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Old 03-26-2010, 05:27 PM   #1 (permalink)
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Underbody panel testing

I found this in Piechna's book. Sardou ([1]) tested underbody panel configurations on the same car in different wind tunnels, both and without a moving floor.



The chart below shows how adding different underbody panels influences aerodynamic drag and lift, but also lift for the front and rear axles.



Worth noting are two things:
  1. Adding panel #1 down the center increases drag,
  2. Adding the center panels (#'s 3, 2, and 1) decreases lift in the rear.

[1] Sardou M., The Sensitivity of Wind-Tunnel Data to a High-Speed Moving Ground for Different Types of Road Vehicles, SAE 880246, 1988.

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e·co·mod·ding: the art of turning vehicles into what they should be

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Piwoslaw's Peugeot 307sw modding thread

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Old 03-26-2010, 06:40 PM   #2 (permalink)
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diffuser

kinda wish they had re-evaluated diffusers to see if there was agreement there.
Looks like a good book.Thanks!
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Old 03-27-2010, 01:13 PM   #3 (permalink)
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tunnel

so from that chart,, pan everything,front and rear but leave the middle of the car unpanned ,,except the middle sides? . wonder if you just pan front to rear but leave the whole middle alone? very interesting. also shows how much pans can drop cd,, thanks for the great info.
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Old 03-29-2010, 12:55 PM   #4 (permalink)
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I bet the middle one increased drag because with all the panels in place the air entering the engine compartment through the grille didn't have enough room to escape so the whole engine compartment became a "parachute"
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Old 03-29-2010, 01:24 PM   #5 (permalink)
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We STILL have accept that this info from the tests could be completely different with a different car!

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Old 03-29-2010, 01:54 PM   #6 (permalink)
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Quote:
Originally Posted by shovel View Post
I bet the middle one increased drag because with all the panels in place the air entering the engine compartment through the grille didn't have enough room to escape so the whole engine compartment became a "parachute"
That sounds like a good explaination.
Nothing a grille block can't partially fix
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Old 03-29-2010, 07:16 PM   #7 (permalink)
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The amount of drag increase from panel 1 is negligible compared to the reduction in rear lift. Though the increase in front lift does support the underhood parachute hypothesis.
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Old 03-29-2010, 08:18 PM   #8 (permalink)
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I think it's amazing that the panels reduced Cd from 0.30 to 0.27.

I will emulate Sardou in starting my underbody paneling at the rear of the car.
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Old 03-29-2010, 11:26 PM   #9 (permalink)
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Quote:
Originally Posted by RobertSmalls View Post
I think it's amazing that the panels reduced Cd from 0.30 to 0.27.

I will emulate Sardou in starting my underbody paneling at the rear of the car.
Gazing at my own Insight, it would seem that panel #5 is the only area not covered, though Honda's design may differ slightly.

I also looked carefully at the rear area. By integrating the cargo well floor with the the bumper cover, even the #5 area is somewhat covered. It does look to me like there is adequate clearance on the torsion beam rear axel to use one large coroplast sheet to cover up everything remaining open, but JMO. I seriously doubt that this improvement will be measurable.
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Old 03-30-2010, 06:05 AM   #10 (permalink)
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the drag resuls are pretty much as expected. while details may vary a full belly pan seems to decrease drag and lift.

what i find strange is the increase in lift caused by the front and rear pannel, and than the spectacular decrease caused by the center pannels.

i wish they'd tested them separately, because the numbers seem to sugest while they only cause a minor decrease in drag they cause a decrease in lift large enough to cancle out the front and rear increase... but one cannot conclude if they do this on their own or together with the first pannels.

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