16 replies to this topic

[Ali_G]

i know that raising the front wings will reduce downforce by reducing the front wings Ground Effect ability.

I can only understand ground effect a little. Is it that when the wing is close to the ground there is less chance of air getting under the wing to cuase a raise in pressure. Ie when closer to ground there is less space for air to come form the sides and inwards.

Please would someone explain. Mr Aerodynamistist maybe ?

[desmo]

The ground effect as regards the front wings in F1 is primarily due to the air below the wing being forced to accelerate by the physical constraint of the ground. The difference in velocity between the airflows above and beneath the wing determines the downforce generated.

Another side effect of the raising of the front wings besides reducing their efficiency will be to reduce pitch sensitivity allowing teams to increase the meager front suspension travel. This should help reduce the mechanical understeer that is inherent given the inch or so of travel neccesitated by the close proximity of the wings to the ground at present.

[Ali_G]

Oh I see now. Its that the ground will sort of grab a hold of the air above it and sort of even reduce the pressure below the wing even more. Finally i understand it properly. At other forums they would just repeat what you would have said. Nice One.

[redline]

Ground Effect - or surface effect - is a phenomenom that occurs when a wing is working in close proximity to a ground plane. The effect of this proximity is to alter the cross-section of the mass of air being worked upon by the wing (ie the span-wise distribution of lift/downforce) as well as increasing the effective span between the trailing (tip) vortices and thus increasing the effective aspect ratio.

This essentially means that the wing works more efficiently when in ground effect than when in the free stream - producing more downforce, without an associated increase in drag.

[desmo]

Is it just me or is that last post incomprehensible techspeak?

[MrAerodynamicist]

Originally posted by Ali_G
Please would someone explain. Mr Aerodynamistist maybe ?

You'll have to ask me when I'm back at uni and tuned into work mode Until then can you stick to beer and TV questions?

[Ali_G]

You don't really live up to your name do you.

[Richard Border]

desmo wrote:"Is it just me or is that last post incomprehensible techspeak?"


It confused me, but that's not hard.

I don't think it's properly called ground effect. Ground effect happens when a plane's wing gets closer than about one wing span away from the ground. The air under the wing isn't free to move downward away from the wing as it would if the wing was say two wingspans high, this causes a increase in pressure under the wing making more lift.

In the case of the wing on the front of the car, you have to remember the car is moving not the air,and the wing is mounted upside down compared to a airplane. The closer the wing is to the ground the harder it is for air to fill the space under the wing, the car's wing imparts a vertical movement on the air. Any horizontal movement of the air is caused by drag and is bad. If the wing's leading edge touched the ground AND you where going supersonic there would be a pretty good vacuum created. The cars aren't supersonic, (dah), so the low pressure under the wing does cause some air to move toward it. The air will try to come from the sides, the end plates work to limit that, from the back, the speed of the car limits that, and from the front, the opening between the ground and the wing limits that. So the closer you can get it to the ground the better.

[MrAerodynamicist]

Yep, there are two different effects that are referred to as ground effect - one is related to wings close to the ground that effects all wings etc. The other is only relevant to cars and is the downforce created by attempting to create a vacuum under the car that reached its peak in the 80's.

A cars ride-height effects the cars overall drag, at first lowering a cars rideheight reduces drag but there becomes a point where it starts to increase the drag. I'll try and post some figures tonight, from a book I'm reading.

[desmo]

O.K., it looks like I'll have to amplify on my original explanation. If you need a more in-depth version I refer you to an excellent article in the June/July issue of Race Tech magazine by Jonathan Zerihan. Here's a relevent snippet:

Basic aerodynamics dictates that air will flow around a wing, so as to generate a pressure surface and a suction surface. The velocity of the air is reduced over the pressure surface, but is increased over the suction surface. It is the pressure difference that exists between the two surfaces that gives rise to lift, or downforce, that a wing produces, although the suction surface is generally more significant in producing downforce than the pressure surface.

