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-   -   Throttle-Stop Test, a granular look (https://ecomodder.com/forum/showthread.php/throttle-stop-test-granular-look-39042.html)

aerohead 01-20-2021 12:02 PM

Throttle-Stop Test, a granular look
 
Some points to ponder:
* Axle lube viscosity can vary 95% during 'warmup'
* Axle mechanical efficiency can vary 14% during 'warmup'
* Axle-related power absorption can vary by 0.8- kW during 'warmup'
* Low-temperature testing in the past has revealed 8-mpg @ 4-miles range
.................................................. ..................... 11-mpg @ 15-miles range
.................................................. ..................... 13-mpg @ 30-miles range
* An 18-mph headwind has shown a 16.4% mpg penalty @ 50-mph
* An 18-mph crosswind has shown a 2.15% mpg penalty @ 50-mph
* A 10-degree-yaw crosswind increases drag by Cd 0.055
* A 12-degree-yaw crosswind lowered the Cd of the Arrivett Brother's NHRA Top Fuel Streamliner dragster, from 0.20, to 0.18
* An 18-mph tailwind has shown a 19.42% mpg improvement @ 50-mph
* An 18-mph quartering wind is an unknown quantity
* Pumping losses are higher @ light load
* Pumping losses vary as the square of engine rpm
* 45- minutes @ 55-mph warmup has demonstrated data 'repeatability' for the USEPA
* 'Cold' tires, @ ambient temperature demonstrate 40% higher rolling-resistance than when fully-warmed
* Electronic engine management relies upon ALL 'normal', real-time sensor signal participation in order for the ECU to perform minute, asynchronous EFI and ESA optimization commands, otherwise, A/F ratio and Spark advance will experience excursions, even precipitating loss of 'closed-loop' function, allowing the engine BSFC map to fall to a less efficient island of operation, sacrificing optimum performance.
--------------------------------------------------------------------------------------
* Any 'assumption' of steady-state performance is extremely dubious.
* Without baseline testing, which happens to capture performance spectra at any 'new' velocity experienced during the course of testing after aerodynamic modifications are accomplished, any success in parsing out the actual contribution of a specific aerodynamic modification could be lost in the signal-to-noise of the uncontrolled engine, and performance variability of an 'un-warmed' test vehicle; easily exceeding any 'signal' from the aerodynamics.
Simply allowing engine speed to increase from 2,400-rpm, to 2,450-rpm introduces a 4.2% increase in pumping losses.

AeroMcAeroFace 01-21-2021 06:18 AM

Julian isn't here to defend this, throttle stop testing is like coast down testing, susceptible to environmental effects. Doing multiple consecutive A-B runs a few minutes apart will mean that the wind is likely to be the same for all tests or at least averaged.

So from your data, we can say that multiple consecutive A-B runs on a warmed up car has no issues other than pumping losses.

Pumping losses depend on the engine, a six cylinder has virtually no pumping losses due to constant crankcase volume. But even if the pumping loss increase is there, it is a very small, virtually insignificant amount increase of the total drag and even then you need to have a reduction in aero/rolling drag to get the engine speed to increase. So it may not be accurate to 1% but I think it is more reliable than coast down tests.

aerohead 01-22-2021 12:28 PM

So from your
 
Quote:

Originally Posted by AeroMcAeroFace (Post 641218)
Julian isn't here to defend this, throttle stop testing is like coast down testing, susceptible to environmental effects. Doing multiple consecutive A-B runs a few minutes apart will mean that the wind is likely to be the same for all tests or at least averaged.

So from your data, we can say that multiple consecutive A-B runs on a warmed up car has no issues other than pumping losses.

Pumping losses depend on the engine, a six cylinder has virtually no pumping losses due to constant crankcase volume. But even if the pumping loss increase is there, it is a very small, virtually insignificant amount increase of the total drag and even then you need to have a reduction in aero/rolling drag to get the engine speed to increase. So it may not be accurate to 1% but I think it is more reliable than coast down tests.

