Landracing Forum
Bonneville Salt Flats Discussion => Bonneville General Chat => Topic started by: fjlee on October 25, 2015, 09:22:07 PM
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At Bonneville and other LSR sites, I often see the term "measured mile".
Exactly how is this mile measured? What is the accepted degree of accuracy that
must be achieved?
Could the same measuring regimen be used to measure and set-up a "measured 10 mile"....?
Thanks folks.......
FjLee Denver CO
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Since the 1980s, electronic distance measurement (EDM) devices have allowed surveyors to measure distances more accurately and more efficiently than they can with tapes. To measure the horizontal distance between two points, one surveyor uses an EDM instrument to shoot an energy wave toward a reflector held by the second surveyor. The EDM records the elapsed time between the wave's emission and its return from the reflector. It then calculates distance as a function of the elapsed time. Typical short-range EDMs can be used to measure distances as great as 5 kilometers at accuracies up to one part in 20,000, twice as accurate as taping.
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They can also measure with GPS. Don't know how they do it at Bonneville or any of the mile and mile n a half tracks. Watched them survey the neighbors place, the guy said he was accurate to about .100 inch to 3mm... I didn't do the math for speeds, but that sounds pretty close... especially if you are placing a rod that is about an inch.
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are you asking how they measure the actual distance for the mile or how they measure how fast a vehicle goes thru said mile?
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are you asking how they measure the actual distance for the mile or how they measure how fast a vehicle goes thru said mile?
"Thank you" for the responses.
I'm asking how the actual distance for the "measured mile" is determined.
I'm also curious as to how a longer distance would be measured with precision. Say 10 or 20 miles.
FjLee Denver CO
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are you asking how they measure the actual distance for the mile or how they measure how fast a vehicle goes thru said mile?
"Thank you" for the responses.
I'm asking how the actual distance for the "measured mile" is determined.
I'm also curious as to how a longer distance would be measured with precision. Say 10 or 20 miles.
FjLee Denver CO
Assumptions: You are talking in a straight line. Line of sight is unobstructed.
GPS measurement would be easiest because you would not need line of sight and could still measure the distance. This would also include elevation changes.
You could use the method above with EDM. While limited to shorter distances than you are talking, you could measure and move the equipment for the next leg. Four or five hops would get you where you need to be.
How accurate do you need to be? You could use a tape measure or a wheel measuring device provided the terrain would support the accuracy you needed. I've laid out a five mile course with an odometer on a car and handheld GPS for bicycling as backup. I don't know that the SCTA or FIA would call that qualified to be record worthy but I can tell you a VASCAR device from a cop car would read the speed to within a mile an hour or two.
What are your goals? what are you trying to accomplish? With a little more context I am sure we can get you what you need or point you in the right direction.
You
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>>>>Assumptions: You are talking in a straight line. Line of sight is unobstructed.
Line of sight=yes, at least for 1 mile.
Line of sight is unobstructed=not necessarily, in the case of the longer distances.
Let's also assume as measured on B. Salt Flats for an LSR event.
>>>>What are your goals? what are you trying to accomplish?
My goals??? I guess my goal, at least for this posting, is to find out how various distances are measured
and marked, out on the salt, prior to an LSR event. Especially the distance that'll ultimately be used to calculate
an average speed.
The AMA, FIM, etc.......what level of accuracy do they spell out?
Is it spelled out in feet and inches.....or is it as a percentage of something?
I find it an interesting mental exercise to realize for instance, that the timers start at POINT A, and timers stop
at POINT B. A to B is laid out so that it is a straight line 1 mile in length 'tween A and B. But no
vehicle ever made will travel that AB line in a perfectly straight line. There hasta be a certain degree of "meander"
to the actual vehicle path. So the vehicle actually travels more than 1 mile during a timed run.
I'm thinking that the calculations assume it's exactly 1 mile tween A and B.
I think that the measurement of "time", on the salt, is more accurate than the measurement of "distance".
But that doesn't detract from my enjoyment of any LSR event I've ever watched.
Thanks, folks.......
