Aero photos from El Mirage SCTA finals
 

Just a handful of pics arranged in an order meant to help you see aero features. Several pics are of the dust trailing wakes of the cars I photographed before their runs.

Here is the wake of the streamliner motorcycle featured in the attached pics:
http://ecomodder.com/forum/attachmen...2&d=1384151834

Here is the wake of a roadster:
http://ecomodder.com/forum/attachmen...3&d=1384151876

Here is the wake of the yellow Austin van featured in the attached pics:
http://ecomodder.com/forum/attachmen...4&d=1384151892

All images taken from almost the same distance, give or take a dozen yards or so...

Great pics! Thanks for sharing. Any additional info on the vehicles in the pics?

Oh yeah, some... that red and white ferguson streamliner has a Hondata engine in it. Earlierin the year it ran 243mph. On the run you see it getting pushed-out for ithit 229mph. That streamliner motorcycle was wicked fast and has been running for several years now, with a best of speed something in the area of 200mph, IIRC. The little white Chevy Spirit with the turbo is a fixture kf the SCTA events, driven by different drivers all the time. It's fastest ever was 117mph. On the run you see it starti g it ran 109mph. It's called "the peanut" on the track even though that nameseems nowhere on the car. The yellow Austin has a Bonneville type spoiler on the back, but it is just to keep dust off the rear windshield at the insistance of the driver, go figure. It can't be helping aero at that size and position, can it? The motorcycle was just too cool to pass up. The rider was awesome. Speed snifting with perfect effectiveness. Forgot to listen for its top speed report. And that last car is my Civic, photographed as the yellow Austin raced by. Was a great day.

I love the detail shots like this one.

http://ecomodder.com/forum/attachmen...p;d=1384150204

Can't really tell much from the dust wake if vehicles speed is not consistant, can we ?

That, and also I suspect it has as much or more to do with weight than turbulent aero wake (the amount of dust the wheels pulverize underneath them). At the Black Rock Desert, a big truck kicks up a dust trail many times larger than a car. - of course, I guess it probably has a bigger turbulent aero wake behind it, too - - - - :confused:

This size of the vehicle as i understand it is closely related to its total drag, in as much as CdA is a calculation of Cd and frontal area. I took these photos partly because aerohead once suggested in a thread hee on EM that a lot can be seen in the dust trails formed behind vehicles at El Mirage. You can't read it for numbers, like the Cd or lift or whatever. But you can plainly see the scale of the wake left y that sleek, small, streamliner motorcycle versus that yellow Austin. It's a flow dramatization, not a measurement. But the dramatization is useful too.

Right.

And for the weight thing, I guess the test would be to drive a fully loaded semi and an unloaded one side by side & compare their dust trails. I guess I'm also thinking about the tracks they leave in the dirt..... those big duals plow up a lot of dirt when they roll over it with all that weight. To me, that has to translate to much more dust in the wake.

Compare it to a motorcycle going the same speed, maybe. Of course, you'll say the motorcycle has a fraction of the frontal area, too..... Hmmmm - - can we somehow load 10 tons onto a motorcycle????? or reduce the weight of said semi truck to 1000 lbs???? Maybe a strict weight vs. frontal area test would be difficult.....

photos
 

The photos are great!
If wind tunnels had test sections this long and you could photograph the test vehicle at a far enough distance we'd see the same thing if smoke was introduced into the wake.
This illustrates the magnitude of the wake and its relationship to fuel economy,and how an internal combustion 1987 Sunraycer would achieve 300 mpg.
Hucho could use these sorts of images in his books.
Thanks mucho! I would have liked to have been there.:)

speed
 

The drag coefficient becomes constant at around 20-mph.So the wake behavior would also be constant up to about 250 mph where compressibility effects come into play.
The magnitude of the energy is following the square/cube relationship,so sure,the wake will be more dramatic if a Bugatti Veyron or Mike Cook's Thunderbird blows by at over 260 mph.
The lake bed dust is already pulverized.And sure,if you've seen video of the Lunar Rover you know that the tires will sling dust even in a vacuum.But it is the low base pressure of the turbulent wake which allows the dust to migrate far afield of the tires 'toss' area.
Ritchie Ginther's first rear spoiler was designed to prevent this 'dust' from moving forward into the cockpit of his Ferrari and killing him.It was only an accident that it also spoiled rear lift.

