CAUTION: throttle-stop testing

[redpoint5]

Originally Posted by freebeard

This thread was a reaction by OP to the method introduced elsewhere. Mr. Edgar only started 4 threads (and Thanked twice) during his speed run through here. Titles not pertinent.

Yeah, and I was critical of this thread, because why take the effort to start a thread criticizing something without laying out what that criticism is? See, I provided the basis for the criticism to this thread. Now was that too hard?

Whenever anyone asks aerohead to clarify something, he avoids it by saying; "study..."

*Economics
*Physics
*Meteorology
*Organic chemistry
*Climatology
*Electronics
*Metallurgy
*Fluid Dynamics
*Boundary layer stagnation
*Alchemy

[freebeard]

In this case, OP has not contributed since 01-15-2021, 03:13 PM.

[Vman455]

Originally Posted by redpoint5

It never was explained why a change in speed and therefore a change in BSFC was not relevant to quantifying aerodynamic treatments at a given engine load (throttle position). Maybe the method gets close enough that the BSFC can be ignored?

It was explained several times: BSFC has nothing to do with throttle-stop testing since throttle-stop testing does not use fuel consumption as a measurement parameter.

Throttle-stop testing works on the principle that for a given throttle opening and over small changes in engine RPM, torque output is nearly constant. On a vehicle with fixed transmission gear ratios, constant torque = constant force at the wheels, so a change in drag force will show up as a change in speed, and the ratio of the squares of each speed will be equal to the ratio of each drag area. That's it. No BSFC. Has nothing to do with this type of test.

The caveats for throttle-stop testing follow, and also have nothing to do with BSFC:
-may not be accurate over large changes in speed (engine torque may not be constant in this case)
-may not work on vehicles with electronically-controlled throttles (actual throttle position and engine torque may vary in this case despite constant throttle pedal position)
-may not work on vehicles with constantly-variable transmission gear ratios (engine torque and wheel torque not necessarily the same ratio in this case)

As always, with any type of testing, you have to try it yourself with a known change in drag such as windows up/windows down to see if it works on your car.

[Cd]

Has anyone here tried this method ?
Anyone ?

[redpoint5]

Originally Posted by Vman455

It was explained several times: BSFC has nothing to do with throttle-stop testing since throttle-stop testing does not use fuel consumption as a measurement parameter.

No, it was not explained at all, ever. A change in BSFC at a given throttle position necessarily results in a difference in power output, and therefore speed. Just because fuel consumption is not being measured doesn't mean a change in BSFC is irrelevant.

Someone insisting something incorrect has still failed to answer the question.

Throttle-stop testing works on the principle that for a given throttle opening and over small changes in engine RPM, torque output is nearly constant.

Power is torque * RPM / 5252. A change in engine RPM at a given torque necessarily means the power output is changing.

On a vehicle with fixed transmission gear ratios, constant torque = constant force at the wheels, so a change in drag force will show up as a change in speed, and the ratio of the squares of each speed will be equal to the ratio of each drag area. That's it. No BSFC. Has nothing to do with this type of test.

Horsepower determines speed, not torque. Since a changing RPM affects how efficiently fuel is burned, and therefore power output at any particular torque, it must affect speed non-linearly.

[Vman455]

Originally Posted by Cd

Has anyone here tried this method ?
Anyone ?

You mean besides me? I think a couple other people have in the past, but overall no.

Originally Posted by redpoint5

No, it was not explained at all, ever. A change in BSFC at a given throttle position necessarily results in a difference in power output, and therefore speed. Just because fuel consumption is not being measured doesn't mean a change in BSFC is irrelevant.

Someone insisting something incorrect has still failed to answer the question.




Power is torque * RPM / 5252. A change in engine RPM at a given torque necessarily means the power output is changing.



Horsepower determines speed, not torque. Since a changing RPM affects how efficiently fuel is burned, and therefore power output at any particular torque, it must affect speed non-linearly.

Power changes with a change in drag when torque is held constant by a constant throttle opening because power = (force)(speed). The change in drag shows up as a change in speed because the tractive force at the wheels is the same. Still has nothing to do with BSFC for this test technique because it doesn't matter how much fuel the engine is consuming in any configuration, only that the throttle opening (and torque output) is held constant.

When I had questions about this, I reached out to a UIUC engineering alum who works for an auto manufacturer. He wrote back, "Assuming a flat torque band in this speed/rpm range, your torque in both scenarios is the same, the speed of the higher drag car is slightly less, and as a result the power of the higher-drag car is slightly less."

