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Author Topic: Bohman bus conversion  (Read 3898 times)
chev49
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« Reply #15 on: February 10, 2012, 08:52:40 AM »

I would like to see it in a bus race, like on UK's "Top Gear" Grin
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« Reply #16 on: February 10, 2012, 09:47:52 AM »

Here you go Top Gear bus racing
http://www.topgear.com/uk/videos/bus-racing
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« Reply #17 on: February 10, 2012, 02:12:59 PM »

Pip,

I think you miss the point, old GMCs are not square topped, they are round, and much stronger than a square metal top.

That is what monocoque construction is all about, the strength is in the cover and not an internal frame. Metal skinned airplanes are built like this, the skin is the structure.

A lot of that strength is in the round top and he has cut a very large hole in it.

#2, An end cap does not replace the cutaway ends of a bus, it covers over it much like the brick veneer around a house which contributes no structural strength to the house - it is just a cover. Since an end cap is just a plastic molding it has very little strength, it mostly changes the shape and look of the bus and provides some extra interior space.

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« Reply #18 on: February 10, 2012, 03:04:11 PM »

That is what monocoque construction is all about, the strength is in the cover and not an internal frame. Metal skinned airplanes are built like this, the skin is the structure.

This isn't really accurate, unless American buses are much cleverer than I thought. Monocoques built from composite materials, such as yacht hulls and the latest airliners, are as close as you get to a large 'stressed skin' structure, but even these have an internal frame in some areas. It's true to say that the skin of a bus contributes to the stiffness of the monocoque, but it adds very little strength - it's the internal frame that does that. Take the skin off and the bus would still work - leave the skin and remove the frame and it certainly wouldn't.

Previously on here (mostly in discussions about slide-outs) people have likened a bus monocoque to a Coke can, and said things like "cut a hole in the side of a Coke can and it collapses". This is true as far as Coke cans go, but they really aren't analogous with bus bodies. Coke cans are a rare example of a thin-wall metal monocoque with no internal frame, and they work because the skin is supported by the gas pressure inside the can. Bus bodies have a substantial internal frame, and if you alter that frame appropriately you can cut any size holes in the side that you wish.


Jeremy
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« Reply #19 on: February 10, 2012, 06:56:01 PM »

Back in the '70s, nearly all of Brewster's MCI buses (Couriers, MC1s, 2s, 3s, 5s, 7s and 8s), had sky-view windows installed along the whole length of the edge of the roof. Those were big. Several of the frame ribs were cut off to do it. The glass was certainly not structural: the only thing holding it up was the rubber molding. I don't remember any problems associated with that. I still have my Courier 96 with sky-views, and I don't have any structural issues after 55 years.



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gus
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« Reply #20 on: February 12, 2012, 06:32:40 PM »

Jeremy,

I completely disagree with you on every point. Monocoque construction by definition means the skin has the stress. The internal ribs or formers you talk about primarily give shape to the body, not strength. Practically every metal skinned light aircraft, in addition to airliners, uses this method. This is totally different from an internal structure such as in a fabric covered aircraft.

I don't know about all buses, especially the square shaped ones, but the metal part of all the old GMCs used pure monocoque construction, there was no structural frame as in a school bus. The central body was built and then the front end piece was hung onto it. The plywood floor is also part of this monocoque, sort of like a walnut shell, although there is a framework that holds the plywood pieces.
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« Reply #21 on: February 13, 2012, 01:46:40 AM »

It's wrong to say "Monocoque construction by definition means the skin has the stress." - the word 'monocoque' is French for 'single shell' - nothing to do with a stressed skin as such. The shell consist of a skin on a framework - on a bus the skin is only stressed insofar as it gives stiffness to the frame underneath it - that's all it does and all it can do, given how thin the material is. The composite skin of yacht or modern airliner is a much thicker sandwich material and does take all the loads in most areas.

When you say "...all the old GMCs....there was no structural frame" - do you really mean that? I'm sure I've seen lots of pictures of tubular steelwork under the skin of GMCs, and I certainly have under lots of other monocoque buses. But maybe those old GMCs are much cleverer than I thought.

