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CookingWithGas
11-13-2006, 04:03 PM
I was watching one of those hook & ladder trucks ambling down the highway. You know, the type with a guy in a bubble at the rear, presumably steering the rear end. I suppose that's so the truck can navigate more easily in the city. Why do they use a driver instead of having a mechanical or electronic linkage to the front so the rear tires make a coordinated turn with the front?

Fir na tine
11-13-2006, 04:07 PM
I was watching one of those hook & ladder trucks ambling down the highway. You know, the type with a guy in a bubble at the rear, presumably steering the rear end. I suppose that's so the truck can navigate more easily in the city. Why do they use a driver instead of having a mechanical or electronic linkage to the front so the rear tires make a coordinated turn with the front?

Because in the few areas that still use them they want to avoid a coordinated turn. The intersections are so sharp that independently steered axles are necessary. Sometimes the rear axle has to cross into the other lane to make the corner.

11-13-2006, 04:16 PM
Why do they use a driver instead of having a mechanical or electronic linkage to the front so the rear tires make a coordinated turn with the front?The rear driver is also important when they arrive at the scene of the fire. It sometimes takes a lot of jockeying to position the truck properly in relation to the burning structure, other vehicles, and the location of the fire hydrant. They can be doing a lot of maneuvering, and an actual driver in back is very helpful.

R. P. McMurphy
11-13-2006, 06:51 PM
New vehicles do use an automatic dynamic steering system. The older ones had the guy in the back that steered the rear end around tight corners by steering away from the direction of the turn. (I used to think that had to be the coolest job in the world.)

It's the same for articulated buses that use dynamic rear steering.

Articulated buses (http://en.wikipedia.org/wiki/Articulated_bus)

KCB615
11-13-2006, 07:16 PM
Those type of trucks are called either "Tractor Drawn Aerials (TDAs)" or, as my part of the country calls them, just "tillers."

The rear axle is steered by the guy called the "tillerman," (I've never heard it called a tillerperson or tillerwoman, though I'm sure the phrase has come about somewhere), who has to be in constant communication with the driver of the tractor portion of the truck. One of the strange phenomenon of driving a tiller is that when the driver turns left onto a street, the tillerman has to steer right for a while to keep the rear of the trailer portion on the original street, then steer left quite fast to swing the back end onto the second street.

They came about from the problem of having to drive a 37 foot long piece of wooden or steel retracted extention ladder down a street (A 100' long, 3 section ladder is about 37' long). The truck, in essence, must be at least 40 feet long to have that ladder on it. Think back to old trucks, how manuverable were they? The front wheels didn't turn worth a darn, and its not like you have a short wheelbase to make up the turn with. Bending the truck in the center was a pretty good idea, but you needed to steer the rearmost axle in the trailer to get down the narrow streets of the northeastern US (ever drive through Boston, Providence, or Newport, RI in a car? Try it in a 55' long truck at a goodly speed).

Of course, in the "good ol' days" there wasn't a compartment in the back of the truck for the tillerman to drive from, there was a seat and an enormous steering wheel that actually sat on top of the ladder. When the truck arrived at a fire, the seat was lifted out of the way (it was on a hinge and swung to one side) and the steering wheel was lifted off of the steering column (which extended through the ladder itself) so that the aerial could come out of the bed. In the 1960's the truck manufacturers extended the trailer portion of the trucks by another 6'-8' or so so the tillerman could have his own seat, and he was lucky enough to even get a windshield. No roof, no sides, no heat, but he had a windshield. It was after 1992 that a fully enclosed compartment (the bubble mentioned above) was required.

Another great benefit of the tiller is the amount of storage space on them. Fire apparatus are just giant tool boxes, and a tiller is the mother of all tool boxes. Look at all the compartment space down both sides, combined with the center of the body where you can store a huge amount of ground ladders. Nothing beats a tiller for storage.

