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Rear wing options???

 
Old 03-04-2009, 03:53 PM
  #166  
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why not make provisions in a lexan hatch for a spoiler to mount through and secure to the rear deck floor?
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Old 03-04-2009, 04:33 PM
  #167  
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Well that's not the main issue as we will just drill the necessary holes through the lexan anyway.
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Old 03-04-2009, 08:00 PM
  #168  
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i meant that there seems to be a discussion about mounting to the hatch vs the frame of the car..
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Old 03-04-2009, 10:07 PM
  #169  
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Right. This has been discussed already in this thread. Tony G and Hans both have wings attached in this manner. This is what I will do also.
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Old 03-13-2009, 12:54 AM
  #170  
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Originally Posted by 333pg333 View Post
Oh, I meant to post this car again just for reference in the thread. I'd like to see more pics of the wing setup
but from what I understand the owner is a bit shady so I doubt this is going to happen anytime soon.



Might not be to everybody's tastes but geez the work in this car is amazing.


I'd like to see more of that body kit. Any info you could provide on where to get it would be appreciated.


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Old 03-13-2009, 01:10 AM
  #171  
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Originally Posted by HansB View Post
This is getting into a very hairy discussion.

Let me try to put a bit of practical science into it.

When we designed our wing (TonyG likes to call it the Kokeln wing, but actually we designed it ourselves) we took a pragmatic approach: We copied a 996 Cup aerofoil, and a friend of mine which is a phd in math actually did some modeling and simulations on it.

The size and position of the wing are regulated : Not wider, higher and behind the body of the car.

Two variables remained:

1. what is the optimal height, and that came out at about the position it is in the picture some 2 pages back, and in my avatar.

2. What is the downforce, the load the support structure needs to carry.
By recollection this was about 500N at 45 m/s. (112 lbs at 100 mph). 45m/s is the speed that we carry in most of the high speed corners. Since the force of the wing increases with v^2, load at higher speeds can be easily calculated.
Top speeds on corners at Francorchamps are a bit higher, like 55 m/s (120+ mph) and then you can calculate the wing to produce 750N downforce (170 lbs)
Of course we wanted the wing not to break at top speeds, which are a bit above 65 m/s. (145mph) the downforce then is a hefty 1075N (240 lbs)

So any structure that you use to carry the wing should be able to carry quite a bit over what I guess to be the average Rennlisters weight.

So it becomes rather easy to get a seat-of-pants feel for all the structures that are presented: Do I dare to sit on it? Over and over again? And does it bend then?

That is how we came to the layout and dimensioning of the mounting HW.

Another SOP observation: I went from a bridge (968 style) wing to this (let us call it Kokeln style) wing, and it was a very noticeable difference.

Hans...

What you said has stuck in my mind. And honestly, when you dictated these numbers I was a little taken back as they were much lower than what I would have guessed.

And on the track, once I cross certain threshold speeds, the difference in rear end grip is night-and-day. In fact, I've had to increase my rear spring rates & slightly raise my rear ride height as a result of the wing in the high speed corners to prevent bottoming out.

After reading a few articles (and I'm by no means an expert), it seems that cars using similar wings are quoting much higher downforce numbers.

Take for example the Dodge Viper ACR. With the rear wing, the front splitter, and the nose mounted dive plane, Dodge quotes a "cumulative 1,000 pounds of downforce".

So how much of that is attributed to the rear wing? And at what speed?

I just can't see how the wing "only" is producing in the range of 170 lbs of down force at 120mph.

Some clarification would be appreciated.

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Old 03-13-2009, 05:34 AM
  #172  
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I downloaded a PDF recently someone linked to. A study of wings on a 944 by a Justin Smith. For a racing wing with 4.69 sq ft at 100 mph it showed around 120 pound downforce with 0 deg angle, and around 300 pound at 12.5 deg angle @ 100 mph.
150 mph gave 678 pound downforce from the 12.5 angle.
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Old 03-13-2009, 06:15 AM
  #173  
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There are two problems here: Claims (Dodge) and memory (mine)
Both can be considerably vague or off.

My friend did the modeling in a aerodynamics package, and I lost that results.
This was done in the time before I put all those on a RAID disc, which I do now.