To me it is not about the amount of dust, but how the wake lifts that dust into the air and reveals the flow pattern. The pattern behind the streamliner motorcycle is totally different than the yellow Austin, which has dust swirling around all the way to the roof.

Thanks. It would have been fun if you and other EM folks had also been there. It is worth noting that the streamliner motorbike has a 665cc engine and goes almost 200 mph, whereas the Austin has a 2.0L and goes something in the 150mph range. That's not just dead weight. It has got to be drag too.

Adding more photos.

A Neon with an unusual rail across the roof:
http://ecomodder.com/forum/attachmen...1&d=1384236575

A fifties coupe with that same rail across the roof:
http://ecomodder.com/forum/attachmen...1&d=1384236575

The trailing razor-edge of that streamliner motorbike in my first post:
http://ecomodder.com/forum/attachmen...1&d=1384236575
That thin sliver probably has a lot to do with the tiny wake left behind.

Lastly, and adjustable angle trailing edge for this wing on the back of a car:
http://ecomodder.com/forum/attachmen...1&d=1384237972

-james

The rails on the roof are there to keep the airflow from rolling off to the sides and crash with the air going along the sides.

Actually, those roof rails are required by SCTA rules for cars going over 200 mph - OR if you're running in a class where the current record is above that speed.

I asked the chairman of the rules committee why exactly that rule existed, and he said it was a safety thing.... If a car is going faster than 200, loses control and goes sideways, the airflow going SIDEWAYS across a car causes lift, as though the car is a blunt wing. So those two rails, which are to be as close to the edges of the roof as practical, are actually little spoilers - to kill lift in the case the car goes sideways at high speed.

The alternative, as Tom Burkland, former land speed record holder, once told me, is "Taking flight without a landing plan"

thanks for explaining that. I had just been in the rulebooks tonight and did not have an explanation yet, but the requirement for 'roof rails' was clearly defined.

Yeah, that's why we asked the rules chairman. At first, I thought it was for structural reinforcement, but when they were saying to use thin aluminum angle pop-riveted on (and that's what others were doing), it was clear that wouldn't have been much reinforcement. So, only after talking to the chief inspector/rules chairman, did we find out it was for safety in the event of a high speed sideways skid.
;)

Good point James.

Interesting. Is that the first time you've gone to an LSR meet?

I like the Ferguson Racing streamliner. Anybody care to hazard a guess at its Cd?

I'm curious- "structural reinforcement" for what purpose?

I also brought my daughter to the 2012 "world of speed" event at Bonneville. That was amazing, and far. It was our first LSR event. My daughter is 11 now, and interested in engineering and so these sophisticated and diy cars are a great bonding point.

Well remember, I had no idea what they were actually for. So the term "roof rails" in the rulebook implied, I thought, something strong. So in my imagination, I was thinking maybe to keep the roof from buckling or blowing off at high speed, or something like that. Or even to help in the event of a rollover, although now I realize that's pretty stupid, since that's what the roll cage takes care of.

But then when I started seeing them, and seeing they were thin aluminum strips with almost no strength at all, I was really curious. Could they be some kind of fins to help keep the car straight at speed? Surely not.

So finally I asked and was told they were basically aerodynamic "stall fences" when turned sideways to the wind. Without them, the shape of most cars is enough like a fat wing to cause it to lift off the ground at speeds over 200 mph. But those two little strips, 3/4" high, running the length of the roof along each side, are enough to break up the lift that would otherwise form.

I had a similar thing explained to me about my air dam, which went almost all the way to the ground. That helps a lot when going FORWARD, I was told, but I should make provisions for it to break away or otherwise vent the air that would be trapped behind it if I ever spun out and went BACKWARDS at high speed. In that case, the air dam would catch the air and turn my car into a hovercraft!!! - Or worse. As Tom Burkland put it, "You could find yourself taking flight without a landing plan..." :eek:

See, I was going around thinking this salt flats racing was the safest thing in the world; nothing to hit. But then it was explained that there IS something to hit - the ground! When these cars get to extreme speed, the danger is some aero forces lifting them into the air and then they impact the GROUND with lots of force. Guess that's what kills most Bonneville guys - and sometimes fire.....

