The Mystery of The R-Pod Total Frontal Area
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Topic: The Mystery of The R-Pod Total Frontal Area
Posted By: Happy Tripping
Subject: The Mystery of The R-Pod Total Frontal Area
Date Posted: 12 May 2019 at 7:00pm
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Ultralight trailers like the R-Pod are touted as being able to be towed by smaller vehicles such as vans and small SUVs. That is their big selling point, a big tow vehicle is not required. Enter - Wind Resistance. Wind resistance is very important for travel trailers. The more that there is, the greater is the stress on the powertrain and wheels of the tow vehicle and the lower the gas mileage is. If the wind is from the front, the speed of the trailer adds to the wind resistance, if from behind, it decreases it. Additionally, wind resistance at slow speeds like 45 mph is relatively minor, however as speeds are increased, it increases much faster than the actual increase in speed. Going from 55 mph to 75 mph is a 35% increase but wind resistance, and the strain on the powertrain, increases about 250%. (People with ‘L’ or ‘M’ rated tires take note) . Obviously, with all these variables, ‘wind resistance’ is not a static number. The wind resistance of a travel trailer is roughly proportional to the ‘Total Frontal Area’ but protruding things like fenders, rooftop a/c units or awning mounts, and the underside of the trailer, also have effects that increase the effective total frontal area. To me, the published Total Frontal Areas of tow vehicles for travel trailers are a subject of great mystery and seem to be nearly worthless. However, this doesn’t bother the tow vehicle product liability lawyers. Using a complicated formula that is based on variables that are not apparently standard throughout the industry and that also are apparently not publicized, they have established required Total Frontal Areas for many if not all tow vehicles. These seem to exclude smaller vehicles. Cynic that I am, I think that the lawyers have jumped in to give their companies the greatest protection possible in their powertrain warranties. The poor travel trailer manufacturers in response have carefully neglected to announce their trailer’s frontal areas in order not to hurt their sales. The R-Pod’s total frontal area is reported to be maybe around 50 sq ft. So, just for fun, please look in your operator’s manual and let us know if your tow vehicle passes or fails its manufacturers’s total frontal area requirements. I know that my entirely satisfactory Jeep Cherokee (towing capacity 4500 lbs) fails, and I am very interested to see who passes. |
Replies:
Posted By: jalong
Date Posted: 12 May 2019 at 7:27pm
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2014 Jeep Grand Cherokee maximum trailer frontal area 55 sq ft for all drive trains ------------- John & Sue 2016 179 - built in April 2015 2014 Jeep Grand Cherokee 3.6L 13-16mpg with 179 - 21-28mpg without |
Posted By: offgrid
Date Posted: 12 May 2019 at 8:11pm
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I agree that the front area A by itself is essentially useless. The important parameter is really CdA or drag coefficient x frontal area. The Cd of rpods is pretty good. And yes, drag force increases with the square of the relative wind speed so the power requirement to overcome drag increases with the cube of the wind speed (because power = force x distance traveled per unit time). Total power requirement is the sum of the rolling resistance and the air drag. Since rolling resistance is relative small at freeway speeds and doesn't vary much, its fairly easy to roughly back into the air drag component based on your fuel consumption if you have that at a couple of different speeds. I did that and got a CdA of about 16 sq ft for my rig, which accounts for about 2/3 of the total horsepower requirement at 60 mph. I estimated A at 45 sq ft which gives a Cd of around 0.35, which is not bad. A boxier trailer would be worse of course. For the record there is no published frontal area towing limit for my 2012 Highlander. If there was one I'd ignore it anyway, for the reasons we've stated. If your vehicle doesn't consume fuel excessively, overheat, or run at a high rpm towing at freeway speeds then air drag is not your limiting factor, weight and weight balance will be much more important to keep track of. Here's a calculator if you want to play around with it. http://ecomodder.com/forum/tool-aero-rolling-resistance.php - http://ecomodder.com/forum/tool-aero-rolling-resistance.php ------------- 1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
Posted By: podwerkz
Date Posted: 12 May 2019 at 9:47pm
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Of course the towing vehicle creates a bit of a vacuum and/or vortices behind it, depending on the shape and size of it. This probably helps reduce trailer drag in calm winds, or slight headwinds, but broadside winds get to have an effect on the entire rig, more or less. You can't win for losing.
