On Sep 30, 10:56*am, Phil W Lee wrote:
Peter Clinch considered Fri, 30 Sep 2011
11:42:23 +0100 the perfect time to write:



On 30/09/11 03:02, Phil W Lee wrote:
Tom Sherman *considered Sun,
17 Oct 2010 18:43:30 -0500 the perfect time to write:

Leave the rear-wheel steering to the forklifts and other low-speed
vehicles, as it is almost impossible to make a rear-steer vehicle that
handles well at speed.

I know this is a bit of thread necromancy, but really, weren't you
aware that the fastest land vehicle ever built has rear wheel
steering?

http://www.thrustssc.com/thrustssc/E.../rearster.html

It handled the transonic region pretty well, which is probably way
faster than anything you were thinking of.

I think if we substitute "difficult" for "almost impossible" we're at a
fair place.

I recall an answer Mike Burrows gave in print to a question asking why a
rear wheel steer recumbent wasn't the obvious thing to do (combined with
front wheel drive) in one of the rags (C+?). *It suggested while it was
possible such vehicles tended to be ridden by people with names like
Koko who possessed particularly large shoes and red noses... *I imagine
MB was basing that on practical experience as well as theory as he's an
excellent engineer quite unafraid of the unconventional.

Pete.

At the lower end of the speed range, I can think of a number of
designs of tradesman's tricycle and rickshaw that are rear-wheel
steered.
The biggest problem seems to be overcoming prejudice.

The mini that was converted to test the principle for ThrustSSC was
thrown together quite quickly (as can be seen by just looking at it -
it looks like the unfortunate result of a mini reversing hard into a
couple of wheelbarrows full of scaffolding poles) but turned out to be
as stable as (in some opinions, even more stable than) the standard
mini.
Quite a surprise, considering that it had the aerodynamics of a
collapsed crane, a weight distribution that would have given Alec
Issigonis nightmares, and a pair of rear wheels offset from each other
so that the wheel plan was asymmetric.

OK, the guys that knocked it together were real engineers, who knew
what they were doing, but the result seems to indicate that it may
actually be /easier/ to design a rear-wheel steering chassis that's
stable at speed than a front-wheel steered one.

The main rationale for front wheel steering seems to be that we've
always done it that way, but there doesn't seem to be any good reason
why we should still be constrained by the fact that early designs
relied on a horse between the shafts to move the steering linkage!

I used to "drive" a rear-wheel steered tadpole trike on a regular
basis while I was learning to fly (J-3 Cub) and I can tell you the
dynamics of the subject have been studied exhaustively. The problem is
handling at the limits, the front wheels have to break loose before
the rear wheel or the vehicle will spin out violently. Part of the
problem with aircraft in this configuration was the large size
differential between the main gear (front tires) and the tail gear
(rear tire) but the biggest problem was that to minimize this effect
you needed a really long wheelbase with almost all the weight on the
front tires. One of the advantages was that a quick and dirty way to
reduce this effect was to make the front track narrower so that the
inside wheel would lift in a turn, causing the front to lose traction
before the rear. For a streamlined trike with a rider that has broad
shoulders but narrow hips (cough coughmecough)you could put the rider
between the wheels without compromising the aero shape for the wheels
since you would just need to make that part of the shell wide enough
to fit the wheels and the drive between the shell and the rider's
hips. With my hip-shoulder difference I could easily stuff everything
next to my hips and still have to make the shell expand to fit around
my shoulders. Admittedly I'm an extreme example (13.5" hips, 24"
shoulders) but the principle would apply to people of more normal
proportions also.