottom of the box. Hopefully they were all taken at the same elevation.

I'm guessing the open bed detail neglected wheel wells. The eddies inside the bed seem to confirm that. It's a minor detail if focusing on covers. Still, I wonder what effect it could have on the baseline and relative difference.

Yup, I definitely see more hours staring at these plots. :)

Cheers
KB

misunderstood
 

Thanks KB,now I'm on the proper page.
I've no solution for tailgaters.I refer to them as 'alonaphobes',incapable of being by themselves on the open road.
The fun thing about streamlining is that,if we do our work correctly,there will be no drafting possible,as a following vehicle would feel the full effect of the air behind our vehicles.
As to innovation and creativity,I'm all for that.I'm also for fully exploiting everything that has already been thought up since 1922,but never put on the road.

possibly
 

Hoerner reported,that in the case of two perfectly streamlined bodies,that when 'tail-gated',the drag of the lead body increased due to destruction of the boundary layer over the aft-body.No NASCAR drafting for low-draggers!

For cars I absolutely agree. Not pickups though. They start with a big flat tailgate for loading 4x8 sheets of drywall or plywood. That alone places a practical limit on how perfect the rear can be tapered. We can minimize the draft zone but not eliminate it. And I'm glad we're working together now, Aerohead. :)

For the aero cap projects I've read here so far their draft zone may already be reduced to a few car lengths. (Hence, the desire to measure it.)

On the highway drafting might not be a big problem for aero cappers. I'm going in a different direction though as my handle might suggest. Bondo's cap is the best I've seen. Not just because it's purdy. It is wicked useful. (Hence, having a truck in the first place.) His camper model can have a comfortable bed, but headroom is low, and not much space for gear.

I reject the industry standard slide in camper. The sleekest, lightest ones available today are still way too heavy and boxy. I'm motivated to do better if only to show how. I don't expect to build it this year. Design and analysis takes time, especially when it's not your day job and other life responsibilities call. Meanwhile, my Scamp 5th wheel is hard to beat. :)

Cheers
KB

Why not the ultimate lightweight "camper", AKA a tent? Otherwise you've got a lot of conflicting requirements: headroom (and legroom for us taller folks with normal pickups (that is, standard Toyota size rather than American oversized), weight, insulation (a metal pickup bed is about the coldest possible place to sleep), aerodynamics...

Make a solid aeroshell, and your gear stays secure while you pop up the tent for sleeping.

Couple of sticks and a tarp, really. Make a lean-to on the pickup.

(bristle) Why stop with a tent? Sleep in motels. Trade the truck for a Prius, or bicycle. Just stay home for that matter. It's a slippery slope that risks more to do with lifestyle preferences. I promise to start a truck camper project thread, eventually. Folks can bash it (or the personal decisions behind it if they really feel they must) at that point. Meanwhile, it seems this discussion needs some course correction.

Bondo's link to the '03 NPS thesis was a wonderful contribution to this thread. If you know of other literature, ideally R&D work, that sheds more light on the wake field of pickups, please share it.

Thank you, everyone!
KB

Glad you enjoyed the thesis KB.
 

Captain Williams put alot of work into it. Years ago I always thought it was optimization of frontal surfaces which allow for a low Cd. I was way off base, it is what you leave behind as you pass through the atmosphere that matters.

The Aerolid was designed with functionality in mind. The fact that it deploys into a camper shell configuration (and can be driven at freeway speeds raised up) and that the roof can easily be removed, allows for extra utility of the truck bed. Below are a couple of pictures (you have probably seen before).

You said in an earlier post you are an Engineer. Good for you. We need more Engineers in this country today.

You also stated you drive a Tundra. I am looking to tool up for a Tundra. If I can be of any help in anyway on your upcoming project let me know.

Bondo

Bondo,

Every time I see pictures of your cap -- Sa-weet! --, I consider selling my
Prius and getting a pickup so I could get one. ;)

I know your heavily involved in marketing/production issues.

Still, have you considered doing rear wheel skirts and a deep front air dam
and being able to offer a full aero package similar to Aeroheads pickup?

I have a scale model already done.
 