------------- r･pod 171 gone but not forgotten! |
Posted By: offgrid
Date Posted: 13 May 2019 at 6:04am
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Good point. The drag of the rig is what matters, not the drag of the trailer separately. Depending on the aerodynamics of the tow vehicle the addition of the trailer might have a more or less dramatic increase on the combined drag. And if you want you can add aero devices like the Purpleline product to the TV, to try to reduce it. The numbers I worked back to in my post were for my combined rig. YMMV (literally). ------------- 1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
Posted By: tcj
Date Posted: 13 May 2019 at 8:30am
2014 Toyota Tacoma Access cab V6 4x4 with towing package. Trailer frontal area is not even mentioned in the owners manual. ------------- 2018 R-pod 180 Hood River Edition |
Posted By: john in idaho
Date Posted: 13 May 2019 at 8:59am
| Seems like I saw a post a few years ago on this forum. Someone added a canoe to the top of the pickup topper and increased gas mileage a few points. but my memory may be faulty. |
Posted By: lostagain
Date Posted: 13 May 2019 at 9:00am
I think the design of the Pod is so sleek and appealing that it magically resists air molecules as though it glides on clouds in a near weightless environment. The only improvement, which I've previously proposed, would be some fin like wings coming off the back of the trailer at about the level of the spoiler. Once installed, it would be like pulling the trailer in the vacuum of space.  ------------- Never leave footprints behind. Fred & Maria Kearney Sonoma 167RB Our Pod 172 2019 Ford F-150 4x4 2.7 EcoBoost |
Posted By: offgrid
Date Posted: 13 May 2019 at 9:16am
i have a kayak I was thinking of taking camping, maybe I'll try it. Another way to determine air drag is through coast down testing. All you need is a couple of miles of dead flat smooth road, no wind, no traffic, and a smart phone to video your speedometer during the tests. ------------- 1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
Posted By: lostagain
Date Posted: 13 May 2019 at 9:22am
.... and if you put the wings on the back edge of the Pod, it'll easily double the coasting distance.  ------------- Never leave footprints behind. Fred & Maria Kearney Sonoma 167RB Our Pod 172 2019 Ford F-150 4x4 2.7 EcoBoost |
Posted By: offgrid
Date Posted: 13 May 2019 at 10:00am
Wings create both lift and drag. So more than likely you'll get both sway AND worse fuel economy. Try it, let us know what happens, I wanna see the youtube video.  ------------- 1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
Posted By: lostagain
Date Posted: 13 May 2019 at 9:51pm
I was thinking of the really nice fin like wings that are not horizontally oriented. I was hoping to get a pair off an old 1950's trailer made of aircraft aluminum and only about an inch thick. They'd operate more as rudders than creating an airfoil for lift. And at the snail like speeds I tend to drive, the wind resistance cause by about 10 sq. in. of leading edge surface area would be de minimus. And if I could score unicorn wings, they'd reduce drag and make fuel unnecessary. If I find them and mount them, I'll certainly post not only photos but a video.  ------------- Never leave footprints behind. Fred & Maria Kearney Sonoma 167RB Our Pod 172 2019 Ford F-150 4x4 2.7 EcoBoost |
Posted By: StephenH
Date Posted: 14 May 2019 at 10:03am
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So, are you trying to make your R-Pod look like a Shasta? (scroll down to first picture in "Original Condition Shasta Trailer") https://nancysvintagetrailers.blogspot.com/2010/08/original-condition-shasta-trailer.html - https://nancysvintagetrailers.blogspot.com/2010/08/original-condition-shasta-trailer.html ------------- StephenH Happy is the man that findeth wisdom,... http://www.rpod-owners.com/forum_posts.asp?TID=7712 - ouR escaPOD mods Former RPod 179 Current Cherokee Grey Wolf 24 JS |
Posted By: lostagain
Date Posted: 14 May 2019 at 10:26am
Ok, StephenH, where can I pick up a pair of those cool fins on the blue trailer in your picture? I think that would add to, not only the aesthetics of the Pod, but to it's aerodynamic efficiency. Imagine the reduction of drag and the increase of lateral stability to to those sleek fins. The only thing that would improve on them would be unicorn wings.  But, I'd never want to hurt a unicorn by harvesting its wings.  ------------- Never leave footprints behind. Fred & Maria Kearney Sonoma 167RB Our Pod 172 2019 Ford F-150 4x4 2.7 EcoBoost |
Posted By: StephenH
Date Posted: 14 May 2019 at 10:33am
