Recce notes
Posted by aj_johnson
Banned Senior Moderator Location: Calgary, AB Join Date: 03/27/2009 Age: Ancient Posts: 1,798 Rally Car: (ex)86 RX-7(built), (ex)2.5RS (bought) |
If your notes typically describe the angle of the corner, where a 3 is typically the same angle, the only thing that artificially downgrading a 'caution' corner will do is hurt your confidence in your notes. You'll inherently not trust your notes because what you 'call' isn't what you always get. This will particularly hurt in poor visibility. There is a particularly narrow stage with exposures in Merritt BC. I'd bet just about everyone's notes for that road are littered with 'keep in' and I know, for a while, our notes were artificially downgraded in spots. When we started to ignore the exposures and just drive the right line on the road, we picked up significant speed and felt safer. Not exactly. He described his system as the number being the gear for the corner - or if the corner was in isolation, what gear would you be in to go around it. With the prevalence of Jemba notes in the US, it makes a lot of sense to write notes that mirror the style and syntax of Jemba. Using a system that is based on an objective measurement, rather than a subjective impression, also makes a lot of sense. First Rally: 2001 Driver (7), Co-Driver (44) Drivers (16) Clerk (10), Official (7), Volunteer (4) Cars Built (1), Engines Built (0) Cages Built (0) Last Updated, January 4, 2015 
Edited 1 time(s). Last edit at 08/01/2012 11:31AM by Morison. |
Jorden Professional Moderator Location: Baraboo, Wisconsin, USA, Terra, Sol, Milky Way Join Date: 01/24/2006 Posts: 372 Rally Car: whichever one i happen to be driving at the time |
bah. notes are cheating. the only reason a codriver has them is because it gives them something to do while they're waiting to have to push/pull/fix the car when it breaks, and to give the driver a frustration venting pathway. But if they realized that's all they're there for, they'd never do it. So they get to keep the notes. And the drivers now use them as a crutch instead of just using their eyeballs. Safety? Vehicle longevity? Avoidance of death? humbug!
 ---** To be in compliance with the Anarchy **--- Jorden R. Kleier Baraboo, Wisconsin, USA 1990 Mazdog Protege 4WD 1973 |
Grant Hughes Junior Moderator Location: Whitefish, MT Join Date: 01/11/2006 Age: Midlife Crisis Posts: 6,818 Rally Car: BMW |
Banned Senior Moderator Location: Calgary, AB Join Date: 03/27/2009 Age: Ancient Posts: 1,798 Rally Car: (ex)86 RX-7(built), (ex)2.5RS (bought) |
My experience is different, at least with drivers who have a lot of experience on notes and who typically trust their notes. I've seen drivers come in to a corner they consiously downgraded for safety, as little as a half grade, who then commit less to the following corners for several KM, if not the whole stage. They aslo regularly ask for a correction, upgrading the corner. In terms of confidence in what the notes are telling you, there's no difference. In terms of being able to commit and push on the notes, the upgrade is clearly has more serious consequenses and will kill confidence in pushing on the notes much qucker. I know it is an example, but a two grades is a mistake, not an adjustment. I'm also not sure what would make someone artificially upgrade a corner. Mostly. But sometimes knowing the consequenses is valuable. (Idaho 2008 had something like a 1000ft drop on the outside of a L1) Generally knowing the severity (care, caution, danger) is enough and avoids any chance of target fixation. First Rally: 2001 Driver (7), Co-Driver (44) Drivers (16) Clerk (10), Official (7), Volunteer (4) Cars Built (1), Engines Built (0) Cages Built (0) Last Updated, January 4, 2015
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steve czwalga Ultra Moderator Location: Pittsburgh, PA Join Date: 09/16/2011 Age: Settling Down Posts: 376 Rally Car: 95 awd celica |
Michel Hoche-Mong Mega Moderator Location: Campbell, CA Join Date: 02/28/2006 Age: Possibly Wise Posts: 1,156 Rally Car: Golf, Golf, RX-3 |
Grant Hughes Junior Moderator Location: Whitefish, MT Join Date: 01/11/2006 Age: Midlife Crisis Posts: 6,818 Rally Car: BMW |
I've done it to see if I could trick myself into not lifting and taking the corner flat out and just dealing with it. Grant Hughes |
Banned Senior Moderator Location: Calgary, AB Join Date: 03/27/2009 Age: Ancient Posts: 1,798 Rally Car: (ex)86 RX-7(built), (ex)2.5RS (bought) |
