Lets Talk Aerodynamics

[SkyHi_33]

And no I will not put this thread in cosmetic/styling section as too many people there are too afraid to spill a bit of sauce off their felafel/yiros/kebab on their hektik chromies. Nor would most of them know a bees dick about aero other then a killa spoiler bro!

So, now that that is out of the way, aerodynamics aid a car in handling, acceleration, braking and aid grip also hence why its in this section and where I hope to find my answers.

Basically, building a 33 gts-t for a variety of motorsport uses (yes I do realize its not the best base) with major ones being time attack, hill climbs and possibly a bit of sideways action (nothing wrong with getting a bit shaky?).

So whats the best way to improve on aerodynamics?

Ive had a few ideas in my head and have started playing around with scale models.

Plan of action for now is:

a) Front splitter

b) Sealed under body

c) Rear diffuser

d) Wing

My main concerns here are:

What designs work well

What materials work well (besides the obvious $$$ carbon, kevlar etc)

How much is this really going to aid me overall? im talking the big picture here... sure race cars use it but how efficient can all these things really be in a lets say tight technical hill climb with short straights?

And lastly,

Has anyone had a tinker with these things before that can guide me in the right direction?

Edited August 13, 2011 by SkyHi_33

[eightsixboy]

This is something I to would like to know about, I'm going to be doing similar mods to mine hopefully with a aero gain.

I think with a rear spoiler most people forget about actually making a support for it so it actually helps with downforce as apposed to just pushing or bending the boot.

At the end of the day it depends on how much money you want to spend and how competitive you want your car to be, things like rear diffusers are pretty expensive and unless you can actually test it in a wind tunnel who knows if it will actually do anything.

The main things I think would be a proper rear wing, so not your auto salon spec ones but a properly designed one which is light weight carbon or similar, I know russman got his made for him so something like that.

Found this link

http://www.skylineowners.com/forum/showthread.php?t=164563

Edited August 13, 2011 by eightsixboy

[SkyHi_33]

Well from what I have gathered:

a) Front splitter

Flat, open design towards the back to still ventilate some of the pressure built up in the engine bay from air going in through bumper/grille. Sealing the whole front of the car without having air venting out of the engine bay creates a high pressure zone which stops the air circulating through radiator/intercooler etc therefore resulting in high temp buildup. Also incorporating a "lip" so to speak in front of the wheels diverting air away from tyres and towards the centre of the car helps with more airflow thus creating a better low pressure zone under the car

b) Sealed under body

as flat as possible seems to be the go, although I have seen raised sections through the middle which apparently help dissipate the air more effectively through the rear diffuser which creates a higher disruption at the diffuser end = less drag, more downforce

c) Rear diffuser

a LOT of different designs ranging from smooth to rough, fins, planes etc etc.. all seem to focus on smoothing the transition between fast moving air from low pressure zone underneath to slow moving air above the car, again creating less drag and more downforce. Seems the smoother the underbody the more ridiculous the diffusers get.

d) Wings

again, a lot of different designs but main points Ive picked up from this is you can never have a big enough wing (within reason, and regularities) but it has to be mounted right with supports extending through to the chassis. The good old vtec bolt on job just doesn't cut it.

That, in a nutshell, is some of what Ive taken in as a focus on this little project of mine. Suggestions, improvements, theories etc. are most welcome

[SkyHi_33]

Thanks for the link btw, interesting design on that wing!

[KiwiRS4T]

The point of a wing is to create downforce and hence grip on fast corners. The down side is that it will slow you down on a fast straight. What I don't know is at what speeds it actually works on a skyline as opposed to an open wheeler - I suspect some where above 140- 150km/hr at least. Therefore if you decide to have a massive rear wing I should think it would need to be adjustable to suit different circuits or ideally adjustable for different parts of the circuit but depending on what kind of racing you are planning there are probably category regulations about the kinds of spoilers you can run. The University of Auckland has a wind tunnel you could fit a full sized car into - it would be worth investigating who in Australia could provide such a facility.

[Rekin]

This site has a lot of info about aerodynamics. Just do a search. Here is one example;

http://autospeed.com.au/cms/A_2456/article.html?popularArticle

Now..someone explain why Nissan made this a factory option (drops down at 80km/h+)

[SkyHi_33]

Autospeed website is the one ive been reading through for most of the information however a lot of their articles focus on fuel consumption and road cars rather then the conventional racing principles. While it is very useful and gives a lot of ideas and concepts its not really very applicable to my needs but its definitely worth a read.

