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offgrid View Drop Down
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Direct Link To This Post Topic: R-Pod 195 Other Options Video
    Posted: 12 Jul 2019 at 7:10pm
Originally posted by GlueGuy

The drag coefficient is not "just" the frontal area, but the overall aerodynamics of the vehicle (or object). You can increase the frontal area, but if you make other changes, you can reduce the drag coefficient.

For example, the rounded high butt on a 179 might very well contribute to a higher drag coefficient. Also, the wheels and fenders poking out from the sides of a 179 most probably contribute to a higher drag coefficient compared to the tucked-in wheels/fenderlettes on the p195.


Yes, drag coefficient is Cd, drag is Cd x A as I stated. The fenders poking out of a narrow rpod aren't any wider than the fenderettes on a 195,  they just look narrower because the trailer is wider. They are small features compared to the whole trailer.  The standard size rPods have a spoiler to deal with rear drag, the 195 apparently does not. 

We could speculate a variety of things, but there is no reason to think that Cd is significantly different for a 195 rig vs a narrower rPod rig. Unless there is actual data to the contrary, the logical conclusion is that a trailer with a 15% larger area that is similarly shaped is going to exhibit higher drag. 

There just ain't no free lunch, a bigger heavier trailer is going require more power and fuel consumption will go up accordingly.  A lighter smaller trailer like say a NuCamp TAB is going to generate less drag than a standard rPod and require less power to tow. Each of us has made that trade off and has our own sweet spot. 

There is no one right answer. Its not taking anything away from someone who chooses a 195 when I give my reasons why I don't want one, or vice versa. What concerns me is if/when folks think that they can use a tow vehicle that would be adequate for a standard rPod for the much larger 195 because, well, its an rPod. That is a safety issue. 

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Direct Link To This Post Posted: 13 Jul 2019 at 7:39am
Originally posted by offgrid


 What concerns me is if/when folks think that they can use a tow vehicle that would be adequate for a standard rPod for the much larger 195 because, well, its an rPod. That is a safety issue. 


On the safety aspect, I agree whole heartedly. I would add, using a tow vehicle that barely meets the r-pod minimum requirements as well. Nobody ever seems to consider payload capacity, just tow capacity. Many 3500 pound tow capacity vehicles have 1000 pound payload caps. A family of 4 probably weighs 500 pounds. A 179, 180, etc., have a tongue weight of about 340 pounds. That leaves 150 pounds for the dog, the cooler, a full tank of gas, and all the other crap we take with us. I am very serious about safety, infact I believe people should not be allowed to purchase, or register a camper if they can not show they have a capable tow vehicle. We could replace the current "We just pack light" method used today, with actual safe standards.
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Direct Link To This Post Posted: 13 Jul 2019 at 8:52am
+ 1. The towing specs on most vehicles appear to assume there is nothing in the vehicle except one skinny driver. When does that happen in the real world? 

As a pilot, on a ramp check by the FAA, I could be stopped and asked to show my weight and balance calculation for that flight. Not every pilot does that every flight of course, because most flights are a repeat of another one, but you sure better be ready to show you know what you have on board where and what your aircraft's limits are. Doing a loading assessment of a rig is basically the same thing as a weight and balance analysis when loading an aircraft. Its not difficult but it does take some thought the first time or two. 

One of my gripes is that the whole industry (vehicle manufacturers, trailer manufacturers, and  the dealers) all have set things up seemingly to encourage new owners to push the limits of their rigs. Sure they are trying to sell stuff on commission and caveat emptor at some point applies but in my opinion an ethical person should stop short of knowingly letting someone put themselves in danger without warning them. 

BTW, if you have dual batteries, a single full propane cylinder,  and full fresh water on board a 179 has a tongue weight well exceeding 500 lbs. 
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Direct Link To This Post Posted: 13 Jul 2019 at 10:36am
Originally posted by offgrid

Originally posted by GlueGuy

The drag coefficient is not "just" the frontal area, but the overall aerodynamics of the vehicle (or object). You can increase the frontal area, but if you make other changes, you can reduce the drag coefficient.

For example, the rounded high butt on a 179 might very well contribute to a higher drag coefficient. Also, the wheels and fenders poking out from the sides of a 179 most probably contribute to a higher drag coefficient compared to the tucked-in wheels/fenderlettes on the p195.


