egn
Adventurer
I don't know any book written about this issue as comprehensive like this. Sorry.
TerraLiner:12 m Globally Mobile Beach House/Class-A Crossover w 6x6 Hybrid Drivetrain
- Thread starter biotect
- Start date
I don't know any book written about this issue as comprehensive like this. Sorry.
Victorian
Approved Vendor : Total Composites
I found this one entertaining: http://www.daerr.de/hauptartikel2_daerr/6CB4F3410a28e27A7FRgoQ21EBF5/staD/27/Bücher / Ratgeber.html
biotect
Designer
.
MOVING ON TO ENGINE PLACEMENT, and ENGINES.......:sunny:
Hi egn, grizzlyj, Haf-e, Victorian, et al,
OK, we seem to have pretty much covered “torsion free chassis”. So this might be a good time to move on to engine placement, and engines types/sizes.
This first series of posts will be very long. RV design is “holistic”, in the sense that every design decision has domino-effects that impact everything else, often in unexpected ways. This holds true even more so for engine placement. So in this series I cover not just placement options, but so too their ramifications, ergo the length.
egn, in your very first post in this thread, on page 1, you wrote:
And again, a bit further along you wrote:
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1. Engine Placement:
COE (Cab-over-Engine) instead of CF (Cab-Forward)?
I very much appreciate what you wrote about engine-placement, and the desirability of a “pusher” type arrangement, with the engine relocated in the back. Like you, I am a big fan of the Rosenbauer Panther, and the Panther has a “pusher” engine mounted at the back of its rigid SX-45 box-frame. However, for reasons that will become clear as these posts unfold, I find myself strongly inclined towards a CBE (cab before engine) placement. And, so too, at least initially, I would like to at least explore the possibility of a COE (cab over engine) arrangement.
So to begin with, I just wanted to ask whether you think the SX-45 can be reconfigured along more civilian lines, to carry a TGS-class engine, in a COE format?
The SX-45 has a “Cab-Forward” or CF design (i.e. "cab-in-front-of-engine"; see http://en.wikipedia.org/wiki/Cab_forward ), probably because MAN-military wants to locate the radiator and air-intake away from the front of the vehicle, where they would get gummed up with mud, be more vulnerable to mine-blasts, and might reduce the approach angle. This was well-illustrated by the link that you provided in the
“pivoting frames and mounting campers” thread, at http://www.expeditionportal.com/for...bane-Truck-Show?highlight=brisbane+truck+show :
Furthermore, as you suggested in your first post, MAN also wanted to mount the engine higher up to improve river-fording ability, while keeping the overall (unloaded) vehicle height low, to facilitate air-tranportability. Therefore necessitating that the engine be placed somewhere other than under the cab. But do the same considerations apply to a civilian, non-military RV, even one that's off-road-capable? Sure, height is still an issue, but not air-transportability.
After all, most ActionMobils and UniCats are based on COE trucks. So it does seem possible that a civilian, fully integrated design, based on the SX-45 rigid box-frame, could also be COE instead, with the engine directly under the cab as per a MAN TGS. Granted, COE means that an engine tunnel would occupy the middle of the Cab, and there would be no through-cab access, as per the Zetros. But even still, if COE is good enough for most ActionMobil and UniCAT conversions, then would you be against it? If you are against it, why?
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2. Fully Integrated COE Truck Conversions
Now granted, in all COE designs the whole cab needs to swing forward so as to give access to the engine for major repairs. But that's not the main reason why ActionMobil and UniCat designs are non-integrated. They are non-integrated, as we have agreed, mostly because their chassis need to flex.
Whereas when it comes to regular, non-expedition conversions based on big trucks – conversions where chassis-flex is a negligible consideration – integrating cab and camper does not seem difficult. Ketterer, for instance, achieves pretty good Cab/Camper integration, complete with swivel seats (albeit the two rear ones, in a 4-seat crew-cab).
First, some photos of interior Ketterer integration:
And second, some photos of exterior Ketterer integration:
Ketterers achieve this integration even though they are based either on an Actros, MAN TGA/TGS, or Scania “Cab-over-Engine” chassis that can flex – see http://www.ketterer-trucks.de/en.html . Also observe that Ketterers typically have a large slide-out immediately behind the Cab.
So interior and exterior integration does seem fully compatible with COE placement, just as long as chassis flex remains minimal. In the case of non-expedition conversions like the Ketterers, chassis flex is probably not a big issue, simply because these motorhomes never go anywhere really difficult. They usually drive on smooth tarmac. In the case of an SX-45 or Tatra conversion, on the other hand, the box-frame or backbone tube would be ultra-stiff, thereby guaranteeing stress-free camper mounting, and making an integrated design possible.
Lots of other examples of COE truck-conversions exist that are fully integrated. For instance, here is a television production truck, based on a Volvo FM chassis:
So my first question is:
“If cab-over-engine (COE) placement is compatible with a fully integrated design, just as long as the chassis remains rigid, why not embrace it? Does an integrated design have to be a rear-engine pusher?”
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CONTINUED IN NEXT POST
MOVING ON TO ENGINE PLACEMENT, and ENGINES.......:sunny:
Hi egn, grizzlyj, Haf-e, Victorian, et al,
OK, we seem to have pretty much covered “torsion free chassis”. So this might be a good time to move on to engine placement, and engines types/sizes.
This first series of posts will be very long. RV design is “holistic”, in the sense that every design decision has domino-effects that impact everything else, often in unexpected ways. This holds true even more so for engine placement. So in this series I cover not just placement options, but so too their ramifications, ergo the length.
egn, in your very first post in this thread, on page 1, you wrote:
And again, a bit further along you wrote:
**********************************************
1. Engine Placement:
COE (Cab-over-Engine) instead of CF (Cab-Forward)?
I very much appreciate what you wrote about engine-placement, and the desirability of a “pusher” type arrangement, with the engine relocated in the back. Like you, I am a big fan of the Rosenbauer Panther, and the Panther has a “pusher” engine mounted at the back of its rigid SX-45 box-frame. However, for reasons that will become clear as these posts unfold, I find myself strongly inclined towards a CBE (cab before engine) placement. And, so too, at least initially, I would like to at least explore the possibility of a COE (cab over engine) arrangement.
So to begin with, I just wanted to ask whether you think the SX-45 can be reconfigured along more civilian lines, to carry a TGS-class engine, in a COE format?
The SX-45 has a “Cab-Forward” or CF design (i.e. "cab-in-front-of-engine"; see http://en.wikipedia.org/wiki/Cab_forward ), probably because MAN-military wants to locate the radiator and air-intake away from the front of the vehicle, where they would get gummed up with mud, be more vulnerable to mine-blasts, and might reduce the approach angle. This was well-illustrated by the link that you provided in the
“pivoting frames and mounting campers” thread, at http://www.expeditionportal.com/for...bane-Truck-Show?highlight=brisbane+truck+show :
Furthermore, as you suggested in your first post, MAN also wanted to mount the engine higher up to improve river-fording ability, while keeping the overall (unloaded) vehicle height low, to facilitate air-tranportability. Therefore necessitating that the engine be placed somewhere other than under the cab. But do the same considerations apply to a civilian, non-military RV, even one that's off-road-capable? Sure, height is still an issue, but not air-transportability.
After all, most ActionMobils and UniCats are based on COE trucks. So it does seem possible that a civilian, fully integrated design, based on the SX-45 rigid box-frame, could also be COE instead, with the engine directly under the cab as per a MAN TGS. Granted, COE means that an engine tunnel would occupy the middle of the Cab, and there would be no through-cab access, as per the Zetros. But even still, if COE is good enough for most ActionMobil and UniCAT conversions, then would you be against it? If you are against it, why?
**********************************************
2. Fully Integrated COE Truck Conversions
Now granted, in all COE designs the whole cab needs to swing forward so as to give access to the engine for major repairs. But that's not the main reason why ActionMobil and UniCat designs are non-integrated. They are non-integrated, as we have agreed, mostly because their chassis need to flex.
Whereas when it comes to regular, non-expedition conversions based on big trucks – conversions where chassis-flex is a negligible consideration – integrating cab and camper does not seem difficult. Ketterer, for instance, achieves pretty good Cab/Camper integration, complete with swivel seats (albeit the two rear ones, in a 4-seat crew-cab).
First, some photos of interior Ketterer integration:
And second, some photos of exterior Ketterer integration:
Ketterers achieve this integration even though they are based either on an Actros, MAN TGA/TGS, or Scania “Cab-over-Engine” chassis that can flex – see http://www.ketterer-trucks.de/en.html . Also observe that Ketterers typically have a large slide-out immediately behind the Cab.
So interior and exterior integration does seem fully compatible with COE placement, just as long as chassis flex remains minimal. In the case of non-expedition conversions like the Ketterers, chassis flex is probably not a big issue, simply because these motorhomes never go anywhere really difficult. They usually drive on smooth tarmac. In the case of an SX-45 or Tatra conversion, on the other hand, the box-frame or backbone tube would be ultra-stiff, thereby guaranteeing stress-free camper mounting, and making an integrated design possible.
Lots of other examples of COE truck-conversions exist that are fully integrated. For instance, here is a television production truck, based on a Volvo FM chassis:
So my first question is:
“If cab-over-engine (COE) placement is compatible with a fully integrated design, just as long as the chassis remains rigid, why not embrace it? Does an integrated design have to be a rear-engine pusher?”
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CONTINUED IN NEXT POST
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biotect
Designer
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CONTINUED FROM PREVIOUS POST
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3. One Major Design Problem with COE
Now the biggest problem with COE for an integrated expedition motorhome, from my point of view, is not that the engine placement will create an engine-tunnel in the cab, but rather, that COE might make a full-length 3-side-hard/1-side-soft pop-up, of the sort I described a few pages back, structurally impossible.