[Mr. Untouchable]

heres a pic of my bar with incorparated splitter. its 400r glass bar i had on my car for years, got pretty beat up so rather than bin it I thought i would have a crack at turning it into something better.

I put it on the car and marked out what i had to cut off the bottom to allow the splitter to be lowest and the very front, slightly angling back up at the rear. cut off what needed to be cut, then i bolted it up to the centre, and made some L shaped brackets to bolt it from the corners, and was nice and strong then I glassed down to the alloy and added the 4 steel turn buckle braces. the splitter itself is 2mm alloy sheet, next time i'll use 1.6mm.

I got the idea & diamensions from local guys with uber fast skylines (brad sheriff & pete nunn) so i cant take credit for the design

I've also added a wing, with a 1440mm carbon blade, 300 mm uprights. the wing has a built in gurney flap design. i'm in the process of designing dual bladed end plates for it out of carbon & alloy. at the moment i dont know if i like it, i may end up getting a big 1700mm origin wing from japan.

next project will be making 1.2 or so mm alloy belly plates from my skirts into the rails. but I've got other more important things to do at the moment, when i have spring rates and other major things dialed in, i will look at belly plates to smooth out air flow under the old bus.

regarding diffuser for the ass, i did a bit of asking around and reading up, seemed that unless that the floor was dead flat after the rear wheels, it was fairly pointless. and at this stage, i'm just starting to look at events like hill climbs, time attack events etc, so just the basics will be more than enough for me and my datsun

cheers

[89CAL]

The point of a wing is to create downforce and hence grip on fast corners. The down side is that it will slow you down on a fast straight. What I don't know is at what speeds it actually works on a skyline as opposed to an open wheeler - I suspect some where above 140- 150km/hr at least. Therefore if you decide to have a massive rear wing I should think it would need to be adjustable to suit different circuits or ideally adjustable for different parts of the circuit but depending on what kind of racing you are planning there are probably category regulations about the kinds of spoilers you can run. The University of Auckland has a wind tunnel you could fit a full sized car into - it would be worth investigating who in Australia could provide such a facility.

Formula 1 Style DRS would be cool lol best of both worlds

[SkyHi_33]

Oh wow, great stuff there! I like your splitter design. Is there any specific reason for the dimensions/shape at the front? Have you tested the splitter and did it generate any difference at the driver end?

[Mr. Untouchable]

design and shape, as i mentioned I've tried to replicate what is on 2 very quick local gtst's. 2ndly, i like the snow plow industrial shape lol.

i havent tested yet no, i'm in the process of... other shit. fixing/flaring front guards so i can get it all painted up at the same time. along with different coilovers/sway bars etc. i dont like changing more than or or 2 things at once so i can feel what does what, but tuff shit it all needs doing at once haha

cheers

[SkyHi_33]

Haha yeah i know exactly what you mean... im undergoing the same process, changing suspension setup, playing with guard clearances and its all in primer and part bare metal so basically same deal, want it all together before a spray!

Edited August 14, 2011 by SkyHi_33

[FloydWestwood]

If you had a completly flat undertray wouldn't you need a vented bonnet to equalise pressure in the engine bay?

I guess diffuser at the back would act like a vortex generator from low to high pressure. Seems like these are essentials that others have said are not a good idea??

[SkyHi_33]

If you had a completly flat undertray wouldn't you need a vented bonnet to equalise pressure in the engine bay?

I guess diffuser at the back would act like a vortex generator from low to high pressure. Seems like these are essentials that others have said are not a good idea??

Yes, a completely flat under tray = high pressure buildup in engine bay = no air flow through radiator/coolers etc. unless you got a form of extracting the air. So a front splitter with a reasonably open space towards the back of the engine bay is a far better idea then a completely sealed under tray. Even if it was completely sealed a simple vented bonnet wouldn't do much, it needs a directional airflow to function properly and on top of that, if it was a directional airflow it also has to be vented at a certain angle to keep the airflow from the bonnet on to the windshield undisturbed (otherwise creating drag)

What I had planned was an extended splitter with vents towards the back and a reasonable ammount of gap to the end of the engine bay, from there on it would be mostly sealed however im still not sure if sealing the driveshaft/exhaust tunnel is a good idea or not due to temp build up from the exhaust. Its something im still working on.