Journey with Confidence RV GPS App RV Trip Planner RV LIFE Campground Reviews RV Maintenance Take a Speed Test Free 7 Day Trial ×
 


Reply
 
Thread Tools Search this Thread Display Modes
 
Old 01-28-2015, 10:13 PM   #21
3 Rivet Member
 
2002 25' Classic
Kalama , Washington
Join Date: Feb 2003
Posts: 189
One way to get help locating the various weights is to use center of gravity calculations similar to those used for aircraft or ships. You can google for details or visit a local airport and ask a pilot to explain it.
Basically, establish a point (datum) to measure distances (called arms) to the weights you'll locate. Each distance multiplied by the object's weight gives a moment. The total moment (possibly made up of both + and - moments depending on whether they are forward of or behind the datum) divided by the total weight gives the center of gravity (CG).
I'd recommend deciding on the needed tongue weight and achieve it with weight forward added or removed to get it, first. The CG with that tongue weight is the one to maintain as you place the other weights.
As others have suggested, it's more than a front to rear balance game… empty weight, max weight, useful load and lateral balance will influence how it travels.
Good luck with your project.
nwclassic is offline   Reply With Quote
Old 01-28-2015, 10:31 PM   #22
Rivet Master
 
Al and Missy's Avatar
 
2002 30' Classic S/O
Fleming Island , Florida
Join Date: Nov 2013
Posts: 4,668
NWClassic beat me to it, but anyway, here goes:

You also need to consider the weight of the trailer itself, but that works in your favor since a majority of the trailer structure is forward of the axles.

As for estimating the tongue weight, the physics of this is pretty straightforward if we ignore the fact that you have dual axles and a suspension. These are reasonable assumptions to estimate tongue weight since, for ideal towing, the trailer would be level and the load on the axles the same. You need to measure the distance from the center of the axles to each of your loads including the trailer structure and the coupler. Call every distance forward of the center of the axles positive and every distance aft of the center of the axles negative. Weights of the trailer are forces down - call them positive. For each load, multiply the weight by the distance, letting the weight of the coupler be T, for Tongue weight. The sum of all these (moments) must be zero.

As a simple example consider a trailer with the dry weight of the trailer centered on the trailer and say that center is 5 feet forward of the axles, and the dry weight is 5000#. The coupler is 15 feet from the axles. There is a load of 200# 2 feet forward of the axles and another load of 500# 10 feet behind the axles. Then starting from the rear:
500x(-10)+200x(2)+5000x(5)+Tx(15)=0
-5000+400+25000+15T=0
20400=-15T
T=-1360
The significance of the negative sign is that there must be a force upward on the tongue of 1360# to balance the weight of the trailer and its contents.

A simple example, and one with too much tongue weight, but hopefully you get the idea.

Al
__________________
“You cannot reason someone out of a position they have not been reasoned into"
Al, K5TAN and Missy, N4RGO WBCCI 1322
2002 Classic 30 Slideout -S/OS #004
2013 Dodge 2500 Laramie 4x4 Megacab Cummins
Al and Missy is offline   Reply With Quote
Old 01-30-2015, 04:26 AM   #23
4 Rivet Member
 
trekerboy's Avatar
 
1979 31' Excella 500
Charlevoix , Michigan
Join Date: Aug 2014
Posts: 350
Quote:
Originally Posted by Earthcreeper View Post
Try to duplicate factory spec for tongue weight.

A Sherline scale will be exactly what you need.

http://www.sherline.com/lm.htm

Thanks for the link, just ordered it!

Quote:
Originally Posted by nwclassic View Post
One way to get help locating the various weights is to use center of gravity calculations similar to those used for aircraft or ships. You can google for details or visit a local airport and ask a pilot to explain it.

Basically, establish a point (datum) to measure distances (called arms) to the weights you'll locate. Each distance multiplied by the object's weight gives a moment. The total moment (possibly made up of both + and - moments depending on whether they are forward of or behind the datum) divided by the total weight gives the center of gravity (CG).

I'd recommend deciding on the needed tongue weight and achieve it with weight forward added or removed to get it, first. The CG with that tongue weight is the one to maintain as you place the other weights.

As others have suggested, it's more than a front to rear balance game… empty weight, max weight, useful load and lateral balance will influence how it travels.

Good luck with your project.

Thanks! This is really helpful!

Quote:
Originally Posted by Al and Missy View Post
NWClassic beat me to it, but anyway, here goes:

You also need to consider the weight of the trailer itself, but that works in your favor since a majority of the trailer structure is forward of the axles.

As for estimating the tongue weight, the physics of this is pretty straightforward if we ignore the fact that you have dual axles and a suspension. These are reasonable assumptions to estimate tongue weight since, for ideal towing, the trailer would be level and the load on the axles the same. You need to measure the distance from the center of the axles to each of your loads including the trailer structure and the coupler. Call every distance forward of the center of the axles positive and every distance aft of the center of the axles negative. Weights of the trailer are forces down - call them positive. For each load, multiply the weight by the distance, letting the weight of the coupler be T, for Tongue weight. The sum of all these (moments) must be zero.

As a simple example consider a trailer with the dry weight of the trailer centered on the trailer and say that center is 5 feet forward of the axles, and the dry weight is 5000#. The coupler is 15 feet from the axles. There is a load of 200# 2 feet forward of the axles and another load of 500# 10 feet behind the axles. Then starting from the rear:
500x(-10)+200x(2)+5000x(5)+Tx(15)=0
-5000+400+25000+15T=0
20400=-15T
T=-1360
The significance of the negative sign is that there must be a force upward on the tongue of 1360# to balance the weight of the trailer and its contents.