FjLee Denver CO
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SCTA=BNI Hires a certified Engineering company from Salt Lake city to survey and mark the courses at Bonneville. Each mile is marked and a survey tag is placed in the salt as well as a red paint strip and a stake.The long course is marked in this order 1 mile, 2 mile 2-1/4 mile 3 mile 4 mile, 5 mile and a 132 trap at end of the 5 mile. This is done on all courses. The 3 mile short courses are only timed to the 3rd mile. There are mile marker flags to the 8 mile for the driver/rider know their position for shut down. If there is a Kilo used for a international event FIA / FIM it is marked in the center of the mile timing trap in the middle of the course depending how long the over all length of that course is. :cheers:
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FJ, you're right about the fact that it's danged near impossible for any of us to ride/drive perfectly straight over the mile(s). The distance is measured between the timing points -- lights, flags, smoke cans, or whatever. And the vehicle's operator does his best to go straight -- but the wind, the course conditions, the vehicle's handling - and all sorts of other things - help make the traveled distance be a tad (or a bunch) more than a mile. YMMV -- so to speak. :-D
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Ok. Do they put 21,120 1-2-3 blocks end to end or do they use a tape measure or do they measure it optically or sonically or GPSally? I'm sorry. I'm having a bit of trouble seeing the answer to the original question. :roll: Wayno
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Wayno, Maybe a Colorado smoke induced question 8-)
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Ok. Do they put 21,120 1-2-3 blocks end to end or do they use a tape measure or do they measure it optically or sonically or GPSally? I'm sorry. I'm having a bit of trouble seeing the answer to the original question. :roll: Wayno
Dang, Elmo............I like it!! I had originally thought that for super precision, maybe they used a whole bunch of Jo blocks, wrung together!!
FjLee Denver CO
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Wow. The cumulative error would be significantly greater with Jo blocks. 1-2-3 blocks would be bad enough. I bet they have a designated 5,282 foot string and they burn a foot on each end. :-D Wayno
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I would be interested to know, historically, the measurement schemes used. For instance, in 1914 (I think?) how the distance was measured for the inaugural FIM landspeed record.
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FJ, you're right about the fact that it's danged near impossible for any of us to ride/drive perfectly straight over the mile(s). The distance is measured between the timing points -- lights, flags, smoke cans, or whatever. And the vehicle's operator does his best to go straight -- but the wind, the course conditions, the vehicle's handling - and all sorts of other things - help make the traveled distance be a tad (or a bunch) more than a mile. YMMV -- so to speak. :-D
If you do the math, is not a lot different( is a "tad"). For instance say the track is 100ft wide and 1 mile long and you start at one edge of the track and end on the other side at the finish line ( and I think generally we do not wander that much) you travel 0.9468feet farther. :cheers:
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I think they use a different system for the roadsters after the 3 mile.
Doug :cheers: :cheers: :cheers:
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Buick, you are correct; for me it was after the 4 mile when I got a tad bit longer course. A 32 grille shell being pushed does not like to run of of horsed power especially over 200. I moved from side to side at least twice, never lifted, and got a red hat. JD
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We like pitting past the three mile so that we can see all sides of the roadsters comming by.
Doug :cheers: :cheers: :cheers:
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We use Topcon global navigation technology and are accurate within .020". We compared it against the SCTA clocks a few years back and we were dead nuts on.
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Not much -- but stipulate that you're traveling at a constant speed for the entire measured mile -- and your true speed is 200.031. but since you've traveled that extra 11 3/8 or so inches -- your measured speed (using the lights set one mile from one another) would be 199.995. Dang! I didn't get my hat -- 'cause I wandered from one side to the other.
Realistically speaking -- making it down the track 100% dead straight ain't very likely to be possible. But still -- the less wandering the better, right? :-D
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Just gives you more space to accelerate :cheers:
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He He He, John. :-D :-D :-D :-D
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Not much -- but stipulate that you're traveling at a constant speed for the entire measured mile -- and your true speed is 200.031. but since you've traveled that extra 11 3/8 or so inches -- your measured speed (using the lights set one mile from one another) would be 199.995. Dang! I didn't get my hat -- 'cause I wandered from one side to the other.
Realistically speaking -- making it down the track 100% dead straight ain't very likely to be possible. But still -- the less wandering the better, right? :-D
...now I understand my 199.665 mph.....the mile was too Long...... :-D :-D :-D :-D :-D :-D :-D :-D
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The mile was the correct length. Your navigation of the mile was the long way there.
