Alfa Romeo 4c - aerodynamics - Alfa Romeo 4C Forums
 29Likes
Reply
 
LinkBack Thread Tools
post #1 of 20 (permalink) Old 04-10-2019, 07:55 AM Thread Starter
Senior Member
 
Join Date: Aug 2016
Posts: 365
Alfa Romeo 4c - aerodynamics

For some time the ideea of the 4c making "lift" instead of "downforce" is bothering me so I studied a bit the shape of the car and some basic aerodynamic concepts.

First I believe the car is making lift due to the following reasons (there may be others but I don't remember now):
1) Almost all street cars are making lift, apart from supercars and exotic ones that have big wings --> Alfa has only a small tiny wing on the rear that I will discuss further on
2) The car feels very agile, gripy and it is extremely fast on low speed corners, however when you get on the high speed corners the car feels unstable and the rear end tends to loose it's grip at considerably lower G forces.
3) I compared the corner speeds on similar tires with my previous track car (VS Scirocco which is known to make some little downforce ... while the same platform golf makes lift)
4) I analyzed the shape of the car --> more on this later

There is one easy way for the car to make downforce: adding a big wing on the rear and a lip / canards on the front. Below are the reasons I will not take this approach and probably 99.9 % of the owners will not do it either:
1) The car looks great in it's oem shape. It's an exotic, streetable, less racier design and adding a big wing will damage it ... not to mention that it will look odd when taking the car for a ride in the town. I drive the car both on streets in town, outside town and racetracks. I enjoy the car on all sorts of roads not only the racetrack.
2) You have to make wholes in the boot cover for a big wing and when I want to remove it I will have problems and additional costs in putting the car in it's original state.
3) Adding a lip on the front will create problems on approaching ramps or street imperfections.
4) When you go to the racetrack is one thing to set a very good lap time with an oem looking car with a 1.74 liter engine and one thing in a car with big wings that it's clearly intended to work on the race track only! Beating a gt3 rs is far more impressive when driving an OEM looking alfa romeo 4c (with not so good online reviews
5) We can create more downforce with what we have (OEM car design) and less drag --> Because the 4c is relatively low on power the car can get close on lap time with a 4c with big rear wing because it would have much less drag.

Now why do I want more downforce (or some downforce instead of lift): Because the car is quite light and making downforce will be extremely well felt in the high speed corners --> These will make the car a lot more faster than it currently is and safer both on street and track. It's enough to see how much faster was that scara 73 alfa with aero than rudi's car (it was considerably faster, much more stable and controllable and this with inferior tires).

Below are my findings and some ideas to improve the aero package of the car while maintain the oem aspect:
1) I installed the autogiano rear wing which looks quite oemish (I opted for the cheaper fiber option and painted in the same color as the car) --> I am in no relation to them apart from buying one rear wing.
https://autogiano.com/list/al/list_al4rsp.html

On the race track I go to, there is one high speed corner (whith speeds around 190 Km/h) that is extremely tricky to approach --> The corner also have some slight deviation that tends to unsettle the car --> This corner is so tricky that if I not approach it in the absolutely perfect angle I may loose the car --> on several occasions with even stock power I loosed the rear end but managed to get it back on trace (at these speeds you can imagine what I felt).
After installing the autogiano rear wing I didn't feel a major improvement however on this corner (even with wind from the back) the car was more stable and easier to approach. I didn't have any more drama --> I felt something similar on other corners (high speed corners): the rear end felt a little bit more planted: Now the difference is quite small and some may not feel it but it's there and it helps and the car became safer.
Another bonus: the wing looks more OEM than the OEM one --> It follows better the line of the car with less protrusions

The OEM rear wing: I don't know who designed it but it's bad because it has a thick margin in the place of contact with the rear hood and it also has a lip (that margin on top of it): these elements will create turbulence's and the air flow is detached from the rear wing and basically it doesn't do anything good.

2) I will test these days the air flow along the rear boot window --> if the flow is not laminar then we can add some vortex generators on the rear window to create vortexes --> This will keep the air flow tied to the rear hood and into the rear wing making it more efficient. I have some suspicions that in OEM format the air flow is not optimal (see the pictures below in wind tunnel --> not much air is getting into the rear wing).
Btw, adding a scope on the rear boot for cooling the engine bay is a bad ideea.

