Vehicle aerodynamics

Road-race engines and ancillaries - general discussion
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Yugo_Turbo

Vehicle aerodynamics

Post by Yugo_Turbo »

Ok,I'm driving Yugo which in stock form has TERIBLE aerodynamics and I want to do somthing about it.
I wass thinking about building front splliter,rear diffuser and flat bottom.
I would built it whole from thin aluminium so it wouldn't be heavy.

Is it good idea,and is it worth of building it?

Here are some pictures(IntegraTypeR,but just to show u what I want to do):
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And here are some aerodynamic basics(this effect is also known as reverse wing,I think :oops: )
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SirYun
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Post by SirYun »

I have had the odd chat on aerodynamics with people who worked on designing jetfighters and such. my conclusions:

*Looks mean very little,

*you don't need much to alter the aerodynamics :
the small and ugly lip on the back of a audi TT added as a cure for
handling.
The ridges in a rear lights of a BWM 6XX


* Altering does not mean inproving

ground effect related aerodynamics are hard enough to get working in a wind tunnel (static that is).

but on a bouncy car you really need proper design tactics

I would think the flat bottom would work as far as drag goes, but could cause all kinds on interesting cooling issues.

A diffusor looks cool but is an art to get it to work. Just slapping a few diffusor shaped bits on a car will probably just cause weird turbulence possibly causing all kinds of grief at high speed.


are you going fast enough for long enough to expect worthwhile gains ? especially considering the basic material you are working with


I would spend the efforts on driving, suspension setup and getting more power..


"Aerodynamics are for people who can't build engines"
Enzo Ferrari

:wink:
Joost M. Riphagen
Guy Croft
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Post by Guy Croft »

I am certainly in favour of shielding the underside of the engine bay. At speed without and undertray this is a turbulent & high pressure zone due to the intrusions into the airstream of the engine, gearbox and vehicle architecture.
In my experience not only does this cause the car to lift off at the front at speed, this has an adverse effect on the cooling system by building up pressure under the engine hood. The heat from radiator, brake system, engine and exhaust cannot escape effectively.

The obvious solution in my view is to vent underhood heat out of the sides and top of the engine bay, but that said, the vents have to exit into low pressure regions of the car body or you'll be no better off.

GC
Julian
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Post by Julian »

Ultimately without some testing it is very hard to prove any changes actually work.

The first step is do some reading - there have been some real atorocities in the name of "aerodynamics" where a little bit of knowledge has been very dangerous indeed. I suggest starting with Simon McBeath's book on the subject (Competiton Car Downforce - ISBN 1859606628) - easy to read but full of lots of very important information. He has also written a long list of articles on the matter for racecar engineering magazine that provide bite-sized information that can help guide you to a practical solution.

The second things to remember is that low drag does not mean low lift - the shape of the car is all wrong for that and low drag usually means big lift - refer back to the last paragraph.

On to practical thoughts

Get the car as low as you are allowed to minimise the intrusion of air under thar car - you won't create ground effect but it will help

Get the underside of the car as smooth as possible - the smoother the air flow the less lift is created from high pressure underneath and low pressure above.

Very little air from the engine bay escapes under the car anyway so this is unlikely to be a factor but you do need to make sure that there is adequate flow through the engine bay!

A front splitter only really works if it extends back - if it is just the lip of the front bumper it isn't doing an awful lot. It also needs to be sufficiently strong in itself and sufficiently strongly mounted to the car. Rigid, brittle materials are not an awful lot of use. Find something tough instead - plywood is popular for both toughness and cheapness (it is going to be destroyed so why make it expensive).

A rear diffuser works by smoothing the air flow velocity change back to "nominal" at the rear of the car and to do that it needs to be the right size, angle and length - experimentation is a poor substitute for calculation but where accurate modelling is not available experimentation and guesswork are all you have so be prepared to do lots of experimentation to get it right.

The other thing to remember is that you have a car with a relatively small frontal area and a short body length - do not expect to make record breaking aero figures. You already have the benefit of relatively low drag simply by being small. One of the biggest gains to be made on these cars is sorting out the air flow over the top of the car at the rear hatch. Cleaning up the front and sides will help but not as much as you might hope.

Finally nearly all of these points are only of any importance if you are reaching high speeds (anything over 90mph - I would hope so with your car) with great regularity. A lot of people spend a lot of time "tuning" the aero on the car when what they really need is proper suspension setup.
Last edited by Julian on August 14th, 2006, 2:40 pm, edited 1 time in total.
SirYun
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Post by SirYun »

I hope GC does not mind that I link to a page that is not mine.

It is the book's page from

http://www.Kimini.com
The guy built a very interesting tubular framed mini shaped mid-engined car over a ten year period. A day without learning is a day wasted! Well the books on this page should keep you from wasting days for quite a long time.
http://www.kimini.com/Reference/index.html
It lists the book Julian mentions as well.
Joost M. Riphagen
Yugo_Turbo

Post by Yugo_Turbo »

Wow,a lot of answers.
This has really cleared out my mind.
It'would be a BIG waste of time and money.
I will just protect my oil-sump with piece of metal sheet and MAYBE fit rear spolier with adjustments from Yugo 1.6CUP(driven od rally's and circuts :roll: ).
Thanks!
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