The Flxible Clippers do not have a frame as such. Instead, they are a unibody construction - the body of the vehicle has been made in such a way that it is its own frame. The various components such as engine, transmission, and suspension are mounted directly to parts of the welded structure.
Not a new idea
Unibody Construction - the "frame" is composed of many elements, and strengthened by the skin - be it steel, aluminum, planking, or plywood.
Although a new departure for buses - and in fact, any vehicles of this size - at the time it was adapted by the Flxible Company, this was not a new concept. The very essence of boatbuilding, this style of construction was the design of choice for aircraft, almost from the very beginning, and Flxible was one of the first companies to adapt the idea to road vehicles. From the early '50's, it became popular with many smaller foreign automobiles, beginning with such as the Morris Minor and Citroen, and today is virtually the standard way in which automobiles are made.
One minor disadvantage does exist with Unibody Construction, and that is that the major chassis elements upon which the major components, such as suspension and drive train, are mounted are generally by nature not as thick and heavy as the frame rails on conventionally-built vehicles. The components of the total framework upon which these are mounted, although slightly thicker than many others, still need not be of the massive proportions found with typical frames. Thus, the unibody construction is considerably more susceptible to rust and corrosion - chronic deterioration of the framework in the area of a spring mount, for instance, can occur much more easily than with a frame bent up of 3/16" - or even thicker - material. This, however, is usually repairable, although such repair involves the same kind of work as it does correcting rot in a boat. All elements which have been rendered unserviceable must be removed - back to the closest point of complete solidity, and each part must then be built or bought, and welded back into the structure until the total integrity is restored.
This is not as serious a problem as it could be with the Flxible Clippers, however, because they incorporate a pair of major longitudinal "frame" members (parts 2 and 3 in the dwg), to which are welded a number of transverse members (5 -12) fashioned of steel of a fairly heavy gauge, and the "meatiness" of these members is sufficient to withstand a lot of corrosive influence. Further, solid as they are, the parts that are left will in most cases provide good anchoring for repairs. Still, if you're looking at a Clipper, be sure to check these parts carefully - restoration would not be an easy process!
The Roof Frame - An Important Part Of The Monocoque Construction
Above the floor, the Unibody is composed of "hoops," or "frames," which run up the sides, between the windows, and over the top, forming the basis for the side skins and the roof. Once all these components are welded/riveted together, the bodywork becomes a monocoque one-piece construction, in which the stressed skin is as much a part of the whole as any other part - a lightweight and very strong chassis.
Of Major Importance...
Thus, it is very important that the ends of, and joints between, each and every element of the total construction are solid, tight, and free or corrosion or deterioration of any kind. However, once your complete Unibody is tight and clean, the chassis as a whole is as strong as it ever was - and that's plenty!
Unibody construction has the multiple advantages of extreme strength, light weight to strength ratio, and is much more rattle and squeak free. The skin is also a structural component, holding the various frames and subframes together, and adding tremendous strength.