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Weight & Balance 101


Dollytrolley

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Lately here in the forum I have posted some basic truck Weight & Balance solutions for a few example units and some basic loading solutions with mixed results. A few forum members have attempted to explain various concepts of arriving at various Weight & Balance solutions with mixed results……

So…..perhaps calculating Weight & Balance solutions might make more sense if we just did a few simple truck and then trailer and then Truck / Trailer combo Weight & Balance calculations to arrive at solutions.

TRUCK / TRACTOR / TRAILER WEIGHT & BALANCE 101

Out of the goodness of his heart….Scrap has used his considerable “charms” to have Kenworth donate Four tractors for our Weight & Balance calculations…...Scraps comments are below:

If it helps, I've built a few of the shorthood, small sleeper lightweight T680's in the past couple of years that are the same kind of thing.  A 13K truck is going to be tough but a single axle truck can probably get there.  DollyT can do the math to add your stuff to these:

Truck 1:  11L, 6x2, 205WB, LH 100gal tank @ 3100, dry = 14257lb, front = 8690

Truck 2:  13L, 6x2, 205WB, LH 100gal tank @3150, dry = 14788lb, front = 9250

Truck 3:  13L, 6x2, 197WB, LH 100gal tank @3000, dry = 14808lb, front = 9280

Truck 4: 13L, 6x4, 208WB, Dual 100gal tans @2800, dry = 16891lb , front = 10190

Truck 4 has all the good stuff, 4 real batteries, sleeper heater, two real seats, a stick w/ overdrive, all the storage cabinets, and on and on.  It was actually one of my favorites.  But it all adds up pretty quick.  Even 1-3 above could be lighter but you are making some real sacrifices that would make for a rough day of trucking.  At that point you might as well drive a mixer truck all day!  You could also delete the disc brakes and save 320 lbs in the front.

So here we go.    (RED ITEMS WERE CUT PASTED AND CALCULATED IN ERROR  BLUE ITEMS ARE CORRECTED ITEMS)

Truck 1 Basic Dry Weight and Balance:

ITEM                                                 WEIGHT (Lbs)        X ARM (Inches from steer) = MOMENT (Inch/ Pounds)

1. Steer axle                                    8,690                    X 0                              = 8,690  0   CORRECTED

2. Drive axle                                    5,567                    X 205                          = 1,141,235

                                                       14,257                                                          1,149,844  1,141,154  CORRECTED

 

Center of gravity is total moment divided by total weight:

C G = Moment 1,149,844  1,141,154/ 14,257 Lbs = 80.65      80.04" CORRECTED   inches C G aft of front steer axle.

Comment: The above C G of 80.65 inches aft of the steer axle is the point where if we placed the above truck on a knife edge sawhorse the truck would balance level with wheels off the ground.

At this point we can assign percentage of weight per axle group by dividing the C G location (80.65”)(80.o4 CORRECTED) by the total wheelbase of 205”

C G 80.65 80.04"/ wheelbase 205 = 0.393414634    0.390439024 or rounded to %39.34   %39.04 weight on drive axle……….and the steer axle is the remaining percentage resulting from subtracting the %39.34    %39.04 drive axle from the total %100 total to arrive at: Wheel base 205 – C G 80.65  80.04= 124.35 124.96 then divide 124.35  124.96 by the 205 = 0.6066 0.6095 or %60.66  %60.95Weight on the steer axle.

 

Simple eh ?

Next post we will fill the fuel tank and see what happens…….

PS.......check my math with this much thumb--typing I am %100 certain to screw up.......it's been a long time since the 3rd grade......... 

Drive on………..(Wt & Bal……...3rd grade math .......CORRECTED......)

97 Freightshaker Century Cummins M11-370 / 1350 /10 spd / 3:08 /tandem/ 20ft Garage/ 30 ft Curtis Dune toybox with a removable horse-haul-module to transport Dolly-The-Painthorse to horse camps and trail heads all over the Western U S

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2 hours ago, Steve from SoCal said:

I think I need a moment !

 

Steve

Ok Steve..........now we know who did all Jay Leno's lines........

