Beware old and new aero data

[JulianEdgar]

Originally Posted by aardvarcus

Can't we all just agree to disagree about brands, transistors, age of stereo equipment, speaker wire, etcetera and just compare our own measured THD figures and REW plots?

Absolutely - let's compare measurements.

But as far as I can see, Fred doesn't actually do measurements eg of heatsink temperature. So it's even worse than you suggest: Fred doesn't measure - and he doesn't look at other people's measurements. He just tells us what measurements we will get, based on his theory.

(For the confused: I am talking about lift/downforce, and surface pressures on cars!)

[aardvarcus]

Julian,
I don't know how much surface pressure or lift/downforce data if any Phil collected when he took his T100 to the Darko wind tunnel for testing in 2014 and 2017. But I doubt he dismisses all measurement data seeing as how he spends time and money on money on wind tunnel testing.

I know from experience all measurements require a grain of salt, and there are things i have seen in print i remain doubtful of based on my past experiences. Thus it doesnt suprise me that the two of you are lending varying levels of credence to different sources based on your past experiences. Thus you dont agree.

I don't actually know either of you, but realize my motivations in this conversation are selfish, in that i enjoy seeing both of your content, and I personally wouldnt want either of you to not post. Both of you have far more experience than I do.

I personally feel that if we were all sitting in a living room and not on the semi anonymous internet removed from broader context we would get along better.

[JulianEdgar]

I would place very little credence on anything measured in the tiny Darko wind tunnel. Vastly more accurate to measure on the road.

No, I would make the same argument face-to-face. I am afraid that rubbish is rubbish, no matter the communication medium.

[Fat Charlie]

Perfect is the enemy of good enough.

With all the variables involved there isn't actually a perfect. Strive for it all you want, You can either come up with the ideal perfect, which ignores all vehicles already produced, or a very specific perfect for one particular vehicle. On the other hand, you can use a rule of thumb that tends to work in more circumstances than not and on more platforms than not.

The rule may be outdated and fall short of modern ideals, and actually fail on many vehicles in many circumstances, but then so do the cars we drive. If it helps more than it hurts, it's a good thing no matter how many instances you can point to where it falls short of ideal.

[j-c-c]

Originally Posted by aardvarcus

I'm going to break my own rule about staying out of others internet discussions...



My expertise is in a different field (electrical). I realize that I disagree with opinions held by some of the people that are working in that field (e.g. grounding vs bonding)..........

I suggest you guys agree to have a bit of mutual respect for each other. Both of you advocate testing, and if the build is flawed the testing will show it. Neither of you are advocating "for looks" aero mods such as bolting on nonfunctional spoilers.

In my eyes:
1. Smart people know the rules, wise men know when to break them.
2. My roommates in college where an AE and an EE, I always thought what they shared in common was the use of "transformers", one electrical and one aero.
3. "nonfunctional" can often be in the eye of the beholder or an example of "confirmation bias".

PS be interesting to here your real world grounding thoughts, I battle civil inspectors constantly on the grounding of temporary festival/concert production gensets.

[aardvarcus]

JCC,
I will admit up front I am less versed in temporary/portable setups than permanent installs. A few perhaps relevant thoughts:

There is a difference between making something that works and is safe and making the inspector happy. Nine times out of ten when I get a "perturbed" call from a friend or colleague about an inspector wanting them to do something "silly" I tell them just to do it. Given the gray areas in the electrical code, no reason to get off on a bad foot and give them a reason to pick the rest of the install apart. Often inspectors feel the need to find something, to prove their worth, and once you fix it you will be good.

I can see how dealing with multiple inspectors in multiple locations for a portable setup would be particularly challenging, not knowing what to expect. Try to not get crossways with them, because you don't want them trying to find more problems. The ornery ones often know where the code contradicts and can make your life miserable.

