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Old 02-14-2009, 07:48 PM   #11 (permalink)
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Quote:
Originally Posted by aerohead View Post
I eliminated the wipers on my CRX at Bonneville and it had no effect on top speed.
No effect, or no significant effect? I thought you mentioned somewhere that shielding the wipers netted a small improvement.

Yes, here it is:

Quote:
Originally Posted by aerohead View Post
July 1991, Bonneville International Speedway, Wendover, Utah, U.S.A., the Phil Knox, 1984 CRX 1.3 streamliner: ... A cardboard and duct-tape cowl fillet over the wiper area demonstrates a 0.28-mph improvement to top speed.
Ah, OK! .28 mph. Could have been a passing bird farting. Never mind!

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Old 02-14-2009, 07:49 PM   #12 (permalink)
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Quote:
During development of their PNGV Car,GM noticed during windtunnel evaluations,that the windshield wiper had virtually no impact on drag.
Not trying to be contrary, but they shielded the wipers anyway on the Precept. Likely just for styling reasons.
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Old 02-14-2009, 08:34 PM   #13 (permalink)
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Quote:
Originally Posted by hypermiler01 View Post
Frank, what's up with you and yaw, yaw, yaw? If you are traveling down the highway at 70, and you have say a 5mph crosswind at 45 degrees, the resulting yaw vector is so small as to be negligible.

If you have hurricane force winds at exactly 90 degrees to the road, yaw might be a concern, but most of the time around here, any breeze is so slow that you can barely feel it.

Just look at all the tuft testing pics posted on this forum. Generally the tufts are pointed straight back.
1. Only 55 mph roads here.

2. 5 mph in the plains? LOL! A CALM day is 15 mph and it isn't uncommon to have 30-35 mph winds.

3. And those winds~ are they EVER lined up with where you are going? Seems like I go East-West a lot and of course the predominant wind is from the North.

So... 15 mph x-wind 90 deg. to the road; travelling 60 mph = 11 deg yaw- right?

30 mph wind = 22 deg yaw?

Imagine 10 to 20 deg yaw flowing over your vehicle on a regular basis.

Or when I'm putzing around at 50 mph or less... even more.

That would really screw up boattailing in the plan view wouldn't it?

I get a visual of it whenever I'm in the rain and snow- the drops/flakes go up and off the windshield at an angle, and the behavior of the drops can sometimes be seen to be different on the side glass.

I guess flying C150s and riding motorcycles and bicycles has also made me acutely aware of x-winds. Try lining a C150 up to the runway in a crosswind and YOU WILL APPRECIATE YAW.

P.S. Tufts straight back: I suppose tuft testing is more fruitful on calm days?

Last edited by Frank Lee; 02-14-2009 at 09:43 PM..
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Old 02-14-2009, 08:44 PM   #14 (permalink)
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Quote:
Originally Posted by aerohead
July 1991, Bonneville International Speedway, Wendover, Utah, U.S.A., the Phil Knox, 1984 CRX 1.3 streamliner: ... A cardboard and duct-tape cowl fillet over the wiper area demonstrates a 0.28-mph improvement to top speed.
Yes I did the no wiper/ cowl fillet thing for quite a while. All it demonstrated to me was that my testing wasn't good enough to pick up a change that small, if in fact there was any change. It also demonstrated that getting caught in the rain or getting splashed on with no wipers is a greater inconvenience than the .0000000000001 mpg gain.
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Old 02-14-2009, 09:22 PM   #15 (permalink)
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BTW, look into the Bosch and RainX single piece blades. They are much slimmer than normal wipers, and the top surface is like a wing, so rather than lift off the windshield they are pushed down.
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Old 02-14-2009, 10:47 PM   #16 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
1. Only 55 mph roads here.

2. 5 mph in the plains? LOL! A CALM day is 15 mph and it isn't uncommon to have 30-35 mph winds.
I don't live in the plains, on a calm day there is no detectable air movement on the ground, 35 is a hella storm, the speed limit is 75, half the people go 80. And the snowflakes go straight up the middle of the windshield.

What state do you live in?

Also, even in high yaw conditions, it is the forces applied parallel to the vehicle axis which have the most effect on fuel economy. The yaw will cause turbulence to the side of the vehicle, but not cause much impedance to the forward direction.

I also ride bicycles. Crosswinds make me wobble back and forth sideways, but they don't slow me down. And if you turn your body like a sail, you can actually get a boost!

Last edited by hypermiler01; 02-14-2009 at 11:01 PM..
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Old 02-14-2009, 11:07 PM   #17 (permalink)
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ND SD MN WI IA all pretty much the same RE: wind as far as I know.

"The yaw will cause turbulence to the side of the vehicle, but not cause much impedance to the forward direction."

That's debatable. Turbulence pretty much wrecks aero.

P.S. Wind resource data: http://www.ncdc.noaa.gov/oa/climate/...d/avgwind.html

and



My area: 10-13mph ave/yr
Yours: 5-8mph ave/yr

My first guess was high. Well, seems the weatherman is always talking about 15-30mph winds!

Yeah, you have sorta half of what I have. That thar is our difference in perception re: yaw.

Well... a lot of us live here!

Last edited by Frank Lee; 02-15-2009 at 12:09 AM..
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Old 02-14-2009, 11:48 PM   #18 (permalink)
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I have been thinking about this on my Honda Insight as it would be easy to remove the left side mounted wiper and just slightly extend the range of the center mounted one and have a set up just like my Jaguar XJ40. I don't know what it would entail but probably just a redesigned bell crank for the wiper....if I could only get to it....#8-) Also I would remove the wiper on the rear window as it does virtually no good anyway and I cant see out of the window even when its clean.
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Old 02-15-2009, 12:42 AM   #19 (permalink)
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Re crosswinds:

Quote:
According to the EPA, crosswinds introduce lateral rolling-resistance to the tires — think of the steering corrections needed to maintain a straight line — and they increase aerodynamic drag in directions a car isn’t designed to handle, both of which affect gas mileage. Greg Fadler, an aerodynamics engineer at GM, expounded: A 14-mph crosswind on a car traveling at 55 mph can affect its drag coefficient enough to increase fuel consumption 13 percent, he said.
source
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Old 02-15-2009, 02:46 AM   #20 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
P.S. Wind resource data: Wind- Average Wind Speed- (MPH)

and



My area: 10-13mph ave/yr
Yours: 5-8mph ave/yr

My first guess was high. Well, seems the weatherman is always talking about 15-30mph winds!
I think weathermen here are usually spouting, '15mph winds with gusts to 25 & 30 mph'.

As to the average wind speed, you're probably mostly driving during the day.
Here in N. Central SD, wind speed at night is usually 3-8 miles less than afternoon wind speed.

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