 

So of course you know if I called your ground-school instructor she would whip you into the fetal position with a plotter because any fly-boy knows that before you can have any m o m o m e n t...........ya gotta have a..........a r m.......

 

Tag.......your......it

 

Drive on........(Steve needs a day job........)

97 Freightshaker Century Cummins M11-370 / 1350 /10 spd / 3:08 /tandem/ 20ft Garage/ 30 ft Curtis Dune toybox with a removable horse-haul-module to transport Dolly-The-Painthorse to horse camps and trail heads all over the Western U S

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16 hours ago, Dollytrolley said:

Lately here in the forum I have posted some basic truck Weight & Balance solutions for a few example units and some basic loading solutions with mixed results. A few forum members have attempted to explain various concepts of arriving at various Weight & Balance solutions with mixed results……

So…..perhaps calculating Weight & Balance solutions might make more sense if we just did a few simple truck and then trailer and then Truck / Trailer combo Weight & Balance calculations to arrive at solutions.

TRUCK / TRACTOR / TRAILER WEIGHT & BALANCE 101

Out of the goodness of his heart….Scrap has used his considerable “charms” to have Kenworth donate Four tractors for our Weight & Balance calculations…...Scraps comments are below:

If it helps, I've built a few of the shorthood, small sleeper lightweight T680's in the past couple of years that are the same kind of thing.  A 13K truck is going to be tough but a single axle truck can probably get there.  DollyT can do the math to add your stuff to these:

Truck 1:  11L, 6x2, 205WB, LH 100gal tank @ 3100, dry = 14257lb, front = 8690

Truck 2:  13L, 6x2, 205WB, LH 100gal tank @3150, dry = 14788lb, front = 9250

Truck 3:  13L, 6x2, 197WB, LH 100gal tank @3000, dry = 14808lb, front = 9280

Truck 4: 13L, 6x4, 208WB, Dual 100gal tans @2800, dry = 16891lb , front = 10190

Truck 4 has all the good stuff, 4 real batteries, sleeper heater, two real seats, a stick w/ overdrive, all the storage cabinets, and on and on.  It was actually one of my favorites.  But it all adds up pretty quick.  Even 1-3 above could be lighter but you are making some real sacrifices that would make for a rough day of trucking.  At that point you might as well drive a mixer truck all day!  You could also delete the disc brakes and save 320 lbs in the front.

So here we go.

Truck 1 Basic Dry Weight and Balance:

ITEM                                                 WEIGHT (Lbs)        X ARM (Inches from steer) = MOMENT (Inch/ Pounds)

1. Steer axle                                    8,690                    X 0                              = 8,690

2. Drive axle                                    5,567                    X 205                          = 1,141,235

                                                       14,257                                                          1,149,844

 

Center of gravity is total moment divided by total weight:

C G = Moment 1,149,844 / 14,257 Lbs = 80.65 inches C G aft of front steer axle.

Comment: The above C G of 80.65 inches aft of the steer axle is the point where if we placed the above truck on a knife edge sawhorse the truck would balance level with wheels off the ground.

At this point we can assign percentage of weight per axle group by dividing the C G location (80.65”) by the total wheelbase of 205”

C G 80.65 / wheelbase 205 = 0.393414634 or rounded to %39.34 weight on drive axle……….and the steer axle is the remaining percentage resulting from subtracting the %39.34 drive axle from the total %100 total to arrive at: Wheel base 205 – C G 80.65 = 124.35 then divide 124.35 by the 205 = 0.6066 or %60.66 Weight on the steer axle.

 

Simple eh ?

Next post we will fill the fuel tank and see what happens…….

PS.......check my math with this much thumb--typing I am %100 certain to screw up.......it's been a long time since the 3rd grade......... 

Drive on………..(Wt & Bal……...3rd grade math)

So on our last post we calculated the dry weight of Scrap's truck # 1 so now we add 90 gallons of fuel…..