DW
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Well put, Dan. I've never thought to put pencil to paper and figure out the extra length we drive down the mile(s), so now that I have -- I see that it's a real issue and worthy of consideration when planning a run - waiting at the line - riding the course in my mind before I leave.
And watch out for those mile markers, too! They've been known to jump out in front of racers, I hear. :roll:
"Oak tree, you're in my way!"
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The mile was the correct length. Your navigation of the mile was the long way there.
DW
Dan,
the navigation on my return run in August 2012 was actually very well....albeit that this morning the fifth mile was a little bit "wet"....through the five I had a clean straight line....what I can't say for the first 1/4 mile after I left the starting line :roll:....on this run I also picked my A license..... :-D......sometimes you can press the pedal through the metal all the way down...and you are still to short......but, d..mn....this was my first record....and happy.....
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PP, You did an outstanding job driving the lakester and you are maybe the only driver that did not break anything except the record :cheers:
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Ya know, it may be a mile on the surface between the markers, but with the earth's curvature, it's a little less in a real straight line (but hard to take that course).
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A measured mile is available. The run is to determine how long it takes
to make that excursion. It matters not at all to the clocks what route
you use inside the measured distance. All it does is record the time.
The clocks don't care what your speed is as you break the beam. All they
record is the elapsed time. With a reliable distance between the clocks and
a repeatable time measurement the speed between the clocks is used as
the record. There's nothing else to it. Obviously going straight is the optimum
method. Have an alcoholic explain the situation. It will compare to driving on the Salt.
FREUD
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.... Have an alcoholic explain the situation. It will compare to driving on the Salt.
FREUD
Freud, that's been what has been happening for the last 2 pages.... :roll:
:cheers:
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Stan, you are correct about the curve and a straight line shot being different,,,
But at El Mirage, the Rod Riders layout the course, with the assistance of the Board. And the measured mile plus is done by calibrated machines inside three vehicles to make sure of the distance. The machines are checked against a know distance of 1000 feet.
So as the vehicles move down the lake bed they are traveling with the curve of the earth and are traveling on the surface there by getting the correct 'measured mile +" for El Mirage.
As they have done for over 20 years.
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Obviously going straight is the optimum method.
The question was about Bonneville and "other" LSR sites. For the pavement flying miles, some entrants might benefit from lengthening the runup by zigzagging a bit.
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Wouldn't the zigzag be counter productive by introducing friction(loss of speed) in the attempt to increase top end? In road racing they tell us to straighten the turn, use as little steering input possible.
DW
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Ya know, it may be a mile on the surface between the markers, but with the earth's curvature, it's a little less in a real straight line (but hard to take that course).
If my math is correct the difference is .065" more or less if the surface follows the curve of the earth rather than being flat. Not a whole bunch. (that's for a mile, longer course the difference is more)
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Thanx!
I thought it would be a little more than that -- but not significant.
Years ago at a Pomona meet, Frank Cannon was running the Torquemaster(?) automatic(?) AA/F dragster and, to me, apparently weaving around down the strip. The car wouldn't ET, but it put up some significant MPH. It supposedly ran the first two 200 MPH runs on the same day.
Who knows?
(The Shadow do.)
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Wouldn't the zigzag be counter productive by introducing friction(loss of speed) in the attempt to increase top end? In road racing they tell us to straighten the turn, use as little steering input possible.
DW
Going straight is a good method. However, a vehicle with a very low power/weight ratio but good aero might benefit from accelerating for a longer time before the trap.
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I use to run a Parabola path until I took out 7 cones. About the time I was closest to the left side of the track my spray went to 100% lifting the front end slightly. Big crosswind gust came along and pushed me into the cones. From now on, it's a straight path for me.
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Wouldn't the zigzag be counter productive by introducing friction(loss of speed) in the attempt to increase top end? In road racing they tell us to straighten the turn, use as little steering input possible.
