Report: Improving the Aero Characteristics of a Dodge Ram Pickup Truck
 

After reading the ToyotaNation truck forum freakout, I went searching for some solid info about truck bed aerodynamics. (This was when I thought I was going to sign up & edumacate the lot of 'em :p.)

• There's this somewhat decent, real world Test: F-150 pickup "cap on" vs. "cap off" @ 60 mph

• And... SAE report: Pickup Truck tailgate aerodynamics... better up, down, or off?

If you search the web for info about tonneau covers vs. efficiency, you find stuff like this:

• Do Tonneau Covers Really Improve Gas Mileage?

That link (and many like it) refer to a report done by senior engineering students @ Western New England College, which not surprisingly shows that a tonneau cover improves efficiency.

But in the list of configurations tested for the report, the best results weren't for the tonneau, but a "new cap design", which wasn't explained any further (at least on those pages that are mostly trying to sell tonneau covers :)).

Long story short: intrigued, I wrote to an engineering professor @ the college. He knew of the report, and kindly made & sent me a copy.

NOTE: the students' report is online here Improving Aerodynamic Characteristics of a Dodge Ram Pickup Truck - including a photo of the aerodynamic "new cap design":

http://web.archive.org/web/200106290...er/new_cap.jpg




The observations/conclusions (from the above web link):


I was not surprised when I opened the report to see an image of the "new cap design" that looks an awful lot like the ones Phil, Brett & big_dave have made for their trucks. (Why this cap style isn't mentioned on all the web pages that reference this report, I don't know.)

I'll post more tomorrow, but that's the crux of it right there.

I actually graduated from WNEC in Mechanical Engineering the fall before these guys did that test. While I don't remember those guys personally, I do remember a white plastic model being prepped for the wind tunnel. I'm not sure if that is what was used or how they were holding it.

The wind and water tunnels are not that dinky. If the students new their stuff they could have good data. The force data from the wind tunnel may be suspect if the measuring instruments we're not calibrated well, or if the truck was tilted at all, or if they were measuring strain on the post holding the truck. All of which were possible.

When I was there, there were numerous tests being done for optimizing the exhaust for jet engines for military aircraft. Some of which have made their way onto real planes so not all of the tunnel data can be bad.

All that said, I would be highly suspect of the data without seeing the test methodology. I would love to see that report.

Geoff

Note that the water apparatus was used for visualization purposes only, not measurement -

The wind tunnel was used to gather data: (p.7)


The Scale Balance was calibrated prior to testing, to "allow measurement from the wind tunnel to be converted to an actual drag force value."

Hi Geoff - Could be. The report states that the 1/18th die cast model was used in the water tank, but...

(Quoting Geoff again...)

I'm not clear on how the scale balance is set up. Can you explain it?

I'm guessing there's an actual scale to measure lift (which the student wasn't measuring for this test). For measuring drag force, is there a pivot on the rod holding the model (at the "floor" of the test area), and drag force is measured on the other side of the pivot point?

As it turns out, I tracked down the author and he got back to me yesterday. I'll ask, and If he gives permission to distribute the report, I'll make a digital copy (photos).

Here's the author's disclaimer about the wind tunnel data, from Construction of Test Apparatus - Wind Tunnel (p.8):

The meat of the matter...
 

Getting to the meat, now.

The aero cap construction differs from the style Phil Knox and Brett Herndon produced for their trucks. Where they set up either a continuous straight line, or gentle arc from the top of the cab to tailgate level, the report author used a "compound" design to maximize storage space under the cap:

From Construction of Test Apparatus - Miscellaneous (p.11)

pickup aero
 

In 1981,Dr.Timothy Maxwell et.al.,with Texas Tech Aero Lab,Dept.of Mechanical Engineering,published a SAE report on windtunnel tests conducted on pickup models,with subsequent tests conducted in full-scale with a F-150 at Lockheed,Marrietta,GA., tunnel.The graphical table appeared in Sport Truck Magazine,Dr. Maxwell and Pat Nixon( Sr.Advisor to graduate studies,Texas Tech Aero Lab),toured the truck show circuit in the U.S. in the 1980s.It was their "aerocap" which was the inspiration for my cap on the Dodge and Toyota.I guess people can research this stuff to death if they want to,but if universities are duplicating effort,its a waste of precious resources.I think pickup airflow is now firmly understood and people ought to just build what's been known to work for a long time now.There aren't going to be any "breakthroughs",Earthlings need to move on to new challenges.I think I posted a photo of the Texas Tech graphic table at maxmpg in the misc.photo section.You'll have to look for it,as there are over 250 photos there.