The following images illustrate why (see http://bettaneyhorseboxes.weebly.com/index.html and http://www.marineindustrialmouldings.co.uk/fibreglass-horsebox.asp ):
It seems that in order for a COE cab to tilt forward, either:
(1) there's no alcove on top, integrated with the camper. Camper and cab are structurally separate, as per ActionMobil and UniCat expedition RVs.
or
(2) any alcove on top attaches only to the cab. When the cab tilts forward for engine repairs, the alcove along with cab separates from the rest of the vehicle.
Of course, in addition to COE making an XP-style 3-side-hard/1-side-soft pop-up impossible, there is the distinct disadvantage that lifting the cab exposes the interior of the motorhome to inclement weather. What if one needs to access the engine when it's raining? What if there's a sandstorm? The pictures above leave little to the imagination: just one sudden thunderstorm, and an interior could be ruined. I don't know if Ketterer conversions open this way as well, but if they do, I would be surprised, if only because Ketterer interiors are luxurious, and no doubt expensive!
However, take a look at the following images from Variomobil's “Alkoven” series of motorhomes, and notice what's missing (see http://www.vario-mobil.com/de/Downl...4_Traummobil-Katalog_VARIOmobil_Wohnmobil.pdf ):
These are all Mercedes and MAN COE conversions, and yet there is no line separating or marking off the alcove from the rest of the vehicle. So how does the cab tilt forward, when the engine needs servicing??
This is a real mystery, so if anyone reading this knows the answer, please post!
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CONTINUED IN NEXT POST
CONTINUED FROM PREVIOUS POST
**********************************************
3. One Major Design Problem with COE
Now the biggest problem with COE for an integrated expedition motorhome, from my point of view, is not that the engine placement will create an engine-tunnel in the cab, but rather, that COE might make a full-length 3-side-hard/1-side-soft pop-up, of the sort I described a few pages back, structurally impossible.
The following images illustrate why (see http://bettaneyhorseboxes.weebly.com/index.html and http://www.marineindustrialmouldings.co.uk/fibreglass-horsebox.asp ):
It seems that in order for a COE cab to tilt forward, either:
(1) there's no alcove on top, integrated with the camper. Camper and cab are structurally separate, as per ActionMobil and UniCat expedition RVs.
or
(2) any alcove on top attaches only to the cab. When the cab tilts forward for engine repairs, the alcove along with cab separates from the rest of the vehicle.
Of course, in addition to COE making an XP-style 3-side-hard/1-side-soft pop-up impossible, there is the distinct disadvantage that lifting the cab exposes the interior of the motorhome to inclement weather. What if one needs to access the engine when it's raining? What if there's a sandstorm? The pictures above leave little to the imagination: just one sudden thunderstorm, and an interior could be ruined. I don't know if Ketterer conversions open this way as well, but if they do, I would be surprised, if only because Ketterer interiors are luxurious, and no doubt expensive!
However, take a look at the following images from Variomobil's “Alkoven” series of motorhomes, and notice what's missing (see http://www.vario-mobil.com/de/Downl...4_Traummobil-Katalog_VARIOmobil_Wohnmobil.pdf ):
These are all Mercedes and MAN COE conversions, and yet there is no line separating or marking off the alcove from the rest of the vehicle. So how does the cab tilt forward, when the engine needs servicing??
This is a real mystery, so if anyone reading this knows the answer, please post!
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CONTINUED IN NEXT POST
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biotect
Designer
CONTINUED FROM PREVIOUS POST
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Here's an image I just came across on ExPo, that illustrates the pop-up problem nicely:
See http://www.expeditionportal.com/forum/threads/26197-Tilt-bed-for-cabover-camper and http://s188.photobucket.com/user/expeditioncampers/media/colin-kerr-2.jpg.html .
Notice how in order to combine a full-length pop-up roof, with a COE tilt-forward cab, the hard base of the alcove has to tilt upwards, to give the cab room enough to lift.
Perhaps this solution works well enough in a smaller vehicle, but in a larger vehicle it would probably not be wise. So again, I wonder how Variomobil manages to pull off something that seems geometrically impossible? Perhaps Variomobil relocates the engine, and there is only a visual illusion that it's still in front?
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CONTINUED IN NEXT POST
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Here's an image I just came across on ExPo, that illustrates the pop-up problem nicely:
See http://www.expeditionportal.com/forum/threads/26197-Tilt-bed-for-cabover-camper and http://s188.photobucket.com/user/expeditioncampers/media/colin-kerr-2.jpg.html .
Notice how in order to combine a full-length pop-up roof, with a COE tilt-forward cab, the hard base of the alcove has to tilt upwards, to give the cab room enough to lift.
Perhaps this solution works well enough in a smaller vehicle, but in a larger vehicle it would probably not be wise. So again, I wonder how Variomobil manages to pull off something that seems geometrically impossible? Perhaps Variomobil relocates the engine, and there is only a visual illusion that it's still in front?
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biotect
Designer
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4. Engine Placement: Zetros CBE (Cab-behind-Engine)
Now in addition to the design problem just discussed, COE placements have many other disadvantages, including noise, lack of ergonomic comfort, and imperfect engine access. As the Wikipedia article deftly summarizes:
[Some shortcomings of COE designs] are that the shorter wheelbase in COE semi-trucks gives a rougher ride than those with conventional cabs, as the driver's seat is above the front axle; and that the cabs tend to be noisier because the engine is directly below, though some of this is dependent on the amount of noise-dampening insulation used in the construction of the individual vehicle.
Because of their flat front design, early COE semi-trucks had significantly worse aerodynamics than conventional tractors. Modern cab-over designs, in both semi-trucks and light- and medium-duty models, have improved aerodynamics significantly over early models, but often still have higher drag coefficients than their modern conventional-design counterparts. This works against fuel economy, and offsets some of the improvement in fuel consumption garnered from the lighter weight of the cab-over truck when running less than fully loaded.
Although the tilting cab gives comparatively unobstructed access to the engine, its deployment causes unsecured items in the cab and sleeper (if equipped) to fall onto the windshield or under the instrument panel. Vehicles without a tilting cab will usually be equipped with removable floor panels through which mechanics can access and service the engine. Unfortunately, some components might require servicing or replacement that either will not fit through the hatch or remain inaccessible. This necessitates removal of the engine by lowering it out from under the vehicle, a time-consuming and expensive procedure.
– http://en.wikipedia.org/wiki/Cab_over .
Although most Mercedes commercial trucks are COE, the Zetros was deliberately formatted as a more American, “conventional”, Cab-behind-Engine (CBE) design:
See http://www.wired.com/2011/04/a-peek-inside-a-rolling-mongolian-xanadu/ , http://luxurylaunches.com/transport/zetros_ultra_luxury_mercedes_6x6_rv_truck_living_station.php , http://www.examiner.com/article/h-nerkopf-neukirchen-sends-two-zetros-expedition-rv-s-to-mongolia , http://www.examiner.com/slideshow/mercedes-benz-zetros-2733-a-6x6-awd-expedition-vehicle#slide=1 , http://www.motorauthority.com/news/...-zetros-6x6-provides-luxury-zombie-protection , http://www.autoweek.com/article/20120621/carnews01/120629962 , http://www.unicat.net/en/info/MD58hvfamily-MBZetros18334x4.php , http://www.unicat.net/en/pics/MD58hvfamily-MBZetros18334x4-2.php , http://www.actionmobil.com/images/pdf/journal/Actionmobil-Journal-2011-4-En.pdf , http://www.actionmobil.com/en/2-axle/atacama , http://www.examiner.com/article/action-mobil-launches-atacama-zetros-1-overland-expedition-rv , http://www.examiner.com/slideshow/a...acama-zetros-1-overland-expedition-rv#slide=1 , http://www.youtube.com/watch?v=w1X_aJV8634 , and http://translate.google.com/transla...com/Product.aspx?BigClassID=2&SmallClassID=10 .
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5. Many Arguments in Favor of CBE
In its Zetros promotional literature, Mercedes provides an exhaustive list of arguments in Favor of CBE:
Created for all kinds of terrain: the Zetros
With its forward-tilting bonnet, cab-behind engine concept and ideal weight distribution, the Zetros displays optimum handling characteristics and steering response.
Safe and relaxed across off-road terrain
The suspension tuning and seat configuration behind the front axle complement each other perfectly to create an ideal off-road working environment.
• Reduced driver workload thanks to improved off-road characteristics
• Easy to operate, thus less need for operator training
The Zetros meets the highest ergonomic standards and delivers outstanding ease of use. The position of the driver's cab minimizes the impact of bumps/jolts and the self-movement of the cab. Such outstanding driving comfort makes life a lot easier for the driver and co-driver.
Interior
• Fully-fledged centre seat (optional)
• Generous stowage space
• Instrument panel from the Mercedes-Benz Atego/Axor series
• Unhindered through-cab access
The generously proportioned Zetros cockpit offers plenty of legroom and an optimum layout of control elements and displays. And the inclusion of the trusted Atego/Axor cockpit ensures safe and simple operation.
A further highlight is the optional climate-control cab without an engine tunnel. It offers plenty of stowage space, complete through-cab access, and full-size seats for up to three people.
Bonnet: all-round worry free when it comes to repairs
• Engine Bonnet can be opened easily and without tilting the cab, enabling occupants/equipment to remain in the cab
• With the help of the integrated access steps, comfortable, swift access for repairs, or to clean the windscreen.
Engine and assemblies are easy to access by simply opening the bonnet, without needing to tilt the cab. Opening is facilitated by a torsion spring, so that a hydraulic cab tilting system is unnecessary. This enables swift, straightforward maintenance, or repairs if these should ever be necessary.
