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Old 04-03-2007, 01:42 PM   #21
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Originally Posted by MetroMPG
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Can we conclude that from water/debris flow patterns?

When I look at the bottom pic, I think we're seeing the effect of water getting channeled upwards and backwards in the skirt's forward seam, and reaching some point where some factor (volume of water?) causes it to spill out of the channel and continue being swept rearwards.
I think I tend to agree. Maybe I should tape the seams and drive through a few puddles
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Old 04-03-2007, 01:58 PM   #22
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This one throws an interesting twist in the aesthetics vs. style debate:



Nissan R89C with rear wheel skirts

I doubt these are on for styling reasons. That said, if they were useful, why weren't they adopted by every race team? Was the theoretical speed gain offset by the extra time the pit crew needed to remove/reinstall the panel for a wheel change? Brake cooling issues?

Inquiring minds want to know...
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Old 04-03-2007, 02:58 PM   #23
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i suppose basically there's nothing wrong with wheelskits themselves, i can't see how they might directly have a negative inpact on drag BUT.
appart from practical issues such a tire maintenance and dirt accumulation (possible corrosion! ) there's also this: for stability reasons most cars seem to have an as broad as possible wheelbase. the instalation of wheelskirts on a lot of current cars would either require the rear wheels to move inward or the skirts to buldge around it. since the desired aerodynamis shape is tapered towards the back, option one may seem the best solution. however you would take the rear wheels out of line with the front ones... i don't know how that will effect road handing, but you'd still add frontal area, since the wheels would not be inline anymore. and possible extra rolling resistance when dealing with foul weather. all these things might counter any benefit generated by skirts...

writing this i suddenly realise a few cars did employed this, even as early as the mid 50's! the citro?n DS for example! but than again the car was revolutionarry in many aspects...even today it still has a futuristic look to it. (in the event of a flat tire the skirts could not be removed but with the aid of just a small pillar and due to the special hydrollic suspention the car was able to lift the wheel that was to be replaced of the ground and drop it out of the wheelwell... talk about advanced!)

finally there's one thing i really like about my car's design is the rear wheel whell...

the shape actually seems to be dictated more by a desire not to desturb the airflow than to echo the front wheel arch (wich is HUGE for the littel wheels but the car leans over quite a bit while conering fast so i think it needs the space sometimes) anyway it's far from a wheelskirt and the tires stand to far out to extend one further, but i thought it was worth mentioning.
afterall it's the little things that matter right? (don't look at the mudfaps )
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Old 04-03-2007, 03:44 PM   #24
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Quote:
Originally Posted by MetroMPG View Post
This one throws an interesting twist in the aesthetics vs. style debate:



[I]Nissan R89C with rear wheel skirts
Wow... I too wonder how fast their wheel changes are/were.


Held the speed record in 1980 @ 63mph (look at that monster chain ring)



You've seen the HPV I'm working on.... From CFD modeling, we know fully enclosing our wheels is beneficial. Empirical testing is a bit more difficult (I don't think anyone is going to cut into our wind tunnel model). Unfortunately, this year spacing is an issue so, we're compromising with wheel disks and minimal wheel arch :P

You can also look at almost every soapbox car -- they will have disks.

I'm not saying they're beneficial or not beneficial. But there's obviously exceptions to the rule. What that rule is (no skirts are better or skirts are better), is what's in the air :P

-------
For flow visualization..... If anyone wants to build a small water tunnel and make a sectioned model (with spinning wheels)
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Old 04-03-2007, 03:50 PM   #25
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Trebuchet - now I understand why you're enclosing the front wheels - well.. if your machine is anything like the ones pictured.

You have drastically constrained steering angles. Which means you can locate the wheels very close to the rider's legs, and you don't have to worry about interference with the bodywork when "turning".
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Old 04-03-2007, 04:01 PM   #26
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Crosswinds and Dirty Water

Looking at the pics of the grimy road marks on vehicles leads me to wonder about airflow patterns that aren't head-on (like pretty much most air).

Around here, it's windier than Chicago, so I'm almost always getting hit with wind to different angles of the car. So from what I understand, if you're driving at a 360-degree heading, winds from 270 to 90 degrees, at highway speeds, is mostly vectored to a front corner and then follows with the car (with most of the extremes of that radius, and winds further down the car, pushing on the flat side of the car -- and rearward winds [90 to 270 degrees] being negligible except again on the ends of the spectrum and further up the car).

Point being, all of this head-on testing only similates driving down a highway with zero wind coming from anywhere but straight ahead.

Shouldn't the car be put on a turntable to see how it fairs with wind vectors?

RH77
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Old 04-03-2007, 04:06 PM   #27
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Good points, Rick. Cd figures do represent a head-on calculation. Cars with the same Cd & A values (but different shapes / aero detailing) could see different results in crosswinds.
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Old 04-03-2007, 04:40 PM   #28
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Quote:
Originally Posted by MetroMPG View Post
Trebuchet - now I understand why you're enclosing the front wheels - well.. if your machine is anything like the ones pictured.

You have drastically constrained steering angles. Which means you can locate the wheels very close to the rider's legs, and you don't have to worry about interference with the bodywork when "turning".

Youu got it Our design different - but the same general idea. Our wheels will be flush with the fairing (hopefully - we'll see once manufacturing is done).

Our only steering constraint is that we must be able to achieve a 25' turning radius or smaller. But, because our CG is low, we can place our front wheels a little closer thus allowing the rear wheel to be a little closer without sacrificing stability..... All of that means - to make that 25', we need less of a steering angle.
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Old 04-03-2007, 04:44 PM   #29
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Cool.

Quote:
Our wheels will be flush with the fairing
So your front wheels will be exposed & disc covered? GoOne style?

This sounds like a really fun project.
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Old 04-03-2007, 04:52 PM   #30
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So just drive really, really fast and drag the apparent cross-wind up closer to on the nose.
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