Looking for a few to try out a WDH spreadsheet

[clamb]

Hi all,
Some of you are familiar with my spreadsheet project which I introduced in another thread.... http://www.airforums.com/forums/f464...nt-149347.html

Another member, dznf0g, has been working with me to develop this, and he has expanded it to include calculations for a Hensley hitch. My own version is intended for a simple WDH, typically with coupling at the ball and 2 spring bars.

My reason for doing this is that, being a good distance from the nearest scale (which is not CAT), I would like to have a good estimation of my axle weights and eliminate the need to go to the scale.

In my preliminary work with this, I am getting good results that are within 100 lbs on each axle, and I feel the main reason I am not getting closer results is because I am not using a certified CAT scale.

This spreadsheet can be used to arrive at the force being applied by your bars.

So, I am looking for someone who has accurate axle and tongue scale weights, both empty and loaded, or can get them easily, and who might also be fluent in Excel spreadsheets.

You will need to take accurate measurements and weights of payload items and locations. A degree from the Columbia School of Weights and Measures is desirable!

Please let me know if you would like to try it out. I want to limit this to maybe 5 so I don't get overloaded, and we'll go from there.

Please no responses telling me it is useless- I've already gotten those!

[dznf0g]

Originally Posted by ROBERT CROSS

Another member went that route awhile back..../Users/brkcro/Library/Containers/com.apple.mail/Data/Library/Mail Downloads/E6F1CEE0-A1F2-41B3-A4D0-A5325B67F94A/Towing weight calculator.xls

Link doesn't work. I'd like to see it, can you double check?

[ROBERT CROSS]

Try this....it went to my downloads and I could open it there....way beyond me, I would prefer a ruler ..sorry



Bob

[clamb]

Bob, thanks and I did try it out. That sheet is fine for weighing a fully loaded rig and comparing to weight ratings, but mine (and Rich's) is used to predict those weights before leaving home. It uses distances such as TV wheelbase, RA to ball, ball to TT axle, and entry of payload items such as 45 lbs of food in fridge at 138 inches from ball. The payload locations are all measured once, and weights are edited when the rig is loaded.

[A W Warn]

Originally Posted by ROBERT CROSS

Try this....it went to my downloads and I could open it there....way beyond me, I would prefer a ruler ..sorry

Bob

Glad to see someone is remembering my spread sheet.
I dropped that subject when there seemed to be no interest.

[dznf0g]

I cross checked it with clambs sheet and some of the calculations agree either exactly or very close. I do question the TW as it relates to PPP hitching and some apparent assumptions made by the author. I'll have to study it some more.

As Clamb says, the sheet he is working on allows for those of us (particularly) who have drastically differing loads on different trips to predict load scenarios pretty accurately. For example, In addition to my usual loads, I only sometimes take along: Generators, portable solar, SIB inflatable boat, 10 hp outboard, boat gear, tank for gennie and boat, 125cc scooter....among other things...and in differing combinations, depending on trip.

The temptation is to throw everything in the bed or back seat area. While developing the sheet, it was quite an eye-opener as to where things need to be and how they affect various loads in varying combinations, including varying the black, gray, and fresh loads...predicting a regular amount of travel days.

[A W Warn]

Originally Posted by clamb

....snip....

So, I am looking for someone who has accurate axle and tongue scale weights, both empty and loaded, or can get them easily, and who might also be fluent in Excel spreadsheets.

You will need to take accurate measurements and weights of payload items and locations. A degree from the Columbia School of Weights and Measures is desirable!

Please let me know if you would like to try it out. I want to limit this to maybe 5 so I don't get overloaded, and we'll go from there.

Please no responses telling me it is useless- I've already gotten those!

I'll be happy to try!
I'm fairly proficient in Excel (but a little rusty after 6 years of retirement), but no degree from CSWM
I have Cat scale results for my vehicles. I do not have individual axle weights for the trailer.

ps: I'm going on a short trip next week so I could stop by the scales and weigh again if needed.

[dznf0g]

Originally Posted by A W Warn

I'll be happy to try!
I'm fairly proficient in Excel (but a little rusty after 6 years of retirement), but no degree from CSWM
I have Cat scale results for my vehicles. I do not have individual axle weights for the trailer.

Yeah, we haven't delved into individual wheel or axle weights of tandems. If I had access to some individual scales, I'd be willing to add that, but there's a whole 'nuther level of complexity to the calculations.

[clamb]

I'm going to go ahead and post the spreadsheet here- anyone is welcome to try it out. Any weights and measures shown are my own- any yellow colored cell can be edited. Note that this is pretty much unloaded- just me, the propane tanks and 50 lbs in the truck bed are listed as cargo.

The idea is to weigh everything as close to empty as possible first. OR weigh with anything that would always be present and not enter that as cargo.

THEN, as you load the TV and trailer, record the weights and measurements and weigh again and compare results. Scale accuracy is critical!

Moderator Note - V4 spreadsheet removed - please see new spreadsheet at post #48

[clamb]

For starters, if you just want to play around with it, try using it as is and add payload here and there and see what changes.

[ROBERT CROSS]

Hey...that's great guys, glad to see the interest.
Hope 'ya get a workable sheet.
Don't let the poo-poo's discourage the operation, who knows maybe even my thick noggin will understand, my problem is figuring out what to forget to make room for what I need to remember.......


