Centre of gravity and downforce

[kensaundm31]

Does the centre of gravity of an f1 car effect the downforcel level?

So would a car with a lower c.o.g. have more downforce?

I want to know because someone said 'a higher centre of gravity will not affect downforce, the two are not related.'

when I said I thought that KERS cars will have less d/f because of higher cog.

[Jersey Tom]

Directly, it has zero impact. If you ran two cars in a wind tunnel, one with a high CG one with a low CG, it would make no difference.

However, lower CG will give you smaller rolling and pitching moments in reaction to inertial forces at the track.. and possibly lead to better orientation control of the aerodynamics of the car, and more average downforce accordingly.

[DaveKillens]

Jersey Tom is correct.

I believe the confusion arises because both have a direct influence on cornering performance. It's just like some people confusing zero gravity with air, and believing that if you have no air, you have no gravity (and vice versa). Hey, truth, I know people like that.

[bettonracing]

Both JT & DK are correct. However, the DDD requires some parts (rear of gearbox) be moved upwards to create space for the diffuser, indirectly coupling CofG with downforce.

One could use similar argument to say that two identical ground effect cars with different ride heights (& therefore CofG) could have downforce as a function of CofG height.

To reiterate what JT mentioned, the relationship is not direct.

Regards,

H. Kurt Betton

[Belatti]

Lets define Downforce first. To me it means this:

Downforce is the force applied to the wheel hub and comunicated to the ground via the tire in the direction to the ground.
It is composed by:
1- vehicle weight (proportional to vehicle mass)
2- aerodinamical loads
3- weight trasference (longitudinal while braking/accelerating and lateral while cornering)

While point no.1 only contributes to downforce, points no. 2 and 3 can go up or down, increasing or decreasing total downforce.

Jersey Tom was talking about point no. 3 but missed the fact that you can neutralize rolling and pitching moments with suspension geometry configuration.

Yep, a car with a higher CoG can pitch and roll less than a similar car with lower CoG if you change suspension geometry! However this "anti" features are not that good because they bring other issues.

The main contribution of a Lower CoG is to decrease the weight transference and so have a more even downforce in all the wheels.

[kensaundm31]

Thanks for the info guys.

So will the KERS cars have more pitch/roll than the nonKERS or will they compensate with springs/bars. Does this compensation force them to compromise on the most efficient setup.

Also how does KERS affect the brakes, because On an ITV segment they said it took power from the engine.

[Belatti]

I think that the KERS issue is that it does not only affect the CoG but the weight distribution. Cars with KERS can no longer distribute ballast to the front or to the rear depending on their setup needs.

This problem will be reduced with mandatory KERS in 2010 but still remaining the "driver weight issue".

I´m still wondering if Alonso didnt carry the liter of drink in Bahrain to save an extra Kg and add it to the ballast.

[RH1300S]

Thanks for the info guys.

So will the KERS cars have more pitch/roll than the nonKERS or will they compensate with springs/bars. Does this compensation force them to compromise on the most efficient setup.

Also how does KERS affect the brakes, because On an ITV segment they said it took power from the engine.

Yes, it will compromise the setup as they will have to run stiffer whatever to compensate - which has an effect on mechanical grip. Also a raised CofG affects mechanical grip.

Belatti is right in that (with the current weight limits) - having KERS limits how far teams can play with fore/aft weight distribution to optimise tyre use.

But you question was about CofG & Downforce - Tom was right on the money with his answer

[RacingManiac]

Lets define Downforce first. To me it means this:

Downforce is the force applied to the wheel hub and comunicated to the ground via the tire in the direction to the ground.
It is composed by:
1- vehicle weight (proportional to vehicle mass)
2- aerodinamical loads
3- weight trasference (longitudinal while braking/accelerating and lateral while cornering)

While point no.1 only contributes to downforce, points no. 2 and 3 can go up or down, increasing or decreasing total downforce.

Jersey Tom was talking about point no. 3 but missed the fact that you can neutralize rolling and pitching moments with suspension geometry configuration.

Yep, a car with a higher CoG can pitch and roll less than a similar car with lower CoG if you change suspension geometry! However this "anti" features are not that good because they bring other issues.

The main contribution of a Lower CoG is to decrease the weight transference and so have a more even downforce in all the wheels.

