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.)
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. |
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http://ecomodder.com/imgs/dodge-ram1500.jpg The report examined a model like this 1995 Dodge Ram 1500 regular cab, with 8 foot bed http://forum.ecomodder.com/attachmen...1&d=1204405182 One cap style tested. The light area between the cab and the cap is not a gap, it's material applied to fair the cab to the bed cover. (Apologies for the poor image quality - it's a a photgraph of a photcopy of a printout!) The cover page of the report: Quote:
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The WNEC professor who forwarded the report to me, Dr. Said Dini (currently a Professor of Mechanical Engineering who is acknowledged in the report as having assisted the project), offered this disclaimer: "I am not certain of the accuracy of the results." The student author also discussed some of the factors which may have affected his calculations/conclusions. I'll get to them as well. More to come... |
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 |
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Note that the water apparatus was used for visualization purposes only, not measurement -
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The Scale Balance was calibrated prior to testing, to "allow measurement from the wind tunnel to be converted to an actual drag force value." |
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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? Quote:
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Here's the author's disclaimer about the wind tunnel data, from Construction of Test Apparatus - Wind Tunnel (p.8):
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The meat of the matter...
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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) Quote:
http://forum.ecomodder.com/attachmen...1&d=1204391783 Design 1, fixed 15 degree alpha angle, variable beta angles http://forum.ecomodder.com/attachmen...1&d=1204391783 Design 2, fixed 8 degree beta angle, rounded termination |
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.
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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. |
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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 |
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