There were two accidents that we were present for last Saturday. I'm not totally sure what happened in the first, but the driver was seriously injured, car wrecked. The second was a spin-out that I saw from the sidelines. Car was probably at 150-200 mph at the time. With the dust trails you could not really see the car at all anymore. There was just suddenly no more forward movement and a big dust cloud kinda stationary over the course. No injury in that second one, perhaps because of what you describe.

weight
 

Aerodynamic drag dominates the road load power at these racing velocities.Rolling resistance is essentially meaningless.
The weight will impact power-to-weight,so it's important to acceleration.
The weight will also impact traction,as many of these cars are capable of wheel spin at over 250 mph+.
Some racers add ballast to improve grip.
Spins are potentially fatal.If the car goes sideways and lifts off,if it lands sideways it can dig in and barrel roll.The centrifugal forces and accelerations of the crash can easily exceed human tolerances.Only an onboard fire is worse.

crash video
 

Well, he stayed right-side-up, so that's a good thing!!

I did a maneuver very similar to that at Bonneville in 2008 at 161 mph. My car stayed flat too, and I was very thankful for that! I wasn't in a cloud of dust - in my case, it was a cloud of smoke because when the engine blew, oil spewed all over all the hot parts, so it was nasty. I couldn't see anything until I came to a stop and was able to open the door.

They have a rule that if you have an "emergency", to pull off onto the right side of the course (if you can). I couldn't see through the smoke, so just nudged the wheel ever so slightly to the right. As luck would have it, I ran right over the right side "2-mile" sign & timing light. I remember seeing the big orange "2" momentarily appear in the windshield. Anyway, they actually "prepare" the course by repeatedly dragging & rolling it. Off to the sides, the salt isn't nearly as flat, smooth, and hard as on the course. So I think what happened is when my right wheels hit that soft salt, it musta tugged on that side enough to upset the equalibrium. So I went into a skid, spinning to the right, & made at least a couple complete turns before finally coming to a stop. At the time, I thought it was a half dozen turns, but now I doubt it could have really been that many.

The year after, my engine blew at 183 mph and there was even more smoke. But that time, I was able to exit the course to the right without spinning out, so just did a big, long arc to the right until my parachute stopped me. There was so much smoke that time, they were sure there was a fire. When the fire truck got there, they were almost insisting I "admit" to a fire & tell them where it was. We opened the hood, the trunk, & nothing was burned. But they kept holding their fire extinguishers with "hair triggers", all dissappointed not to be able to spray anything.

Later, I discovered I'd forgotten to "arm" my on-board fire suppression system before taking off on that run. It's a good thing there wasn't a fire, because I'm not sure I would have had presence of mind enough to think to pull those safety pins if I'd tried to hit the extinguisher and nothing happened while bathed in flames!!! There was actually SO much smoke, I was halfway wondering if there was a fire for awhile. But I couldn't feel heat or see any orange light, sooo.... But the smoke was so thick, I was having trouble breathing and actually got just a little worried about smothering at one point! I was sure glad when I was able to release the door net & roll down the window! It was quite an adventure, I can tell you that!!! :eek:

No worries, and it's not stupid or anything.

Dry lakebed dust on my '98 Civic
 

Last images from El Mirage.

In the first, you see the dust collected at the trailing edge of the trunk lid, where a line marks a curve downward (dust collected there fairly consistently), dust collected on the ledge just below the license plate, and lots of dust on the top of the bumper cover (but not at the ends of the cover).

http://ecomodder.com/forum/attachmen...1&d=1386028292

In this second image, dust has collected on the aft side of the opening for the driver side door. It is smashed into the sheet metal and the trim, but not on the forward edge (on the door itself).

http://ecomodder.com/forum/attachmen...1&d=1386028292

Those roof fences have been on NASCAR race cars for many years.