 

TRUCK / TRACTOR / TRAILER WEIGHT & BALANCE 101

Out of the goodness of his heart….Scrap has used his considerable “charms” to have Kenworth donate Four tractors for our Weight & Balance calculations…...Scraps comments are below:

 

If it helps, I've built a few of the shorthood, small sleeper lightweight T680's in the past couple of years that are the same kind of thing.  A 13K truck is going to be tough but a single axle truck can probably get there.  DollyT can do the math to add your stuff to these:

Truck 1:  11L, 6x2, 205WB, LH 100gal tank @ 3100, dry = 14257lb, front = 8690

Truck 2:  13L, 6x2, 205WB, LH 100gal tank @3150, dry = 14788lb, front = 9250

Truck 3:  13L, 6x2, 197WB, LH 100gal tank @3000, dry = 14808lb, front = 9280

Truck 4: 13L, 6x4, 208WB, Dual 100gal tans @2800, dry = 16891lb , front = 10190

Truck 4 has all the good stuff, 4 real batteries, sleeper heater, two real seats, a stick w/ overdrive, all the storage cabinets, and on and on.  It was actually one of my favorites.  But it all adds up pretty quick.  Even 1-3 above could be lighter but you are making some real sacrifices that would make for a rough day of trucking.  At that point you might as well drive a mixer truck all day!  You could also delete the disc brakes and save 320 lbs in the front.

 

So here we go.

Truck 1 Basic WITH 90 gal of fuel added Weight and Balance:

    ITEM                       WEIGHT (Lbs)        X          ARM (Inches from steer)        =         MOMENT (Inch/ Pounds)

1. Steer axle                8,690                  X            0                                 =          8,690

2. Drive axle                5,567                  X           205                               =         1,141,235

3. Fuel (90Gal)              648                    X           122                               =          79,056

                                14,905                                                                       1,228,900

 

Center of gravity is total moment divided by total weight:

 

C G = Moment 1,228,900 / 14,905 Lbs = 82.45 inches C G aft of front steer axle.

Comment: The above C G of 82.45 inches aft of the steer axle is the point where if we placed the above truck on a knife edge sawhorse the truck would balance level with wheels off the ground.

At this point we can assign percentage of weight per axle group by dividing the C G location (82.45”) by the total wheelbase of 205”

C G 82.45 / wheelbase 205 = 0.402195122 or rounded to %40.22 weight on drive axle……….and the steer axle is the remaining percentage resulting from subtracting the %40.22 drive axle from the total %100 total to arrive at: Wheel base 205 – C G 82.45 = 122.55 then divide 122.55 by the 205 = 0.5978 or %59.78 Weight on the steer axle.

So……..

Steer axle is: %59.78 of the truck weight of 14,905 Lbs, so…...14,905 X .5978= 8,910 Lbs Steer axle

Drive axle is: %40.22 of the truck weight of 14,905 Lbs, so…...14,905 X .4022= 5,995 Lbs Drive axle

Simple ?

Next post we will add the 5th hitch and bed and see what happens…….

Who wants to go back to my First post and calculate the Steer and Drive axle weights for that post and then post the answer in this thread?  ?

Drive on………..(Wt & Bal……...more 3rd grade math)

97 Freightshaker Century Cummins M11-370 / 1350 /10 spd / 3:08 /tandem/ 20ft Garage/ 30 ft Curtis Dune toybox with a removable horse-haul-module to transport Dolly-The-Painthorse to horse camps and trail heads all over the Western U S

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4 hours ago, mptjelgin said:

I believe that 8690 x 0 = 0, not 8690. In the big scheme of things it doesn't make a big difference (80.05" vs. 80.65"), but you might as well have the math correct going forward. 

Mpt,

Great catch......so not only are I not.....good at proof reading..... but I also fell into the trap of trying to make the wheelbase to focus of the C G range when that is were a "shortcut" might have a "gotcha-moment"........here is how stupid I can be......IF I had used my darn spreadsheet to run these numbers it would have returned a ZERO Moment so I guess I need to go back to using the spreadsheet instead of showing my bad typing and dumb non-use of a calculator......

Now you do bring up a interesting thing about a shortcut of only using the wheel base of the truck to define the C G range inputs of the truck so that begs the question ..........what about the part of the truck in FRONT of the steer axle??  ?