Bob

[A W Warn]

I've taken a few minutes to look over the spreadsheet, cell formulas, etc...
My first questions: How do you arrive at the number for "location" on the first two sheets? Is it a measurement from some point (in inches)?

Once I get the answer, I think I can fairly quickly fill in the blanks. I have already weighed and made a list of most of the cargo item that are inside both my tow vehicle and trailer. My wife even tells people I weighed her and added her to the list. (and that's true )

[dznf0g]

On the truck sheet 0" is at the front hub and numbers increase working backward on your particular TV.

On the trailer sheet the ball coupler is 0" and the numbers increase as you move rearward on your particular trailer.

These numbers are CRITICAL for accuracy. Eyeballing it don't work, as rounding errors, one on top of another multiply quickly.

I used a line drawing of my AS frame which I got from AS a couple years ago; and line drawings for my truck from the upfitter manual online. That was after using a tape and eyeballs. I was off by .5" here and there and it made a significant difference in the end.

[A W Warn]

I'm withdrawing my offer to participate. For me, that is too much measuring to get exact weight placement of every item added to the vehicles so that the results will be accurate. I'm not willing to take the time to do it.
I live 10-15 minutes from a CatScale, so actual weighing will be my method.


ps:
I now understand what you were speaking of, in other threads and posts, about the difficulty of placing COG of items in vehicles in a linear dimension.
For example: the driver's center of gravity would be difficult to accurately place at a specific "Location" dimension from the spindle center line. The bulk of that person's weight would be on the seat, but a large portion (legs and arms) would be forward of the body, moving the COG forward of the body. It would be impossible to place accurately and would vary with any seat adjustment and driver movement. In the case of two or three people in front, it's more complex and more variable.

[dznf0g]

It is some work up front, but when it's done one time, that $16 three-pete ends. Plus the time and miles to get it done properly.

[dznf0g]

Btw, ypu can probably find automakers cog of drivers position online. It's about 5" forward of the seat back at the cushion level.

[clamb]

[QUOTE=A W Warn;1787484]I'm withdrawing my offer to participate. For me, that is too much measuring to get exact weight placement of every item added to the vehicles so that the results will be accurate. I'm not willing to take the time to do it.

No problem- I appreciate your looking at it. I myself am not too fussy about being exact, and if I am off by 50 lbs or so on the axle weights, I'll be happy because I'll shoot for being under my ratings anyway.

[dznf0g]

AW, also the placement of items has an additive effect and isn't as crucial as the dimensions of the vehicle and AS. That's where the multiplication effect comes in. The formulas are all based on TV wheelbase, tv overhang, AS ball to axle, ball to receiver, distances. If these are off, every item placed anywhere is inaccurate by a multiplier. Add together each item which is off and you get a big number. I'm like clamb, axle weights Tha are off by a dozen pounds and the whole rig off by 150 pounds is fine. That's within the accuracy of the cert scales and works for me.

[guskmg]

Like I said before, it is the same as weight and balance calculations for an aircraft before flight. as far as the longitudinal axis is concerned. The TV is one part of the problem the TT is the second part of the problem and the third part is the combination. What to do: weight both TV & TT empty or full, but separately, then calculate where the center of gravity (CG) is for each. If you weigh the TV & TT full then you do not have to calculate the additional weight and distance of things you later add. Think moments = weight X distance (or torque if you prefer). Pick a datum like the TV front bumper and the tip of the TT coupler for measuring distances. Make your measurement from that point for each vehicle. On the TV it is somewhere between the axles and on the TT it is some where between the coupler socket and the center of the axle(s). Everything always must be level or else the distances used for calculation wii be in error. Once you have the moments calculated you can add or subtract them, depending on weight added or subtracted to reach a final moment. Moment divided by weight = distance. If that is your final moment then that is your CG. Do that for both TV & TT. Remember Airstream recommends a TT tongue weight of 10-12% of GW as an acceptable range for towing. Is your CG within this range?
Now the TV: weight axles and calculate the TVs CG. Take the numbers off the door placard and figure that CG. It may vary greatly because that is aft maximum CG. On pickups that CG will be very far aft. On the tow vehicle the CG you compute should be further forward or you will experience understeer. Too far forward and you have oversteer. Now Connect the two together, tighten up the equalizer bars and recalculate the TV CG with the TT attached. To recap: figure the TT CG, then when it is with in the 10-12% range add that weight to the tow vehicles calculation and see how much the TV CG shifts forward. The TV's forward CG (with driver and minimum fuel (as close to empty as you can get and still drive) verses the maximal allowable weight CG would be the TV operating CG range. Bear in mind that at either ends of this range are under and over steer conditions that may not feel comfortable on long trip. Once you make a diagram of the above basics all you have to do future weight changes is weigh the item and measure the distance, multiply then add or subtract the moment, divide the new moment by the new weight for the new CG.
guskmg

[J. Morgan]

If I only had a truck scale....

(Yeah, that is a scale in the foreground, less than 50 feet from me as I type this)

I have at different times taken down different weights, some axle weights, some unit weights, and some cargo weights on my Airstream Combo, but never a true tongue weight or all of these at the same time.

Who knows, maybe I might do all of that next time I move it.


Superat stultitia.