# Aerodynamics of the Nissan R35 GTR



## mindlessoath (Nov 30, 2007)

Read some of the story - Aerodynamics of the Nissan R35 GTR
The challenge for the designers of the Nissan R35 GTR was to create a car that drew on lessons learned from the development of the successful Nissan Le Mans prototypes, and to apply this to the new GTR. Yoshi Suzuka was on the design team and explains how this was achieved.
gtraero
ON this link there is a PDF at the end of the page, thats where the story is.



Read the whole story in 24 HOUR Race Technology (Vol.3) magazine 
As of November 2009, no other car matches this performance.
The new 2009 Toyota Prius has lowered the Cd value to 0.25 and the new 2009 Honda Insight has 0.28 with zero lift or negligible lift.
The electric three wheeler Aptera has a mere 0.15 Cd value but lift value is not announced.
If you increase the tire width, the Cd value goes up instantly.
The Prius and Insight use 175-185mm wide tires while GTR is equipped with very wide 285mm tires.
If you try to modify dangerous lift force to downforce, usually the drag value will jump up significantly.
So what is the secret to make the traditional 4 seater Grand Touring car style GTR have such low Cd with front and rear downforce?
Freelance aerodynamicist Yoshi Suzuka explains the secret and development story in 
24 HOUR Race Technology (Vol.3) magazine.



500km/h GT-R... This is in the PDF posted above...
Yoshi Suzuka is a freelance automotive aerodynamicist who
started his career in race car engineering in 1968 after obtaining
an MSc degree in mechanical design. He later became a fulltime
aerodynamicist. Since then, Suzuka has created many successful
race cars in IMSA GTP, Indy car, Le Mans car and GT car fields
and the Nissan GTR is his first production car.* He is also involved
in a project to develop a 500 km/h world speed record Nissan
GTR.* Alongside four factory Nissan R90CKs and two R89Cs,
Suzuka***146;s Group C Nissan R90CP qualified 3rd on the grid at Le
Mans in 1990 finishing 5th, the highest place finisher of any of the
Nissan entries that year.
And this link on his site was for a 350Z... im guessing he changed his mind after the R35 released... He might still be looking for funding?
http://www.suzukaracing.com/GTR%20page/5%20F-5%20.html

More video here.


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## PETERJH (Nov 14, 2010)

I am now feeling utterly guilty for having tampered with my car and fitting splitter,bonnet and wing.Top speed on the autobahn was down and fuel consumption was up.Good article.:clap:


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## Godders (Oct 7, 2009)

Excellent... link to the pdf is HERE


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## Adamantium (Jun 24, 2002)

There's no way on earth you'd catch me fitting anything not approved by Nissan to the bodywork of the car now!

I'm not even sure the wrap is ok! (not kidding!).

Then there's the front facing camera to consider. Bear in mind in that article, tidying up the engine bay wiring loom cost them significant aerodynamic efficiency!

It does make me wonder how they managed to up downforce by 10% (tiny when you look at the numbers involved) and reduce cD from 0.27 to 0.26 at the same time. Why didn't they do that in the beginning?


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## MidLifeCrisis (Apr 29, 2011)

Adamantium said:


> There's no way on earth you'd catch me fitting anything not approved by Nissan to the bodywork of the car now!
> 
> I'm not even sure the wrap is ok! (not kidding!).
> 
> ...


I've spent the morning washing squashed bugs off the front, after reading the outstanding article, it's quite obvious the bugs were costing me several nanoseconds on the drive into work :runaway:

Seriously, extremely interesting reading.


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## Marky_GTSt (Dec 31, 2005)

PETERJH said:


> I am now feeling utterly guilty for having tampered with my car and fitting splitter,bonnet and wing.Top speed on the autobahn was down and fuel consumption was up.Good article.:clap:


Well, Nissan do know what they are doing, Ask yourself how long you think the people who sell aftermarket parts spent in the wind tunnel ? or are the products they sell more for looks than function  

I am often puzzled as to why people want to modify a GTR, to me it seems like the most complete and capable package money can buy. A bit more power yes, anything else I cant see as an improvement.


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## Fuggles (Jul 3, 2001)

This is nothing new. I recall several conversations with Hiroshi Tamura-san talking about the R33 and R34. The rear spoilers were designed in a way and set at a certain height for optimum performance at a given speed. People changing them, lowering and raising did nothing to improve the overall aerodynamic performance. However, he was a pragmatist and agreed that people wanted to put an individual stamp on the cars and most people could not drive the cars at the level where they would be deemed to be performing at the very pinnacle. Mizuno-san, on the other hand, is a purest and he hates anyone who does anything to the GT-R and changes it.

*Project-TM*'s first detailed drawings were completed in London in 2004. if you look at them you can see today a lot of design features that were created way before the first drawings of 2004 when all these ideas were brought together. However though it was designed with a purpose, that being to outperform most cars on the road for a lesser price, there were still some areas that were given over to design rather than function. The most optimal front nose and bumper actually sits lower than the current (MY2010 and MY2011) design and has a smaller and lower top air intake. However a slight adjustment to the front made it look far more aggressive and only had a marginal affect on the overall aerodynamic performance. 

Other changes to affect the cars overall look were also made and there were other compromises but, sadly, I don't recall these in such detail; maybe I should ask Mike to remind me again of what they were

The Nissan GT-R is a phenominal piece of enginnering and a master of aerodynamic design, but every now and again some changes to the design were made just to make it look better. Whatever you think of the design of the car it's nice to know it's not all 100% computer designed and optimsied and somewhere in there are elements of style over function.


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## Robbie J (Jan 8, 2005)

project-tm  but where is mike now???

as Fuggles knows there is a design phase for the look of the car then the detailed aero package

its interesting on seeing the different approaches merge to get the car in the end

my stillen stuff is not going to change the characteristics much and the rear spoiler is the same as what came off


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## Fuggles (Jul 3, 2001)

If you can find out I'd like to get him to come to the AGM this year


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## mindlessoath (Nov 30, 2007)

anyone get any good idea's for mods using this information? anyone calling Yoshi Suzuka for there parts development? the GT-R can be modified as seen here, its made as a GT car, not a race car, so loads more can be done for a track car or even just better aero for fuel econ, more downforce, etc.

here is the nordring front lip that has a vent on it - very impressive...
http://www.nagtroc.org/forums/index.php?act=attach&type=post&id=22505 (must be logged in at nagtroc to view)
http://www.nordring.jp/contents/products/img/prd01.jpg
the nordring engine cover http://www.gtr-world.net/media/1/20090912-nordring-18.jpg

nordring rear bumper/diffuser http://www.gtr-world.net/media/1/20090912-nordring-19.jpg

nordring wing and trunk flap http://www.gtr-world.net/media/1/20090912-nordring-24.jpg

more here: http://www.nagtroc.org/forums/index.php?showtopic=36632

you can see all these products from nordring help the actual aero of the car.


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## Fuggles (Jul 3, 2001)

How can you "see" these help the aerodynamics of the car? I don't see any wind tunnel or other proof to demonstrate that. That is not to say they could not help but there is absolutely nothing to support the argument. Do you know how many full sized wind tunnels with rolling roads there are in the world that are capable of very high speeds - I can tell you it's not many! I had dinner this evening with a chap from the industry who knows more than a fair bit about this stuff and he was quite damning of "all these parts manufacturers and 'tuners' coming up with aero parts and absolutely no proof to support any of their claims"

As said earlier the GT-R was designed very specifically and every line and curve is for a reason. For example the small crease on the C-post is there not for aesthetic reasons but actually guides more air through the rear spoiler and therefore aids downforce. Some minor adaptations were, however, made to imporve the aesthetic appeal and continued development of the car has show more advantages for example in the MY2011 car; and there will be more to come in later models. But, there is no such thing as being able to look at a part and say it will be able to help aero and I doubt any after market parts supplier has the budget to run to the type of R&D that is required to test these parts.