A simple example, and one with too much tongue weight, but hopefully you get the idea.

Al

Thank you Al, I'm a visual learner so seeing your example really connected the dots for me.
trekerboy is offline   Reply With Quote
Old 01-30-2015, 05:04 AM   #24
Rivet Master
Commercial Member
 
Vintage Kin Owner
Naples , Florida
Join Date: Dec 2005
Posts: 7,508
Quote:
Originally Posted by TommieDee View Post
My 30ft Flying Cloud is set up with 4 Lifeline 6 volt AGMS batteries, total amps:880, total weight: 264#, no venting needed! I have a Magnum MS 2000 Inverter. I haveThese GPL-4CT batteries will last years verses the old style! Another issues is to keep the inverter and batteries as close together as possible,more efficient, less loss of voltage. Most of the installation I've seen, including my trailer with a forward couch or bed is to place the system underneath, then run shore power to the inverter and then back to the distribution( breakers, fuses)point. This setup keeps all the weight forward of the axles, yet 4ft to 10ft behind the hitch, centered left to right and easily accessible. This setup tows great. I also use a Hensley Hitch. You also have room for a solar panel controller.
Tommie,

Just a quick note;

Your lifeline GPL-4CT batteries are 6VDC and 220 amp/hours, so you have 2 in series pairs to make 12VDC and then paralleled. Your total capacity is 440 amp/hours, not 880.
__________________
lewster
Solar Tech Energy Systems, Inc.
Victron Solar Components and Inverters, Zamp Solar Panels, LiFeBlue and Battle Born Lithium Batteries, Lifeline AGM Batteries
lewster is offline   Reply With Quote
Old 02-11-2020, 06:36 PM   #25
2 Rivet Member
 
1968 26' Overlander
Los Gatos , California
Join Date: Oct 2018
Posts: 72
Still confused...

Hi forum!

I am in the middle of a gut job on my 1968 Overlander. I had not even considered weight distribution until I posted plans of my electrical system and got feedback to move my battery bank to the front of the trailer to avoid swaying. But now I'm reading things about not wanting to overload the tongue either! I plan on updating to lithium batteries, so lighter weight - but I want a big battery bank to support week(s) of boondocking. So I imagine it will be heavy.

The original batteries were in the rear of the trailer. I can move that setup to the front of the trailer BUT the fresh water tank sits above the subfloor there (under the couch) and is sort of fixed because of the input nozzle for the hose...So do I move the fresh water tank and put the batteries in the very front? Do I keep the original layout of fresh water in front batteries in back? Do I put the battery bank on the streetside of the trailer just behind the fresh water tank? (My couch will be in an L shape so they could go there also).

I appreciate any input!
__________________
Summer
1968 Overlander
Stargirl is offline   Reply With Quote
Old 02-11-2020, 09:45 PM   #26
"Cloudsplitter"

 
2003 25' Classic
Houstatlantavegas , Malebolgia
Join Date: Jun 2007
Posts: 20,000
Images: 1
I wouldn't worry too much...

...eight BB Lithium's=248lbs. 👍
Four or six even less of a concern.

Most all trailers are off balance curbside to Streetside.
I would...Put your batt's on the light side, as close as possible to the axles.

Bob
🇺🇸
__________________
I’m done with ‘adulting’…Let’s go find Bigfoot.
ROBERT CROSS is offline   Reply With Quote
Old 02-11-2020, 09:49 PM   #27
Rivet Master
 
57Vintage's Avatar
 
1958 26' Overlander
Battle Ground , Washington
Join Date: Jun 2013
Posts: 871
Images: 22
If you want to boondock for a week, have you considered how much fresh water you're going to take along and where that weight will be? Your diagram shows empty tanks, but doesn't designate which tanks. Just making sure you take it into account if necessary.

Look forward to see your progress.
__________________
Harold & Rebecca

Our thread:
https://www.airforums.com/forums/f97...er-172124.html
57Vintage is offline   Reply With Quote
Old 02-12-2020, 10:18 AM   #28
2 Rivet Member
 
1968 26' Overlander
Los Gatos , California
Join Date: Oct 2018
Posts: 72
Thanks!

Thanks for the feedback!

I know my fresh water tank will be heavy in the front of the trailer then progressively get lighter and fill up the grey water tank in the back.

I'm going to fiddle around with my design a bit more - perhaps the best place for the battery bank is under my closet space, right on top of the front axle.
__________________
Summer
1968 Overlander
Stargirl is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
2 batteries outside and two batteries inside timmaah Electrical - Systems, Generators, Batteries & Solar 14 08-25-2011 07:18 AM
Table Position When Traveling davidz71 Cabinets, Counter Tops & Furnishings 19 03-11-2006 05:29 AM
Parts source for four position light switch overlander76 Electrical - Systems, Generators, Batteries & Solar 6 11-16-2003 08:24 PM
Batteries..All about batteries FrankR Batteries, Univolts, Converters & Inverters 0 07-17-2002 09:05 PM
New electrical in position FrankR Electrical - Systems, Generators, Batteries & Solar 5 05-18-2002 11:47 PM


Featured Campgrounds

Reviews provided by

Disclaimer:

This website is not affiliated with or endorsed by the Airstream, Inc. or any of its affiliates. Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.



All times are GMT -6. The time now is 01:52 AM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.