Aerodynamics - Page 4 - GT-R Register - Nissan Skyline and GT-R Drivers Club forum

Want to buy a banner ad? Find out more here.

Go Back   GT-R Register - Nissan Skyline and GT-R Drivers Club forum > General > Nissan Skyline > Tuning: General
Register Garage FAQ Members List Calendar Search Today's Posts Mark Forums Read Insurance


Reply
 
LinkBack Thread Tools Rating: Thread Rating: 9 votes, 5.00 average. Display Modes
Old 11th September 2002, 07:47 PM   #61 (permalink)
[email protected] M/S is looking forward to racing on the circuits again soon
GTR Register Trader
 
Mark@Abbey M/S's Avatar
 
Join Date: Feb 2002
Location: The workshop...
Cars owned: Skylines...
Posts: 3,663
Aero

Boys and Girls,

I am just trying to help people out to understand a princlpe that During my years as a race car mechanic/ chief mechanic I picked up some very usefull information about a number of devices that can be helpful on road cars. I was using a friends intelligence to sort out the aero debate it was just a conversation we were having and he said he would have a look at the thread, that was his reply.
Andy, when my dyno is up and running I will re data log the temps and post them on the board . The previous temps were on my old computer I dropped this a few months ago.
The fans in the dyno room are spec to supply a wind speed the same as running at 130/140 mph at full spedd so it will provide a
good sound enviroment to check temps etc.
I will now stop being involved in the aero debate I have said I do not agree with all the ideas and I feel it should be tried in a stable enviroment i.e awind tunnel.
And if the "race" drivers could feel all the small and large changes in aero/suspension,gearbox,diff changes then "data logging systems that cost millions are a complete waste of time.



Mark
__________________

I am a sponsor of the GTR Register!
Mark@Abbey M/S is offline   Reply With Quote
Old 11th September 2002, 07:50 PM   #62 (permalink)
Lee_Pendlebury is unaware they can edit their status
 
Join Date: Nov 2001
Posts: 1,348
Its Peters Pic. I have a GTiR!

I could send you the underside of that, but I wont be doing anything anyhow. I like the rally slag look

Cheers
Lee
__________________
Lee_Pendlebury is offline   Reply With Quote
Old 11th September 2002, 09:42 PM   #63 (permalink)
SteveC is vorsrungdurchripoff, £1000 for 2 injectors fitted
GTR.co.uk seasoned Member
 
SteveC's Avatar
 
Join Date: Jul 2001
Location: West Sussex
Cars owned: a crap one
Posts: 1,885
Thanks for that Mycroft,

I thought you were still underneath the car, it all makes sense now.

This portion deflects air that would normally go under and around the inside of the wheel area then ?

/Steve
__________________
tdi
SteveC is offline   Reply With Quote
 
Old 11th September 2002, 10:10 PM   #64 (permalink)
Mycroft is unaware they can edit their status
 
Join Date: Apr 2002
Posts: 3,561
Yep, where the 'sidies' join the sill the air cascading down the flank of the car is forced to adhere to the bodywork, it is accelerated slightly as it passes across the rearwheel arch, this is 'cloaking' a trick discovered back in the 50's by Ferrari designer Chiti and used a few times on the 'Bread Van' Ferrari Le Mans cars.
__________________
Mycroft is offline   Reply With Quote
Old 12th September 2002, 02:17 AM   #65 (permalink)
Peter is unaware they can edit their status
GTROC Member
 
Peter's Avatar
 
Join Date: Jun 2001
Location: East Sussex.
Cars owned: Audi S6
Posts: 9,034
Cool, it worked!

Mycroft,

As you can see, there is in fact a hollow void behind the splitter which reduces at the sump tray. Would this cause any kind of down force or just create dirty air? There are mounting points along the back edge of the splitter which could be used to attach an undertray. I have seen a 33 with an undertray here, don't know if UK models had one fiited a standard....?

Peter.
__________________
Peter.
Peter is offline   Reply With Quote
Old 12th September 2002, 10:09 PM   #66 (permalink)
Peter is unaware they can edit their status
GTROC Member
 
Peter's Avatar
 
Join Date: Jun 2001
Location: East Sussex.
Cars owned: Audi S6
Posts: 9,034
Calling Mycroft....
__________________
Peter.
Peter is offline   Reply With Quote
Old 13th September 2002, 12:53 AM   #67 (permalink)
Mycroft is unaware they can edit their status
 
Join Date: Apr 2002
Posts: 3,561
Whaddya want, I'm thinking..........
__________________
Mycroft is offline   Reply With Quote
Old 25th September 2002, 08:49 AM   #68 (permalink)
Peter is unaware they can edit their status
GTROC Member
 
Peter's Avatar
 
Join Date: Jun 2001
Location: East Sussex.
Cars owned: Audi S6
Posts: 9,034
Mycroft,

Finished yet.....?