Now lets suppose that Scrap gave us this truck because he had a little too much Dr Pepper (or Crown Royal) to drink and he forgot to have a Barden 50 Ton Hyd winch installed right behind Custom Stainless  front bumper........hummm ....that is in front of the steer axle that I have deemed Datum "Zero"........hummm what are we going to do now?

Hummmm..........my "shortcut" of using the steer axle as "Zero" is fine as long as we add weight Aft of the steer axle BUT what do we do about adding Weight in front of the steer axle? ?

Hint(s)......one way might be to use a ........number type we don't often use ....... or maybe change the location of "Zero" ?

What do you think we should do next.........(no we can't use the spreadsheet that is cheating like using a GPS instead of a old truck atlas...)

What can we do?    

Drive on............(maybe math does not work after all......)

97 Freightshaker Century Cummins M11-370 / 1350 /10 spd / 3:08 /tandem/ 20ft Garage/ 30 ft Curtis Dune toybox with a removable horse-haul-module to transport Dolly-The-Painthorse to horse camps and trail heads all over the Western U S

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Actually as long as you are working off of measured axle weights to determine CG you'll be fine, no matter where the loads are to begin with. But if you decide to add a big bumper/winch combo in front of the steer axle and want to determine it's effect, the math will get a bit more complicated. Since you are using your front axle as the "0" point, any load added in front of the axle would have a negative moment arm. Once you've got a handle on that, the math continues to work as long as you keep track of the signs (positive vs. negative). The impact of the big weight added in front of the steer axle will be to decrease weight on the drive axle and add not only the bumper/winch weight to the steer, but also the amount of weight that was unloaded from the drive. 

Mark & Teri

2021 Grand Designs Imagine 2500RL, 2019 Ford F-350

Mark & Teri's Travels

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3 hours ago, mptjelgin said:

Actually as long as you are working off of measured axle weights to determine CG you'll be fine, no matter where the loads are to begin with. But if you decide to add a big bumper/winch combo in front of the steer axle and want to determine it's effect, the math will get a bit more complicated. Since you are using your front axle as the "0" point, any load added in front of the axle would have a negative moment arm. Once you've got a handle on that, the math continues to work as long as you keep track of the signs (positive vs. negative). The impact of the big weight added in front of the steer axle will be to decrease weight on the drive axle and add not only the bumper/winch weight to the steer, but also the amount of weight that was unloaded from the drive. 

MPT,

Great answer.......

What other "methods" might we use if we don't want to deal with "negative's"......???

Drive on.......(Maybe "negatives" have a place......sometimes but......)

97 Freightshaker Century Cummins M11-370 / 1350 /10 spd / 3:08 /tandem/ 20ft Garage/ 30 ft Curtis Dune toybox with a removable horse-haul-module to transport Dolly-The-Painthorse to horse camps and trail heads all over the Western U S

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3 hours ago, Dollytrolley said:

MPT,

Great answer.......

What other "methods" might we use if we don't want to deal with "negative's"......???

Drive on.......(Maybe "negatives" have a place......sometimes but......)

Rather than jump on that train, I think I will wait right here at the STATION.

 

John

Southern Nevada

2008 Volvo 780, D13, I-Shift

2017 Keystone Fuzion 420 Toyhauler 

2017 Can-Am Maverick X3-RS

 

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16 minutes ago, VegasFlyer said:

Rather than jump on that train, I think I will wait right here at the STATION.

 

John.......What if someone gives you the ARM.........for a MOMENT.........at the STATION......and then your C G is out of limits.......and its only 102f out right now..........

Drive on.......(too cool to.........calculate)

97 Freightshaker Century Cummins M11-370 / 1350 /10 spd / 3:08 /tandem/ 20ft Garage/ 30 ft Curtis Dune toybox with a removable horse-haul-module to transport Dolly-The-Painthorse to horse camps and trail heads all over the Western U S

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I'm a Civil Engineer (Bridge Design) for 36 years now, so I'm comfortable with using negative numbers in calculations. No need to avoid them at all.

