SW20 aero theory. (56k = if u patient)

[RomanV]

Hi there folks.

I have heard a bit of discussion here and there, about SW20s generating
lift at the front, at high speeds. (noticable at 80+)
Some suggested that a deeper front lip helps alleviate this.
However, surely the difference is minimal, compared to rerouting the
path that the radiator air takes. If you look at the radiator
arrangement, it is... weird. The radiator itself is slightly leaned back
at the top. The air flows in at the front or the car, gets pushed
through the radiator, and then pushed out straight under the car. If you
look at the cross sectional area of the radiator, compared to the
larger lip, it is a huge difference. Plus, Wouldnt the lip just be
scooping more air up into the radiator anyway? Which goes straight back
under the car.
I have seen a few MR2s that cut a hole into the front area where the
spare wheel is. Then, they vent the air up through the bonnet, over the
top of the car.
This is actually a very clever idea! the air moving upwards creates
downforce on the front, as well as reducing the pressure of the air
under the car.

It is also a good idea, because it is REDUCING lift, rather than
creating more downforce, to counteract the lift. As you may be aware,
both lift and downforce create drag. If you add a wing or whatever to
the front, you are increasing the drag created to produce downforce, but
not addressing the actual problem.
At first when I saw vents on the front bonnet of an SW20, I thought it
was just 'wank factor'. How wrong I was!
This is how almost all other mid engined cars vent the radiator air. (see
a lotus elise, ferrari f40, etc.)

Its just something I have been pondering for a while.

I have run a cross section of the SW20 through my wind tunnel simulator.

After 3 days of number crunching and calculations, this is what my super computer spat out.


Now there are some interesting observations to be made here. You can see what I mean about the standard radiator positioning. This air gets pushed back under the car. This means that the air under the car is at a higher pressure than it would be otherwise.

The second picture down shows how I think the radiator mod would work. One thing that I noticed however, is the shape that is made between the top of the radiator venting, and the front part of the bonnet. It is a classic aeroplane wing shape. Would this generate lift anyway? Perhaps a downwards facing bulge would help prevent this. (making it more of a teardrop shape.)
One thing that is concerning about this idea, is the increased pressure on the front wind screen/roof. Would this create more drag, than if the air simply travelled under the car? Especially since there will be more air going off the 'drop off' where the rear window is.
Perhaps diverting the air out the top, and then around the sides of the car would be the ideal solution.

One thing that I havent drawn in, but I think is relevant is the stock muffler. Notice how it is oval shaped, and spans across the whole length of the back of the car? Perhaps this was designed to work as a crude venturi, or working on the same principal as a spoiler, but for the air flowing underneath the car. If so, very clever.
Also, I havent included the side vents. Not for any reason, I just forgot.

The bottom pic, is what I think will happen with a larger front lip. I mean the air has to go somewhere, right? I am sure it helps though, perhaps it diverts the air around the car, rather than under/over.

So, in conclusion, there is no real point to this post.
I just had to get that out, my friends start looking at me like a nutter when I harp on about air flow, pressure, venturis, etc.

[Al]

The Madpsi vented hood can incorporate the Border radiator relocation kit, it lays the radiator back further, then you simply remove the black plastic cover under the frunk, and your vented hood is now functional

[RomanV]

Aaah, true!

Actually, you will notice that the radiator is orignially lying down like that, the kit tilts it UP.

[Al]

Shows how much attention I pay

[Adamal]

Sounds interesting! And not cheap probably

[KinLoud]

My thoughts - if you had a lower lip, you decrease the amount of air going directly under the car.
Most of the air that would normally go directly under the car then flows through the radiator. SO
1 - you could blank off part of the radiator so that the same mass of air goes through the radiator as before - the excess air will tend to spill up over the bonnet due to the stagnation point being lowered due to lower lip and radiator blanking.
2 - go the whole hog and relocate the air intake that leads to the radiator lower than standard. This means that the same mass of air will pass through the radiator but less will go directly under the car and more air will go directly over the bonnet.
BUT
the lovely curved bonnet shape causes the air passing over it to accelerate, causing a lower pressure therefore lift.
SO
Think about venting the radiator air out the side of the car. Best would be via the front wheel wells as these are low pressure areas. The air will flow better towards a much lower pressure area and so you could get away with a smaller and lower radiator air intake.
Feel free to pick holes in my thoughts but the theory is sound.

Ken
Ham
021 408 863

[RomanV]

Thanks for the input Kenloud.

Yeah, I suppose the wheel wells would be a good place for it, assuming that they are low pressure zones.... I was under the impression that they werent however?

Like the later model SW20s have 'speed flaps' to disrupt the air heading towards the front wheel wells. Or perhaps it is to disrupt the air hitting the foward facing part of the tire? These supposedly make a noticable difference.

If you think about it, lowering your car is probably the best solution here.

That way the cross sectional area of air flow under your car is already dramatically decreased. It also effectively puts your radiator and your air scoop closer to the ground aswell.

My SW20 has had the suspension done before I got it, and it is a bit lower than stock. So perhaps on my vehicle, it is not so much of an issue to start with. Plus, the fact that I dont travel at 180kph probably helps too.

Whether or not these things will make a real life difference on a road car is irrelevant I suppose, but I find it interesting none the less.