DW
Going straight is a good method. However, a vehicle with a very low power/weight ratio but good aero might benefit from accelerating for a longer time before the trap.
some zig zag has been discussed earlier, at least in theory. Pretty much all you get is a few feet unless really going back and forth a lot that that clearly would not be conducive to speed. YMMV so to speak :roll: pun intended
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I would think that by doing a zig zag while going down the race course could make the opportunity more likely that you will spin out, thus ending you run. :?
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I did enough zig zaging in 2009 between the 4 and 5 mile, I didn't like that at all.
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In my early days on big industrial construction, we laid out mile long tracts at times, using what is called a surveyors chain. which, for as long as I have been involved, is not a real chain at all. It is a 100 foot long piece of precision steel tape that is stretched to a certain tension using a precision tensioning weight scale that has a clamp attachment for holding the tape. The ambient temperature was also factored in based on the expansion co-efficient of the steel alloy of the chain. It was actually quite accurate but a rather time consuming process as the course was measured literally 100 feet at a time. Maybe that is why there was such resistance on the part of the executives of SCTA/BNI to multiple courses as recently as the very early 1990s.
In the 70s, I believe that Elmo Gillette, who was a representative of Kueffel & Esser (makers of high quality surveyor equipment), used to do this ..... Later on, I know he had optical devices that were quite accurate in double checking (I guess, it was nice to be able to borrow this stuff on an as needed basis)
Now, I cannot state with certainty that the courses of 100 or so years ago were measured as I described but the process for doing so had been developed back then....
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Here's an excerpt from Bret Kepner's 4-page article in the 2014 SpeedWeek Program about the first "timed" event at Bonneville . . .
"Many of the drivers limbered up their mounts by racing the trains, much to the astonishment of passengers. Initially, electric timers were to be used to conform to new AAA guidelines. Unfortunately, voltage fluctuations in the telegraph lines made the clocks useless. It was discovered heat waves and the blinding glare from the salt made the waving of the officials’ flags at the start and finish of the flying mile attempts impossible to see. This led to a decision which would dramatically affect the event’s place in history. Rishel and Moross decided to use stopwatches to time the runs over a half-mile course."
Don't remember how it was measured, but with the stopwatches, who cares.
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We used to take that steel tape out and "chain" distances. A mile would take twenty six chains with a 200 foot plus a little one at the end. It was hard work. Fortunately the highway department allowed us to have a beer or two during lunch. (This was in the good old days.) Almost always, we would foul up the calculations after lunch and spend an hour or two mixing them up even more while we tried to straighten them out. Now we used electronic distance meters and a couple of educated chimps can do twice as much with more accuracy than a crew of four did thirty years ago.
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Which brings us to today. GPS? What is the opinion on this?
Doug :cheers: :cheers: :cheers:
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It is more accurate than us after our lunchtime beers.
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Anecdote offered for the sake of the discussion:
A handful of years - (10++?) one of the companies represented in the local engineering club's roster put on a presentation on using GPS for surveying. One of the principals on the board is a "LS" - the next notch up from regular licensed surveyor, I guess, and therefore knows his stuff. Anyway, he reported that the GPS was still kinda new to them - and the industry - so on one long line -- about ten-fifteen miles -- they used both GPS AND traditional surveying chains and stuff, just for the sake of comparing.
In that long line -- they came out dang near exactly identical. As I remember, Gerry reported that the difference in the two methods, after all those miles of hills and trees -- was about the diameter of a DIME.
And that was a bunch of years ago when things weren't as developed as they are now. Geez, maybe that GPS stuff will work some day soon, hey? :-D
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Lets say the timing should be accurate to 0.01 second. A bike or car traveling at 60 mph moves 0.88 feet in 0.01 seconds. The distance marks should be within a few inches to get accurate times.
A guy or gal traveling at 400 mph travels 5.87 feet in 0.01 second. The timing marks need to be within a couple of feet to provide plenty of accuracy.
A skilled operator with a GPS setup made for accurate work should be able to set the timing marks up plenty good for the 60 mph guy and much more accurate than needed for Poteet and Main.
Fortunately at Bonneville there are plenty of GPS satellites in the line of sight. This is a big help.
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Lets say the timing should be accurate to 0.01 second.
Based on what? A bike or car traveling at 60 mph moves 0.88 feet in 0.01 seconds. The distance marks should be within a few inches to get accurate times.
