Rear Wing and or Spoiler

Alfa Romeo ONLY please!
Post Reply
Joemart
Platinum
Platinum
Posts: 288
Joined: Sun Dec 25, 2011 12:25 am
Location: South Africa - JHB

Rear Wing and or Spoiler

Post by Joemart » Fri Jan 11, 2013 10:55 am

Hi All

I think this topic may have been covered before in some way (MD?) - But was reading an article in the latest "TrackDriver" magazine - Volume 14 and in it they have done a CFD (Computational Fluid Dynamics) test - :?: (I know what it is but by NO MEANS am I an Engineer :( )...on the effect that a Rear wing / Spoiler has on a standard saloon car...In Volume 14 it is in effect a "spoiler", but in Volume 12 it was the effect of a rear wing...

The results of this, I thought were rather revealing and interesting, in that - and I quote - "

Test done at 100Mph
"Standard Baseline Model - Lift = +1078.9(NM) & Drag = 1139.2(NM)"
"30Deg, 60mm Spoiler Lift = -116.6(NM) ....& Drag = 1044.1(NM)" ... The "-" is actually "downforce".. (yes, a change of 1195.5 NM)
"60Deg, 140mm Spoiler Lift = -692.5(NM)...& Drag = 1304.6(NM)"...A change of 1770NM (180KG)

So, the REAL intersting part is that "option 2" generated NEGATIVE (Downforce) of 692.5 NM, (from a POSITIVE of 1078NM)which is apparently equivalent to approximatly 180KG Change of weight on the rear, WITH a relatively small increase in drag

and Option 1, in fact created about -116.6 NM of downforce (and my simple calculation, which I am sure is not accurate) says that it would be equivalent to about 121KG of CHANGE in weight , BUT with a REDUCTION in drag..

Anyway, thought this may be interesting and was wondering if there are any "real" world tests or analysis done on the GTV???

Thanks
:)
Joemart
Platinum
Platinum
Posts: 288
Joined: Sun Dec 25, 2011 12:25 am
Location: South Africa - JHB

Re: Rear Wing and or Spoiler

Post by Joemart » Fri Jan 11, 2013 11:02 am

Oh, here is the link to the Magazine - (not sure if it will work though) :roll:


http://ezine.trackdriver.com/TD14
Duk
Verde
Verde
Posts: 527
Joined: Sun Aug 19, 2007 9:15 pm
Location: South Australia

Re: Rear Wing and or Spoiler

Post by Duk » Fri Jan 11, 2013 12:43 pm

I think your best bet would be doing your own testing and data logging.
Key will be a good test straight, a consistent test speed (at least 160km/hr/100mph) and data logging equipment.
Fit the rear suspension with suspension travel sensors and feed that info to your data logger.
Monitoring your engine's performance will be harder. I'd simply use a linear TPS and monitor that. Another more accurate approach would be to monitor the output of an air flow meter, especially a hot wire/film meter.

The way I would test would be:
With the car in standard aerodynamic condition and with above data logging equipment fitted and logging, travel down your test straight at 160km/hr. Then test again on the same straight but in the other direction (will help allow for minor wind direction differences).
Then fit your rear wing/spoiler and test again in the same manor.

Then simply compare your data logging results of before and after aero-additions.
Additional down force will show as a lower average suspension position (not expecting your test straight to be billiard table smooth) and an increase in drag will show as a higher throttle opening angle to maintain your test speed.
Further testing could be done by putting your car on a brake style dyno and see how much power the engine need to make at your chosen test speed at the 2 (invariably) different throttle angles. If you needed say 50% throttle for your original body configuration, then hold the car on the dyno (obviously in the same gear as your test) at an indicated 160km/hr and at 50% throttle.
Then if the post rear wing/spoiler showed that you needed 60% throttle to maintain your test speed, do the same test on the dyno but with the throttle open too 60%.
The power difference could probably be calculated as an increase in drag coefficient, but do you really need it to be?

Actual down force would need to be replicated to get some sort of meaningful number. If your data logging showed that the rear suspension dropped by (say) 10mm more at your test speed, then with the driver in the car and while monitoring the data logger, have weight added to the car just under the mounting points for the wing/spoiler until the data logger showed the rear suspension is compressed the same amount. Then weigh the amount of additional weight added and that should be pretty damn close representation of your added aero-down force. 8)
User avatar
Mats
Verde
Verde
Posts: 4059
Joined: Mon Nov 29, 2004 12:26 am
Location: Gothenburg, Sweden
Contact:

Re: Rear Wing and or Spoiler

Post by Mats » Tue Jan 15, 2013 10:51 pm

+1 on the suspension sensors but I would definetly do coastdown instead of trying to keep a certain pace. Also you need to make quite a few passes in each direction and in a very tight timeframe. The conditions need to be exactly the same for all tests so no use going back another day with a new setup because the environment has changed. You could do a baseline run though and try to correlate data but it's difficult when you only have relative data.

What results did the test with the wing yield?

Just a correction: Force is measured in Newton (N), torque is measured in Newton meters (Nm).
Mats Strandberg
-Scuderia Rosso- Now burned to the ground...
-onemanracing.com-
-Strandberg.photography-

GTV 2000 -77 - Died in the fire.
155 V6 Sport -96 - Sold!
Post Reply