Yes, drag coefficient is Cd, drag is Cd x A as I stated. The fenders poking out of a narrow rpod aren't any wider than the fenderettes on a 195,  they just look narrower because the trailer is wider. They are small features compared to the whole trailer.  The standard size rPods have a spoiler to deal with rear drag, the 195 apparently does not. 

We could speculate a variety of things, but there is no reason to think that Cd is significantly different for a 195 rig vs a narrower rPod rig. Unless there is actual data to the contrary, the logical conclusion is that a trailer with a 15% larger area that is similarly shaped is going to exhibit higher drag. 

There just ain't no free lunch, a bigger heavier trailer is going require more power and fuel consumption will go up accordingly.  A lighter smaller trailer like say a NuCamp TAB is going to generate less drag than a standard rPod and require less power to tow. Each of us has made that trade off and has our own sweet spot. 

There is no one right answer. Its not taking anything away from someone who chooses a 195 when I give my reasons why I don't want one, or vice versa. What concerns me is if/when folks think that they can use a tow vehicle that would be adequate for a standard rPod for the much larger 195 because, well, its an rPod. That is a safety issue.

Actually the coefficient of drag is more complicated than that. It's 

Cd = D / (.5 * r * V^2 * A)

Please refer to this NASA explanation for more.
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Direct Link To This Post Posted: 13 Jul 2019 at 11:48am
Speaking of aerodynamic drag...I often wonder if it would be practical, cost effective, reasonable, and 'accepted' to adopt some of the streamlining efforts used in the transportation industry.

Yeah, you can hang some aerodynamic hardware on a towable camper, but would it be 'acceptable' to the buyers? All this hardware adds weight and cost, but they do save fuel in most cases.

Can you see the buying public paying more to have tow vehicle cab-extenders and rooftop spoilers, under-trailer skirting, smooth wheel-covers, and foldable trailer-tails? 

I don't think they would, but it would be interesting to see what effect those might have on fuel mileage.


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Direct Link To This Post Posted: 13 Jul 2019 at 1:26pm
Originally posted by podwerkz

Speaking of aerodynamic drag...I often wonder if it would be practical, cost effective, reasonable, and 'accepted' to adopt some of the streamlining efforts used in the transportation industry.

Yeah, you can hang some aerodynamic hardware on a towable camper, but would it be 'acceptable' to the buyers? All this hardware adds weight and cost, but they do save fuel in most cases.

Can you see the buying public paying more to have tow vehicle cab-extenders and rooftop spoilers, under-trailer skirting, smooth wheel-covers, and foldable trailer-tails? 

I don't think they would, but it would be interesting to see what effect those might have on fuel mileage.
I've seen some discussions of adding vortex generators to help with the giant vacuum bubble that follows behind an R-pod, or most other trailers for that matter. I have seen no definitive study, scientific or otherwise that shows that they actually reduce drag. Considering the number of travel trailers on the roads these days, it seems like someone would want to do this.

I would think that Forrest River did some kind of study before they added the spoiler that is at the rear of most of the "fat butt" R-pods, but maybe that is wishful thinking?
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Direct Link To This Post Posted: 13 Jul 2019 at 1:48pm
Actually, the best fuel saver on any RV is the driver. Not pressing as hard on the 'go pedal' saves a lot of fuel!

When towing my r-pod (or any trailer) I typically drive at about 55-62 mph unless traffic dictates otherwise. I tend to accelerate smoothly, stop gently, and 'play' the lights if possible. 

Recently I made a 200 mile leg of a 700 mile trip with another camper pulling a Tab 400 and I was very surprised at how much faster he preferred to travel. I watched my Scangauge II register lower mpg than I normally get for most of the mileage we did on mostly flat terrain.