I have a lot of aftermarket parts on my car and they are there because I believe (but don't know) they may help and can see the logic in how they might or are there for aesthetic reasons. But none of them have ever been proved in anything like the conditons needed to provide proper evidence to support the designers gut feelings and my belief


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## ANDYR35 (Sep 1, 2008)

Oh great!!.....now i am in two minds as to fit my new Rays nuts or not!


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## Robbie J (Jan 8, 2005)

nuts worked for me





but only on the car....


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## Robbie J (Jan 8, 2005)

there is some good stuff here


what Fuggles is trying his best not to say is that a few of us chatted to a few of the designers and there is more to it than aero than meets the eye....

somebody should look at Fuggles's pictures sometime

it would be good to get a GTR tech section going but there is always issiues with rights on who own's what....


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## andrew186 (May 3, 2010)




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## mindlessoath (Nov 30, 2007)

Robbie J said:


> there is some good stuff here
> 
> 
> what Fuggles is trying his best not to say is that a few of us chatted to a few of the designers and there is more to it than aero than meets the eye....
> ...


I agree with his opinion... However not everyone is Aero retarded and more than a few people know aero... And I would also consider the guy that works for Nissan ie nordring is making parts that work. I gave only nordring as an example for that very reason and if u look at the nagtroc link iirc some parts have explanations and they coincide with the information in the pdf in some respects and others from other aero books i have read.


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## Fuggles (Jul 3, 2001)

I don't disagree with you at all. But there is a gulf between what a manufacturer or car racing team can do with all the facilities it has at it's disposal and that of some guy with a sketch pad and an enclave. That said somewhere inbetween there are people with good ideas, a detailed knowlegde and good products that may well make a difference. Just be careful with all these aero packages and understand just how many are able to offer a real advantage and how many are just "seems like a good idea". I subscribe to the philosophy that "downforce=drag".

I once had a very "interesting" conversation (admittedly over a number of drinks) with a chap (Simon somebodyorother) who did a research PhD at Cambidge, his thesis was on the aerodynamics inside an engine bay! 




Robbie J said:


> somebody should look at Fuggles's pictures sometime


I'll bring them to the AGM and dinner


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## Guy (Jun 27, 2001)

Great article.

Aero-design is far more complex than engine design IMHO. In fact I believe that the reason that the GTR was so good when introduced was primarily down to chassis, aero and the gearbox. The engine is actually not really that special and very comparable to many other cars.

This also reminds me that the Aero-parts sellers get away with selling stuff with no proven gains, that may even make the car worse. How many aero parts come with a proven reduction in cD or a proven increase in downforce etc - none I've ever seen!


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## Fuggles (Jul 3, 2001)

Totally agree. Hence why you have two very different camps even in Nissan:

Tamura-san: Head of Product Planning for the R34 and Chief Designer for the R33. Does not believe that anyone should change any parts for aero improvement but understands people want to do it for aesthetic reasons and is fine with that because he believes in individuality
Mizuno-san: the current "_Mr GT-R_". Does not understand why anyone would want to change anything from a car that has been designed so (almost) perfectly aerodynamically. Mizuno-san believes the entire Nissan GT-R fleet should be the same as there is no reason to change and almost no-one can get more out of the car than the very best drivers he has working for him. Mizuno-san really does not like people changing his car!
Where they are the same, is that neither of them believes any parts out there have been properly tested and can make any provable difference. Tamura-san once even suggested that claims made by suppliers might be something Nissan want to challenge in the future under the 'sale under false pretences' argument


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## mindlessoath (Nov 30, 2007)

Fuggles said:


> I don't disagree with you at all. But there is a gulf between what a manufacturer or car racing team can do with all the facilities it has at it's disposal and that of some guy with a sketch pad and an enclave. That said somewhere inbetween there are people with good ideas, a detailed knowlegde and good products that may well make a difference. Just be careful with all these aero packages and understand just how many are able to offer a real advantage and how many are just "seems like a good idea". I subscribe to the philosophy that "downforce=drag".
> 
> I once had a very "interesting" conversation (admittedly over a number of drinks) with a chap (Simon somebodyorother) who did a research PhD at Cambidge, his thesis was on the aerodynamics inside an engine bay!
> 
> ...


Always a tradeoff when doing aero. your right alot of aero packages might make the car unballanced or create too much drag. adding aero to tune the way the car reacts... you may loose top speed due to more drag, but downforce added will likly help in the corners. ride hight also affects the way the installed aero works and could mess up that ballance the manufactures has created for that package. and some aero packages just dont work in any advantage.

Aero inside the engine bay is very interesting to me. 

Browser Warning has some great aero articles for people to read if interested in home brew aero and testing techniques.


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## David.Yu (Jun 28, 2001)

andrew186 said:


>


Good point, well made.
Unlikely many of the aero mods on this car were purely for aesthetic reasons!

Going to see them race in person in Portugal on Sunday... :smokin:


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## Aerodramatics (Feb 10, 2008)

Nice article. Got me thinking. The science of grip can be quite fascinating... saddo that I am! :wavey:

From what I understand, in the simplest model, cornering speed increases by the square root of the fractional increase in relative axle weight, i.e. by the factor of the square root of fraction of original axle weight per wheel + the aerodynamic download all divided the original axle weight per wheel. 

For a car with a 50:50 weight distribution in a balanced throttle constant speed corner (i.e no fore or aft weigh transfer due to braking or application of throttle) nominally each wheel experiences the same down load and all tyres will break traction at the grip limit simultaneously. Add in other factors like pitch (brake dive), roll, yaw and ride height of the changing the aerodynamic forces on the chassis, lateral weight transfer, then throw in the effect of crosswinds and changes in tyre contact patch due to suspension geometry, and the model swiftly gets more complex. 

However sticking with the simple ideal model, consider that for a formula 1 car with the oft quoted ability to create its own weight in downforce at typical F1 cornering speeds of 130mph then the cornering speed due to down force increases by the factor of:

square root of (1+1)/1 = square root 2 =1.41, i.e. some 41% higher than with zero downforce. :clap:

Based on 130mph cornering speed with downforce, without downforce the cornering speed would be approximately 92mph (130/1.41). The downforce is worth a stonking 38mph if the driver knows how to use it. The big grippy slick tyres are worth 22mph or so :thumbsup:

Now take typical road car able to corner at 70mph on a typical track corner radius, like the TT with a total lift coefficient of 0.35 as quoted in the linked paper. What is the maximum improvement in cornering speed due to aerodynamics alone, i.e. switching to the better aerodynamics of a GT-R with a zero pitch attitude download of CL = -0.08?

Well, 0.35 CL at 70 mph is about 42kg of total lift for the TT.

For the GT-R it's producing about 10kg of total download.

So we're looking at a net 52kg improvement.

