current F1 front suspension

[golfpin]

newbie here,
current F1 front suspension layout would seem to indicate the front roll centre at perhaps ground level or lower. Is this the case, and if so would this not aggravate the "jacking effect". Have been out of the design loop for a long time am I missing something or is there a heavy "aero" package influence here that I am unaware of, any comments would be greatly appreciated from what appears to be very well informed panel.
with thanks.

 

[slowM]

Hi,

Sorry if I'm sticking my nose where it may be lopped off, but I have a question. If aero downforce is as dramatic as I am hearing, seeing the car at rest doesn't tell the whole story, as it would with, say, a Rolls Canardly. I suspect that the dynamic system, the car progressing around a circuit, loaded with driver and aero effect, would be a better starting point for discussion. "Static, in a Formula One car, then, might be taken as meaning at a given (average) velocity.

Once in motion, the reaction point would move further away from the CL of the car, and also up, slightly, correct? Therefore, the the roll center would move down. So, my question is: Why is "static" even considered in the same way for a production sedan as it is for a high downforce racing car? Wouldn't it make more sense to look at the vehicle at some steady state that is more representational of its "norm?" Maybe that normative value is the average velocity around a track, and has to be different from one track to the next?

Thanks in advance,to anyone willing to edify,
Bernard.

 

[Cashmo]

I think the instant centers would move up/out and with them the RCH. Between the stiff front springs and any built in anti-dive I don't think the front suspension compresses much. Another example from this years Lotus...

 

[NormPeterson]

If you're tuning for track performance you should probably be looking at some combination(s) of roll and dive and calling that sort of a "steady state". I don't see why you'd ignore this completely is a road car with sporty handling intent.


Norm

 

[slowM]

Thanks.

Best,
B.

 

[NormPeterson]

I think the instant centers would move up/out and with them the RCH.

Given that the FVICs lie outboard of their respective wheels, are you suggesting that the FVICs and the GRC would both move upward with downward chassis travel?


Norm

 

[golfpin]

Ignorance at large, again please elucidate FVIC = FV?insant centre G?roll centre the acronyms have got me thanks Golfpin

 

[NormPeterson]

FV = Front View.

There is also a Side View IC (associated with pitch rather than roll), so using "IC" by itself isn't a sufficiently descriptive term (unless you're talking to most drag racers, who don't much care about suspension behavior in front view).


Norm

 

[FeX32]

That video posted by Cashmo was very informative. Back 10 years ago they had different priorities as is evident from this front view

http://www.italiancar.net/site/news/06/0606/forSaleF1/FerrariF1_Australia2006_29_lg.jpg

"Simplicity is the ultimate sophistication." L. da Vinci
- Gian

 

[dynatune]

Maybe this extra info could help you guys understand Suspension's better:

Just let go of all links and so on, just concentrate on the knuckle/upright. The "vertical" movement of the knuckle/upright can be seen as a rotation around an axis. This axis may be nearby or far away. This axis is called the Instantaneous Axis of Rotation of the suspension and where this axis "hits" the axle center line it is called the Instantaneous Front View Center and where the axis hits the Track Width Plane it is called the Instantaneous Side View Center. From the movement of the Wheel Center and The Contact Patch all suspension characteristics can be derived via vector algebra (the actual position of the links is completely irrelevant).

Now this "Instantaneous Axis of Rotation" has some very particular characteristics that allow a fundamental approach to define Suspension Types:

1) If the axis of rotation is more or less stable in space the suspension is called a "Plane Suspension" Plane revers to the fact that the suspension can be "easily" drawn "in plane" on a 2D drawing book. Typically SLA suspensions and McPherson Struts are "Plane" Suspensions and do not have many interactions between parameters. This means that their instantaneous FV & SV centers are quite well "tunable" and over wheel travel remains pretty much constant

2) If the axis of rotation moves BUT always goes through one specific point the suspension is called "Spherical Suspension" due to the fact that one point of the actual suspension is always acting as a spherical center for the instant axis of rotation (the axis "cones" around that joint). These type of suspensions are not so easily to be drawn on a 2D piece of paper and need the help of some 2,5D tricks in order to design them (on paper). Most famous representative of this type of Suspension is the BMW E36 (M3) or Toyota RAV4 where the "Spherical Joint" the trailing arm to Chassis Joint is On these suspensions you will always find a strong interaction between Toe, Camber and Roll Center Height. Due to the interaction of Toe Camber and Roll Center the FV instantaneous center can only be "tuned" marginally whereas the SV IC is almost always "fixed" next to the trailing arm. A computer program helps here a lot.