My first real job before going to school was doing construction building houses working for a GC. We did it all, including wiring. Our GC was "grandfathered in" as a licensed electrician, having been doing it prior to licenses being required. Stapled a lot of romex to studs. That GC was very picky about how the wiring looked. All the bends in the box and following the studs were all sharp 90s. No twists or turns in the romex anywhere. He had me do a lot of it, as he knew I had an eye for detail and would do it as asked. The other workers would mock behind his back, claiming the electricity didn't know how the wires were bent. (Mostly true given the application.) However the secret sauce was when the inspector showed up, everything looked impeccable (whether it actually was or not) and they would promptly pass the inspection. Usually they didn't even look at the whole house, just a short walk around, making comments about how great it looked, and the approved sticker went on. The actual function of the wiring was no better than the average homes around it. It was brilliant on his part, he paid this kid a little more since it took a little longer, but he didn't have to rip our or redo anything on an inspectors whim. The wiring wasn't bad, but looking back I do recall a few things that didn't really meet code.

So if at all possible, make your setup look professional, sharp, and pretty. "Silly" things like clean bends, labeling, not-rusty boxes, etcetera go a long way to set perceptions from the get go.

If you are dealing with different inspectors wanting it different ways, consider ways to make it flexible (e.g. able to add or remove a ground or bond jumper) upon request. (Using appropriately rated devices to do that of course.)

[California98Civic]

Originally Posted by aardvarcus

Julian,
I don't know how much surface pressure or lift/downforce data if any Phil collected when he took his T100 to the Darko wind tunnel for testing in 2014 and 2017. But I doubt he dismisses all measurement data seeing as how he spends time and money on money on wind tunnel testing.

I know from experience all measurements require a grain of salt, and there are things i have seen in print i remain doubtful of based on my past experiences. Thus it doesnt suprise me that the two of you are lending varying levels of credence to different sources based on your past experiences. Thus you dont agree.

I don't actually know either of you, but realize my motivations in this conversation are selfish, in that i enjoy seeing both of your content, and I personally wouldnt want either of you to not post. Both of you have far more experience than I do.

I personally feel that if we were all sitting in a living room and not on the semi anonymous internet removed from broader context we would get along better.

THIS!

Originally Posted by Fat Charlie

Perfect is the enemy of good enough.

With all the variables involved there isn't actually a perfect. Strive for it all you want, You can either come up with the ideal perfect, which ignores all vehicles already produced, or a very specific perfect for one particular vehicle. On the other hand, you can use a rule of thumb that tends to work in more circumstances than not and on more platforms than not.

The rule may be outdated and fall short of modern ideals, and actually fail on many vehicles in many circumstances, but then so do the cars we drive. If it helps more than it hurts, it's a good thing no matter how many instances you can point to where it falls short of ideal.

AND THIS!

[JulianEdgar]

We now seemed to have progressed(?) to rationalising incorrect statements as better than nothing.

I am sorry; I don't agree.

Rules of thumb that aren't stated with qualifiers but instead as absolutes, are deceptive. It's pretty odd that people then turn around and say "But I am sure most people realise that they're not absolutes". Why not just say that at the time? It's not hard:

Very approximately (it depends on the car, engine and other factors), at 55 mph, a 10% drag reduction translates to a 5% increase in fuel economy. At 70mph,a 10% drag reduction translates into a 4% increase.

There we are, a useful rule of thumb that won't lead anyone astray.

A template that is presented as the absolute best approach, when there's very little evidence that it actually is, and the shape isn't even mentioned (as far as I am aware) in any current aerodynamic technical literature, is deceptive. That is, when it is presented without a great deal of qualification.

When I started reading this site I was surprised by:

(1) The way pat numbers were thrown around as if, of course, just following these will give you the best results. (Then I realised most of that information seemed to be coming from one source.)

(2) The complete ignoring of vertical aerodynamic forces, as if lift (and induced drag) didn't exist. (Then I realised most of the misinformation on that topic was coming from one source.)

Someone said that I should expect my statements to be scrutinised. Well, fine. If it's something theoretical, let's compare references, with obviously greater weighting given to most recent research. If it's something practical, let's compare on-road test results.

I only take exception to criticism when it's from a keyboard warrior - someone who hasn't actually done what I am describing, but just knows I am wrong (eg in my test results)... without their presenting any evidence to support their statements whatsoever. (That is, it's all just what they think.)

As I have said, the content of my book was vetted by four top automotive aerodynamicists. I am pretty confident that a lot (but certainly not all) of the advice on this forum would never have made it past them.

I just want accurate, useful and effective advice being given to those who wish to modify the aerodynamics of their cars!

And, in my opinion, bad advice is worse than no advice.

[aerohead]

Originally Posted by aardvarcus

I'm going to break my own rule about staying out of others internet discussions...

