replacing spoiler on rpod 179 - R-pod Owners Forum

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GlueGuy

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Topic: replacing spoiler on rpod 179
Posted: 28 Aug 2019 at 5:56pm

I have seen Youtube videos demonstrating that the spoiler does break the vacuum bubble at the back of an R-pod. That is the alleged intent is my inference. Any square-back TT will have a giant vacuum bubble that will alternately build and collapse. The point of the spoiler is to induce the airstream to tumble, which is supposed to collapse the bubble. Key word in the last sentence is "supposed". Unless someone employs a wind tunnel or something, that's pretty much all we have to go on.

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

offgrid

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Posted: 29 Aug 2019 at 4:14am

When I do my solar installation, I'll try to get some data. I''ll start with some coast down test runs with the spoiler on there, then some without, and see if there is any measurable difference at all. I want the initial data anyway to see what effect the solar array has.

But first we have hurricane season to get through.... Thumbs Down

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

Tibof

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Posted: 29 Aug 2019 at 5:30pm

It is my understanding that the spoiler is there for the lights it contains, as required by NTSB. IIRC, early Pods didn't have it. Showed up in 2014-15 I believe. I have removed it and out of necessity replaced it with a new one. The problem was what the dealer called "the notorious leak issue." No help at all from Forest River (it was two years old) or the dealer. FR sold me a new spoiler at full freight. The old one was too badly warped to reuse. Using my own approach to sealing the thing, it has been entirely successful. I've described the details on another post in this forum.

2015 Pod Hood River Edition
2012 Tacoma Crew Cab 4 Liter

podwerkz

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Posted: 29 Aug 2019 at 6:27pm

Originally posted by offgrid

You don't have data to support that statement, so its your opinion, Nor do I.

In my post #4, that's what I said, it's my OPINION, which means: no, I don't have supporting data in this case.

Quoting myself here:

I have a different opinion about that spoiler, I believe it IS for looks

So yeah, its an opinion, but it is an opinion based on some experience and knowledge gained over the years, not just a random wild guess.

At any rate, if a person had a way to raise and lower that spoiler with the push of a button, a simple device like the scangauge hooked up to the tow vehicle OBD port, and reading out instantaneous horsepower, might provide some insight to the effect the spoiler has...I'm betting it slightly increases overall drag. (yes, that's an opinion!)

r･pod 171 gone but not forgotten!

offgrid

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Posted: 30 Aug 2019 at 7:14am

Originally posted by podwerkz

That is my point....there is nothing about the spoiler on the r-pod that is done 'properly' (aerodynamically speaking)......so the OP should not worry about it at all.

I was referring to THIS post when I pointed out that it was ALSO an opinion.

In any case, I don't think we are having any significant disagreement, bottom line is that we really just don't know. Confused

There are 3 conventional ways to evaluate drag on a vehicle:

cfd modelling

wind tunnel testing

coast down testing

Wind tunnel testing is crazy expensive. I had some done once on a solar array roof mount system and it was well over $100K.

You've just added a interesting 4th option. Rather than a button to run it up and down, why not make a few runs, get the average hp data, remove the spoiler, and run another set of tests? Like with coast down testing you'd need to have a nice flat piece of road, no wind, and consistent temperature and humidity. But you wouldn't need to hold up traffic while coasting.

There are now some free personal use cfd software packages available, I'm thinking about downloading one and trying it out. Once the model is set up it would be possible to try out different aero details and see what effect they have. It would be good geeky rainy day fun if nothing else. Geek

These are interesting but not really very enlightening, other than showing that you don't want a low mounted spoiler.

https://www.youtube.com/results?search_query=rpod+airflow

furpod, are there any links to that aerodynamics work you mentioned that you know of?

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

GlueGuy

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Posted: 30 Aug 2019 at 11:19am

Originally posted by offgrid

furpod, are there any links to that aerodynamics work you mentioned that you know of?

I'm not furpod, but here are the airflow videos that I saw. please note they are from 2009, and they are looking at the original R-pod (not the "big butt" versions now in vogue).

This is without the spoiler:
https://www.youtube.com/watch?v=4HLBy-ui_FI

This is with the spoiler:
https://www.youtube.com/watch?v=3_qVNtlB1DE

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

offgrid

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Posted: 30 Aug 2019 at 5:12pm

GlueGuy, thanks.

Looks like those are the same ones I had found, I was wondering if there was something else that furpod was referring to in his post?

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

furpod

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Posted: 30 Aug 2019 at 7:42pm

There was another guy who did some modeling also.. But I don't know where it was hosted, though I do know it wasn't you tube. I think it was a nasa server actually. It was in '11 I think when I saw it. I do not remember the guys name/handle, he traded to a vintage Shasta not long after he posted up his results. When the spoiler first appeared there was some serious arguments about the thing, it's purpose, and it's effectiveness at air flow management.

At the time we had owners who HAD been stopped and ticketed for not having proper clearance lighting, as delivered from the factory.

EDIT: also, somewhere in the way back of the site.. there was a guy who did in fact experiment with the "Air Tabs". He put hundreds of them on his pod. Claimed he saw a 15% or so increase in MPG.. Looked like crap though.. LOL

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

furpod

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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.