1) I've identified eleven ( 11 ) unknowns.
2) Pre-conditioning the test vehicle to achieve thermal equilibrium at any given ambient temperature will certainly whittle away at this list.
------------------------------------------------------------------------------------
Beyond the warmup, the following issues remain:
3) Asynchronous A/F ratio optimization signals are rendered impossible. The BSFC can drift.
4) Asynchrounous ignition timing optimization ( best torque spark advance ) signals are rendered impossible. BSFC can drift.
5) Asynchronous EFI frequency and duration optimization signals are rendered impossible, due to drifting Oxygen sensor voltage signals being over-ridden by a non-participating TPS prompt. The ECU may default to 'Open-Loop', power-enrichment without veto from the TPS.
6) Any presumption as to 'constant torque' is a presumption.
7) Powertrain mechanical efficiency is predicated upon ' transferred power' and is not a constant.
8) No provision for knowing vehicle performance at velocity-2, is available for comparison the the baseline velocity-1. They're all unknown quantities.
* Rolling resistance road-load power
* Engine accessory loads which vary arithmetically with velocity
* Pumping-losses are non-linear, having to do with hydrodynamic, tribological losses, which vary with lubrication viscosity, as the square of engine rpm, oil pump, and with water pump hydrodynamic drag, which also varies geometrically. If say, the Insight develops it's maximum Bhp @ 6,000 rpm, and we choose 2400-rpm as our test velocity, even a 50-rpm increase at velocity-2 will create a 4.2% rise in pumping losses alone.
* BSFC
------------------------------------------------------------------------------------
It can be a setup for false-positives, or false-negatives.
Any 'true' effect from an aerodynamic modification could be lost in the 'noise' of the unknowns.
And we know that, typically, a smaller load-load fraction leads to a higher BSFC, even when all engine management components are 'communicating.'
-------------------------------------------------------------------------------------
Hucho tried to inform us in his 2nd-Edition, and it is he would cited Sovran's SAE Paper 830304 for those interested enough to check it out.
Why the 'select panel of experts' went into the ditch is beyond me.

AeroMcAeroFace 01-22-2021 01:51 PM

But other than accessory losses, everything else is changing due to the increased engine speed.

I am not saying that a 5% increase in top speed means an exact 10% decrease in drag, there are too many variables at play to say absolutely. The error between measurements is perhaps 10%.


However you can say with absolute certainty that a fixed throttle position will give you a higher top speed if drag is reduced, there is no way you can argue against that.

At least a few mph difference, averaged over multiple readings, it can't all be down to the car suddenly becoming more fuel efficient or is that what you are saying?

aerohead 01-22-2021 02:17 PM

accessory and ................
 
Quote:

Originally Posted by AeroMcAeroFace (Post 641366)
But other than accessory losses, everything else is changing due to the increased engine speed.

I am not saying that a 5% increase in top speed means an exact 10% decrease in drag, there are too many variables at play to say absolutely.
however you can say with absolute certainty that a fixed throttle position will give you a higher top speed if drag is reduced, there is no way you can argue against that.

1) Technically, if the accessories are belt-driven, hysteresis losses in the rubber of the serpentine or cog-belt will increase losses arithmetically with rpm, like the tires with velocity.
2) For drag versus top-speed, Hucho reported a 30% delta- Cd -to-10% delta- velocity relationship as of December, 1986. There may exist more contemporary reporting on this. Don't know.
3) Yeah, lots of variables, which Julian spells out many in the video. I've collected materials since 1974, and I may have some obscure data easily missed in all these intervening decades.
4) You're absolutely correct about expectations for a higher top speed. I don't think it could be argued otherwise. Top-speed testing is a form of ' throttle-stop' testing. Spirit picked up 19-mph ( 31- km/h ) that we know of. And that was with a 920-lb weight penalty ( 418 Kg ).

freebeard 01-22-2021 02:32 PM

Quote:

Julian isn't here to defend this...
And who does he have to blame for that? Probably me for provoking him.

Do we know if it is temporary? Wasn't there someone who was banned for like a week?

AeroMcAeroFace 01-22-2021 03:29 PM

So we can agree that it is possible to ascertain drag reduction from throttle stop testing?