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Ask in a Shasta forum? Likewise, harvesting unicorn wings would not be a good thing. Maybe buffalo wings? ------------- StephenH Happy is the man that findeth wisdom,... http://www.rpod-owners.com/forum_posts.asp?TID=7712 - ouR escaPOD mods Former RPod 179 Current Cherokee Grey Wolf 24 JS |
Posted By: lostagain
Date Posted: 14 May 2019 at 11:19am
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I thought I might take a look in some junkyards around area 51. It's only about 3 1/2 hours from home. Who knows what I might find; maybe some flying saucer parts. I'd have to go all the way to Buffalo, NY, to get Buffalo wings. That may be in the plans for next summer. But I don't know the aerodynamic characteristics for them. ------------- Never leave footprints behind. Fred & Maria Kearney Sonoma 167RB Our Pod 172 2019 Ford F-150 4x4 2.7 EcoBoost |
Posted By: David and Danette
Date Posted: 14 May 2019 at 12:44pm
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How about wings like the 59 Chevy impala had. Maybe could make them adjustable.
------------- 2018 Vista Cruiser 19BFD (2018- 2012 Vibe 6503 (2014-2019) 2009 r-pod 171 (2009-2014) Middle Tn 2014 Ram 1500 Quad cab |
Posted By: lostagain
Date Posted: 14 May 2019 at 1:03pm
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They may provide too much lift, thus creating the phenomena about which offgrid warned. To keep on topic, the purpose of the fins would be to assist in the frontal drag and cut through the wind with a minimal amount of fuel, kind of like a streamlined locomotive of 1938.
------------- Never leave footprints behind. Fred & Maria Kearney Sonoma 167RB Our Pod 172 2019 Ford F-150 4x4 2.7 EcoBoost |
Posted By: GlueGuy
Date Posted: 14 May 2019 at 1:15pm
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You all know that if it was "just" frontal area, it would be a simple thing. Problem is, it's not. The real issue is total drag, and to be fair, it is the total drag of the TV/TT combination. If your TV is a pickup (as are a lot of TVs), then there is also the length/height of the bed of the pickup and whether it has a tonneau or not, and what sort of thing(s) might be on any rack that may or may not be there. And finally, there is the issue of the GIGANTIC vacuum at the tail end of the R-pod. I think the only way to figure this out is to rent the https://www.nasa.gov/content/behold-the-worlds-largest-wind-tunnel - wind tunnel at Moffett Field . I have not checked what the rental rate is on that puppy. ------------- bp 2017 R-Pod 179 Hood River 2015 Ford F150 SuperCrew 4WD 3.5L Ecoboost |
Posted By: lostagain
Date Posted: 14 May 2019 at 3:00pm
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There were some videos of a Pod with wind in different colors, I think late last year or early this year. But there would be nothing cooler than testing a Pod in the Moffett Field wind tunnel. When can we sign up? ------------- Never leave footprints behind. Fred & Maria Kearney Sonoma 167RB Our Pod 172 2019 Ford F-150 4x4 2.7 EcoBoost |
Posted By: offgrid
Date Posted: 14 May 2019 at 4:49pm
Its waaay too much. But, its not the only way. You can use coast down testing as I mentioned earlier. This is how folks evaluate the effectiveness of aero add-ons for semis. There are free calculators to input the data into, and as you are coasting from a high speed where aero drag dominates to a low speed where rolling resistance dominates, you can get decent numbers for both factors. The calculators use linear regression analysis to obtain the two coefficients. I dd it for my Highlander last year and got pretty decent initial results. I haven't done it for the combined rig yet because I want to remove my a/c unit and install my solar array first. I'm going to shoot for 1 kW. Once that's on I want to do coast down testing to optimize the solar module tilts to see if I can get them to act as spoilers. Not only saving energy towing but simultaneously producing energy, that will beat lostagain's Shasta wings ------------- 1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
Posted By: lostagain
Date Posted: 14 May 2019 at 6:51pm
But not my unicorn wings. ------------- Never leave footprints behind. Fred & Maria Kearney Sonoma 167RB Our Pod 172 2019 Ford F-150 4x4 2.7 EcoBoost |
Posted By: David and Danette
Date Posted: 14 May 2019 at 8:20pm
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The Curtis Wright Clipper may be the first camper to be built with wind drag in mind. I think for the r-pod to have less wind drag it would need to have a tapered back to minimize wind turbulence creating drag.