If you are bound and determined to avoid negative numbers, you could re-run all of your calculations using the front bumper of the truck as your datum (assuming you don't plan to add any load in front of that point), or you could choose the very back of the truck, assuming that you don't plan to add any load behind that point. You would need the distances from your chosen datum to both axles to proceed, as well as the distance from your datum to the  "center" of any proposed added loads (fuel, winch, bed and hitch, small dog, etc...).

Mark & Teri

2021 Grand Designs Imagine 2500RL, 2019 Ford F-350

Mark & Teri's Travels

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2 hours ago, mptjelgin said:

I'm a Civil Engineer (Bridge Design) for 36 years now, so I'm comfortable with using negative numbers in calculations. No need to avoid them at all.

If you are bound and determined to avoid negative numbers, you could re-run all of your calculations using the front bumper of the truck as your datum (assuming you don't plan to add any load in front of that point), or you could choose the very back of the truck, assuming that you don't plan to add any load behind that point. You would need the distances from your chosen datum to both axles to proceed, as well as the distance from your datum to the  "center" of any proposed added loads (fuel, winch, bed and hitch, small dog, etc...).

 

 

 

1 hour ago, noteven said:

A customer and I laid out these type units (not this particular rod rig but units like it)59348eb5d326d_Jagorodrig.jpg.98f370540ecfe4b1d5839ed8b7a9122a.jpgusing hand calculated weight distributions (front axle group 0" ) prior to ordering the truck with certain wheelbase dimensions. We later built a simple spreadsheet based on the hand formula to accumulate all the mounted equipment. If I remember we used negative numbers for loads ahead of the steer axles and behind the drive axles - as they are cantilever loads.  A truck is a bridge standing on it's axle groups. 

We got within 250lbs on the front and rear axles. This was critical to allow the units to move during spring road restrictions. 

MPT & Not

Right on the money again........

Obviously negative numbers have a comfort level for some folks and other folks can get a little confused at times.

To make things a bit more confusing some aircraft will have a datum "0" defiled by a part of the airframe such as a firewall of a engine compartment and that often leads to a main landing gear that is a positive number and a nose gear that is a negative number............hummmm

Once in a while someone will define a Datum "0" as a certain distance AHEAD of the foremost structure to allow all numbers aft of the datum as positive numbers..........EXCEPT when removing previous mass from a previous Wt & Bal............Negative numbers need to be considered often as more and more Wt & Bal solutions are considered. For example if we were to locate the Datum 24 inches forward of the front of the factory bumper edge and then installed a 12” extended front bumper and Heavy winch we would still have positive numbers…….however after the revised Wt & Bal was solved we would need to use negative numbers to remove the extended bumper and winch when we returned to the original factory bumper and calculating the 2nd revised Wt & Bal solution….

We used to operate sectional crane-barges and often we would extend the datum to fall within the farthest crane hook position within the crane load scope of the barge…….but we still had plenty of negative numbers with heel, list, roll, center of ballast , center of buoyancy, etc, etc,,,,,,,,,,

So…….do we want to use negative numbers or……..extend the datum in front of the truck? ?


 

Drive on……….(+ or - ? ? )


 

 

97 Freightshaker Century Cummins M11-370 / 1350 /10 spd / 3:08 /tandem/ 20ft Garage/ 30 ft Curtis Dune toybox with a removable horse-haul-module to transport Dolly-The-Painthorse to horse camps and trail heads all over the Western U S

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8 hours ago, Dollytrolley said:

What other "methods" might we use if we don't want to deal with "negative's"......??

Training wheels?

KW T-680, POPEMOBILE
Newmar X-Aire, VATICAN
Lots of old motorcycles, Moto Guzzi Griso and Spyder F3 currently in the front row
Young enough to play in the dirt as a retired farmer.
contact me at rickeieio@yahoo.com

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17 minutes ago, rickeieio said:

Training wheels?

Depends.......opps that's next year maybe........

