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Old 11-23-2009, 10:35 PM   #15
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Originally Posted by HiHoAgRV View Post

Watching the mirrors was super important. As a rig overtook, you had to turn the slack toward the shoulder, the turn back toward the rig as it overtook. 1/2 a turn with extended arms on the wheel is quite a dramatic driving maneuver.

I can feel an overtake of my current setup acting basically like your diagram.
Yeah, we had a big ol' motorhome like that in the '70's. 55 mph was plenty fast. I usually had the wheel fairly far over in winds, waiting for the moment they slacked. It was just part of training.

Never forget my old man, p.o.d and coming forward as I was driving the six of us eastbound one afternoon along I-10 'cause I had us one wheelset over on the shoulder and was still rolling. He didn't see what I had, a big truck coming along at over 100 mph. The steering correction I'd have needed to stay in Lane 2 would have been too much. At 17 I'm sure I'd never been passed at such a speed by so much mass with a speed differential of 50 mph. Half a dozen troopers and a helicopter had that desperado over at the I-10/I-20 split near Van Horn, TX about 5-miles ahead.

As to pulling the trailer, I "feel" the truck bow wave as it hits my pickup bed topper, not the trailer. A Hensley (or PP or PR) is worth it. Next upgrade to the TV is a rear anti-roll bar and some poly bushings on the front one. Truck already has IFS and rack & pinion steering. I have to stay with my Load Range E tires (stock size and type), and am undecided about the rear suspension springs at present.

The perspective from the lower point on the road (TV, versus tractor cab) is that it is harder to "see" the point at which the bow wave will hit. From one big truck to another it is easy to gauge.
I'm sorry I no longer have access to truck safety statistics and training guidelines.
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Old 11-24-2009, 05:40 AM   #16
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Best description of tractor-trailer "bow wave" (involving a wrongful death suit from an accident on I-81, Virginia, in 1986):

Garst, a driver with over 20 years' experience in driving vehicles pulling horse trailers and campers, testified that just prior to the accident, he had been driving at a speed between 50 to 55 miles per hour in the left lane of the two northbound lanes of I-81. As Garst got to the bottom of a hill, he noticed a tractor-trailer "coming right fast" in the right lane, and "about the time that the tractor-trailer got to the rear of the camper, [he] felt the wind force pushing the camper."

As Garst felt the wind force push the camper to its left, the front of the Suburban was also forced to its left. This caused both vehicles to begin "swinging." Garst unsuccessfully tried to stop the "swinging" by turning the Suburban slightly back to the right and applying both vehicles' brakes. Then Garst applied the trailer brakes and accelerated the Suburban, but the more corrective action he took, "the worse everything got." Garst testified that "then, all of a sudden, everything went around, and that's the last thing I remember."

------------------------------------------------------------------------

Walter A. Johnson, who had made government-funded studies of the wind forces from tractor-trailers and their effects on other vehicles on the highway, qualified as an expert witness in the field of automobile and tractor-trailer aerodynamics. Johnson testified about the effect of such wind forces upon a vehicle being passed by a tractor-trailer.

According to Johnson, the front of a tractor-trailer pushes the air out of its way as it proceeds down the highway, creating a "bulging out of the wind [which] is referred to as a bow wave. It is much the same as a bow wave of a boat going through the water." At the aft, or rear end, of the tractor-trailer, the air is sucked back in behind the vehicle. As the bow wave progresses along the side of the overtaken vehicle, the wave's force pushes on those parts of the overtaken vehicle closest to that force, and as the rear end of the tractor-trailer passes the other vehicle, the force of the suction pulls on the parts of the overtaken vehicle closest to its force. Johnson testified that the bow wave and suction forces grow disproportionately at higher speeds and closer proximities between the vehicles.


Passenger, Girl Killed by Unknown Truck Driver Get Justice - Roanoke, Virginia | The Krasnow Law Firm

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Old 11-24-2009, 06:17 AM   #17
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Of 2Airs links above, reading them (re-reading in the main), these single posts stuck out:

http://www.airforums.com/forums/223871-post11.html

http://www.airforums.com/forums/442188-post41.html

Understanding trailer sway

http://www.airforums.com/forums/467652-post8.html

http://www.airforums.com/forums/248511-post46.html

http://www.airforums.com/forums/220472-post50.html

http://www.airforums.com/forums/245990-post24.html

Loss of control "caused" by other traffic on the road, is, of course, one part of a larger picture.

From a post I was going to make on another forum, concerning the "necessity" of a WDH on a 16' cargo trailer:

DODGE
2004 Ram Truck Diesel
(Owners Manual; co. 2003 DaimlerChrysler Corporation)

pp. 278

TRAILER WEIGHT AND TRAILER TONGUE WEIGHT

"Equalizing hitch[es] are required for CLASS III or IV trailer hitches and tongue weights above 350-lbs (159kg) and use of trailer sway is recommended".

I don't see trailer type being excluded. To those who say that a well-loaded cargo trailer won't sway I would only agree that the sway is lessened in comparison to a large TT. Take a look at the design of the U-Haul 12-footer. It's far better than what most can buy, and it trails beautifully.

