replacing spoiler on rpod 179 - R-pod Owners Forum

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marwayne

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Joined: 25 Oct 2011
Location: Edmonton AB Can
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Topic: replacing spoiler on rpod 179
Posted: 03 Sep 2019 at 7:21pm

If you want something done right, do it yourself.
2011 RP172, 2016 Tundra 5.7 Litre, Ltd.

offgrid

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Posted: 31 Aug 2019 at 5:25pm

yah, on the smaller pods you have a pretty short deck. If you don't put the spoiler on before you get to where the roof slope exceeds 15-20 degrees the airflow will separate anyway, so the smaller pods might have a problem there.

I found that software and I'm working on getting some new airflow videos now. I'm using my 179 and Highlander TV. One problem with the models in those videos is that it looks like the Reynolds number might be set too low, allowing for some laminar flow, which we don't have at the speeds and dimensions we're working with. I reset it higher to get rid of that.

If anyone wants to fool around with this software, here's the link, its pretty easy to use. The hardest thing is to get a good photo uploaded. Stand way back when you take the picture. You have to use a .bmp not a .jpg and it can't be wider than 1400 pixels. To get rid of the background you can use Paint and carefully cut everything else out so its all white except the trailer and TV. Once you get the profile in you can draw in whatever aero feature you want really quickly.

http://www.flowillustrator.com/

1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold

podwerkz

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Joined: 11 Mar 2019
Location: Texas
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Posts: 966

Posted: 31 Aug 2019 at 3:00pm

I watched those airflow videos....the one with the spoiler apparently shows that spoiler down farther, and farther away from the A/C unit than I see on the roof of my r-pod.

On my r-pod the spoiler is directly 'shadowed' by the A/C unit and the roof vent cover. This is what I refer to by being improperly placed to improve aerodynamics. It may be that on the longer r-pods, the spoiler sees some undisturbed air...but on mine, I am sure it does not.

https://photos.app.goo.gl/fGpvgz1QqYMhFDaq9

r･pod 171 gone but not forgotten!

GlueGuy

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Posted: 31 Aug 2019 at 12:45pm

Originally posted by offgrid

Kinda like a car wing sloped down rather than up? I'm not sure it it would reduce drag or not but it would produce lift at the rear of the trailer. That's a bad thing in a race car but might be good for sway reduction on a trailer.

Kind of like that, but much smaller. What I see in my mind's eye is something relatively small just to cause the airflow to follow the downslope. I don't think it would provide any lift, as it would be too far forward to actually push down on anything. That, and we don't travel fast enough for any significant lift.

bp
2017 R-Pod 179 Hood River
2015 Ford F150 SuperCrew 4WD 3.5L Ecoboost

offgrid

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Posted: 31 Aug 2019 at 12:39pm

Originally posted by GlueGuy

IIRC, Stephenh had tried the Purpleline Aero. I don't recall whether he felt it provided any benefit or not. Kind of noodling out loud is whether a reverse spoiler would provide any benefit? Something that was actually curved downward and sitting above enough to encourage the airstream at the back of the R-pod to stay attached long enough to fill the vacuum bubble.

Kinda like a car wing sloped down rather than up? I'm not sure it it would reduce drag or not but it would produce lift at the rear of the trailer. That's a bad thing in a race car but might be good for sway reduction on a trailer.

1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold

StephenH

podders Helping podders - pHp

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Posted: 31 Aug 2019 at 12:07pm

I found more benefit when we had the Escape and not as much with the Frontier. This is mainly because it sat closer to the RPod on the Escape and the Frontier, even with the tonneau cover, has the 5' bed space between the AeroPlus and the hitch plus the additional distance between the hitch and front of the trailer. It still helps deflect some of the bugs though.

StephenH
Happy is the man that findeth wisdom,...

ouR escaPOD mods
Former RPod 179
Current Cherokee Grey Wolf 24 JS

offgrid

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Posted: 31 Aug 2019 at 11:35am

Originally posted by furpod

As far as "why an R-Pod if it isn't aero?" I think because the shape is pleasing, and the original sizes were "just right". Sometimes, things don't have to be perfectly efficient, or the very best, at anything, to still be pleasing in people's eyes, or minds.

Thanks furpod,

Yah, I was only being half serious there. Tongue

But I do think lots of folks (myself included) think that the teardrop shaped front ought to be better aerodynamically. I'm not at this point convinced that it's not without seeing more data.

The rear is another story, it clearly drops off too steep to keep the airflow attached, that needs to be 15-20 degrees tops. You can see the detaching airflow on those youtube videos. So a proper spoiler placed where the curve reaches 15-20 degrees ought to help control it. i'm wondering if the new larger rPod spoiler is an attempt to do that.

I'm personally not a fan of FB. If someone is interested enough and finds something useful over there let me know.

1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold

GlueGuy

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Posted: 31 Aug 2019 at 9:23am

IIRC, Stephenh had tried the Purpleline Aero. I don't recall whether he felt it provided any benefit or not. Kind of noodling out loud is whether a reverse spoiler would provide any benefit? Something that was actually curved downward and sitting above enough to encourage the airstream at the back of the R-pod to stay attached long enough to fill the vacuum bubble.

bp
2017 R-Pod 179 Hood River
2015 Ford F150 SuperCrew 4WD 3.5L Ecoboost

furpod

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Location: Central KY
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Posted: 31 Aug 2019 at 7:36am

Not sure which is which as far as context there.. But, yes that is one of them. And it could be the particular guy I am thinking of wasn't on THIS forum. There used to be several, maybe 5 I think. Only 3 are any kind of active now, the one at FR Owners forum, The Nation, and Here.

