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Hans
| | Posted on Monday, December 30, 2002 - 08:30 am: | 
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A human body in free fall, not a special diving attitude, is supposed to reach a maximum speed of 320 km/hour = 198 MPH
So, if you start to sit upright on a bike with that speed you have that 1G deceleration already and you have already to apply the brake to avoid that the more streamlined bike runs from under you forward. Braking harder, till you get good pressure on your wrists, will sum up with that 1G and it seems me likely that you can reach at least 2G deceleration at that speed.
Hans |
Dynarider
| | Posted on Monday, December 30, 2002 - 08:34 am: |
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If you were to travel at 198 mph & then nailed the brakes as hard as you could, what would happen if you tried to fart at that exact moment? Would it come out? |
Libnosis
| | Posted on Monday, December 30, 2002 - 10:21 am: |
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Quote:"Sliding front tires can ruin your day."
Confucious say - "Stoppie at low speed = Sliding front tire".
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S320002
| | Posted on Monday, December 30, 2002 - 10:30 am: |
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Dyna and Jim4,
Sometimes Blake needs to have a BS alert called on him. Once he realizes what he has really seemed to say he becomes like a snake swallowing its own tail.
Greg;-) |
Spiderman
| | Posted on Monday, December 30, 2002 - 11:08 am: |
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Ummmmm I got an Idea GO RIDE. It is easy to figure that out on paper but get your math doin, pocket protectin ass out there and do a few, then you will be able to see how the puckering of your ass also accounts into the equation.
BTW Dyna been 220 in a door slammer and tried to fart almost decompressed my ass.  |
Blake
| | Posted on Monday, December 30, 2002 - 02:00 pm: |
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<FONT COLOR="0000ff">"I was just responding to your statement
"Factors affecting superior braking of an F1 car versus a superbike?
Braking surface/weight? Nope.
Width and stickyness of tires? Nope. "...</FONT>
If you were "just responding to (my) statement", you did a very poor job of staying on topic.  How do you get from my statement to putting drum brakes and motorcycle tires on an F1 car?  You certainly do have a good imagination. I'll give you that. Yeah, a motorcycle with a car's wheel wouldn't handle worth dog doo. It won't stop any better either.
We are comparing the capability of one vehicle to that of another while discerning the aspects that allow one to be superior to the other.
"All I'm saying is the braking surface of 4 hot carbon fiber Brembo brakes on a light 650 Kg car are able to out-brake a Superbike with a pair of Brembo carbon fiber brakes..."
Actually you said the car weighed two tons, that'd be 1,800 Kg. Anyway, are you now agreeing that the configuration of the brakes is not determining the F1 car's big advantage in braking performance? Cause that was what I was trying to convey.
Consider that you could put conventional metal disks/pads on an F1 car and put the best available carbon brakes on a superbike; the F1 car will still outbrake the superbike. The brake design is not what gives an F1 car its big advantage in braking versus a superbike. Likewise, you could put small hard compound tires on that same F1 car with its conventional metal brakes and it would still outbrake a superbike running soft qualifiers. The tires are not what give a Fromula One car its huge advantage in braking versus a superbike.
Why? Because the huge advantage is the low center of mass that keeps the car from wanting to flip over along with the massive aerodynamic downforce that the F1 car is able to exploit.
"As far as sitting up at 180MPH on a Superbike - Do you think that is possible? Ask Richard Nallin if he as ever sat up at 180, and lived to tell about it."
I tried to give you a hint on this one. Hans nailed it (as usual  ). Motorcycle road racers can hit the brakes while simultaneously sitting up at high speeds, an interesting balance is attained.
"And any more than about 1.5 g of deceleraton, and you will not be able to stay on the seat of a bike, even with your knees velcro'd to the tank."
Really? I disagree. I think most superbike and Moto GP racers will also disagree. You've sat on a Duc racebike haven't you? Recall how your legs were wedged under and your crotch butted firmly against the tank? Regardless, we both know, that is not the limiting factor in braking hard on a racing motorcycle. The limiting factor is the high center of mass that gives the rider/machine a propensity to flip over. Right?
This is a great discussion. You have me thinking hard about lots of interesting stuff.  |
Steve_A
| | Posted on Monday, December 30, 2002 - 03:40 pm: |
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Blake is right with his basic physics. The most important variable is the ratio of x/y, the ratio of the cg distance behind the front contact patch to the cg height. That ratio gives the deceleration rate in g's to cause the bike to just balance on the front wheel. Greater deceleration than that, or added pitch induced by other factors such as suspension movement, and the bike performs a stoppie. On baggers, that ratio is considerably greater than 1, and they don't readily do stoppies.
