eb145 wrote:
So if you have a 8,000 lb GVWR trailer, the ball and coupler MUST be able to handle 24,000 lbs. of force in either direction (forward or reverse). I think the force on each chain from compressing the bushing for a heavy trailer can be around 1,000 pounds per chain.
This means 2,000 pounds of force (more or less) is applied to the coupler (1,000 lbs. per chain) that is rated for 24,000 pounds of force. This seems like a pretty good safety margin. But again, these are calculations (that I think I got right) - only time will tell for sure.
Ed
So if you have a 8,000 lb GVWR trailer, the ball and coupler MUST be able to handle 24,000 lbs. of force in either direction (forward or reverse). I think the force on each chain from compressing the bushing for a heavy trailer can be around 1,000 pounds per chain.
This means 2,000 pounds of force (more or less) is applied to the coupler (1,000 lbs. per chain) that is rated for 24,000 pounds of force. This seems like a pretty good safety margin. But again, these are calculations (that I think I got right) - only time will tell for sure.
Ed
Hi Ed,
Welcome to the discussion! When you came up with 1,000# per chain load, what are the assumptions surrounding this?
- TT loaded tongue weight
- Rear overhang on the truck (ball to center of the rear axle)
- Truck wheel base
- TT ball center to TT front axle center
- Your "target" for returning the front end of the TV from WD from unhitched weight
On this post of this thread, page 2 John's calc's I backed into an approx chain force on my camper and truck setup with a simulated 1,000# and 1,400# loaded TW. I was targeting returning the truck front end back to slightly above unhitched weight, ~ 100# lighter
I backed into this on how much torque needs to be created in the receiver by a conventional spring bar WD hitch and then recreated that using an approx fulcrum length of 8" on the Andersen. I am significantly more then your 1,000# / chain.
Naturally this is all based on what assumptions are used. I'm not saying 1,000# is not correct in your case, just it was very different than what I came up with. While you are sorting this out for yourself, I am just trying to help make sure you did not miss something. Or to help correct my missed assumptions.
On the ball coupler, I tried to connect with coupler manufacture of my brand coupler. After 3 tries, getting the same admin who said she gave him the message and he never called back...well, I gave up. I understand, this guys wants to know our design specs on some new hitch out there and I don't have time for this....
By the specs, the latch side of the coupler can take as much as pulling forward. I have read the spec myself, and it was pretty clear. And yes I know they are lab tested in the way the test was done. Just to date, there are not many, (if any) other than the Andersen towing by the WD chains of the hitch and having those "constant" forces that alternate as you tow down the road into the coupler latch. If any one has fatigue data on a ball coupler latch, forward or reverse, please help point us to it.
I know about FEA model simulation as I am exposed to it often/daily in failure analysis. It is a very proven and accurate science. However I also know it is only as good as the inputs to the system. If you do not know where all the forces are coming from or their magnitude, the end result of the FEA can point you in a misleading direction. Ideally, create the model, apply all your knows, run the simulation and then, go strain gage the entire system and confirm the real known forces under use. Now you tweak the model for actual forces in the field and increase the confidence you have it right. This costs a lot of money, I know.
The RV industry has found out many times when working towards new light weight trailer A frames, trailer frames etc. The extra saftey factor of years gone by got them through, until they removed some of it by accident down sizing components, gave them to the open public to use and wow, how did they do that....
Point: As you work your way through this decision, you will need to sort through the ball coupler decision and WD ability for your rig.
The reports by users on the camping forums have been mixed. Many to most all have reported a positive increase in the smoothness of towing. They should, as the urethane has that going for it as a force dampener. Actual WD on the TV for higher TW's within the rating of the Andersen is the area of most controversy. Campers with lower TW's have done well. Higher TW's, some have had issues getting to what they feel is proper WD on the truck. A limited few with higher TW's have reported failure of the urethane under load.