Jeremy
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« Reply #22 on: February 13, 2012, 03:26:51 AM »

Let's make sure we aren't arguing over a difference in common understanding between British and American vocabulary or restricting it to industry-restrictive meanings.

http://www.merriam-webster.com/dictionary/monocoque
mono·coque noun \ˈmä-nə-ˌkōk, -ˌkäk\
Definition of MONOCOQUE
1: a type of construction (as of a fuselage) in which the outer skin carries all or a major part of the stresses
2: a type of vehicle construction (as of an automobile) in which the body is integral with the chassis
Origin of MONOCOQUE
French, from mon- + coque shell, probably from Latin coccum kermes — more at cocoon
First Known Use: 1913

http://en.wikipedia.org/wiki/Monocoque
Monocoque (pronounced /ˈmɒnɵkɒk/ or /ˈmɒnɵkoʊk/) is a construction technique that supports structural load by using an object's external skin, as opposed to using an internal frame or truss that is then covered with a non-load-bearing skin or coachwork. The term is also used to indicate a form of vehicle construction in which the body and chassis form a single unit. The word monocoque comes from the Greek for single (mono) and French for shell (coque). The technique may also be called structural skin, stressed skin, unit body, unibody, unitary construction, or Body Frame Integral. A semi-monocoque differs in having longerons and stringers.
(follow the link for much more discussion)

http://en.wikipedia.org/wiki/PD-4501_Scenicruiser
The GMC PD-4501 Scenicruiser, manufactured exclusively for Greyhound Lines, was a three-axle monocoque two-level coach used by Greyhound from 1954 to the 1970s. It was introduced in July 1954, and in total, 1001 were made between 1954 to 1956.
(more at link)
« Last Edit: February 13, 2012, 03:35:19 AM by Nusa » Logged
Jeremy
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« Reply #23 on: February 13, 2012, 04:20:00 AM »

It did occur to me after my earlier post that when Gus said "GMCs have no frame" what he meant was that they had no chassis, and perhaps by 'skin' he means the frame of the shell, not the skin on the frame

Jeremy
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« Reply #24 on: February 13, 2012, 05:06:00 AM »

Jeremy, you got it right the GM's have plenty of uprights and roof trusses just no chassis frame,you need to see one it's scary the engine hanging from the roof but it works and has for a long time lol


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« Reply #25 on: February 13, 2012, 05:59:15 AM »

I think the Wiki entry is incorrect.  To the best of my knowledge, GM buses were always referred to as semi-monocoque.
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« Reply #26 on: February 13, 2012, 06:21:26 AM »

len is right of course...
as webster says only a portion of the load is carried by the skin, something we kept in mind while working on my brothers 4106.
the main load is carried by all that inside framework, etc. Unless it's a GMC school bus.
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« Reply #27 on: February 13, 2012, 06:50:33 AM »

Looks like something I might do!  Why because someone said:  You Can not! Outside the Box. I am sure the builder paid attention to stress points and probably had that covered before cutting hole for mod. At least that is the way I approach doing something by doubling area stress/strength by 2x . Gm and MCI 's have been doing the rear engine sling thing for 60 plus years. I know BK had one just about fall out MCI due to a failed weld  but not necessarily a design flaw.   Observation only.   Bob 
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« Reply #28 on: February 13, 2012, 02:35:01 PM »

Nusa,

I couldn't have said it any better.

Len,

You are correct, it is more of a semi-monocoque because the floor does have a framework. You will also note that I said the metal part is monocogue in that the skin is, indeed, stressed and is the primary structure of the bus. The real meaning of monocoque is stressed skin. These buses have no frame either underneath or on the sides. Again, the wall posts are there primarily to give shape to the metal, the skin carries the load.

This is more obvious in airplanes. If you look at the structure of a fabric covered lightplane compared to a metal covered one you will see that the metal one has very little interior framework.

Unibody automobiles are not monocoque. A unibody has a  molded and welded sheet metal bottom framework which replaces the separate frame so it is one piece instead of two. This is done to eliminate body to frame twisting and is much stronger than the old two piece system.

Unibodies are more like a walnut shell which has interior webbed structure which provides a lot of its strength so the skin is not carrying most of the load.

Stressed skin is the point.
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« Reply #29 on: February 13, 2012, 03:03:57 PM »

I realise this is an Eagle, but it does go to show that some monocoque (or semi-monocoque etc) buses aren't reliant on their skins, and can be driven about without them. I don't know how much the frame of a GMC differs from an Eagle, or whether it's skin is really any more important.







Jeremy
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