That's where modifiers come in. Flat R4 or if you think you'll still lift Deceptive Flat R4 In this case 'flat' means 'flat out' or 'flat to the floor' - but in some instances 'flat' could mean something else. 'Flat Crest' could simply describe the profile of the crest, not how to attack it. Pick any word that is distinct and that tells you to commit. You could use Ruckus R4 to indicate that you can give it all the power you have and still not be in over your head. :-) First Rally: 2001 Driver (7), Co-Driver (44) Drivers (16) Clerk (10), Official (7), Volunteer (4) Cars Built (1), Engines Built (0) Cages Built (0) Last Updated, January 4, 2015
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Josh Wimpey Mega Moderator Location: VA Join Date: 12/27/2006 Age: Midlife Crisis Posts: 649 Rally Car: Sneak the Golf |
^^^This ____________________________________________________________- One. Class -- 2WD www.quantumrallysport.com http://www.facebook.com/home.php?#/pages/Quantum-Rally-Sport/281129179600?ref=nf |
Josh Wimpey Mega Moderator Location: VA Join Date: 12/27/2006 Age: Midlife Crisis Posts: 649 Rally Car: Sneak the Golf |
Steve Thompson Elite Moderator Location: Troy Michigan Join Date: 12/08/2011 Age: Midlife Crisis Posts: 13 Rally Car: 2004 Impreza being prepped, going backwards |
Hmmmm...., no. If we assume that a normal car has approximately a 2.5 deg/g understeer gradient, a wheelbase of 115" and an overall steering ratio of 15:1 the math works out as follows: Assume a 0.1g lateral acceleration at 15mph. This yields a turn radius of 151ft (R = V^2/a). Ackermann front wheel steer angle A = L/R = 9.58ft(wheelbase in ft)/ 151ft = 0.063rad = 3.61deg Steer angle due with understeer component = A+u = 3.61deg + (0.1g * 2.5deg/g) = 3.86deg Steering wheel angle at 15mph = Front wheel angle * Steering Ratio = 3.86deg * 15 = 57.9 deg Repeating the above for the same radius corner of 151ft and 40mph yields: Ay = V^2/r = (40*1.47)^2/151 = 22.9ft/sec^2 = 0.71g Ackermann = 3.61deg Steer angle due to understeer component = 3.61deg + (0.71g * 2.5deg/g) = 5.385deg Steering wheel angle at 40mph = 5.385deg * 15 = 80.8deg. Increase in SWA is 40%. There is some rounding error above, but you get the point. Not that this has any bearing whatsoever on stage notes, or how you would construct them, but this is how a real car, and math, actually works
Slip angle, btw, is present from the moment the car starts moving and is a function of how a tire works. Any lateral acceleration at all creates a slip angle. Period. In general you can assume around 3-5 deg/g in the linear range of the tire with things going non linear after 0.3-0.4g. The squeal is a function of a large amount of the contact patch operating in sliding friction which increases with increased slip angle. Peak slip angles for radials on pavement are somewhere around 6-9 degrees, from the data I've seen, with crossplys being a bit higher. FWIW slip ratio, which is the longitudinal slip of the tire, is required for any tractive force to be generated. How the steering wheel angle changes wrt speed and lateral acceleration is a function of the difference between the front and rear slip angle gradients. If they are the same, as in a neutral steering car, there is no change in steering wheel angle. If the fronts generate more slip for a given lateral acceleration, the car understeers and more steering angle is required. If the rears generate more slip the car oversteers (even well below limit) and less steering angle is required. All production cars understeer as do the majority of pavement based racecars, although to a lesser degree. Steve |
Michel Hoche-Mong Mega Moderator Location: Campbell, CA Join Date: 02/28/2006 Age: Possibly Wise Posts: 1,156 Rally Car: Golf, Golf, RX-3 |
John Vanlandingham Infallible Moderator Location: Ford Asylum, Sleezattle, WA Join Date: 12/20/2005 Age: Fossilized Posts: 14,152 Rally Car: Saab 96 V4 |
Steve Thompson Elite Moderator Location: Troy Michigan Join Date: 12/08/2011 Age: Midlife Crisis Posts: 13 Rally Car: 2004 Impreza being prepped, going backwards |
Banned Senior Moderator Location: Calgary, AB Join Date: 03/27/2009 Age: Ancient Posts: 1,798 Rally Car: (ex)86 RX-7(built), (ex)2.5RS (bought) |
For the purpose of the comparison, wheelbase and steering ratio are constants so their actual value don't matter, just like the radius of the corner. The only number that changes is the understeer component because of the speed of the corner. What troubles me, slightly, is that an example designed to show that more steering input is needed at higher speeds starts off with the assumptions that under steer is directly related to the g-force of the corner and that the under steer tendencies of a chassis are linear - which guarantees the result. In short, it is like saying 'OK, to prove I'm right lets assume I'm right.' First Rally: 2001 Driver (7), Co-Driver (44) Drivers (16) Clerk (10), Official (7), Volunteer (4) Cars Built (1), Engines Built (0) Cages Built (0) Last Updated, January 4, 2015
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