I myself do not agree with Andersen's concepts of how they declare what is proper WD. It is only my opinion, not anyone else's and the user/owner of the hitch needs to come to grips with this for their TV and TT combination.
Good luck as you sort through this, if you get one, please report back. Curious to always learn more.
Hope this helps
John
* This post was edited 05/04/13 08:39am by JBarca *
John & Cindy
2005 Ford F350 Super Duty, 4x4; 6.8L V10 with 4.10
CC, SB, Lariat & FX4 package
21,000 GCWR, 11,000 GVWR
Ford Tow Command
1,700# Reese HP hitch & HP Dual Cam
2 1/2" Towbeast Receiver
2004 Sunline Solaris T310SR
(I wish we were camping!)
TomG2 wrote:
How many and what kind of failures are they reporting?
For those who do not follow the big Andersen Hitch thread on airforums.com --How many and what kind of failures are they reporting?
the latest word from Andersen regarding coupler failures can be found in this post - #1752.
Ron
* This post was edited 05/04/13 09:29am by Ron Gratz *
Ron Gratz wrote:
the latest word from Andersen regarding coupler failures can be found in this post - #1752.
Ron
TomG2 wrote:
How many and what kind of failures are they reporting?
For those who do not follow the big Andersen Hitch thread on airforums.com --How many and what kind of failures are they reporting?
the latest word from Andersen regarding coupler failures can be found in this post - #1752.
Ron
To save some the trouble of checking out the link, here is the most pertinent part:
"...Response:
Great question Kurt. Only the Atwood 88xxx series couplers are incompatible with our Weight Distribution Hitch. ALL OTHER Atwood couplers are fine (80xxx, 81xxx, 82xxx, etc). We are still doing testing, but our initial findings are that the best solution for the 88xxx series is to change out the coupler. Luckily it is not a common coupler, but is popular on Airstream trailers."
Thanks. I have neither an Airstream or 88xxx coupler, so I should be good to go. Still don't see but one documented failure.
Anyone interested in the Andersen WDH might find all of this report to be "pertinent".
Ron
both the length of the ball/shank an issue (solve by increasing either that length
and/or the amount of force via the bushings)
What isn't or hasn't been discussed is that the regular or traditional WD Hitch
systems 'do' beat up the coupler latch over time WITHOUT the constant contact
and force of the bushings.
The dynamic forces are NOT just from braking, or acceleration, but from all
directions during a common road trip over the less than pristine roads, RR crossings,
potholes, etc AT SPEED
What would you guys think or guess the forces on the latch is during a severe
whoop-do ?
Where the hitch is driven downwards to stretch the bottom plate to chain to rod to bushing?
There has been reports of the bushing shattering, or when the set screws employed
that they did not hold (allowed that bracket to move)
This thread was one of the 1st on the new Andersen WD hitch. It has been educational and enjoyable by many. And some, do not like the analytical nature of it. Both points of view are fine, but lets respect each other in the process.
Our forums are filled with most every brand of WD hitch on the market. And if we dig deep enough, there have been negative and positives on everyone of those brands. Many brands have failed or put the RV'er is a very negative situation and it has been discussed here on our forum. This includes the brand I own. Through education and understanding, now I know what not to do and why and so do many others.
There is no one size fits all even if some manufactures claim this to be the case. By "us" talking about them, RV net has helped many fellow RV'ers at least stop and "think" about their hitch, adjust it properly or get a better perspective to ask better questions to see if it fits "their" application. Lets keep that positive momentum going.
So don't see their comments to have me comment back...
![[emoticon]](http://www.coastresorts.com/sharedcontent/cfb/images/biggrin.gif "biggrin")
Even asked the admin (not moderators) to increase the allowed number
on my blocked list (yes, hit the limit several times...think mine now
has an unlimited number)
Better now, as I don't see their posts...just a line that states
'Post not shown due to blocked member xyz'
Still think the Andersen original and elegant, but their execution
lacking, IMHO
The novel use of plastic springs solves one huge problem with the traditional
spring bar and that is the rate of 'released' of energy, which contributes to
'bouncing' or 'porpoising' A few here used 'dampening', which it
does so with a slower stored energy release rate
If only they could be used in a traditional WD hitch...would that
solve that problem?
