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Weight and balance & hitches


phoenix2013

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Dolly, it seems that you are [and are not] taking the weight shift from the front axle. The difference in your 2 numbers is 1430 pounds and the weight shift from the steer axle to the drive axle is 1440 lbs with no bikes loaded. Loading the bikes shifts some weight from the drive axle back to the front axle.......at least that is the way I sorta figured weight and balance on our old C-47's many years ago. Pigs, out of their cages, and Vietmamese farmers trying to get them re-caged made a significant in-flight shift of CG and caused the pilot to see-saw just a bit as the pin weight changed on the fly, so to speak. Charlie

Heck Charlie if I get within the weight of a jug of rot-gut when I am in bean-counter mode I am pretty close to spot on for a geezer.....

 

It's been a few decades since had to do a ba$$akwards weight and balance where after a bird augured-in you had to try to figure out how many farmers and pigs ran back into the far tail of the gooney-bird before Wilber and Homer ran out of nose down trim and elevator at the same time....not a good day....

 

Charlie they say if you live too long things start to repeat...

 

Here is the scary part ... you are talking about of pigs in the back end of a gooney-bird and this thread started about the effect of loading a couple of Hogs in the back end of a fancy RV.... .

 

Charlie the more things change... the more they stay the same....

 

One of my numbers from the spreadsheet shows the total mass distribution of the hitch-up and the other number is the hitch pin weight .... both Estimates were WITHOUT any wheelbase dimensions or hitch locations defined so I simply took the few weights that were derived from the scale slips and let the spreadsheet run wild defining the layout of the truck Trailer and hitch.....pretty a much a wilda$$ guess..

 

Drive on.....(what's the layout?)

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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Dolly, the truck will be in my shop in a week or so, to upgrade his ET to Super Sr. I'll have a chance to measure carefully the wheelbase and the "hitch base". This will give us the first set of parameters to establish the mass and length moments.

I'll ask the owner to do the same on his fifth. Math is math, we should be able to understand what is going on.

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Dolly, the truck will be in my shop in a week or so, to upgrade his ET to Super Sr. I'll have a chance to measure carefully the wheelbase and the "hitch base". This will give us the first set of parameters to establish the mass and length moments.

I'll ask the owner to do the same on his fifth. Math is math, we should be able to understand what is going on.

Merry Christmas Henry...shucks it's been fun flogging the old spreadsheet into a frenzy....I should have been a investment banker...

 

I suppose the higher end RV'$ might need to check weight and Balance somewhat but it seems that many of the high end units may have somewhat better ability to sustain some less than ideal loads and balance defect....

 

Our rig is somewhat prone to unbalanced conditions due to the odd dimensions of our truck and our low end toy box is in my opinion overrated in gross weight and payload as well. I am likely the only fellow on the forum trying to down-rate his trailer gross weight by a substantial margin ....I consistently run the toy hauler below 80% gross and sometimes near 70%...

 

We seldom run the flatbed anymore and often load the 20ft cargo box with a lot of hay, water, Samuria or Blazer, or even a one ton truck so we do need to consider where and how we load the cargo box.

 

I am just spit balling here but it seems that the folks that might benefit from my weight and balance spreadsheet might be the pickup / large trailer group however IF they ran the numbers it's likely they would NOT like the answers that they would see....

 

For the most part the RV HDT has a lot of margin above its listed capacity and even some of the largest RV HDT'$ seldom get too far into the margins I suspect.

 

I will agree with you that many RV'$ are poorly thought out and lack much engineering moxie but a HDT tends to overcome many of the shortfalls of many trailers...

 

Merry Christmas...

 

Drive on....(Happy new year)

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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Mike-

You would be surprised how close to max some of the HDT's run on the rear axle. The trucks that are singled carrying a bed, drom box, smart car and then 5-7k of pin weight will usually push the axle capacity..... even with a 19k axle.

Alie & Jim + 8 paws

2017 DRV Memphis 

BART- 1998 Volvo 610

Lil'ole 6cyl Cummins

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Back in the day I ran a p-30 chevrolet step van. Total weight was 14000 pounds GVW was supposed to be 10000. I broke leaf springs, went through brakes and a set of tires only lasted 20000 miles, but never repaired the rear end. Sold it at 180000 miles.