Low exterior height
• Easy, safe boarding and exit
• Ideally suited to negotiating low clearances
• Crane or special-purpose bodies can be mounted along entire vehicle length
• Excellent protection against external factors
See http://www.tunisia.mercedes-benz.co.../truck_home/home/trucks/zetros/advantage.html , http://www.tunisia.mercedes-benz.co...ros/advantage/conventional-design.fb0002.html , http://www.tunisia.mercedes-benz.co...ros/advantage/conventional-design.fb0003.html , http://www.tunisia.mercedes-benz.co...me_mpc/truck_home/home/trucks/zetros/cab.html , http://www.mercedes-benz.com.cy/con...me/construction/zetros/advantages.fb0003.html , http://www.mercedes-benz.com.cy/con...mpc/trucks_/home/construction/zetros/cab.html , http://www.autoblog.com/2008/06/24/mercedes-introduces-their-new-zetros-military-truck/ .
For a fairly comprehensive list of Zetros links, see http://www.unimogcanada.com/zetros.pdf , http://www.tradingeurope.at/Downloads/Zetros_engl.pdf , https://bus-chassis.mercedes-benz.c...at/INT/en/Zetros_090528_Basic_Brochure_en.pdf , https://bb-portal.mercedes-benz.com...at/INT/en/Zetros_090528_Basic_Brochure_en.pdf, http://www.pchristensen.dk/Files/Filer/pc/brochure/Zetros-Construction-Brochure.pdf , https://bb-portal.mercedes-benz.com.../_INT/en/MB_Zetros_Folder_Agrologistik_EN.pdf , http://www.google.co.uk/url?sa=t&rc...dhAwd6NJLlnSgbDRyODitoA&bvm=bv.64507335,d.bGE , http://www.mercedes-benz.com.cy/con.../home/special_segment/fire_rescue/Zetros.html , https://www.mercedes-benz-media.co.uk/commercial/model/144/Zetros ,
https://www.mercedes-benz-media.co.uk/doc/2124/zetrostechnicaldata.pdf , http://www.special-trucks.eu/webspecial_mercedes-benz_zetros/e/technische_daten_en.pdf , http://www.google.co.uk/url?sa=t&rc...wIDIDw&usg=AFQjCNHp0smZ3XcolD42mSAVT2fFeeVn0g , http://www.mercedes-benzsa.co.za/me...Trucks/Military_Vehicles_SA-Brochure_2010.pdf , http://www.mercedes-benzsa.co.za/mercedes-benz/eMB/CV/Military/Actros_Zetros_Cabs_Specs.pdf , http://www.mb-military-vehicles.com/fileadmin/downloads/ZETROS Armoured.pdf , https://bb-portal.mercedes-benz.com/portal/ar_mbs.html?&no_cache=1&L=en , and https://bb-portal.mercedes-benz.com/portal/136.html?&L=en .
Autoblog elucidates the advantages of the Zetros CBE placement as follows:
The cab-behind-engine design reduces the workload on the crew and delivers that unique feeling of safety known from the Unimogs with an concept that reduces driver fatigue and simultaneously enhances driver performance. It provides a practically ideal weight distribution with payload reserves on the front axle. The all-wheel chassis with cab-behind-engine provides a much more comfortable ride than cab-over-engine trucks, and so enhances the vehicle's operating safety. It also contributes to the truck's exceptional off-road capability, including in extreme terrain.
The integrated design of the Mercedes-Benz Zetros includes a level cab floor with a comfortable seating position for the 2nd co-driver and easy through-cab access. In addition, the low cab design enables the 4x4 and 6x6 vehicles to be air-lifted in transport aircraft such as the Hercules C 130 or the Transall C 160 with a minimum of preparation. Rail transportability is also assured as the vehicle conforms with the international loading gauge.
– see http://www.autoblog.com/2008/06/24/mercedes-introduces-their-new-zetros-military-truck/ .
And these images sum up just how comparatively convenient a Zetros-like CBE placement would be:
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4. Engine Placement: Zetros CBE (Cab-behind-Engine)
Now in addition to the design problem just discussed, COE placements have many other disadvantages, including noise, lack of ergonomic comfort, and imperfect engine access. As the Wikipedia article deftly summarizes:
[Some shortcomings of COE designs] are that the shorter wheelbase in COE semi-trucks gives a rougher ride than those with conventional cabs, as the driver's seat is above the front axle; and that the cabs tend to be noisier because the engine is directly below, though some of this is dependent on the amount of noise-dampening insulation used in the construction of the individual vehicle.
Because of their flat front design, early COE semi-trucks had significantly worse aerodynamics than conventional tractors. Modern cab-over designs, in both semi-trucks and light- and medium-duty models, have improved aerodynamics significantly over early models, but often still have higher drag coefficients than their modern conventional-design counterparts. This works against fuel economy, and offsets some of the improvement in fuel consumption garnered from the lighter weight of the cab-over truck when running less than fully loaded.
Although the tilting cab gives comparatively unobstructed access to the engine, its deployment causes unsecured items in the cab and sleeper (if equipped) to fall onto the windshield or under the instrument panel. Vehicles without a tilting cab will usually be equipped with removable floor panels through which mechanics can access and service the engine. Unfortunately, some components might require servicing or replacement that either will not fit through the hatch or remain inaccessible. This necessitates removal of the engine by lowering it out from under the vehicle, a time-consuming and expensive procedure.
– http://en.wikipedia.org/wiki/Cab_over .
Although most Mercedes commercial trucks are COE, the Zetros was deliberately formatted as a more American, “conventional”, Cab-behind-Engine (CBE) design:
See http://www.wired.com/2011/04/a-peek-inside-a-rolling-mongolian-xanadu/ , http://luxurylaunches.com/transport/zetros_ultra_luxury_mercedes_6x6_rv_truck_living_station.php , http://www.examiner.com/article/h-nerkopf-neukirchen-sends-two-zetros-expedition-rv-s-to-mongolia , http://www.examiner.com/slideshow/mercedes-benz-zetros-2733-a-6x6-awd-expedition-vehicle#slide=1 , http://www.motorauthority.com/news/...-zetros-6x6-provides-luxury-zombie-protection , http://www.autoweek.com/article/20120621/carnews01/120629962 , http://www.unicat.net/en/info/MD58hvfamily-MBZetros18334x4.php , http://www.unicat.net/en/pics/MD58hvfamily-MBZetros18334x4-2.php , http://www.actionmobil.com/images/pdf/journal/Actionmobil-Journal-2011-4-En.pdf , http://www.actionmobil.com/en/2-axle/atacama , http://www.examiner.com/article/action-mobil-launches-atacama-zetros-1-overland-expedition-rv , http://www.examiner.com/slideshow/a...acama-zetros-1-overland-expedition-rv#slide=1 , http://www.youtube.com/watch?v=w1X_aJV8634 , and http://translate.google.com/transla...com/Product.aspx?BigClassID=2&SmallClassID=10 .
**********************************************
5. Many Arguments in Favor of CBE
In its Zetros promotional literature, Mercedes provides an exhaustive list of arguments in Favor of CBE:
Created for all kinds of terrain: the Zetros
With its forward-tilting bonnet, cab-behind engine concept and ideal weight distribution, the Zetros displays optimum handling characteristics and steering response.
Safe and relaxed across off-road terrain
The suspension tuning and seat configuration behind the front axle complement each other perfectly to create an ideal off-road working environment.
• Reduced driver workload thanks to improved off-road characteristics
• Easy to operate, thus less need for operator training
The Zetros meets the highest ergonomic standards and delivers outstanding ease of use. The position of the driver's cab minimizes the impact of bumps/jolts and the self-movement of the cab. Such outstanding driving comfort makes life a lot easier for the driver and co-driver.
Interior
• Fully-fledged centre seat (optional)
• Generous stowage space
• Instrument panel from the Mercedes-Benz Atego/Axor series
• Unhindered through-cab access
The generously proportioned Zetros cockpit offers plenty of legroom and an optimum layout of control elements and displays. And the inclusion of the trusted Atego/Axor cockpit ensures safe and simple operation.
A further highlight is the optional climate-control cab without an engine tunnel. It offers plenty of stowage space, complete through-cab access, and full-size seats for up to three people.
Bonnet: all-round worry free when it comes to repairs
• Engine Bonnet can be opened easily and without tilting the cab, enabling occupants/equipment to remain in the cab
• With the help of the integrated access steps, comfortable, swift access for repairs, or to clean the windscreen.
Engine and assemblies are easy to access by simply opening the bonnet, without needing to tilt the cab. Opening is facilitated by a torsion spring, so that a hydraulic cab tilting system is unnecessary. This enables swift, straightforward maintenance, or repairs if these should ever be necessary.
Low exterior height
• Easy, safe boarding and exit
• Ideally suited to negotiating low clearances
• Crane or special-purpose bodies can be mounted along entire vehicle length
• Excellent protection against external factors
See http://www.tunisia.mercedes-benz.co.../truck_home/home/trucks/zetros/advantage.html , http://www.tunisia.mercedes-benz.co...ros/advantage/conventional-design.fb0002.html , http://www.tunisia.mercedes-benz.co...ros/advantage/conventional-design.fb0003.html , http://www.tunisia.mercedes-benz.co...me_mpc/truck_home/home/trucks/zetros/cab.html , http://www.mercedes-benz.com.cy/con...me/construction/zetros/advantages.fb0003.html , http://www.mercedes-benz.com.cy/con...mpc/trucks_/home/construction/zetros/cab.html , http://www.autoblog.com/2008/06/24/mercedes-introduces-their-new-zetros-military-truck/ .
