TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker or making a Paypal contribution here: paypal.me/SupportTMC

Safe G-Force Limit

Discussion in 'Model S: Driving Dynamics' started by gavine, Dec 18, 2015.

  1. gavine

    gavine Petrol Head turned EV Enthusiast

    Joined:
    Apr 1, 2014
    Messages:
    1,007
    Location:
    Southern New Jersey
    #1 gavine, Dec 18, 2015
    Last edited by a moderator: Mar 13, 2016
    It has been reported that the g-force during acceleration on the P85D can cause passenger's vision to go blurry as well as difficulty breathing. I presume the P90DL, at 1.1g is even worse.

    With the talk of future Teslas accelerating to 60 in under 2 seconds (Maximum Plaid Mode), what kind of force will that be and will the everyday civilian be able to handle that? Sure, fighter jet pilots train for it, but you and I don't.

    Will Tesla have to dial-back the power output to smooth out the acceleration so as to not cause people to black-out?

    Hard to believe this is even a topic, but now that it's a possibility, I'm curious about it.

    This video comes to mind regarding the P85D blurry vision (from 2:00 to 3:15):



    And this one in the P90DL (@ 3:10 he says "jeez", you can hear it in his voice):

     
  2. ScepticMatt

    ScepticMatt Member

    Joined:
    Nov 5, 2014
    Messages:
    453
    Location:
    Austria
    The P90DL acceleration isn't anywhere near problematic levels for health. On top of that positive linear horizontal acceleration is the easiest for the human body to handle, the car accelerates more than an order of magnitude less than problematic levels.

    g-force - Wikipedia, the free encyclopedia
     
  3. gavine

    gavine Petrol Head turned EV Enthusiast

    Joined:
    Apr 1, 2014
    Messages:
    1,007
    Location:
    Southern New Jersey
    Agreed....I'm talking about FUTURE cars that do sub-2-seconds to 60.
     
  4. lolachampcar

    lolachampcar Active Member

    Joined:
    Nov 26, 2012
    Messages:
    4,445
    Location:
    WPB Florida
    I routinely pull 2.5G in aerobatics with all kinds of people in the front seat. No one has an issue with short bursts at this level (short being longer than MS can pull its G).

    I think what you are getting is the surprise factor and people banging their head on the head rest :)
     
  5. Todd Burch

    Todd Burch Electron Pilot

    Joined:
    Nov 3, 2009
    Messages:
    4,731
    Location:
    Smithfield, VA
    The reports of "Blurry Vision" are exaggeration. And really the effect of g forces on vision are not that it makes your vision blurry. Instead, you lose color vision, then start to get tunnel vision (your peripheral vision starts going away). And all of that is due to positive gs, in which blood is forced from your brain toward your feet. I've experienced both of these effects many times, and 1.1 horizontal gs just isn't going to induce any of this.

    When I flew for the Air Force, it wasn't until beyond 4 *vertical* g's, without any techniques that help keep blood in your head, before my vision would start to get impaired. This of course depends on the health/age of the individual, but 4 vertical gs is far, far, far worse than 1.1 horizontal gs, and even in that case you don't get blurry vision-you start to "grey out" (lose color vision), and then you start to get tunnel vision (your vision is lost at the periphery, and as you keep pulling, the "tunnel" gets narrower and narrower. It's a weird feeling.

    Both of these effects go away almost instantly when the g's come off as well, and they have zero health impacts.
     
  6. sillydriver

    sillydriver Member

    Joined:
    Oct 19, 2014
    Messages:
    542
    Location:
    Middleburg, va
    I think the thing that's special about Teslas, and also to some degree launch modes in ICE cars, is not acceleration (2nd derivative of position), but surge: the sudden change in acceleration (3rd derivative of position). That's what makes people scream, but it's physiologically harmless.
     
  7. Todd Burch

    Todd Burch Electron Pilot

    Joined:
    Nov 3, 2009
    Messages:
    4,731
    Location:
    Smithfield, VA
    As for health effects, probably nobody's been subjected to more routine g forces than John Stapp, and he died of old age at the age of 89.
     