That is of course assuming the following:
Accessory load is the same (no-air con, no extra lights, heating, etc.)
Tests are done back to back multiple times on the same day to average out any wind changes.
The vehicle is appropriately warmed
The fuel is the same

Whether it is safe to block your throttle, or accurate enough to measure a 1% or 0.5% drag reductions is yet to be decided/ascertained, I will not argue for or against either of those.

aerohead 01-22-2021 03:32 PM

isn't here
 
Quote:

Originally Posted by freebeard (Post 641372)
And who does he have to blame for that? Probably me for provoking him.

Do we know if it is temporary? Wasn't there someone who was banned for like a week?

He usually comes in later in the day. With the time difference, sometimes he's posting at 3:00 A.M. Texas time. He's gotta sleep at some point.:p

aerohead 01-22-2021 04:01 PM

can agree
 
Quote:

Originally Posted by AeroMcAeroFace (Post 641376)
So we can agree that it is possible to ascertain drag reduction from throttle stop testing?

That is of course assuming the following:
Accessory load is the same (no-air con, no extra lights, heating, etc.)
Tests are done back to back multiple times on the same day to average out any wind changes.
The vehicle is appropriately warmed
The fuel is the same

Whether it is safe to block your throttle, or accurate enough to measure a 1% or 0.5% drag reductions is yet to be decided/ascertained, I will not argue for or against either of those.

1) I'm in total agreement that we can.
2) Accessory load will increase at the new, higher velocity, after the aero modification, and we have no baseline data for that.
3) Same for rolling resistance
4) Same for powertrain mechanical efficiency ( it's at a new rpm and lower load )
5) Same for BSFC as the engine is 'blind' to some former signal input
6) From the EPA, we know that A-B-A testing doesn't cancel wind effects, as the vehicle demonstrates different reactions to, say, headwind / tailwind.
7) If we're in 'quartering' winds, there's no available data for that, one way, or another. A complete unknown.
8) Fuel Btu content won't vary.
9) Fuel density ( coefficient of thermal expansion ) WILL vary with temperature, however, probably not, in the timeframes we're working with.
10) As to accuracy, one thing not mentioned, but of some assistance to us, would simply record the fuel economy for a spectra of higher velocities which happen to include the new, higher, velocity-2 with no modifications, to compare to the modified car at velocity-2. Some things could be reverse-engineered from that kind of data.
11) The more 'book-keeping' we can perform, the higher the resolution when attempting to isolate the aerodynamic effects.
12) Qualitatively, the throttle-stop test will demonstrate the trend, without countless hours and liters ( gallons ) of fuel going up in smoke. It's worth the fuss.

MeteorGray 01-24-2021 07:12 PM

Are these factors in conflict?

Post #9:

7) If we're in 'quartering' winds, there's no available data for that, one way, or another. A complete unknown.

vs Post #1:

* An 18-mph crosswind has shown a 2.15% mpg penalty @ 50-mph
* A 10-degree-yaw crosswind increases drag by Cd 0.055
* A 12-degree-yaw crosswind lowered the Cd of the Arrivett Brother's NHRA Top Fuel
Streamliner dragster, from 0.20, to 0.18

Or does "quartering wind" relate only to certain degree yaw angles implied by the term?

It seems that the direction of an angling wind will make a difference, just as it makes a difference whether a wind is a headwind or a tailwind. And that an angling headwind will be detrimental, but to a lesser degree; and that an angling tailwind will be beneficial, but to a lesser degree.

AeroMcAeroFace 01-25-2021 09:03 AM

Quote:

Originally Posted by aerohead (Post 641379)
1) I'm in total agreement that we can.
2) Accessory load will increase at the new, higher velocity, after the aero modification, and we have no baseline data for that.
3) Same for rolling resistance
4) Same for powertrain mechanical efficiency ( it's at a new rpm and lower load )
5) Same for BSFC as the engine is 'blind' to some former signal input
6) From the EPA, we know that A-B-A testing doesn't cancel wind effects, as the vehicle demonstrates different reactions to, say, headwind / tailwind.
7) If we're in 'quartering' winds, there's no available data for that, one way, or another. A complete unknown.
8) Fuel Btu content won't vary.
9) Fuel density ( coefficient of thermal expansion ) WILL vary with temperature, however, probably not, in the timeframes we're working with.
10) As to accuracy, one thing not mentioned, but of some assistance to us, would simply record the fuel economy for a spectra of higher velocities which happen to include the new, higher, velocity-2 with no modifications, to compare to the modified car at velocity-2. Some things could be reverse-engineered from that kind of data.
11) The more 'book-keeping' we can perform, the higher the resolution when attempting to isolate the aerodynamic effects.
12) Qualitatively, the throttle-stop test will demonstrate the trend, without countless hours and liters ( gallons ) of fuel going up in smoke. It's worth the fuss.

