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PostPosted: September 18, 2008, 6:59 pm 
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The first thing I think of is 2nd to 3rd degree burns when a tube fails on you in a wreck or if corrosion creates a pinhole in the tubing.

I can't visualize this going very well.


rongaudier wrote:
I know this subject has come up before, but here it is again. How about the rear mounted radiator idea? It would solve alot of problems for me based on my planned build.
How about taking advantage of the low pressure area that builds behind the car? Furthermore, by reducing pressure under the rear of the car (as illustrated) rear end lift should be reduced at high speed.
Also the use of a pointy nose should reduce form drag somewhat.
As far as coolant lines are concerned, how about using round tube in lieu of square tube in the bottom of the trans tunnel? Coolant could be routed through these tubes. The radiator could be covered in the back with a louvered panel.
Image

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PostPosted: September 18, 2008, 7:16 pm 
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rongaudier wrote:
Sucker Car Brought Ground Effects To Auto Racing
If you're thinking about building a sucker car, you should read up on the twin turbocharged sucker Corvette that was in the Grassroots Motorsports $2007 Challenge.

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PostPosted: September 18, 2008, 8:54 pm 
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I think there's plenty of downforce to be had just with normal airflow and the vacuum behind the car.

Taking a guess at the car's area to be around 24 square feet, that's around 3500 square inches. If you could get about 0.1 psi, that would provide a considerable 350 lbs. of downforce. That would be something like about 3" of water pressure...

Hard to do on anything like a street car, but a track car with 2" of ground clearance might be able to make some use of this, even without real skirts...

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PostPosted: September 18, 2008, 10:31 pm 
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olrowdy had a few comments about my lengthy Areo entry.
one of the comments was that narrower trans tunnels are not as strong as the wider/original design. This could very well be true, Ive read a couple of articles on cad testing on the strength/weakness of the book frame. Ive made a number of small modifications per these articles to provide increased rigidity, less flex. Most of the changes are to the "front box" where the suspension attaces to the frame, and additional bracing in the engine bay area which is where a lot of the flexing occurs in the book chassis. I'm pretty confident that the chassis will be quite stiff. But I appreciate the heads up.
You also mentioned using rivnuts to secure the top panel of the trans tunnel. I agree. this is a must, partiqularly if you've done what I have which is to enclose the underside of the car.
regarding the fold down screen and the brooklands set up. I acknowlege that the main windscreen down mode will throw a stream of wind right up over the scuttle, and it's unlikely I'll get a lot of relief from the brooklands screens, but, being a life long motorcyclist, I'm not too bothered by straight on wind, its the turbulent wind that spills off the sides of the typical 7 windshield that bug me, and that's what I seek to eliminate. Wish me luck.
The nose cone photos a poster put up from either Kinetic of COLD, cant remember which, are actually what inspired me to design my own. My nosecone is like a hybred of the two pictured, not as noticably fish mouthed as their low model, and not nearly as blocky and upright as their tall model. I think it is a nice compromise. I'll try to post a pic at some point. Cheers.


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PostPosted: September 19, 2008, 7:50 am 
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Good point, I've already decided that the rear radiator idea probably isn't workable.


fourthmeal wrote:
The first thing I think of is 2nd to 3rd degree burns when a tube fails on you in a wreck or if corrosion creates a pinhole in the tubing.

I can't visualize this going very well.


rongaudier wrote:
I know this subject has come up before, but here it is again. How about the rear mounted radiator idea? It would solve alot of problems for me based on my planned build.
How about taking advantage of the low pressure area that builds behind the car? Furthermore, by reducing pressure under the rear of the car (as illustrated) rear end lift should be reduced at high speed.
Also the use of a pointy nose should reduce form drag somewhat.
As far as coolant lines are concerned, how about using round tube in lieu of square tube in the bottom of the trans tunnel? Coolant could be routed through these tubes. The radiator could be covered in the back with a louvered panel.
Image


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PostPosted: September 19, 2008, 7:55 am 
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No, not thinking of building a sucker car. I was just under the impression that some on this board doubted the high pressure under the car thing.
Obviously, it's that pressure differential between the bottom and top of the car that causes all cars to develop lift at speed. Early ground effects efforts were meant to reduce this pressure, thus in effect creating more downforce. Not really...reducing the pressure differential between the top and bottom of the car and thus the resulting lift vector.