Downforce to me is aerodynamic load. I call the 3 things you mentioned "Normal load" at the tire contact patch, meaning the vertical force applied to the tire by all the means mentioned. C of G height does not affect aeroload in direct relation. It could be due to secondary packaging relation that allows you to have more or less downforce, but thats exactly it, it could be more more or less. Take RBR for example, with the pull rod it "might" have a lower CofG, which gives it less diffuser volume, but it "might" have a more effective rear wing that gives it more downforce because of the lower rear deck height. Just like Brawn might have more downforce because of the possibly higher C of G because they moved some components higher to get a more effective DDD, but might lose out on the effectiveness of the rear wing. Key difference between downforce compare to other normal load, is that it has no inertia or mass associated to it(aside from the mass added from aerodynamic devices, but in a weight limited formula, it means nothing), which gives you the benefit of added normal load on the tire(which tire likes, up to a point), without the problem of accelerating mass.

No one here is saying that C of G height does not effect how the car handles, because that would be a silly thing to say, but to answer the question posted, it does not meaningfully affect downforce.

[RacingManiac]

Additionally, the whole deal of Push/Pull rod and their relation to CG height, thats not set in stone neither. Since you also don't know how much ballast they run comparatively and where they are located. You can have push rod and if you have enough to ballast the car low enough your vehicle CG will be low still....so moot point again...

[kensaundm31]

So if the KERS energy is derived from the inertia of the engine under braking, how does this affect the brakes, because I thought it made the brakes harder to manage.

Also, next year when all the teams have KERS I would have thought all the drivers will be using it at the same time so it will be invisible.

Seems like a lot of money and effort to maintain the status quo.

I would have thought that when KERS is 'bedded in' the major differentiating factor will be rear-end traction, so the quicker the rear is planted, the earlier you can press the button.

[RacingManiac]

Think of brake as taking away energy as a form of heat, and that normally as you brake, you heat up the brake disc and the dissipate that heat in air. With KERS, instead of heating up the brake disc, you take the energy of the rear wheel, which as you braked it is not receiving power from the engine(relatively), and is spinning under inertia(of the wheel, the engine and the vehicle), and you use that through the drivetrain to back drive a eletric motor to charge the battery(or a flywheel). The energy that would otherwise be dissipated as heat is now being stored into the that storage medium. And when you deploy KERS, the process reverses and the additional energy aside from pure engine power goes into propelling the car.

How it would affect braking, I think, is that because there is a physical limit as to how much KERS can store(limited by rule), that because it shares part of the braking capacity of the vehicle, and it acts only on rear axle, that it will shift brake balance when it does take energy away from the drive axle. And then when it is full, it does not take that energy and you ended up having more front bias than you might have wanted. Now according to that Mercedes/McLaren KERS article, it takes only about half a second to charge the full capacity. I wonder, at the end of the straight, when say the driver have used up his 6.6 sec, and KERS is empty, and when he gets on the brake, for the first 0.5 sec KERS charges, then it stops, what happen to the car's brake balance?

[jmfdvm]

Hello, I am new to the site and not an engineer but there is an interesting aspect of the flywheel KERS that I have not seen addressed anywhere. I don't think this applies to the Williams electromagnetic flywheel but it could apply if the system were designed to do so. And, if it does apply no one at Williams would admit it...

With the flywheel placed in a horizontal axis rotating clockwise, it will create "Downforce" due to downward vector of angular momentum. If the flywheel has enough mass, the "downforce" created by this effect would create a scenario where downforce could be varied independent of forward speed, aerodynamics, and ride-height. Somewhat akin to the "vacuum cars" or a moveable wing which were regulated out of existence. Underbraking, the flywheel would speedup and increase "downforce" at a time when it is presumed to be desired, e.g. moving into a corner. When the KERS is activated, the flywheel transfers its rotational energy to the drive wheels and therefore the flywheel slows down, reducing its angular momentum and consequent "downforce" effect in the straights where downforce is not needed.

If this system were developed sufficiently, a team could vary the angle of the flywheel axis such that it was slightly off vertical thereby creating a vector of angular momentum primarily down but slightly in any direction they want. It would need to be at a fixed angle thru an entire race, but not necessarily the same from track to track. This would offset the disadvantage of having a higher center of gravity and potentially replace some of the adjustable ballest weight.

I looked thru the rules and did not see anything addressing use of KERS as a means of altering "Downforce" or center of gravity. They only cover how much energy may be used to create forward acceleration.

Any thoughts?

[Jersey Tom]

With the flywheel placed in a horizontal axis rotating clockwise, it will create "Downforce" due to downward vector of angular momentum.

It will not create downforce.

Nor would the angular momentum vector be downward.

[xpensive]

I think JT has a strong position here, the way I humbly understand things.
An elevated CoG, would only shift the reaction force from inner- to outer wheel?