Agreed, Phil.

The motivation for posting this thread is to create an online reference to some reasonably good data supporting the aero cap idea. (I'll go have a look over at MaxMPG for that supporting image from Texas Tech.)

While it may be clear to US what works & what doesn't, recent events (see the ToyotaNation fracas over Brett's cap) suggest that there may be some use in posting some documentation online. Thus this thread.

The best i can remember (I never used the tunnels) is the center of the model is attached to a vertical rod that is hinged at its base. Then another rod is attached perpendicular to that and creates a lever arm. The lever arm creates a downward force on a scale.

I was hoping these guys may have come up with a better method because as force (wind) is applied to the model the deflection of the lever/scale might tilt the model thus throwing every thing off.

Geoff

Thanks for the explanation.

I was thinking the same thing - about the possible tilt. Perhaps I'll get the answer from the author this week.

It's possible too that the scale doesn't necessarily have to physically move much to register the pressure on it. They could also play with fulcrum location to optimize - I'm sure they considered these things.

This was an undergraduate senior project, not a sponsored grad student research project. This college allows students after 3 years of theory to perform a hands on project from start to finish. The students create a test procedure, perform tests, interpret data, re-perform tests, write a report, then present their findings to their peers. None of their results need to be correct, it is really a full immersion method to learn the process they may have to do in the real world.

The majority of people in the world (including student engineers) have no idea what is aerodynamic or not. By performing testing that helps reinforce the aerodynamic concepts known to people here, that aerodynamic knowledge may be passed on to others who don't subscribe to the Pop. Sci. way of thinking.

Geoff

This is true, however, I think some people were using rods no bigger that coat hangers to minimize the air drag from the rod and ended up with bad data because the rod would bend and tilt the model.

aerodynamics
 

I suggest that you review Prof. Kamm's aerodynamic theories. I think that you will find that the traditional pickup truck CAN benefit from MY simple modification which smooths the airflow over the rear of the vehicle, taking full advantage of his theory. You know, the "large bubble of air" that exists in the rear of the vehicle that "aerodynamicists" claim to use as a design feature exists because of the 10 sq. ft of additional frontal area
created by having a tailgate in place. My boxes eliminate the "bubble" and drag and provide substantial gains in fuel economy. By the way, wind tunnel tests are generally conducted to determine improvements or enhancements.
Vehicles are NEVER designed with aerodynamics solely in mind. Aerodynamics is secondary to ergonomics, crash and powertrain package. There is a lot of room for improvements on ALL trucks. www.alateinc.com

Student research project
 

Geoff,I apologize if my comments came off as a personal attack,that was not my intent.What frustrates me is that there is a firmly established body of knowledge which has undergone independent,empirical verification at one of the world's most renowned wind-tunnel facilities,and it appears to pass without notice.Its as if PhDs are standing around arguing about how to design a manual typewriter,when laptop computer and word-processing technology exists.If working through a complete exercise, as was done by the students, was the premise of the education,well then they succeeded.If they published their work to push the state-of-the-art in pickup truck drag reduction,what am I or anyone else to think,when all this work was already accomplished in the 1980s and no mention of it made.It's like digging the same hole over and over again.And shouldn't students embarking on a project(any project) check their environment to see what has already been accomplished,and expand beyond level of intellectual achievement? Sorry,I'm probably to "close" to these issues,as I see ramifications of folly rippling out throughout the globe.

idiot
 

They do when they are in the airflow,idiot

LOL do you keep you tail gate on top of the roof?

Actually, I discovered that after driving pickup trucks for 35 years that I dont use the tailgate very often. I leave it at home unless I need it. Otherwise, I have tiedowns
and I keep ropes and chains in the boxes. I also offer 2 versions of stowable tailgates that are kept stowed until required.