3) The rear diffuser: This part is more interesting and here are the biggest gains to be made.
The diffuser I believe is well designed and with some minor tweaks the aerodynamics can be dramatically improved:
- We have a high angled diffuser (around 19 degrees on the margins towards the fences and around 14 degrees in the middle) --> this type of diffuser is more effective with high ground clearance. However our car is too high --> even with OEM sport suspension the diffuser entry point sits at around 130 mm above the ground and at this "height" it have almost no effect (you can clearly see this from the graphic attached). If we manage to lower the car then the diffuser should gain much effect (I'm sure that those who lowered the car with a few centimeters while maintaining the rake angle did feel something) -- with adjustable suspension we can lower the car on the race track and lift it back for the street (it takes some time and those who did it can share this info).
- The car bottom is "relatively" flat and it has a rake angle (which again is very good) --> The bottom have some protrusions where the carbon fiber sheets meet and these are creating turbulence. Turbulence is bad and it detaches the air flow from the bottom of the car and ultimately from the diffuser. We need somehow to smooth those parts
- The diffuser is only a central piece --> This is the most effective zone but we can extend it towards the rear wheels and I believe this will add some downforce (see the undercar picture).
- On the front of the car we have a lip under the front spoiler: The reason for this I believe is to keep some of the air away so basically there will be less air under the body so it will move faster and should create some downforce. However, this lip will also create turbulence's and I don't really know if it's effect is good or bad --> I could not find any example online with a similar approach.
I will try to add a bigger lip (4cm or so) more towards the front wheels --> This should deviate some of the air towards the front brakes and also away from under the car --> Will see what happens
Attached Images
File Type: jpg Untitled-9.jpg (263.8 KB, 71 views)
File Type: jpg Untitled-11.jpg (333.3 KB, 74 views)
File Type: jpg DiffuserPerformanceWithFencesDifferentRampAngles.jpg (105.0 KB, 65 views)
File Type: jpg IMG_20190408_155431.jpg (227.1 KB, 69 views)
mdpsk, Alfanut, Alipapa and 1 others like this.

Last edited by Alfanut; 04-10-2019 at 05:50 PM. Reason: Sp
cipsony is offline  
post #2 of 20 (permalink) Old 04-10-2019, 08:35 AM
Senior Member
 
Philster's Avatar
 
Join Date: Feb 2017
Location: Greater Philadelphia, PA; U.S.A.
Posts: 1,074
The 4C has downforce, which was never quantified by Alfa Romeo, but press releases in 2014 quoted the coefficient of drag and noted to the press that it had achieved a negative downforce coefficient (i.e. downforce) simply through the aerodynamics of the body shape and controlled, fast airflow under the body (the most underrated and overlooked opportunity for downforce).

So, from AR, we know it has downforce in stock form. I have not seen it quoted as a number in kg or pounds.

Fast cars need more downforce to not feel light at speed (not to give an impression of lift), because surfaces are not 100% level and the angle of attack vs the air changes, and any turn, curve, yaw, etc requires great downforce to counteract the inertia/momentum that would cause tires to brake traction.

You might sense lift, even in a car with actual downforce, at high speeds. It's a subjective sensation.

EDIT: AR did quantify drag/downforce to the press and I have added info below.
.
massimo4c and DetroitDave like this.

LE 221/500, Rosso Alfa

Last edited by Philster; 04-10-2019 at 08:47 AM.
Philster is online now  
post #3 of 20 (permalink) Old 04-10-2019, 08:46 AM
Senior Member
 
Philster's Avatar
 
Join Date: Feb 2017
Location: Greater Philadelphia, PA; U.S.A.
Posts: 1,074
Following a PowerPoint presentation about the 4C, with fresh data from Alfa, Motor Trend got to test the 4C at a launch. Alfa presented to them these numbers: .33 CD and -.05 COL (negative = downforce)

''Carefully managing the flow of all cooling airflow under the body and out the rear diffuser helps deliver a 0.33 Cd with a -0.05 coefficient of lift (meaning there's modest downforce) balanced front to rear, without any gigantic spoilers, wings, or splitters.''


.
https://www.motortrend.com/cars/alfa...4c-first-test/
4Canada, Alfanut, DrDuke and 1 others like this.

LE 221/500, Rosso Alfa
Philster is online now  
Sponsored Links
Advertisement
 
post #4 of 20 (permalink) Old 04-10-2019, 11:15 AM
Senior Member
 
Join Date: May 2017
Posts: 354
Quote:
Originally Posted by Philster View Post
Following a PowerPoint presentation about the 4C, with fresh data from Alfa, Motor Trend got to test the 4C at a launch. Alfa presented to them these numbers: .33 CD and -.05 COL (negative = downforce)

''Carefully managing the flow of all cooling airflow under the body and out the rear diffuser helps deliver a 0.33 Cd with a -0.05 coefficient of lift (meaning there's modest downforce) balanced front to rear, without any gigantic spoilers, wings, or splitters.''