2-3) I think they will be a linear thing and can be all integrated into "rolling resistance"

4) Mechanical resistance is maybe 5% of the total drag, even if it changes by an extreme 10% it is only 5.5% of total drag and so while not irrelevant it is not a huge difference.

5) BSFC if it does change will be tiny and I believe will be negligible over the few percent increase/decrease in engine speed.

6) Wind, well nothing can change that, but on a calm day I see no problem with multiple bidirectional averaged runs a-b-a-b-a-b as a minimum. So, just don't do it on a particularly windy day, unless you are specifically testing crosswind drag.

AeroMcAeroFace 01-25-2021 09:26 AM

Quote:

Originally Posted by freebeard (Post 641372)
And who does he have to blame for that? Probably me for provoking him.

Do we know if it is temporary? Wasn't there someone who was banned for like a week?

That is if he comes back, he may decide not to come back, which would be a shame, he was the most prolific modder/tester on here. Mods and big results are what generates interest rather than discussions on how to remove badges on the side of your car to reduce drag, or whether to remove the stickers from the apples you buy to reduce weight.

aerohead 01-27-2021 11:17 AM

2-6
 
Quote:

Originally Posted by AeroMcAeroFace (Post 641520)
2-3) I think they will be a linear thing and can be all integrated into "rolling resistance"

4) Mechanical resistance is maybe 5% of the total drag, even if it changes by an extreme 10% it is only 5.5% of total drag and so while not irrelevant it is not a huge difference.

5) BSFC if it does change will be tiny and I believe will be negligible over the few percent increase/decrease in engine speed.

6) Wind, well nothing can change that, but on a calm day I see no problem with multiple bidirectional averaged runs a-b-a-b-a-b as a minimum. So, just don't do it on a particularly windy day, unless you are specifically testing crosswind drag.

2) engine accessory power absorption would be linear if belt driven
3) rolling resistance would be linear all the way to standing wave, beyond the performance envelope of the vehicle
4) I have 8% powertrain loss for an overdrive, manual transaxle powertrain, like the gen-I Insight. It's not as significant as BSFC, although, rates #2 in Sovran's research.
5) A BSFC map for the specific test vehicle would be welcome. This is the #1 bone of contention in Sovran's SAE Paper. It must be known in order to sort out any actual benefit of an aerodynamic modification, lacking gear-matching
6) Wind is really problematic. Datalogging would be imperative if one were to undertake testing during wind.

freebeard 01-27-2021 02:53 PM

Quote:

Originally Posted by AeroMcAeroFace
That is if he comes back, he may decide not to come back, which would be a shame...

That would be as I expected, although I don't think I made a prediction so as not to prejudge the situation.

JulianEdgar tried to siphon off views to LinkedIn and Youtube. So far as I know aerohead doesn't have a presence elsewhere. [amirite?]

aerohead 01-27-2021 04:07 PM

amirite
 
Quote:

Originally Posted by freebeard (Post 641691)
That would be as I expected, although I don't think I made a prediction so as not to prejudge the situation.

JulianEdgar tried to siphon off views to LinkedIn and Youtube. So far as I know aerohead doesn't have a presence elsewhere. [amirite?]

EcoModder.com has been a full-time affair, two days a week since 2007.
We do have the two You-Tube videos from DARKO.
Other than that, I've provided some charts to AeroStealth for his You-Tubes at his electric vehicle Facebook site. He usually provides links to those.

MeteorGray 01-27-2021 04:54 PM

Julian has added an enormous amount of knowledge to this site in a short period of time, and he has done so in clear, concise and interesting ways.