For a fairly comprehensive list of Zetros links, see http://www.unimogcanada.com/zetros.pdf , http://www.tradingeurope.at/Downloads/Zetros_engl.pdf , https://bus-chassis.mercedes-benz.c...at/INT/en/Zetros_090528_Basic_Brochure_en.pdf , https://bb-portal.mercedes-benz.com...at/INT/en/Zetros_090528_Basic_Brochure_en.pdf, http://www.pchristensen.dk/Files/Filer/pc/brochure/Zetros-Construction-Brochure.pdf , https://bb-portal.mercedes-benz.com.../_INT/en/MB_Zetros_Folder_Agrologistik_EN.pdf , http://www.google.co.uk/url?sa=t&rc...dhAwd6NJLlnSgbDRyODitoA&bvm=bv.64507335,d.bGE , http://www.mercedes-benz.com.cy/con.../home/special_segment/fire_rescue/Zetros.html , https://www.mercedes-benz-media.co.uk/commercial/model/144/Zetros ,
https://www.mercedes-benz-media.co.uk/doc/2124/zetrostechnicaldata.pdf , http://www.special-trucks.eu/webspecial_mercedes-benz_zetros/e/technische_daten_en.pdf , http://www.google.co.uk/url?sa=t&rc...wIDIDw&usg=AFQjCNHp0smZ3XcolD42mSAVT2fFeeVn0g , http://www.mercedes-benzsa.co.za/me...Trucks/Military_Vehicles_SA-Brochure_2010.pdf , http://www.mercedes-benzsa.co.za/mercedes-benz/eMB/CV/Military/Actros_Zetros_Cabs_Specs.pdf , http://www.mb-military-vehicles.com/fileadmin/downloads/ZETROS Armoured.pdf , https://bb-portal.mercedes-benz.com/portal/ar_mbs.html?&no_cache=1&L=en , and https://bb-portal.mercedes-benz.com/portal/136.html?&L=en .
Autoblog elucidates the advantages of the Zetros CBE placement as follows:
The cab-behind-engine design reduces the workload on the crew and delivers that unique feeling of safety known from the Unimogs with an concept that reduces driver fatigue and simultaneously enhances driver performance. It provides a practically ideal weight distribution with payload reserves on the front axle. The all-wheel chassis with cab-behind-engine provides a much more comfortable ride than cab-over-engine trucks, and so enhances the vehicle's operating safety. It also contributes to the truck's exceptional off-road capability, including in extreme terrain.
The integrated design of the Mercedes-Benz Zetros includes a level cab floor with a comfortable seating position for the 2nd co-driver and easy through-cab access. In addition, the low cab design enables the 4x4 and 6x6 vehicles to be air-lifted in transport aircraft such as the Hercules C 130 or the Transall C 160 with a minimum of preparation. Rail transportability is also assured as the vehicle conforms with the international loading gauge.
– see http://www.autoblog.com/2008/06/24/mercedes-introduces-their-new-zetros-military-truck/ .
And these images sum up just how comparatively convenient a Zetros-like CBE placement would be:
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biotect
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6. More on CBE: Zetros-like, but not Zetros
But here, pace grizzlyj (
) I should emphasize “Zetros-like”. The previous post advocated CBE placement and a bonnet, i.e. a Zetros-like bonnet. It did not advocate the Zetros truck itself, flex-frame and all. At least not as a solution to the kind of design-problem that this thread has been exploring.
I have something different in mind: a Zetros-like bonnet and CBE cab, mounted on top of a Tatra chassis. Again, Tatra does make a 6x6 CBE “chassis only” product, although granted, the frame needs to be lengthened 1 - 1.5 m:
See the comprehensive Tatra military catalog at http://www.tatratrucks.com/underwood/download/files/tatra-military-vehicles_en-2.pdf , pages 28 – 35, and also the independent brochures at http://www.tatratrucks.com/underwood/download/files/tatra-t815-790rk9-6x6-chassis_en.pdf and http://www.tatratrucks.com/underwood/download/files/tatra-t815-790r99-8x8-chassis_en.pdf .
Again, the big contrast here is with a COE design, where one has to lift up the whole cab to gain significant access to the engine:
Take a look at the following Mercedes Actros video, and just imagine everyone having to leave the cab and wait outside, perhaps in rough weather, as the cab lifts to provide engine access. Do you really want to be doing this in the middle of the Sahara?:
http://new-actros.trucks-mercedes-b... in the exterieur/Exterior/Tilt cab/zoom.html
And also see:
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7. EarthRoamer CBE
For what it's worth, on its website Earthroamer makes most of the same points as the Zetros product literature, justifying CBE placement:
As much as we would like to imagine that the majority of our time in an EarthRoamer will be spent camping in remote and exotic places, the fact of the matter is you will likely spend a significant amount of time driving on improved roads before reaching that perfect camp spot. Being able to cover long distances comfortably at highway speeds becomes more than just a luxury when you are on an extended expedition. Many RVs and expedition vehicles on the market are simply not capable of traveling safely and comfortably at sustained highway speeds. Most large commercial and military trucks are designed for hauling large, heavy loads at relatively slow speeds and driver comfort is at best an afterthought…..
Finally, the long wheelbase of the XV-LT and a seating position well behind the front axle minimizes the effect of bumps on the driver and passengers. On cabover trucks and van conversions, the effect of bumps on the driver and passenger is much more pronounced since the driver is much closer to the front axle. An optional air ride suspension is available that improves ride quality even further.
See http://earthroamer.com , http://earthroamer.com/model-overview/ , http://earthroamer.com/xv-lt/driving/on-road/ , and http://earthroamer.com/xv-lt/driving/off-road/ :
In short, there do seem to be significant advantages, both on-road and off, to CBE placement.
The only major advantage of a COE design that I can see, is that by reducing the length of Cab + Engine, the overall available length for a camper-body increases for any given wheel-base size. But given a choice between a COE vehicle that's 11 m long overall, versus a CBE vehicle that's 12.4 or 12.6 m long, because the engine bonnet adds 1.4 – 1.6 m of length, it seems that CBE vehicle is preferable. Given all the considerations above – and especially the design-problem of locating an alcove area above a COE cab that has to tilt forwards – CBE seems hands-down superior.
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6. More on CBE: Zetros-like, but not Zetros
But here, pace grizzlyj (
) I should emphasize “Zetros-like”. The previous post advocated CBE placement and a bonnet, i.e. a Zetros-like bonnet. It did not advocate the Zetros truck itself, flex-frame and all. At least not as a solution to the kind of design-problem that this thread has been exploring.I have something different in mind: a Zetros-like bonnet and CBE cab, mounted on top of a Tatra chassis. Again, Tatra does make a 6x6 CBE “chassis only” product, although granted, the frame needs to be lengthened 1 - 1.5 m:
See the comprehensive Tatra military catalog at http://www.tatratrucks.com/underwood/download/files/tatra-military-vehicles_en-2.pdf , pages 28 – 35, and also the independent brochures at http://www.tatratrucks.com/underwood/download/files/tatra-t815-790rk9-6x6-chassis_en.pdf and http://www.tatratrucks.com/underwood/download/files/tatra-t815-790r99-8x8-chassis_en.pdf .
Again, the big contrast here is with a COE design, where one has to lift up the whole cab to gain significant access to the engine:
Take a look at the following Mercedes Actros video, and just imagine everyone having to leave the cab and wait outside, perhaps in rough weather, as the cab lifts to provide engine access. Do you really want to be doing this in the middle of the Sahara?:
http://new-actros.trucks-mercedes-b... in the exterieur/Exterior/Tilt cab/zoom.html
And also see:
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7. EarthRoamer CBE
For what it's worth, on its website Earthroamer makes most of the same points as the Zetros product literature, justifying CBE placement:
As much as we would like to imagine that the majority of our time in an EarthRoamer will be spent camping in remote and exotic places, the fact of the matter is you will likely spend a significant amount of time driving on improved roads before reaching that perfect camp spot. Being able to cover long distances comfortably at highway speeds becomes more than just a luxury when you are on an extended expedition. Many RVs and expedition vehicles on the market are simply not capable of traveling safely and comfortably at sustained highway speeds. Most large commercial and military trucks are designed for hauling large, heavy loads at relatively slow speeds and driver comfort is at best an afterthought…..
Finally, the long wheelbase of the XV-LT and a seating position well behind the front axle minimizes the effect of bumps on the driver and passengers. On cabover trucks and van conversions, the effect of bumps on the driver and passenger is much more pronounced since the driver is much closer to the front axle. An optional air ride suspension is available that improves ride quality even further.
See http://earthroamer.com , http://earthroamer.com/model-overview/ , http://earthroamer.com/xv-lt/driving/on-road/ , and http://earthroamer.com/xv-lt/driving/off-road/ :
In short, there do seem to be significant advantages, both on-road and off, to CBE placement.
The only major advantage of a COE design that I can see, is that by reducing the length of Cab + Engine, the overall available length for a camper-body increases for any given wheel-base size. But given a choice between a COE vehicle that's 11 m long overall, versus a CBE vehicle that's 12.4 or 12.6 m long, because the engine bonnet adds 1.4 – 1.6 m of length, it seems that CBE vehicle is preferable. Given all the considerations above – and especially the design-problem of locating an alcove area above a COE cab that has to tilt forwards – CBE seems hands-down superior.
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biotect
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8. CBE verus Pusher, and slide-outs
Gven a choice between COE and CBE for off-road applications, CBE seems superior
So what about a “Pusher”, a rear-mounted engine as per many American Class-A motorhomes – see http://en.wikipedia.org/wiki/List_of_recreational_vehicles , http://uk.ask.com/question/what-is-a-diesel-pusher-rv , and http://rv-roadtrips.thefuntimesguide.com/2009/12/pros_cons_rv_diesel_pusher.php ? Is COE also superior to a Pusher engine placement?