Note also that coefficient of friction for pneumatic tires is not constant with speed, but is noticeably greater at very low speeds, and drops measurably as speed increases. That's why it's much easier to perform a stoppie on any bike at parking lot speeds than at 60 -- except for the new XB's and other short sportbikes, where you can pick the back end up at any speed on reasonably tractive asphalt. Buell worked hard to keep the cg low on the XBs to make the short wheelbase idea work. |
Jima4media
| | Posted on Monday, December 30, 2002 - 04:30 pm: |
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Blake,
OK, I forgot about braking force and aerodynamic deceleration at the same time, and balancing each other out. You win that one.
On the Formula one car, don't you think if you took the wings off, that car would still stop faster than a Superbike? I do.
The reason I said motorcycle tires on two ton car with drum brakes, is because YOU said tires, brakes and weight weren't a factor.
Steve,
Most baggers don't readily do stoppies, but Nicky Hayden can do one on a Honda GoldWing 1800 bagger. (empty bags) Harley's don't have that good of brakes, I'll admit.
Hans,
A human being has free fallen at 703MPH for a world record. That is the fastest a person can go without a vehicle A woman is going to try to break that record soon.
What is the fastest a human has gone in a vehicle? Trick question.
Jim |
Jima4media
| | Posted on Monday, December 30, 2002 - 04:37 pm: |
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Oh and Dyna,
Yes it would. The fart and the body are traveling at the same speed, and the fart is going into a partial vacuum. ;-) |
S320002
| | Posted on Monday, December 30, 2002 - 04:49 pm: |
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Blake,
Glad you weren't too offended by my snake swallowing comment. I don't respond well to subject changing and double talk.
Your free body diagram works well to describe the physics of a motorcycle with its rear wheel already off the ground. What it doesn't do well is describe how it got there. In order to lift the rear wheel you have to generate a vertical component to raise the mass of both the bike (partial) and rider (all) to the desired height. Therefore the following statement doesn't fly (pun intended).
"So the mass of the rider and bike have zero/nadda/nothing to do with getting the rear wheel to lift off of the ground due to braking."
Spidey,
I'm guilty of many things, farming in Iowa, hauling dynamite in Montana, riding motorcycles on race tracks from Arizona to California to Wisconsin. I've herded cattle from horseback. I've done a few wheelies and even some stoppies. I've even designed some parts for the Space Station. But I've never, EVER used a pocket protector. What do I look like, some sort of geek?
Greg;-) |
Spiderman
| | Posted on Monday, December 30, 2002 - 05:01 pm: |
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quote
__________________________________________________
A human being has free fallen at 703MPH for a world record. That is the fastest a person can go without a vehicle A woman is going to try to break that record soon.
__________________________________________________
Don't forget that 50% of that free fall was through the uppermost atmosphere where there is little or no air. If he were to do that in a normal air enriched environment he would have never reached those speeds. |
Blake
| | Posted on Monday, December 30, 2002 - 05:21 pm: |
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"On the Formula one car, don't you think if you took the wings off, that car would still stop faster than a Superbike?"
Jim, you are not listening to me amigo. Yes, the F1 car would still stop more quickly... due to it's low center of mass and thus no real limitation on how hard the brakes can be applied. It could tickle the absolute limit of tire grip whereas the bike/rider will endo in attempting to do so.
"The reason I said motorcycle tires on two ton car with drum brakes, is because YOU said tires, brakes and weight weren't a factor."
You need to finish that quote. I said that they weren't "factors affecting superior braking of an F1 car versus a superbike".
Certainly you understand that the world record for the free falling speed of a human was accomplished in a straight dive and at extreme altitude (significantly thinner air). I think the record holder needed a vehicle to get to altitude.
The fastest a human has ever traveled in a vehicle? Depends on the frame of reference. The Earth's surface at the equator is spinning at around 1,000 miles per hour, and the Earth is traveling at around 67,000 mph around the sun.
The Apollo missions to the moon escaped Earth orbit at about 25,000 mph relative to the Earth.
So I guess, relative to the sun, the Apollo moon shots might have reached near 90,000 mph. ![:]](http://www.badweatherbikers.com/buell/clipart/proud.gif) |
Hans
| | Posted on Monday, December 30, 2002 - 05:35 pm: |
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Jim
Yeah, that is a pretty fast free fall. Thin air on 130,000 feet altitude.
That is what is needed at LSRs: Thin air for less drag, thick air for the engine.
How fast would an astronaut fall, if he cuts the umbilical cord with the mother vessel and has engaged a brake rocket, before he burns up in outer space ?