It's very rare to find someone who does so much original research and hands-on experimentation and is so willing to share his knowledge. His results are not guesswork, but instead involve empirical processes that are so important in advancing real knowledge. And he encourages others to do such research and testing, even if just to challenge his results if they think he's gone astray.

Julian actually does things out in the real world. He shows how he does them. He shares his findings. He encourages others to do the same. A rare man indeed.

And if he sells a few books while doing it, good for him. The books' purchasers get the in-depth knowledge that only detailed books can provide, and those who don't buy the books still get a lot of free information given right here on this site and in the you-tube videos he has made.

Now, could he use more tact in confronting those proffering what he sees as continuing and uncorrected misinformation? Sure he could, and often should. It would make him more effective.

But tactfulness, although usually desirable, sometimes doesn't get the job done, especially if incorrect information is treated with the same gravitas as correct information and keeps on being repeated and often otherwise unchallenged.

It brings to mind several TV documentaries I've seen recently about airplane crashes in which the pilot is doing something wrong that ultimately destroys the plane and its passengers. The copilot, knowing that the pilot is making a mistake, tries to tell the pilot using a polite, tactful approach that fails to get the pilot to recognize the problem. So everybody goes down in the crash.

The copilots were nice, but ineffective.

Had their passengers known what was going on in the cockpit, I doubt they would have applauded the tactfulness being employed up there.

AeroMcAeroFace 01-28-2021 04:53 AM

Quote:

Originally Posted by aerohead (Post 641690)
2) engine accessory power absorption would be linear if belt driven
3) rolling resistance would be linear all the way to standing wave, beyond the performance envelope of the vehicle
4) I have 8% powertrain loss for an overdrive, manual transaxle powertrain, like the gen-I Insight. It's not as significant as BSFC, although, rates #2 in Sovran's research.
5) A BSFC map for the specific test vehicle would be welcome. This is the #1 bone of contention in Sovran's SAE Paper. It must be known in order to sort out any actual benefit of an aerodynamic modification, lacking gear-matching
6) Wind is really problematic. Datalogging would be imperative if one were to undertake testing during wind.

3) & 4) can't the powertrain loss be attributed under "rolling resistance" and be approximated to linear over the small amount of increase in speed though?

Quote:

Originally Posted by MeteorGray (Post 641705)
And if he sells a few books while doing it, good for him. The books' purchasers get the in-depth knowledge that only detailed books can provide, and those who don't buy the books still get a lot of free information given right here on this site and in the you-tube videos he has made.

Why are people complaining that he is writing and selling books? BMW use air curtains and no-one on here complained that it is unfair that they are making money off innovation. I think the problem is that some people on here, and I don't believe aerohead is one of them, just seem to despise Julian for pointing out flaws in their beliefs, whether that is the template misuse, the 12-degree rule of thumb or any other rule of thumb.

MeteorGray 01-28-2021 09:56 AM

In defense of Aerohead (and to those who might notice and criticize it, I, too, reflectively use traditional capitalization rules despite the Internet norms; the ghosts of my English teachers haunt me yet), I will say this: the man is unusually dedicated to the advancement of aerodynamics and has devoted much of his free time to it over a period of many years.

And I'll further say that Aerohead, generally speaking, has taken the body blows criticizing some of his beliefs in a remarkably resilient and gentlemanly manner, although it has resulted in some exceptions in which he has made some less-than-tactful comments himself, sometimes at the expense of outside experts who are not even in the discussion here. I'll leave it at that.

I hope both posters continue here on E(e)comodder. I think Aerohead provides a lot of valuable historical data, even though he may fault in some of his interpretations and applications of same. And I think that Julian provides a wealth of new, empirically derived data that are so valuable to those who are working to improve the aerodynamic properties of today's variety of cars.

Now, off of the soapbox and on to the day's work for me.

aerohead 01-29-2021 10:35 AM

powertrain
 
Quote:

Originally Posted by AeroMcAeroFace (Post 641741)
3) & 4) can't the powertrain loss be attributed under "rolling resistance" and be approximated to linear over the small amount of increase in speed though?