.
https://www.motortrend.com/cars/alfa...4c-first-test/

Nice find - I was looking for this since ages xD
In my opinion the aero problems some experience is more related to the oem suspension than the shape of the car. The progressive springs in the back compress quit a bit under acceleration. This changes the angle of attack (rake). Low nose high back gives downforce and more resistance. High nose and low back reduces downforce and resistance. Alfa used this trick to make the car faster on straights. The downside is that at certain corner speeds (under full trottle) the car gets a tendency to understeer. To counter this just lift trottle a bit before turning in. With the stock tires I had this problem in the parabolica in hockenheim (with headwind).



IMHO cipsony, your oversteer problem sounds more like the setup/alignment of your 4c doesn't fit that particular corner or there is something wrong with your suspension.
Philster likes this.
DrDuke is offline  
post #5 of 20 (permalink) Old 04-10-2019, 11:32 AM
Senior Member
 
Philster's Avatar
 
Join Date: Feb 2017
Location: Greater Philadelphia, PA; U.S.A.
Posts: 1,074
I had a 911 with the GT3 Porsche Factory AeroKit (no ground clearance from big front chin spoiler, big bi-plane rear wing, etc) and after 125 MPH it felt like the front of the car was coming off the ground. That's the sensation, probably because it was rear-engined.

I seriously doubt the downforce was ever lost on a GT3 factory AeroKit 911... and I was not the only person with this GT3 spec feeling it. Just keep that in mind.

.
DrDuke likes this.

LE 221/500, Rosso Alfa
Philster is online now  
post #6 of 20 (permalink) Old 04-10-2019, 12:28 PM
Senior Member
 
Join Date: May 2017
Posts: 354
Your feeling is certainly right. Today most racecars haven oversteering mechanical setup and an understeering aero setup. From experience this delivers the best lap times.
Front and rear aero influnece each other. If a squall hits the car the rear wing will lift the nose a bit. The aero balance is also shifting a bit over speed.
Philster likes this.
DrDuke is offline  
post #7 of 20 (permalink) Old 04-10-2019, 12:53 PM
Senior Member
 
DrPyro2k's Avatar
 
Join Date: Oct 2015
Location: Houston, TX
Posts: 1,222
Garage
Quote:
Originally Posted by cipsony View Post
2) The car feels very agile, gripy and it is extremely fast on low speed corners, however when you get on the high speed corners the car feels unstable and the rear end tends to loose it's grip at considerably lower G forces.

Quote:
Originally Posted by DrDuke View Post
Nice find - I was looking for this since ages xD
In my opinion the aero problems some experience is more related to the oem suspension than the shape of the car. The progressive springs in the back compress quit a bit under acceleration. This changes the angle of attack (rake). Low nose high back gives downforce and more resistance. High nose and low back reduces downforce and resistance. Alfa used this trick to make the car faster on straights. The downside is that at certain corner speeds (under full trottle) the car gets a tendency to understeer. To counter this just lift trottle a bit before turning in. With the stock tires I had this problem in the parabolica in hockenheim (with headwind).

IMHO cipsony, your oversteer problem sounds more like the setup/alignment of your 4c doesn't fit that particular corner or there is something wrong with your suspension.

Interesting comments Guys.... I have been wondering about this myself. I have lost the back end at 100 mph (160 km/h) and it is not fun. This is my first mid-engined car, so I'm learning about its dynamics. I have tried stickier tires and +1 wider, which did result in an improvement in lateral Gs that I can pull (as measured by a VBOX), but not THAT much. I'm still learning track driving, but rarely do I have a problem with Understeer, unless I completely blow the corner entry. I know a lot of people have complained about this, but I don't have the issue. Perhaps it is my style of driving (slow in, fast out) or that I'm over braking on entry (also true). I have gotten fairly good about maximizing traction on corner exit and feeling when i'm about to loose traction. With a Stock 4C, I would estimate maximum lateral Gs around 0.95 (or so). With stickier and wider tires (+1) and Rudi's Uni-balls, I would estimate a maximum 1.0 or so. As I have said, I have always felt that I should be able to pull more lateral Gs. Granted with a mid/rear engined car you will always loose the back end first, but I always felt it should be better. Is it because we need more Aero? Poor Setup of my suspension? A Rear wing would improve rear end planting in high speed corners.... @cipsony , I know you don't want a big rear wing, but is this really the best solution?