One of the dynamics of tillers is in the way they are stabilized at a fire scene when you want to "throw the stick," or use the aerial ladder. A straight chassis truck requires you to deploy outriggers, or jacks, to keep the truck from rolling over when the aerial is rotated to the side. Some manufacturers have four jacks, some have as many as six, but for a 100' aerial, you need to put these jacks down to take the weight of the truck off of the wheels and suspension system and transfer it to the jacks. This takes about 45 seconds to 2 minutes, depending on what manufacturer built your truck and how much you need to play around to get the thing level. With a tiller, though, you usually only have two jacks, right underneath the 5th wheel (where the trailer hangs on the tractor). You get the rest of your stabilization by jackknifing the truck, which the tillerman does as you're pulling into the scene. The tillerman can swing the back end of the truck off to one side while the tractor is moving forward, then the tractor swings to the same side. A crew that's talking amongst themselves can do it quite nicely every time, and quick.

Today, tillers are kind of on their way out. They take a minimum of three firefighters to operate (driver, officer, and tiller), most municipalities are trying to cut costs by reducing the size of fire companies, two firefighters on a ladder is pretty common. Technology has also reduced the size of trucks, most ladder trucks today are a "straight chassis" truck, not a tiller. A 100' ladder is now a 4 section ladder made from steel or aluminum, so the sections are only 27' long, thus shortening the truck by quite a bit. Steering axles turn much tighter than in the past, and some trucks even have steerable rear axles.

There's still nothing like a tiller, though.

More tillers:
http://e-one.com/index.asp?n=70&p=70&s=70&pid=10
http://piercemfg.com/apparatus/tractor_drawn.cfm

R. P. McMurphy
11-13-2006, 07:30 PM
Further on the point:

A fire truck sees a limited amount of milage so they can last for many, many years. They are necessarily very expensive so they are not quickly made obsolete.

A bus, on the other hand, just rolls up the miles. As KCB615 indicated, the tillerman will gradually disappear.

KCB615
11-13-2006, 07:48 PM
I won't deny that the tillerman's job is going out of style, but I don't think I could see the fire service adopting the articulated bus type of vehicle. The reason for such a long trailer on a tiller is because of the aeiral's length. The articulated busses are bent in the center, not at the end, so you can't put an aerial device on it. Plus, the great benefit of an aerial is that you can swing the back around where you want it, independant of the tractor. I can't see a driver driving both the front and rear ends at the same time - its difficult enough to do one job, let alone two.

R. P. McMurphy
11-13-2006, 08:36 PM
I won't deny that the tillerman's job is going out of style, but I don't think I could see the fire service adopting the articulated bus type of vehicle. The reason for such a long trailer on a tiller is because of the aeiral's length. The articulated busses are bent in the center, not at the end, so you can't put an aerial device on it. Plus, the great benefit of an aerial is that you can swing the back around where you want it, independant of the tractor. I can't see a driver driving both the front and rear ends at the same time - its difficult enough to do one job, let alone two.

What I was getting at is the development of dynamic rear stearing which is used in articulated buses. The same technology can be adapted to a hook and ladder. I didn't mean to suggest that they are the same. I am saying that the tiller was used for a practical purpose but, as the OP was asking, why not have an electronic or mechanical linkage that will do the job? Now, they do have such systems and can render the tillerman obsolete,

danceswithcats
11-14-2006, 12:59 AM
Color me dubious regarding an electronic system capable of making the judgement inputs needed to operate the tiller. Going forward is all great, but backing can be done in different ways, and human operator tiller coordination is irreplaceable if you don't wish to bend the BRT.

David Simmons
11-14-2006, 09:39 AM
Color me dubious regarding an electronic system capable of making the judgement inputs needed to operate the tiller. Going forward is all great, but backing can be done in different ways, and human operator tiller coordination is irreplaceable if you don't wish to bend the BRT.i once saw a ladder truck slip into a narrow alley in West LA. It looks to me like a person steering the back of the truck from a seat in the front would need a lot of really wide angle TV in order to judge the turn needed to do what that truck did. And TV with good depth perception at that.

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