On an 1800kg vehicle, that's square root of 1810/1758, i.e. about the square root of 1.03 = 1.015, or a 1.5% increase in cornering speed. (1758kg = 1800kg less 42kg lift, 1810=1800kg + 10kg downforce)

Which is about 1mph better, i.e. 71mph cornering speed. :bawling:

So Fuggle's comment is worth noting. When assessing the benefit of any aero mods, road sports cars mechanical grip is fairly modest and downforce is more less negligible compared to race cars, so just like Fuggles says a lot of aero mods are largely aesthetic airbrakes imho. :flame:

Fitting slicks seems like the way to go for our road cars on track days if want to corner a bit faster. Otherwise the aero mods need to by pretty severe to make significant gains. :runaway:

Mk 1 Exige drivers (with a decent big wing giving maybe 80kg) start to get a 3-4% improvement in cornering due to downforce. A good driver could probably find and exploit these improvements into a faster lap (provided the increase in drag is offset by tuning in a bit more power). Add fade resistant brakes and it all adds up through a session and probably explains why I get lapped ! :banned:

I'm generally of the view for road cars, other than aesthetics, yer better off with a couple of sacks of potatoes in the boot, as you get the down load without any drag + get plenty of mash afterwards for a slap-up sausage and gravy tea. :squintdan

P.S. A lot of people will have come across the concept of the traction circle, where a typical high performance road sports car can corner at 1g, brake at 1g and ok, accelerate at maybe 0.4-0.5g up to the tonne.

Thus all other things being equal, the fastest possible lap should be posted when the car is being driven at the grip limit all the way around the track - the art of the racing driver - where all the grip is used to brake, turn and accelerate back out of the turn and any combination of the above up to the grip limit. Fundamentally downforce is one of the many ways to increase the size of the traction circle for our cars, then it's down to us to have the skillz to use the traction circle to its full extent!

For beginners, one way to approximate this is to:

1. Brake in a straight line, at the grip limit using threshold braking and get in the right gear
2. Smooth entry into a constant radius balanced throttle turn through the apex at the grip limit
3. Progressively feeding in the throttle out of the turn while dialing out lock using all width of the track at the grip limit clipping the kerb onto the straight. The tighter the turn, the slower it is (Hence the term "finding the right line" to maximise turn radii and carry the most speed).

Easy as 1-2-3. Cheers Colin! :squintdan

(Mr Hoad is a complete master at this! - just check the fella out on his handling track!) :bowdown1:

Hot sticky tyres anyone? (Now that would be extreme for a club track day). Gowan, who does it?!


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## Guy (Jun 27, 2001)

Great post.

The point about the effect on laptimes of downforce is well-made, albeit that for a long lap like the 'ring a lowly sounding 2-3% increase in cornering speed could take many seconds off a lap that lasts around 450 seconds.

Also the more notable effects of good or bad aero are when running at much higher speeds, in terms of stability. Some cars feel planted at 150mph, others very unstable. 



Aerodramatics said:


> I'm generally of the view for road cars, other than aesthetics, yer better off with a couple of sacks of potatoes in the boot, as you get the down load without any drag + get plenty of mash afterwards for a slap-up sausage and gravy tea. :squintdan


Unfortunately simply adding weight also blunts the acceleration and braking and by far far more than the benefit of extra traction. Thats why ALL cars go quicker on laptimes when lighter and why most race-classes have a minimum weight not a maximum!


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## David.Yu (Jun 28, 2001)

Guy said:


> Great post.
> 
> The point about the effect on laptimes of downforce is well-made, albeit that for a long lap like the 'ring a lowly sounding 2-3% increase in cornering speed could take many seconds off a lap that lasts around 450 seconds.
> 
> ...


Hmm, that does tie in neatly with Mizuno-san's belief that weight distribution and the "correct" weight for the size of tyres used is critical to getting the best overall grip over the widest range of speeds and conditions.

GT-R is all about "anyone, anytime, anywhere", not just flat out on a track.


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## TB993tt (Apr 21, 2008)

Guys
This subject has fascinated me since I first saw the original presentation of the R35.
The 0.27 Cd claim WITH downforce was/is incredible.

Dragging the only independant test of the aero of a GTR, the Sport Auto test where they use the Mercedes wind tunnel, results below:

I can't paste the picture - not enough posts but in summary:
measured data:
Cd 0.32
Frontal Area: 2.25
Front lift at 200kph = 12kg
Rear downforce at 200kph = 17kg

Now it would be easy (and obvious) to say the Germans are being patriotic and are pissed off that the Nissan could actually have the numbers claimed.

Maybe the methodology is different for measuring Cd, and maybe they didn't have the ride heights set correctly but really, do we think German engineer types are like that ? I don't.
So the measured lift forces are positive lift at the front and a bit of downforce at the back at 200kph - this is NOTHING like what Nissan is claiming !

I think it certainly shows that using a standard testing methodology at the Merc tunnel the Porsche GT2 eg gets virtually spot on with its drag and downforce claims as do most other Porkers that get tested so at at the very least it shows that "testing the way Porsche do it" the GTR has way different numbers than Nissan claim so their comparisons are not valid.

It piqued my interest when the 2011 GTr was announced with a Cd of 0.26 and downforce at 250kph (from memory) of 110kg front and 55kg rear.

All a progression from the claims on the original R35, but what really raised my alarm bells was an article where the Nissan head engineer said they knew they needed 530PS to hit the top speed target for the 2011 model.

Now if you look at the Nissan claims 0.26 with frontal area 2.09 gives CdA of 0.54
Compare to Porsche 997GT2 Cd 0.32 frontal area 1.9 gives CdA of 0.61

Both cars have 530PS so why can the Nissan only do 194mph and the Porsche manages 204mph - this is a big difference.

If you take the Sport Auto measured aero numbers they measured the GTR at Cd 0.32 and frontal area 2.25 so CdA 0.72 - This is the reason it will "only" manage 194mph

The differences must be in the testing methodology but in the (excellent) pdf presentation on this thread they use Porsche GT2 numbers and Nissan claimed numbers side by side as if comparable - they clearly are not.....


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## thistle (Oct 27, 2007)

Nissan claim 196 mph for the new car, but the old one did 195 mph when Motortrend tested it. The 6th gear is too short with the stock rev limiter for much higher speeds, but I don't have the exact rev limit of the new car to hand, the mph/1000 RPM figure and the engine speed at which it is supposed to make peak power. I suspect this gearing effect is significant enough that it makes a top speed comparison invalid to draw any aerodynamic comparisons.


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## TB993tt (Apr 21, 2008)

thistle said:


> Nissan claim 196 mph for the new car, but the old one did 195 mph when Motortrend tested it. The 6th gear is too short with the stock rev limiter for much higher speeds, but I don't have the exact rev limit of the new car to hand, the mph/1000 RPM figure and the engine speed at which it is supposed to make peak power. I suspect this gearing effect is significant enough that it makes a top speed comparison invalid to draw any aerodynamic comparisons.


Here is the quote from Mizuno:
_We calculated the engine power and the gear ratios based on the target Cd figure. We did not start the engineering development of the GTR with the engine but we designed the powertrain and aerodynamics to be capable of 193mph_

I have an image shot of the article but apparently cannot post images til 15 posts.

This quote isn't eaxctly what I said but it indicates to me that they set the 193mph target or at least had that in mind when speccing the aero and power. Like I said with the aero they are claiming, it should be much faster than the 193mph target with 530hp.....


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## David.Yu (Jun 28, 2001)

As Thistle said, the car is rev-limited in 6th gear. A higher ratio would see a higher top speed, but the GT-R's ratios are geared for acceleration more than top speed or fuel economy.


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## mindlessoath (Nov 30, 2007)

The gearing is the limiting factor of top speed. by modifying the engine/ecu it can go higher. highest recorded top speed is 205mph in one mile - iirc set by AMS performance. with gearing changes it can go higher which they are setting out to do. also HKS also did around 200mph too.

Nissan use a differnt wind tunnel than what sport auto use and the R35 has alot of wind tunnel testing. the PDF clearly describes alot that sport auto doesnt take into consideration.