Aerohead- good response. I discovered that 25 years ago. GIGO Garbage in, garbage out. These people only know how to solve problems with what they have been taught.
"You cannot solve problems using the logic that created them" AE If you can only solve problems using what you know from training then there can be no problems. All that you have been taught provides the answers to ALL problems so all of the answers are already known. Thats why we have "alternative energy" instead of solutions to the problem. If our government is so interested in solving our energy problems why is the Department of Energy's program for energy conservation and innovation not funded? With the oil companies making 11 BILLION per quarter, why is there no tax to fund energy conservation programs?

Tail gates do not affect frontal area one way or another.

The "rod" could be a "sting." Texas Tech uses one from the tail of a military jet.The sting contains piezio (sp?) transducers which measure strain in six axis and their output can be interfaced with computer to measure real-time loads (ie. lift,drag,torsion).

ptg0: Please define frontal area so we can all learn something.

Ok now that you've googled it you can go back and edit your previous posts...but I'll save the best part for posterity.

Your site is interesting too. I particularly liked this passage:

Man I wish I had a ground effect vehicule :rolleyes:

Dodge RAM aero mods
 

I have been slowly working on this almost since I bought my truck. I dug up several websites about pickup truck aerodynamics and improvements. Here are a few:
A Truck That Drinks Less Than a Car? | Popular Science
http://gcep.stanford.edu/pdfs/ChEHeX...0_11_trans.pdf
Improving Aerodynamics to Boost Fuel Economy
RoadandTrack.com -- Tech Tidbits - Tech Tidbits — September 2004 (9/2004)

I also took a close look at a RAM SRT10 about 2 years ago. Some of the interesting things are the front air dam/bumper cover/splitter, the full tonneau cover w/integrated spoiler (said to improve airflow), lowered 2 inches to cut aero drag, and I noticed the air conditioner condensor and the radiator are inline, not side by side like other RAMs. There is about a six inch space on the driver's side of the radiator that is covered with a piece of black plastic, to cut drag through the grille.
I looked at my wife's 08 Avenger and discovered it has a full belly panel under the engine bay. I have been working toward several of these mods since I got back from Iraq. I will see if I can add the pix to my gallery or garage...
My truck will get over 23 mpg on the highway at 65mph now. I am aiming for 30...

[edit] I also need to ask if there is a how to for measuring Cd via coast down?

Measure the drag coefficient of your car :thumbup:

Cd
 

I'll let others help you with the coastdown stuff but wanted to share another back door to Cd.
For 55 mph and 70 mph,a 10% drag reduction will net you a 5% and 6% mpg increase respectively.
So if you'd done a mod,and after comparing mpg to your baseline you showed a 5% improvement at a steady 55-mph,then you would have reduced your Cd by 10%.
This is a very easy way to determine your numbers.If you have the OBD-II Scan-Gauge or other instantaneous mpg display technology,you can get your results without having to burn a bunch of fuel.

aero mod pix
 

Here are a couple pix of my work so far:
I included the gap filler between the cab and bed, my belly panels covering the gaps between the frame rails and the body, and my front end splitter with another picture of the mounts to the bumper.
Guess I will have to break down and buy a ScanGauge or the software from Auterra so I can monitor this thing better...

That air dam - is it an OEM piece?

(EDIT: removed my earlier comments about the air dam. Need coffee.)

Highly recommend you get the ScanGauge. It'll pay for itself in fuel savings, and you'll use it more regularly than a laptop based gauge.

Original link to Western New England College Study
 

Did you Know

It is quite remarkable how close the two students Cd numbers are to the real world. Their water tunnel and sensors worked quite well.

I have to admit, this is where I first got the idea for the Aerolid. These two young men deserve all the credit for showing what a large reduction in Cd can be achieved through pickup truck body aerodynamic optimization.

Bondo

bondo: thanks for posting that link to the archived study the students did.

You're welcome MetroMPG
 

I would have posted the link the study sooner but I just found out where I had saved it yesterday.