Drive on........(Weighty subject......Rick is off his balance again...:D)

97 Freightshaker Century Cummins M11-370 / 1350 /10 spd / 3:08 /tandem/ 20ft Garage/ 30 ft Curtis Dune toybox with a removable horse-haul-module to transport Dolly-The-Painthorse to horse camps and trail heads all over the Western U S

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  • 1 month later...

DT,

I’ll do my best to tackle this but will need a great deal of help. 

First a quick intro.  I’m a many year lurker of escapees  and rv.net.  The DW and I want to travel when we fully retire so we will need a bigger rig and truck.  That lead to research on MDT’s such as F550’s.  That lead to this other category called HDT.  I am completely fascinated by HDT’s.  You guys have done great work in both categories.  I don’t know which path I will take but research is the key.

On to Weight and Balance.  I think you and mptjelgin have discussed the basics so the next step is to define the rules.  My experience with this is as the lowest form of life, a pilot (can I still hang out with you guys?).  My HDT knowledge doesn’t go much beyond what I’ve read here so this is where the help comes in.  For this to work we have to have standards and definitions or one driver’s W&B will not be the same as another’s.  I will make some proposals but these will need to be tweaked to fit.

Proposed Definitions:

Basic Weight (in aircraft AKA zero fuel weight, ZFW) is the truck with all fluids (oil, coolant, washer etc.) but no consumables, i.e. fuel or DEF, or crew.  This is the starting point to which I add fuel, people, toad, 5er etc.  This weight my not have applicability to HDT outside of those that do modifications to them.  Nobody is going to weigh their truck empty tanks.

Curb Weight (a car term I know) is Basic Weight plus driver and full fuel and DEF.  In aircraft it does not include additional gear.  In trucks this would mean fixed equipment such as Drom/tool box but no tools.  Also no deck load, no food etc in truck.

Operating Weight is Curb Weight plus pin weight, toad, truck/condo load to include passengers and all tools, compressors etc.

Center of Gravity (CG) is the longitudinal location of the truck’s weight at any given time.  It may not move much when driving but it should move as you burn fuel.

Datum is the standard position of measurement for W&B and in Naval aircraft is always in front of the aircraft.  This gets into the discussion of positive or negative values for moment arms.  Positive values are for additions to W&B and negatives for removed gear.

Reference Mark is various fixed point on the truck used to measure an object’s longitudinal position.  I propose one RM on the front axle to make things easy.

Datum Offset (DO) the distance in front of a RM.  We need to fix the DO value to keep the moment arm sign convention consistent.  With most front axle setback being about 5 feet DO should be higher to allow for front bumper mods and keep moments positive.  Ten feet (or 100 inches if you like round numbers) should do it.

Station is an object distance in inches from Datum.  If the condo couch is 10 feet behind front axle then its station is DO + 120 inches.  Later the moment will be people weight on couch multiplied by station to be added to the moment summation which will give CG and axle weight distribution.

From this a spreadsheet would be easy.  I would need an individual truck details:  A weight ticket with exact conditions, fuel, tools people, all dimensions cab, condo, WB, pin in inches behind front axle.  I was looking at Scraps numbers but do not understand all the terms in Truck 1:

Truck 1:  11L, 6x2, 205WB, LH 100gal tank @ 3100, dry = 14257lb, front = 8690

Have I over complicated this? Or missed to point altogether?

This form has been of great help to me so it’s important to give back where/when I can.

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41 minutes ago, Stepchild said:

DT,

I’ll do my best to tackle this but will need a great deal of help. 

First a quick intro.  I’m a many year lurker of escapees  and rv.net.  The DW and I want to travel when we fully retire so we will need a bigger rig and truck.  That lead to research on MDT’s such as F550’s.  That lead to this other category called HDT.  I am completely fascinated by HDT’s.  You guys have done great work in both categories.  I don’t know which path I will take but research is the key.

On to Weight and Balance.  I think you and mptjelgin have discussed the basics so the next step is to define the rules.  My experience with this is as the lowest form of life, a pilot (can I still hang out with you guys?).  My HDT knowledge doesn’t go much beyond what I’ve read here so this is where the help comes in.  For this to work we have to have standards and definitions or one driver’s W&B will not be the same as another’s.  I will make some proposals but these will need to be tweaked to fit.

