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Old 05-03-2006, 12:56 PM   #29
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What about when a big rig passes you going the other way on a two lane highway at a high rate of speed? Wouldn't this be the worst case vortex scenario?

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Old 05-03-2006, 01:16 PM   #30
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Originally Posted by wacnstac
What about when a big rig passes you going the other way on a two lane highway at a high rate of speed? Wouldn't this be the worst case vortex scenario?
wouldn't think so. while the wave of air that a truck is pushing ahead of itself in that scenario will bump into you and give you a push, there wouldn't be any "vortex" or sucking, because you are moving in different directions...and also, the close contact would be of such a short duration when you're at a closing speed of 120mph or greater.....

when the 2 vehicles are going in the same direction, the close contact time is much longer, and there is a column of air coming off each vehicle, going in the same direction (between the vehicles) that is accelerated. that increase in speed creates a corresponding decrease in pressure (Bernoulli). the suction that results will be trying to pull the vehicles together.

when they're going in opposite directions, the air column between the vehicles never forms, because air flowing off of one vehicle bumps into air flowing off the other in the opposite direction, creating a mix-master effect...and for a very brief period of time, at that. no suction.

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Old 05-03-2006, 01:35 PM   #31
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Originally Posted by wacnstac
What about when a big rig passes you going the other way on a two lane highway at a high rate of speed? Wouldn't this be the worst case vortex scenario?
I don't believe so. My non-rigorous, non-mathematical understanding of this is as follows: For simplicity, assuming there is no wind relative to the earth at the time, a tractor trailer compresses air in front of it, and this high pressure air escapes down the sides and over the top of the rig air to fill the low pressure area behind the tractor trailer (The "hole" in the air it leaves behind). While it is whistling past the rig, this stream of air is squeezed between the sides of the rig and the mass of surrounding air. To get through this "squeeze effect" (otherwise known as a choke, or venturi), the flow of air accelerates, and, by Bernoulli's Law, this produces a low pressure area along the side of the tractor trailer, and this is what sucks your trailer towards an overtaking tractor trailer or moho, after you have first been pushed away by the high pressure wave at the front of the passing vehicle.
If you are travelling at 60 mph, and the overtaking vehicle is doing 70 mph, it will take about 7 seconds for a 55 foot tractor trailer to completely clear a 50 foot Airstream and tow vehicle combination. That's from the time the tractor's nose is level with the Airstream's rear bumper, to the time the rear of the tractor's trailer clears the front of the Aiurstream, and you still have to deal with the hole behind the tractor's trailer. 105 feet at a relative speed of 10 mph (about 15 feet per second), gives about 7 seconds of disturbance.
If the tractor trailer is approaching from the opposite direction, the relative speed is 130 mph ( about 200 ft per second), and the time for the vehicles to clear each other is just half a second. With the large mass of the Airstream and tow vehicle, half a second is too short a time to cause significant movement, compared to the previous situation. When the tractor trailer or moho is overtaking, it has far more time to push your rig sideways. Fourteen times more time. That's my humble intuitive understanding of this situation, without resorting to a mass of equations.
Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
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Old 05-03-2006, 04:40 PM   #32
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Originally Posted by wacnstac
What about when a big rig passes you going the other way on a two lane highway at a high rate of speed? Wouldn't this be the worst case vortex scenario?
The two "bow waves" of air will tend to mostly cancel each other out, and the remainder will be only a second or two at the very most.
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Old 05-03-2006, 08:14 PM   #33
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Glad to here they are OK! Very scary story but glad to see people are trying to learn from it.

Since we are analyzing what happened here is my take.

My guess is owners "unintentional" fault with a problem with the hitching.

Most people remember the "over hitched" post a while back. Go reread it if you don't so this will make sense.

Ford expedition has load leveling suspension. PROBLEM 1!

This causes a problem with setting up the load bars. They were "over hitched" because the load leveling suspension tricked them into thinking they had plenty of tension on the load bars.

If they did indeed have a Reese DC then what happened is the suspension leveled and the load bars were not pulled up tight enough. The Dual cam DEPENDS ON A LOT OF LOAD AND FLEX OF THE BARS! Its a friction design and the more pressure on the saddle the more effective it becomes.

When the truck passed it got them out of shape because the lack of load and made the DC ineffective. Once they started oscillating in the slip stream the trailer started over riding the dual cam and shoved the rear of the relatively short wheel base truck (119 inches) around. Hitting the trailer brakes probably would have pulled it back in line. If she hit the brakes and nose dived the truck it probably was the last ingredient for certain doom. Nose diving the truck would have taken even more load off the DC.

