Is there any science behind pucker factor?

[jbrumberg]

Two different, but accurate definitions of the factor. N80 accurately describes the physiologic process. 3RRL adds the cognitive interpretation of the process. Jay

 

[texasjohn]

I believe what N80 and 3RRL say... I also believe that I've seen animals, birds, etc. exhibit the pucker factor... I think it makes them lighter during the flight response, perhaps confuses the attacker and assists in escape. Are we so different?

 

[TMcD_in_MI]

So the center of gravity never changes?

Not unless something about the machine changes, like raising the loader or filling an empty fuel tank, etc. Otherwise, the CG is always in the same place relative to the tractor. Relative to the ground is another story.

Lets talk stability for a second. Hold a string on the ground and walk all the way around your tractor until the string is tightly touching all four tires at the ground level. Call that region the base of the machine.

Now, if you drop a plumb bob from the CG of an tractor and that bob points at a spot inside the base of the tractor, then it is stable and won't tip over. When you move onto a slope, the plumb bob will move toward the downhill edge of the base. You're OK as long as the bob stays within the base. If you get to a steep slope where the bob is pointing right at the edge of the base, you're on the razor edge, and you'd better not have had beans for dinner, 'cuz that's all it might take to roll you over. You're basically riding on two wheels. All the while, the CG hasn't moved within the tractor, just it's vertical location relative to the base has.

Same thing is true for fore and aft rollovers.

Hope this helps. If not, sorry!

Tom

 

[N80]

I think of "puckering" as a feeling that is creeping up on you, like as you approach a dangerous situation rather than (as opposed to) a sudden exposure to one.

That has never been my understanding of puckering. That's not to say you're wrong, I may be totally off base. But when it comes to human physiology, and the physiology of an actual butt pucker, it does not have a lot to do with a 'feeling' that you are aware of. That type of thing is supratentorial. In other words, awareness of impending danger is processed in the parts of the brain above the tentorium, the parts of the brain that do the thinking and processing. And while I would not describe a butt pucker the same as a simple reflex like when someone goes Boo! and you jump, I would also not describe it as a cognitive process such as dread, foreboding or horse sense.

I think a sudden one causes shock, then some kind of immediate reaction. IMHO, that is different than the pucker factor. Like a situation you know is dangerous but if you stopped, you could get out of it. Like tracking a wounded lion or getting on a slope that gets steeper and steeper if you keep going. I think it has something to with that kind of feeling, more like a warning system? You would know better than me, so maybe I'm wrong?

Like I say, I know the physiology but I don't know for sure what people mean in popular terms when they say 'pucker'. So you may be right about popular usage of the term.

But let me describe my understanding of it. Let's say you feel that you are pushing your tractor to the limits of its ability to stay on 4 wheels. Even as a beginner you will start, at some point, to get a 'feeling' that you are on the verge of rolling. This could potentially cause things like a faster heart rate, a sense of fear, maybe even sweaty palms, sharp breathing, intense concentration. But then, you hit a little bump, or get just a little more 'diagonal' and you actually feel it is going to roll over NOW! This is IT! That's when butt pucker hits. You may have been working up to it, but its pucker when you think it IS it. This version may not be what most people think of when they say pucker, but it is at least supported by the physiology. And I've had this happen. There is a big difference between being worried that you might roll and thinking that you are starting to roll. Fortunately, my brain was wrong. I did not roll. But the visceral experience of thinking I was about to, is enough to keep me from pressing it that far again. My pucker was premature, but that is better, by far, than puckering too late.

I'll relate one other experience that others may identify with that kind of describes this process. We had an ice/snow storm here a few years ago. I have big pines all around my house. Some had come down, some had lost branches but most of that seemed to be over. Well I was walking around inspecting the mess when I heard a huge crack and a pop. I looked up and there was a pine branch bigger around than my leg coming down at me fast. I'm not the most quick or agile guy in the world but fortunately the ends of this huge branch brushed some others and slowed it down a tiny bit. I took one step and this thing crashed down all around me onto the driveway. It hit the concrete so hard that the branch literally shattered. I'm sure it weighed hundreds of pounds. As soon as it dawned on me that I was not dead, I remember getting a chill up my spine, goose bumps all over and the hair on my head stood straight up. I've never had that feeling before (and hope not to again) but that was like an uber butt pucker. There was no thinking that went into it. I would agree that it was not a reflex but it was not just 'wow I was almost killed' either. It was involuntary and visceral.

