On reduced air gap between tractor and trailer:
A number of posts calling into consideration the noticeably small gap between the tractor cab and the trailer in the teaser photo of the Semi.
First, the turbulence caused by such a gap is a big item. Its existence reduces efficiency significantly; over the past thirty years a lot of attempts have addressed that fuel-eater.
Second, it was that which specifically drew my attention when I saw the teaser photo.
Now, at highway speeds, which is when airflow, drag and performance numbers all come into play, there are
lim---> ∞ no sharp turns. The driver of a tractor-trailer combo can confidently negotiate his or her route with these segments very close to snug against each other.
When negotiating parking, backing up, cloverleaf exit ramps and so forth, however - all of which are performed at highly reduced speeds - there most definitely is a sharp angle between the tractor and its hauled trailer; one which, as neroden and others have pointed out, would wreak havoc upon the two segments.
The suggestion of ggr to articulate the trailer axle assemblies so that they turn with the drive axles is one way mechanically to alleviate that. It does, however, fail the simplicity test, the cost test and, most critically, the use-flexibility test. Although the European heavy-truck model
does champion the unified cab-cargo model, the "semi-", aka tractor-trailer model used in NoAm, Australia and some other locations is supremely efficient in that it allows the same drive unit (the driver's tractor) to haul any of a variety of disparate trailers - all of which are "dumb", or, at the very least, mechanically simple.
My read on what the teaser photo shows is different. What I envision is one or a combination of the following two innovations: What Tesla has done is either (or both):
- emplace a variable-length king pin such that the tractor draws the trailer closer or further away as a function of truck speed plus driver override selection
- create a cab-entire cowling such that this entire element can slide back so that under appropriate circumstances (high-speed, low-curvature route) it diminishes the gap to the trailer. This also would be driver-selectable.
The former is a more robust approach: it could be achieved, inter alia, by having the king pin slide forward and back along the length of the rear portion of the tractor frame. Such a system is not completely new - one can find modern-day tractors with some of that ability. It also is of critical importance in long-distance hauling in that jurisdictions (usually state- and province-specific) have differing axle-length restrictions; the way a trucker can be legal is to alter that apparent tractor length in this fashion. Heretofore it is a cumbersome, time-chewing pain in the keister.
The latter is a more elegant approach but no examination of the photos yet to have appeared suggest the cab assembly has such a feature. Above, I wrote that you don't get sharp turns at highway speeds. The exception occurs during accident avoidance and other such hideosities. I cannot envision a variable-king pin method being able quickly enough to alter itself then. A movable cowling
could also incorporate real flexibility so that it might be able to be pushed by the trailer without damage.
I think we'll know more in about twelve hours....
Edited to reduce
drag confusion.
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