Peter.
__________________
Peter is offline   Reply With Quote
Old 25th September 2002, 04:52 PM   #69 (permalink)
Pavlo is unaware they can edit their status
GTR.co.uk seasoned Member
 
Join Date: Sep 2002
Location: zen
Cars owned: [email protected] flat 4
Posts: 568
busy lear, sorry revising......
__________________
Pavlo is offline   Reply With Quote
Old 25th September 2002, 11:14 PM   #70 (permalink)
Mycroft is unaware they can edit their status
 
Join Date: Apr 2002
Posts: 3,561
I have indeed to ensure I post exactly right info, we had 3 whole days worth of results with my car and the Aerodynamicist at the WT and I have passed lots of correspondance on this particular matter, I have also been weighing tyres and trying to fill out the blanks in the datasheet, deal with a serious I-net virus, remove and re-dye my leather interior, re-carpet the whole car including over mats and upgrade the stereo and do my normal work, all excuses to some extent, but I have only so much time for this stuff.

Please be patient.

I am also trying to photoshop stuff to illustrate my findings and frankly my photoshop skills are...pish-poor.

EDIT, Pavlo maybe I'm overworking but I have just re-read your post, was that a 'snide' comment? I hope it's just me overworking and reading too much into it, well I hope so anyway. If you have a 'problem' with me or my posts e-mail me this site ain't the place, if I have hold of the wrong end of the stick then please accept my apologies.
__________________

Last edited by Mycroft; 25th September 2002 at 11:21 PM..
Mycroft is offline   Reply With Quote
Old 26th September 2002, 11:48 AM   #71 (permalink)
Pavlo is unaware they can edit their status
GTR.co.uk seasoned Member
 
Join Date: Sep 2002
Location: zen
Cars owned: [email protected] flat 4
Posts: 568
No Mycroft, you were spot on, it's a snide comment.

But I suppose allowances can be made if you have gone to the trouble of going WT testing.

A petro-chemist and an aerodynamicist?

You'll have to excuse my scepticism, but after looking at the a picture of the underside of the engine bay of a car that's doesn't actually have the aero aids fitted, you claimed to have a good understanding of the aero package of said car. So I've been looking at the same pictures, and been thinking there's a nice gap to put something useful in, but that's about it.

I am also puzzled by the "anything over this line is too complex" statement. Too complex for what exactly?

Paul
__________________
Pavlo is offline   Reply With Quote
Old 26th September 2002, 01:27 PM   #72 (permalink)
Mycroft is unaware they can edit their status
 
Join Date: Apr 2002
Posts: 3,561
I have tested only a Soarer (my car in the Tunnel, it has a very different design of undertray set-up, which means i have have to glean further info from richard, he is an 'Aerodynamicist' I am not, also I am not a Petro-chemist.

It does in fact have an aero aid, that 'cavern' is very important to the way the car behaves and you don't mess with things unless you can be sure you will at the worst no harm and hopefully give some added advantage.

I have explained that confined air or air that has a uniform (across makes/designs) behaviour, above that line you HAVE to go to a WT and nothing else will do.

This is not book learning this is real data gleaned from the testing and there are almost 400pages of info, most of it just stress gradings but it does take time to relate this, even to the car in the tunnel, making a reasonable fist of taking it to another car is altogether harder still.

On the 'learning' bit you allude to, well, you're right, I am learning, so is Richard and any valid human being on this planet, it's all about learning curves, Richards is much smoother than mine and I to some extent pass on the his knowledge here as much (probably more) as my own.

If you want to partake rather than snipe at me from the sidelines then go to the net/library/bookshop and get yourself armed with some knowledge, if not frankly your contribution here is pointless.

Mods if this is too harsh or sounds nasty, well the truth is I mean it that way, if you wish to edit my post, then please do so, but I make no apology for not being as tolerant as perhaps I should be.
__________________

Last edited by Mycroft; 26th September 2002 at 01:34 PM..
Mycroft is offline   Reply With Quote
Old 26th September 2002, 02:04 PM   #73 (permalink)
Pavlo is unaware they can edit their status
GTR.co.uk seasoned Member
 
Join Date: Sep 2002
Location: zen
Cars owned: [email protected] flat 4
Posts: 568
Well, my comments were written rather tongue in cheek, mainly due to the length of time we had been waiting since you last reply.

Anyway, I am glad you have straightened out your position, because some of your previous posts came accross in a rather knowitall manner.

