The Frameless Semi-trailer

The Frameless Semi-trailer

 

Trailer with frame beneath

In the late 1940’s, Detroit based Fruehauf Trailer Company’s Chief Engineer Keith Tantlinger developed a new semi-trailer design that has since been copied by every trailer manufacturer throughout the world. Prior to this, the semi-trailer van body was basically a covered box mounted on a heavy chassis that took the weight.

Sidewall to assembly line

Fruehauf introduced an aluminum riveted body using a semi monocoque construction based on designs developed for aircraft fuselages and wings. The trailer sidewalls were built using thin (.057”) aluminum sheet with extruded aluminum wall posts riveted to the panels. The lower edge of the sidewall was riveted to an aluminum extruded lower rail which in turn was riveted to horizontal steel crossmembers that supported the flooring. The upper edge of the side panels was riveted to an upper rail extrusion to which was attached an aluminum one piece panel with bonded stiffeners.

Assembly line view before roof installation

The resulting box was strong enough to carry the load weight from the crossmembers to the sidewall panels. The tractor kingpin was attached under the front of the box, and the suspension attached under the rear providing a trailer that could carry maximum loads with no frame, and that was much lighter overall. The design also allowed the trailer to be built in sub-assemblies that could be put together on a moving assembly line, resulting in a drastic reduction in the cost. It was quickly copied by all North American volume manufacturers.

Fred Davies was president of Trailmobile Canada, and was using similar construction in his Canadian production. On a visit to England in the mid 1950’s, he was astounded at the construction methods still used by the trailer manufacturers there. In Fred’s words, “Crane, (who later became Crane Fruehauf) was one of the archaic builders. Fine people but they were rusticating in the wilds of Norfolk. I decided to go over there myself and take advantage of the situation”. He left Trailmobile, took his chief engineer with him and with some help from the banks and Jim Hanson (Hanson trucking) began manufacturing the North American design of trailer, naming his company York Trailer. Within a few years, York had taken a major chunk of the UK market with a new plant, first in Corby, and then in North Allerton, Yorkshire.

Typical modern van type semi trailer

Today, practically every highway van type semi- trailer throughout the world is built in this manner with the load being carried by the sidewalls of the box. Even the ubiquitous ISO steel container is built using the same engineering principles.

 

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