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Sorry Dave, I'm a little late to the game, but I keep coming up with 1.862"
Of course I'm just using my old TI-59, not a fancy CAD program...
GUSTO
I agree with the 1.862". You could be specious with the accuracy and state 1.8615418", but given the initial parameters which held a degree of precision to one decimal place (5.7"), then the answer should be 1.9".
In a 327 Corvette engine, with a 3 1/4" stroke, and 5.7" connecting rods, if the crankshaft is rotated 90° from piston TDC, how far down is the piston in the cylinder?
I am working on it , but there is no doubt that my crankshaft will move a rod very fast at 80 to 90 degrees
. it is a Post Versalog...) a picture of a 'thing of beauty',
Bill
:
Every engineering student had one of those on his belt until about 1974, then bang, they were replaced by expensive, barely functional scientific calculators that year. A couple guys were hold outs and could make their slide rules heat up from friction with how quick they were with them. I lost that skill shortly after the digital calculators arrived.
But yeah, the tests went from four to six questions with the intro of calculators.
I was going to post (pun intended.. it is a Post Versalog...) a picture of a 'thing of beauty', but Jackfit beat me to it....
Bill
btw, I like 'blue' better, and I have a red car....
My dad's K & E Log Log Duplex Decitrig he used in engineering school and then passed down to me to use in engineering school. My son saw it when he was in high school and asked me what kind of ruler it was.
Does anyone have a program in their computer thatll allow you to draw a side view of the C/L's on the crankshaft, rod journal and wrist pin in both TDC and 90° ATC? Then we could show the arc of the rod journal C/L as it would be if allowed to swing back to cyl C/L?
That would show the additional distance that the wrist pin/piston moved downward. If not, I'll try to draw a pic and scan/post.
That should make it easier to understand why pistons move further and faster in the 1st 90° of C/S rotation.
I am late for the party, but my father taught me to visualize the connecting rod with the big end on the main bearing centerline and note the wrist pin is half way down the bore. Then move the big end out to the crank throw at 90 degrees, and visualize the wrist pin dropping the extra distance of the length lost due to the big end offset.
While this math seems academic, the value is in predicting the dynamic compression ratio when the intake valve closes on the compression stroke (or in my initial education, the roof of the exhaust port of a 2-stroke is blocked by the top ring as the piston rises). If the intake valve closes at 90 degrees before TDC, the cylinder can experience more than 1/2 of the static compression ratio (dependent upon the chamber volume). The dynamic compression ratio at the point of ignition is critical to design around detonation and to idealize the spark advance map. In the design of a Diesel it determines the rpm where compression ignition provides maximum combustion efficiency and torque.
During my youthful motorcycle focus I was all wrapped up on designing the ideal 2-stroke exhaust port height to achieve expansion chamber scavenging from cylinder pressure and pipe restriction and resonant wave backpressure. My father watched me resolve the math wrong, and then correctly, before commenting to focus on the three things needed for combustion first (air/fuel, heat of compression, ignition). It took a while to recognize it is much easier to motivate movement of burnt exhaust gas at 200 PSI, than to motivate movement of a mixed air/fuel intake charge at 14.7 psi (or in my 2-stroke world the crankcase pressure). The intake valve closing point, or dynamic compression start point, drives the one element of the combustion requirements that cannot be easily changed once the engine is assembled. Get the dynamic compression correct and the rest follows (the rest being mixed flow fluid dynamics in the intake and the scavenging pressure wave dynamics in the exhaust, and all the stuff the Taylor text in a University IC Engines course barely covers).
Solving the mystery of the optimal internal combustion engine never ends...
I am late for the party, but my father taught me to visualize the connecting rod with the big end on the main bearing centerline and note the wrist pin is half way down the bore. Then move the big end out to the crank throw at 90 degrees, and visualize the wrist pin dropping the extra distance of the length lost due to the big end offset.
That's exactly right.
I did it the other way around though. I visualize the rod connected to the crankshaft at 90°, then swinging back to main bearing centerline. Same thing, just a different way to get there.
And this is why piston velocity and acceleration is greatest in the top half, or first 90° of it's travel. (somewhere around 70-80°)
And that brings up several new subtopics for this discussion but I'll go there a little later.
As a Freshman Engineering Student back in the 60's I couldn't afford one of these, so I had to make do with the standby plastic one's from the book store. Later as a Flight Student with a steady pay check I managed to afford, not just one, but two Pickett's. (The white one solves Electrical Engineering formulas on the back.) If you're old enough to remember them (Pickett's that is), you're probably old enough to remember when they rolled out the '63 Corvette as well.
When my son was in High School, I took them out and taught him how to use them. Surprisingly he thought it was pretty cool, but not nearly good enough for his engineering courses. Most folks don't realize that these things were used (at times) to put a Man on the Moon. We were even issued a round one we affectionately called the "Wiz Wheel" at flight school to calculate wind drift. Particularly useful for long overwater flights, well before GPS and many aircraft that weren't yet equipped with Inertial Navigation.
