mazdeuce - Seth said:I'm not necessarily condoning this idea, but it might not hurt to have a cooler labeled "Questions for AngryCorvair" filled with a lubricating beverage at the Challenge. The only real question is whether that cooler should be larger or smaller than the one labled "Questions for stafford1500"
Maybe instead of bickering about rules at the Town Hall we could get them both up to answer questions?
morello159 said:An interesting/fun exercise to do that really accentuates the phase lag from front to rear axle is to steer back and forth at the same frequency as the phase lag. On tires with low lateral stiffness it's pretty easy to do, as this frequency is low, and you can actually get the car to "pivot" back and forth about the center while driving down the road.
My parents had a 78 Lincoln Town Car when I got my license, and although I didn’t drive it frequently, when I did, I drove it like I stole it(some things never really change). Going around the “35-mph” s-curves outside town at about 50, I experienced exactly what you described. The amount of yaw from the body, relative to the direction of travel, was fascinating. Especially since it didn’t have *that* much body roll.
In reply to Dirtydog :
Just ask. Even with a complete book of materials that has been refined and taught for years we were still asking questions about what different symbols meant in class.
And if there is anything else you're wondering about, ask that too. I'm in no way covering everything from the class, just some of my personal highlights.
Thanks. I will. I remember years ago, training for my motorcycle instructor certification, some of the things learned in class, were intuitive in the field. But the book work, and actually doing it, were eye opening. There is a rhyme to the reason.
Pete Gossett said:mazdeuce - Seth said:I'm not necessarily condoning this idea, but it might not hurt to have a cooler labeled "Questions for AngryCorvair" filled with a lubricating beverage at the Challenge. The only real question is whether that cooler should be larger or smaller than the one labled "Questions for stafford1500"
Maybe instead of bickering about rules at the Town Hall we could get them both up to answer questions?
Pete/Seth.
I would suggest the pool area at the host hotel would be a better venue for this sort of discussion. I am happy to answer questions on the fly and trying to help others come to grips with aero stuff. It might even turn into a long session, if the beverages keep flowing... I won't commit anyone but myself to this sort of question-answer session, but I suspect that things would evolve pretty easily into more categories that others have more experience with. That might be a good thing to start trying to sort out ahead of time, the who part anyway.
Is there a public SAE dictionary/glossary? I've found these discussions frequently hampered by people inferring two definitions for the same word. I've frequently wondered how many online discussions could have been simpler if two parties agreed on a definition, at professionally my engineers and accountants use the same words but have different sets of governing rules that apply different definitions to them.
dclafleur said:Is there a public SAE dictionary/glossary? I've found these discussions frequently hampered by people inferring two definitions for the same word. I've frequently wondered how many online discussions could have been simpler if two parties agreed on a definition, at professionally my engineers and accountants use the same words but have different sets of governing rules that apply different definitions to them.
SAE does have a set of standard definitions, but since SAE encompasses so many things/areas they too have some areas that have varied definitions.
SAE = Society of Almost Everything
dclafleur said:Is there a public SAE dictionary/glossary? I've found these discussions frequently hampered by people inferring two definitions for the same word. I've frequently wondered how many online discussions could have been simpler if two parties agreed on a definition, at professionally my engineers and accountants use the same words but have different sets of governing rules that apply different definitions to them.
This one may be relevant to our discussion here, but I'm not sure that it's publicly available.
SAE J670_200801 Vehicle Dynamics Terminology
Just here to say I love this thread. Thanks all!
Terminology is an issue. For instance, how we use oversteer (which is an over yaw compared to steering angle) or understeer (which is under yaw compared to steering angle) doesn't fit the SAE definition because the SAE definition of those events is ONLY applicable in a steady state. So how we use the term every day to describe what the car is doing in a transitional environment isn't right, but those terms are so useful that we still used the terms to describe what we were feeling in the cars.
Let me search around a bit to see if I can find a good chart that explains understeer gradient and how that is plotted. It's fun.
mazdeuce - Seth said:Terminology is an issue. For instance, how we use oversteer (which is an over yaw compared to steering angle) or understeer (which is under yaw compared to steering angle) doesn't fit the SAE definition because the SAE definition of those events is ONLY applicable in a steady state. So how we use the term every day to describe what the car is doing in a transitional environment isn't right, but those terms are so useful that we still used the terms to describe what we were feeling in the cars.
Let me search around a bit to see if I can find a good chart that explains understeer gradient and how that is plotted. It's fun.
interesting.... looking forward to going down this rabbit hole
Here's a fun spreadsheet to play with to see how various suspension parameters can impact under/oversteer (he calls it Front Roll Couple)
Basic relationships below (milliken ch.5) (mods yell at me if it's not ok to post this!)
Understeer. Oversteer. We all know what these are, yes? Well, SAE wants to tell you that you're wrong, and I'm going to tell you why.
Just to break down your ideas, lets ignore the terms to get out of our comfy place. Let's instead pretend that I grew up driving in circles and I'm now turning both ways. Old habits die hard and I come in yelling at my crew chief (that's you) saying the car is loose as hell and completely useless and I throw my helmet and stomp into my motor home. Your job is to fix it. Take out some rear bar? Add some rear wing? Those shock knobs aren't going to turn themselves. But wait, is the car loose on entry? Loose on exit? Loose in big sweepers? Loose under braking? Is the whole thing fundamentally loose? Saying the car is loose and walking away isn't nearly enough information to actually fix things. Crap. The inability to fix things is your fault by the way.
