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Thread: moment diagram with weight transfer

  1. #21
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    Quote Originally Posted by NickFavazzo View Post
    He was just proving a point...
    He wasn't proving anything. It was an entirely made up scenario, grossly exaggerated to make his point look better. Ironically, he prefaced this made up scenario by telling Tim he needed to spend more time in the "real world".

  2. #22

    Take it to the limit...

    Most papers that focus on designing a lap sim or dynamics model of a vehicle usually end with a conclusion along the lines of:

    "In conclusion (cliche) this model accurate models and predicts how our perfectly set-up car can handle around XXX track and correlates well to the car when we have a good day. However, this tool is still not useful for making set up decisions because it puts the car into highly unstable conditions that a driver would normally not run in. A normal driver would have hit the wall with words coming out of his mouth faster than the revs out of his engine. The simulation would drift gracefully within 1mm of every single cone, maximizing the necessary acceleration and yaw moment possible. Future work includes designing a driver control model to make the tool realistic in the limitations that are allowed to occur during operation. For example, a barrel roll is not considered a standard obstacle avoidance technique in ground vehicle motorsport."
    Kettering University Vehicle Dynamics
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  3. #23
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    Quote Originally Posted by MCoach View Post
    ... For example, a barrel roll is not considered a standard obstacle avoidance technique in ground vehicle motorsport."
    That's called the Spiral Jump, not meant for motorsports, but a good way to validate a dynamic vehicle model -- see RCVD pages 458-460 <grin>.

    Back on topic, perhaps you aren't looking deep enough in the literature? Try our 1994 paper -- "MRA Moment Method — A Comprehensive Tool for Race Car Development, SAE #942538". This is included on the CD that comes packaged in "RCVD: Problems, Answers and Experiments". The second half of the paper describes correlation, done in cooperation with Lotus F1.

  4. #24
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    The "Astro Spiral Jump" (seen in "Man With the Golden Gun" was perfected using a version of DK4, a Fortran program I worked on as a Co-Op at GM Proving Grounds. This program originated with Ray McHenry at Cornell Aero Labs (now Calspan) for use in helping the Chevrolet Racing circuit teams. It ran from PUNCHED CARDS boys and girls. Back then, aero effects and wings linked to suspensions were the big thing

    A fellow we hired from Calspan, Dennis Kunkle, had pulled out the DK4 transient solution leaving the fast steady state summary for use in calculating the first Moment Methods. I can still remember Calspan's Roy Rice's singing the praises of the Moment Method at a GM Vehicle Dynamics Department meeting chaired by Tom Bundorf (another name Blast from the Past: Father of the "Cornering Compliance Concept"). Later, DK4I (the IRS version) was used for development of the mid-70's Corvettes.

    I still have the DK4 manuals in my "from GM to be burned" pile, unless my ex-wife already took care of that. The Astro Spiral filming in Thailand only took ONE film shot ! Behold the Power of Simulation.

  5. #25
    I have read a lot about that particular maneuver for the Bond movie and referenced it for that exact reason. Also, the post was getting too serious and needed to rush it to the emergency room for a healthy injection of fun back into the conversation.
    I don't think I have read that particular paper, but will check it out. The reason I say most is that most are published by those who are proud enough to get something working the first time rather than the top tier giants whom are focusing on things such as the influence of brake cooling on the tire tread and tire degradation. (http://scarbsf1.com/blog1/2013/09/06...ut-wheel-rims/)
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  6. #26
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    To Summerize

    Loose is Fast.

  7. #27
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    Tim,

    If you think you are able to pull an extra 0.5g of steady trim by reducing stability at the limit its quite clear which one of us has never engineered a car in his life...
    Of course it is possible! Think it through.

    Or else, can you give a well reasoned argument why it is IMPOSSIBLE? (I note that I am still waiting for you to justify your claim that increasing R% reduces response time so much that it is not worth doing.)
    ~o0o~

    JT A.,

    ... an entirely made up scenario, grossly exaggerated to make his point look better...
    Where is the exaggeration?

    There are countless cars (of all types) that are very well balanced with Max Ay around ~1.0 G. Putting wider and stickier racing-slicks on such cars can easily push Max Ay up to ~2 G, albeit with unbalanced (= non-neutral) limit behaviour. Such a car with balanced trim around 1.5 G is quite normal.
    ~o0o~

    Claude and Pat keep harping on about how new members of this Forum should always introduce themselves.

    I would rather see ALL members being expected to ALWAYS give an engineering justification to support whatever claims they wish to make.

    EGs 1 & 2. Tim's claims above.

    EG 3. Still waiting for Claude to explain why "Parallel Axes Theorem" must be used when calculating a Car-Body's dynamic motion about its "Pitch/Roll/Yaw axes".

    And many more...

    Please, a bit more engineering analysis, a bit less "I'm right, you're wrong, so there!".

    Z
    Last edited by Z; 03-22-2015 at 09:09 PM.

  8. #28
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    Quote Originally Posted by BillCobb View Post
    The "Astro Spiral Jump" (seen in "Man With the Golden Gun" was perfected using a version of DK4, ...
    Hi Bill, sorry but http://xkcd.com/386/

    Ray McHenry used a different model at CAL/Calspan for the spiral jump development -- HVOSM. The "Highway Vehicle Object Simulation Model" was initially funded by Bureau of Public Roads, part of the USA government. He and his son Brian (a high school classmate of mine) tell the story best on their own website:
    http://www.mchenrysoftware.com/mhvos...-Spiral%20Jump

    Last year I helped arrange for Ray to give the second William Milliken Invited Lecture at a big ASME conference. He did a great job of telling the story of the spiral jump design and the initial tests run behind CAL/Calspan:
    http://www.asmeconferences.org/IDETC2014/Keynotes.cfm

    There are also some amusing stories from the very first public jump in the Houston Astrodome (several years before the James Bond version was filmed). CAL engineers went down from Buffalo to help with the production, as detailed in "Equations of Motion", pages 561-563.

    -- Doug

  9. #29
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    Well then i'm going to make a car with EVEN WIDER and EVEN STICKIER tires than your car, and it's going to pull 6 g's unbalanced, but still a quite respectable 4 g's with balanced limit trim. And it's going to lap your car 3 times per every one of your laps. This is entirely supported by facts and engineering analysis, and not exaggerated at all.

    You people and your silly little matlab simulations need to spend more time in the real world if you want to have any chance at keeping up my & Z's cars.
    Last edited by JT A.; 03-22-2015 at 12:09 AM.

  10. #30
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    Hvosim

    Ah, you're right. It all comes back to me now. Thanks for the references.

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