The effect of the ground is to constrain the flow in the low pressure region, between the suction surface and the ground. If the ground height is reduced, the effect is to increase the suction between the wing and the ground(represented by higher velocities), as the low pressure sucks in more of the surrounding flow. Bernoulli's principle relates pressure to velocity; a high pressure corresponds to a low velocity, and a low pressure (suction) corresponds to a high velocity.

To explain the ground effect, consider the distance between the ground and the wing. As the flow moves from the leading edge to about 20% chord ('c', the width of the wing in a fore & aft direction) it is accelerated due to the curvature of the wing surface. The distance between the wing surface and the ground does not vary significantly on this case (illustration shows an inverted airfoil at 0.4 chord height above the ground), along this part of the wing. For the small ground height (illustrating an airfoil at 0.2 chord height) there is an added effect from the ground. From the leading edge to about 0.2c (point of the wing with the largest cross-section e.g. nearest to the ground), the distance between the wing surface and the ground reduces significantly. This results in an additional acceleration of the flow due to the ground effect, as the flow is made to accelerate from the physical constraint of the ground.

Please find and read this article as it explains it better than I can without illustrations as well as raising some very interesting issues that merit further discussion.

MrA: Good to have you talking tech, I thought you had lapsed into beer and TV mode for the summer!

[redline]

I appologise if my previous post was incomprehensible - English is not my first language... Also, without the aid of diagrams its quite hard to explain.

MrA is right in saying that there are two ground effects - I was refering to the aeronautical term, applicable to a wing which is less than its cord length away from the ground.

In any case, Desmo & Mr.A subsequently explained it very well....

[desmo]

Redline,

I apologise as well. Your explanation made more sense after re-reading it a couple more times. I wish my French (my language which I studied in school) was half as good as your English. We Americans are famously inept at acquiring second and third languages as our rather insular culture makes it hard to apply them in real-world usage. The internet really is a help in this regard. If anyone knows of a French language F1 forum where I can practice I would be indebted.

[Vitek]

The explanation of ground effect makes a lot of sense - thanks Richard. Given this theory, however, why have Ferrari opted towards a nose cone design that has the front wing close to and the nose parallel to the ground? The nose is declined at about 10deg below horizontal compared to McLaren's 25deg (approx). Surely Ferarri's design would result in a larger volume of air finding its way underneath the car. I would have thought that, consequently, the front wing air flow would then separate such that part of it flows back under the front wing to equalise the low pressure, effectively reducing any ground effect. Just a thought.

[Ali_G]

I would guess that the high nose would send more Air to the Rear Diffuser which would give a more stable back. Its well known that Ferrari have the best front in F1 racing. So the High Nose must be doing something right.

[Richard Border]

Vitek:
I think the reason for less wing in the center is to get the air to "spill" off the wing moving in toward the car. The airflow between the tires and the body is unclear to me. I noticed that both F and Mc both have little endplates on the top edges of their nose sections. The endplates would keep the air from "spilling" off the nose helping add downforce. Behind the tires should be low pressure, so if you've got the air trying to go toward the center and down as it leaves the front wing it may continue on around behind the tire to fill that low pressure area. A picture of the cars on the wet might show how the air is flowing, but it may get confusing because the water thrown of the tires may not be following the airflow, water being 800 times as dense as air.

[Ali_G]

There is a sort of a wind breaker at the bottom of te nose buried deep in the car. Air from the underside of the nose is either thrown left and right and this would support the idea of building up the pressure behind the two front wheels.

Ali_G

[desmo]

This is referred to as the "splitter" and has been an integral part of every high-nose aero package. It's primary function is to take the air from beneath and above the narrower-chord inner portion of the front wing and force it beneath the car while increasing it's velocity. This, courtesy of Bernoulli's Principle, produces a significant portion (perhaps 30% depending on the set-up) of the car's total downforce.