A guy or gal traveling at 400 mph travels 5.87 feet in 0.01 second. The timing marks need to be within a couple of feet to provide plenty of accuracy.
A "couple of feet" error in a measured mile is .038% . That's .15 mph error for a 400 mph run: way too much. Records are posted to thousandths of a mph.
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A record measured to the thousandth of am MPH would need the course laid out so the mile marks are within the distance the bike or car would travel in one thousandth of a second. 0.001 second x (60 miles / hour) x (1 hour / 60 minutes) x (1 minute / 60 seconds) x (5,280 feet / 1 mile) = 0.088 feet The vehicle would travel 0.088 feet in 0.001 second. That is a little more than an inch at 60 mph.
Today I asked our survey crew about GPS accuracy. They said the typical hand held one you buy at the store is good for 20 or 30 feet accuracy. This can be increased by using an antenna. They have a survey grade GPS setup that costs $20,000 to $30,000 dollars typically. It can locate a point within a tenth of a foot accuracy. This is 1.2 inches.
The typical way of doing these measured miles is by an electronic distance meter. These are fairly cheap and give good accuracy. Measuring them out in short segments like 200 or 300 feet helps to take into account the curvature of the earth.
"Hire a registered land surveyor and tell him/her the accuracy you need and they will lay the course out. The precision needed to time a vehicle to the nearest 0.01 second is a bit much for the average person. Some real good equipment and skill is needed." This was the final advice the survey crew gave me. This advice is even more applicable for a course laid out to time vehicles to the nearest 0.001 second.
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You have to factor in the margins required by the FIA/FIM, much closer than you states. Did you know that the Rice Brothers, Allen and james, who are the officail timers for SCTA, BMST, FIA and FIM are certified to set the track? They use modern laser technology equipment.
DW
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You have to factor in the margins required by the FIA/FIM, much closer than you states.
Appendix D of the FIA international Sporting Code.
"D5.1.2 Measurement. The length of the Course must be
measured and duly certified to within 1/10,000 of its length."
That's 6.336" for a measured mile.
Go figure.
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A record measured to the thousandth of am MPH would need the course laid out so the mile marks are within the distance the bike or car would travel in one thousandth of a second. 0.001 second x (60 miles / hour) x (1 hour / 60 minutes) x (1 minute / 60 seconds) x (5,280 feet / 1 mile) = 0.088 feet The vehicle would travel 0.088 feet in 0.001 second. That is a little more than an inch at 60 mph.
A record is not measured to 0.001 mph. Although record speeds are reported to three decimal places. The measured parameter is time, which may be recorded to many decimal places but is then truncated to 3dp for (FIA) record purposes.
This means it is not possible for many mph numbers to be reported as record speeds. For example:
- If the time recorded is 8.999 seconds, then the speed is 400.044 mph
- If the time recorded is 9.000 seconds, then the speed is 400.000 mph
- If the time recorded is 9.001 seconds, then the speed is 399.955 mph
So speeds of 400.001, 400.002, etc. are not possible using the (FIA) rules for calculating average speeds.
The above analysis does not apply to SCTA record calculations.
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A record is not measured to 0.001 mph. Although record speeds are reported to three decimal places. The measured parameter is time, which may be recorded to many decimal places but is then truncated to 3dp for (FIA) record purposes.
Hmm . . .
So if you're timed at 7.2009 for the mile, which figures to 499.9375 mph, you'd be credited as going 500.
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A record is not measured to 0.001 mph. Although record speeds are reported to three decimal places. The measured parameter is time, which may be recorded to many decimal places but is then truncated to 3dp for (FIA) record purposes.
Hmm . . .
So if you're timed at 7.2009 for the mile, which figures to 499.9375 mph, you'd be credited as going 500.
Yep. It needs someone smarter than me to explain why this is considered to be the "correct" way to do the calculation.
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A record is not measured to 0.001 mph. Although record speeds are reported to three decimal places. The measured parameter is time, which may be recorded to many decimal places but is then truncated to 3dp for (FIA) record purposes.
Hmm . . .
So if you're timed at 7.2009 for the mile, which figures to 499.9375 mph, you'd be credited as going 500.