Drive like there is a fresh egg between your right foot and the gas pedal, and you will save fuel, guaranteed!
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Direct Link To This Post Posted: 13 Jul 2019 at 4:05pm
195 Heads Up - picked this up off another forum, FYI ONLY - "Word of caution for future 195 owners: cover panels under the cushions in the little seats can bounce loose and the rear one can (will?) jam underneath when deploying the slideout. Mine did and nearly ripped out the pantry door frame. Devil of a time getting it loose and now I have repair job to plan and execute."
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Direct Link To This Post Posted: 13 Jul 2019 at 4:49pm
New 195 upgrade from our 182G.  Just did a 3 day shakedown trip to Millersylvania SP, WA. Except for the little seat panel issue, invisible until I heard the cracking noise, it all went well.  Large efficient fridge ran well on the road without using propane.  Solar panel and inverter worked great.  Enjoyed the power awning w/LED light strip.  Gotta love our dry bath with an actual, albeit small, sink and med cabinet.  Stowage under the RV queen bed now more useful since I added a pair of 1x2 braces to hold the lid up.  Better than my head.  Rear kitchen has a nice single handle faucet at a large deep sink.  Overhead storage tempts one to overstock snacks.  Pantry huge!  My portable ice maker fits in the bottom alongside a small poly bin.  Ice maker lives on the storable table when we're camped.  So much storage capacity equals temptation to fill it!  I moved more than a few things from the Jeep to the Pod so I think my total combination weight stayed about the same.  Towing with a 2018 Jeep Grand Cherokee V8 (small HEMI, tow cap. 7000+) I couldn't see any real difference in fuel economy compared to hauling the 182G on the same route.  Ladder on the back makes it easy to survey the roof top fir needle and bird dropping collection.  Makes a good place to strap on a short step ladder that you will need for installing shade curtains on the end(s) of the awning.  That's enough for now.  We're lovin' every minute of it.  Keep havin' fun!
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Direct Link To This Post Posted: 14 Jul 2019 at 4:19am
Originally posted by GlueGuy

 

Actually the coefficient of drag is more complicated than that. It's 

Cd = D / (.5 * r * V^2 * A)


Yeah, my bad, to be accurate I should have said the piece of the drag equation associated with the vehicle itself is CdA. If you rearrange the above equation you get

D = Cd*A*ρ*V^2 /2

Breaking that into three parts we have the vehicle size and shape piece Cd*A (rig drag coefficient multiplied by rig frontal area), the air density piece ρ (which is generally used rather than r) and the speed related piece V^2. The whole thing is divided by 2 but we can ignore that because its a fixed constant we can't change. 

So, the levers we have available to pull are the size. shape, and aerodynamic details of the rig, and the speed we drive at. You could argue that we can also control the air density say by only driving at high altitude but as we're not talking about airplanes here we really don't have a whole lot of choice. In airplane cruise flight it makes a big difference in fuel burn though. 

So to podwerk's  comments, yes by far the easiest way to improve fuel economy is to slow down. Running my rig through the mpg calculator I sent the link to, changing from 60 in cruise on the freeway to 65 costs me about 1.5 mpg. So, that 5 mph increase in speed is roughly equivalent to the difference between the frontal area of a 195 and a standard size rPod (and in the other direction probably also a Tab vs a standard rPod but I haven't checked that).  Similarly, dropping from 60 to 55 saves about 1.5 mpg.

Re the "egg over the pedal" driving style, that's what the Prius hypermilers do. It won't of course do much for you driving straight and level on the highway but in urban traffic its a significant savings. Best thing I think on a flat open freeway is to set your cruise control at the lowest speed you and the surrounding traffic will tolerate and just relax and enjoy the trip. If you have a 200 mile trip the difference between 60 and 65 is all of 15 minutes, not a big deal most of the time. 

Re adding some aero tricks to our trailers I've been thinking about that too. One that some of our members have tried is to add a deflector to the rear of the tow vehicle. I've been thinking about doing that with a solar module rather than spending a bunch of money on an inert chunk of plastic. I also don't see why cleaning up under the trailer would cause anyone heartburn, and it could do combined duty as freeze protection as well. Skirting which reduced ground clearance would probably not be very acceptable. 

As to the rear treatment, tapering the aft roof area down more gently for awhile followed by a sharp cutoff like the trailer tails or the rear of a Prius is a proven solution (originally invented in the 1930's  by a German aerodynamicist and called a Kammback). The slope can't be more than 15-20 degrees or the airflow separates too soon so some of the teardrop trailers you see probably don't really get the benefit.  Not sure it could be done on an rpod but I'm thinking about placing a solar module over the rear window at about a 15 degree angle with aluminum support plates to close in the sides.  That would shade the rear window as well. 
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