FB has become the de facto "big dog" currently closing hard on 15,000 members.. literally hundreds of posts a day. On FB there are also several, much smaller, mostly specialty groups, like "R-Pod owners who tow with Jeep JK's", "Sunshine State R-Podders" etc etc.. I am a member in a couple of those groups, just because...

As far as "why an R-Pod if it isn't aero?" I think because the shape is pleasing, and the original sizes were "just right". Sometimes, things don't have to be perfectly efficient, or the very best, at anything, to still be pleasing in people's eyes, or minds.

I know a couple owners have tried the spoiler on the truck cap or rear of an SUV, I cannot recall any EUREKA!! moments being posted.

I did spend some time last year visiting with a work from the camper couple who had a ginourmous fiver. Biggest thing Grand Design makes. Towing with a F450.. They had a spoiler on the truck cab that they said gave them 20% better mileage.. which was something like 12 without, 15 with.. They had scaled at just under 18K pounds for the camper.. almost 28K for the whole rig.

offgrid

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Posted: 31 Aug 2019 at 5:46am

Thanks furpod,

It's unbelievable that FR would release a product without he required clearance lighting. But, it happened...

I found this post by Tidalwave4455 from 2012, was he the guy you're thinking of?

"The final aerodynamic simulations I ran were putting spoilers on the TV. I placed a rooftop spoiler midway on the TV and then at the rear...I also changed the angle of attack. There was only minor variations in turbulence. Again the deciding factor was the open gap between the TV and the Pod roof. There really is no way to smooth the airflow between the TV and the Pod because of the curved frontal roof of the Pod. That long gap really causes a lot of turbulence and pressure fluctuations.
It seems that you can gain 2+ mpg if your trailer has a rectangular 'breadbox' shape. The roofline

helps eliminate that open turbulent gap always present in the Pod."

That is a little surprising as the curved front shape is generally thought to improve aerodynamics, but maybe only if there isn't another vehicle in front of the trailer creating turbulence. If Tidalwave4455 is correct then I would think that a large spoiler like the Purpleline Aeroplus on the rear of an SUV tow vehicle ought to help more than anything.

If not and a box on wheels is really better aerodynamically and provides more useable internal space then what is the point of the rPod or any of the teardrop trailers' shapes?

When I looked for the airtab guy I didn't find anyone you actually did it but I did find this response from Airtab to a question about where to put them. Looks like he was looking at an original first gen trailer. I think I'll call FR next week and see what their reasons were for the more aggressive spoiler they have now.

"The Rpod trailer has a particularly evil fastback design (in side view) that much like the early Porsche 911 fastback body style, suffers from terribly high aero drag. That's because the location of flow separation on the curved roof top surface wanders forward & backward over the tail. As the rooftop's separation line wanders aft, the adverse pressure gradient builds to unsustainable levels and the flow separates, then the flow attachment line snaps forward and gets re-established. This unstable flow oscillation builds and collapses much like the current in an old ignition coil. Every time the flow separation location snaps forward it creates a huge unwanted burble of large scale turbulence that migrates back into the near wake. This unsteady flow has a periodicy that varies with vehicle speed.

Porsche stopped it by inventing the Whale Tail which also gave some downforce. Today's modern VW "Bug" has a smaller lip above the rear window. The purpose it is to fix the separation point at one location (in side view) so it doesn't migrate fore-and-aft over the rear window (which creates very high drag). A side benefit is that the vehicle then becomes more stable.

The little teardrop-shaped Rpod trailer badly needs a similar "lip" installed transversely across the entire rooftop - to fix the point of separation at one point. I would suggest it be located about one-foot aft of the rear of the rooftop air conditioning housing.

You could place a row of Airtabs across that station on the rooftop, but the vorticity would simply help the flow remain attached further aft. Unfortunately, eventually the flow would separate farther downstream, and then the unsteady flow mechanism would once again occur. Only this time it will be worse, because the unsteady aero forces are occurring farther aft on the trailer - which might make the tail wag the dog so to speak.

So don't let him use Airtabs transversely across the roof. Instead, have him mount them only on the sides - not in a straight vertical line but following the side contour. In other words, the trailing edge apex of each Airtab should be located just a couple of inches forward of the trailing edge of the side of the trailer. The line of Airtabs will be curved to mimic the side contour as viewed from the side. Much like the red painted "swoop" graphic except positioned far enough aft that the line of Airtabs will fit aft of the side window.

========================

The customer, JC, writes back in May 2012 saying this....

Mr. Latimer- again a very helpful reply, which I greatly appreciate. Forest River must have been talking to your aero guy, because they began installing a “lip” or spoiler, that goes transversely across the roof in 2012 (my unit has it) and all the units going forward. It looks exactly like what your aero guy is recommending. I’ll sketch out, my understanding of your air-tab scheme for the side of the trailer, scan and e-mail it, to make sure that I am understanding the advice. Then I can get a count together and place the order. Again thanks for your follow-up, which is both rare and appreciated."

1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold