escape drag
#1
03-16-2006, 11:26 AM
escape drag
In the 2004 book "Propulsion Systems for Hybrid Vehicles" the author did some drag tests on a non-hybrid 4WD Escape, which ought to be almost the same as the Hybrid---except for drive-train friction. He tried to fit the results to the standard model, constant rolling friction and quadratic air drag, and claims a good fit for his parameters. The upshot (if one is to believe the numbers) is that the time (in seconds) to roll to a stop from a starting speed v is t=157arctan(v/50), with v in mph. That means:
60 to 50: 14 sec
50 to 40: 18.5 sec
40 to 30: 21 sec
30 to 20: 25 sec
20 to 10: 29 sec
10 to stop: 31 sec
and finally 60 to stop: 137.5 seconds.
(For the really daring, 70 to 60 is 12 seconds.)
It would be fascinating if someone with time on his hands, and an FEH to play with, could try some of these on a level road, coasting down in neutral with no wind, to see how closely this standard model actually fits the car we all have.
If these numbers are right, they tell us exactly how much power has to be supplied (and therefore gasoline burned) to run the car at the various speeds. That's useful information.
Hal
60 to 50: 14 sec
50 to 40: 18.5 sec
40 to 30: 21 sec
30 to 20: 25 sec
20 to 10: 29 sec
10 to stop: 31 sec
and finally 60 to stop: 137.5 seconds.
(For the really daring, 70 to 60 is 12 seconds.)
It would be fascinating if someone with time on his hands, and an FEH to play with, could try some of these on a level road, coasting down in neutral with no wind, to see how closely this standard model actually fits the car we all have.
If these numbers are right, they tell us exactly how much power has to be supplied (and therefore gasoline burned) to run the car at the various speeds. That's useful information.
Hal
#2
03-16-2006, 12:09 PM
Re: escape drag
Originally Posted by hallewis
In the 2004 book "Propulsion Systems for Hybrid Vehicles" the author did some drag tests on a non-hybrid 4WD Escape, which ought to be almost the same as the Hybrid---except for drive-train friction. He tried to fit the results to the standard model, constant rolling friction and quadratic air drag, and claims a good fit for his parameters. The upshot (if one is to believe the numbers) is that the time (in seconds) to roll to a stop from a starting speed v is t=157arctan(v/50), with v in mph. That means:
60 to 50: 14 sec
50 to 40: 18.5 sec
40 to 30: 21 sec
30 to 20: 25 sec
20 to 10: 29 sec
10 to stop: 31 sec
and finally 60 to stop: 137.5 seconds.
(For the really daring, 70 to 60 is 12 seconds.)
It would be fascinating if someone with time on his hands, and an FEH to play with, could try some of these on a level road, coasting down in neutral with no wind, to see how closely this standard model actually fits the car we all have.
If these numbers are right, they tell us exactly how much power has to be supplied (and therefore gasoline burned) to run the car at the various speeds. That's useful information.
Hal
60 to 50: 14 sec
50 to 40: 18.5 sec
40 to 30: 21 sec
30 to 20: 25 sec
20 to 10: 29 sec
10 to stop: 31 sec
and finally 60 to stop: 137.5 seconds.
(For the really daring, 70 to 60 is 12 seconds.)
It would be fascinating if someone with time on his hands, and an FEH to play with, could try some of these on a level road, coasting down in neutral with no wind, to see how closely this standard model actually fits the car we all have.
If these numbers are right, they tell us exactly how much power has to be supplied (and therefore gasoline burned) to run the car at the various speeds. That's useful information.
Hal
The number 50 in the formula should really be 48 (I flunked an arithmetic test),
so the numbers in the table should be 14, 17.5, 21.5, 25.5, 30, and 32 seconds, respectively, with 141 to stop from 60. Not much of a change, but mea culpa.
Hal
#3
03-16-2006, 02:07 PM
Ridiculously Active Enthusiast
Join Date: Jun 2005
Location: Boston (north suburbs)
Posts: 743
Re: escape drag
Hey Hal,
Haven't seen you around lately - how are you enjoying the FEH? How's the mileage?
I think there is a guy in Florida that if we ask him really nicely, he would probably make time run these tests. You out there still Gary?
I'd give it a try but two problems: there isn't a straight, level road within 50 miles of Boston where you can do 60 (that I know of) and the wind has been 20+ knots for the last week with no sign of it letting up.
Was this testing the author did performed in a wind tunnel or real world? Be interested to see how much friction there is caused by rolling resistance and other frictional losses besides air drag.
Ray
Haven't seen you around lately - how are you enjoying the FEH? How's the mileage?
I think there is a guy in Florida that if we ask him really nicely, he would probably make time run these tests. You out there still Gary?
I'd give it a try but two problems: there isn't a straight, level road within 50 miles of Boston where you can do 60 (that I know of) and the wind has been 20+ knots for the last week with no sign of it letting up.
Was this testing the author did performed in a wind tunnel or real world? Be interested to see how much friction there is caused by rolling resistance and other frictional losses besides air drag.
Ray
#4
03-16-2006, 02:33 PM
Re: escape drag
Hi, Ray:
Yes, he's still there, but I didn't want to put pressure on anyone. And yes, if the numbers are right they give us the breakdowm between air and rolling friction (including the drive train). The actual formula (which I didn't show) is proportional to 1+(v/48)^2, showing the air drag and the rolling friction equal at 48 mph. My memory (from long ago) is that that happened around 60 mph, but this is a bigger car, so this could be right. The manual says that 60 mph uses 20% less fuel than 70, FWIW.
Cheers,
Hal
Yes, he's still there, but I didn't want to put pressure on anyone. And yes, if the numbers are right they give us the breakdowm between air and rolling friction (including the drive train). The actual formula (which I didn't show) is proportional to 1+(v/48)^2, showing the air drag and the rolling friction equal at 48 mph. My memory (from long ago) is that that happened around 60 mph, but this is a bigger car, so this could be right. The manual says that 60 mph uses 20% less fuel than 70, FWIW.
Cheers,
Hal
#5
03-16-2006, 06:24 PM
Re: escape drag
Hey Hal, Ray, Rich, Philip, Randy, Bill and all.
Yes, I'm still around and posting. Xcel and friends are at a new site, CleanMPG.com that I just joined. The site is still working out the bugs but has some real FE interest that I share. We are meeting in Sebring and xcel and I are carpooling from Orlando in my FEH to Sebring. I'm sure we both will have a real shootout on FE to compare notes with. This should be a kodak moment that Bill Ford and his Engineers would love to document for the FEH. Thinking of turning on the Max A/C while Wayne's driving to even things out for me. Just kidding, but stay tuned.
GaryG
Yes, I'm still around and posting. Xcel and friends are at a new site, CleanMPG.com that I just joined. The site is still working out the bugs but has some real FE interest that I share. We are meeting in Sebring and xcel and I are carpooling from Orlando in my FEH to Sebring. I'm sure we both will have a real shootout on FE to compare notes with. This should be a kodak moment that Bill Ford and his Engineers would love to document for the FEH. Thinking of turning on the Max A/C while Wayne's driving to even things out for me. Just kidding, but stay tuned.
GaryG
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