But take a longer look at ANY trailer type you are following to see the "disconnect" between TV and trailer. The "looser" it is (design, speed; hitch rigging) the more wiggle you'll see.

Disbelieve those who say that they have driven X-miles with no incident. What they observe (and feel) is to be severely discounted when following them in traffic. Even the best "little" trailer can flip a truck under unlucky circumstances.

Pretty much any trailer of 2,500-lbs meets the TW rule above (375-lbs @15%), and it only makes sense to avoid trouble. To minimize risk.

There are adaptors for single pole trailers to fit a WDH with anti-sway.



I've learned quite a lot from the threads and problems posed by members of Airforums on this, and, as my parents had a loss-of-control accident more than a dozen years ago, I was determined to avoid that if at all possible.
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Old 11-24-2009, 07:24 AM   #18
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This is great information. It has helped me understand the dynamics at play in these situations.

Brian
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Old 11-24-2009, 09:33 AM   #19
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Info-Reading-thanks

To begin a response: Thank you for the information, related reading
in previous threads and general feedback. Folks here are good folk.

My main conclusion at this point is that the "Hand Controller" of the
trailer brakes seems to be the best defense at the point where the
blast of air hits the rear of the trailer (through steps 2 and 3 in the
images above).

I thought about this off/on all yestreday evening. Another conclusion:

60MPH = 1 mile per minute
1 mile = 5280 feet
5280 / 60 seconds = 88 ft/sec
So......
60MPH = 88 ft/sec
30MPH = 44 ft/sec
15MPH = 22 ft/sec

If an 18 wheeler passes at an est speed of 80MPH, and I am towing
at a speed of 60MPH - that is a difference of 20MPH - or - calculated
29.33ft/sec.

If these numbers are very close, then a family with a 30ft trailer
would experience steps 2 and 3 above in approx 1 second. I think
that what happened to the family in Thoughts and Blessings...
could happen to any of us regardless of all the best rigging.
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Old 11-24-2009, 10:06 AM   #20
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Have done some more reading around:

Post by ib516 (thread on RV.net)

"What contributes to trailer sway? A number of things. Top suspects on my list are:
- Side winds
- Trailer tongue higher than it should be (level or slight nose down is best)
- Too much weight at the rear of the trailer - this creates more angular momentum once any swaying begins. More weight further away from the trailers CG acts like a lever and can cause sway to increase once it starts. This is especially true if the weight is water which can slosh or a weight that can shift.
- Soft TV suspension and tire sidewalls
- A phenomenon known as "rearward amplification" (in my collision reconstruction training anyway, I'm sure there are other terms for it) - it's kind of like cracking a whip. For example, in a A or B train (OTR truck with two trailers attached, a large one, than a smaller one behind). The rear most trailer does the most swaying first, and will "pull" the other trailer around which will begin to pull the rear of the tractor side to side. The effect is the same in OTR trucks that rollover. The rear of the rearmost trailer can be 90* to the roadway (ie: on it's side) before that motion is transferred to the power unit. The driver never feels the truck begin to roll until it's waaaay too late. The trailer will act like a spring, "wind up" tension, then slam the power unit on it's side. I've seen video of it. Very interesting.

My training on this is mostly based around commercial vehicles (OTR trucks). The instructor was the former head of collision reconstruction for BC (Canada). He investigated hundreds od commercial vehicle rollovers (tip overs) in hilly/mountainous BC - mostly at the bottom of a grade on a corner.

Tried to keep the explanations from sounding too "scientific".


RV.Net Open Roads Forum: Towing: Dynamics of trailer sway 101? The basics?



Post by Ron Gratz (from a thread on RV.NET)

"When the bow wave of the passing truck hits the rear of the TT, the TT's center of gravity will be a "dynamic pivot point". The right-directed force on the rear of the TT will produce a left-directed force on the rear of the TV via the ball coupler.

The left-directed force will push the rear of the TV toward the left and will cause the TV to yaw CW. This will make it seem as though the TV and TT are being sucked in; but in fact, at this point, the force on the TT is away from the truck.

As the truck moves forward relative to the TT, the bow wave eventually will be pushing toward the right on the front of the TT and the rear of the TV. Also, there can be a time during which the high-pressure bow wave is pushing right on the front of the TT and the low-pressure area at the rear of the tractor is pulling left on the rear of the TT. This will increase the right-directed push on the rear of the TV.

With a Hensley Arrow, [a Pro-Pride] or a PullRite, the initial yawing of the TV is reduced because the lateral force from the TT is applied closer to the TV's rear axle. With a Dual Cam or Equal-i-zer, the initial yawing is reduced because the hitch tends to stiffen the connection between TV and TT.

Some things which can minimize the effect are:

1] Get a good sway control hitch.

2] Ensure there is good weight distribution on the TV's axles.

3] Move to the right when you see the truck about to pass.

4] Don't overcompensate with the steering corrections when you feel the initial movement and yawing of the TV.

RV.Net Open Roads Forum: Towing: Interstate Towing ?