Thanks Rokeby for the compliments. I wish I was dealing with production and marketing issues. My story is like a stuck record, capital, capital, capital. I had hoped one of my Senators was going to help get me a tax credit for the Aerolid. After some encouraging first communications, now I get no response from them at all. I need to go ahead and make that campaign contribution.

I have a scale model finished with side skirts, rear wheel close outs but no front air dam. The late model trucks are getting real good in that area and a low hanging front air dam can be a real drag. I would like to market a full aero package like you suggest.

I too get tired of reporting the same thing on the status of the Aerolid. I do appreciate all the interest here on ecomodder and my hats off to all those who step on out there and build their own aerocaps.

When I feel like stop beating my head against the wall, I remember those word's Winston Churchill spoke to the English people when they were being heavily bombed by the German air force in the early years of WWII.

" Never, never, never Give up!".

Bondo

Indeed!

I have seen those pix but thanks for sharing them again. You have great ideas and first class execution. For some it may be the perfect solution. My needs are just different, which I trust is okay. My eventual designs will certainly be less aerodynamic than yours. Interior space and layout is a priority since so much time will be spent inside the unit. The aero challenge is how to minimize its wake. Weight reduction will just be a bonus. The current offerings in the slide-in market leave a lot of room for improvement.

Hopefully, using my engineering skills and sharing knowledge will benefit others too. If not, I fail a pledge. :)

I don't know how your demographic data looks but my Tundra is Gen-1 with extended cab (suicide doors) and short box (6.5' long). It may be the most popular body for that era but the Gen-2 models are very different as you probably know. If you think it a target market and need some key dimensions, let me know.

This raises a good point. There can be so many differences between pickups. As a result what works best to optimize one (allowing for different design goals) may be a weak solution for another. I'm interested in doing CFD so geometry will be needed. It would be great if we had an open library of solid models for various pickups. I know they can be purchased (and I am morally opposed to stealing so please don't go there) but we might be able to develop our own. They don't have to be perfect; just good enough. Google Sketchup is free, friendly and powerful so maybe sketchup drawings could do the trick. Other suggestions welcome.

Cheers
KB

FWIW, I camped for a summer in an '81 Toyota Celica Liftback, whose hatch is roughly analogous to a small aerocap. I set out with a nice Coroplast rig to enclose the back section for camping with the hatch open, so I could sit in bug-free splendour and enjoy a picture window. Overall, I found the biggest improvement over bicycle camping was the ability to camp on gravel or mud.
By the second month, I'd quit using the extension, and made the interior arrangements more compact. I'm following that trend in Stealth RV. One of the tidiest spaces I've ever seen was inside a 19' sailboat, Tiny Dancer, on her way around the world.
A place to stand up is the only real luxury increment in these things - I'd be inclined to have a swing-up cap to allow that, while travelling as an aerocap.
BTW, an inflatable tail cone can be added to the tailgate - a big, bluff stern is not mandated. A lot of wake reduction might be managed with underbody tunnels, too.

Not a whole lot of motels to be found around here Toquima Range - Wikipedia, the free encyclopedia

or here Toiyabe Range - Wikipedia, the free encyclopedia

or here Santa Rosa Range - Wikipedia, the free encyclopedia

or even here Black Rock Desert - Wikipedia, the free encyclopedia

All right I was saving this for later but this is one rig I want to model for grins.
http://kamperbob.com/EU3kReceiver/GenMounted.jpg

Tents were the good ole days. This is my A rig for a nomadic lifestyle. :)

Cheers
KB

Thats' cool... Here's mine:

http://www.boners.com/content/800460.1.jpg

:thumbup:

Not sure if you guys have seen this before, but it is a good read.

Velocity Field Measurements in a Pickup Truck Model

Any reason you couldn't use the lowered tailgate to be the bottom part of a small boattail/cap?

No, if you could get the proper angle with a lowered tailgate. You'd have buick/cadillac fins, though.

Craig, thanks a bunch! That looks very interesting indeed. :)

Cheers
KB

Sorry to dig a zombie up from the grave... anyone have a copy of that KFUPM paper? The link is dead.

Thank you so much!

Another posted elsewhere in the forum.

http://www.wseas.us/e-library/confer.../FMA/FMA17.pdf