rjsa wrote:But wouldn't the floor/track opening choke at a given speed/tight entrance combination? Then it would be like you had some kind of skirt sealing the air entrance?
The step from the plank to the rest of the floor (step-plane) makes that pretty much impossible.
And a mass-flow choke can only happen for sonic flow.
What I want to know is this. If the pressure is so low under the car, what causes the floor to move up?
In the article it mentions that they test the floor for deflection but they did not say in which direction.
Do they just a big ole hydraulic ram and compress the middle of floor upwards?.. Or do they just bend the front spoiler or the step plate edges up and down (like a loaded cantilever)?
All it said was the floor moves up while racing, but no mention of the motivation of the floor.
Article 3.17.4 of Formula One's technical regulations states that no bodywork, such as the floor, can deflect more than 5mm vertically when exposed to a 500 Newton load upward.
kilcoo316 wrote:Simply the car pushing the plank into the ground under either aero load (simple high speed), or pitch (braking).
But would floor produce downforce if there's no ground clearance?
Maybe it is local pressure maximum at the front of splitter that pushes it up? That way the amount of air going under splitter will regulate itself.
timbo wrote:But would floor produce downforce if there's no ground clearance?
Yeap. The local section in contact with the ground (the plank) won't, but the area immediately around it will.
If you can, have a look at the back of the plank on a current car - the boat-tail gives away alot of information on where the designers are concentrating on getting their downforce from.
timbo wrote:
Maybe it is local pressure maximum at the front of splitter that pushes it up? That way the amount of air going under splitter will regulate itself.
Pressure acts normal to a surface.
To have the ram effect pushing the splitter plate up, first the splitter plate must have its leading edge higher than the trailing 'edge' (pivot line effectively here)... which would mean it is deflected up before the force deflects it up can be brought to bear...
chicken and egg.
I don't see it happening myself. Which is why I disagree with the whole idea of it curving up to stall the diffuser.
kilcoo316 wrote:Yeap. The local section in contact with the ground (the plank) won't, but the area immediately around it will.
If you can, have a look at the back of the plank on a current car - the boat-tail gives away alot of information on where the designers are concentrating on getting their downforce from.
But the flow under the body would be less and therefore the net downforce would be less.
I guess this is how they limit downforce in high speeds then? You have steeper angles to get more downforce on medium speeds but at high speed the splitter is touching the ground and downforce is limited?
timbo wrote:But the flow under the body would be less and therefore the net downforce would be less.
It is really the exit area that determines the massflow rate under the car, not the entry area.
timbo wrote:
I guess this is how they limit downforce in high speeds then? You have steeper angles to get more downforce on medium speeds but at high speed the splitter is touching the ground and downforce is limited?
Change that to rake angles and your getting there.
More rake = more downforce
Under braking especially, the splitter will be down to the ground, but the diffuser up off it - getting more downforce from the diffuser - helping to balance the front wing's added downforce due to it being closer to the round.
timbo wrote:
One question, though. How far ahead is the plank?
Ahead of?
I reckon the splitter plate is around half a metre ahead of the sidepods...
timbo wrote:But the flow under the body would be less and therefore the net downforce would be less.
It is really the exit area that determines the massflow rate under the car, not the entry area.
Limits or determines?
Under braking especially, the splitter will be down to the ground, but the diffuser up off it - getting more downforce from the diffuser - helping to balance the front wing's added downforce due to it being closer to the round.
timbo wrote:
One question, though. How far ahead is the plank?
Ah, that is interesting. That way you can further tune aero-balance.
Ahead of?
I reckon the splitter plate is around half a metre ahead of the sidepods...
But that is just a rough guess....
My question mainly is plank protrudes as far ahead as the splitter.
As fas as I remember (I may be wrong of course) the plank is at full length of the floor. And that means that even if the floor flexes it still would scrape the ground.