Yep. It needs someone smarter than me to explain why this is considered to be the "correct" way to do the calculation.
SCTA/BNI does not round up numbers.It's always been that way.
I was the chief timer for many years and that's the rule.
I also remember where a chain was used to mark off the miles, as I remember it was 100 feet long with links marked for the 1/4 and the feet in miles/ft. Took a long time to measure but we only had one course. :roll:
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Use of the GPS is what I am typing about. This is a complex subject and there is much more to it than this.
Setting points with the GPS is dependent on the proper equipment, skill, and calibration. The end product is two points located on the salt. The big question is, are they within the allowed error tolerance? One can assume if the equipment and operation is adequate that the points are correctly placed. This is an unproven assumption.
Chaining or EDM are surface measurements. The crew proceeds from the first point to the second. They set that point. Then they measure back to the first. The difference between the two is closure. The closure needs to be within the allowed tolerance. One has been mentioned in a previous post. One problem is if the instrument is out of calibration. Then, using the same instrument to go both there and back gives good closure but the point is set at the wrong distance. We can go out with the EDM and come back with the chain. A consistent difference between the two instruments readings indicates a calibration problem. Or, the EDM can be checked across two points of known distance. This last is easier. We have two markers set in concrete in the parking lot and we know how far they are from each other. We check the EDM calibration every morning.
In summary, a GPS that is accurate enough to set points is pretty expensive and needs to be operated by a professional. There is no good way to check the closure unless the distance is measured by calibrated instruments. Heck, if the distance measurement tools are needed, they can be used to mark off the course and there is no need for the GPS.
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Use of the GPS is what I am typing about. This is a complex subject and there is much more to it than this.
Why bother?Heck, if the distance measurement tools are needed, they can be used to mark off the course and there is no need for the GPS.
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You guys are making this sound extremely complicated. I was of the belief that the timing equipment will measure elapsed time to 1/10,000 of a second. With electronics of as far back as 30 years ago, in industry, I know it was possible. Then the elapsed time is factored to the measured distance and the average speed over that distance is what the given number represents. The terminal velocity speed is a timed reading, in order to give a mph speed "accurate" to one thousandth of a mile per hour would need to be timed to (at least) four decimal places...
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Ok Guys, and Gals
I did not read through all the posts, sorry. But here is how the Rod Rider Racing Club lays out the 1.1 mile course for El Mirage, and have been doing it for over 20 years.
We have three vehicles with electronic foot distance counters in side. We start at the start line with two vehicles at the course edge and move towards what we plan as the course and finish. Every 20 feet we drop a cone. Once we reach the 'finish line' we mark it for timing lights location. We also wheel the spread for the course and wheel to the safety cones on the edge.
While one part of the crew lines up the cones from start to finish, another part of the crew lays out the Patrol positions so that a different club can lay out the side cones.
Now for a two day event, we have to make sure the course we 'slide' over to is good enough to race upon. And at the end of the first day we move one line of cones over to the next course, making sure they are line up for the racers.
Some have tried to gps the course and like mentioned the finish line was off from 10 to 20 feet.
The counters are checked every meet by driving a known 1000 foot course to make sure of any changes to the machine or tires. The machine run off a magnet on the drive shaft.
Now, exact? As possible. But by having the same group with the same equipment every-time one has a better chance of being consistent.
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Tony, I think that's a great concept - the way you measure and lay it out. By having the same crew do it the same way for years -- you've at least added greatly to the "repeatability" of the measurement even if the absolute accuracy is not within microns or whatever.
Your chances of getting it close to exactly the same each time -- are better for the practice you get. :cheers:
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OK Tony. So how do you lay out the 1.3 mile course at El Mirage? :roll: :cheers: Wayno
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How long have we been using 1.1 miles at El Mirage? Do we have to toss all the records set since that date?
DW
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The accuracy of time is 20 nS (.000000002 seconds), So we can discount that error.
The accuracy of position is within 3 mm, regardless of distance. For two points that increases to 6mm, or .23622 inches, or +/- 0.000001864 miles. This includes any change in altitude too (which traditional systems don't do)
200 mph is 1 mile per .005 hour
1.000001864 miles / .005 hour is 200.000372 miles per hour
0.999998135 miles / .005 hour is 199.999627 miles per hour
so the answer is +/- 0.000372 miles per hour
800 mph is 1 mile per .00125 hour
1.000001864 miles / .00125 hour or +/- 0.00149 mph accuracy at 800 mph.