 

[N80]

you'd better not have had beans for dinner, 'cuz that's all it might take to roll you over.

Then that would make tworeasons you'd better not have had beens.

Hope this helps.

Tom

It did. Excellent explanation. Now we know the physics and the physiology behind the pucker experience! Where else on earth but TBN?

 

[3RRL]

I think you're right George.
there may be different interpretations of "pucker" factor. You have explained the actual butt "pucker" moment and I was conveying (trying) the feeling leading up to it. I didn't think of the factor as the actual moment, since I've personally hit that point only to find there is an additional pucker factor beyond the first point. LOL ... That's when I realized I was still alive but the situation got even worse.

So I was thinking more in terms of approaching it as well as part of the definition. But you're a Dr. and I'm a Mold Maker so what can I say? Anybody else had that happen, to hit the double pucker? hahaha

 

[SPYDERLK]

Not unless something about the machine changes, like raising the loader or filling an empty fuel tank, etc. Otherwise, the CG is always in the same place relative to the tractor. Relative to the ground is another story.

Lets talk stability for a second. Hold a string on the ground and walk all the way around your tractor until the string is tightly touching all four tires at the ground level. Call that region the base of the machine.

Now, if you drop a plumb bob from the CG of an tractor and that bob points at a spot inside the base of the tractor, then it is stable and won't tip over. Tom

I thnk yould have to modify that a little due to the pivot on the front axle, but in general absolutely correct -- except....... . When you get anywhere near it small, quick transient groundchanges become ever more important. They can literally throw you over if you dont do appropriate steering countermeasures. Thats where a conservative PF helps. Gives you some slop.

I think PF is modified by experience to a more and more accurate interpretation/feel of the instant risk. Unfortunately, this brings you closer and closer to the limit where any change will put you over. Subtle feelings in the machine contribute to assessing this limit. Anywhere near it you should be scared - - and be going very slowly.
larry

 

[jmc]

I used to think the pucker simply came from the amount of tilt until someone mentioned here on TBN that he felt safer mowing a certain slope on his property with one tractor compared to his other tractor. I noticed it too when I upgraded to a bigger tractor on the slope I hated mowing with the smaller one. The bigger one measures about a 20 % wider but the COG is somewhat less that 20% higher, I'd guess by just looking at them.

So the brain is sensing something besides pure tilt. My theory is this: as you drive, the tractor is bouncing up and down, which causes the tractor to oscillate from side to side. Your brain has a pretty good memory of how long each of those oscillations lasts ("period" is the term, if you remember your physics). The thing is, the closer the tractor is to its balance point, the longer the period of oscillation. When the oscillation occurs near the balance point, the tractor is more or less "teetering"- another name for extended period. So our brains sense this extended period and sends an alarm to our anuses.

Can't prove it though.

John

 

[N80]

I didn't think of the factor as the actual moment, since I've personally hit that point only to find there is an additional pucker factor beyond the first point.

Good point. And it goes to show that pucker isn't necessarily a single event but can occur in degrees. And I guess, as long as you're still puckering everything is still okay...or at least you're still alive!

But you're a Dr.

Don't let that fool you. Some of the dumbest people I've ever met were doctors. They might can cut you up and put you back together again or diagnose some rare ailment, but some of them (us) have got less common sense and/or intellectual capacity than a bowling ball. Edumacation isn't what makes one smart and certainly not wise.

 

[Egon]

I would think that the center of gravity will change for every change in the longitudinal and vertical axis of the object in question.:D :confused: :confused: :confused:

Please disregard this post. At the time an upcoming endoscopy was occupying my thoughts.