I bet the bars were rated 1K and they should have been using 550's. Andy in several posts recommended load leveling suspension be disabled because of this EXACT problem.
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Old 05-03-2006, 08:49 PM   #34
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You Mean...

...this thread ISN'T about high speed surfing the internet while you're driving down the interstate?
If I had known it was just about another near tragedy I wouldn't have read it.
We're all exposed to a greater risk as we haul these clunky, unweildly contraptions down the road. Most of us are novices (at best) at pulling them.
Seems to me that we should hear about more near misses. Cept near misses don't sell the 5 oclock news.
My take is that that particular semi driver in that particular wind pattern wasn't negligent. Maybe we should check the the weather/wind patterns (via high speed internet?) before we go down the road.
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Old 05-03-2006, 09:08 PM   #35
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hi tarheel, zomby, nick and others

sure hate to read about this accident and that a high speed driver may end the trailer life for this couple...

zomby i too use and trust the haha for towing....
there are many threads here on the haha (hensley arrow hitch apparatus) and reading them may be useful....but towing with the haha will provide a better understanding of it.

no 2 accidents are the same and stories don't prove much,
but i meet a gent last year pulling a new 34 slide with a 1 ton srw gmc and a haha.
he too was overtaken by a semi; happened so fast he didn't see it till they were side by side....
said he felt a little 'bump' that he assumed was the airwave effect noted here.
his rig tracked straight and he yelled something at the trucker....
traveled on to the next rest area without issues.
while walking the streetside of his trailer,
he noted with much surprise that the semi had sideswiped him.....
leaving rubber circles along the side and slightly creasing the new aluminum skin....

we met at jackson center while getting new skin.

chuck the engineers suggest that the haha pretty much eliminates the traditional pivot at the ball. i've studied the patent info and available design info and the haha is unique....althought the patent and extension should be nearly out....
a virtual pivot is created several feet forward that is close to the rear tv axle...
depending on overhang.
i'm not gonna debate with you regarding how the haha works....but it does work.
folks that don't get it....just don't get it.
in order for the trailer to wag/sway or whatever term.....
the rear t.v. tires would have to slide/move sideways....

there are many good threads here and on rvnet forums that provide insight into how&why the haha works....
yes, many issues from tire pressure, loading, cross winds, road grooves, driver correction/overcorrection, and so on.....contribute to loss of control.
but there are soooo many examples of happy haha owners,
and having used one now i am completely in that camp.
unless you have towed with one and tried to induce sway or felt how it works....
it is pointless to comment on what it does or does not do....

i sure am sorry to read about the accident that started this thread.
whatever towing set up one safe and be careful.

and nick another great description...thanks.

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Old 05-03-2006, 09:43 PM   #36
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Sorry to hear about your unit members problem with trucks. I live in Tennessee where the highway patrol allows trucks on I40 to run 75-80 nearly anywhere. Towns such as Nashville have had 4-5 deaths per year due to trucks out of control in congested areas. I enjoy driving in Ohio. Outside of the cities, the HWP has put the trucks in the right lane at 63mph ( except for cowboys who haven't been caught) and they operate their trucks with some degree of control and rarely pass. Indiana and Illinois are fairly good as well but, I hate driving in states such as Tenn., Missouri I70, Kentucky I75, Florida I75. I haven't been in Europe for quite a few years but, they can't be as stupid as the USA.
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Old 05-03-2006, 09:50 PM   #37
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Originally Posted by zombyw00f
I have never towed before... We just ordered a new rig with a Hensely Hitch. Do any of you use one? Does it prevent these types of problems discussed in this thread?
The day we took our 34' triple-axle up to Jackson Center (60 or so miles away), a strong front was moving through with 35 mph winds out of the west and we were moving north. Gusts were to 65 mph and 18-wheelers were pulling off the road. Our 34 was moving around, but we didn't FEEL A THING in the truck.

Coming back from Jackson Center, we'd just done the cloverleaf to switch from I-75 South to I-70 East, when I saw concrete barracades on both sides of the two lanes. I looked in the left mirror and saw an 18-wheeler coming up behind us in the left lane at about 85 mph (and we were doing about 55). I looked dead ahead, relaxed, and eased as far to the right as I dared. He blew by us hard and in my peripheral vision it looked like he only cleared our McKesh mirror by inches. We barely felt a wobble. Had we wobbled much, we'd have been into him or the barricade.