Why are people complaining that he is writing and selling books? BMW use air curtains and no-one on here complained that it is unfair that they are making money off innovation. I think the problem is that some people on here, and I don't believe aerohead is one of them, just seem to despise Julian for pointing out flaws in their beliefs, whether that is the template misuse, the 12-degree rule of thumb or any other rule of thumb.

* Sovran distinguished the unknown powertrain mechanical efficiency, only second to unknown BSFC as the two, top-tier unknowns in the eleven unknowns identified in the throttle-stop road test phenomena.
* At equilibrium, the engine is just balancing road load power absorption, plus the drivetrain losses.
* Mechanical efficiency of the driveline components are a function of transmitted power.
* As Road Load varies, so does this efficiency.
* It's an unknown quantity, the crux of the powertrain issue.
------------------------------------------------------------------------------------
* Rolling resistance is a simple linear function of load and velocity. It's a 'known quantity' once its coefficient is derived. If we had enough data for the test vehicle to reverse-engineer the coefficient of power absorption for the tires, we could just plug that in, with the 'new' velocity, compute the rolling drag and power, and have the value to work with. In this way, it could be isolated from the mix. Better book-keeping.

AeroMcAeroFace 01-30-2021 06:23 AM

Quote:

Originally Posted by aerohead (Post 641791)
* Sovran distinguished the unknown powertrain mechanical efficiency, only second to unknown BSFC as the two, top-tier unknowns in the eleven unknowns identified in the throttle-stop road test phenomena.
* At equilibrium, the engine is just balancing road load power absorption, plus the drivetrain losses.
* Mechanical efficiency of the driveline components are a function of transmitted power.
* As Road Load varies, so does this efficiency.
* It's an unknown quantity, the crux of the powertrain issue.
------------------------------------------------------------------------------------
* Rolling resistance is a simple linear function of load and velocity. It's a 'known quantity' once its coefficient is derived. If we had enough data for the test vehicle to reverse-engineer the coefficient of power absorption for the tires, we could just plug that in, with the 'new' velocity, compute the rolling drag and power, and have the value to work with. In this way, it could be isolated from the mix. Better book-keeping.

So "mechanical efficiency of the driveline components are a function of transmitted power" a linear one? It can certainly be approximated to linear over the 5% speed increase, so it can be incorporated into "rolling resistance"

How much does BSFC actually vary by? It is a tiny amount that is negligible over the small speed increase, and so can be ignored altogether.

aerohead 02-03-2021 10:43 AM

mechanical eff. and BSFC
 
Quote:

Originally Posted by AeroMcAeroFace (Post 641838)
So "mechanical efficiency of the driveline components are a function of transmitted power" a linear one? It can certainly be approximated to linear over the 5% speed increase, so it can be incorporated into "rolling resistance"

How much does BSFC actually vary by? It is a tiny amount that is negligible over the small speed increase, and so can be ignored altogether.

1) Under the circumstances of constant-throttle, and a variable load, according to Sovran, mechanical efficiency would be non-linear. SAE may have papers dedicated to this specific topic.
2) Personally, I'm reluctant to combine variables, choosing the 'long-hand' approach, just for book-keeping purposes. There may be a particular vehicle road test which incompasses all data, from which one could run the numbers each way in order to detect whether or not something 'funny' was introduced into the quanta.
3) At Bonneville, I experienced over a 10% change in speed, over redline rpm. Technically, engine efficiency would be falling. Without a dyno, it's problematic assigning numerical values of a certain precision. We would have no 'a priori' knowledge of a velocity increase with a given modification.
4) The BSFC question is the most important of all, and again, it's an unknown quantity. An engine map from the manufacturer would be of some help. Perhaps.
5) We know for a fact that, any conclusions about a drag reduction from any particular modification could be off by 40% without gear-matching. That's the sticking point for the whole exercise. Any presumptions about quanta cannot have any degree of confidence above 60%.
-------------------------------------------------------------------------------------
Any thought exercise I come up with that might help requires a test track, away from public traffic.