Proposed Definitions:

Basic Weight (in aircraft AKA zero fuel weight, ZFW) is the truck with all fluids (oil, coolant, washer etc.) but no consumables, i.e. fuel or DEF, or crew.  This is the starting point to which I add fuel, people, toad, 5er etc.  This weight my not have applicability to HDT outside of those that do modifications to them.  Nobody is going to weigh their truck empty tanks.

Curb Weight (a car term I know) is Basic Weight plus driver and full fuel and DEF.  In aircraft it does not include additional gear.  In trucks this would mean fixed equipment such as Drom/tool box but no tools.  Also no deck load, no food etc in truck.

Operating Weight is Curb Weight plus pin weight, toad, truck/condo load to include passengers and all tools, compressors etc.

Center of Gravity (CG) is the longitudinal location of the truck’s weight at any given time.  It may not move much when driving but it should move as you burn fuel.

Datum is the standard position of measurement for W&B and in Naval aircraft is always in front of the aircraft.  This gets into the discussion of positive or negative values for moment arms.  Positive values are for additions to W&B and negatives for removed gear.

Reference Mark is various fixed point on the truck used to measure an object’s longitudinal position.  I propose one RM on the front axle to make things easy.

Datum Offset (DO) the distance in front of a RM.  We need to fix the DO value to keep the moment arm sign convention consistent.  With most front axle setback being about 5 feet DO should be higher to allow for front bumper mods and keep moments positive.  Ten feet (or 100 inches if you like round numbers) should do it.

Station is an object distance in inches from Datum.  If the condo couch is 10 feet behind front axle then its station is DO + 120 inches.  Later the moment will be people weight on couch multiplied by station to be added to the moment summation which will give CG and axle weight distribution.

From this a spreadsheet would be easy.  I would need an individual truck details:  A weight ticket with exact conditions, fuel, tools people, all dimensions cab, condo, WB, pin in inches behind front axle.  I was looking at Scraps numbers but do not understand all the terms in Truck 1:

Truck 1:  11L, 6x2, 205WB, LH 100gal tank @ 3100, dry = 14257lb, front = 8690

Have I over complicated this? Or missed to point altogether?

This form has been of great help to me so it’s important to give back where/when I can.

Step,

Oh to be a child again......this being a geezer tends to make one do silly things like wt & bal for wanna be trucker geezers.......

Too many decades and too many thousand hours ago I stumbled into steering some flying machines around this ball of Earth that we camp on.....so like you and a few other geeks here I have a pilot cert somewhere in my wallet amount all the hundred dollar bills saved by having a HDT......

 

Child.....you seem somewhat oraginized and perhaps your definations are the cat's meow to help the trucker-geezers here get with the program.....

The reality here Child is......terms are not the problem here on the forum....it's the details are the problem here ......most folks do NOT want to measure the stations to the load centers......they just want the axle weights computed out of thin air.......

It's like pulling teeth getting basic information to even start a weight & balance......

Folks tend to think weight & balance calculations are high math and I have given examples countless times but most folks just like to have me do a thumb in the air calc with very little detail......

Many folks seem to fear what the weights MIGHT be ........

I have sent my auto-calc truck & trailer spreadsheet to several folks and have limited results.......the spreadsheet auto-updates with every entry of each cell for both truck and trailer......

After a few hundred rig calcs I have some concerns regarding some folks steer axle heavy weights but most folks seem to trust truck tire capacities more than I do......

Child......perhaps you could take my spreadsheet and become the go-2-guy for weight and balance????

Shoot me a email at mmcdan3189@aol.com and I'll send you a copy of the spreadsheet and then you could become the weight and balance go-2-guy.......

 

Drive on.......(the devil is in the.....detail)

 

97 Freightshaker Century Cummins M11-370 / 1350 /10 spd / 3:08 /tandem/ 20ft Garage/ 30 ft Curtis Dune toybox with a removable horse-haul-module to transport Dolly-The-Painthorse to horse camps and trail heads all over the Western U S

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Yes devil is in the detail.  If the devil is in your aircraft he can be a mean SOB but that is another story.....

