Active suspension and "Active" underbody

[NoDivergence]

A recent concept has been brought to my attention for a road going vehicle regarding the use of a second, active underbody floor to maintain the proximity of this floor to the ground. Supposedly the purpose is to decouple the relationship between the suspension and the ride height of the floor. The intention is to maintain a good ride quality with the suspension while developing stable and additional downforce, perhaps with the use of skirts for a road going car. It is a further development of Chapman's original ground effects concept

Would current day active suspension technology combined with decoupled suspension concepts negate the need for this when used in coordination with a Group C level ground effects floor?

Any deficiencies to this concept?
Please discuss

[DaveW]

More details, perhaps with a reference, would be useful...

[gixxer_drew]

definitely doable with modern technology and aerodynamically it would be a massive simplification of the design work and enable massive leaps in performance. I would be really shocked if they ever make it legal. Never really understood why ground effect stuff got regulated into the history books. It was the most significant innovation performance wise and is surely relevant to road cars for both safety and efficiency.

[NoDivergence]

More details, perhaps with a reference, would be useful...

Concept for the patent and application is explained here
http://www.mclarenlife.com/forums/mclar ... or-16.html and continues to next page. I may have looked at this backwards, it may or may not have potential. Are they other methods to achieve the same end? Not sure

[DaveW]

So far as I can tell, he is proposing (or, perhaps, built?) an active version of the Lotus 88. The '88 was passive, with two suspensions, one of which (the aero one) was intended to become pulled rigidly down on to the uprights at relative low airspeeds. If tyre deflections can be tolerated (without inducing instability), why would you do more?

I suspect there would be an issue with the stability of an underfloor installation - Note that the '88 was structurally a twin chassis car (both had torsional stiffness).

I think also that sliding skirts might be an issue in a road vehicle.

[Belatti]

Interestingly, I have thought about this a while ago.

In a more controlled environment (like F1) where rules wont allow such things, my idea diverged to bodywork pieces with calculated vibrational effects (the bodywork has mass, stiffness in 3 directions and can be damped). The exitation force would be aerodynamic and maybe in some range of turbulent condition even similar to a sinusoidal.

A couple of years after I commented this in the forum, RedBull appeared with flexi wings and Ferrari with a "hummingbird" front wing...

[NoDivergence]

My point was more like isn't self leveling and height control already a staple of active suspension? Is decoupling the suspension and underbody even worth anything on top of that?

[Belatti]

The way I see it, it has pros and cons...

[Lycoming]

why would a road car need this? skirts especially are ridiculous for a road car.

Also, why not just mount the floor unsprung? then the only flex is from the tyre, which is significant, but not easily removed in any case. The only reason for active suspension back in the 90's was bceause they were not allowed much unsrpung downforce, and active suspension let it operate at the ideal orientation.

It is fully within the realm of possibility to have the floor and both wings as one single piece, the only remaining challenge would be to mount it to the uprights. No need for finicky electronics and sensors.

My point was more like isn't self leveling and height control already a staple of active suspension? Is decoupling the suspension and underbody even worth anything on top of that?

the point of that self levelling/height control is to decouple the suspension in the sense that it virtually eliminates changes in pitch, ride height and roll. It doesn't make sense to use a suspension system to decouple something from the supension.

[NoDivergence]

Could you further elaborate on that last point? I had previously thought that active suspension would virtually eliminate the need for anything further like what this person is proposing. Are you agreeing with me? The unsprung floor is an interesting idea.

[bhallg2k]

Sounds a lot like this.

[DaveW]

My point was more like isn't self leveling and height control already a staple of active suspension? Is decoupling the suspension and underbody even worth anything on top of that?

Yes, but (with apologies to those with a good memory) that has been done before. Nobody would pretend that an Elan was a serious ground effect car, but the '99T, which used essentially the same system, was.

Actually, if good "comfort" levels are to be attained with high levels of downforce, then there is some point in pursuing the "twin chassis" route. However, a high down force super-car (if that makes any kind of sense) would probably not be required to be "comfortable" (in the Rolls-Royce sense).

[DaveW]

Sounds a lot like this.

The above reference contains the following:

Q: Now that you have driven the secret new Lotus, what do you think of its chances in 1981?
Elio:"To be perfectly honest, it's not working yet. But I am hopeful that it will make a big improvement when we have done some more work."

That is a true statement, as I recall. The car was black flagged on every appearance before serious development was possible. I was informed fairly recently that the car is now run occasionally in classic events, and the suspension does work as originally intended...