To begin with, many of the ergonomic arguments made by Mercedes and Earthroamer against COE will also typically apply to a Pusher. For instance, in order to maximize camper length the seating in Pushers is usually “bus style”, with the driver sitting directly above the front axle. Sure, this provides greater visibility, and no front-end “blind spots” -- see http://en.wikipedia.org/wiki/Blind_spot_(vehicle) . But on the downside, probably a rougher ride, and no bonnet protection in case of an accident.
However, I want to focus on the design-implications of a Pusher engine placement, in particular, the implications for slide-outs.
Horizontal slide-outs may or may not be desirable – this is another sub-theme that needs to be discussed. In expedition motorhomes horizontal slide-outs appear only rarely. And if they do appear, they are usually small ones that contain only beds. The big exception seems to be ActionMobil's “Desert Challenger” – see http://www.actionmobil.com/en/4-axle/desert-challenger , http://www.examiner.com/article/action-mobil-desert-challenger-the-world-s-best-off-road-rv , and http://www.examiner.com/slideshow/action-mobil-desert-challenger-the-world-s-best-off-road-rv .
But otherwise, the hydraulic “volume expanders” that have created the most space in expedition motorhomes, are UniCat's pop-ups.
With that said, it's worth noting that a Zetros-like, CBE design seems perfectly compatible with abundant horizontal slide-outs. See the following “Command Center” Zetros conversion, at http://www.czerwonesamochody.com/search.php?search_keywords=220E99 and http://www.czerwonesamochody.com/details.php?image_id=36584 :
\
In fact, a Zetros-like CBE design is probably more compatible with slide-outs than a Pusher, because in a Pusher the engine typically rises 4 or 5 feet about the RV's base-line floor height. So in a Pusher, the slide-outs cannot extend the full length of the coach. They have to stop about 1 – 1.5 m short of the back of the coach.
Now granted, usually manufacturers of RV pushers will locate the master bed on a raised platform above the engine in back, so that the last 1.5 m of length is not totally “lost”. But in an alcove-over-cab design, the alcove will also cantilever perhaps 30 or 40 cm over the front windshield, as per the Earthroamer images posted above, or the Variomobil images posted much earlier. So if a Zetros-like bonnet were 1.4 m long, at most one might “lose” 1 m of vehicle length because of CBE engine placement. Sure, every meter is important, but given all the other advantages of CBE, including a more ergonomic driving position, losing that 1 m might be worth it?
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8. CBE verus Pusher, and slide-outs
Gven a choice between COE and CBE for off-road applications, CBE seems superior
So what about a “Pusher”, a rear-mounted engine as per many American Class-A motorhomes – see http://en.wikipedia.org/wiki/List_of_recreational_vehicles , http://uk.ask.com/question/what-is-a-diesel-pusher-rv , and http://rv-roadtrips.thefuntimesguide.com/2009/12/pros_cons_rv_diesel_pusher.php ? Is COE also superior to a Pusher engine placement?
To begin with, many of the ergonomic arguments made by Mercedes and Earthroamer against COE will also typically apply to a Pusher. For instance, in order to maximize camper length the seating in Pushers is usually “bus style”, with the driver sitting directly above the front axle. Sure, this provides greater visibility, and no front-end “blind spots” -- see http://en.wikipedia.org/wiki/Blind_spot_(vehicle) . But on the downside, probably a rougher ride, and no bonnet protection in case of an accident.
However, I want to focus on the design-implications of a Pusher engine placement, in particular, the implications for slide-outs.
Horizontal slide-outs may or may not be desirable – this is another sub-theme that needs to be discussed. In expedition motorhomes horizontal slide-outs appear only rarely. And if they do appear, they are usually small ones that contain only beds. The big exception seems to be ActionMobil's “Desert Challenger” – see http://www.actionmobil.com/en/4-axle/desert-challenger , http://www.examiner.com/article/action-mobil-desert-challenger-the-world-s-best-off-road-rv , and http://www.examiner.com/slideshow/action-mobil-desert-challenger-the-world-s-best-off-road-rv .
But otherwise, the hydraulic “volume expanders” that have created the most space in expedition motorhomes, are UniCat's pop-ups.
With that said, it's worth noting that a Zetros-like, CBE design seems perfectly compatible with abundant horizontal slide-outs. See the following “Command Center” Zetros conversion, at http://www.czerwonesamochody.com/search.php?search_keywords=220E99 and http://www.czerwonesamochody.com/details.php?image_id=36584 :
\In fact, a Zetros-like CBE design is probably more compatible with slide-outs than a Pusher, because in a Pusher the engine typically rises 4 or 5 feet about the RV's base-line floor height. So in a Pusher, the slide-outs cannot extend the full length of the coach. They have to stop about 1 – 1.5 m short of the back of the coach.
Now granted, usually manufacturers of RV pushers will locate the master bed on a raised platform above the engine in back, so that the last 1.5 m of length is not totally “lost”. But in an alcove-over-cab design, the alcove will also cantilever perhaps 30 or 40 cm over the front windshield, as per the Earthroamer images posted above, or the Variomobil images posted much earlier. So if a Zetros-like bonnet were 1.4 m long, at most one might “lose” 1 m of vehicle length because of CBE engine placement. Sure, every meter is important, but given all the other advantages of CBE, including a more ergonomic driving position, losing that 1 m might be worth it?
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biotect
Designer
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9. The Problem with Pushers, and the UFO Chassis
Perhaps the best way to illustrate the design problems that a Pusher engine placement creates, is to refer to the product literature of a recent RV chassis innovation, pioneered by the American manufacturer “Workhorse”.
Having recognized the “slide-out length limitation” that a pusher engine-placement creates, in the early 2000's Workhorse developed the innovative UFO chassis – see http://workhorse.com/default.aspx?tabid=478 , http://www.prweb.com/releases/2006/12/prweb493781.htm , http://www.rvcruzer.com/UFO.php , http://www.roamingtimes.com/rvbusiness/workhorse-ufo-chassis.htm , http://www.roamingtimes.com/rvnews/first-rv-with-ufo-chassis.asp , http://www.rvbusiness.com/2006/08/workhorse-ufo-chassis-breaks-mold/ , and http://deserttruckservice.com/pdf folder/workhorse_chassis.guide.pdf :
Again, I am providing the UFO pdf as jpgs, because the UFO pdf no longer seems available on the web.
However, the jpgs provide only limited text resolution, so here are the most important text passages for our purposes:
**********************************************
"The RV world has been waiting a long time for a motor home that knows no limitations. That motor home is finally within view.
 It's a concept so revolutionary, the best way to understand it is to set aside what you've always associated with Class-A coaches.
• Forget traditional floor-plans. Think of having the freedom to spread out in a living area at the back of the coach — with two slide-outs, a rear bay window and overstuffed chairs to help you enjoy the view. Say goodbye to noisy cockpits. Imagine no more front doghouse because there is never an engine in the cab! Now, you can enjoy friendly conversation or the rich sounds of your premium audio system. All while going full throttle down the interstate.... Welcome to the motor home of the future. Open up to discover the creation of a new Class A category, the emerging world of the Workhorse UFO.......
*********************
To fully appreciate all of the experiences you can enjoy with the workhorse UFOchassis, consider this: towable rv buyers can choose from hundreds of floorplan layouts. yet, variations of only six basic layouts exist for class a motor homes. This is because until now, the chassis has dictated how motor homes are designed, significantly limiting freedom and flexibility.
• Until now, gas has meant a front engine with a doghouse and a power plant at your feet. The mandatory mid-entry door limits floorplan options in the living area, and the long driveshaft makes pass-through storage impossible. Plus, you have to cope with a loud rear generator at night.
• And until now, diesel [Pusher} engines have posed significant floorplan constraints. To hide the engine and cooling system, the wardrobe and bed are positioned at the back of the coach, making it difficult to move around. How about a rear living room? No way!
Now you can set all that thinking aside. WorkhorseUFO, the first-of-its-kind platform, frees you up to enjoy the motor home lifestyle as it was meant to be.
*********************
DRIVING YOU INTO THE FUTURE.
Thanks to the obstruction-free Workhorse UFO platform, you can own a motor home that has all the benefits of rear power, a choice of your favorite type of engine (Universal Fuel Option), and a floorplan you never thought you'd find in a motorized coach (Universal Floorplan Options). The Workhorse UFOTM is our latest innovation. That's not surprising. We're the only chassis company fully dedicated to giving you a better motor home experience through forward-thinking, customer-driven chassis innovations.
Unlimited floorplans.
• .....Workhorse UFO'sTM advanced, true flat-floor design creates Universal Floorplan Options. We put everything below the floor. Everything. As a result, everything above the floor can go anywhere. Well, except for the steering column which you'll still find in the front left corner.
• This means the end of floorplan constraints in a motor home. No more rules that say the bed goes here, the wardrobe goes there, the door is over there. Thanks to the Workhorse UFOTM, motor home companies are now creating the most unique, exciting floorplans ever. Now, you finally get to enjoy RVing like never before!
*********************
ENGINEERED FOR ULTIMATE PERFORMANCE
New technologies have a way of undercutting traditional icons of performance, comfort and efficiency. Digital imaging replacing film. Electronic sensors in place of mechanical controls. In designing the Workhorse UFOTM, we integrated the latest and best technologies to ensure superior performance, no matter the driving condition.....
• Everything's cool, above and below. It's no secret that rear engines are harder to cool — be it a gas engine or a new, '07 emissions-compliant diesel power plant. We created a unitized cooling system that effectively cools the engine and transmission by routing fluids through the same cooling dam. This also minimizes power requirements and keeps the coolpack below the floor level — an industry first."
**********************************************
In sum, Workhorse developed the UFO chassis to solve the design problems and restrictions that a Pusher engine placement creates, by locating everything, including the Pusher engine, below the camper floor.