I think everyone needs to take a deep breath and relax. I own and often read Julians Book, I have also read a large percentage of everything Aerohead has posted on this site. They are both full of useful information, as a percentage I feel the disagreements between the two are rather small.

For example, based on Aerohead's postings I built a 6' full tapered bed cover for my 2005 Tacoma. The MPG increase was near spot on with my estimates based on projected drag coefficients and rules of thumb. Would that have worked on my 2001 2500HD? Probably not, because I understand the issues that drive it out of the "normal range" for those sort of parametric estimates. I don't think that most people need spoon fed the constraints.

Does that bed cover produce lift? Based on drawings i have seen in Julians book and other sources, and with a mediocre understanding of what is occurring with the airflow, I would surmise yes. I have not had time yet to build a pressure measuring gauge, but detailed instructions are in Julians book and i hope to one day. However, does the bed cover produce more lift than the prior configuration? (Open pickup bed) No, it certainly does not, measured at the rear end dyno based on speeds I can take turns at comfortably.

So as a largely uninformed DIY user that has at this point built at least a dozen different aerodynamic devices, I do not feel that I have been lead astray by anyone. The information I have received from both sources is certainly worth what I paid for it. The discrepancies are minor where the rubber meets the road.

My expertise is in a different field (electrical). I realize that I disagree with opinions held by some of the people that are working in that field (e.g. grounding vs bonding). But my father in law occasionally reminds me that even those people could help impart knowledge to an average person (e.g. No your breaker isn't broken because it won't reset, why did you wire nut the hot wire directly to the ground wire?!?!?).

I suggest you guys agree to have a bit of mutual respect for each other. Both of you advocate testing, and if the build is flawed the testing will show it. Neither of you are advocating "for looks" aero mods such as bolting on nonfunctional spoilers.

I'd have to dig it out of my rat's nest,but I believe that Texas Tech's 1988 SAE Paper on the GM aeroshell indicated something on the order of a 60% reduction in rear lift,along with the 20% drag reduction.It was a 'two-fer.'

[aerohead]

Originally Posted by JulianEdgar

Unlike what you write, the material in my book (which basically I am quoting from for nearly everything I write here) was checked before publication by four expert car aerodynamacists.

They included:

• the head of aerodynamics at a major car company
• an F1 aerodynamicist
• a professor of aerospace (and author of two major books on car aero)

...and of course my official technical consultant and reviewer for every page in the book, Dick Barnard. Dick's CV:

Richard Barnard is a world-renowned aerodynamicist. He started his career as an undergraduate aeronautical engineering apprentice at Handley Page Ltd, and later became Principal Lecturer and Postgraduate Research Tutor at the University of Hertfordshire, and is currently a Visiting Research Fellow. He is also a founder member of the UK Wind Engineering Society, and a Fellow of the Royal Aeronautical Society (FRAeS). He has been a consultant for numerous companies, including Jaguar and Rolls-Royce Bentley. Richard is the author of Road Vehicle Aerodynamics and has written many technical papers.

That is why I am very confident in the material.

So when I read what you write, which is very often completely or in part wrong, I am cross that you are leading people astray. It becomes even worse when you persist in saying the same thing, despite the errors in what you are saying being pointed out.

Misconceptions are fine - no one is perfect - but to continue to give people poor advice, is in my opinion, unforgivable.

I have this really odd moral belief that people modifying their cars should actually be given the best advice available. That way, they spend less of their money, time, effort and enthusiasm being wasted by pursuing courses of action that result in outcomes that often don't achieve what was promised.

*Expert doesn't account for much if they're just supplicants,smearing the blueprint ink around a bit,while the stylist remains overlord.Do your 'experts' drive Cd 0.12 automobiles? I'm certain that they're at an income level that would allow it.
*So far,you haven't demonstrated such a command of aerodynamics that I consider you a peer.Your appraisal of my abilities means nothing to me.Which goes back to my comment about Donald Rumsfeld. It's what you don't know that makes you stand out.I truly don't believe that you'd be able to discern if any of us were wittingly attempting to deceive. That knowledge appears to lie ahead of you.
*Please take a look at the University of Cambridge,Cd 0.11,CUER,Eco solar racer,and explain where my recommendations have gone off the rails.I remain the student forever.