Caulking the 'spoiler' |
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offgrid
Senior Member Joined: 23 Jul 2018 Online Status: Offline Posts: 5290 |
Topic: Caulking the 'spoiler' Posted: 20 Jul 2020 at 3:37pm |
We have had at least one rpod owned by someone on this forum where the frame failed at the axle location. So they can break, no question. I've done the stress calcs and I'll be generous and say that the frames are not over engineered. If you were to assume that anywhere aft of the axle was equally good to place load, with no regard for the distance to the axle, then that would certainly exacerbate the likelihood of that kind of failure happening. That's pretty obvious, and most owners know not to hang heavy stuff way out there. LA, you have done the smart and prudent thing and measured your tongue and trailer weight accurately, one time. Once you have done that there isn't any need to repeat the process unless you make significant changes to your trailer or its loading. Barring coming across those gold bars camping in the CA gold country sometime your loading for the next trip isn't going to be much different from the last one. I don't check mine each time either. Its the same with flying, the FAA says you are supposed to do a weight and balance calc every time you fly but if you are loaded with the same ppl and stuff in the same seats and places there is no reason other than regulations. So pilots don't do it. They at most just keep the same w&b sheet in the plane so they can show it to the FAA inspector if they get ramp checked. I know for sure that some of the semis roll along I81 here at well over 80 because they handily pass me in my Prius while I'm cruising in the high 70's. Not all, but many do. I81 has more tractor trailer rigs than street cars on it most of the time. If your fore/aft trailer balance is good you will get a very noticeable buffet but not a wag. My guess is that the spoiler does a little to reduce drag but it would need to be larger to be really effective. Someone correct me if I'm wrong but I believe it is larger on the newer rpods. |
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
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lostagain
Senior Member Joined: 06 Sep 2016 Location: Quaker Hill, CT Online Status: Offline Posts: 2587 |
Posted: 20 Jul 2020 at 5:26pm |
I always load my gold bars just forward of the axle. I leave the trailer hitch platform on the back of the trailer for the silver. Remember we are gifted with both here in the Comstock Lode.
Good point on the broken frame, OG. I forgot about that one. Was there ever a cause determined? Was it from overloading fore and aft of the axle, or from something as mundane as mid-west salt corrosion? How do those bridges stay standing back there? Some look like the rust is the only thing holding them up. If it were up to me, I'd pay truck drivers by the hour not the mile, so they wouldn't be pushed to drive way, way too fast. But that's another issue for another forum and has nothing to do with spoilers. Doesn't the spoiler wind deflection push the back of the trailer down, i.e. more "weight" aft of the axle? True their so small it's probably inconsequential, but what's the point of putting them on in the first place. Kind of like the fins on a 1957 DeSoto.
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Never leave footprints behind.
Fred & Maria Kearney Sonoma 167RB Our Pod 172 2019 Ford F-150 4x4 2.7 EcoBoost |
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offgrid
Senior Member Joined: 23 Jul 2018 Online Status: Offline Posts: 5290 |
Posted: 20 Jul 2020 at 6:11pm |
it was Olddawgsrule's trailer that had the frame failure, I don't think it was from rust, but maybe we could get an update.
When I did the stress calc on it I assumed uniform loading in the trailer and 3500 lbs axle load and got a safety factor of less than 2. That's really not enough considering bump loading. Really it could happen to any of us if we were heavily loaded and hit a good big pothole, especially if that load was hanging off the rear bumper and not uniformly distributed.
I think some of the bridges just haven't figured out yet that they should fall down. Some have. The Silver Bridge across the Ohio at Pt. Pleasant WV being perhaps the most famous. Some folks blame the Mothman for that one but it was just plain old corrosion stress fracturing. There is a Richard Gere movie about it if you want to hear the Mothman theory. Wings are different from spoilers. High performance cars use inverted wings to create downforce to hold the cars down at high speed for better handling. Those produce lots of drag so are doing the opposite of what spoilers are intended to do. The spoilers on the backs of regular passenger vehicles and trailers don't create much downforce, their purpose is to subtly redirect airflow so it doesn't get trapped in a pocket behind the vehicle. As far as truck drivers travelling too fast, that can spoil you whole day....There are a certain number of drivers that are gonna speed. When you have a rural freeway posted at 70 for both trucks and passenger cars you're gonna see some folks driving in the mid 80's. I see significantly less truck drivers doing that than car drivers, so that speaks well for them overall. |
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
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StephenH
podders Helping podders - pHp Joined: 29 Nov 2015 Location: Wake Forest, NC Online Status: Offline Posts: 6288 |
Posted: 20 Jul 2020 at 8:23pm |
Speaking of spoilers, has anyone tried adding AirTabs to the RPod? Do they help or is it hype?