Numbers are good for comparison, but I hope you got some smoke test footage. It can sometimes reveal interesting flow phenomenon that the pressure figures won't convey by them selves. I find that flow visualization is invaluable for finding a way forward, but the numbers will generally tell you if you made the correct changes or not.

A good example is the use of turbulators the front of the car, or on the underside of the wing. You may find improvements in both drag and downforce, that defy the nature of such a small physical change. But flow testing often reveals fundamental changes to the flow regime that are unexpected, but will go to explain the improvements. In knowing these things, you can tweak them using something a little better than guesswork.

It is possible to do meaningful testing outside a wind tunnel if you don't have the facilities available. Ultimately all the tweaks are done in the name of speed, and a stopwatch and/or datalogging system can give you a good indication of whether things are better or not. For instance you don't need a wind tunnel to test a gurney flap (or 3), wing height, wing angle, air dam height and I'm sure a few other things on the Skyline.

As previously mentioned, ride height and attitude control is critical to getting the underside of the car to work. As is using a wind tunnel with a moving or detached ground plane.

I take you you went to MIRA for the tunnel testing?

Paul
__________________
Pavlo is offline   Reply With Quote
Old 26th September 2002, 02:13 PM   #74 (permalink)
Mycroft is unaware they can edit their status
 
Join Date: Apr 2002
Posts: 3,561
Now we have established you have some knowledge, perhaps you could postulate how to generate additional suction under that damned 'cavern', I have found the control of mass air flow means that to some extent a simple venturi effect on the nose is not the best, as the low pressure zone is in the wrong place for this, causing a huge turbulence just behind the lip of the bottom spoiler, your thoughts?
__________________
Mycroft is offline   Reply With Quote
Old 26th September 2002, 02:44 PM   #75 (permalink)
Pavlo is unaware they can edit their status
GTR.co.uk seasoned Member
 
Join Date: Sep 2002
Location: zen
Cars owned: [email protected] flat 4
Posts: 568
To be honest, the front ot the car, under the nose is the worst place to try and work. I've no formal training testing in this area, and it's no wonder, it's such a pain to do anything predictive and correct, that there is little info on the right way to go about it, and what info there is closely guarded. It's very much trial an error, even in F1, where they only just figured that by rasing the underside of the nose all the way back to the drivers seat, you can improve airflow over the front wing. It's common sense when you think about it, but it's taken years for anyone to just try it.

Anyway, in general you would look to increase the flow velocity adjacent to the skin of the underside (this is how a wing generates lift). So a venturi type aproach is obviously an option, the trouble with them is you need to have clean airflow. It's no good if you put a venturi in the cavern, but all the high velocity flow is detached, as you're only going to get a fractional effect.

On most production cars the front air damn (how ever small it appears) is mostly used to aid cooling through the rad. You may see sports car racers with small radius lip on the bottom edge of the air dam. But much of the time, this is used to aid the diffuser at the rear, encouraging high velocity under the car as a whole.

THe all out solution tends to consist of a wing element/diffuser at the front, using the ground effect, and partially feeding the rear diffuser or feeding rads and such like. In addition, flow over the top of the wing is used to help feed the rear diffuser. The problems that can occur is you try and ram air into the underside, instead of letting the diffuser efficiently sucking it through. Or the front completely messes up the rear so you end up with crap flow throughout and stalling. Turbulence isn't all bad though, gurney flap being the prime example.

Basically, the underside is a pain in the backside.

As for the "carvern" in question, I can't help but think that you would need to put something in well below the level of the air damm. And the trick would be to get the air flowing through any sort of diffuser, so that means clean exit path to somewhere, maybe out through the wheel arches, or the back. The other option is to use the some of the air exiting the rad, and feed in into a ventri under the engine, but how you accomodate a diffuser for said venturi is anyones guess.

Paul
__________________
Pavlo is offline   Reply With Quote
Old 26th September 2002, 04:48 PM   #76 (permalink)
Mycroft is unaware they can edit their status
 
Join Date: Apr 2002
Posts: 3,561
#As for the "carvern" in question, I can't help but think that you would need to put something in well below the level of the air damm. And the trick would be to get the air flowing through any sort of diffuser, so that means clean exit path to somewhere, maybe out through the wheel arches, or the back. The other option is to use the some of the air exiting the rad, and feed in into a ventri under the engine, but how you accomodate a diffuser for said venturi is anyones guess.#

yes, my thoughts went along similar lines, I think a deep element wing (thats a fat one, with a sectional profile similar to the of a 'Fat Boy' bomb) section just below the lowest front skirtforcing some of the flow up and around that cavern and creating a high acceleration zone below it thus creating a very nice low pressure zone in front of the wheels, each end of this LPZ will also help any SMIC as it expands at speed and approaches the wheels, I'm glad to say that Richard agrees that this approach seems the way to go.
__________________
Mycroft is offline   Reply With Quote
Old 27th September 2002, 09:00 AM   #77 (permalink)
SteveC is vorsrungdurchripoff, £1000 for 2 injectors fitted
GTR.co.uk seasoned Member
 
SteveC's Avatar
 
Join Date: Jul 2001
Location: West Sussex
Cars owned: a crap one
Posts: 1,885
Chaps,

From a non aerodynamicist !!