I attribute this stability to the Hensley Arrow hitch. Once upon a time, I was an RV tech and delivered trailers, motorhomes, etc for a living. I've felt severe sway more than once, but was young and quick on the brake controller manual lever to stop it. I'm older, smarter, and slower now. You made a wise choice with the Hensley.

[edit] BTW, I've eased our 34 up to about 90 mph, a little at a time. If I can't pull a trailer that fast and do normal lane changes at that speed, I have no confidence it can handle emergency manuvers without sway at 60 mph, my usual towing speed.
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Old 05-04-2006, 07:46 AM   #38
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Vehicles passing that cause the most problems

I've been able to compile my list of vehicles that seem to cause the most airflow problems when passing me on the Interstate.

1. Over the road busses (Greyhound etc.).
2. Class A motorhomes.
3. Tanker trucks
4. Flat faced 18 wheelers.
5. Auto transport carriers.
6. Cargo trucks (like the big U-Hauls).

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Old 05-04-2006, 08:57 AM   #39
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Give 2Air a good one for the 'haha' acronym. It certainly fits.

No offense to the HA as it is a good hitch, escpecially at small angles such as you have trying to go down the road in a straight line. But I think folks need to be very careful in how they interpret their perceptions.

Yes indeed it is much scarier and more likely to be dangerous when an articulated rig bends in the middle at speed.

But the forces that caused such behavior don't go away if you make it more difficult to bend in the middle. Instead, they show up in a different way.

There was a thread over on RV.NET about folks returning from an Ohio ralley in severe winds where those following an HA owner could compare and contrast observations with the driver. Very interesting insight.

Wind or other conditions will have their way. A good hitch just changes the boundaries of safety which are also influenced by the driver and many other factors. It is up to all of us to drive safely and to not be overconfident if we think we have some special edge - circumstances have a tendancy to catch up to such hubris.
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Old 05-04-2006, 09:00 AM   #40
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Originally Posted by 2airishuman
chuck the engineers suggest that the haha pretty much eliminates the traditional pivot at the ball.
I dont' think they suggest that at all. and if they did, they'd be wrong. I've seen them in action, just last weekend. when the rigs turned, they pivoted right there at the point at which the 2 vehicles attach, just like any other tow vehicle/trailer rig.
I'm not saying that the "ha ha" ain't the bees' knees and all that...the best available, or that we shouldn't alll run out and buy one right now, and the world wouldn't be a better place if we did.
I'm merely being a stickler for language, here, and the use of "absolutes". like the word "impossible". its not impossible. its just highly unlikely. I guarantee you that I could take RKM's rig out there on the highway and roll that sucker in 2 seconds. It would be very unlikely for that to happen unintentionally in real world conditions...but not impossible.

Originally Posted by 2airishuman
in order for the trailer to wag/sway or whatever term.....
the rear t.v. tires would have to slide/move sideways....
that can be arranged. quite easily, under some road conditions.
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Old 05-04-2006, 10:52 AM   #41
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Originally Posted by Tarheel
...Don't socialize while hooking up. Don't help others unless they request. Talking to them can make them over look a step.
We had just had some work done on our trailer & while leaving the shop a friend was pulling in to have some work done on his. Our 'visit' lasted until we left. The next day on my walk-around I noticed the marker lights were not working. 400 miles away, 400 miles back to find out some wires had been shorted while the work was being done . If I had been left alone during the hook-up this would have been caught. COST: 3 days, & 60 gals. of fuel.
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Old 05-04-2006, 12:00 PM   #42
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So, which is the "best" stabilizer system?

Ok, this might open up a whole box of Pandoras (as a former gov. of New Mexico was fond of saying), but what do the very experienced in the group recommend for a newbie? I don't know the brand/name of what came with my AS, but it looks a little funky and old to me. Since I don't have a tow vehicle yet, I figure I should probably start over from the bumper back with everything. I've read many, many thread here about the stabilizer systems and it seems to get more confusing with options specific to the type and year of AS, none of which seem related to my 72 23 footer. One thing I have determined is that the tow vehicle needs to be as long as possible, so that part I get. But the rest of it? Just point me to a simple tutorial.

BTW, I really liked (was it Nick's?) description of how big moving masses get sucked into each other.

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