Bondo

No, the splitter is not an OEM piece, but I did model it after the Rumble Bee lip spoiler. That spoiler is thicker, but gives the same basic appearance. Here is a picture of a Dodge RAM Rumble Bee. (it is still a prototype. :) ) RumbleBee.org - The Dodge Ram Rumble Bee Owner Community :: Album
The lip spoiler I refer to is the black piece at the bottom front of the spoiler. I doubt it extends back more than a couple inches. Mine is 16 inches from the center straight back.

Econoram:

Have you thought about adding fuel log info on your truck? I'm curious about how well you're doing with your mods as I've considered doing some very similar things to my truck but haven't made the time. If it looks like there's enough benefit it might incentivize me to make time.

I don't know if Dodge fixed or changed the A-pillar design on later model years but I've always noticed that at high speeds (70+ or even 65 near trucks or with crosswinds) air separates the door from the bulb seal at the top of the windshield because air shedding sideways off the windshield will get underneath the door and push outwards combining with the outward force of the pressure low along the front side windows. A lip seal similar to what you used as a bed fairing might help prevent this as long as it doesn't rub and cut on the bulb seal when opening the doors.

BTW the "Rumble Bee" air dam is part of a Mopar aftermarket body kit that was available since the 02's first went on sale. I think the air dam only fits on Sport package trucks though. I'd be willing to test fit one on my truck and test it out, but last I checked they were pretty expensive.

I noticed on your vehicle profile you're running an electric fan...would you mind telling me which model and where you got it? Have you noticed any gains from it?

Hi MechEngVT,
I am running a Zirgo 2700 cfm unit. I had a weaker 2100 cfm unit from Flex-a-lite (did not know it was not strong enough until after I installed it), but when it would not cool the truck down enough, I stepped up to the Zirgo. I got both off of Ebay. I could have simply bought a full up Flex-a-lite 180 kit from AIRRAM or Moe's Performance, but I figured I could do it all myself. I did, but still bought a fuse holder, thermo switch, relay, and some mounting hardware.
Yes, I was toying with getting a Rumble Bee lip spoiler, but I do not have a sport bumper, and don't want to spend the extra money on one because it still will not have proper flare around the front wheels for good aerodynamics.
I am looking next at sealing the gaps around the windshield, and the door to body gaps. Figure that should help a bit too.
I do keep a logbook, but it is all hand written. Guess I could type it into the site, so you all can see what I've been up to. :) I hope to take a nice long trip down to St. George or Las Vegas at Christmas to get the truck on the road for a while and see what it will do. I have measured 23-24 with my in-cab mpg meter, and tracked the changes in the mpg with the distance covered, but a long trip would be better.

were you able to increase your FE since ditching your mechanical radiator fan? are your coolant temps slightly higher as a result? are you running a
205 deg thermostat?

Hi max_frontal_area, I did not do before and after tests, so I cannot say if there's a significant FE gain or not with the fans. There was no weight change; the clutch fan and the electric fan with relays weighs the same...
I did swap more for the noise reduction, as the engine startup fan noise really bothered me. I do have the stock 193* thermostat. I also learned that the air in Utah is thinner, such that is actually makes a noticeable FE improvement. I've restarted monitoring the truck, as I've only hit a max average of 20.5 mpg here in OK.

EconoRAm; what did you use to help fill the gap between the cab & box? would it be better to have it attach to the cab vs. the box?

one thing I dislike about my 3rd gen Ram and holds true for your 4th gen, is that the bumper and front lip get narrow at the bottom exposing more of the tire. I am trying to come up with a way to address that without it looking tacky.

Hi Jungle, mine is actually a 3rd gen also. I agree, the exposure to the airstream the front tires get isn't a good thing. My ultimate preference would be a RAM SRT10 bumper cover. But when I started this process, they were $1K a piece. So, I've tried a couple things along the way. Most to my wife's chagrin, but effective. Here's the latest flavor:
I have used foam weatherstripping between the cab and bed. Ideally, I'd weld it together but that would be difficult to do properly... I am looking to get some rubber weatherstripping for the gap, or maybe cover both sides with some saran wrap and spray in some expanding foam.