But there is another, much simpler way to achieve exactly the same result: locate the engine up front. Opt for CBE instead. A CBE engine-placement provides exactly the same camper design freedom as a Workhorse chassis, and has many other benefits as well.
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CONTINUED FROM PREVIOUS POST
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9. The Problem with Pushers, and the UFO Chassis
Perhaps the best way to illustrate the design problems that a Pusher engine placement creates, is to refer to the product literature of a recent RV chassis innovation, pioneered by the American manufacturer “Workhorse”.
Having recognized the “slide-out length limitation” that a pusher engine-placement creates, in the early 2000's Workhorse developed the innovative UFO chassis – see http://workhorse.com/default.aspx?tabid=478 , http://www.prweb.com/releases/2006/12/prweb493781.htm , http://www.rvcruzer.com/UFO.php , http://www.roamingtimes.com/rvbusiness/workhorse-ufo-chassis.htm , http://www.roamingtimes.com/rvnews/first-rv-with-ufo-chassis.asp , http://www.rvbusiness.com/2006/08/workhorse-ufo-chassis-breaks-mold/ , and http://deserttruckservice.com/pdf folder/workhorse_chassis.guide.pdf :
Again, I am providing the UFO pdf as jpgs, because the UFO pdf no longer seems available on the web.
However, the jpgs provide only limited text resolution, so here are the most important text passages for our purposes:
**********************************************
"The RV world has been waiting a long time for a motor home that knows no limitations. That motor home is finally within view.
 It's a concept so revolutionary, the best way to understand it is to set aside what you've always associated with Class-A coaches.
• Forget traditional floor-plans. Think of having the freedom to spread out in a living area at the back of the coach — with two slide-outs, a rear bay window and overstuffed chairs to help you enjoy the view. Say goodbye to noisy cockpits. Imagine no more front doghouse because there is never an engine in the cab! Now, you can enjoy friendly conversation or the rich sounds of your premium audio system. All while going full throttle down the interstate.... Welcome to the motor home of the future. Open up to discover the creation of a new Class A category, the emerging world of the Workhorse UFO.......
*********************
To fully appreciate all of the experiences you can enjoy with the workhorse UFOchassis, consider this: towable rv buyers can choose from hundreds of floorplan layouts. yet, variations of only six basic layouts exist for class a motor homes. This is because until now, the chassis has dictated how motor homes are designed, significantly limiting freedom and flexibility.
• Until now, gas has meant a front engine with a doghouse and a power plant at your feet. The mandatory mid-entry door limits floorplan options in the living area, and the long driveshaft makes pass-through storage impossible. Plus, you have to cope with a loud rear generator at night.
• And until now, diesel [Pusher} engines have posed significant floorplan constraints. To hide the engine and cooling system, the wardrobe and bed are positioned at the back of the coach, making it difficult to move around. How about a rear living room? No way!
Now you can set all that thinking aside. WorkhorseUFO, the first-of-its-kind platform, frees you up to enjoy the motor home lifestyle as it was meant to be.
*********************
DRIVING YOU INTO THE FUTURE.
Thanks to the obstruction-free Workhorse UFO platform, you can own a motor home that has all the benefits of rear power, a choice of your favorite type of engine (Universal Fuel Option), and a floorplan you never thought you'd find in a motorized coach (Universal Floorplan Options). The Workhorse UFOTM is our latest innovation. That's not surprising. We're the only chassis company fully dedicated to giving you a better motor home experience through forward-thinking, customer-driven chassis innovations.
Unlimited floorplans.
• .....Workhorse UFO'sTM advanced, true flat-floor design creates Universal Floorplan Options. We put everything below the floor. Everything. As a result, everything above the floor can go anywhere. Well, except for the steering column which you'll still find in the front left corner.
• This means the end of floorplan constraints in a motor home. No more rules that say the bed goes here, the wardrobe goes there, the door is over there. Thanks to the Workhorse UFOTM, motor home companies are now creating the most unique, exciting floorplans ever. Now, you finally get to enjoy RVing like never before!
*********************
ENGINEERED FOR ULTIMATE PERFORMANCE
New technologies have a way of undercutting traditional icons of performance, comfort and efficiency. Digital imaging replacing film. Electronic sensors in place of mechanical controls. In designing the Workhorse UFOTM, we integrated the latest and best technologies to ensure superior performance, no matter the driving condition.....
• Everything's cool, above and below. It's no secret that rear engines are harder to cool — be it a gas engine or a new, '07 emissions-compliant diesel power plant. We created a unitized cooling system that effectively cools the engine and transmission by routing fluids through the same cooling dam. This also minimizes power requirements and keeps the coolpack below the floor level — an industry first."
**********************************************
In sum, Workhorse developed the UFO chassis to solve the design problems and restrictions that a Pusher engine placement creates, by locating everything, including the Pusher engine, below the camper floor.
But there is another, much simpler way to achieve exactly the same result: locate the engine up front. Opt for CBE instead. A CBE engine-placement provides exactly the same camper design freedom as a Workhorse chassis, and has many other benefits as well.
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biotect
Designer
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10. Rexhall Dual Full-Length Slide-Outs
Notice how in the UFO chassis the engine is so “low slung”, that it locates completely below the RV floor, thereby allowing full-length slide-outs.
An American class-A specialist, Rexhall, was one of the first manufacturers to take up the design challenge of this engineering innovation, and Rexhall is somewhat unique in having produced vehicles with two, full-length slides – see http://www.rexhall.com/index.php?option=com_content&view=category&layout=blog&id=2&Itemid=5 , http://www.rexhall.com/index.php?option=com_content&view=article&id=18&Itemid=9 , http://www.rexhall.com/index.php?option=com_content&view=article&id=10&Itemid=6 , http://www.rexhall.com/index.php?option=com_content&view=article&id=12&Itemid=16 , and http://www.rexhall.com/index.php?option=com_content&view=article&id=7&Itemid=3 , http://www.travelizmo.com/archives/001431.html , http://www.motorhome.com/rv-reviews/motorhome-reviews/2009-rexhall-aerbus-t-rex-375-ss/ :
You already know how I feel about colonial-style wood cabinetry, so I won't comment on that. But the American slide-out technology that makes such vast internal space possible is quite astonishing. From the Rexhall website:
Our 100% Welded Uni-Body Steel Super-Structure is the foremost reason to choose Rexhall over the other guys. From the very beginning Rexhall's founder, Bill Rex, chose to completely weld the entire inner structure together instead of using bolts and screws which can come loose over time…..
Our always innovative floorplans were revolutionized in 2005 when Rexhall Industries patented the T-Rex Full Body Slide Room. Creating more headroom and square footage per slide room than any other on the market. Additionally, keeping our focus on safety we more than triple the industry
 standard with 9 steel arms of tubing to carry the load of each slide room, 7 on the outside and 2 on the inside. T-Rex slide rooms are built like nothing else on the market. These slides are so sturdy you don't even need to put your jacks down!
- see http://www.rexhall.com/index.php?option=com_content&view=article&id=9&Itemid=17
It's not clear whether the UFO Chassis is still being manufactured and used by fabricators such as Rexhall – see http://www.irv2.com/forums/f22/is-the-ufo-chassis-a-thing-of-the-past-55262.html . And granted, no engine in an expedition RV could ever be so low-slung, so some will protest that all of this is moot. But it's only all moot if one opts for a Pusher engine.
However, if instead one opts for CBE, the design options for the camper radically open up. Very long slide-outs become possible, and so too rear living rooms, rear exits, and rear decks, as per the Wothahelizat -- see http://robgray.com/graynomad/wothahellizat/index.php . Right now I don't want to get caught up in the details of which slide-out, pop-up, or rear deck options are most "realistic" for an expedition RV. The point I am trying to make here is more general than that.
Workhorse came up with the UFO chassis precisely in order to free up the design space of a fully integrated RV. The standard format of diesel Pusher engine in the back of a Class A always dictated certain design solutions, and excluded others. Whereas with the advent of the UFO chassis, RV interior designers suddenly experienced the spatial equivalent of a blank sheet of paper, a "clean slate", so to speak. So if CBE is a realistic option, and if it has much else to recommend it in any case, then why would one want to mess with the design freedom that CBE can open up in a camper space, by putting a big pusher engine back there instead?
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CONTINUED IN NEXT POST
CONTINUED FROM PREVIOUS POST
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10. Rexhall Dual Full-Length Slide-Outs
Notice how in the UFO chassis the engine is so “low slung”, that it locates completely below the RV floor, thereby allowing full-length slide-outs.
An American class-A specialist, Rexhall, was one of the first manufacturers to take up the design challenge of this engineering innovation, and Rexhall is somewhat unique in having produced vehicles with two, full-length slides – see http://www.rexhall.com/index.php?option=com_content&view=category&layout=blog&id=2&Itemid=5 , http://www.rexhall.com/index.php?option=com_content&view=article&id=18&Itemid=9 , http://www.rexhall.com/index.php?option=com_content&view=article&id=10&Itemid=6 , http://www.rexhall.com/index.php?option=com_content&view=article&id=12&Itemid=16 , and http://www.rexhall.com/index.php?option=com_content&view=article&id=7&Itemid=3 , http://www.travelizmo.com/archives/001431.html , http://www.motorhome.com/rv-reviews/motorhome-reviews/2009-rexhall-aerbus-t-rex-375-ss/ :
You already know how I feel about colonial-style wood cabinetry, so I won't comment on that. But the American slide-out technology that makes such vast internal space possible is quite astonishing. From the Rexhall website:
Our 100% Welded Uni-Body Steel Super-Structure is the foremost reason to choose Rexhall over the other guys. From the very beginning Rexhall's founder, Bill Rex, chose to completely weld the entire inner structure together instead of using bolts and screws which can come loose over time…..