Small aero mods will likly change the way the car drives and that could be what the driver wants, so the minor downforce added may benifit in that way as well... limiting the top speed wouldnt matter too much and the peices usually do look good and in some cases are lighter than the stock parts they replace. cost is the downside and picking a kit that works the way you want is another downside especially at those high costs, so many kits out there do nothing or hurt performance. a mph here and there could be the differnce in winning.

There are modifications that are for adding lots of downforce that do make a differnce. check out the top speed motorsports R35 TopSpeed Inc. - Follow any special events and projects as they unfold you can read his posts at nagtroc for the details of it. Sure there are downsides but these guys won the one lap of america 2011 and recorded the fastest quarter mile time ever in that event. aero comment from the blog http://topspeedsales.com/blog/?p=682 

lots of people also add the aeromotive wing which is movable for reduced drag in strait line and more df in the corners, pretty proven to add a few secounds to a lap (generaly combined with a front splitter).


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## TB993tt (Apr 21, 2008)

David.Yu said:


> As Thistle said, the car is rev-limited in 6th gear. A higher ratio would see a higher top speed, but the GT-R's ratios are geared for acceleration more than top speed or fuel economy.


OK, so I mis-interpreted the Mizuno quote. What about the Supertest data etc, what do you guys think ?


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## thistle (Oct 27, 2007)

It may be that the aero may not be what they are claiming, but I don't think your argument that doing 196mph instead of 204mph with the same claimed 530 PS and claimed lower CdA supports it. They designed the powertrain and aero to be capable of their target maximum speed. It doesn't say they used the minimum possible power to reach their maximum speed target. It doesn't say that the powertrain only had the maximum speed target in mind, it would also have emissions, reliability, cooling, economy, NVH contributions.

Without a taller 6th gear (which would generally reduce acceleration up to the intended maximum speed), or adding a 7th gear which would add weight and costs if they had a 6 speed design, or making final drive or wheel/tyre changes to change the effective gearing, they would need a higher rev limiter to make over 200 mph.

We had to raise the rev limiter substantially so Boost Logic could do their ~204mph in a standing mile last spring. Even though they had the power to do 204+ mph, without that rev limiter they couldn't have done it.

Perhaps Nissan wanted the rev limiter at the previous model's 7000 RPM for reliability, IIRC it is 7300 RPM in the new model.


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## TB993tt (Apr 21, 2008)

thistle said:


> It may be that the aero may not be what they are claiming, but I don't think your argument that doing 196mph instead of 204mph with the same claimed 530 PS and claimed lower CdA supports it. They designed the powertrain and aero to be capable of their target maximum speed. It doesn't say they used the minimum possible power to reach their maximum speed target. It doesn't say that the powertrain only had the maximum speed target in mind, it would also have emissions, reliability, cooling, economy, NVH contributions.
> 
> Without a taller 6th gear (which would generally reduce acceleration up to the intended maximum speed), or adding a 7th gear which would add weight and costs if they had a 6 speed design, or making final drive or wheel/tyre changes to change the effective gearing, they would need a higher rev limiter to make over 200 mph.
> 
> ...


OK. I understand the rev limit thing, thanks for explaining :thumbsup:

It is the Sport Auto discrepancies which I find troubling.


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## thistle (Oct 27, 2007)

There is also a huge amount of fuel dumping going on in 6th gear at over about 155mph from a standing start (it is on a timer) which blunts acceleration and smokes but helps to control temperatures with a full set of cats and variable pump fuel quality. The air fuel ratio target goes about 1 AFR richer, as Mr Yu found when the ECU on his stage 2 car still on stock injectors then complained about him running the injectors wide open.

For this reason it will be making less power at top speed than it makes in the lower gears. Whether either are more or less than 485 or 530 PS for the early and late models respectively is entirely another debate, but does colour the debate over whether the peak quoted power is at sustained top speed or a rip through the lower gears...


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## Cris (Sep 17, 2007)

TB993tt said:


> Guys
> Now if you look at the Nissan claims 0.26 with frontal area 2.09 gives CdA of 0.54
> Compare to Porsche 997GT2 Cd 0.32 frontal area 1.9 gives CdA of 0.61
> 
> ...


Not wanting to pee on anyone's fireworks but many moons ago when I studied schoolboy aerodynamics there were more types of drag than form drag and frontal area. I think it was called surface drag. Does the Cd factor include the surface drag as well as form drag?

Also if both the Porsche and the Nissan had 530PS at the crank and we assume that both gearboxes are as efficient as each other I would imagine that the GT2 being 2WD would transmit more force at the wheels. The Nissan has more parasitic losses with it's front propshafts and because it spins a driveshaft from the front of the car to the back. The Porsche has it's engine right next to the driven wheels.


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## mindlessoath (Nov 30, 2007)

Nissan has said the nissan gt-r has a 10% friction loss. iirc you can put it in N and push it with a couple of fingers without any issues. also you may want to check out the nissan GT-R press kit... it uses its chassis design to aid with aero, it explains something like all the weight over each axel so when acceleration is appiled the front doesnt lift but the car pushes down. NISSAN GT-R press information...

NISSAN GT-R press information...

Im not sure the sport auto aero tests go into the detail that nissan has done. but i have never been to a windtunnel so im not a huge expert in the whole thing. i think nissan might use a rolling road windtunnel where as sport auto is not. also im not sure if that in engine compartment cooling is taken into account... thats where it says they made ALOT of improvements. if sport auto didnt take that into account, thats why the numbers would be off. you will get differnt numbers from wind tunnel to wind tunnel anyways (from what im told from an expert, guessing because not everyone is the same).


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## ANDYR35 (Sep 1, 2008)

Robbie J said:


> nuts worked for me
> 
> 
> 
> ...



Put mine on yesterday and the car defo feels lighter 
Gun Metal grey nuts look good with the wheels too.


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## Fuggles (Jul 3, 2001)

Great to see some really detailed knowlegde being shared here and links to good quality information. I'm not sure i understand all of it but it's all very interesting all the same. 

As regards the Mercedes wind tunnel I have it on very good authority this is a static wind tunnel and not a moving belt design which is one type of design and one not used by some other companies. In Sport Auto Mizuno-san mentioned that the moving belt design gives as closer 'real world' figure than any other design. All the GT-R work was done in a moving belt wind tunnel. Sport Auto use a static wind tunnel. So whilst cd figures can be posted the figures have to be related back to the tunnel and the design of the technology used to measure the cd. Hope that helps! :nervous:


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## TB993tt (Apr 21, 2008)

Fuggles said:


> As regards the Mercedes wind tunnel I have it on very good authority this is a static wind tunnel and not a moving belt design which is one type of design and one not used by some other companies. In Sport Auto Mizuno-san mentioned that the moving belt design gives as closer 'real world' figure than any other design. All the GT-R work was done in a moving belt wind tunnel. Sport Auto use a static wind tunnel. So whilst cd figures can be posted the figures have to be related back to the tunnel and the design of the technology used to measure the cd. Hope that helps! :nervous:


That is really interesting.....

What I don't quite get is surely Porsche also use state of the art moving belt wind tunnel (can't remember where but read somewhere about a massive Porsche investment in latest wind tunnel tech) and the merc tunnel still manages to match the quoted Porsche numbers very accurately (I have loads of Sport Auto Supertests on Porsches and they are mostly pretty spot on) why should the GTR measurements be so far out ?