[Perky]

Yes, it is interesting -- and difficult to find useful information about.

You mention both 80+ and 180km/h -- is the 80+ mph?

There is an Aussie magazine online that did some experiments which demonstrate that the front wheel well is a low-pressure area, so not the best place for a cold air intake. I'll post it if I remember it.

As for the car being shaped like an aircraft wing, I take it that this is always a problem and is the point of rear spoilers. That is, they disrupt the flow of air over the car. (As opposed to rear wings, which are inverted relative to aircraft wings and produce downforce.)

[vvega]

My thoughts -
BUT
the lovely curved bonnet shape causes the air passing over it to accelerate, causing a lower pressure therefore lift.
SO
Think about venting the radiator air out the side of the car. Best would be via the front wheel wells as these are low pressure areas. The air will flow better towards a much lower pressure area and so you could get away with a smaller and lower radiator air intake.
Feel free to pick holes in my thoughts but the theory is sound.

Ken
Ham
021 408 863

intersting how a lot of the new supercars now run a vented bonnent in the fashion that is indicated

ill print out ya pictures mate and take them to one of our designers tomorrow i have disscussed this with one of them before and seem to remeber he thought the bonnet vet would create pressure on the vent itsself
obviuosly the apeture sizes would have much to play
and from my understanding if the front hole was larger than the exit hole then downforce woudl be created

the idea of the lower lip is to lessen the air flowing under the car to create a low pressure area...thus downforce

have a google about ground effects..was used many years ago on f1 cars but was banned

v

[2fas4u]

interesting, with the hole on your bonnet, how do you prevent the water from building up in the spare tyre well in the even of rain

[RomanV]

Well, you would have it sealed directly down to the radiator. Shite loads of silicon should do the trick if you have any leaks.

Then you have the added bonus of a air/water cooled radiator.

But seriously, you would have to sort out some sort of drainage, but Im sure it wouldnt be a huge issue.

[2fas4u]

Well, you would have it sealed directly down to the radiator. Shite loads of silicon should do the trick if you have any leaks.

Then you have the added bonus of a air/water cooled radiator.

But seriously, you would have to sort out some sort of drainage, but Im sure it wouldnt be a huge issue.

excellent

[vvega]

you would have to make the vent integral with the body or it will just bend with the pressure exerted on it urathan and rivits would keep it in place and it would also seal well
i had a chat to one of our designers today and his opinion was that the angles the size's of the inlet and outlet are crtical in the success of gaining benafits
perhaps kens idea of venting into the wheel well sould be investigated more and this could well have far less impact on the cars aerodynamics both positively and negativelly
but you are garenteed of a posative change doing it that way and less thought into other area's are afforded

v

[CozmoNz]

water to air radiator! wicked! haha

anyway, ive got a guide in my mr2 book on how to do this!

same image that al has there is in the book too!

i might go scan / take pix later on!

[Mr Revhead]

years ago bruce mclaren noticed one of his cars was a bit "light" in the front and the bodywork between the front wheels had an inspection flap there and he noticed at speed it would rise up....

so he cut a big vent there in behind the radiator.... what he found was an imediate improvment in front grip ans stability....

notice sports racers use a style discussd above, the vent in the front. id suspect if the wheel well was a good pplace to use it would have been, instead of the wheel wells. also what happen to the airflow after its entered the wells? where does it go? if your building a car from scratch you could build vents and side profile to make that work, but i think youll find that with the sw20 a vent in the bonnet will work best.

roman, what did you use to get those pictures? did you actually use a program? or draw then after your own research?

[lill fuk]

hi guys jst reading all this an u guys seem real on to it so prehaps u can help me i wnt to tighten the handling of my sw2o but before getin into all the arodynamics ill start with the suspension ne ideas on where to start would be great cheerz

[Mr Revhead]

hello there.

first bit of advice is to start a new thread, after doing a search

[FST4RD]

When i had the veilside kit on the front of the '2' it was extremly stable and the front stuck to the ground really well at any speed over bout 80kmph, when i took it off though and put the standard front back on, it was is if there was no downforce at all (Well i suppose there wasn't being the standard kit )

[RomanV]

Re: the picture.
I had an idea in my mind about what I was trying to describe, with the changes to the aerodynamics of the car. I have a basic understanding of aerodynamic flow. The pictures are basically what I THINK would happen.
I just drew them by hand in MSPaint.
I decided to draw the pictures, as it was probably the easiest way to try and explain myself.


If I ever decided to try this out (dont worry I would get a spare bonnet to hack up first!)
Does anyone have any good ideas on how to test the results?
I was thinking that I could mount a vaccuum sensor at various places around the front of the car, before and after the modifications. (at a constant 100kph of course) Hooked up to a multimeter, or an accurate vaccuum gauge or something.
Also, I could rig up an AFM to the underside of the car, to see if the air speed increases. (Mr bernoulli states that as pressure drops, speed increases. We are aiming for a pressure drop under the car.)

Does an AFM just output a variable voltage, that you could measure with a multimeter or something? Im not sure if it would work, just an idea at this stage. I suppose that you might have to restrict the inlet, so you wouldnt overload it. I would also have to figure out a power supply for it too I suppose.

[RomanV]

Also I have been thinking about why mods like this arent very common.... Because what other car could you do this do? most cars have an engine in the way.