Throttle-Stop Test, a granular look

[AeroMcAeroFace]

Originally Posted by aerohead

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]

Originally Posted by freebeard

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]

Originally Posted by AeroMcAeroFace

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]

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]

Originally Posted by freebeard

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]

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]

Originally Posted by aerohead

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?

Originally Posted by MeteorGray

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]

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]

Originally Posted by AeroMcAeroFace

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.
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* 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]

Originally Posted by aerohead

* 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.