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Anyone have Aero questions?


@NineLivesJohnny
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calculus was explained to me as a "how close you can get to an object without actually touching it". splitters' performance  could be explained in the same way.  closer to the ground the better it will work, right up to the point it touches the ground and then it stops working all together.  so get it close but if it's too close it will purpose. aka bounce off the ground as it goes from Downforce, to stall rapidly. the perfect height depends on your splitter, tire and suspension combinations, just keep it off the ground.  

 

 

On 11/26/2020 at 9:46 PM, WTFover said:

So I've got an aero question regarding front splitters.  How low is too low? We run your splitter and mounts on the Miata, and we haven't really seen any indication of dragging/scraping or other contact with the ground, even after Sebring.  I know you want some air going underneath the nose of the car so that it can be accelerated and cause a pressure drop.  I also  know the Nascar guys try to run the nose as low as possible.  Our car is about as low as it can get without negatively affecting suspension geometry.     

 

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On 11/28/2020 at 10:07 AM, @NineLivesJohnny said:

is that our wing?

No, it's a $35 swap meet special. Think he said it was from a Top dragster, 23 lbs and 15" chord with about a 2" thickness so definitely not your wing! Big and clunky but it seems to work - for now. And of course it's the right size to look like a lawnmower handle. ;)

 

Not sure if this picture helps to see the wing better:

331 (13).JPG

 

I'm thinking of extending the splitter another inch or so and lowering it as well (the mounts are adjustable), looks like there's still a little room. I had to tape the front edge of the hood down, when I added the splitter it pushed a bunch more air over the nose, enough to change a light flutter at the front lip to a serious bowing up at speed.

 

I don't have any pictures of the splitter at higher speeds but am considering adding teflon vertical rub strips near the front edge under each of the brake ducts and parallel to the direction of travel, both to check to see how much flex I'm getting (1/2" birch plywood) and to keep the edge up a little if it is flexing. 

Edited by mender
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On 11/28/2020 at 12:14 PM, @NineLivesJohnny said:

calculus was explained to me as a "how close you can get to an object without actually touching it". splitters' performance  could be explained in the same way.  closer to the ground the better it will work, right up to the point it touches the ground and then it stops working all together.  so get it close but if it's too close it will purpose. aka bounce off the ground as it goes from Downforce, to stall rapidly. the perfect height depends on your splitter, tire and suspension combinations, just keep it off the ground.  

 

 

 

Thanks! What is your take on the splitters with the raised center section? I've seen plenty of prototype cars using them over the years, and I saw a picture of a miata running in the series with one recently.    I always thought the prototypes were using it to divert air to under car tunnels, so not sure if the juice would be worth the squeeze to develop something like that for our little series.  

Edited by WTFover
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13 hours ago, WTFover said:

Thanks! What is your take on the splitters with the raised center section? I've seen plenty of prototype cars using them over the years, and I saw a picture of a miata running in the series with one recently.    I always thought the prototypes were using it to divert air to under car tunnels, so not sure if the juice would be worth the squeeze to develop something like that for our little series.  

My understanding is that the raised section is to reduce pitch/roll sensitivity of the splitter, so that it doesn't stall when it inevitably touches the track surface. Not only the prototypes, but many of the GT cars have these features as well.

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2 hours ago, collinskl1 said:

My understanding is that the raised section is to reduce pitch/roll sensitivity of the splitter, so that it doesn't stall when it inevitably touches the track surface. Not only the prototypes, but many of the GT cars have these features as well.

I heard the same.  It is to help stop porpoising. 

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2 minutes ago, petawawarace said:

Are the splitter “ramps” legal in CC as part of the splitter? Obviously they can’t be CF. 

You mean the ones on the bottom side that act like little diffusers?  I know a lot of people in champcar are running them.

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48 minutes ago, petawawarace said:

Yeah. Just wanted to make sure they are not an extra aero device.  I know I know....tech desk.  