Well - the massflow rate will change with ambient airspeed till there are sonic conditions somewhere.
timbo wrote:Ah, that is interesting. That way you can further tune aero-balance.
Its what separates the great cars from merely the good.
My question mainly is plank protrudes as far ahead as the splitter.
As fas as I remember (I may be wrong of course) the plank is at full length of the floor. And that means that even if the floor flexes it still would scrape the ground.
I think the plank is roughly up to 1 wheel radius behind the front axle-line.
F = mu*R
Where:
F is frictional force,
mu is coefficient of friction
R is reaction force of surface to object
By allowing the plank (through its associated supports) to bend, the reaction force of the ground is significantly reduced, reducing the amount of real friction on the plank, and hence plank wear.
It is routine and common knowledge to setup up a car's ride height to the lowest point possible. This "lowest" point is when the front plane of the floor (in this the "chin" spoiler) touches and skips on the ground underbraking. Banging the plane on the ground would cause damage and wear to floor, and is too low for running the car. This is the physical limitation of ride height.
The movable ground plane allows this skipping to take place with a lower ride height than without it moving and would be physically not possible without damaging the undertray.
"Stalling Diffuser"-
Geometry of the suspension and attitudes that the car can move into, whether in squat, dive, heave, warp, roll and any or all combinations, on a stepped bottomed car will always provide an air flow to the diffuser UNLESS the design of the floor and diffuser is way off. (Though the pace of the car would render it very uncompetitive) Even if the plank (lowest point of the floor) made full contact with the ground completely along the entire floor, the diffuser would not only still recieve air, it would actually become highly efficent, and increase the size of the throat low pressure areas and further the effect, with less air acting on it but also with less intervention of turbulent air (high pressure) able to get into the side gaps of the diffuser.
Though if the car maintained a very high ride height, the diffuser would cease to create a strong low pressure area in it's throat (it would still exist though it's size is greatly reduced, and along with the reduction, lift would dominate the bottom of the car), the diffuser would return to it's truest state of being a diffuser in a windtunnel instead of a downforce enhancer and fill to capacity with high pressure air. The vortices created out the back would increase in size, due to the "full" capacity of high pressure and created/ added vortices and turbulent air at the gap created and the "full volume" of high pressure air in the diffuser with increasing, "uncontrolled" high pressure directly below the the diffuser, due to packing.
Add one more element to this, the intrusion of the rear wheel pumping more air underneath (in a lateral direction) and ultimately attempting to enter a full diffuser.
Now for 100 dollar question, the diffuser is now acting..like a diffuser (one in a wind tunnel), and has only lost most of it's ground effect properties and along with it the ability to scavenge out the high pressure under the upstream floor and now directly under it also.
This device has not stalled, but lost most of it's ground effect and scavenging properties and returned to the life that gave it, it's name. It is still returning the air to the headwind speed.
If this were a wing (it isn't), it would stall with the high pressure that is present and the vortices and turbulance that is created in this condition. Though a wing would also stall, in a diffuser's correct position,close to the ground and still full of slowing velocity and gaining high pressure. This can't happen on the lower surface of an inverted wing and is a stall condition.
To stall a diffuser, on a stepped floor car, IE- you have to stop air getting to it, and this means stopping the air flow completely. In the geometry of the suspension, this means parts of the chassis would have to achieve a below ground posture, which would be possible in a gravel pit and I suppose if it dug into the asphalt or yaw, beyond the slip angle of the tires OR take to flight.
Lastly, a completely flat bottom car with diffuser, that has completely bottomed, and sealed the sides of the diffuser to the ground, is now in stall conditions, though even here, and the above paragraph, the car is no longer "maintaining the highest possible acceleration in the appropriate direction"-- Peter Wright, Lotus...
"Driving a car as fast as possible (in a race) is all about maintaining the highest possible acceleration level in the appropriate direction." Peter Wright,Techical Director, Team Lotus
Anything is wrong in the picture?