Our always innovative floorplans were revolutionized in 2005 when Rexhall Industries patented the T-Rex Full Body Slide Room. Creating more headroom and square footage per slide room than any other on the market. Additionally, keeping our focus on safety we more than triple the industry
 standard with 9 steel arms of tubing to carry the load of each slide room, 7 on the outside and 2 on the inside. T-Rex slide rooms are built like nothing else on the market. These slides are so sturdy you don't even need to put your jacks down!
- see http://www.rexhall.com/index.php?option=com_content&view=article&id=9&Itemid=17
It's not clear whether the UFO Chassis is still being manufactured and used by fabricators such as Rexhall – see http://www.irv2.com/forums/f22/is-the-ufo-chassis-a-thing-of-the-past-55262.html . And granted, no engine in an expedition RV could ever be so low-slung, so some will protest that all of this is moot. But it's only all moot if one opts for a Pusher engine.
However, if instead one opts for CBE, the design options for the camper radically open up. Very long slide-outs become possible, and so too rear living rooms, rear exits, and rear decks, as per the Wothahelizat -- see http://robgray.com/graynomad/wothahellizat/index.php . Right now I don't want to get caught up in the details of which slide-out, pop-up, or rear deck options are most "realistic" for an expedition RV. The point I am trying to make here is more general than that.
Workhorse came up with the UFO chassis precisely in order to free up the design space of a fully integrated RV. The standard format of diesel Pusher engine in the back of a Class A always dictated certain design solutions, and excluded others. Whereas with the advent of the UFO chassis, RV interior designers suddenly experienced the spatial equivalent of a blank sheet of paper, a "clean slate", so to speak. So if CBE is a realistic option, and if it has much else to recommend it in any case, then why would one want to mess with the design freedom that CBE can open up in a camper space, by putting a big pusher engine back there instead?
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CONTINUED IN NEXT POST
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biotect
Designer
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CONTINUED FROM PREVIOUS POST
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11. Unobstructed Camper Space
In short, I brought up Rexhall and the Workhorse UFO chassis to demonstrate a larger issue. In the initial stages of a design process, if it seems likely that one will be able to enjoy more design freedom down the road by choosing option A instead of option B, then option A is the preferred choice. Sure, I know that there is a 1 m length-penalty if one goes CBE, but when everything else is placed in the balance, CBE does seem a good choice.
Of course, I also provided these images because eventually (I hope!) we will begin discussing slide-outs and pop-ups in detail. It's then good to keep them mind, "on the back burner" so to speak, recognizing that engine placement will have an impact on what's possible down the road. So these images were also intended to illustrate what is now possible in RV slide-outs, if the available camper space remains unobstructed.
For instance, consider the Rexhall GT-310 T (floor plan below), a 9.78 m long motorhome. It's not the longest RV that Rexhall makes, but it's a good size for our purposes:
Doing the calculations, it's 385 inches long (9.78 m) x 98 inches wide (2.48 m) when the slides are retracted, providing roughly 24.25 square meters of floor space. But when the slides are extended, the interior expands to 146 inches wide (3.71 m), albeit granted, not for the total length of the vehicle. Still, by my calculations, the interior floor space increases to 32.4 square meters, or 34 %.
Rexhall also makes “pusher” motorhomes that are not mounted on the Workhorse UFO chassis, and observe the difference. In pusher motorhomes the engine in the rear rises above the base-line floor height, so at the back of the coach, like other manufacturers, Rexhall will locate either a raised bed or raised bathroom above the engine:
However, in an expedition RV of the kind that we are considering, this bed-platform above the pusher engine will be much higher, because axle ground clearance (for instance) will be approximately 55- 60 cm, with big Michelin tires. It's then an open question just how high the raised bed-platform will be; it all depends on the size of the engine. As that photograph I posted a while back of the MAN pusher engine illustrates, if the engine were really big, then there will not be much space left above it for anything, and certainly not for much of a bed-platform:
In short, there is no getting around the fact that an engine has to go somewhere. Somewhere in the vehicle we will lose volume and length because of the engine. If the pusher engine were small enough, and could be mounted low enough to allow for a usable bed-platform, then sure, putting the engine in back might make sense. Even if the slide-out lengths reduce as a consequence. But if a large engine means that we're going to lose a meter in back in any case, then why not instead lose the a meter in front, with a CBE design?
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12. Engine Placement: CBE better than COE, CF, and Pusher?
In summary, it's clear that the only things we'll want to take from the Tatra or the SX-45, are the rigid torsion-free frame, the drive-train, and the progressive coil-spring suspension. But not the engine-placement in the SX-45, i.e. we most definitely do not want to follow the SX-45's CF design. It seems that the best choices are either a pusher design, as you advocate, egn , or a Zetros-like CBE design.
I've now fielded my best arguments for CBE, and would love to hear your response, as well as the responses of others. I focused on the overall design issues, because they are every bit as important as the more immediate "ergonomic" ones, but perhaps less obvious. To reiterate the ergonomic arguments, a CBE design also seems superior to a pusher because the cab and driving position will locate well behind the front axle, improving driving comfort and safety, and the engine will be more accessible for repairs. Although engine access in a pusher is much better than COE, it's still not quite as good as CBE.
So my second question for you, egn, is:
“If a bit more overall length were acceptable, would you now agree that a CBE design is preferable to a rear-engine pusher?”
And if you do not, why not?
That was a great deal to take in, so needless to say, I don't expect answers any time soon! But I thought a series of posts like this, which try to address the "design domino effects" in a systematic way, might prove a good way to begin the engine discussion. And needless to say, any and all who read this are most welcome to fire away with observations, comments, criticism, advice, etc. Posting to a public forum like this only has value if one receives constructive feedback!
All best wishes,
Biotect
CONTINUED FROM PREVIOUS POST
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11. Unobstructed Camper Space
In short, I brought up Rexhall and the Workhorse UFO chassis to demonstrate a larger issue. In the initial stages of a design process, if it seems likely that one will be able to enjoy more design freedom down the road by choosing option A instead of option B, then option A is the preferred choice. Sure, I know that there is a 1 m length-penalty if one goes CBE, but when everything else is placed in the balance, CBE does seem a good choice.
Of course, I also provided these images because eventually (I hope!) we will begin discussing slide-outs and pop-ups in detail. It's then good to keep them mind, "on the back burner" so to speak, recognizing that engine placement will have an impact on what's possible down the road. So these images were also intended to illustrate what is now possible in RV slide-outs, if the available camper space remains unobstructed.
For instance, consider the Rexhall GT-310 T (floor plan below), a 9.78 m long motorhome. It's not the longest RV that Rexhall makes, but it's a good size for our purposes:
Doing the calculations, it's 385 inches long (9.78 m) x 98 inches wide (2.48 m) when the slides are retracted, providing roughly 24.25 square meters of floor space. But when the slides are extended, the interior expands to 146 inches wide (3.71 m), albeit granted, not for the total length of the vehicle. Still, by my calculations, the interior floor space increases to 32.4 square meters, or 34 %.
Rexhall also makes “pusher” motorhomes that are not mounted on the Workhorse UFO chassis, and observe the difference. In pusher motorhomes the engine in the rear rises above the base-line floor height, so at the back of the coach, like other manufacturers, Rexhall will locate either a raised bed or raised bathroom above the engine:
However, in an expedition RV of the kind that we are considering, this bed-platform above the pusher engine will be much higher, because axle ground clearance (for instance) will be approximately 55- 60 cm, with big Michelin tires. It's then an open question just how high the raised bed-platform will be; it all depends on the size of the engine. As that photograph I posted a while back of the MAN pusher engine illustrates, if the engine were really big, then there will not be much space left above it for anything, and certainly not for much of a bed-platform:
In short, there is no getting around the fact that an engine has to go somewhere. Somewhere in the vehicle we will lose volume and length because of the engine. If the pusher engine were small enough, and could be mounted low enough to allow for a usable bed-platform, then sure, putting the engine in back might make sense. Even if the slide-out lengths reduce as a consequence. But if a large engine means that we're going to lose a meter in back in any case, then why not instead lose the a meter in front, with a CBE design?
**********************************************
12. Engine Placement: CBE better than COE, CF, and Pusher?
In summary, it's clear that the only things we'll want to take from the Tatra or the SX-45, are the rigid torsion-free frame, the drive-train, and the progressive coil-spring suspension. But not the engine-placement in the SX-45, i.e. we most definitely do not want to follow the SX-45's CF design. It seems that the best choices are either a pusher design, as you advocate, egn , or a Zetros-like CBE design.
I've now fielded my best arguments for CBE, and would love to hear your response, as well as the responses of others. I focused on the overall design issues, because they are every bit as important as the more immediate "ergonomic" ones, but perhaps less obvious. To reiterate the ergonomic arguments, a CBE design also seems superior to a pusher because the cab and driving position will locate well behind the front axle, improving driving comfort and safety, and the engine will be more accessible for repairs. Although engine access in a pusher is much better than COE, it's still not quite as good as CBE.
So my second question for you, egn, is:
“If a bit more overall length were acceptable, would you now agree that a CBE design is preferable to a rear-engine pusher?”
And if you do not, why not?
That was a great deal to take in, so needless to say, I don't expect answers any time soon!
But I thought a series of posts like this, which try to address the "design domino effects" in a systematic way, might prove a good way to begin the engine discussion. And needless to say, any and all who read this are most welcome to fire away with observations, comments, criticism, advice, etc. Posting to a public forum like this only has value if one receives constructive feedback!All best wishes,
Biotect
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The big problem with Mercedes' eloquence regarding the Zetros bonnet position advantage is all the other trucks they themselves manufacture, probably citing a raft of reasons why having the cab over flat fronted design is vastly superior to anything else for those.
