| Using a duty cycle meter to measure wind resistance [message #782017] |
Sun, 23 July 2006 05:39 |
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I know a guy who wanted to determine the optimal speed for
his car, to avoid wasting gas due to wind resistance from
going unnecessarily fast.
He attached a duty cycle meter to one injector, and then set
his car to cruise control at various speeds (presumably
on a flat road and no wind), and noted the duty cycle for
various speeds.
His findings were (for his car obviously) that the cycle was
1% up till about 80km/h, and 13% at 100km/h, so now he
drives at 80 when he can in order to save gas.
Comments on the reliability of this method?
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| Re: Using a duty cycle meter to measure wind resistance [message #782026 ] |
Sun, 23 July 2006 14:12 |
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Old Wolf wrote:
> I know a guy who wanted to determine the optimal speed for
> his car, to avoid wasting gas due to wind resistance from
> going unnecessarily fast.
>
> He attached a duty cycle meter to one injector, and then set
> his car to cruise control at various speeds (presumably
> on a flat road and no wind), and noted the duty cycle for
> various speeds.
>
> His findings were (for his car obviously) that the cycle was
> 1% up till about 80km/h, and 13% at 100km/h, so now he
> drives at 80 when he can in order to save gas.
>
> Comments on the reliability of this method?
>
only valid if the car is in the same gear at both speeds. I was
originally going to say that he needed to factor in RPM and then road
speed, but then before I even started typing I realized that those two
would factor each other out and then you would be left with basically a
scaled value for fuel used per engine rev, which would be proportional
to distance traveled, assuming the car is in the same gear. Therefore
your friend's idea is theoretically very elegant, although I don't know
how accurate it is possible to actually make measurements like this in
real life and get any useful info. from them.
I'm pleasantly reassured to see someone trying something this ingenious,
however.
nate
--
replace "fly" with "com" to reply.
http://home.comcast.net/~njnagel
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| Re: Using a duty cycle meter to measure wind resistance [message #782027 ] |
Sun, 23 July 2006 14:12 |
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Old Wolf wrote:
> I know a guy who wanted to determine the optimal speed for
> his car, to avoid wasting gas due to wind resistance from
> going unnecessarily fast.
>
> He attached a duty cycle meter to one injector, and then set
> his car to cruise control at various speeds (presumably
> on a flat road and no wind), and noted the duty cycle for
> various speeds.
>
> His findings were (for his car obviously) that the cycle was
> 1% up till about 80km/h, and 13% at 100km/h, so now he
> drives at 80 when he can in order to save gas.
>
> Comments on the reliability of this method?
>
BTW an old dwell meter is basically a duty cycle meter with a scale in
degrees instead of percent, but you probably knew that.
nate
--
replace "fly" with "com" to reply.
http://home.comcast.net/~njnagel
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| Re: Using a duty cycle meter to measure wind resistance [message #782028 ] |
Sun, 23 July 2006 14:47 |
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Old Wolf wrote:
> I know a guy who wanted to determine the optimal speed for
> his car, to avoid wasting gas due to wind resistance from
> going unnecessarily fast.
>
> He attached a duty cycle meter to one injector, and then set
> his car to cruise control at various speeds (presumably
> on a flat road and no wind), and noted the duty cycle for
> various speeds.
>
> His findings were (for his car obviously) that the cycle was
> 1% up till about 80km/h, and 13% at 100km/h, so now he
> drives at 80 when he can in order to save gas.
>
> Comments on the reliability of this method?
>
There is another way, but it requires calculus. One can find a level
road and run coasting tests. One must time the coasting- the time it
takes to reach various speeds. One then plots the results on semi-log
paper, speed vs time. The slope of the curve relates to the retarding
forces. The slope at slow speeds is representative of rolling friction.
The slope is higher at high (highway) speeds, as it is the sum of
rolling and air resistance. One can extrapolate the two slopes, and
where the two extrapolated slopes intersect is a break-point between air
resistance and rolling resistance.
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| Re: Using a duty cycle meter to measure wind resistance [message #782031 ] |
Sun, 23 July 2006 16:08 |
|
Old Wolf wrote:
> I know a guy who wanted to determine the optimal speed for
> his car, to avoid wasting gas due to wind resistance from
> going unnecessarily fast.
>
> He attached a duty cycle meter to one injector, and then set
> his car to cruise control at various speeds (presumably
> on a flat road and no wind), and noted the duty cycle for
> various speeds.
>
> His findings were (for his car obviously) that the cycle was
> 1% up till about 80km/h, and 13% at 100km/h, so now he
> drives at 80 when he can in order to save gas.
>
> Comments on the reliability of this method?
Sounds like it is good to me but I am just a 'shade tree'.
Looks like he is trying to re-invent the wheel though as there are
gauges that measure instantaneous fuel use/mile on the market and some
are standard with some trim options.
Harry K
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| Re: Using a duty cycle meter to measure wind resistance [message #782032 ] |
Sun, 23 July 2006 16:36 |
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On 22 Jul 2006 20:39:09 -0700, "Old Wolf" <oldwolf [at] inspire.net.nz>
wrote:
>I know a guy who wanted to determine the optimal speed for
>his car, to avoid wasting gas due to wind resistance from
>going unnecessarily fast.
>
>He attached a duty cycle meter to one injector, and then set
>his car to cruise control at various speeds (presumably
>on a flat road and no wind), and noted the duty cycle for
>various speeds.
>
>His findings were (for his car obviously) that the cycle was
>1% up till about 80km/h, and 13% at 100km/h, so now he
>drives at 80 when he can in order to save gas.
>
>Comments on the reliability of this method?
It doesn't seem right...
1% at all speeds up to 80km/h?
Wouldn't that make the air/fuel ration a little off at most RPMs?
IOW, it doesn't seem as his measuring system is anywhere near
accurate.
--
Bill Funk
replace "g" with "a"
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| Re: Using a duty cycle meter to measure wind resistance [message #782033 ] |
Sun, 23 July 2006 16:38 |
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"Bill Funk" <BigBill [at] there.com> wrote in message
news:1827c2l982jtnnkngvuvebmqe3cn6rm0pd [at] 4ax.com...
> On 22 Jul 2006 20:39:09 -0700, "Old Wolf" <oldwolf [at] inspire.net.nz>
> wrote:
>
>>I know a guy who wanted to determine the optimal speed for
>>his car, to avoid wasting gas due to wind resistance from
>>going unnecessarily fast.
>>
>>He attached a duty cycle meter to one injector, and then set
>>his car to cruise control at various speeds (presumably
>>on a flat road and no wind), and noted the duty cycle for
>>various speeds.
>>
>>His findings were (for his car obviously) that the cycle was
>>1% up till about 80km/h, and 13% at 100km/h, so now he
>>drives at 80 when he can in order to save gas.
>>
>>Comments on the reliability of this method?
>
> It doesn't seem right...
> 1% at all speeds up to 80km/h?
> Wouldn't that make the air/fuel ration a little off at most RPMs?
>
> IOW, it doesn't seem as his measuring system is anywhere near
> accurate.
I surmise he means 10% not 1%.
What's an air/fuel 'ration' anyway ? Is it something they had during the
war?
--
Dave Baker
www.pumaracing.co.uk
Usenet - a collection of people who only open their mouth to change feet.
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| Re: Using a duty cycle meter to measure wind resistance [message #782036 ] |
Sun, 23 July 2006 18:29 |
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Post removed (X-No-Archive: yes)
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| Re: Using a duty cycle meter to measure wind resistance [message #782041 ] |
Sun, 23 July 2006 20:08 |
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Old Wolf wrote:
> I know a guy who wanted to determine the optimal speed for
> his car, to avoid wasting gas due to wind resistance from
> going unnecessarily fast.
>
> He attached a duty cycle meter to one injector, and then set
> his car to cruise control at various speeds (presumably
> on a flat road and no wind), and noted the duty cycle for
> various speeds.
>
> His findings were (for his car obviously) that the cycle was
> 1% up till about 80km/h, and 13% at 100km/h, so now he
> drives at 80 when he can in order to save gas.
>
> Comments on the reliability of this method?
A lot of work when easier choices are available. Most cars made in the
past 10 years have an instantaneous and averaging mpg meter which will
be more accurate and certainly less work. And there are some
aftermarket displays that plug into the obd port.
And most of us know that if we drive our car at around 50mph to 55 mph
(1800 rpm) that we will use less gas than at 80mph.
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| Re: Using a duty cycle meter to measure wind resistance [message #782043 ] |
Sun, 23 July 2006 20:21 |
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"Dave Baker" <DaveBaker [at] nowhere.com> said in rec.autos.driving:
>What's an air/fuel 'ration' anyway ? Is it something they had during the
>war?
Whoops!
I hate it when that happens (all too often!).
--
Bill Funk
replace "g" with "a"
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| Re: Using a duty cycle meter to measure wind resistance [message #783062 ] |
Sun, 23 July 2006 14:12 |
|
Old Wolf wrote:
> I know a guy who wanted to determine the optimal speed for
> his car, to avoid wasting gas due to wind resistance from
> going unnecessarily fast.
>
> He attached a duty cycle meter to one injector, and then set
> his car to cruise control at various speeds (presumably
> on a flat road and no wind), and noted the duty cycle for
> various speeds.
>
> His findings were (for his car obviously) that the cycle was
> 1% up till about 80km/h, and 13% at 100km/h, so now he
> drives at 80 when he can in order to save gas.
>
> Comments on the reliability of this method?
>
only valid if the car is in the same gear at both speeds. I was
originally going to say that he needed to factor in RPM and then road
speed, but then before I even started typing I realized that those two
would factor each other out and then you would be left with basically a
scaled value for fuel used per engine rev, which would be proportional
to distance traveled, assuming the car is in the same gear. Therefore
your friend's idea is theoretically very elegant, although I don't know
how accurate it is possible to actually make measurements like this in
real life and get any useful info. from them.
I'm pleasantly reassured to see someone trying something this ingenious,
however.
nate
--
replace "fly" with "com" to reply.
http://home.comcast.net/~njnagel
|
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| Re: Using a duty cycle meter to measure wind resistance [message #783063 ] |
Sun, 23 July 2006 14:12 |
|
Old Wolf wrote:
> I know a guy who wanted to determine the optimal speed for
> his car, to avoid wasting gas due to wind resistance from
> going unnecessarily fast.
>
> He attached a duty cycle meter to one injector, and then set
> his car to cruise control at various speeds (presumably
> on a flat road and no wind), and noted the duty cycle for
> various speeds.
>
> His findings were (for his car obviously) that the cycle was
> 1% up till about 80km/h, and 13% at 100km/h, so now he
> drives at 80 when he can in order to save gas.
>
> Comments on the reliability of this method?
>
BTW an old dwell meter is basically a duty cycle meter with a scale in
degrees instead of percent, but you probably knew that.
nate
--
replace "fly" with "com" to reply.
http://home.comcast.net/~njnagel
|
|
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| Re: Using a duty cycle meter to measure wind resistance [message #783066 ] |
Sun, 23 July 2006 14:47 |
|
Old Wolf wrote:
> I know a guy who wanted to determine the optimal speed for
> his car, to avoid wasting gas due to wind resistance from
> going unnecessarily fast.
>
> He attached a duty cycle meter to one injector, and then set
> his car to cruise control at various speeds (presumably
> on a flat road and no wind), and noted the duty cycle for
> various speeds.
>
> His findings were (for his car obviously) that the cycle was
> 1% up till about 80km/h, and 13% at 100km/h, so now he
> drives at 80 when he can in order to save gas.
>
> Comments on the reliability of this method?
>
There is another way, but it requires calculus. One can find a level
road and run coasting tests. One must time the coasting- the time it
takes to reach various speeds. One then plots the results on semi-log
paper, speed vs time. The slope of the curve relates to the retarding
forces. The slope at slow speeds is representative of rolling friction.
The slope is higher at high (highway) speeds, as it is the sum of
rolling and air resistance. One can extrapolate the two slopes, and
where the two extrapolated slopes intersect is a break-point between air
resistance and rolling resistance.
|
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| Re: Using a duty cycle meter to measure wind resistance [message #783076 ] |
Sun, 23 July 2006 16:08 |
|
Old Wolf wrote:
> I know a guy who wanted to determine the optimal speed for
> his car, to avoid wasting gas due to wind resistance from
> going unnecessarily fast.
>
> He attached a duty cycle meter to one injector, and then set
> his car to cruise control at various speeds (presumably
> on a flat road and no wind), and noted the duty cycle for
> various speeds.
>
> His findings were (for his car obviously) that the cycle was
> 1% up till about 80km/h, and 13% at 100km/h, so now he
> drives at 80 when he can in order to save gas.
>
> Comments on the reliability of this method?