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StephenH
Happy is the man that findeth wisdom,... ouR escaPOD mods Former RPod 179 Current Cherokee Grey Wolf 24 JS |
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offgrid
Senior Member Joined: 23 Jul 2018 Online Status: Offline Posts: 5290 |
Posted: 21 Jul 2020 at 5:21am |
If they work its because the air stays away from them because they're soooo ugly....I can't imagine putting those things on my trailer.
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
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StephenH
podders Helping podders - pHp Joined: 29 Nov 2015 Location: Wake Forest, NC Online Status: Offline Posts: 6288 |
Posted: 21 Jul 2020 at 8:29am |
I did some searching and came up with two things: 1. They can help with increasing attached air flow. 2. They do increase drag. The caveat is that the wind tunnel testing I saw was on a race car being modified for aerodynamics. They were testing a lot of other modifications as well. OTOH, there are other opinions that while they may increase drag a bit, they do significantly decrease wind buffeting and increase stability, especially when being passed by the big rigs. That in itself might be very helpful. As for the appearance, they can be painted. Trying to color-match the RPod though might be difficult.
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StephenH
Happy is the man that findeth wisdom,... ouR escaPOD mods Former RPod 179 Current Cherokee Grey Wolf 24 JS |
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lostagain
Senior Member Joined: 06 Sep 2016 Location: Quaker Hill, CT Online Status: Offline Posts: 2587 |
Posted: 21 Jul 2020 at 9:20am |
AirtabĀ® is a brand name for a vortex generator. There are lots of different ones on the market, most of which seem to be grossly overpriced for little sticky back pieces of injection molded plastic. Here is an interesting discussion regarding vortex generators used on an SUV: http://dspace.calstate.edu/bitstream/handle/10211.9/1780/Sevilla%20-%20Thesis%20Final.pdf?sequence=5
It looks like vortex generators can improve the wind turbulence problem. The question remains which shapes work best for a travel trailer and are they really worth the cost, especially given the limited use of trailers. For a semi-tractor/trailer on the road nearly every day at highway speeds, the savings in fuel may make it cost effective in a few months. For a travel trailer, they may get brittle and break or fall off long before you've gotten your money's worth.
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Never leave footprints behind.
Fred & Maria Kearney Sonoma 167RB Our Pod 172 2019 Ford F-150 4x4 2.7 EcoBoost |
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Phil from Maine
Newbie Joined: 12 Jul 2020 Location: 04074 Online Status: Offline Posts: 19 |
Posted: 21 Jul 2020 at 9:55am |
One has to assume that Forest River did the design calculations to at least meet min. safety standards and that the TT is balanced correctly. The R-POD 172 only weighs 2113 pounds and is presumably proportioned at 60-40 at the axle rear and with 10 to 15 percent being tongue weight. My add on rear bumper minus the weight of the stock bumper probably doesn't exceed the weight of a fifty pound additional house battery mounted near the tongue of the TT. If it does exceed it, the difference is insignificant. The GVWR is 3179 pounds. I highly doubt that I add more than a 100 pounds to the POD in personal items while traveling. As was said by others, the real safety variables for us are speed and the occasional very poor (dangerous) highway infrastructure. |
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offgrid
Senior Member Joined: 23 Jul 2018 Online Status: Offline Posts: 5290 |
Posted: 21 Jul 2020 at 10:32am |
There is no formal specification for safety factor in vehicle frame design. In fact the numbers used by vehicle manufacturers are considered trade secrets. Guidance in the trucking industry is 2.5 to 3x for bump loads. Cars and pickups are higher. Rpods are significantly less than that. There have been numerous instances of axle failures in rPods. So I would assume nothing about the way FR did their design calcs.
That being said, the 172 is probably in the best shape as far as the frame and axle goes as it is a light rPod. The failures have all been in the heavier trailers in the series I believe. OTOH, 172's are one of the ones that has exhibited sway. It will most likely occur when the black and gray tanks are full as they are both behind the axle. Loading additional weight on the rear won't help that. Like I said, you can do what you want but my recommendation remains to verify your actual tongue weight percent under worst case aft loading conditions and be sure you're over the magic 10% number.
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
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Phil from Maine
Newbie Joined: 12 Jul 2020 Location: 04074 Online Status: Offline Posts: 19 |
Posted: 21 Jul 2020 at 10:55am |
Actually, on the 2011 R-POD both the black and gray tanks are located forward of the axle. The fresh water tank is located aft of the axle. However, I understand the concept you are putting forth. You obviously know your stuff. Thanks for the education.
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