  8. AudubonB

    AudubonB Mild-mannered Moderator Lord Vetinari*

    Joined:
    Mar 24, 2013
    Messages:
    4,219
    Location:
    Denali Highway, Alaska

    Thanks for your perspectives and explanation. This is a little point, but I'm thinking, however - and based on my single experience in Ludicrous - that your "...forced toward the feet..." must, as logic also dictates, be a function of those vertical g's. My wife and I both incontrovertibly felt the blood peeling away from our feet and lower legs toward the trunk, and from our face toward the back of the skull.

    Putting my 91-year old father in a Roadster Final Five was as far as I think most uninitiated may want to go, but YourBlurrinessMayVary.
     
  9. stevezzzz

    stevezzzz R;SigS;P85D;SigX

    Joined:
    Nov 13, 2009
    Messages:
    6,062
    Location:
    Colorado
    Vector addition. A 1g acceleration force acting straight back through the body, when added to the existing 1g gravitational force results in a 1.414g net force acting at a 45° angle to the vertical, back and down. As the other pilots on the list have already pointed out, this is hardly physiologically significant, but it is well outside the experience of most non-pilots and those who avoid roller coasters.
     
  10. Cottonwood

    Cottonwood Roadster#433, Model S#S37

    Joined:
    Feb 27, 2009
    Messages:
    5,062
    Location:
    Colorado
    #10 Cottonwood, Dec 18, 2015
    Last edited: Dec 18, 2015
    The rate of change (derivative) of acceleration is called Jerk as well as Surge. See Jerk - Wiki for more detail. In particular, Physiological effects and human perception of physical jerk - Wiki speaks to how we as humans react to Jerk.

    Because Force is equal to Mass times Acceleration, when acceleration changes, we have to change our forces to offset changes in acceleration. If we are not braced against the seats and head rest, this requires muscle forces. Until we have offset the force of the changed acceleration, we feel out of control.

    What is very different about a Model S launch compared to most ICE launches is the sudden increase (change) in acceleration causing a large Jerk. That creates what I will call Launch Shock in our passengers. I have found that by warning my passengers of the upcoming launch and suggesting that they rest their heads back against the headrest, the Launch Shock can be greatly reduced. OTOH, for some special friends, no warning can be great fun. :biggrin:


    As others have said, the g's produced by a Tesla Launch are far from physiological limits. For more detail, see g-force - Wiki. Here is a quote from that article on horizontal g-force tolerance:

    Early experiments showed that untrained humans were able to tolerate a range of accelerations depending on the time of exposure. This ranged from as much as 20 g for less than 10 seconds, to 10 g for 1 minute, and 6 g for 10 minutes for both eyeballs in and out.[15] These forces were endured with cognitive facilities intact, as subjects were able to perform simple physical and communication tasks. The tests were determined to not cause long or short term harm although tolerance was quite subjective, with only the most motivated non-pilots capable of completing tests.

    When we get anywhere close to 10 g acceleration, that will be fun! Of course, it may take better tires... I remember flying in the back seat of an alpha jet over the old 4-mile Honda test track. We were flying almost 400 kts at 500 ft AGL. To stay over the oval track required 4g turns. The pilot then asked why cars couldn't stay on the track at that speed. I immediately replied that while the alpha jets wings could easily create the force to sustain a 4g level turn, there were no tires that could do that, and few tracks have 80˚ banked turns...
     
  11. mguw

    mguw Member

    Joined:
    Oct 9, 2015
    Messages:
    14
    Location:
    FR
    Hello

    I don't think the blurr, that I experienced myself, is due to the G's themselves. On motorcycles I have often the same kind of accelerations and no blurr at all.
    So either it is because the helmet holding the head, or it is an optical / internal ear discrepancy due to the steady cockpit around you?
     
  12. ScepticMatt

    ScepticMatt Member

    Joined:
    Nov 5, 2014
    Messages:
    453
    Location:
    Austria
    Not even a problem if it were 0.2 seconds to 60. Then again I doubt we'll see rocket cars soon :biggrin:
     

Share This Page