How can the frontal area calculation be so wrong, I must say the GTR does look like it has a big frontal area doesn't it  

As the article says in this thread, aero numbers cannot be measured like hp numbers...... It bodes the question what for example a Porsche 997GT2 would measure in terms of Cd and frontal area using the Nissan tunnel using their methodology, the fact that Nissan quote Porsche's own stated aero numbers in all their comparison literature smells a bit of Nissan selecting the bits of data (about the competition) which they want to use to present their product in the best possible light - I guess what they all do :chuckle:


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## Fuggles (Jul 3, 2001)

Of course, every company would use the bits they want. They would either use the published information available or, if they can, get information from independent sources, such as JATO, and use the bits that work to their advantage. Not sure why the Merc tunnel quotes the same as the Porsche one, I guess we would need to know what type of tunnel Porsche have to be sure of the detail


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## David.Yu (Jun 28, 2001)

Windtunnels, shmindtunnels. All that matters is the performance figures, and on those the GT-R cannot be faulted, especially for a £60k-£70k pricetag! :clap:


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## TB993tt (Apr 21, 2008)

David.Yu said:


> Windtunnels, shmindtunnels. All that matters is the performance figures, and on those the GT-R cannot be faulted, especially for a £60k-£70k pricetag! :clap:


When a manufacturer goes to such awesome detail in their press packages and in various publications with copious amounts of technical data, for me it really adds to the experience of the car but obviously when some of the data is questioned I'd like to get to the bottom of it,,,,, others needs/wants may vary


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## mindlessoath (Nov 30, 2007)

not sure how to embed these so here are the links.
YouTube - Miniature windtunnel Part1.wmv
YouTube - Miniature wind tunnel Part2.wmv
YouTube - Miniature windtunnel Part3.wmv
YouTube - Miniature wind tunnel Part4.wmv
YouTube - Miniature windtunnel Part5.wmv


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## Aerodramatics (Feb 10, 2008)

Guy said:


> Great post.
> 
> The point about the effect on laptimes of downforce is well-made, albeit that for a long lap like the 'ring a lowly sounding 2-3% increase in cornering speed could take many seconds off a lap that lasts around 450 seconds.
> 
> ...


Point accepted. Totally agree that a small aero gain in downforce for competition is always taken ruthlessly, but in instances where a massive improvement over road car aerodynamics has already been achieved across the field of competitors. 

Generally it's my experience that downforce targets are relatively straight-forward to engineer for a given set of regulations but it's the overall holistic flow management where the lion's share of the aero effort and thinking goes.

The trick is to make sure all components integrate in harmony and mutual benefit without harmful interference, especially for diffusers and for maximising cooling flows, be it brake or radiators. Much of the testing effort is expended mapping car balance with fore-aft ride height to understand sensitivity and optimum settings for fastest laps (on a particular track). This provides a tuning range for different handling characteristics to suit different race driver, which is not necessarily the fasted according to the simulators, but sometimes the best drivers can beat the race engineers predictions!

To synthesis these data, a combination of computer modelling, sub-scale wind-tunnel testing and full-scale track testing is used, not to mention a good dollop of engineering judgement based on experience.

I was taking the proverbial about the diddy aftermarket aero mods for road cars, which are imho mostly about style and the "race car look" on a street car, but for me only add a tiny and imperceptible and practically inacessible real improvement in cornering performance. Hence my sentiment that road car aero mods are "about as useful as a sack of spuds!" 

I think some Exiges with decent aftermarket big slotted wings get closest to actually adding a decent slug of exploitable cornering speed, but it's still small beer compared to doing a proper job.

Agreed. "High speed" stability, dynamics and control and resultant handling and feel is also partly subject to aerodynamic design targets and criteria as well as car performance. Design is holistic. Light steering wheels due to axle lift and reduction of directional stability due to crosswind is really unsettling.

Totally agree on weight too. For all high performance machines, weight is king. It's hard to argue against the engineering sense of Colin Chapman's famous maxim: "Simplify, then add lightness!"


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## Fuggles (Jul 3, 2001)

Aerodramatics said:


> Hence my sentiment that road car aero mods are "about as useful as a sack of spuds!"


Spuds usually weigh more, so not a good idea to improve performance, even if it does help with stability :chuckle:


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## Aerodramatics (Feb 10, 2008)

Fuggles said:


> Spuds usually weigh more, so not a good idea to improve performance, even if it does help with stability :chuckle:


LOL. :chuckle: Yes, I'd have to agree. Although the weight is reassuring, I do find spud-tank slosh a dynamic balance problem in the twisties, especially the chicanes, but it makes for a good mash though. Best policy is to brim it. :runaway:

Like you, I'm still not convinced road car aero mods do much better  

No matter, each to their own and whatever makes ones boat float. 
If it makes people happy, it can't be that bad :thumbsup:


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## Aerodramatics (Feb 10, 2008)

TB993tt said:


> Now if you look at the Nissan claims 0.26 with frontal area 2.09 gives CdA of 0.54
> 
> Compare to Porsche 997GT2 Cd 0.32 frontal area 1.9 gives CdA of 0.61
> 
> ...


For fun I ran the numbers.

Assuming a typical road car on tarmac rolling resistance coefficient of 0.01 and 18kN weight, then rolling resistance is about 180N and that absorbs about 21bhp @ 194mph.

Using the CdA figure of 0.61, then power absorbed due to drag is 332bhp.
A total of 353bhp at the wheels.

If the off-quoted R35 dyno loss 25% is correct, then this would approximate
353/.75 = 471bhp or 478PS. :bowdown1:

Seems suspiciously spot-on to me ! :thumbsup: :clap:

CdA 0.72 is 399bhp for the aero drag, 560bhp at the flywheel.
CdA 0.54 is 294bhp due to aero drag, 420bhp at the flywheel.

So it seems a reliable estimate of the R35's and Porka's average high speed running transmission loss + rpm limit due to gearing and power curve (at wheel and flywheel) is needed then one could infer who measured CdA best and who measured it worst.

Hope this helps a little :runaway:


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## thistle (Oct 27, 2007)

25% dyno loss is high, includes rolling resistance (increased due to double contact patch and tie down) as well as losses from rotating the dyno.

Since you've already included the tarmac rolling resistance there is no value in adding an inflated version of it again, and the losses from rotating the rollers and retarders (bearings and windage) don't apply on tarmac also.


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## Aerodramatics (Feb 10, 2008)

Aha. Good point.

So, taking off the 21bhp which is already included (+ subtracting say another 450kg tiedown load), i.e. about 5bhp extra rolling resistance, we'd have:

CdA 0.54 @ 194mph = 420bhp-21-5= 396bhp or (294whp|aero)/.75 +5 = 392bhp+5 = 397bhp
CdA 0.61 @ 194mph = 471bhp-21-5= 445bhp or (332whp|aero)/.75 +5 = 443bhp+5 = 448bhp
CdA 0.72 @ 194mph = 560bhp-21-5= 534bhp or (399whp|aero)/.75 +5 = 532bhp+5 = 537bhp

depending on whether the rolling resistance losses should be subtracted from the bhp or the tiedown power loss added to whp.

Second calc seems most right, as it doesn't scale rolling resistance losses by 4/3, i.e. first calc is total whp/rolling road factor less double-accounted rolling resistance losses. And total whp = rolling resistance power + aero power. It's late. I'll sleep on it. Both corrections are close to one another in result.

Which now leaves a correction for the rollers and windage to do + 6th gear rpm limit power output to find the closest match to a CdA which produces the best power match.

Anyone know some representative figures?

P.S. if the double contact patch doubles rolling resistance (or some proportion thereof) and then the tiedown adds again then the above figures could be due another 10 to 20 bhp correction on top of those done.