On the Touring car versions of the 33 there is a plate that bolts onto the underside of the front splitter and travels about halfway into the engine bay just behind the front wheel hubs.

Surely using the whole frontal area to pull air up near the undertray on the road car (in Peters pic) would create an area of high pressure and effectively lighten the front end ?

Using the vortices generated in that undertray get us into the realms of a spoiler on the top half of the car complexity wise.

Would it not be better to reduce that gap as much as possible by putting a plate across the front third of the car, touring car style, using the mounting positions provided on the spoiler ?

sorry if I'm way off here.

/Steve
__________________
tdi
SteveC is offline   Reply With Quote
Old 27th September 2002, 11:07 AM   #78 (permalink)
Pavlo is unaware they can edit their status
GTR.co.uk seasoned Member
 
Join Date: Sep 2002
Location: zen
Cars owned: [email protected] flat 4
Posts: 568
I don't think that's way off, it depends what you're trying to acheive.

The racing skylines tend to have big bonnet vents after the rad, so dumping air behind the air dam isn't an issue. Half the battle is getting consistant airflow, clean is generally good, but steady turbulence can be okay.

Full length under tray will promote good airflow under the car, and if you put a degree or 2 of rake on the car (front lower than rear) you have in effect created one long diffuser.

The idea of the diffuser is to allow high velocity air to rejoin the bulk flow at the same speed again, so by gradually increaseing the volume it has, it expands, slows and it's pressure increases.

If you were running the car on the deck, it may well be that just by putting a flat undertray on the front, with a few degrees of rake, you can generate some downforce at the very front. However, it's going to be very dependant on ride height, and if you boot it out of a corner, and the rear dips leveling the undertray, all your downforce would dissapear. So this is where active suspension really comes in.

Running a pukka venturi on the front is going to be much less dependant on rake, and to a degree, ride height. But you have to work on cleaning up the air both in and out of it.

Paul
__________________
Pavlo is offline   Reply With Quote
Old 27th September 2002, 11:17 AM   #79 (permalink)
Peter is unaware they can edit their status
GTROC Member
 
Peter's Avatar
 
Join Date: Jun 2001
Location: East Sussex.
Cars owned: Audi S6
Posts: 9,034
Quote:
Originally posted by Pavlo
Full length under tray will promote good airflow under the car, and if you put a degree or 2 of rake on the car (front lower than rear) you have in effect created one long diffuser.
Oh well, that's answered one thing that's always intrigued me, a stock 33 non-v is lower at the front by about 20mm than the rear, good old Nissan.

On the void after the front splitter issue and again I'm no aerodynamicist, when the air rushes under the splitter, it clearly has to expand into the void to a degree creating 'negative' pressure. Is this a type of venturi effect?

Peter.
__________________
Peter is offline   Reply With Quote
Old 27th September 2002, 02:17 PM   #80 (permalink)
Mycroft is unaware they can edit their status
 
Join Date: Apr 2002
Posts: 3,561
If a road car has a flat plate just aft of the apron it usually needs to be lifted slightly toward the front and vented to allow the air to be pulled into the engine bay, this is how it is on my car, this allows cooling air to hit the radiator and that air is to some extent sucked into the bay by the fan smmothing the flow and adding slightly to the downforce, my recent dilemma was whether to promote this type of solution to your cars, it is a well known trick that can be credited to Chiti, Ferraris engineer/aerodynamicist and made its debut on the 250GTO (I think?) the only problem is of course that there is at present no way to get this now separated air to the radiator/engine bay without serious modding.
It pleases me no end that it has already been (sorta) done on track cars, this means that it should work, the advantage of lots of little scoops on this plate is that is it not so dependent on the angle of attack, by lifting it on the leading edge you remove the need for a controlled venturi.
__________________
Mycroft is offline   Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT. The time now is 11:58 PM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
http://www.Tyreforums.com

tyreforums

 

Garage Plus vBulletin Plugins by Drive Thru Online, Inc.