GVWR>GAWR and Stabilizer Issues |
Post Reply | Page <1 34567> |
Author | ||
Vikingr
Newbie Joined: 25 Dec 2018 Location: Maryland Online Status: Offline Posts: 24 |
Topic: GVWR>GAWR and Stabilizer Issues Posted: 07 Jan 2019 at 10:16am |
|
Below is axle sticker on my 172. Also, assuming it makes a difference, it's mounted in a diamond, not square, configuration.
|
||
lostagain
Senior Member Joined: 06 Sep 2016 Location: Quaker Hill, CT Online Status: Offline Posts: 2587 |
Posted: 07 Jan 2019 at 9:50am | |
offgrid, thanks for the info on weighing each bearing point with the Sherline scale. I was thinking of doing an initial tongue weight check with the trailer in it's mostly empty state state [just the normal junk we keep inside such as pots pans], then use it when loaded to get an idea where, relative to for and aft, the weight was shifting. It wouldn't take but a few minutes to check this with the trailer parked. Since we use a WDH the actual axle weight on our truck and trailer would change everything around, but if the rig is basically straight and the truck is balanced fore to aft, then we should be ok.
For us, going to a public scale is would take over an hour round trip and I figure I can get the basics using the little Sherline scale in about half that time. And since we travel with relatively light loads in the trailer, I hope [maybe more accurately, fantasize] that we will not be overweight. From experience, the heaviest loads we've carried have never presented any driving anomalies which would be of concern. Indeed, driving with the trailer attached is smoother than without, though we certainly won't win a drag race.
|
||
Never leave footprints behind.
Fred & Maria Kearney Sonoma 167RB Our Pod 172 2019 Ford F-150 4x4 2.7 EcoBoost |
||
offgrid
Senior Member Joined: 23 Jul 2018 Online Status: Offline Posts: 5290 |
Posted: 07 Jan 2019 at 8:37am | |
Well that was interesting.
I measured the overhang of the axle.spindle and the distance between axle attachments, and also took a look at how much it might be possible to reduce the overhang. I assumed that the wheel loads are applied at the midpoint between the inner and outer bearing races. I get an overhang of about 13.75 inches and a distance between supports of 60.5 inches.
I also was able to see the axle tube wall thickness at the ends. I couldn't get my micrometer in there but I estimated it to be 3 inch box tubing with a 3/16 wall thickness. That gives an axle bending stress of about 12ksi (12000 psi) for a 1750 lb load on each wheel. Mild steel has a yield strength of about 35 ksi so that would imply the axle could take a bump load of just under 3g's. From what I've seen on vehicle design, a minimum load factor of 2.5-3 g's is pretty typical, so the current design is right in there, about as light as you'd ever want it to be for the loads it takes, but not severely under designed either. Its worth noting that this stress is uniform over the whole axle tube if the same load is applied to both wheels, so if you were to generate a high bump load on both wheels (say by going over a speed bump too fast) you could end up bending the axle anywhere along its length. If you went over a bump on one wheel only then it would of course be likely to fail first on that overhang. It also looks like by extending the axle attachment points outward we could get the overhang down to about 6.75-7 inches, which would reduce the axle bending stress by a factor of about 2! I think that's well worth exploring further. One thought I had on an easy way to improve this would be to simply strap a 2.5-3 inch steel angle to the full length along the bottom of the axle. I'll take a look at the numbers on that and report back. |
||
1994 Chinook Concourse
1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
||
offgrid
Senior Member Joined: 23 Jul 2018 Online Status: Offline Posts: 5290 |
Posted: 07 Jan 2019 at 4:04am | |
The problem with going by the label on the side of the 171's/172's to determine axle rating is that the 3000 lbs listed there could easily just be derated from what's really the same 3500 lb axle used on the heavier rPods. There should be a sticker on the axle itself with the manufacturer, a weight rating, a part number, and a "variant number". If someone wants to take a photo of that and post it I can compare it to the data on my 179 axle.
|
||
1994 Chinook Concourse
1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
||
offgrid
Senior Member Joined: 23 Jul 2018 Online Status: Offline Posts: 5290 |
Posted: 07 Jan 2019 at 3:53am | |
+1. The Timbren solution won't work on an rPod without adding a structural weldment to mount it to, which would need to extend laterally across the trailer to take the torsional loads. That would negate the claimed benefit of having an "axle-less" design.
