Vertical CG? Not quite sure what you mean. Do you mean height of the CG?xpensive wrote:Since the traction thread, I have wondered about the front/rear distribution of contact-force between tyre and surface.
This should of course be dependent on acceleration, positive or negative, but also on the location of vertical CG.
Does anyone have an idea of where this is and how it changes with fuel-load?
only fuel loads above 135mm height would rise the CG.So anything more than around 30%of total fuel capacity filled into the car would seriously affect the cornering abilty of the car whereas everything below this would actually lower CG height but at the expense of added weight.So to my mind the best design for the fuelcell would use the maximum allowed planeview area to keep the maximum amount of fuel under or close to those 135mm...to optimise tyre use.This is in my view one of the areas where you have to decide a compromise aero vs mechanical in the 2010scarbs wrote:I would say the dry CofG is somewhere between 100mm & 165mm (say 135mm..?). The 100Kg of fuel over the 600Kg chassis would have an impact (with its own CofG at approx Z300mm), would only raise the total CofG by 15-20%
I doubt vertical (Z) CofG is as high as the wheel centres. No Tech director has ever given me much of an insight into its position. Some vague reference to being around the crankshaft centre height in the early noughties, but probably much lower now.
Some assumptions (Ignoring fuel load, ride height which is a few mm at most and all but zero at speed). The wheel centres are at Z330mm, less than half way up the car, the cockpit opening at just Z550mm. Excluding the roll structure there is precious little structure above this point and lots of heavy bottomed parts and ballast at zero height. A monocoque being around 80Kg with probably half that again in ballast at zero height.
The engine (100kg) and gearbox (30Kg) total height is no more than 300mm. Assuming the gearbox CofG is some way in between the gear shafts, the high diff being offset by the ballast low down (input shaft at Crank centre line Z58mm and output shaft 85mm above that) giving an approximate CofG height of Z100mm, then the engine CofG is mandated in the rules at Z165mm.
I would say the dry CofG is somewhere between 100mm & 165mm (say 135mm..?). The 100Kg of fuel over the 600Kg chassis would have an impact (with its own CofG at approx Z300mm), would only raise the total CofG by 15-20%
This sounds like sound logic for a rigid body. The COG height won't affect the reaction force. However i think when the vehicle pitches from the reaction (non rigid body, with suspension movement) then the height would be a factor.DaveW wrote:A simple "thought experiment":
Suppose a vehicle has its rear wheels driven directly via drive shafts by an electric motor attached to the chassis. Suppose that the electric motor is constrained laterally, vertically and longitudinally, but is allowed to rotate about the drive shaft axis (I know, but this is a thought experiment). What will happen when a current is applied to the motor?
My mind suggests that the wheels will start to rotate in one direction, whilst the motor will start to rotate in the other. If that is correct, then it suggests that the act of constraining the motor's rotation relative to the chassis will cause a torque to be applied to the chassis, which must be reacted at the contact patches. The reaction loads appear to be independent of the height of the centre of gravity, & hence must be independent of changes in the contact patch load distribution caused by accelerating the chassis.
What is wrong with my logic?
BTW my logic implies that a fundamental difference exists between outboard & inboard brake installations (I think).
