Overcut sidepods?

[timbo]

So, we've seen RB using ducting to transfer air from around the sidepods to prevent it from interacting with exhaust flow. Wouldn't it be better to create a sidepod with low outer edge and little undercut so that air is moving above the sidepod edge along the desired exhaust flow route? Something like 2011 McLaren sidepods, but not in |_||_| share, but rather _||||_ if you get what I mean.

[turbof1]

If I am right they don't do that because that air above the sidepod is dirty (influenced by the tyres).

[Kiril Varbanov]

If I am right they don't do that because that air above the sidepod is dirty (influenced by the tyres).

The air above the sidepod is not dirty because it's influenced by the tires. The tires flow essentially goes away (outside) and up. The sidepod flow is affected by the front wing's main plane. Even a small incorrect adjustment of the AoA on the front wing robs your sidepod flow as there's lot less air passing by, thus creating high pressure zone. Teams try to overcome this with the small vertical fins called Vortex generators, which are there to re-energize the boundary layer, where the particles velocity is 0; or with downwash wings a la Mclaren and Red Bull.

Personally I didn't understand what exactly the OP meant, perhaps a bit of elaboration would help.

[stfn_ger]

Personally I didn't understand what exactly the OP meant, perhaps a bit of elaboration would help.

If i got it right he meant a shape like on the 1991 Lamborghini 291. The chance that i got it right is only 50% though.

[godlameroso]

It doesn't work because the undercut increases the relative pressure on the chassis on the top side of the car, this leads to increased downforce as evidenced by the turning vanes and little flick ups along that part of the floor. You want that undercut, otherwise you would be throwing away some potential downforce.

[shelly]

Overcut sidepods have beenn widely discussed last winter on this forum iirc, posting pictures of the 1991 Lambo.

With regard to overcut, the rebul rb6-7-8 was the car showing the widest sidepods, with the wider part of them touching the outside edge of the floor.
This is a very interesting feature worth discusssing in my opinion.

[timbo]

Personally I didn't understand what exactly the OP meant, perhaps a bit of elaboration would help.

If i got it right he meant a shape like on the 1991 Lamborghini 291. The chance that i got it right is only 50% though.

Well, you've got the idea right, although the configuration has to change somewhat due to side-impact protection.
Imagine a cross between this and 2011 McLaren.
The point being that it seems like there's excessive airflow around the sidepods that necessitates use of the ramp. If less flow is guided around undercut more can be sent above to improve exhaust flow stability and brake-duct DF.

I'd try to draw a picture.

[timbo]

So here it is, please forget the quality of my cellphone photo and my shabby drawing skills (damn I could draw pretty well, didn't do that for years though )

[DaveKillens]

It's a novel idea, but it completely ignores why the sidepods have undercuts, and the way it's presently shaped.

Most of the downforce is generated by the underbody, so it's still a critical design element. After the tragedies of 1994, the FIA moved to control the height of the car and the size of the underbody. Design refinement became more relevant, and the designers went hard to work maximizing the underbody. The broad concept is to produce a zone of low pressure under the car.



But the cars of that era had sidepods relatively straight from top to bottom. And in order to maximize the low pressure under the car, they had to address the leakage flowing down the sidepod and under the body of the car. Skirts had been banned, so a different solution came about. The sidepods gradually adopted undercuts, and the sidepod took on a coke bottle shape.



What happened was that the air was accelerated around the sidepod, creating a low pressure zone. That was beneficial, because having a low pressure zone directly above the underbody drastically reduced the leakage under the body.Now one other element is that the edges of the underbody are sharp edges. Anyone familiar with airflow is that air just loves flowing over a rounded curve, but hate a sharp edge. That sharp edge inhibits the air from flowing downwards.

Many elements of the car, from the rake to diffuser to shaped sidepod are there to seal off the underbody and create a low pressure zone under the car.

[Absolutelee]

Forgive my non-engineer mind, but I have always wondered something. I follow you about the undercut sidepods creates a low pressure zone between the sidepod and floor and helps seal the underbody...I get that, but does that low pressure zone create lift on the floor? Or does this not happen because the pressure under the floor is even lower?

[shelly]

@dave killens: I partly disagree with you post. The undercut was first proposed by ferrari in 2003. Its origin traces back to the notorious atempts at double floor in 1992 f92a and 1996 f310.

Migeot has said that the spread of the undercut vindicated his 1992 double floor idea.
The undercut reduces losses along the low part of the sidepod: less acceleration, higher pressure, lower losses in decelerating in the coke bottle.
The idea of having a low pressure over the floor edge, which you attribute to the undercut, is instead in my opinion what's behind the overcut solution adopted by redbull in the last 3 years.

PS The coke bottle concept is just partly linked to the undercut concept, and it dates back to Durand, 1984 (not barnard's idea iirc).

[godlameroso]

Remember if the pressure drops on the top side of the vehicle you get positive lift, which is the opposite of what you are trying to achieve. You're not creating low pressure so much as you are exploiting a difference of pressure, it doesn't matter the shape if there's more pressure on one side than the other the tendency is for the high pressure to flow towards the low, the greater the difference the greater the tendency.

[DaveKillens]

I'm not going to disagree on the history, what to me is relevant is what's happening right now. The waisted sidepod, sharp floor edges, and undercut is there to assist in sealing the edges of the floor from leakage, which is vital in generating underbody downforce.

[timbo]

I'm not going to disagree on the history, what to me is relevant is what's happening right now. The waisted sidepod, sharp floor edges, and undercut is there to assist in sealing the edges of the floor from leakage, which is vital in generating underbody downforce.

The undercut was adopted to channel as much good-quality air over the diffuser. However, you can see that RB8 has ducts that channel some of this air away. On Sauber the shape of the sidepods is actually a step away from classical coke-bottle. McLaren/Ferrari-type exhaust solutions have ducts in the coke-bottle area which was clean at previous years. So, apparently, there's no need for that much air with current diffuser/exhaust rules there. What if we channel some of it over the sidepods to the exhausts/diffuser?

@ godlameroso that's true, but if look on F1 car there's a bunch of lifting surfaces anyway. If a body creates some lift but makes diffuser more efficient to offset that lift, then all is good.

[PlatinumZealot]

You mean remove the undercut at the rear of the side-pod or the undercut at the radiator inlet?
The RB5 had no undercut at the back.