AeroMcAeroFace 02-04-2021 07:23 AM

Quote:

Originally Posted by aerohead (Post 642018)
1) Under the circumstances of constant-throttle, and a variable load, according to Sovran, mechanical efficiency would be non-linear. SAE may have papers dedicated to this specific topic.
2) Personally, I'm reluctant to combine variables, choosing the 'long-hand' approach, just for book-keeping purposes. There may be a particular vehicle road test which incompasses all data, from which one could run the numbers each way in order to detect whether or not something 'funny' was introduced into the quanta.
3) At Bonneville, I experienced over a 10% change in speed, over redline rpm. Technically, engine efficiency would be falling. Without a dyno, it's problematic assigning numerical values of a certain precision. We would have no 'a priori' knowledge of a velocity increase with a given modification.
4) The BSFC question is the most important of all, and again, it's an unknown quantity. An engine map from the manufacturer would be of some help. Perhaps.
5) We know for a fact that, any conclusions about a drag reduction from any particular modification could be off by 40% without gear-matching. That's the sticking point for the whole exercise. Any presumptions about quanta cannot have any degree of confidence above 60%.
-------------------------------------------------------------------------------------
Any thought exercise I come up with that might help requires a test track, away from public traffic.

Are you saying that a 3% increase in speed will be 40% down to gearing? That is ridiculous.

Are you saying that a 3% increase in speed is down to BSFC suddenly jumping? Again that is ridiculous.

Gearing may be significant if the drag reduction is large, but it is typically not and so can be ignored.

AeroMcAeroFace 02-05-2021 11:09 AM

Quote:

Originally Posted by aerohead (Post 642082)
--------------------------------------------------------------------------------------
3) Typically, in mechanical engineering, it's common to assume a constant BSFC, with respect to predictions surrounding road load hypotheticals. As a mechanical engineer you would know that.
--------------------------------------------------------------------------------------

Glad we can agree on that now

aerohead 02-05-2021 11:16 AM

will be
 
Obviously, your post-doctoral education and 40-years of research in a world-class laboratory have found complete fault with the SAE.
I apologize for wasting your precious time.
I'm sure your students and faculty members will be make the proper correction, by dismantling the stacks from your technical library, and banning any communication with the global automotive community.
Please accept my heartfelt sorrow for inflicting such a intellectual insult to your magnificent command of the subject.
It is only in this moment, that I can properly discern the infinitude of your scientific mastery.

Cd 02-06-2021 12:34 PM

Will there be an effect on the test if I hesitate to fully press the throttle by a second or so after seeing my start point ? ( Starting the test at a landmark, such as a tree by the side of the road. )

AeroMcAeroFace 02-07-2021 07:26 AM

It depends where you take the measurements, if you are using time taken to cover the distance then maybe, but I think the way Julian recommended to do it was to keep your foot in the same place on the throttle and wait for the speed to settle to a stable value and then take the measurements using an accurate speedometer/GPS/Mobile phone app.

If you are using the time taken to cover a distance, you need to be at the top speed before you get to the tree so get your foot on the throttle well before you start the measurements. Hope that helps

aerohead 02-10-2021 10:55 AM

3)
 
Quote:

Originally Posted by AeroMcAeroFace (Post 642083)
Glad we can agree on that now

1) The issue is that we have an 'atypical' situation.
2) any assumption regarding a constant BSFC would necessarily be predicated upon the ECU sensing 'driver intent', which is impossible if the signal from the TPS has been disabled.
3) on the merits of 2) I'm not in agreement.
But let's all get our heads together and explore all options. The beauty of Julian's technique is it's simplicity and avoidance of the necessity of a 'large' sample, in order to arrive at useful quanta.
' Watch out where the huskies go, and don't you eat that yellow snow.' Zappa

aerohead 02-10-2021 11:03 AM

if I hesitate
 
I agree that, you want to already be at 'equilibrium' for the configuration you're testing for when you begin measurement.

Piotrsko 02-11-2021 10:33 AM

Why would the acceleration / deceleration data not be smooth-able or be able to be integrated into the overall bucket? @ the rocket site we had the same issue with thermocouples not measuring instantaneous, but the whiz kid engineers from Stanford used the data anyways since they found it was actually linear.


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