More on electric cars.

No it's not. Why not stick to subjects that you know about? The silence would be refreshing.

Formula 1 balances many requirements of which aerodynamic performance is one component and downforce is one element of that component.

Oh. You have moved the goalposts AGAIN. You contention was that cars dint cause air pressure changes.

Largely because they are built like tanks

In message , "Dave Plowman (News)" writes

I should have said that it was auto, of course. Unfortunately I never did the same sort of driving in the 3 previous Omegas, all of which were far better vehicles than that last one. Maybe it was just a dud.

No I didn't. Anything which moves causes an air pressure change.

OK, so I'll dig it out. This google find me a Spit (of some sort or other!) has about 22 sq metres of wing area, and 2600Kg. So 26Kn/22 sq metres ~= 1.2kPa. Or just over 1% of an atmosphere.

Boyle's law will give you a similar compresssion. Shall we say 2% at peak, seeing as it isn't the same over the whole wing?

Wind pressure with a wind speed approximating to motorway speeds seems to be about 0.5kPa. Even less.

I really think you won't notice.

Andy

So far so good

So 26Kn

I think you missed out the ability of a spitty to pull 6 g in a turn

So thats 25497.29 * 6=

/22 sq

so abiout 7% of an atm,ospere

More like 15% when pulling hard..

well you would actually. Since a car is not a very aerodynamic device

Wings are designed to be low drag high lift devices. Cars suffer from form drag.

In essence the way to understand this is as a pressure differentual between the front and the back: the lack of laminar flow at the rear where the flow breaks into vortices at high reynolds numbers creates a partial vacuum behind the car and the compression of the air in front creates a pressure rise.

The difference is the drag

Ah but a ship is weightless because its weight is in equilibrium with the water it displaces. Otherwise it would sink...

On a related topic, how come the small bit of tyre that touches the ground can support a van? There might be 40psi in the tyres, but multiply that by the area of tyre touching the road and it doesn't seem to come to much. It must do though.

Time for a snooze I think. All this hard thinking is beginning to hurt.

Bill

It's lucky it's a function of speed or when you jumped into a rowing boat it would shoot to the other bank and get stuck in the mud.

Bill

Well you wouldn't be allowed to anyway. The driver would be hopping mad.

Bill

And when they flex the two sides rub on the road in opposite directions, so that's friction.

Bill

Only an infinitely hard wheel on an infinitely hard road would waste no energy on deforming the road or the wheel.

Bill

Well there are 4 tyres.. so if the van is two tons that's 1/2 ton per wheel. say 1000 lb each wheel. and at 40 psi that's 25 sq in per tyre.

that's only 8x3.125" and a van tyre is easily 8" across

no you wouldnt.

What ARE you talking about. The sidewalls don't touch the road.

No, its simple stupidity.

deformation is not friction. Nor does it cause it.

I agree with you: That is not what we were talking about.

To repeat: at low speeds the major drag on a car is due to rolling resistance which is 90% or more about tyre deformation, not friction.

I don't see why this is so hard to grasp.

Then buy an Ampera

Electric makes most sense with short range microcars. Microcars use less en= ergy per mile, reducing battery weight and cost for a given range. Short ra= nges only mean a major reduction in battery cost and weight, and thus again= energy use. So if you live on the edge of town and only want the car to he= ad into town and back with, and you're not getting out of 30mph zones, a le= ad acid mcirocar can make sense to an extent. But only if you're ok with it= s various downsides. Such a beast can be homebuilt cheaply, but with all th= e issues it won't suit many people.

Full size electric cars don't make good sense today. Maybe they will with s= ome as yet unknown battery technology that combines low cost, weight and ch= arge time.

NT

Long time no hear dribble... what brings you back?