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Thanks Ed. I think! :roll:
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Wow!
I'm feeling great! We're nearly breaking records set at 1.3 miles. Another 1056 feet and we'd be there.
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We've been NHRA'd. :-o Wayno
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Umm... what was F104A describing? :?
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Umm... what was F104A describing? :?
I think GPS accuracy.
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The accuracy of time is 20 nS (.000000002 seconds), So we can discount that error.
The accuracy of position is within 3 mm, regardless of distance. For two points that increases to 6mm, or .23622 inches, or +/- 0.000001864 miles. This includes any change in altitude too (which traditional systems don't do)
200 mph is 1 mile per .005 hour
1.000001864 miles / .005 hour is 200.000372 miles per hour
0.999998135 miles / .005 hour is 199.999627 miles per hour
so the answer is +/- 0.000372 miles per hour
800 mph is 1 mile per .00125 hour
1.000001864 miles / .00125 hour or +/- 0.00149 mph accuracy at 800 mph.
Yes, but as everyone will say there is a big Acura difference between 199.999627 and 200.000372. :cheers: :dhorse: :dhorse:
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...Yes, but as everyone will say there is a big Acura difference between 199.999627 .....
...if I had only done this.....
........ and 200.000372......
... a big smile and a vist with Dan 8-) 8-),
Sumner
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A record is not measured to 0.001 mph. Although record speeds are reported to three decimal places. The measured parameter is time, which may be recorded to many decimal places but is then truncated to 3dp for (FIA) record purposes.
Hmm . . .
So if you're timed at 7.2009 for the mile, which figures to 499.9375 mph, you'd be credited as going 500.
Yep. It needs someone smarter than me to explain why this is considered to be the "correct" way to do the calculation.
Not sure if the rule book helps, but the FIA rules follow. At no time could 499.9375 be anything greater than 499.937.
FIA D12.3.2 Time accuracy. Record time with an accuracy of 1/1,000th of a second and calculate the mean time with an accuracy of 1/1,000th of a second with no rounding off.
FIA D12.3.3 Speed Accuracy. Calculate and record speed with an accuracy of 1/1,000th of mph or kph
FIA D12.3.4 Conversion. Convert speed thus calculated to kph or mph with no rounding off using the defined conversion factor.
FIA D12.3.5 Precision. If the timekeeping equipment has accuracy greater than 1/1,000th of a second, its precision shall be set to record times to 1/1,000th of a second with no rounding off to allow direct use of all readings.
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A record is not measured to 0.001 mph. Although record speeds are reported to three decimal places. The measured parameter is time, which may be recorded to many decimal places but is then truncated to 3dp for (FIA) record purposes.
Hmm . . .
So if you're timed at 7.2009 for the mile, which figures to 499.9375 mph, you'd be credited as going 500.
Yep. It needs someone smarter than me to explain why this is considered to be the "correct" way to do the calculation.
Not sure if the rule book helps, but the FIA rules follow. At no time could 499.9375 be anything greater than 499.937.
FIA D12.3.2 Time accuracy. Record time with an accuracy of 1/1,000th of a second and calculate the mean time with an accuracy of 1/1,000th of a second with no rounding off.
FIA D12.3.3 Speed Accuracy. Calculate and record speed with an accuracy of 1/1,000th of mph or kph
FIA D12.3.4 Conversion. Convert speed thus calculated to kph or mph with no rounding off using the defined conversion factor.
FIA D12.3.5 Precision. If the timekeeping equipment has accuracy greater than 1/1,000th of a second, its precision shall be set to record times to 1/1,000th of a second with no rounding off to allow direct use of all readings.
Malcolm, I think tortoise's point was that if you apply the above rules then 7.2009 rounded off becomes 7.200 and, hey presto, 500 mph.
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...Yes, but as everyone will say there is a big Acura difference between 199.999627 .....
...if I had only done this.....
........ and 200.000372......