Down side is that their limited stroke married with the short moment
of the ball/shank limits the Andersen to lighter tongue weights.
Maybe an increased stack of those same plastic bushings, but just a
thought that would need more noodling
John, you posted some pictures a while back of your trailer coupler
that had thousands of miles with a traditional WD Hitch system.
It looked very typical vs the miles on it and the latch pawl was
beat up. I've seen much worse and NOTE that is with a traditional WD
Hitch system that does NOT have the constant contact that the Andersen
architecture has
Anyone have an image or reference link to the coupler mentioned in
that Airstream link? I'd like to see it vs the others that Andersen
endorses
Agree that these discussions are GREAT and am now leaning towards a
new to me, Blue Ox system. Knew of them, saw images of them, but never
looked closely till someone posted in another thread. I am now leaning
towards them...instead of PullRite (still will consider PullRite)
As for the derogatory comments/commenters...block them and if anyone
finds me offensive, please block me !!!!
JBarca wrote:
Hi Ed, Welcome to the discussion! When you came up with 1,000# per chain load, what are the assumptions surrounding this?
John, I don't know how Ed did it, but here is my approach to defining the relationship between tension and load transfer.Hi Ed, Welcome to the discussion! When you came up with 1,000# per chain load, what are the assumptions surrounding this?
First we need to define some dimensions and variables. Let:
a = tow vehicle wheelbase
b = ball overhang (longitudinal distance from TV rear axle to ball)
c = distance from ball to mid-point between the TT's axles
d = perpendicular distance from Andersen chain to center of ball (reported by Andersen owner to be 6.5")
TW = tongue weight
LTT = load transferred to TT's axles
LF1 = load removed from TV's front axle due to TW without WD applied
LF2 = load transferred to TV's front axle when WD is activated
T = Andersen chain tension per chain
M = moment (torque) generated by Andersen chain tension (total for 2 chains)
then (assuming zero pitch-axis rotational friction between ball and coupler)
M = 2*d*T
LTT = M/c = 2*d*T/c
LF2 = LTT*(b+c)/a = 2*d*T*(b+c)/(a*c)
also
LF1 = TW*b/a
If we want to restore a load equal to some percentage (call it FALR) of that which was removed from the front axle, we have:
LF2 = LF1*FALR/100, or 2*d*T*(b+c)/(a*c) = FALR*TW*b/(a*100)
solving for chain tension (per chain) gives
T = FALR*TW*b*c/{2*d*(b+c)*100}
for example, if: b=60", c=200", d=6.5", TW=600#, and you want to restore 50% of the load removed (FALR=50)
T = 50*600*60*200/(2*6.5*260*100) = 1065# per chain
Ron
BenK wrote:
Anyone have an image or reference link to the coupler mentioned in that Airstream link? I'd like to see it vs the others that Andersen endorses
Ben, I believe the coupler which is the subject of this post - #1772, Atwood 88010, is depicted in these Repair Kit Instructions.Anyone have an image or reference link to the coupler mentioned in that Airstream link? I'd like to see it vs the others that Andersen endorses
A coupler cross-section is shown on page 2.
I have not seen a schematic for the Atwood 81911 which is being considered as a replacement for the damaged 88010.
Anyone who is considering using the 81911 with the Andersen WDH should be aware of this information from an etrailer.com expert:
"I spoke with my contact at Atwood and there is not a repair kit available for the Atwood # 81911, 2-5/16 inch Ball, A-Frame Tongue coupler.
If this coupler is damaged the complete unit will need to be replaced."
expert reply by: Bob G
The date of the "expert reply" is unknown, so it would be good for potential 81911 buyers to see if a repair kit is currently available (just in case one might be needed).
Ron