My life and reference is down to earth: Only a few feet above or under sea level J
Hans |
Blake
| | Posted on Monday, December 30, 2002 - 05:38 pm: |
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Greg,
Yes, the bike and rider must have *some* mass. I guess I should have stated that as one of my assumptions? 
The free body diagram really doesn't describe *all* the physics of a motorcycle in mid stoppie. It is however 100% valid even for the beginning of a stoppie; just split the weight reaction between front and rear accordingly. We would need a few more arrows to address the dynamic effects of any rapid changes in the bike/rider's attitude.
You need to "generate a vertical component"? Nope, the horizontal force will do just fine.
Cool! What space station parts did you design? |
Spiderman
| | Posted on Monday, December 30, 2002 - 05:42 pm: |
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Were all speed record holders. Do you have any Idea how fast the Earth is zooming through space around the sun right now, or even how fast our solar system is moving through the milky way?
A cookie goes to the first person who can tell me |
Blake
| | Posted on Monday, December 30, 2002 - 05:45 pm: |
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Gee Hans, you even clarified originally that "A human body in free fall, not a special diving attitude, is supposed to reach a maximum speed of 320 km/hour = 198 MPH." |
Hans
| | Posted on Monday, December 30, 2002 - 06:49 pm: |
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Blake, It was written in an explanation of the survival of a WWII bomber pilot who`s parachute has been burnt when he had to leave the plane at high altitude. He landed on a huge pine with a heap of snow under it. I can imagine how he fell just next the top, his fall broken by the first thin branches, which put him also somewhat sideways so he met each time the ends of the next heavier branches. It is thinkable that 60 feet for deceleration can be enough to survive a speed of 200 MPH. The story was told as being true. The crashes at formula 1 races make it also acceptable.
Hans |
Stormfool
| | Posted on Monday, December 30, 2002 - 06:50 pm: |
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I'll take a wild guess 28,000 feet per second? (I guess I could have looked it up in my astrophysics textbook) Okay do I get my cookie? |
S320002
| | Posted on Monday, December 30, 2002 - 07:19 pm: |
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Blake,
I did the mechanical and thermal design for several power supplies. I also helped design the system that is used to switch from solar panel power to battery power when the Station goes into eclipse. There was more but those are some of the high points.
By the way. If your butt don't go up it ain't no stoppie. I think you're arguing semantics here.
Greg;-) |
Jima4media
| | Posted on Monday, December 30, 2002 - 11:01 pm: |
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OK, the guy jumped out of a balloon at 108,000 feet, but he came down feet first, and not spread eagle or head first.
The woman attempting this jump wants to use an aerodynamic helmet, that will break the sound barrier.
The 25,000 MPH figure was what I was looking for Blake.
I would like to know how fast our solar system is rocketing away from the point of the big bang. Anybody have that figure? |
Dynarider
| | Posted on Monday, December 30, 2002 - 11:28 pm: |
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I would like to know how these folks are freefalling faster than terminal velocity? |
Dynarider
| | Posted on Monday, December 30, 2002 - 11:38 pm: |
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Found these little tidbits...."However, by diving or "standing up" in free fall, any experienced skydiver can learn to reach speeds of over 160-180MPH. Speeds of over 200MPH require significant practice to achieve. The record free fall speed, done without any special equipment, is 321MPH. Obviously, it is desirable to slow back down to 110MPH before parachute opening." |
Dynarider
| | Posted on Monday, December 30, 2002 - 11:41 pm: |
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And this from Joseph Kittinger..."An hour and thirty-one minutes after launch, my pressure altimeter halts at 103,300 feet. At ground control the radar altimeters also have stopped-on readings of 102,800 feet, the figure that we later agree upon as the more reliable. It is 7 o'clock in the morning, and I have reached float altitude.... Though my stabilization chute opens at 96,000 feet, I accelerate for 6,000 feet more before hitting a peak of 614 miles an hour, nine-tenths the speed of sound at my altitude." |
Aesquire
| | Posted on Tuesday, December 31, 2002 - 01:50 am: |
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Average human in free fall, spread stable position, about 120mph in street clothes. Up to 200mph in a delta "track" position. I think the fastest humans have traveled in a vehicle is Apollo 13 on the return trajectory from the moon. |
Hans
| | Posted on Tuesday, December 31, 2002 - 02:01 pm: |
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"Average human in free fall, spread stable position, about 120mph in street clothes."
Ha, even much better, that very moderated speed by the wind drag.
Hailstones, as big as dove eggs, shooting down with sound speed, would frighten me.
Happy New Year. |
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