[aerohead]

I've spent around 24-hours reviewing my library, notes, and criticism of my criticism of the so-called throttle-stop test technique.
Best I can surmise is that, all the controversy stems from ignorance, some willful, lack of critical thinking skills, and lack of perspicacity, for some of those participating in the conversation.
I've tried to give advocates of the T-S T technique the bona-fides which would convince them of the fallacy of their logic, a back door with which to provide a soft landing, save some face, admit mistakes, and move on.
Years on now, providing facts hasn't appeared to move the dial.
--------------------------------------------------------------------------------------
The T-S T is a 'fail.'
Hucho, Janssen, and Emmelmann reported the failed logic of it in 1976, in SAE Paper 760185, the fruit of which can be seen the 3rd chapter in Hucho's 2nd Edition, coincidentally authored by the same Hans Emmelmann who reported the 1976 T-S T logic failure; a book the 'inventor' of the so-called throttle-stop testing has been in possession of, by his own admission. ( It pays to actually READ books, and take pains to comprehend their content, before you stick both feet in your mouth, losing what little credibility you might have ever had ).
--------------------------------------------------------------------------------------
Hucho attempted to re-report the logic failure in his 1986 book, citing his friend and mentor, Gino Sovran's two SAE Papers which laid out the particulars which illustrated the 'outcomes' one could expect, should they ignore the 'science'.
--------------------------------------------------------------------------------------
I did bring my 'Proctological Home Surgery Kit' with me, and I'm willing to go ahead with T-S T advocate alimentary tract, stereo outlet enhancement surgery today.
However, I'm happy to allow a grace period, in which originators and devotees of the T-S T technique may review Chapter 3 of Hucho's 2nd-Edition, Road Vehicle Aerodynamics, review the reference materials, and decide whether or not they'd like to print a retraction for the T-S T technique on their own terms, with their own language.
There's nothing in the extant scientific literature which supports the premises underlying the technique.
It must suck, not be to mechanical engineer.

[redpoint5]

We get paragraphs this time, but still not even a hint as to the objection, just the usual "study everything in the world and you'll agree with me".

What's the point of a thread dedicated to being critical, yet containing no criticism? Best I can tell, is to antagonize people.

[aerohead]

Originally Posted by redpoint5

Yeah, and I was critical of this thread, because why take the effort to start a thread criticizing something without laying out what that criticism is? See, I provided the basis for the criticism to this thread. Now was that too hard?

Whenever anyone asks aerohead to clarify something, he avoids it by saying; "study..."

*Economics
*Physics
*Meteorology
*Organic chemistry
*Climatology
*Electronics
*Metallurgy
*Fluid Dynamics
*Boundary layer stagnation
*Alchemy

-----------------------------------------------------------------------------------
Texas Tech University is a liberal arts institution.
The requirement for the undergraduate degree in mechanical engineering required:
Acoustics & Vibration ( as an elective )
Algebra
American History
Analytic Geometry
Calculus 1 & 2
Chemistry ( with lab )
Dynamics
Economics 101 ( an elective )
Electricity & Electronics
Engineering graphics
Fluid Mechanics
Fortran 4 computer programming ( with IBM 360 mainframe lab )
ASHRAE HVAC design and engineering
Internal Combustion Engines & Air Pollution ( with dynamometer lab )
Literature ( as a Dean's List honors class )
Marketing 101 ( as an elective )
Metallurgy
Physics ( with lab )
Public Speaking ( as an elective )
SAE Journals & Transactions ( all extant document access via university library 'stacks'
Sociology (as an elective )
Solar Energy ( as an elective )
Special Problems for Engineers
Statics
Strength of Materials
Texas Tech University Sailing Club (available to all students )
Thermodynamics
University Library reference collection ( fluid mechanics )
Waste Treatment design ( elective @ College of Civil Engineering )
West Texas Solar Energy Society student member ( extracurricular activity )
-------------------------------------------------------------------------------------
The multi-disciplinary background doesn't 'hurt,' in the context of how one experiences the world, how one informs themselves, and how one perceives and connects 'dots' which remain invisible to many.

[aerohead]

Originally Posted by redpoint5

We get paragraphs this time, but still not even a hint as to the objection, just the usual "study everything in the world and you'll agree with me".

What's the point of a thread dedicated to being critical, yet containing no criticism? Best I can tell, is to antagonize people.

I'm gonna give VMAN and others some time to do their due diligence and act accordingly, or not.
If you were actually interested in the subject you would have had ample time to acquaint yourself with the particulars, study the formulas, do the math, and discover for yourself the utter folly of the technique.
I led you to the water. It's up to you whether or not to 'drink'.
Since you're no doubt aware that, I've made transcription errors in the past, a reading of the actual particulars on the part of all interested parties makes it possible to maintain the fidelity of the data. Method in the madness.