Andy Thomson, on Eliminating Trailer Sway

http://www.rvlifemag.com/file316/hitchhints316.html


Some big truck related info, FYI. (It is not directly related to the TT/TV combination as to using trailer braking).

DRIVING COMBINATION VEHICLES SAFELY
Driving Combination Vehicles Safely

A SIMPLE MODEL FOR DETERMINATION OF (TRACTOR-TRAILER) JACKKNIFING
http://fcrar.ucf.edu/papers/fa1_omgt_fau.pdf

I remember one company safety director repeating that slowing down was job one, with a six-second follow of the vehicle ahead (when loaded) crucial.

I prefer traveling at about 63 mph -- on an open road -- as I can quickly drop a gear, touch the brakes and be at 50 mph (where I can maneuver, nastily, all day long). And I detest traveling in a pack as there is NEVER any room to maneuver; whether or not I cause that/those maneuver[s].
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Old 11-24-2009, 10:26 AM   #21
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Quote:
Originally Posted by kennethowens View Post
To begin a response: Thank you for the information, related reading
in previous threads and general feedback. Folks here are good folk.

My main conclusion at this point is that the "Hand Controller" of the
trailer brakes seems to be the best defense at the point where the
blast of air hits the rear of the trailer (through steps 2 and 3 in the
images above).

I thought about this off/on all yestreday evening. Another conclusion:

60MPH = 1 mile per minute
1 mile = 5280 feet
5280 / 60 seconds = 88 ft/sec
So......
60MPH = 88 ft/sec
30MPH = 44 ft/sec
15MPH = 22 ft/sec

If an 18 wheeler passes at an est speed of 80MPH, and I am towing
at a speed of 60MPH - that is a difference of 20MPH - or - calculated
29.33ft/sec.

If these numbers are very close, then a family with a 30ft trailer
would experience steps 2 and 3 above in approx 1 second. I think
that what happened to the family in Thoughts and Blessings...
could happen to any of us regardless of all the best rigging.
The tests I made, confirm your numbers.

Also, if the big rig is coming from the opposite direction, on a single lane road, the individual speeds become additive, as measured with an "airspeed indicator".

Complicating that issue, is the wind speed and direction.

Andy
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Old 11-24-2009, 07:14 PM   #22
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Quote:
Originally Posted by Gen Disarray View Post
Has anyone else noticed that they get worse push from the box type trucks such as the moving vans?


Yup, short, sharp and hard.

Straight trucks (so-called as their is no trailer) are often maxed out as to height/width. And sometimes, not even rounded corners.

I've read today, elsewhere, that the old COE combinations hit the hardest (Cab-Over-Engine; flat front); that they could force aside 18-tons of air at 60 mph. (See link below).

-------------------------------------------------------------------------

In the reading around I had the leisure for today, I came across the product called AIRTABS (with which some of you are familiar). They may not save much in the way of fuel (small measurement best applied across a fleet), yet it is remarkable how often, how consistently, other RV'ers are reporting them to be good for mitigating wind-induced sway. Granted, the rolling boxes benefit most:

Air Tabs (vortex generators)

NASA & Vehicle Aerodynamics: Spinoff Technology

Aerodynamics Research Revolutionizes Truck Design


RV Applications: Airtab

Motorhome Test, 2009

http://www.airtab.com/vm/newvisual/a...r2009page2.pdf


Car Hauler Test (rv.net)

I towed down to Watkins Glen and back to Hamilton, [Ontario] on the weekend, first test for the Airtabs. I found that the gas mileage was probably better, but not by enough to really test without some greater mileage, probably on the order of 5% better. The truck pulled fifth gear easier and we ran along easily at 120 Km/hr (75 mph)for a significant part of the trip.

The gain in handling was more pronounced - almost no tractor-trailer induced sway, down from fairly bad sway, and the trailer was more stable in cross-winds as well. Even a bus blowing by at 15 mph faster than I was doing didn't cause a minor heart attack the way it did before. I would say the claims are proven, but with the number of miles I do a half MPG will take a long time to pay back. The improvement in sway control is impressive and worth the money to me.

RV.Net Open Roads Forum: Towing: Airtab test results


One year with Airtabs on motorhome

Coast Resorts - Cookies


Airtabs for [3] years (Airstreamer67)

7.3 PowerStroke in a 1996 F250 towing a 6000 pound JayFeather 25F between 55 and 60 mph when on the highway.

The idea is to prevent as much of the suction effect on the rear as possible. Honestly, I don't think the AirTabs increase the economy significantly, but they surely increase stability in windy conditions and when 18-wheelers zoom by.


RV.Net Open Roads Forum: Towing: how make my Ram increase more MPG towing?


--------------------------------------------------------------------


Finally, a bit of nostalgia. I remember reading this article ca. 1973:

How You Look to a Truck Driver
Popular Mechanics, May 1969

Popular Mechanics - Google Books


There is hope that fuel economy concerns will finally allow us to see more aerodynamic commercial traffic. Hopefully, these "green" tractor-trailers will manage airflow to our mutual benefit in re the topic.
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