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## Aerodramatics (Feb 10, 2008)

Cris said:


> Not wanting to pee on anyone's fireworks but many moons ago when I studied schoolboy aerodynamics there were more types of drag than form drag and frontal area. I think it was called surface drag. Does the Cd factor include the surface drag as well as form drag?


Agreed. Although the size of the aero power figures suggests the "CdA"s quoted are whole car drag coefficients not components. But valid point all the same.

As an aside, Aerodynamicists have as many names for different drag components as they can either:

a. measure, or
b. calculate using theory, or
c. imagine

However, there are only two physical mechanisms that transfer the fluid dynamic forces to the body moving through the fluid, namely:

1. (surface) skin friction drag
2. (surface) pressure drag

where the drag force opposes the relative motion of the body, i.e. drag is the component of the resultant force parallel and in opposite sense to the instantaneous velocity vector, i.e. a wind axes component force. Not to be confused with body axes axial force. Although handily for zero incidence only both axes systems values are the same, i.e. if the car was tested at zero pitch attitude at zero incidence and CdA data reported axes convention confusion would be avoided.

Another aero convention is to use lower case for "2-dimensional (2D)" calcs or measurements and upper case for "3-dimensional (3D)" calcs or measurements. Obviously 2D data are either a simplification or component of overall 3D data.

So CdA and CDA could signify 2D or 3D data. Or not.

Also in the aerospace industry the reference area in not frontal projected area as in the car industry, but usually the mainplane projected wing reference area, which is conventionally denoted as Sref or just S, i.e.

CdS or CDS.

Road cars are fundamentally "bluff bodies" (poor aero shapes) to exploit great usable volume & then cleaned up with aero cunning and trickery, whereas high speed aircraft or high performance sailplanes by necessity insist on a starting point of good aero shapes and for a common car-sized 2metre ref. area produce "car equivalent" zero-lift CDs of low 0.1s and some exceptional designs in the sub-0.1s. However things like a 1950s era 4 seat Cessna 182 will have zero-lift CDs of circa 0.2 to .25 (0.025 to 0.03 using wing ref. areas) , i.e. not much better than a GT-R!

Also reference areas are sometimes the original early days concept reference areas even if the true reference area has changed due to sizing design changes a little. It doesn't matter, as the same forces and moments are calculated dimensionally. The engineers working on the projects will know these "insider" conventions but outsiders won't. Confusing if insider Cd values get published by marketeers without explicit definition.

After all, non-dimensional drag coefficients are just by convention the drag force divided dynamic pressure and a reference area.

If a Cd created with one reference area is converted into a CdA with A being a second reference area then the CdA figure is in error. Easily done if the source reference area is not publish and a logical alternative (like measured frontal area) is applied. This could only be a couple of percent difference in practice, but adds to confusion and discrepancies. 

So when figures are bandied about on tinterweb, these hidden traps can be innocently fallen into in blissful ignorance. I definitely include my *** pack calcs in that category!

Still, makes for a lively debate on petrolhead pages around the world :chuckle:

P.S. 

Skin friction drag, pressure drag, parasitic drag, form drag, vortex or induced drag, wave drag, interference drag, trim drag, extra-to-elliptic drag, zero-lift drag are all in common use to name but a few! :runaway:


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## David.Yu (Jun 28, 2001)

Aerodramatics said:


> complicated stuff...


Did you see the Mythbusters episode when they added golf-ball inspired dimples to a car and measured a distinct improvement in fuel consumption, i.e. they measurably improved drag?

Why haven't any planes or cars adopted a similar approach? Ok, nobody wants to drive around in a car that looks like Daleks have gang-banged, but if it results in significant drag reductions? And on a plane there could be huge efficiency improvements?


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## Aerodramatics (Feb 10, 2008)

David.Yu said:


> Did you see the Mythbusters episode when they added golf-ball inspired dimples to a car and measured a distinct improvement in fuel consumption, i.e. they measurably improved drag?
> 
> Why haven't any planes or cars adopted a similar approach? Ok, nobody wants to drive around in a car that looks like Daleks have gang-banged, but if it results in significant drag reductions? And on a plane there could be huge efficiency improvements?


LOL. Gang-banged by Daleks! :chuckle: No, I hadn't seen this. But thanks to t'internet I now have! The clip I saw starts with the dimpled car having the clay dimples put on the back seat in a box:

mythbusters-dimpled-car-minimyth

I don't know what they mention about the golf ball effect, but the old adage goes that players used to use smooth golf balls but when they became old the surface became pitted and rough but players found they could hit old balls further than new balls, and the dimpled golf-ball was born.

Fundamentally, the dimples purpose on a golf ball is to reduce the region of flow separation which created a separated wake which causes a large pressure drag. They are effectively another type of VG (Vortex Generator).

It is conventionally explained by the fluid physics of the boundary layer of air, i.e the air in direct contact with the surface and a little bit above which is slowed down by the effects of surface friction. In a simple 2D sense, the dimples nominally cause the boundary layer to change type from a natural low skin friction laminar boundary layer to an artificially forced turbulent boundary layer. That's the "what they do", the "How they do this" is a more complicated affair. Coming back to to the "what" happens...

The smooth ball has a laminar boundary layer, the dimpled ball a laminar-turbulent or fully turbulent boundary layer. Basically the laminar boundary layer produces less friction, but cannot travel all the way around the ball before separating causing more pressure drag. Whereas the turbulent boundary layer produces more friction but travels further around the ball producing more friction drag but a lot less pressure drag. The reduction in pressure drag out weights the increase in friction & a large net reduction in total drag is observed.

Typically under lab test conditions a laminar boundary layer flow gets to about 110 degrees (taking nought degrees as the leading edge of the ball), so just past the top before it separates due to pressure distribution effects. So most of the back of the ball is a big wake. When the boundary layer is turbulent, the separation can be delayed to 130 degrees or more, depending on how cunning one is.

Ok, that's the ideal simple 2D result. Spin of the ball modify this result. Hence the value spin in ball sports for swerving the ball and throwing off the opposition.

The "How" dimples work is reasonably sophisticated, but fundamentally the pressure disturbances they produce causes the air to form vortices. The aerodynamics of both bumps and dimples are subject to serious scientific research as their flow physics are of academic and practical interest. 

Ok, coming back to the car and bearing in mind the effect of the dimples is similar to VGs and that their purpose is to reduce the size of separated flow. Looking at the dimples and the surface of the clay they are bigguns. The size of the devices is important, too many, or too big and they add unuseful "excrescence drag" and weight; too small or in the wrong place, they don't enough effect. From the test results there seem to be enough to produce an improvement, but not too many to cancel the gains. (3mpg, 11% improvement @ 65mph quoted)

Taking as an example the GT-R Computational Fluid Dynamics flow viz streamlines at the bottom of pg 32. of Godder's link to the pdf article on pg.1 of this thread, then you can see "pockets" of separation at the base of the front and rear windscreens + the large "base drag" at the cars rear face across the rear bumper. These three zones are obvious sources of large pressure drag. Other sources not shown are the vortices shed from the box edges of the car (which cause vortex drag, i.e. the energy to make them comes from the car). 

So I'd reckon the big dimples are energising the boundary via their vortex shedding mechanism and reducing the size of the separation zones and favourably reducing the strength of the edge vortices for an overall drag saving.

The side door panels dimples might be dispensed with as the are in fully attached flow zone with at close to static pressure (i.e. same pressure as air far from the car), adding energy to the flow here might be producing little or no benefit or even wasting energy.

