New steering system concept to minimize aerodynamic drag

[Blue Bomber Man]

So I thought about the physics of the rear wheel steering as per Big_dave's warnings and I realized he is almost certainly right. The rear wheel turning causes the rear end of the vehicle to travel in a direction opposite of that the front of the vehicle will be heading. This in turn torque the body and cause the real wheel to likely sputter across the road surface. Kinda like a semi trailer backing up and jacking at high speed.

So that brings us back to front wheel steering =)

What makes the idea of "wagon" steering work so poorly. The only issue I can see is with the varying frontal wheel base. The wheels spin independently from each still so I don't see issues with the effective differences between inner and outer wheels during a turn.

Thoughts?

[Blue Bomber Man]

Originally Posted by dcb

Yup, that's where drive by wire comes in (a-la stealth bomber or other "can't fly it without a computer" aircraft).

The rear wheel could also just caster, and manipulate the front wheel torque to steer, maybe.

Explain a bit more?

[dcb]

The stealth bomber doesn't have a vertical stabilizer, this reduces the radar signature, but also means the design is inherently unstable. It steers by using these little air brakes in the wing tips, open the left one a little and the plane yaws left, etc.. But keeping the plane pointing in the right direction requires more computations and reactions per second than humans are known for possesing. A human trying to steer it manually would undoubtedly tumble out of the sky. But with the help of a computer it does fly.

[trikkonceptz]

Why not use a combination of ideas. Honda some years back had a prelude that was all wheel steering, albeit not much but it did improve cornering. Now take that idea and marry it with more modern computing and you get a front wheel with reduce turning radius to not pertrude out from the fenders and the rear wheels turning to compensate.

[pasadena_commut]

Originally Posted by Blue Bomber Man

So I thought about the physics of the rear wheel steering as per Big_dave's warnings and I realized he is almost certainly right. The rear wheel turning causes the rear end of the vehicle to travel in a direction opposite of that the front of the vehicle will be heading.

There are two effects to consider with rear wheel steering:

1. The direction the car turns is the opposite of the direction the wheel turns (this is like steering a boat with a rudder).

2. The steering is not self centering.

Computer controlled steering could compensate for the second effect. As others have pointed out, with the computer making adjustments, inherently unstable vehicles can be controlled such that, from the operator's perspective, they are stable. Cars are moving in this direction anyway, with computers applying brakes at various wheels during extreme handling situations to maintain vehicle stability.

The first issue cannot be compensated for. Consider what happens to a rear wheel steered vehicle which is parked directly next to a curb. It isn't (in general) possible to pull out forward, because to do so the rear wheel has to turn towards the curb, and the closer rear wheel will run right into the curb as the car moves forward. To pull out from the curb one must back out. Rear wheel steering does mean that in some instances the car just has to be driven differently.

If there is a single rear wheel, and it is both driven and steered, extreme steering angles become feasible. (Losing the drive linkage to another wheel permits this.). Imagine the car parked at the curb with cars very near each bumper. The rear wheel could be turned 90 degrees to move the back end directly away from the curb until it clears the rear car (which due to the narrow rear end, is not nearly so far as for a regular car), and then turned about halfway back towards center to pull the rest of the car out of the parking space.

Hmm, if the rear wheel can turn like that it might be possible to pull forward out of some parking spaces. Method: move as far back parallel to the curb as possible, crank the rear wheel straight towards the curb, drag the butt of the car to it, turn the rear wheel straight (parallel to the curb), move forward keeping the rear wheel parallel to the curb. This will push the front of the car to the left.

I suspect one could get used to driving a car with these properties, but it would be hard to drive this car one day, and a normal car another day.

[Frank Lee]

Is the idea here to make something as complex as possible?

[Blue Bomber Man]

LOL Frank, was not my intention. This is exactly why I love posting about stuff like this on these boards. You can toss an idea around and get a lot of different insights to the benefits and complications of a scenario.

After all this talk I've decided to stick with a traditional steering system and will probably just design a part that attaches to the steering system that fills in the wheel wells at the body to smooth airflow.

I might consider making the wheels internal, but probably won't because it would require a larger wheel base/more frontal area. No sense killing the all the benefits of shielding the airflow from the wheels.

[aerohead]

The 1962 18-wheeler that GM researchers came up with utilized this configuration,although the curvature of the cut-line is reversed to make the leading edge of the trailing structure a prolate hemisphere rather than a parachute as appears in your graphic.No matter the position of the "lead" structure,the air is always striking a radiused "nose" of the trailing structure,with no flow separation.

[Blue Bomber Man]

Ya have the curve flipped would make more sense. What sort of results did they have with this sort of steering mechanism?

[Big Dave]

Most engineers find Kelly Johnson's dicta of KISS - Keep It Simple Stupid - is a good policy.

I like the idea of fully enclosing the front (steering) wheels with a shell that attaches to the steering link. Another possibility is take basjoos' roller operated skirt and make it cover the wheel more fully.

Your vehicle is fairly short and should be a snap to park.