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Old 11-23-2009, 02:07 PM   #1
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18 Wheeler Air Flow

While reading about an accident in a recent thread, I had also
noticed concerning movements when 18 wheelers passed me
going in the same direction. So I wanted to see what ya'll thought
about this and drew some images to illustrate my initial thoughts.
Attached Images
    
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Old 11-23-2009, 03:03 PM   #2
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hi kenneth

nice pics.

web search 'bow wave' and winnow the results for rvs/trucks...

all sorts of wave pix will appear and nasa research and so on...

or search here for EITHER term (bow/wave) in the towing/hitch sub forum....

a turbulent bunch of threads will rise to the surface.
__________

some of those threads are lively, while others are jejune, dull as dishwater exchanges with the occasional PUSH/SHOVE ...

lots of castigating too, but only the members with RANK R allowed 2 use this approach.

http://www.airforums.com/forums/f464...rol-37238.html

http://www.airforums.com/forums/f238...res-37009.html

http://www.airforums.com/forums/f438...ing-23695.html

http://www.airforums.com/forums/f464...bar-12309.html

http://www.airforums.com/forums/f142...trol-3091.html

http://www.airforums.com/forums/f238...ing-38292.html

http://www.airforums.com/forums/f464...ion-22248.html

http://www.airforums.com/forums/f464...ars-12157.html

of course there are EXAMPLE thread scattered about that add to the drama, grab our attention and learning...

http://www.airforums.com/forums/f48/our-loss-35568.html

http://www.airforums.com/forums/f42/...eam-32547.html

for graphics i like hiho's pics in this thread the best (some squeeling/crash/broken glass audio would enhance them) ...

there is also good music and diy demos of engineering wizardry to round out the postings...

http://www.airforums.com/forums/f464...ied-37000.html

but dozens of haha threads have info on bow waves and how they do/don't feel or affect steering control...

cheers
2air'
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Old 11-23-2009, 03:23 PM   #3
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2Air - thanks for the references. I suppose
my question is related to "what can the operator do
at pic 1?
at pic 2?
at pic 3?

It seems we have folks who know what
they are doing and have the right stuff
in place on the rig. And still...that BLAST
of wind comes by and all bets are off.

It concerns me in view of my own experiences
and the recent family that had the "roll-over".
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Old 11-23-2009, 03:37 PM   #4
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Originally Posted by kennethowens View Post
2Air - thanks for the references. I suppose my question is related to "what can the operator do...
wild guess, you haven't actually READ the links yet...

'what 2 do or NOT do' is covered in many of those threads, by experts and idiots.

and many other threads provide insight and guidance, but without the ability to practice the moves on line.

sometimes the best thing 2 do is NOTHING but hold on...

since the b/w will pass.

corrective action often leads to MORE trouble.

so just pick a maneuver (steering, braking, accelerating, shifting, wacking the controller) and some1 will post the perfect steps...

with the haha/pp steering control is often just 2 fingers even with b/waves.
________

i don't know what roll-over prompted this thinking or your concerns, which are important.

gotta link?

or perhaps add your own experience and someone will sooth/fix or otherwise address the turbulence

cheers
2air'
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Old 11-23-2009, 03:40 PM   #5
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maybe this one... http://www.airforums.com/forums/f161...ngs-56634.html
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Old 11-23-2009, 04:02 PM   #6
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ah.

wicked awful.

and see they are now considering a haha/pp.

hate to post ANY hitch stories, especially when connected to others' misfortune, but....

i met a senior retired pilot having repairs in j/c a few years ago.

brand new 34/slide towed with 2500HD and a haha.

crossing kentucky in a big rain he was passed by 2 18s going way faster than him or conditions permitted.

the first semi slowed after passing because another vehicle was in FRONT of the semi, in the left lane but not visible due to the RAIN.

the 2nd drafting semi SLAMMED on the brakes just as pulling up2 his left side...

there was a LOT of turbulence at that moment.

he felt a little nudge (assumed to be b/wave) from the truck/s but just kept driving at the same speed, without doing anything.

his wife mentioned that the trucks seems a "little close" as they passed.

at the next rest area they stopped for lunch and to wait out the rain.

upon inspection he discovered the ENTIRE street side of his 'stream scuffed and INDENTED with black circular markings....

apparently 1 of the semis had RUBBED against the trailer, probably the 2nd one.
_________

he was totally confounded that the impact of this contact/disturbance was just barely noticed while driving.

and of course he became a "it' happened to me" testimonial giver for these fancy hitches.

cheers
2air'
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Old 11-23-2009, 04:37 PM   #7
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Quote:
Originally Posted by kennethowens View Post
2Air - thanks for the references. I suppose
my question is related to "what can the operator do
at pic 1?
at pic 2?
at pic 3?

It seems we have folks who know what
they are doing and have the right stuff
in place on the rig. And still...that BLAST
of wind comes by and all bets are off.

It concerns me in view of my own experiences
and the recent family that had the "roll-over".
If you have heavy sway movement, as you indictae in your photo's, then I would look at the complete rigging to assure that it's rating is correct, properly installed, and properly adjusted.