2002 Beaver Marquis Emerald   C-12 Cat 505 HP

2014 Volvo 630 D-13 I Shift SOLD

2017 New Horizons SOLD

 

 

 

 

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Mike-

You would be surprised how close to max some of the HDT's run on the rear axle. The trucks that are singled carrying a bed, drom box, smart car and then 5-7k of pin weight will usually push the axle capacity..... even with a 19k axle.

Jim, indeed it's a fact of life with the larger rigs that the singled trucks may nudge up to or some over the rated axle limits...

 

I suppose if someone could get Scrap tipsy-drunk we might worm out of him the margin of safety factored into various axles...problem is after the hangover he would have to bite the cyanide pill in the secret compartment of his KW Leatherman tool....or the truck-lawyers might just firing squad him.....

 

As Glenn mentions you don't seem to see many HDT with broken axles so it seems even the over rated axle crowd are skating by within the margins....maybe..

 

Drive on....(what's your margins)

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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With an AM transmission, you'd be hard pressed to brake an axle, especially at the weights RV'ers pull. You have 12,000 lbs-ft of torque? Well that's nice but if you don't have traction, you'll never see it. I'm sure duty cycles comes into the equation as well but, no one here comes close to life-ing out a drive train.

"There are No Experts, Do the Math!"

2014 Freightliner Cascadia DD16 600hp  1850ft-lb  18spd  3.31  260"wb
SpaceCraft S-470
SKP #131740

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I've been "trying hard" to do my part, almost 100K miles, in almost a decade of RVing (from 800K to 900K on the odometer).

It'll be interesting to see the pricing trend on the many trucks, purchased in recent years brand new for the single purpose of RV puling. A ten year old truck is worth $10-15K, "age wise". A ten year old truck with 100,000 miles? Let the bidding war begin.

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With an AM transmission, you'd be hard pressed to brake an axle, especially at the weights RV'ers pull. You have 12,000 lbs-ft of torque? Well that's nice but if you don't have traction, you'll never see it. I'm sure duty cycles comes into the equation as well but, no one here comes close to life-ing out a drive train.

As my feeble mind seems to recall ...Scrap was more concerned about the lightweight axle housing cracking outboard of the spring hangers.. the axle shafts float so they don't really carry the mass loads related to cargo... the axle shafts seem to have adequate margins to deal with the drive train torque loads...

 

After WWII Grumps bought huge pile of Mack GI boogies and they looked fairly small compared to a Eaton driver of the day but he never lost A Mack GI boogie and trust me some of the trips with a full dress CAT D9 on the tandem lowboy would test any set of drivers (and Tires)...

 

Scrap likely knows the real story so... maybe if he gets tipsy at the KWopper New Years party SOMEONE could get him to tell the rest of the story..

 

Drive on....(what's the real limit($))

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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Mike-

You would be surprised how close to max some of the HDT's run on the rear axle. The trucks that are singled carrying a bed, drom box, smart car and then 5-7k of pin weight will usually push the axle capacity..... even with a 19k axle.

You know Jim you seem to be referring to a situation in the aviation world often called the....."Coffin-Corner"...

 

In layman's terms the "Coffin-Corner" is the extreme corner where a aircraft runs out of the ability to climb to a higher alitude, fly any faster, fly any slower, AND carry any more Weight...in other words the pilot is now in a corner of the flight envelope where down IS the major direction the bird is headed if he screws around much......

 

You know that plastic coated card in the seat pocket in your first class seat on good luck airlines seems to never mention the....."Coffin-Corner" ...However most airline flights tend to eventually climb up to a Flight Level where Wilbur and Homer up front can tickle the "Corner" if they get a little silly.....It seldom happens in the airlines much these days mostly because the airlines buy birds with a pilot named Auto-pile-it bolted into the dashboard and Auto has been programmed to fly fairly close to the "Corner" but not too close to bumble into the corner like humans do from time to time.....

 

Private aircraft tend to skate past the "Corner" on regular basis....but usually only once....

