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Guests ![]() Guest Group ![]() |
![]() Posted: 16 Oct 2009 at 9:16pm |
Flow...with and without the A/C...with the spoiler at the rear and a 30" spoiler at the rear
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Note how many pressure pulses are produced by simply adding the A/C to the roof. There is a build up not only much higher at the upper rear...but also a pressure field out in front of the R-Pod.
I think that the A/C on the RP 170+ units with its longer roof line and using a longer and higher TV helps keep the flow much smoother (see Outbound's flow images at the beginning of this thread). It appears that by moving the A/C to the roof of the RP-151, Forest River really decreased the efficiency of the RP-151s. I wonder how much less mpg I will be getting from the 2010 Pod versus the older units? |
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Wow! That's really amazing!
I've noticed that when driving on wet pavement for the first time, I almost thought the brakes might be on as the spray that was burbling off the back of the trailer was so fine it looked like smoke. I'll have to try this program with the Tiguan when I have a minute. I can see by the illustrations that it is definitely an advantage to be pulling the trailer with an SUV as it 'fills' the gap between the car and the trailer more aerodynamically. I would imagine this would also apply to a 1/2 ton pulling the trailer with a cap on it as opposed to one without. with It would sure be interesting to see what a standard tandem box shaped trailer would look like using this program. Thanks for the quick lesson in aerodynamics! Doug ![]() ![]() ![]() ![]() ![]() |
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A comment was made about airflow over a pickup truck... I used a 2010 Ford Extended Cab with
a length of about 221 inches. The first image is an 'open box'...Flow Illustrator does a two-dimensional analysis, so the PU box looks like an open box with a tailgate on the end: suprisingly the flow was quite smooth over the R-Pod...the open box not doing much to the flow. There were large amounts of pulsing behind the R-Pod and upward from the pavement behind the rear (suggestion...cover the box!) The second image is a 'closed box'...a covered box...there were some lower frequency pulsing at the top rear of R-pod and some rear pavement upward pulses The third image is with a truck 'topper' covering the box...there was also some pulsing at the top rear of the R-Pod the rear upward pulses were more gentle Putting a 20 inch wind deflector at the back of the pickup cab suprisingly caused both pulsing at the top rear and lower rear of the R-Pod...not very efficient flow Moving the wind deflector to the rear of the topper really smoothed the flow...no upper pulsing, no longer period pulsing, with a nearly constant low pressure zone at the lower rear (probably the most efficient flow of any of the cases!) ![]() |
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Here is a flow image of an 18ft rectangular travel trailer. The flow is extremely smooth over the truck and trailer roof. But there is a huge roller being dragged behind. It would be nice to know the drag coefficient of an R-Pod versus a rectangular travel trailer.
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techntrek ![]() Admin Group - pHp ![]() ![]() Joined: 29 Jul 2009 Location: MD Online Status: Offline Posts: 9062 |
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Has anyone tried adding a deflector to the back of the 'pod? I'm thinking at a 45 degree angle, mounted above the rear window. That should even out the airflow back there.
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see Outbound's airflow run on first page
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techntrek ![]() Admin Group - pHp ![]() ![]() Joined: 29 Jul 2009 Location: MD Online Status: Offline Posts: 9062 |
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Ah, I missed that first time around.
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Well I guess I'm all kinds non efficient airflow. Not only do I have a smaller truck, small cab, open bed and now I have a trike rack in truck bed to cause more problems.
I'm going to take some good side and front pictures (for editing) on my next trip. I'd really like to see a deflector on the cab, will i lose some of the turbulence in the truck bed? Now the big question? What does all this tell us? What is the gain the MPG as we correct the airflow? In the Deflector thread, http://www.rpodnation.com/forum_posts.asp?TID=587&KW=deflector&title=deflect-or-not-to-deflect-is-the-question there didn't seem to be a big gain in MPG. Just wondering? Lee ![]() |
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Butterfly_Lee
The following is just my opinion. The pictures and "airflow analysis" are a nice visualization of one set of conditions with the model presented and the boundrary conditions in the program. The author of the program warns that the results are "not " a scientific result and should be considered a work of art and not a scientific result. Now, that is not to say the results don't have worth , they do and can provide some 2 dimensional visualization of air flow across the various vehicles and r-pods. I have enjoyed seeing the contributions and look forward to making my own when I get my Pod. You should not put to much credence in the results you see as far as making a judgment of gas mileage etc. First of all I don't think the program allows input of vehicle speed etc to set the criteria under which the airflow takes place. I have purchased a devise called a "scan gauge", which will give me instantaneous gas mileage, transmission temperature, alternator output, and several other readings and plan to use the hard data I get from the gauge readouts to improve my driving habits to improve gas mileage. Maybe somewhere down the road, I may fool around with spoilers etc but for now I just plan on enjoying the R-Pod as much as I can when I receive it. Bottom line is to go enjoy your r-pod and don't worry too much about the gas mileage. Remember back a few years when all the big rigs had huge spoilers mounted on the tractors ? How many do you see today ? I don't think they helped as much as the people selling them said they did. |
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