Thoughts? I know @Call me Al runs a big spitter and rear wing, and he can pull some serious lateral Gs. It is one of the reasons why a higher downforce is interesting to me (like a Radical SR3).
Alfanut likes this.

2015 Alfa Rosso Coupe (SE) -
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

EuroCompulsion V1 AIS | Pogea Silicone | Capristo Exhaust (Valved) |
Ohlin 2-way | S111 Swaybars & endlinks | Girodisc Rotors | PFC-11 pads | Rudi's UniBalls (Rear) |
S111 Harness Bar | Technocaft T2S Seats | Schroth PROFI II 6-point |
OZ ALLEGGERITA 17/18 - Falken RT615K+ | OEM 18/19 - Pirelli PZero | XPEL Ultimate (Full)

Last edited by DrPyro2k; 04-10-2019 at 12:57 PM.
DrPyro2k is offline  
post #8 of 20 (permalink) Old 04-10-2019, 01:28 PM
Senior Member
 
Philster's Avatar
 
Join Date: Feb 2017
Location: Greater Philadelphia, PA; U.S.A.
Posts: 1,074
Isn't a Radical pulling 2+ Gs!?
.

LE 221/500, Rosso Alfa
Philster is online now  
post #9 of 20 (permalink) Old 04-10-2019, 01:50 PM Thread Starter
Senior Member
 
Join Date: Aug 2016
Posts: 365
I honestly doubt the information coming from that article, however a coefficient of -0.05 would be almost zero and we can assume that accelerating a bit and lifting the front end a bit transform this -0.05 into a "+".

It is very strange that the car was taken to a wind tunnel, tested but no official data is coming from Alfa Romeo in a brochure or something --> I believe the car had some major issues and they somehow improved the aerodynamics of the car without affecting too much the design --> After this they probably stopped due to investment constrains.

But most important is what is felt and tested by us (the end users) on the racetrack --> I personally will not rely on a article and give up on improving the car because I believe it has a huge potential.
It was proven by Jamie just by upgrading the rear bushings to uniballs - before him doing this we would probably argue that the alfa romeo engineers knew what they were doing and there is no need for a change.
cipsony is offline  
post #10 of 20 (permalink) Old 04-10-2019, 01:52 PM Thread Starter
Senior Member
 
Join Date: Aug 2016
Posts: 365
Quote:
Originally Posted by DrPyro2k View Post
Interesting comments Guys.... I have been wondering about this myself. I have lost the back end at 100 mph (160 km/h) and it is not fun. This is my first mid-engined car, so I'm learning about its dynamics. I have tried stickier tires and +1 wider, which did result in an improvement in lateral Gs that I can pull (as measured by a VBOX), but not THAT much. I'm still learning track driving, but rarely do I have a problem with Understeer, unless I completely blow the corner entry. I know a lot of people have complained about this, but I don't have the issue. Perhaps it is my style of driving (slow in, fast out) or that I'm over braking on entry (also true). I have gotten fairly good about maximizing traction on corner exit and feeling when i'm about to loose traction. With a Stock 4C, I would estimate maximum lateral Gs around 0.95 (or so). With stickier and wider tires (+1) and Rudi's Uni-balls, I would estimate a maximum 1.0 or so. As I have said, I have always felt that I should be able to pull more lateral Gs. Granted with a mid/rear engined car you will always loose the back end first, but I always felt it should be better. Is it because we need more Aero? Poor Setup of my suspension? A Rear wing would improve rear end planting in high speed corners.... @cipsony , I know you don't want a big rear wing, but is this really the best solution?


Thoughts? I know @Call me Al runs a big spitter and rear wing, and he can pull some serious lateral Gs. It is one of the reasons why a higher downforce is interesting to me (like a Radical SR3).
Yes, but if I wanted to buy a car with big wings I would probably buy a radical in the first place.
cipsony is offline  
Reply

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Similar Threads
Thread Thread Starter Forum Replies Last Post
Tonale bryanrmorris The Car Lounge 9 03-06-2019 04:51 AM
Driving the 1934 Alfa Romeo That Beat the Nazis Haha Alfa Romeo 4C Reviews 11 12-09-2017 09:15 PM
Could Alfa Romeo make a F1 Racing Comeback? mdpsk Alfa Romeo 4C General Discussion 22 04-08-2016 05:28 PM
I Shouldn’t Love the Alfa Romeo 4C, But I Do: Review Haha Alfa Romeo 4C Reviews 11 05-29-2015 01:52 AM
How many LE units ? CCCC Canada 4 07-06-2014 09:52 PM

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

 
For the best viewing experience please update your browser to Google Chrome