We think of loose and oversteer as the same thing. We talk about them like the same thing. The problem is that having a million different variables (accelerating, decelerating, decreasing radius, aero, how hard are we braking, track camber and on and on) that can make a car loose (oversteer) or tight (understeer) makes it impossible to use it as a measurement and the SAE hates to not be able to measure things that describe cars. So what they did is this, they took out all of the transient factors. Take acceleration, braking, radius changing, take out all of it and drive a constant radius circle at a range of constant speeds (or lateral accelarations). That's something we can measure across many different cars. It's repeatable. Nice.
This is how it's done. Lay out a circle and drive your car around it at sub walking speed. I'm talking slooooooooow. So slow that we can ignore lateral slip when we measure how far we've turned our wheel. This is our fundamental ackerman steering angle on this circle. Now go faster. Bring things us to .1 G. The tires must be slipping to be generating that bit of force. So we have slip angle and that affects our steering wheel angle. If the front is slipping more than the rear then we have to dial in a bit of steering angle. We should plot that steering angle vs. G. Now speed up and plot more. And more. And more. If your car is on the understeer side of the line you have to dial more and more steering angle in to stay on your circle. If your car is on the oversteer side the tail is hanging out and you have to put less and less steering in. Eventually you're generating enough slip that no amount of extra steering keeps you on the circle and you're done.
Now we can measure cars, not people. We can compare cars. We can look at how a single change affects the car. We can make sure all of the cars in our "family" behave the same by tailoring our initial angle and the slope of the curve. We can make a new car feel like home.
Whether a car is oversteering or understeering at a given time while you're out wailing on it is totally irrelevant. Understeer cars are on the top side of the line and oversteer cars are on the bottom and whether a car does one or the other is a quantifiable measurable thing. Now when I come in from driving in my circle and ever increasing G's and I hand you the plot of steering angle vs. lateral acceleration, you know EXACTLY how to change things. Thank you SAE.
In reply to morello159 :
mmmm, mmmm, mmmm.... I do love me some slugs, don't get to see them that often though, people keep forcing them around
sleepyhead said:In reply to morello159 :
mmmm, mmmm, mmmm.... I do love me some slugs, don't get to see them that often though, people keep forcing them around
In reply to stafford1500 :
you don't know how hard it was for me to not be a jerk and make jokes on page 2 about the derivative of acceleration
In reply to sleepyhead :
oh snap, you probably don't even know the 2nd derivative of acceleration!
In reply to AngryCorvair :
I've got the neck crackles and pops to prove that I do
mazdeuce - Seth said:I had a conversation with an Electrical Engineering teacher last fall while we were waiting for our daughters to get off the bus back from college. He said the biggest difference in school right now is information availability. Everything you need to become an engineer is publicly available. Why do we even need college then? Even among those 18 year olds who want to become an EE a significant portion don't finish the program. Having information available isn't the same as learning and processing it for use.
I have no doubt that everything I'm about to learn is publicly available and a lot of if I've already seen, but (I hope) that doesn't mean that I can't learn a substantial amount.
So my new gig after 20 years in video games is working for EBSCO one of the main providers of data base and journal access for schools. The big gap with getting access to the material online is in terms of students not being familiar with information literacy which is the process of vetting, compiling, refining searches etc this a big focus for the educational sector right now
sleepy, stafford, and angry - I have an undergrad degree in engineering physics but you guys are true nerds.
Robbie said:sleepy, stafford, and angry - I have an undergrad degree in engineering physics but you guys are true nerds.
Um, thanks I think
stafford1500 said:Robbie said:sleepy, stafford, and angry - I have an undergrad degree in engineering physics but you guys are true nerds.
Um, thanks I think
thanks, for sure! also, i have only seen crackle and pop used in an informal training so i thought the instructor just used them to be funny.
Jaynen said:So my new gig after 20 years in video games is working for EBSCO one of the main providers of data base and journal access for schools. The big gap with getting access to the material online is in terms of students not being familiar with information literacy which is the process of vetting, compiling, refining searches etc this a big focus for the educational sector right now
In grad school 12 years ago (Knowledge Management/Library Information Science) that was my counterpoint to patrons finding information online. So many were focused on the accuracy of information which I argued was already there or would come quickly, I was more concerned about clarity of information. The right information is worthless if the vocabulary is opaque or misunderstood. I was a big proponent of creating separate classes of tags/assets/information for embedding definitions in-line with a topic. Why bury everything in footnotes? Anyways this is a sidenote to the main discussion but it frustrates me to this day. I really love how clear this discussion has been in how the terms are being defined.
I’ve never done anything with crackle or pop... I know them mainly from Wikipedia. But, jerk and jounce (snap) are important in simulator motion base calculations/limits.
sleepyhead said:I’ve never done anything with crackle or pop... I know them mainly from Wikipedia. But, jerk and jounce (snap) are important in simulator motion base calculations/limits.
i learned of them in a camshaft design class taught by Billy Godbolt and Scooter Brothers of Comp Cams. At the time they were using jerk and snap, and included crackle and pop just as FYI that they exist.
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