StephenH, I saw that video too, but because it requires a new axle its only a solution for an rPod owner who already has a bent axle so has to buy a new one. GlueGuy's concept would allow us to reinforce our existing axles before they fail. I'll try to take a couple measurements today and see how much bending load reduction we might expect to get with GlueGuy's approach. If anyone either knows or has access to an old axle they can cut open, the wall thickness of the axle tube would be useful for that calculation. lostagain, using a Sherline tongue scale would work for what you're suggesting and also allow someone to measure the side to side weight imbalance of their trailer. mcarter suggested that several months ago in another thread. You would need to jack up one wheel at a time and lower the trailer onto the scale while raising the opposite wheel so the trailer winds up level side to side. Should work as long as you're careful. In my case, I've obtained my tongue weight and axle weight the cheap and lazy man's way using a public scale, so its really only the side to side imbalance that's a question mark. I'm not sure I want to spend $125 just to know that. It's really only a one time measurement. But if any folks here want to split the cost of one I'd be game. |
||
1994 Chinook Concourse
1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
||
StephenH
podders Helping podders - pHp Joined: 29 Nov 2015 Location: Wake Forest, NC Online Status: Offline Posts: 6289 |
Posted: 06 Jan 2019 at 3:44pm | |
|
||
StephenH
Happy is the man that findeth wisdom,... ouR escaPOD mods Former RPod 179 Current Cherokee Grey Wolf 24 JS |
||
David and Danette
podders Helping podders - pHp Joined: 24 Nov 2009 Online Status: Offline Posts: 1215 |
Posted: 06 Jan 2019 at 3:37pm | |
Do you think Timbren Axle-Less Suspension would work on the a r-pod?
|
||
2018 Vista Cruiser 19BFD (2018-
2012 Vibe 6503 (2014-2019) 2009 r-pod 171 (2009-2014) Middle Tn 2014 Ram 1500 Quad cab |
||
StephenH
podders Helping podders - pHp Joined: 29 Nov 2015 Location: Wake Forest, NC Online Status: Offline Posts: 6289 |
Posted: 06 Jan 2019 at 2:08pm | |
Actually, I was considering that myself. I was not told that by FR. It makes sense that the additional distance between the mounting points and the wheels means more force able to be exerted on the axle beam than if the mounting point were closer. In addition, I saw this video that indicates the same thing:
The video shows one solution, but it also included not only fabricating a new support bracket and welding it to the frame, but ordering a new axle with mounting brackets closer to the wheels. e
[/QUOTE]
|
||
StephenH
Happy is the man that findeth wisdom,... ouR escaPOD mods Former RPod 179 Current Cherokee Grey Wolf 24 JS |
||
lostagain
Senior Member Joined: 06 Sep 2016 Location: Quaker Hill, CT Online Status: Offline Posts: 2587 |
Posted: 06 Jan 2019 at 1:40pm | |
So, if you weigh the tongue weight with one of those little Sherline tongue weight scales, and weigh each wheel weight with same, you'd have the total trailer weight by adding the results? Seems that for the price of that scale, a lot of uncertainty could be clarified and you could easily balance the trailer if you were in doubt about the balance and total weight. In my imagination, which is very fertile, one could complete this process much faster than going to a public scale.
Ok, our Pod Board engineers, will this work, or do I need to lay off the arguardiente again? michaeln, our posts crossed in cyberspace. So, how come your data plate looks so nice and new. Could it be my trailer is a 2009 and yours is nice and new?
|
||
Never leave footprints behind.
Fred & Maria Kearney Sonoma 167RB Our Pod 172 2019 Ford F-150 4x4 2.7 EcoBoost |
||
michaeln
Groupie Joined: 08 Dec 2018 Location: Avery, CA Online Status: Offline Posts: 40 |
Posted: 06 Jan 2019 at 1:16pm | |
Here is the label from my 16-171:
|
||
---
Avery, CA |
||
Post Reply | Page <1 34567> |
Forum Jump | Forum Permissions You cannot post new topics in this forum You cannot reply to topics in this forum You cannot delete your posts in this forum You cannot edit your posts in this forum You cannot create polls in this forum You cannot vote in polls in this forum |