Aero photos from El Mirage SCTA finals

[California98Civic]

Originally Posted by wmjinman

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.

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.

Originally Posted by aerohead

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.

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:


A fifties coupe with that same rail across the roof:


The trailing razor-edge of that streamliner motorbike in my first post:

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:


-james

[euromodder]

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.

[wmjinman]

Originally Posted by euromodder

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"

[skyking]

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.

[wmjinman]

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.

[kach22i]

Originally Posted by California98Civic

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.

Good point James.

[sgtlethargic]

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?

[sgtlethargic]

Originally Posted by wmjinman

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.

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

[California98Civic]

Originally Posted by sgtlethargic

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 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.

[wmjinman]

Originally Posted by sgtlethargic

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

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..."

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.....