As a Freshman Engineering Student back in the 60's I couldn't afford one of these, so I had to make do with the standby plastic one's from the book store. Later as a Flight Student with a steady pay check I managed to afford, not just one, but two Pickett's. (The white one solves Electrical Engineering formulas on the back.) If you're old enough to remember them (Pickett's that is), you're probably old enough to remember when they rolled out the '63 Corvette as well.
When my son was in High School, I took them out and taught him how to use them. Surprisingly he thought it was pretty cool, but not nearly good enough for his engineering courses. Most folks don't realize that these things were used (at times) to put a Man on the Moon. We were even issued a round one we affectionately called the "Wiz Wheel" at flight school to calculate wind drift. Particularly useful for long overwater flights, well before GPS and many aircraft that weren't yet equipped with Inertial Navigation.
Still can't bring myself to part with them...
GUSTO
I remember Picket slip sticks. Never saw one like your white one, though. Pretty cool.
I was a junior in high school and I definitely remember the '63 roll out. I didn't like them. I preferred the '59 - '62. But, that's been the story for me for every newly released Corvette model. Eventually I warm up to them (except the C4 )
You know, if that guy that had the stuck distributor had a couple of them there fancy slide rules, he coulda' put one on one side and one of the other and popped that sucker right outa' there!
Every engineering student had one of those on his belt until about 1974, then bang, they were replaced by expensive, barely functional scientific calculators that year. A couple guys were hold outs and could make their slide rules heat up from friction with how quick they were with them. I lost that skill shortly after the digital calculators arrived.
But yeah, the tests went from four to six questions with the intro of calculators.
Doug
at Purdue we were NOT allowed to use calculators as it was a unfair advantage to those who could afford them....
think of the 'eons' in which 'things' were designed and built to "slide rule accuracy"....
As a Freshman Engineering Student back in the 60's I couldn't afford one of these, so I had to make do with the standby plastic one's from the book store. Later as a Flight Student with a steady pay check I managed to afford, not just one, but two Pickett's. (The white one solves Electrical Engineering formulas on the back.) If you're old enough to remember them (Pickett's that is), you're probably old enough to remember when they rolled out the '63 Corvette as well.
When my son was in High School, I took them out and taught him how to use them. Surprisingly he thought it was pretty cool, but not nearly good enough for his engineering courses. Most folks don't realize that these things were used (at times) to put a Man on the Moon. We were even issued a round one we affectionately called the "Wiz Wheel" at flight school to calculate wind drift. Particularly useful for long overwater flights, well before GPS and many aircraft that weren't yet equipped with Inertial Navigation.
Still can't bring myself to part with them...
GUSTO
I had one of those "Wiz Wheels" too when I was in the flight program at Embry-Riddle in Daytona in '69.
Finally had a chance to click on the links that you posted. (2nd link was the best) Very good description of piston position/motion. Much better than what I tried to explain. Thanks.
Finally had a chance to click on the links that you posted. (2nd link was the best) Very good description of piston position/motion. Much better than what I tried to explain. Thanks.
I agree, and this is essentially how I came up with the solution of 1.862 ". Except, I didn't utilize sine, cosine, or tangent, at least not directly. I just used the Pythagorean theorem or A² + B² = C² In any right triangle, the length of the hypotenuse squared is equal to the length of side A squared and the length of side B squared.
At TDC we know that the distance from crank center-line to the wrist pin center-line is equal to ½ the stroke plus the length of the connecting rod (1.625" + 5.7") or 7.325"(where the piston starts from) For the sake of this problem, we can ignore the distance from the top of the piston to the wrist pin center-line.
Now we will need to determine the new distance from the wrist pin center-line to the crank center-line when the crank throw is at 90°. We will call the distance A, and since we’re dealing with a right triangle that will make the length of the connecting rod C(or the hypotenuse). That will leave B as the distance from the crank center-line to the big end of the rod, or ½ the stroke. We need to solve for A and subtract that from the same distance at TDC to determine how far down the cylinder the piston has traveled.
Using the Pythagorean theorem, we need to solve for A or A = the √ (square root) of C² minus B²
C² = 32.490 and B² = 2.641 therefore C² minus B² = 32.490 – 2.641 or 29.849 the √ of which is 5.463 = A
Subtract A from the distance we calculated above at TDC (7.325) and you have the distance the piston has traveled down the cylinder at 90° or 1.862"
Man, all this math makes my head hurt... I need to go stare at Jackfit's picture above for a few minutes...
I agree, and this is essentially how I came up with the solution of 1.862 ". Except, I didn't utilize sine, cosine, or tangent, at least not directly. I just used the Pythagorean theorem or A² + B² = C² In any right triangle, the length of the hypotenuse squared is equal to the length of side A squared and the length of side B squared.
At TDC we know that the distance from crank center-line to the wrist pin center-line is equal to ½ the stroke plus the length of the connecting rod (1.625" + 5.7") or 7.325"(where the piston starts from) For the sake of this problem, we can ignore the distance from the top of the piston to the wrist pin center-line.