3) If the axis of rotation moves in space and is also characterized by a "thread movement" fore/aft along the axis the axis will be called "Momentary Screw Axis" and the suspension becomes a true fully 3 dimension multilink suspension. These suspensions cannot be calculated on a piece of paper and are characterized by a very significant interaction off all Parameters. Changing one point will change almost all characteristics. This means that the movement of FV IC and SV IC can be a lot and most of all change a lot over wheel travel. Without a computer and vector algebra one is completely lost.

I hope this helps understanding the FV & SV IC, I have btw started a new thread about my new suspension design tool. If you like have a look at it !

Cheers,
dynatune,

http://www.dynatune-xl.com

 

[Cashmo]

I threw some quick numbers into an online suspension pgm (VSUSP.COM) and it indicates the RCH would move down upon suspension compression. I'll try linking to it below...

(.general.roll_center.y}]VSUSP.COM)


VSUSP.COM

 

[golfpin]

TO ALL YOU GUYS WHO HAVE TAKEN THE TROUBLE TO ADD,PROD,ARGUE, MAKE SAGE COMMENTS AND MAKE MY AGEING BRAIN TRY AND WORK AGAIN, A DEEP THANK YOU, CERTAINLY FOR YOUR PATIENCE IN YOUR REPLIES. I THINK THAT IN THIS WORLD OF TURMOIL THE DISSEMINATION OF KNOWLEDGE IS CRITICAL FOR ALL, MY THANKS AGAIN AND I HOPE NOT INAPPROPRIATE FOR THIS FORUM, TO WISH YOU ALL, AND YOUR LOVED ONES A GREAT FESTIVE SEASON AND WONDERFUL NEW YEAR..
YOURS IN ENGINEERING,
GOLFPIN

 

[FeX32]

Cheers golfpin


"Simplicity is the ultimate sophistication." L. da Vinci
- Gian

 

[golfpin]

Hi Dyanatune,
have just reread your last posting and wanted to thank you for a great effort. It helps enormously for people like myself who think they know a bit about suspension geometry to be updated so to speak, am out of the design loop by quite a few years but appreciate and enjoy the effort that people such as yourself, and many others, who give of their time to explain.

Thanks again and all the best for the coming new year.
Golfpin RSA

 

[dynatune]

Golfpin,

Thank you for the kind words. As a "teacher" it does make a lot more fun to have "students" that are willing to learn ...

I have lived and breathed suspensions (and cars) now for more than 25 years and I had the fabulous opportunity when I was a starting engineer that I came to work for an "old" experienced engineer. Although the guy was close to retirement he was driven by passion for his job, he told me all his achievements and his biggest errors. I was amazed, like a baby in a candy shop. He was one of those people that wanted to share without "protecting" his position (not that anyone could be a danger) and I understood there that a pupil will always honor a good teacher and by now, I now that the greatest satisfaction for a good teacher is to see his pupil proceed into unknown territory. So this guy did for instance have a "library" of every article published on suspensions starting somewhere in the 50s of the last century and I was allowed to copy them all and read read read. What a time. He challenged me, making bets that for any question I could not answer I had to pay him a beer, for any question he could not answer I was offered a crate of beer .....needless to say that I did never win. From there on I did have the fortune to work on almost everything that had wheels on it, from a 40t 18 wheeler truck to an F1 car. So this little story is basically the main reason why you find sometimes replies here and why I did bother to write the dynatune software.

Cheers and a happy 2014 to all of you !!

Paul