Sounds like it is good to me but I am just a 'shade tree'.
Looks like he is trying to re-invent the wheel though as there are
gauges that measure instantaneous fuel use/mile on the market and some
are standard with some trim options.
Harry K
|
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| Re: Using a duty cycle meter to measure wind resistance [message #783081 ] |
Sun, 23 July 2006 16:36 |
|
On 22 Jul 2006 20:39:09 -0700, "Old Wolf" <oldwolf [at] inspire.net.nz>
wrote:
>I know a guy who wanted to determine the optimal speed for
>his car, to avoid wasting gas due to wind resistance from
>going unnecessarily fast.
>
>He attached a duty cycle meter to one injector, and then set
>his car to cruise control at various speeds (presumably
>on a flat road and no wind), and noted the duty cycle for
>various speeds.
>
>His findings were (for his car obviously) that the cycle was
>1% up till about 80km/h, and 13% at 100km/h, so now he
>drives at 80 when he can in order to save gas.
>
>Comments on the reliability of this method?
It doesn't seem right...
1% at all speeds up to 80km/h?
Wouldn't that make the air/fuel ration a little off at most RPMs?
IOW, it doesn't seem as his measuring system is anywhere near
accurate.
--
Bill Funk
replace "g" with "a"
|
|
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| Re: Using a duty cycle meter to measure wind resistance [message #783082 ] |
Sun, 23 July 2006 16:38 |
|
"Bill Funk" <BigBill [at] there.com> wrote in message
news:1827c2l982jtnnkngvuvebmqe3cn6rm0pd [at] 4ax.com...
> On 22 Jul 2006 20:39:09 -0700, "Old Wolf" <oldwolf [at] inspire.net.nz>
> wrote:
>
>>I know a guy who wanted to determine the optimal speed for
>>his car, to avoid wasting gas due to wind resistance from
>>going unnecessarily fast.
>>
>>He attached a duty cycle meter to one injector, and then set
>>his car to cruise control at various speeds (presumably
>>on a flat road and no wind), and noted the duty cycle for
>>various speeds.
>>
>>His findings were (for his car obviously) that the cycle was
>>1% up till about 80km/h, and 13% at 100km/h, so now he
>>drives at 80 when he can in order to save gas.
>>
>>Comments on the reliability of this method?
>
> It doesn't seem right...
> 1% at all speeds up to 80km/h?
> Wouldn't that make the air/fuel ration a little off at most RPMs?
>
> IOW, it doesn't seem as his measuring system is anywhere near
> accurate.
I surmise he means 10% not 1%.
What's an air/fuel 'ration' anyway ? Is it something they had during the
war?
--
Dave Baker
www.pumaracing.co.uk
Usenet - a collection of people who only open their mouth to change feet.
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| Re: Using a duty cycle meter to measure wind resistance [message #783089 ] |
Sun, 23 July 2006 18:29 |
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Post removed (X-No-Archive: yes)
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| Re: Using a duty cycle meter to measure wind resistance [message #783093 ] |
Sun, 23 July 2006 20:08 |
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Old Wolf wrote:
> I know a guy who wanted to determine the optimal speed for
> his car, to avoid wasting gas due to wind resistance from
> going unnecessarily fast.
>
> He attached a duty cycle meter to one injector, and then set
> his car to cruise control at various speeds (presumably
> on a flat road and no wind), and noted the duty cycle for
> various speeds.
>
> His findings were (for his car obviously) that the cycle was
> 1% up till about 80km/h, and 13% at 100km/h, so now he
> drives at 80 when he can in order to save gas.
>
> Comments on the reliability of this method?
A lot of work when easier choices are available. Most cars made in the
past 10 years have an instantaneous and averaging mpg meter which will
be more accurate and certainly less work. And there are some
aftermarket displays that plug into the obd port.
And most of us know that if we drive our car at around 50mph to 55 mph
(1800 rpm) that we will use less gas than at 80mph.
|
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| Re: Using a duty cycle meter to measure wind resistance [message #783095 ] |
Sun, 23 July 2006 20:21 |
|
"Dave Baker" <DaveBaker [at] nowhere.com> said in rec.autos.driving:
>What's an air/fuel 'ration' anyway ? Is it something they had during the
>war?
Whoops!
I hate it when that happens (all too often!).
--
Bill Funk
replace "g" with "a"
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