For the car tested, the rear window seems a bit steeper, so it'd probably have a worse boot lid junction separation pocket than our GT-R.

Anyway, that's my guess on why the golf ball dimples are working on the car, for what's it's worth! :chuckle:

The reason they are not used Aeroplanes, I'll ansa, if you are still awake, alive and kicking... not easy to explain it well in a sentence over the tinterweb!


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## David.Yu (Jun 28, 2001)

Don't need the detailed answer, but would like to know why similar principles haven't been applied general in vehicle design.


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## Aerodramatics (Feb 10, 2008)

P.S. They didn't explicitly mention in the clip if they corrected for the weight of the clay covered car compared to the un-clayed car, but do mention they did measure the fuel consumption for the car with smooth clay and no dimples, so I guess they have done so.

P.P.S. No myth was broken, at least not for aerodynamicists.

Hydraulically smooth surfaces (at the microscopic scale) do have much less skin friction drag than hydraulically rough surfaces and are better for less skin friction.

Check out the Moody Hydraulic Roughness Chart derived from a huge body of experimental results:

Moody Chart

The smooth surface drag is much less than the rough surface drag due to friction. The dimpled clay surface was not hydraulically rough but looks hydraulically smooth (so the cars would have had same skin friction) but the VG effect of the dimples seem to have reduced the size of draggy separated flow zones. Overall result equals improvement.

However, it's true to say smooth surfaces do not strongly influence pressure drag only friction drag. Hence if you want to affect pressure drag, smoothness won't help. Only shape changes or passive or active flow control devices (such VGs -physically or airjet, etc) will help reduce the size of local separation zones or reduce wake size due to base drag.

This was already well known to engineers and scientists. A matter of horses for courses.


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## David.Yu (Jun 28, 2001)

So what you're saying is that for the crappy base car Mythbusters tested, the dimples improved drag overall, but for a well designed modern sports car, like the GT-R, they wouldn't?


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## Aerodramatics (Feb 10, 2008)

David.Yu said:


> Don't need the detailed answer, but would like to know why similar principles haven't been applied general in vehicle design.


The answer is they are, but only when there is a problem area to tidy up where they can be helpful or a better more effective choice (shape redesign or better alternative solution)

In the case of aircraft and race cars they are designed to have fully attached flows (i.e no appreciable wakes or separation zones), so adding the dimples won't necessarily produce a worthwhile aero benefit, perhaps a penalty.

Could be useful for combat aircraft performing ACM and also for transonic transports trying to reduce shock wave drag by modifying shock-boundary interactions (for which they are researched heavily!)

For road or race cars I think you hit the nail on the head with ugly Betty reason:

1. Radical! and butt ugly! +
2. Potential increase in manufacturing and tooling costs (complex curvatures)
3. Potential increase in parts and maintenance costs.
4. Potential increase in detailed design costs (panel edges with bumps)
5. Potential added weight to structural panels
6. Potentially waste internal volume at the big boy scale
7. Complex "off-design" adverse handling effects for aircraft
8. Only tuned to work well at a single design point with less benefit off-design
9. Can't solve some problems
10. Better gains to be had from investment in developing other system areas - a big reason!

Old story of needing to hit a break even point where the cost of change in recurring or non-recurring cost is reduced or is outweighed operational economics and there is sufficient customer demand and the proviso it's a better investment choice than competing technologies and other options 

Not to say much smaller versions of these sort of devices aren't under active research and development.

Mother nature is a wonderful teacher. Dolphin and shark skin has super low friction drag characteristics and led to the development of large eddy break-up devices in the 80s; and in the 90s a lot of effort was put in to researching so-called sub-boundary layer devices (i.e. minature VGs or "synthetic airjet VGs). Then there's the aerodynamic and other engineering tricks of fish, insects and birds.

Leeds 2, QPR 1... Durty Leeds. Does it matter? Up the hoops win or lose!


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## Aerodramatics (Feb 10, 2008)

David.Yu said:


> So what you're saying is that for the crappy base car Mythbusters tested, the dimples improved drag overall, but for a well designed modern sports car, like the GT-R, they wouldn't?


Oh no. Just saying the dimples improve zones where there are big separations and produce big drag reduction benefits. So if you've got these features on your design the idea of dimples is worth serious thought.

From the tests, they might work for the GT-R too, just given it might be a better starting point, could have less problem areas to tidy, so will produce less beneficial effects.

On the other hand, for a fully attached flow design with no high drag separation zones to remove, they could add to the overall drag. Dimples can't fix what ain't broken!

Horses for courses. They are not suitable for every design situation. T'is all. :thumbsup:

P.S. I bet automotive aerodynamic specialist engineers around the world have been tempted to check out the Mythbuster effect in their R&D to see if they can understand it and improve upon it. Might lead to a break-through but not necessarily devices which are dimples but devices which achieve the same physical effect.

We might be surprised yet. 

P.P.S. 

I *know* you did Purplezilla.... will you be the first to try a Dimplezilla mod?


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## mindlessoath (Nov 30, 2007)

There is a dimple WRAP for cars and iirc a thread on nagtroc with it on a gtr. Would it be worth an article to try that out?
http://www.fastskinz.com/
http://www.nagtroc.org/forums/index.php?showtopic=34730

Edit: Since a comment was made about this above in my skim of reading the above posts...
http://www.nagtroc.org/forums/index.php?showtopic=45629
found this. Jun says that the wind drag of the trunk is large. The wind drag is decreased with the Wet carbon Rear glass garnish









ALOT of people making R35 aero are not modeling and taking into consideration in engine and under diffuser airflow... Does this make for huge incorrect calculations? air from the rear diffuser comes out the vent above the diffuser and below it in real life, but when i see the 3D models they designed it flows from under the car not the vent. example http://www.nagtroc.org/forums/index.php?showtopic=49883&st=100 and http://aeromotions.com/the-story/


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## mindlessoath (Nov 30, 2007)

found this link just now 500 km/hr (311 mph) Nissan GT-R | 2009 Nissan GT-R

500km/h gtr


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## Aerodramatics (Feb 10, 2008)

mindlessoath said:


> ...There is a dimple WRAP for cars and iirc a thread on nagtroc with it on a gtr. Would it be worth an article to try that out?...


Thanks for that. Not seen the Fastskinz product before. It's essentially very similar to a wind-tunnel test technique called transition dots, which is a simple method of "transition fixing".

The dots force a laminar boundary layer to become a turbulent boundary layer. A key difference between full scale testing (real vehicle at real speeds) versus sub-scale testing (model vehicles at tunnel speeds) is ensuring the amount laminar and turbulent boundary layer is a fair match to real life. 

For sub-scale testing @ say 70mph tunnel speed, the natural state of boundary layer is laminar for about the first 12 inches of flow, which is a a little more than a quarter of a 3& 3/4ft 1/4th scale GT-R model, but at full scale only one fifteenth. So on the model, we need a way to force transition at 1/15th of model length, i.e. the first couple of inches, to match real life which has a turbulent boundary after this.

By placing the dots just ahead of the first 2 inches, the turbulent boundary layer is artificially "fixed" in the correct full size position.

Fastskinz appear to have adopted this concept and cleverly designed it into a low cost, tough film appliqué. However, here the dots are used as sub-boundary layer devices to mix faster moving air into an already turbulent boundary layer near the surface. Essentially they are "micro-vortex generators".

It is probably true that covering the entire vehicle with dots is overkill, but if there is an overall gain, then no problem.