... a big smile and a vist with Dan 8-) 8-),
Sumner
Sumner,
I think you taking about the very exclusive 199,5+ mph club at the salt....for a short time I was also a member of this club.....but may be they ask Betty Burkland...she had this experience for 15 years....she run 199,997 mph.....before finally she could get her red hat....
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Malcolm, I think tortoise's point was that if you apply the above rules then 7.2009 rounded off becomes 7.200 and, hey presto, 500 mph.
The figure of 7.2009 is never 'seen' by the FIA timekeeper as the rules are written. The fourth decimal place is just ignored.
Not sure how you could ever arrive at the average or mean time being 7.2009.
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. . . The fourth decimal place is just ignored.
Nonetheless, our notional vehicle is actually going less than 500 mph, but is credited with that speed. Not a big deal, just a curiosity.
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Malcolm, I think tortoise's point was that if you apply the above rules then 7.2009 rounded off becomes 7.200 and, hey presto, 500 mph.
The figure of 7.2009 is never 'seen' by the FIA timekeeper as the rules are written. The fourth decimal place is just ignored.
Not sure how you could ever arrive at the average or mean time being 7.2009.
OK, using the rules as written you could arrive at a mean time of 7.2005 seconds.
Andy Green's outright record works like this. The calculated mean time was 4.7185 seconds but this is truncated to 4.718 before converting to a speed. Thus the quoted record speed is slightly faster than his "real" speed.
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Effects of truncating 4th digit after the decimal point.
I hear Mr. Green's shooting for 1000 mph. A scenario:
His first run , if recorded to .0001 second, would have been 3.6009, but is recorded as 3.600 second.
Second run, if recorded to .0001 second, 3.6019, recorded as 3.601 second. Mean of 2 recorded times is 3.6005 second, recorded as 3.600. Record set at 1000 mph. Mean of 2 times as read to .0001 seconds, 3.6014, calculates to 999.611 mph.
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Effects of truncating 4th digit after the decimal point.
I hear Mr. Green's shooting for 1000 mph. A scenario:
His first run , if recorded to .0001 second, would have been 3.6009 mph, but is recorded as 3.600 second.
Second run, if recorded to .0001 second, 3.6019, recorded as 3.601 second. Mean of 2 recorded times is 3.6005 second, recorded as 3.600. Record set at 1000 mph. Mean of 2 times as read to .0001 seconds, 3.6014, calculates to 999.611 mph.
Your logic and arithmetic are correct tortoise.
I suggest that the way to think of it is this: imagine a stop watch that ticks once a second. Start the watch at zero; then after one second has elapsed the watch clicks over to show one second; after two seconds the watch will click over to show two seconds; etc. So when the time that has really elapsed is between n and n.99999999999 seconds the watch will show n seconds.
The FIA watch effectively ticks every one thousandth of a second.
As your example shows the overall effect is always to exaggerate the quoted speed slightly. I suppose that if Andy's 'real' average speed was 999.611 mph then it is a near certainty that he would have exceeded 1,000 mph at least some of the time. Plus the rules are the same for everyone.
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I suppose that if Andy's 'real' average speed was 999.611 mph then it is a near certainty that he would have exceeded 1,000 mph at least some of the time.
I object. Witness's comment is irrelevant and immaterial. The records in question are for average speed over a prescribed distance. . . . the rules are the same for everyone.
Just so. The exercise shows, though, that the possible error, (if we choose to call it an error), is greater than many would intuit, when seeing speeds quoted to the thousandth.
Not a big deal, just a curiosity.
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tortoise and I seem to have killed this thread almost stone dead. :-(
Getting back to the original point, two questions that intrigue me are:
- Suppose you are confident your measuring system is accurate to +/- 6 inches. Does your licensed surveyor lay out a course that is 1 mile +/- 6 inches (and thus risk that the "measured mile" is actually slightly shorter than that) or does he add 6 inches margin for error?
- Is the course re-measured after a record has been set, to check for any changes that might have occurred since it was laid out?
Reading about the early days (pre-1920 say), there are hints that distance measurements were sometimes fairly lax. For example, a crowd dissatisfied with the speeds being achieved before lunch might move the finish line to "increase" the speeds being achieved later in the day. :-o :-o
It couldn't happen today of course. :| :-)