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Old 04-26-2013, 03:21 PM   #311 (permalink)
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tow

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Originally Posted by freebeard View Post
Me too! I might see you there.

What would happen if you put your rig on the end of a tow strap behind another vehicle; incorporating a spring scale at the attachment point, with a webcam or periscope pointed at it? All the tow vehicle driver would have to do is pull.
Actually the big dogs used to do such a thing,but inside what they called a 'shrouding trailer.'
This fully-enclosed trailer had an open bottom with rubber skirting all around and the towed vehicle inside was connected by only a strain-gauge.
With the trailer shielding all the air from the test vehicle,only the rolling-resistance of tires and differential would be measured,then later,the already known driveline loss could be deducted,leaving the R-R profile at any speed of interest.
I'd have only deceleration profiles from which to compare,but it would be way out ahead of nothing.
A BUB motorcycle guy I hung out with said his Harley really suffered speed loss on the salt,compared with the interstate.
If I GOOGLE around I find anectdotal comments about R-R on and off the salt,but no real quanta.
Jeff Mcvey's normally-aspirated Mazda 3 lost 13% top speed,from 130 mph,to 113.
Sarah Curtis's 139 mph Mini Cooper could barely squeek up 130 mph after icing down the turbocharger inter-cooler.A 6.4% speed loss.
I was happy to see a speed increase,from 96(on pavement at sea level) to 105.
If the 'stock' T-100 had been run,it might have had a speed as low as 83 mph due to the damp salt conditions.If so,that would be a 26% velocity improvement for the 'streamliner'(and not yet to terminal velocity).
You hear about 'good years' and' bad years' at Bonneville.I think 2012 will score pretty low.

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Old 04-28-2013, 06:48 AM   #312 (permalink)
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I'm of the opinion that we just don't have the power-to-weight ratio to learn what we need from Bonneville...If you have a good baseline,I think we'll be able to figure your new Cd from your MPG data...I'm gonna try for the A2 Wind Tunnel in late August/early September and see what their load cells say.
This is what I was responding to; but I thought the RR would simply be estimated. This suggests an A-B test that would quantify both.
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Old 04-30-2013, 03:52 PM   #313 (permalink)
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estimated

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Originally Posted by freebeard View Post
This is what I was responding to; but I thought the RR would simply be estimated. This suggests an A-B test that would quantify both.
With a large database baseline we'd know the mpg at a given velocity with Volkswagen's original configuration.
With SAE Paper# 649A,from Kelley & Holcombe of GM,if the only variable is the Rabbit's shape,the Rolling-Resistance portion will be embedded within the relationship,and with the new mpg,the new Cd will fall out of the equation.
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If the weight has been altered,Ricardo Associates Inc. has some pretty current mpg penalty as a function of weight addition curves we can use to adjust the Cd.
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Coastdown tests could tell us as much as a wind tunnel,however,so far,we've yet to take on the data acquisition and mathematical rigor necessary to make a proper go of it.It's beyond my capabilities.

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