I'd be happy to run with this.  I just need actual truck numbers to bounce things against.  A spreadsheet should help with math problems but there must be rules and definitions or garbage in will equal garbage out.

Email sent.

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10 hours ago, Stepchild said:

Yes devil is in the detail.  If the devil is in your aircraft he can be a mean SOB but that is another story.....

I'd be happy to run with this.  I just need actual truck numbers to bounce things against.  A spreadsheet should help with math problems but there must be rules and definitions or garbage in will equal garbage out.

Email sent.

 

3 hours ago, Wrknrvr said:

 I am really glad I build my bed years ago.

 

 If I did it today you guys mite put me in jail.

 

 Big 5r has been looking for me for years.

 

 Smooth shifting,  Vern

 

 

Child,

Wrknrvr comments pretty much sum up most of the feelings regarding truck & trailer weight and balance for HDT RV rigs as a whole.......

 

Sure once in a while someone contacts me about running a weight & balance mostly on the truck but Never have I had one person supply ALL of the items that you listed even though I have requested these   "weight ticket with exact conditions, fuel, tools people, all dimensions cab, condo, WB, pin in inches behind front axle."

You wrote:

I was looking at Scraps numbers but do not understand all the terms in Truck 1:

Truck 1:  11L, 6x2, 205WB, LH 100gal tank @ 3100, dry = 14257lb, front = 8690

Translation:  11L = engine liters,  6X2= type truck axle config,  205WB = 205 inches from steer axle to avg center of tandem axles,   LH 100 gal tank at 3100 = Left Side fuel tank of 100 gal with the center 3100 cm  from Datum ,  14,257 Lb dry = total dry tractor weight,  Front 8690 = the steer axle weight dry.

So child what scrap has supplied is likely the MOST information that you may ever get and so then I become Dick Tracy and ferret out the rest of the DETAILS needed to make some sense of a wt & bal for the RV .......it can be more work than you imagine............Details matter.....

 

I will email you the spreadsheet but don't hold your breath waiting for the flood of details........for the most part Vern has a point........sometimes getting "lucky" is just as good as fiddling with the..........details

 

Drive on.............(ya feel'n lucky.......punk)

 

 

m

97 Freightshaker Century Cummins M11-370 / 1350 /10 spd / 3:08 /tandem/ 20ft Garage/ 30 ft Curtis Dune toybox with a removable horse-haul-module to transport Dolly-The-Painthorse to horse camps and trail heads all over the Western U S

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DT,

See if this is the direction you want to go.  This a basic spreadsheet but can be improved.  I had to improvise on some things.  Dry weight is without fuel, oil, people, condo items etc. so I added fuel to two tanks, driver.....

310 cm is 122 inches for the tanks.  I guessed on the seat positions.

Another thread is about singling long.  What does a tandem axle weigh (axle, 4 tires, pumpkin, suspension)? 

SC

 

WB101.xls

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On 7/16/2017 at 1:46 PM, Stepchild said:

DT,

See if this is the direction you want to go.  This a basic spreadsheet but can be improved.  I had to improvise on some things.  Dry weight is without fuel, oil, people, condo items etc. so I added fuel to two tanks, driver.....

310 cm is 122 inches for the tanks.  I guessed on the seat positions.

Another thread is about singling long.  What does a tandem axle weigh (axle, 4 tires, pumpkin, suspension)? 

SC

 

WB101.xls

Child,

Like a lot of things regarding truck weight & balance here on the forum most of the time you do not have access to ACTUAL weights so......you wind up with a WAG-weight......so to answer your question about removing the front drive axle legend has it that they WAG-Weigh 900 to 1200 lbs....

Oh the joys of RV jiggering....

Drive on......(how much does Crown Royal Weigh ?)

97 Freightshaker Century Cummins M11-370 / 1350 /10 spd / 3:08 /tandem/ 20ft Garage/ 30 ft Curtis Dune toybox with a removable horse-haul-module to transport Dolly-The-Painthorse to horse camps and trail heads all over the Western U S

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