Now we will need to determine the new distance from the wrist pin center-line to the crank center-line when the crank throw is at 90°. We will call the distance A, and since we’re dealing with a right triangle that will make the length of the connecting rod C(or the hypotenuse). That will leave B as the distance from the crank center-line to the big end of the rod, or ½ the stroke. We need to solve for A and subtract that from the same distance at TDC to determine how far down the cylinder the piston has traveled.
Using the Pythagorean theorem, we need to solve for A or A = the √ (square root) of C² minus B²
C² = 32.490 and B² = 2.641 therefore C² minus B² = 32.490 – 2.641 or 29.849 the √ of which is 5.463 = A
Subtract A from the distance we calculated above at TDC (7.325) and you have the distance the piston has traveled down the cylinder at 90° or 1.862"
Man, all this math makes my head hurt... I need to go stare at Jackfit's picture above for a few minutes...
GUSTO
Thanks Gusto. That shows that there's more than one way to get there. We may have lost a few folks on the way though.
The solution for all triangle problems is also found in "Machiners Handbook". A wealth of information about everything to do with everything.
As a Freshman Engineering Student back in the 60's I couldn't afford one of these, so I had to make do with the standby plastic one's from the book store. Later as a Flight Student with a steady pay check I managed to afford, not just one, but two Pickett's. (The white one solves Electrical Engineering formulas on the back.) If you're old enough to remember them (Pickett's that is), you're probably old enough to remember when they rolled out the '63 Corvette as well.
When my son was in High School, I took them out and taught him how to use them. Surprisingly he thought it was pretty cool, but not nearly good enough for his engineering courses. Most folks don't realize that these things were used (at times) to put a Man on the Moon. We were even issued a round one we affectionately called the "Wiz Wheel" at flight school to calculate wind drift. Particularly useful for long overwater flights, well before GPS and many aircraft that weren't yet equipped with Inertial Navigation.
Still can't bring myself to part with them...
GUSTO
Wow, this thread brings back a LOT of memories! Somewhere packed away in storage i have a number of old slide rules, including my grandfathers which, IIRC what my Dad told me, is in fact real ivory veneer overlaid on a mahogany inner core.
As for myself, I went through engineering school using both plastic and metal ones - the one I used the most was (I think) aluminum with porcelain like yellow finish. No way my Dad was gonna trust me with the family heirloom one at that point!
In civil engineering/surveying the demand for trig functions was huge. Remember those thick reference books of trig tables? That and the slide rule were key tools of the trade. We also used a Curta calculator - see pic below -remember those?
When I got out of school in 1971 we were still using those old tools and references. In 1972 HP came out with the HP-35 digital calculator with built in trig functions, and eliminated the need for those ponderous books of trig tables. Why it was darn near God's gift to engineering!
I was making $800.00 per month, and couldn't move fast enough to spend half my monthly salary on an HP-35 at only $395.00 each!
Those were the days - when technology actually made things simpler and easier!
Last edited by tuxnharley; Feb 6, 2017 at 03:15 PM.
Reason: typo
Wow, this thread brings back a LOT of memories! Somewhere packed away in storage i have a number of old slide rules, including my grandfathers which, IIRC what my Dad told me, is in fact real ivory veneer overlaid on a mahogany inner core.
As for myself, I went through engineering school using both plastic and metal ones - the one I used the most was (I think) aluminum with porcelain like yellow finish. No way my Dad was gonna trust me with the family heirloom one at that point!
In civil engineering/surveying the demand for trig functions was huge. Remember those thick reference books of trig tables? That and the slide rule were key tools of the trade. We also used a Curta calculator - see pic below -remember those?
When I got out of school in 1971 we were still using those old tools and references. In 1972 HP came out with the HP-35 digital calculator with built in trig functions, and eliminated the need for those ponderous books of trig tables. Why it was darn near God's gift to engineering!
I was making $800.00 per month, and couldn't most fast enough to spend half my monthly salary on an HP-35 at only $395.00 each!
Those were the days - when technology actually made things simpler and easier!
I also went to work for a civil engineering company in 1971. Shortly thereafter, I bought this Radio Shack 4-function hand-held calculator for $100. As I recall, it was about the same dimensions as an iPhone 7 BUT about 1" thick. My how things have changed.
Was so inspired by this trip down memory lane that I went looking for my old yellow K & E to no avail. I did however come across these that belonged to my father. One, from The Frederick Post Co., No. 1441, is labeled, "Hemmi" and "Made in Japan" on the back side. The other simply bears an inscription, "DIETZGEN," in the area under the slide. Since my father was a lawyer and an FBI Agent, I've often wondered how he might have used these items. I do remember him teaching me the basics of their operation while I was in elementary school. Much later in college, I remember having to stick with a slide rule and not being allowed to use an electronic calculator as that would have been an "unfair advantage." I so hated the whole math thing that I also went to law school, became a prosecutor, then a judge - all because of slide rules.
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Slideshow: A Jaguar designer's personal project imagines what a modern front-engined Corvette might look like if Chevrolet revisited the golden age of the Stingray.
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