A slight pushing feeling is not uncommon when being over taken by a big rig.

The type sway control you may be using, plays a huge part of the ability to control, or not control, during that situation.

What you can do, in anticipation of a sway, from the big rig, is have your hand on the brake controller. As the truck begins to pass the trailer bumper, activate the brake controller, ever so slightly, without taking your foot off the gas pedal.

That will not slow you down, but it will cause enough brake drag from the trailer, to minimize the sway issue.

Andy
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Old 11-23-2009, 05:04 PM   #8
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I should have added, that when on a 2 lane highway, and a big rig is coming towards you, slightly apply the brake controller, just before the front of the truck is even with the front of your tow vehicle, about 20 to 25 feet usually works.

Andy
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Old 11-23-2009, 05:23 PM   #9
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As a truck driver I watched the reaction of RV's often. We, most of us, made it a point to pass as far away as possible. I hope that readers recognize that many truck drivers would love to be "an obstacle on the road" (said kindly), and many are, in off hours.

When I see them coming, my first reaction is to get off of the cruise control and make sure forward momentum is "positive".

While I rarely worry about truck drivers (and I'll use the CB to point out the jerks by company name, direction, etc; I called on and called IN one jerk in Arkansas for the way he passed a FEMA trailer hauler a few years ago), using ones mirrors is a bit of a skill that ought to be thought through more often. There are ways to handle oncoming or overtaking traffic and it all depends on using the space one has to maneuver at the speed being run. What is behind is sometimes more important than what is ahead.

There is NO substitute for the best hitch and rigging. This is a given, IMO.

As always, thanks for the links, 2Air, I appreciate the directions to more reading.
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Old 11-23-2009, 05:48 PM   #10
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you are welcome red'.

it IS interesting that NOT ONE thread here has 'bow wave' in the title.

as a result most of the discussions of this issue are sprinkled into other threads requiring the reader to scan a lot.

here are some other useful links to this issue...

http://www.airforums.com/forums/f464...not-26261.html

http://www.airforums.com/forums/f238...nts-40264.html

http://www.airforums.com/forums/f464...ars-23809.html

http://www.airforums.com/forums/f238...why-21559.html

http://www.airforums.com/forums/f464...ace-58335.html

http://www.airforums.com/forums/f463...nger-1887.html

http://www.airforums.com/forums/f464...rol-17986.html

and as expected MOST of the haha/pp threads touch occasionally on the b/w issue and control.

cheers
2air'
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Old 11-23-2009, 06:12 PM   #11
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Yep, the bow wave of a big truck is it's most interesting feature to watch from the cab. I could cry the number of times the brain-dead "trying" to pass me would get caught behind it, and just sit there. When seconds are more accurately counted as minutes.

Or, to see it's affect in the mirrors on other traffic in either direction. It's a two-moment phenomenon as both the tractor and trailer exert separate and combined pressure.

When following a big truck, observe the effects on the verge grasses, you will see this one-two punch and THEN the trailer rear effect.

There is "general agreement" among truck drivers that four-wheelers, all of 'em, should not be able to have cruise control installed and used until they passed a test demonstrating proficiency. I leave no one exempt, myself included. The number of four wheelers who pass a big truck with knowledge of what to do can be reckoned at fewer than one in every several hundred. On a good day.
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Old 11-23-2009, 06:22 PM   #12
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kenneth - I think I started you thinking about producing your diagram. You got it exactly right.

I just finished driving 2700 miles of I-35 (consider that the entire Duluth-San Antonio length is only 1403 miles...). Gave me lots of time to observe and think - except I wasn't towing.

You might do one of three things:
  1. Best - Be alert & apply appropriate minor reaction to steer through it.
  2. Sleep or text through the experience? (ie, don't observe, don't anticipate, do nothing) 99.9% of the time your oscillations may be more than us following behind might like to see. It's the 0.1% that will make you throw your phone out the window ... if your fellow passengers survived the experience. [anesthesiology or flying = 99% boredom + 1% sheer panic] Not paying attention is just plain dangerous.
  3. Worst - Stiffen your arms and create 'pilot induced oscillations.' See ah-one, anna-two. That film of the space shuttle makes you wonder where we're recruiting astronauts! I'd wear a diaper too...
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Old 11-23-2009, 07:59 PM   #13
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YEARS ago, we drove the interstate in a home-made rv based on a '61 Ford Econoline cabover truck that had tandem rear axles, a huge rear overhang and 1/2 turn slack in the steering. An overtaking semi had the effect you draw of the rig w/o a trailer.

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 manuver.

1st time passengers were absoutely freaked out, 'specially since we didn't tell them the speed-o-meter was reading 25% too high and it looked like we were doing 80+ mph.

I can feel an overtake of my current setup acting basically like your diagram.
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Old 11-23-2009, 08:53 PM   #14
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Side note

Has anyone else noticed that they get worse push from the box type trucks such as the moving vans?
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