Legal ground effect?

kilcoo316 · Post 27 Jul 2005, 19:02

"Why are the noses raised than? "

To direct air around the sidepods and over the diffuser

manchild · Post 27 Jul 2005, 19:51

The raised nose does not necessarily send more air under the flat bottom - to look at it, there is often a projecting shelf at the front of the floor I can visualise air forming high pressure on the top surface of this. Is'nt the high nose about managing air to the sidepod intakes and then around and over the sidepods (i.e. you get a cleaner flow into the intakes and also back to the ever important rear wing)?

I think, that "shelf" at the front is there due to regulations not because it was invented by designers...

More air does not mean lower pressure, faster air does (EDIT: which is what Dave said - I was typing this while he posted!). Sending too much air under could easily slow it down surely?

I agree, but if can let more air out than can be brought in than that is a plus to downforce.

Or, to put it another way, you want more air out than in..........

manchild · Post 27 Jul 2005, 20:01

kilcoo316 wrote:"Why are the noses raised than? "

To direct air around the sidepods and over the diffuser

We obviously don't agree about this one... When high noses were introduced it was only to provide more air under the car (that was before plank was imposed and rear end downforce "killed").

Directing air "around" the sidepods is not what I believe high nose is doing better than low nose. If you want air flowing more sideways than why bring it to the middle of the car and split it there instead of splitting it on the very front end of the car?

Same goes for directing the air "over" diffuser. I don't get it...

RH1300S · Post 27 Jul 2005, 20:33

Don't confues the "shelf" with the little mirror plates that the regs required.

I just don't buy the idea that a raised nose is to shove more air under the car (I'm just being stubborn here

). It's easy to visualise a whole chuck of it coming of the front wing, then almost being lifted as the chassis rises - surely much of that mass of that air will go to the sidepod intakes and then be directed (squeezed between the pod & the barge boards) around the side. Certainly some goes under, that's the nature of the beast - I just don't see why you would encourage more. As long as the back end is working (getting boring - sorry) whatever it needs will find it's way there and be accelerated across the underside.

manchild · Post 28 Jul 2005, 08:49

Just wait until Max bans diffuser from 2008

StiK · Post 28 Jul 2005, 17:37

Less air under can mean less pressure because if you have less air for the same volume the density is lower.

Apex · Post 28 Jul 2005, 21:11

From a static point of view - then less air in the same volume means means a lower pressure. But you have to consider the velocity!

I think that there is a really simple example to explain this:

If you have large scoops that try to force the air into the diffuser then: The scoops increase drag due to their size
Because the diffuser is not sealed there is a maximum flow rate that you can cram under the car before the air just flows out the sides.

If you have very low down entry then:
The boundry layer on the road will esientially prevent 'any; air from flowing, which causes the low pressure.

So we need a compromise between letting enough air in, and waisting the air by it spilling out the sides - the wasting causes more drag

kilcoo316 · Post 29 Jul 2005, 19:41

manchild wrote: We obviously don't agree about this one... When high noses were introduced it was only to provide more air under the car (that was before plank was imposed and rear end downforce "killed").

Directing air "around" the sidepods is not what I believe high nose is doing better than low nose. If you want air flowing more sideways than why bring it to the middle of the car and split it there instead of splitting it on the very front end of the car?

Same goes for directing the air "over" diffuser. I don't get it...

High noses laterally splits the airflow cleaner, sure if they wanted to put the airflow under the car, they wouldnt have a splitter, but drop the monocoque to the ground at the front of the current splitter plate.

The reason its not split on the front of the car is yaw.

manchild · Post 18 Aug 2005, 14:35

After seeing pic. of bottom and diffuser on RBR I started questioning my own acceptance of comments that suggested that diffuser couldn’t bare with more air fed into it and that it only works by sucking the air flowing beneath the plank/middle of the car.

This picture shows that RBR diffuser on high downforce circuit is actually partially closed below and opened sideways in order to suck the air flowing beneath the sidepods! If that is the case than it means that diffuser can suck out much more air than plank area provides. That is why I started questioning comments suggesting that more air beneath the sidpods would choke the diffuser…

manchild · Post 18 Aug 2005, 15:29

First drawing shows approximately what the situation on that RBR photo is. Second drawing shows my questioning what the situation would be with even more streamlined stepped floor.

DaveKillens · Post 18 Aug 2005, 18:27

Maybe you need to examine this underbody from a different perspective. You appear to want to make it more streamlined.... and that is possibly in opposition to the goals for the underbody.
The diffuser exists to create as powerful a negative pressure area as possible. If you attempt to "clean it up", you're probably reducing the drastic negative pressure desired in that part of the bodywork.

manchild · Post 18 Aug 2005, 19:01

I was suggesting more streamlined shape having in mind how it looks on RBR... What I'm trying to say is that it looks to me that they've already streamlined it as much as the whole engine/gearbox assembly allows?

manchild · Post 12 Jan 2006, 10:13

Here is finally much better evidence that diffuser doesn’t suck the air below the plank (middle of the car) – it sucks the air that flows under sidepods (sucks sideways). So, enabling more air to get under sidepods at front makes sense?

Williams FW26

Monstrobolaxa · Post 12 Jan 2006, 11:29

Hummm.....you're forgetting one thing!

Most of the downforce isn't really created by the difuser! Most of the downforce is actually created in the mainplane area....after the inlet!

Try to find a copy of "Racecar Engineering" - April 2004, Vol14 No 4 - in the Aerobytes section it's all explained.

The thing is that the air is sped up in the inlet area, a convergent venturi. Basicly it's like this:

\__________..... (this represents the inlet....in the "RC Eng" I suggest they try diferent angles for the inlet to show the variation in downforce.

The acelerated low-pressure air flows through the mainplane area....the horizontal part of the difuser....being at low pressure creates downforce due to the higher pressured air flowing over the car.

Now the difuser is an area that has a divergent venturi, where the low-pressure-high-flowing air slows down and expands. The slowing down mechanism is aimed to put the air from under the car at the same speed as the air above the car in order to reduce vortexs behind the car...basicly to reduce pressure drag. The expanision mechanism is aimed at reducing the pressure of the "slowing down air" in order to "suck" and speed even more up the air in the mainplane section. (you can confirm this in the book: "Competition Car Downforce" - Simon Mcbeath

Front of car (inlet) \______mainplane______// rear (difuser)

Made is simple it's more or less like this!

Now concerning your moving floor.....

Well due to the low pressure under the car it would tend to pull the floor to the ground and not pull it up! So you'd need a mechanism that pulled it up! Now there are 2 things in the regulations that in my point of view deem it illegal....first having that mechanism would make it a moving aerodynamic device....(illegal).....and also in the regulations it's mentioned that the floor of the car has to be flat....so moving it would make it....not flat!

Besides that the way I look at it....opening the inlet and giving the air more a bigger area to flow to would basicly create some lift and not the desired downforce. I can't find a pratical example to explain it! (probably someone else know what I'm talking about...so can try to explain it better).

Let's give it a go....think of your road car as an aproximation of an airfoil! Why don't you instead of having the front like this |_O__.... why don't you try changing it to something like this \__O___....at the same speed you'll see that your CL has changed....and has grown! So for the same speed you'll have more lift!

manchild · Post 12 Jan 2006, 11:35

No, I'm not into discussion about my idea, just wanted to point out that situation is different that as it was suggested by some forum visitors. Suggestion was that there is no point to get more air under sidepods since diffuser is fed only by air that flows below the plank (middle of the car).