Driven5 wrote:
rongaudier wrote:
Sucker Car Brought Ground Effects To Auto Racing
If you're thinking about building a sucker car, you should read up on the twin turbocharged sucker Corvette that was in the Grassroots Motorsports $2007 Challenge.


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PostPosted: September 19, 2008, 8:58 am 
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Be carefull making generalizations. There are both high and low pressure areas on both the top and bottom of the car. It's not an all-or-nothing kind of deal. Additionally not all cars develop lift at speed, not even all street cars. Most street cars do, but certainly not all...even straight from the factory. As I previously mentioned, a significant reason for that (aside from the rounded top) is because most cars also dump the high pressure air from the engine bay out the bottom of the car as well. For some strange reason, once you put a full underbody tray on the same car it can quickly be made to produce significant downforce.

I'm curious exactly how "high" you think the pressure under a car is though? You said yourself that it's a pressure differential, which means it likely isn't just one side doing all the work. Are you sure it isn't of equal, or greater, effect that the air going over the top of the car creates significant amounts of "low" pressure, thus creating much of your obvious lift by pulling up on the body?

As far as I can tell, the only talk of pressure under the car generally not being as high as you'd think, comes from your idea pull radiator air from the underside of the car...But the idea is that a mere fraction of 1psi total pressure differential, while enough to help create some lift or downforce, is probably not going to be enough to drive a sufficient amount of air through a radiator.

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PostPosted: September 19, 2008, 12:08 pm 
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On this matter, I think I'll scan my sketches for the group's consideration tonight or tomorrow. I think I may have some workable designs.

Yes, it won't look like an original 7, but really I'm after a unique and beautiful car that is its own original, and I know some of you are as well.

You know, we should consider the concept Corvette Stingray as its front wheel design might help our free-air front wheels.

I once found a picture for this beast, but now I'm coming up short. Does anybody know what vehicle I'm talking about? It had a front like a hammerhead shark, and extreme aero features all over. It was slick!

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PostPosted: September 19, 2008, 12:41 pm 
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Well if it was updated and you got the front end down from being WAY up in the air.

I'm with you in that I think some sort of body could look and function well on a 7 type chassis. I don't think it would ever replace the 7 but it would be a nice adjunct to it.

Now a full body that would fit on a book chassis that could be swapped back to the traditional body during the summer would be the ultimate. 2 cars in one.


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PostPosted: September 19, 2008, 12:56 pm 
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IIRC there were some glass bodies that were made to fit over the book frame in the UK running in the 750 motor club. They looked decent.

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PostPosted: September 19, 2008, 1:22 pm 
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Driven5 wrote:
Be carefull making generalizations. There are both high and low pressure areas on both the top and bottom of the car. It's not an all-or-nothing kind of deal. Additionally not all cars develop lift at speed, not even all street cars. Most street cars do, but certainly not all...even straight from the factory. As I previously mentioned, a significant reason for that (aside from the rounded top) is because most cars also dump the high pressure air from the engine bay out the bottom of the car as well. For some strange reason, once you put a full underbody tray on the same car it can quickly be made to produce significant downforce.

I'm curious exactly how "high" you think the pressure under a car is though? You said yourself that it's a pressure differential, which means it likely isn't just one side doing all the work. Are you sure it isn't of equal, or greater, effect that the air going over the top of the car creates significant amounts of "low" pressure, thus creating much of your obvious lift by pulling up on the body?

As far as I can tell, the only talk of pressure under the car generally not being as high as you'd think, comes from your idea pull radiator air from the underside of the car...But the idea is that a mere fraction of 1psi total pressure differential, while enough to help create some lift or downforce, is probably not going to be enough to drive a sufficient amount of air through a radiator.


When I was considering the aft mounted radiator, I had not considered the effect of flow restriction caused by the radiator on the natural tendancy for high pressure air to migrate to low pressure areas. I believe your assessment is probably correct, there is not enough differential in pressure to overcome said resistance. Therefore, I have already decided to scrap the aft radiator idea as basically unworkable (hence my revised drawing).