I did look into it myself again ( I am an engineer, but not in this area) , and I found an on line simulator from NASA

If I assume our wings have an area of 5 square feet, some playing around with this simulator generates in optimal conditions (laminar flow = no turbulence, optimal shape and angle)downforce of 375 lbs (Area=5 ft, angle=-12 degrees) at 100 mph. So, you are right, it is 3 times more then the numbers I originally presented

Last edited by HansB; 03-13-2009 at 10:57 AM.
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Old 03-13-2009, 07:39 AM
  #174  
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So when we are saying X pounds downforce, is this literally like placing that amount of dry weight on the wing itself and the resultant effects? Does this also reflect in the spring rates? What does eg 500lb/in mean? Surely not something as simple as it take 500lb to compress it an inch? If my basic logic is correct then wouldn't adding wing have a possible strong effect on spring rate? Hence Tony's assertion that he had to upsize to avoid bottoming out?
In fact I asked this question just the other day to my mechanic. Will I need to get stiffer springs? How will I know if I do? Is this merely determined by bottoming out or not? I have fairly stiff spring rates but I'd be interested to know what rates other be-winged cars have and if they had to be increased due to downforce. Also what about bump and rebound, did the wings require an alteration to these settings?
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Old 03-13-2009, 07:43 AM
  #175  
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remember to check out the APR wings, they have actual datasheets on the wings... apr gtc 300 is the one I want. just need some $$$, patric, if I can scrape enough $$ together Im going 996TT (same tranny as you got) got a good deal on one now, but low on cash after buying the 7 series + misc ****.
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Old 03-13-2009, 07:54 AM
  #176  
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Anders, we got the wing for now. It looks very good but it's a copy so no hard data. See other thread with test pics. https://rennlist.com/forums/944-turb...ng-teaser.html
You will do the tranny conversion before me possibly. Depends if the new motor destroys my current one. We have an idea how to fit it, but in this car it might be harder than a dedicated track car. We'll look into it in more detail over the coming months. Mine's had the 'operation' done to it already for working in the 'flipped' position too. Just sitting in a crate now...waiting.
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Old 03-13-2009, 11:04 AM
  #177  
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Originally Posted by 333pg333 View Post
So when we are saying X pounds downforce, is this literally like placing that amount of dry weight on the wing itself and the resultant effects?
Yes


Does this also reflect in the spring rates? What does eg 500lb/in mean? Surely not something as simple as it take 500lb to compress it an inch?
Yes

If my basic logic is correct then wouldn't adding wing have a possible strong effect on spring rate? Hence Tony's assertion that he had to upsize to avoid bottoming out?
Yes

In fact I asked this question just the other day to my mechanic. Will I need to get stiffer springs? How will I know if I do? Is this merely determined by bottoming out or not?
Yes

That was easy.

I have fairly stiff spring rates but I'd be interested to know what rates other be-winged cars have and if they had to be increased due to downforce. Also what about bump and rebound, did the wings require an alteration to these settings?
That is harder. Increasing wing has only an effect on higher speeds, and all the other parameters work over the entire speed range. So this would be trial and error to find the optimal rates. But then, bump and rebound rates are trial and error anyway.
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Old 03-13-2009, 05:21 PM
  #178  
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Heheh, thanks Hans, that was easy for you. What rates are you running? I assume you've removed Torsion bars?
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Old 03-13-2009, 05:22 PM
  #179  
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Originally Posted by TonyG View Post
I'd like to see more of that body kit. Any info you could provide on where to get it would be appreciated.


TonyG
Tony I believe that is not a bodykit but some one off stuff. It looks like a LOT of time and money has gone into that car. It's in Sweden I think and allegedly owned by someone with a 'colourful' character.....
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Old 03-14-2009, 02:13 AM
  #180  
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Originally Posted by Duke View Post
I downloaded a PDF recently someone linked to. A study of wings on a 944 by a Justin Smith. For a racing wing with 4.69 sq ft at 100 mph it showed around 120 pound downforce with 0 deg angle, and around 300 pound at 12.5 deg angle @ 100 mph.
150 mph gave 678 pound downforce from the 12.5 angle.
So what if the angle was at say 15 degrees at 135mph?


How many lbs of downforce would that equal?

And do you mind point us to the same spreadsheet so that we could do the calcs on our own?

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