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The one thing that can't be argued with is the speed a Zetros can become armoured. Since the cab is separate from the engine and flat floored, it only takes a day to swap a normal cab for an armoured one so I've read. This can't be very important to many people since I believe the German army have stuck with flat fronted all wheel drive Actros and ignored Zetros almost entirely.
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Driving, positioning such a big vehicle is much, much easier if you sit at the front. My Mog has a smallish bonnet and its really good. Sitting in a round cab U500 I can't believe how much better it is, although I can't actually see the front corners, it just looks like there isn't anything at all infront of the windscreen. I've also had a brief ride in a Zetros, the bonnet didn't intrude as much as I thought but it still means there is a big chunk of ground you can't see. Its probably a similar view to Landys I've had, but the extra height means that much more is hidden.
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My overcab bed is slightly wider than the cab (Mogs do have relatively narrow cabs though), and removing the floor and front overcab wall allows the cab to rotate up and through the gap. It still opens the camper interior, but at least the roof stays on.
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In the pic you posted I did wonder if the pointy front to the overcab concealed a join, I don't think it does but there could be one. Depending where the pivot was you wouldn't have to remove all of the front panel to allow a cab tilt to go through?
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The one thing that can't be argued with is the speed a Zetros can become armoured. Since the cab is separate from the engine and flat floored, it only takes a day to swap a normal cab for an armoured one so I've read. This can't be very important to many people since I believe the German army have stuck with flat fronted all wheel drive Actros and ignored Zetros almost entirely.
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Driving, positioning such a big vehicle is much, much easier if you sit at the front. My Mog has a smallish bonnet and its really good. Sitting in a round cab U500 I can't believe how much better it is, although I can't actually see the front corners, it just looks like there isn't anything at all infront of the windscreen
. I've also had a brief ride in a Zetros, the bonnet didn't intrude as much as I thought but it still means there is a big chunk of ground you can't see. Its probably a similar view to Landys I've had, but the extra height means that much more is hidden.-
My overcab bed is slightly wider than the cab (Mogs do have relatively narrow cabs though), and removing the floor and front overcab wall allows the cab to rotate up and through the gap. It still opens the camper interior, but at least the roof stays on.
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In the pic you posted I did wonder if the pointy front to the overcab concealed a join, I don't think it does but there could be one. Depending where the pivot was you wouldn't have to remove all of the front panel to allow a cab tilt to go through?
Attachments
biotect
Designer
Hi grizzlyj,
I thought you were pro-CBE?
Good point about Mercedes: almost all of their other trucks are COE.
However, according to Mercedes’ press-release, CBE in the Zetros was a deliberate, conscious design choice:
“Cab-behind-engine design is number one choice for off-road applications
The cab-behind-engine design was chosen deliberately, since it is the number one choice for off-road vehicles for a number of reasons. It allows for compact, low profiles, as well as simple servicing, and provides significantly better vehicle control and ride comfort under extreme conditions compared with the cab-over-engine truck design. Overall this translates into less stress on the driver, but at the same time increased performance in the form of significantly higher possible speeds, longer periods of operation and therefore shorter round trip times.
It is no coincidence, therefore, that the Zetros series has generated a great deal of interest in the energy and exploration sectors, and also among the firefighting and emergency services: the exceptionally good off-road ride comfort of the cab-behind-engine truck gives the driver permanent control over the off-road speeds, something which would only be possible for brief periods at best in a cab-over-engine vehicle. And when it comes to safety and ergonomics for the driver, as well as the tasks he has to perform and the period of operation, the advantage enjoyed by the Mercedes-Benz Zetros really comes into play. Compared with cab-over-engine vehicles, it is the most suitable and safest design for extreme applications."
- see http://media.daimler.com/dcmedia/0-921-1130193-1-1288142-1-0-0-0-0-0-0-1549054-0-1-0-0-0-0-0.html .
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1. COE vs "conventional", Europe vs North America
I’ve tried discussing COE versus CBE with friends, other students, proffs, but even in the transportation design community opinions are diverse, and seem to track nationality. The Europeans naturally enough tout the benefits of COE, whereas North Americans favor CBE or “conventional” trucks. Since the laws changed in 1976, big COE semi trucks have virtually disappeared from North American roads:
Out of Favor in the U.S.
Because shortening the cab in North America won’t get you a longer trailer and more cargo space, there’s no economic incentive in North America for COE, and “conventional” or CBE designs with ample sleeper space now completely dominate the American market. So when legal constraints are removed, market pressure propelled by driver preference eliminates COE as a design choice, suggesting that CBE is “better”. On the other hand, for an expedition or overland vehicle shorter is better vis-à-vis handling, so there’s “design pressure” to keep the vehicle as compact as possible, even if there isn’t legal pressure.
Now at design schools, for whatever reason, students who work on futuristic truck-concepts – often in response to design competitions – almost always address COE instead of CBE. “Euro” = COE = “more cool”. I am European, but I strongly disagree. For an exception to this general trend, see http://www.foxnews.com/leisure/slideshow/2012/06/14/big-rig-future/?intcmp=related#slide=1 .
So there is probably no “objective” answer as to which is better, from ergonomic, fuel efficiency, safety, or service points of view. Which is why I focused on the overall design implications of different engine placements instead. The problem at hand in this thread is COE vs CBE vs Pusher for a motorhome, and not for trucks in general. And for an expedition motorhome specifically, and not for motorhomes in general.
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2. COE vs "conventional" on ExPo
Right here on ExPo, there is a short, two-page thread titled “Conventional vs cab over”, at http://www.expeditionportal.com/forum/threads/27575-Conventional-vs-cab-over . It doesn’t go into detail about the design implications, but the following are some choice quotes:
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grizzlyj, above you wrote:
Would you be willing to post some pics of this tilt-forward solution in your mog, or other similar mogs with overcab beds?
All best wishes,
Biotect
I thought you were pro-CBE?
Good point about Mercedes: almost all of their other trucks are COE.
However, according to Mercedes’ press-release, CBE in the Zetros was a deliberate, conscious design choice:
“Cab-behind-engine design is number one choice for off-road applications
The cab-behind-engine design was chosen deliberately, since it is the number one choice for off-road vehicles for a number of reasons. It allows for compact, low profiles, as well as simple servicing, and provides significantly better vehicle control and ride comfort under extreme conditions compared with the cab-over-engine truck design. Overall this translates into less stress on the driver, but at the same time increased performance in the form of significantly higher possible speeds, longer periods of operation and therefore shorter round trip times.
It is no coincidence, therefore, that the Zetros series has generated a great deal of interest in the energy and exploration sectors, and also among the firefighting and emergency services: the exceptionally good off-road ride comfort of the cab-behind-engine truck gives the driver permanent control over the off-road speeds, something which would only be possible for brief periods at best in a cab-over-engine vehicle. And when it comes to safety and ergonomics for the driver, as well as the tasks he has to perform and the period of operation, the advantage enjoyed by the Mercedes-Benz Zetros really comes into play. Compared with cab-over-engine vehicles, it is the most suitable and safest design for extreme applications."
- see http://media.daimler.com/dcmedia/0-921-1130193-1-1288142-1-0-0-0-0-0-0-1549054-0-1-0-0-0-0-0.html .
***********************************************
1. COE vs "conventional", Europe vs North America
I’ve tried discussing COE versus CBE with friends, other students, proffs, but even in the transportation design community opinions are diverse, and seem to track nationality. The Europeans naturally enough tout the benefits of COE, whereas North Americans favor CBE or “conventional” trucks. Since the laws changed in 1976, big COE semi trucks have virtually disappeared from North American roads:
Out of Favor in the U.S.
- The less restrictive tractor-trailer length laws of 1976 quickly pushed the cabover out of the limelight in the United States. Its popularity was mostly due to its convenient dimensions, but conventional truck configurations provided more comfort, less engine noise and greater power, according to "Kings of the Road."
- Although out of favor in North America, Europe's strict tractor-trailer rig dimension laws have made the COE the truck of choice for most trucking businesses. Narrow roads, tight corners and difficult access to urban areas from the highway have made the cabover a necessity, particularly in the United Kingdom. Japan also uses cabovers almost exclusively. German-made Mercedes-Benz and Man, and Japan's Suzuki, are prominent makes of COEs, according to "Kings of the Road.
Because shortening the cab in North America won’t get you a longer trailer and more cargo space, there’s no economic incentive in North America for COE, and “conventional” or CBE designs with ample sleeper space now completely dominate the American market. So when legal constraints are removed, market pressure propelled by driver preference eliminates COE as a design choice, suggesting that CBE is “better”. On the other hand, for an expedition or overland vehicle shorter is better vis-à-vis handling, so there’s “design pressure” to keep the vehicle as compact as possible, even if there isn’t legal pressure.
Now at design schools, for whatever reason, students who work on futuristic truck-concepts – often in response to design competitions – almost always address COE instead of CBE. “Euro” = COE = “more cool”. I am European, but I strongly disagree. For an exception to this general trend, see http://www.foxnews.com/leisure/slideshow/2012/06/14/big-rig-future/?intcmp=related#slide=1 .
So there is probably no “objective” answer as to which is better, from ergonomic, fuel efficiency, safety, or service points of view. Which is why I focused on the overall design implications of different engine placements instead. The problem at hand in this thread is COE vs CBE vs Pusher for a motorhome, and not for trucks in general. And for an expedition motorhome specifically, and not for motorhomes in general.
***********************************************
2. COE vs "conventional" on ExPo
Right here on ExPo, there is a short, two-page thread titled “Conventional vs cab over”, at http://www.expeditionportal.com/forum/threads/27575-Conventional-vs-cab-over . It doesn’t go into detail about the design implications, but the following are some choice quotes:
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grizzlyj, above you wrote:
Would you be willing to post some pics of this tilt-forward solution in your mog, or other similar mogs with overcab beds?
All best wishes,
Biotect
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