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Aero talk
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Cedric  



Joined: 27 Aug 2004
Posts: 2600
Location: Sweden

PostPosted: Sat Feb 12, 2022 10:41 pm    Post subject: Reply with quote

During my professional life ive come to the conclusion that its better to not do CFD than to do a bad CFD. Since it only confuses and might yield wrong conclusions. But as a learning exercise it could be fun for sure. But in this case we already know what needs to be done more or less for the big gains, especially if you start from an untouched car.

If i remember correctly the 924 has a Cd of 0.36 without the rear wing and 0.34 with the rear wing. I think the CGT had 0.34 aswell despite the wide body, due to the front end, flush windscreen etc.


Side skirts arent guaranteed to improve things, as can be seen in some testing that Simon Mcbeth did in one of the "aero bytes" articles, as most stuff it depends on many many parameters. But they are fairly easy to make though.
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gegge  



Joined: 27 Jul 2007
Posts: 1124
Location: Sweden

PostPosted: Wed Feb 16, 2022 6:58 pm    Post subject: Reply with quote

For a low Cd? Check out the 924 world record car...

https://www.youtube.com/watch?v=Il5uav5bj7I
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Carl Fredrik Torkildsen

924 turbo -81 Carrera GT RESTOMOD
924 turbo -80 Dolomite De Luxe
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Juho  



Joined: 03 Oct 2018
Posts: 377
Location: Finland

PostPosted: Thu Feb 17, 2022 7:29 am    Post subject: Reply with quote

i want downforce too but boy that front bumper looks nice
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2596
Location: MI

PostPosted: Thu Feb 17, 2022 8:34 pm    Post subject: Reply with quote

gegge wrote:
For a low Cd? Check out the 924 world record car...

https://www.youtube.com/watch?v=Il5uav5bj7I



That rear end is SWEEET!!
Love the exhaust out the front fender too..
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Juho  



Joined: 03 Oct 2018
Posts: 377
Location: Finland

PostPosted: Mon Feb 21, 2022 8:44 pm    Post subject: Reply with quote

so acquiring data drag could be measured by simple coast test and lift/downforce with monitoring suspension travel. what u think would be easiest way to monitor suspension travel?
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Cedric  



Joined: 27 Aug 2004
Posts: 2600
Location: Sweden

PostPosted: Wed Feb 23, 2022 7:04 pm    Post subject: Reply with quote

Juho wrote:
so acquiring data drag could be measured by simple coast test and lift/downforce with monitoring suspension travel. what u think would be easiest way to monitor suspension travel?


Have you done coast down before? I think it will be hard to use for small changes , if you cant use very high speeds. Maybe Julians throttle stop technique could be something, especially if it could be used at a slightly higher speed like 120km/h. And you will need a pitot tube for reference pressure and actual speed measurments.

Logging the ride height with potentiometers is common, but you will have to log the signal so you can do some signal processing to make it useful. Maybe check what FSAE teams uses.
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Juho  



Joined: 03 Oct 2018
Posts: 377
Location: Finland

PostPosted: Thu Feb 24, 2022 1:03 am    Post subject: Reply with quote

havent done cost down before, have to try it when the car is hopefully running.

We use these potentiometers https://www.soe.fi/collections/soe-motorsport/products/liikeanturi Pretty inexpensive-ish

Im going to run some laptime simulations today to see if aero is worth it
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Juho  



Joined: 03 Oct 2018
Posts: 377
Location: Finland

PostPosted: Thu Feb 24, 2022 2:19 am    Post subject: Reply with quote




This what the lap time improvement would be with aggressive aero on track in sweden called Ring Knutstorp, very marginal....
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Cedric  



Joined: 27 Aug 2004
Posts: 2600
Location: Sweden

PostPosted: Thu Feb 24, 2022 2:27 am    Post subject: Reply with quote

Ive done quite some optimumG on my car, its a decent way of predicting lap time for different type of changes.

I don't think knutstorp is a good place for evaluating Df, since it has pretty much one fast corner. Very very fun track though
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Juho  



Joined: 03 Oct 2018
Posts: 377
Location: Finland

PostPosted: Thu Feb 24, 2022 2:28 am    Post subject: Reply with quote

I know but these type of tracks we have here though

Power increased and aero increased.




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