The box cars used in the demos are chosen, because they are draggy and benefit most. Even so, you could probably get away with a few well chosen strips of a few feet at specific locations. However, the low pressure (sub-static pressure) suction areas on the bonnet (hood), roof and boot (trunk) pillars tend to relaminarise a turbulent boundary layer, so rather than determine these positions and amounts for each and every design via analysis and test, they play it safe and cover the entire vehicle to maximise possible beneficial interaction.

I suspect they could make the dots the same colour as paint, so to the eye they would much more aesthetic. Presumably they are black dots on white/yellow paint to highlight the product dot features for marketing & comms purposes.

However, it also occurs to me you make more money covering the entire vehicle if you sell your product by the square foot or metre! And why not, they need to recoup their R&D, production & marketing costs + they've taken the risk with their investment, they should reap the rewards if they are successful. A practical approach which also maximises profit :squintdan

P.S. If the aero separation zone is sufficiently strong due to the shape, then no amount of dots or VGs can help and adding them is a waste of time. Aerodynamic fixes work best on marginal designs or help good designs do more at large but critical off-design points or achieve multipoint design points they otherwise could not without the devices. Even then, they can get pretty big and rad! -although the strong technology push is to achieve more with active micro devices nowadays. The fact is Aero fixes struggle to correct bad design and almost never do.


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## Aerodramatics (Feb 10, 2008)

mindlessoath said:


> ...The wind drag is decreased with the Wet carbon Rear glass garnish...


Following your links, I saw this picture of a R-35 sub-scale wind-tunnel test using laser light-sheet flow visualisation along the car centreline:

R35 flowviz withlaser light sheet

Looks like there is appreciable suction over the the windscreen (windshield) B-pillar and a degree of downstream boundary layer thickening and potential separation. Without corresponding surface oil flows, it's easy to read too much into smoke and lasers.

As to the trunk fairing, it might reduce drag a little, but the main source of the drag is likely a local upstream separation on the rear windscreen which it can't help + the junction itself is a natural separation zone. Looks nice though. I figure that's why Nissan did nothing in terms of trim as the zone shouldn't be that sensitive as the flow is already separated.

I really like what Aeromotions are all about, a professional outfit making proven claims, no bull:

AEROMOTIONS THE DATA

and offering a realistic street-car sized wing for the trackday warrior and club amateur racer. The base wing offers a good second on a two minute lap, and they've eked-out 2 and a bit seconds a lap by going active and a minor mod.

On an 18 lap club race, all things being equal, that should translate into a 30 second lead.

I like the simplicity of the product on offer:

Aeromotions R-Series Rear Wing

It's a straight-forward single element wing design with modest endplates. From the numbers Aeromotion mention, I've estimated the following clean air down-force data for this wing:

100lbs (45kg) @ 70 mph apex corner speed costing 4bhp 
200lbs (91kg) @ 100 mph costing 11bhp
450lbs (204kg) @ 150mph costing 37bhp
800lbs (363kg) @ 200mph costing 87bhp

Drag is about 1/5th downforce and operating downforce coefficient is ~1.7 which is wholly respectable for a low-aspect ratio (6.4) single element design. It's only got about a 5" overhang either side.

I like it. When I bling my R-35, I might well get one. Just for the race look, knowing it's the real deal. :smokin:

Mr. M.O. I think you've sent me on the path of temptation with Aeromotions when you mentioned them a couple of years back. Still tempted. Deffo on my wishlist along with a nice skirt and splitter kit A street car with great race car looks and a smidgen of extra performance! :chuckle:


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## Aerodramatics (Feb 10, 2008)

mindlessoath said:


> ALOT of people making R35 aero are not modeling and taking into consideration in engine and under diffuser airflow... Does this make for huge incorrect calculations? air from the rear diffuser comes out the vent above the diffuser and below it in real life, but when i see the 3D models they designed it flows from under the car not the vent. example


Does it make for hugely incorrect calculations? No, not for a upper surface rear wing design. Depends on the area of interest. Engineers will model what represents the problem they are solving, and only add detail if it helps.

I suspect for aftermarket suppliers, they simply can't be doing with the ball-ache! :runaway:

They need to disassemble the rear end to get to the internal geometry, then laser-scan it (if they can - probably not possible), then usually get a CAD designer to make sense of the STL cloud-point data and remodel into a standard CAD format and then output the geometry.

Alternatively the CAD designer or CFD modeller schemes the internal geometry from pictures and measurement.

Takes time and effort, and whilst nice to have a wholly representative model, it doesn't always help improve answers.

Complex models usually have lots of glitches due to their complexity, so engineers tend to simplify the geometry whenever they can to get to an answer most quickly and efficiently, so they can spend more time on the design thinking and less on model building (which can be time consuming).

Obviously, if one is designing a diffuser or improving the underbody flow to help the diffuser drive the underbody tray suction in conjunction with sideskirts, then perhaps its worth modelling.

However, experienced race engineers already know 9/10th of the answer for these well-known problems and can get to a working design by eye and experience alone in short order.

It's the last 10% of performance better than the competition that really costs sweat :flame: and tears :bawling: in my experience! :chuckle:

P.S. Another maxim favoured by experienced engineers: "All models are wrong; some are useful."


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## mindlessoath (Nov 30, 2007)

F430 Aero Development - 6speedonline.com Forums
since you like them, thought i would share the link


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## Aerodramatics (Feb 10, 2008)

mindlessoath said:


> F430 Aero Development - 6speedonline.com Forums
> since you like them, thought i would share the link


Proper gud! Ta. Nice read. It's great to have serious money


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## mindlessoath (Nov 30, 2007)

check this out!
Yoshi DN Duckbill CF Trunk - NAGTROC - The Nissan GT-R Owners Club
He created this wingless duckbill trunk for the R35
cost looks pretty good.

*Designed with Yoshi Suzuki.
*The trunk is uniquely designed with a low drag but high downforce focus.

- Revozport GTR-DN Trunk = US$1000 (FRP)
- Revozport GTR-DN Trunk = US$1500 (Carbon Fibre)
- Revozport GTR-DN Trunk = 15% additional charge. ( Matte Dry Carbon Fibre )

A group buy is also available if we are 5 or more. 15% off

btw guys, the 3rd light you see in the renders will not be there for the production model. It can only be done with the FRP model but you have to send them your 3rd light or purchase a new one and sent to them.


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## PETERJH (Nov 14, 2010)

I want one in matte cf.It looks great:thumbsup:


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## David.Yu (Jun 28, 2001)

The SSP GT-R I drove across America in the 2009 Gumball 3000 had an active Aeromotions wing on it. You could definitely feel the extra drag when deployed as an air brake. 
Will it cause more drag than the stock wing when "flat"?

I personally don't like the look, but if it doesn't increase drag when flat but dramatically improves downforce when angled, it does make sense over any other kind of aftermarket wing.



Aerodramatics said:


> Following your links, I saw this picture of a R-35 sub-scale wind-tunnel test using laser light-sheet flow visualisation along the car centreline:
> 
> R35 flowviz withlaser light sheet
> 
> ...


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## Aerodramatics (Feb 10, 2008)

David.Yu said:


> Will it cause more drag than the stock wing when "flat"?


Ooh. The difference in drag to the standard spoiler will be in the weeds, when the Aeromotion wing is dumping downforce.

Just a tad more skin friction due to bigger wetted area. The spoiler may have a little camber, which means its probably carry a small load all the time (and producing a little extra downforce dependent drag because of it).

Presumably the standard spoiler helps manage the base drag a little (every little helps) + provides signature styling too!


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## mindlessoath (Nov 30, 2007)

Just got word the duckbill trung suppose to produce more downforce than stock wing while still keeping drag low. No exact numbers because I think it was tested on miniature scale model.


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