I don't see why you cant.  The rule doesnt specify shape does it?  Just flat in fromt of the car....

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  • 2 weeks later...
  • 2 months later...

Out of curiosity, any idea what the CFM flow created by fans would be required to make measurable downforce?

 

Say a guy was to lay his radiator flat, parallel with the ground, integrated into the splitter, and run a 8000 cfm rad fan on it. Noticeable gain or not likely?

 

Off to see if the cfm rating of Jim Hall's fan is stated anywhere...

spacer.png

Edited by Bandit
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I think Jim's fan was powered by a 40 ish hp engine.... But hey, who says you can't carry around a weed eater engine :)

How many cutoff wheels will it take to section 3 inches from the Falcon like the old Holman Moody Challenger cars?  Couldn't do the long roofline though too many points.

Falcon.jpg

62+Nassau+Marvin+Panch+Falcon.jpg

65089183_482391632533404_2150407236533354496_n.jpg

Falcon1.png

Edited by 67Mustang
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30 minutes ago, 67Mustang said:

I think Jim's fan was powered by a 40 ish hp engine.... But hey, who says you can't carry around a weed eater engine :)

How many cutoff wheels will it take to section 3 inches from the Falcon like the old Holman Moody Challenger cars?  Couldn't do the long roofline though too many points.

Falcon.jpg

62+Nassau+Marvin+Panch+Falcon.jpg

65089183_482391632533404_2150407236533354496_n.jpg

Falcon1.png

Heck with the falcon, I'd give the Lotus Elite in the second picture a go! 

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After a little further research it's not just the CFM but how much vacuum one can pull. This aero stuff is hard.... I doubt the fan I have in mind can pull 10 inches, no chance as it's 1.2hp, but it seem feasible it could make a small difference. I seem to recall, perhaps Black Magic mentioned it, that Gibbs racing got popped for using brake duct fans for downforce. Those guys are looking for the tiniest advantage so while it may not be noticeable, it may be measurable.

 

btw-That Falcon is ugly as hell. But that rear window probably has some serious 60's aero going on.

 

eta-Chopping a roof is a lot easier when using lexan windows. However I recently came across an article where they wind tunneled a Bonneville car and found lowering the roof line didn't have as big of a drag reduction as one would think. Very minor improvement.

 

Lowering the whole car, and keeping air out from underneath, made a big difference.

Edited by Bandit
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I'm sure you probably already found this, but it's pretty impressive lol.  This is from the R&T article.

The Chaparral 2J is powered by an aluminum Chevrolet ZL1 engine, 427 cubic inches and producing 650 horsepower at 7000 RPM. It is paired to a clutchless semi-automatic three-speed transaxle. With a fiberglass resin body, it weighs hardly over 1800 pounds. The auxiliary engine, mounted behind the rear wheels, is a Rockwell JLO 247cc two-stroke, two-cylinder, 45-horsepower engine, usually found powering snowmobiles. At full power, it makes an ear-splitting, high-pitched drone, like the buzzing of mechanical wasps from hell. The two rear fans are lifted from a M-109 Howitzer and capable of pushing out 9650 cubic feet of air per minute at 6000 RPM. With the Chevrolet engine off, rumor has it, they can even push the car forward at 25 to 40 miles per hour. 

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Vic Elford said if the car would have been reliable it would have been unbeatable. Said it was amazing to drive due to the grip in braking and cornering. Hall said he always braked too early in testing as he couldn't get his head around it. I think it was on pole for all three races it ran. Outran second by 2.2 seconds at Riverside.

 

I had to chuckle at this vid due to the cloud of two stroke smoke behind it from the old JLO snowmobile engine.

 

 

Way back in 2008 a team ran the Grassroots challenge with a sucker Vette that had a M1 tank blower fan powered by a 33hp snowmobile engine that created 1000 pounds of DF. Jim Hall actually drove it afterwards and had a huge grin. Car was donated to the Corvette Museum.

Edited by Bandit
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