Okay, generally speaking there is a pressure differential generated between the top and bottom of the car at speed. Just how much this differential is, I have no idea. I do know that it was one of the reasons ground effects became popular in the 70's and 80's. Sure, cars that have wings or other downforce generating devices can overcome said lift, but at the cost of induced drag.


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PostPosted: September 19, 2008, 1:41 pm 
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It would be sweet to be able to do that. You could build a body buck that elevates and stores the body in the garage, and drive under it, and drop it on when temps drop.

I'm highly interested in making this work, so as soon as I get a frame built and a car resembling a 7 constructed (to pass NV custom car inspection as a replica Lotus 7), I'm going to start work on the fiberglass body. I figure that if I end up with a car that doesn't look a thing like a 7, I could run into difficulty getting it registered, but that may or may not be true. Hell, they could call it a 2009 custom (thus I'd pay massive taxes), so I think I'll shoot for "replica".

I think the most important part about doing a body on this car is to keep the motorcycle fenders. It just looks awesome. If some smooth shape can come from the nose to push air up and over these without breaking up, I think it will work. Personally, I was interested in using a turbocharged I-6, so I'm wondering if a low-pressure high-flow area behind the wheels could be used to suck air through the intercooler, and flow smoothly out of the top of the rear of the front wheel area.

Does anybody know the average angle of attack air will accept before breaking up and becoming turbulent? I'd have to imagine that it isn't much more then 40-45 deg. This would be at 60+mph of course. Another thing to know is how air flows off one object on the car to another, and if the boundary layer of air will allow a gap (for the motorcycle fenders to maneuver), and what size gap is allowed? I wish I could visualize the effects of a wind tunnel test in my head (like Tesla could, I bet), but it isn't within my grasp. I visualize air like flexible rays, and in that way when I draw a "line" of air, I try to see what it would it if it were given a path to take. My goal then is to create a smooth path for as many "rays" as possible, and to take advantage of Bernoulli's neat laws of fluid physics of low pressure, high flow. Is this right?

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PostPosted: September 19, 2008, 1:50 pm 
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fourthmeal wrote:
<snip>

I think the most important part about doing a body on this car is to keep the motorcycle fenders.
It just looks awesome. If some smooth shape can come from the nose to push air up and over these without breaking up, I think it will work. Personally, I was interested in using a turbocharged I-6, so I'm wondering if a low-pressure high-flow area behind the wheels could be used to suck air through the intercooler, and flow smoothly out of the top of the rear of the front wheel area.

Does anybody know the average angle of attack air will accept before breaking up and becoming turbulent? I'd have to imagine that it isn't much more then 40-45 deg. This would be at 60+mph of course. Another thing to know is how air flows off one object on the car to another, and if the boundary layer of air will allow a gap (for the motorcycle fenders to maneuver), and what size gap is allowed? I wish I could visualize the effects of a wind tunnel test in my head (like Tesla could, I bet), but it isn't within my grasp. I visualize air like flexible rays, and in that way when I draw a "line" of air, I try to see what it would it if it were given a path to take. My goal then is to create a smooth path for as many "rays" as possible, and to take advantage of Bernoulli's neat laws of fluid physics of low pressure, high flow. Is this right?


I think if aero is your goal that keeping the cycle fenders would be a huge mistake. Sure they look cool, but they are also a big reason these cars have such a lousy CD. Look at how Colin Chapman solved this... by covering them with a body.

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PostPosted: September 19, 2008, 1:57 pm 
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Agreed, open-air cycle fenders are horrible for drag and turbulence.

But...what about cycle fenders that are themselves covered in the front with some form of smooth air deflection and the back with some form of guidance for the air to smooth back up to the body. That's what I was talking about.

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PostPosted: September 19, 2008, 2:21 pm 
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fourthmeal wrote:
Does anybody know the average angle of attack air will accept before breaking up and becoming turbulent? I'd have to imagine that it isn't much more then 40-45 deg. This would be at 60+mph of course.
Without additional physical testing (this is where the yarn tufts come into play) the generally recommended diffuser angle to avoid flow separation is between 5 and 10 degrees.

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