 

Now if we go back to the original weight slips on this thread I wonder IF the RV owner were to desire to load a Smart car on the back of the truck would he have to buy (and load) more Hogs into the back of the toy hauler to lessen the pin load to allow the truck to operate within rated axle loads at the risk of the greater rear-mass-loaded trailer becoming dynamically-latterleee-un-$table...(tail-wagging)

 

Now for the most part a HDT towing a RV is a pretty good prescription for staying out of the "Coffin-Corner".....BUT, it can happen .... one day when I was a kid Grumps got the old Kenworth too far into the "Corner" with no way out and she tipped over with me riding shotgun.....bad juju...

 

Drive on....(where is your....corner)

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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We didn't call it a coffin corner, but in the marine world overloaded and unbalanced would usually give you that sinking feeling....

The faster we pushed the boats, the more the balance became critical. Somewhere around 35-40mph side to side balance becomes apparent, around 60-100mph any sudden weight change, even a cooler sloshing, can cause balance/roll issues. Somewhere around 140 to 180ish mph fore and aft balance becomes really clear, the thrust of the props have to be able to carry the weight of the boat.... when the props come out of the water and loose thrust, having the bow drop before the stern is really really making for a bad day. Over the 160mph mark, we transition into your territory of aerodynamics. There is so much of the boat out of the water that wind resistance becomes apparent. Having a steady cross wind is ok, having sudden crosswind hit the bow at 180mph makes for an unbalanced/pushing effect that can be driven thru.... or swam thru....

We use ballast tanks located in various locations to help keep the craft trimmed. As fuel burns off, we can add water to tank #1, #3 etc.

Not the same as pigs running around in a cargo hold, but the effect can be the same...... except we're much closer to the water.....

Alie & Jim + 8 paws

2017 DRV Memphis 

BART- 1998 Volvo 610

Lil'ole 6cyl Cummins

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So Jim, Do you knowe Ken Warby? He has some experience in this. I think his record of ~380 mph on water still stands ( made a one way pass over 400). Man, is he a nut case, but still alive. Hw lives about 15 miles from here.

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 rickeieio1@comcast.net

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I know who he is, but never met him. All my experience is in Off shore, Vee- hulls primarily Fountain Power Boats. I worked there for 15 yrs in R&D.

IMO.... strapping yourself into 6000lbs of fiberglass with 3000hp of V-8 engines is one thing....

Strapping yourself into 1500lbs with 4900lbs of thrust is.... ahhh, lets say above my threshold of what is nuts....

There are many Super Cats that run turbines that are hitting 225 or so. It's really ugly when they blow over though which usually happens.

Alie & Jim + 8 paws

2017 DRV Memphis 

BART- 1998 Volvo 610

Lil'ole 6cyl Cummins

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Since we have wondered into stupid things that go too fast I'll throw in a odd way to almost kill yourself.

 

I used to fly with a guy that likely still holds the unofficial record for tumbling a air-breathing aircraft....

 

He got a gig testing a concept of guiding a F-104 up into "near-space"....

 

The concept was to strap into the old 104 and climb up to 60,000 feet and put the pedal to the metal and accelerate up to warp 9 and then pull the nose up into a ballistic arc and....fling the old 104 out of the atmosphere....gulp...

 

So now that you have flung yourself out of the atmosphere how do those wingy things work....answer....they don't work...so...the wonder kids had cobbled some cute little retro-rockets on the 104 and rack rocket had a push button the you pussed to jog the rocket....neat idea...sorta...

 

So Willy has flung himself into space and the 104 is sorta wobbling some and the nose is a bit too high and the right wing is a tad low so....blip the right button and raise the right wing so easy...next blip the tail rocket button to lower the nose.....humm .....did the boys on the ground know this DAMN button sticks in the ON position.....bad juju.... thankfully the pressure suit stayed intact and it shuck so bad it rattled all of the fillings out of his teeth and blacked both of his eyes he tumbled over 80,000 feet....

 

Here is the best part a company is preping a herd of old 104'$ to launch pico-sattelites in the near future using ....you guessed it... ballistic arc...

 

More things change...the more they stay the same...

 

Fly on....(hate those cheap switches)

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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