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Author Topic: "Ground Effects" Tunnels  (Read 34968 times)

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Offline akk

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Re: "Ground Effects" Tunnels
« Reply #15 on: May 31, 2011, 05:34:15 AM »
Yes rolling resistance exists and at speed is small compared to aero drag.

My earlier comments about lead are not meant to belittle underbody design! My point is that there are better ways to get down force at Bonneville. Properly shaping the underbody can result in significant drag reduction!!!!! Don't waste drag reduction trying to get down force....below 350 mph...

Akk
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Offline Rex Schimmer

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Re: "Ground Effects" Tunnels
« Reply #16 on: May 31, 2011, 09:22:17 AM »
I could not agree more with AKK's comments regarding using aerodynamics for down force on a Bonneville car. All methods of aero down force have a lift/drag ratio, even under body tunnels and both the down force and the drag increase as the square of the speed, which means the horse power to over come the drag increases at the cube of the speed, so even what may appear to be a small amount of drag can become considerably larger with only a small increase in speed. We have discussed before the possibility of controlling a wing angle such that it produces a set amount of down force at any speed which would also control the drag but I have not seen anyone try it.

Rex
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Offline Bville701

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Re: "Ground Effects" Tunnels
« Reply #17 on: June 06, 2011, 11:56:58 PM »
Quote from: akk on May 30, 2011, 06:31:05 PM
The fact that you saylift to drag ratio should cause you to stop and think....

We have a very long straight away...any drag will slow you down!!!!!!!!!!

computer simulation shows that until you are running 350 mph...lead is better every time!!!

LEAD = "DRAGLESS DOWN FORCE"

Akk

Akk, how much do your cars weigh?
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Ryan LeFevers

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Offline akk

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Re: "Ground Effects" Tunnels
« Reply #18 on: June 08, 2011, 04:16:05 PM »
The 23T 920/928 with lead rack full...2928 lbs. rear and 1358 lbs. front....total weight 4286 lbs.

with lead rack empty 2182 lbs. rear and 1350 lbs. front... total 3532 lbs....(note the car is built with a lot of steel and has 800 lbs. of lead built into the floor)

One year running B/GMR on the long track with good salt coefficient of friction=0.6, with a  full lead rack was 3 mph slower than with empty lead rack!

We have learned the hard way that too light in the rear causes spins! Our discipline is to add weight if the tires spin in second gear...if we cannot spin the tires in first gear we remove weight....

The logic is ....second gear is about 1.5 to 1ratio... thus in high gear with 1 to 1 ratio we have a 50% traction safety factor!!!!!!

The 23T has no up or down aerodynamic force, it is neutral..ie zero lift to drag ratio... no induced drag

Akk
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Offline Bville701

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Re: "Ground Effects" Tunnels
« Reply #19 on: June 08, 2011, 05:09:47 PM »
Thanks for the info Akk!  :cheers:

Your cars are VERY impressive! Have either one been in the wind tunnel? If so what kind of drag are you seeing, if any? Thanks again for the info, and I agree that weight is better than a wing at Bonneville but what do you do when there aren't any more places to put weight? Do you think that ground effects are the way to go? Wing? Fin?
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Ryan LeFevers

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Offline George Fields

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Re: "Ground Effects" Tunnels
« Reply #20 on: June 08, 2011, 06:15:15 PM »
If it spins the tires, add weight, if it doesn't add nitro!
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Offline Bville701

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Re: "Ground Effects" Tunnels
« Reply #21 on: June 08, 2011, 06:22:00 PM »
Quote from: George Fields on June 08, 2011, 06:15:15 PM
If it spins the tires, add weight, if it doesn't add nitro!

LOL!    :cheers:
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Offline Bob Drury

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Re: "Ground Effects" Tunnels
« Reply #22 on: June 08, 2011, 07:27:22 PM »
  In the word's of the late, great Randy "Macho Man" Savage: Ooooooooooooooooooh yeah!
  Tip the can............. then tip a Beer.............   :cheers:
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Offline akk

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Re: "Ground Effects" Tunnels
« Reply #23 on: June 08, 2011, 09:38:47 PM »
I am trying to pull this thread back to aerodynamics....
Carroll Smith has written some good books about building race cars...he is a straight shooter as he admits that his earlier books were not right on ground effects...however he has some good points...the nose of the car should have the same ground clearance as the body at the rear...the middle can be closer and form a venturi in the middle...the high velocity can create down force with minimal drag...our car has never been in a wind tunnel...
Akk
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Offline WOODY@DDLLC

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Re: "Ground Effects" Tunnels
« Reply #24 on: June 08, 2011, 09:54:15 PM »
More than half the HP is inertial - you still have to accelerate the lead!  :-o You don't have to accelerate down force!   :-)

You have to push hard against both but there is a balance or sweet spot in all things!  :cheers:

Still easier to find than the G-spot though!  :-D
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Offline Rex Schimmer

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Re: "Ground Effects" Tunnels
« Reply #25 on: June 09, 2011, 12:30:00 AM »
When you are entering the 5th mile and you are looking for that last 200 rpm on the tach, the last 4 or 5 mph, it ain't inertia and acceleration that you are fighting it's aero drag.


Rex
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Offline akk

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Re: "Ground Effects" Tunnels
« Reply #26 on: June 09, 2011, 07:55:58 AM »
Put a wing on it and you will never get a chance to find that last few mph's! You will have downforce and be running 20 mph slower......

Akk
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Offline SPARKY

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Re: "Ground Effects" Tunnels
« Reply #27 on: June 09, 2011, 09:42:04 AM »
Akk,
why no rake  :? 

with a round shape on the bottom how would you determine the ground clearance
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Offline akk

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Re: "Ground Effects" Tunnels
« Reply #28 on: June 09, 2011, 11:09:45 AM »
In the middle ...where the oil pan and transmission hang down...ground clearance is about 2.5 inches....nose about 8 1/2 inches...back bottom of turtle deck about 11 inches...the small rake is to prevent the flat part of the bottom from ever being higher in the front than in the back...suspension travel +_ 1 inch ie.9.5 front 10 rear...

The goal was to have the whole car neutral...the suspension allows ride height/spring rate verification of up or down forces....the car is aero neutral...but you can see torque lift of the nose and rear squat...about 1/4 inch...

Akk 
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Offline SPARKY

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Re: "Ground Effects" Tunnels
« Reply #29 on: June 09, 2011, 04:54:58 PM »
Question rephrase   Have you ever read how much clearance a cylinder needs agl  :?
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Miss LIBERTY,  changing T.K.I.  to noise, dust, rust, BLUE HATS & hopefully not scrap!!

"Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure or nothing."   Helen Keller

We are going to explore the racing N words NITROUS & NITRO!
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