------------- 2018 Vista Cruiser 19BFD (2018- 2012 Vibe 6503 (2014-2019) 2009 r-pod 171 (2009-2014) Middle Tn 2014 Ram 1500 Quad cab |
Posted By: offgrid
Date Posted: 15 May 2019 at 5:51am
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Yes, as i understand it, to reduce flow separation and turbulence, you want to try to bring down the rear (or sides)of an object at no more than about a 20 degree taper as long a possible. Then, when you can no longer continue to do that you make as clean a break as possible so that the turbulent flow separates from the rear of the object, "spoiling" the airflow and reducing the area of low pressure immediately behind the object. Take a look at the rear of a Prius for example. Or at the tail fairings you see on some semi trailers now. I was thinking to try to do that with a full width 350 watt-ish solar module on the top rear of my rPod overhanging the back window. It would also provide some summer shade in that area. I'm thinking the side treatment would be 0.090 aluminum sheeting which i would extend forward to enclose the sides of two additional solar modules in front of the rear one. The a/c unit and tv antenna would go away, so that the front modules would drop down to meet the existing roofline. I would also need some type of small front fairing to smooth the airflow where the front module comes down to the roof. That's about as far as I've gotten with the concept so far. ------------- 1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
Posted By: offgrid
Date Posted: 15 May 2019 at 10:09am
Here's roughly what I have in mind ------------- 1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
Posted By: podwerkz
Date Posted: 15 May 2019 at 11:38am
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Just mount a pair of JATO's under the frame...you wont worry about too much drag ever again! ------------- r･pod 171 gone but not forgotten! |
Posted By: GlueGuy
Date Posted: 15 May 2019 at 5:02pm
------------- bp 2017 R-Pod 179 Hood River 2015 Ford F150 SuperCrew 4WD 3.5L Ecoboost |
Posted By: podwerkz
Date Posted: 15 May 2019 at 5:08pm
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Yes I was referencing that 'story'....and no more worries about aerodynamic drag...ever again! Rocket-Pod, anyone?  ------------- r･pod 171 gone but not forgotten! |
Posted By: offgrid
Date Posted: 15 May 2019 at 5:57pm
No worries about anything else ever again either. ------------- 1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
Posted By: podwerkz
Date Posted: 15 May 2019 at 7:43pm
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That Darwin dude was right after all.... ------------- r･pod 171 gone but not forgotten! |
Posted By: Billy Bob
Date Posted: 15 May 2019 at 7:56pm
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back in the 80's commuter turbo props airline planes had a jato bottle for engine failures.....you never wanted to fire one of those as they were quick burning and not enough power. we have come along way since then. ------------- 2019 RPOD 190 2017 Chev Colorado 4 X 4 Yellow Lab and English Springer Spaniel |
Posted By: podwerkz
Date Posted: 15 May 2019 at 8:19pm
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Yep. Now we install MCAS and auger big airliners into the dirt. ------------- r･pod 171 gone but not forgotten! |
Posted By: GlueGuy
Date Posted: 15 May 2019 at 8:36pm
------------- bp 2017 R-Pod 179 Hood River 2015 Ford F150 SuperCrew 4WD 3.5L Ecoboost |
Posted By: podwerkz
Date Posted: 15 May 2019 at 8:50pm
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And substandard aircraft manufacturers.  ------------- r･pod 171 gone but not forgotten! |