Everything you Love and Hate about
09-05-2007, 06:10 PM
#51
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09-05-2007, 06:17 PM
#52
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09-05-2007, 06:21 PM
#53
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06 EuroElites E55
make sure you plan your trip around a test and tune night! i noticed the prep was 100 times better than grudge night.
09-05-2007, 06:22 PM
#54
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09-05-2007, 06:23 PM
#55
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09-05-2007, 06:27 PM
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06 EuroElites E55
09-05-2007, 07:01 PM
#60
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Enzom you are not seeing the forrest you are focusing on the tree.
DA is ALTITUDE.
Altitude is calculated from measuring Air Pressure, ever heard of an Altimeter?
what you guys fail to see over and over and over and over again is that the correction table provided by NHRA is from SAE and it is based ON DENSITY OF THE ATMOSPHERE AT CERTAIN ALTITUDES. The density of a column of air at sea level is compared to the density of a column of air at altitude and a correction factor assigned to adjust the times.
. . .
You guys keep pointing to an altitude table that is calculated from SAE standard pressure at SEA LEVEL which many folks have pointed out.
DA is ALTITUDE.
Altitude is calculated from measuring Air Pressure, ever heard of an Altimeter?
what you guys fail to see over and over and over and over again is that the correction table provided by NHRA is from SAE and it is based ON DENSITY OF THE ATMOSPHERE AT CERTAIN ALTITUDES. The density of a column of air at sea level is compared to the density of a column of air at altitude and a correction factor assigned to adjust the times.
. . .
You guys keep pointing to an altitude table that is calculated from SAE standard pressure at SEA LEVEL which many folks have pointed out.
As everyone knows, DA's change from moment to moment. That is not because altitudes change. That is because temperature, humidity and barometric pressures change.
The NHRA chart - however the heck it is put together by the NHRA - provides a constant calculation. Run at 2,700 ft above sea level - the NHRA says you multiply your e.t. and speed by a pre-set number. If you run at 2,700 ft on a 90 degree day or you run at 2,700 ft on a 45 degree day, you use that same constant multiplier - it doesn't change. Whether or not weather factors were taken into consideration by the NHRA in determining how to create the multipliers is besides the point. The multiplier is fixed.
What you are doing, I think, is making ADDITIONAL calculations based on weather conditions. The NHRA does not recognize weather related modifications as valid. And there is good reason for that.
If you want to argue that the DA-specific calculation is better than what the NHRA recognizes, then you can argue that. I am just trying to figure out if it is your view that there is room in the NHRA calculation for weather-related modifications.
Help a brother out, will ya?
P.S. - I changed my sig for you guys.
Last edited by enzom; 09-05-2007 at 07:04 PM.
09-05-2007, 07:26 PM
#61
MBWorld Fanatic!
Juiecee read the article from the page I linked early, it will make everything clear. At least I hope it finally sinks in, here is a direct copy and paste for you.
What is density altitude?
The density altitude is the altitude at which the density of the International Standard Atmosphere (ISA) is the same as the density of the air being evaluated. (The Standard Atmosphere is simply a mathematical model of the atmosphere which is standardized so that predictable calculations can be made.)
So, the basic idea of calculating density altitude is to calculate the actual density of the air, and then find the altitude at which that same air density occurs in the Standard Atmosphere.
In the following paragraphs, we'll go step by step through the process of calculating the actual density of the air, and then determining the corresponding density altitude.
And finally, at the very end of this article, we'll compare the accurate density altitude calculations with the results of a greatly simplified equation that ignores the effects due to water vapor in the air.
Some different meanings of the word "altitude":
An aircraft altimeter measures only air pressure... nothing else. If the air pressure changes, due to temperature or humidity, then an aircraft altimeter will of course change to indicate the actual air pressure. Nonetheless, the aircraft altimeter is simply measuring air pressure.
As odd as it may seem, an aircraft altimeter does not actually measure altitude, it only measures pressure. Hence, the name "pressure altitude" is properly applied to any aircraft altimeter reading.
For pilots, it is very important to understand that an aircraft altimeter only measures air pressure (not altitude). This point is especially important to understand with the advent and use of GPS. An aircraft flying at a specific pressure altitude (as indicated by an altimeter) may note some other altitude displayed on the GPS (which measures actual distance above mean sea level). In some cases this difference is small... but in some cases it could be enough to cause a mid-air collision if a pilot was flying on a GPS altitude rather than pressure altitude. (To solve that problem, some GPS units do include an air pressure sensor so that they can indicate pressure altitude.)
Therefore, it is crucial to always verify what is meant by "altitude", and differentiate a pressure-based measurement of "pressure altitude" from a distance-based measurement of actual altitude.
Density altitude is a concept based on solely on air density, and is neither "pressure altitude" nor "mean sea-level altitude", but is strictly "density altitude".
Now... on to Density Altitude.....
Density and Density Altitude:
Although the concept of density altitude is commonly used to help express the effects of aircraft performance, the really underlying property of interest is actually the air density.
For example, the lift of an aircraft wing, the aerodynamic drag and the thrust of a propeller blade are all directly proportional to the air density. The downforce of a racecar spoiler is also directly proportional to the air density. Similarly, the horsepower output of an internal combustion engine is related to the air density. The correct size of a carburetor jet is related to the air density, and the pulse width command to an electronic fuel injection nozzle is also related to the air density.
Density altitude has been a convenient yardstick for pilots to compare the performance of aircraft at various altitudes, but it is in fact the air density that is the fundamentally important quantity, and density altitude is simply one way to express the air density.
(Note: If you're just hunting for a simple, but not very accurate, approximation for density altitude, be sure to study the "Simpler Methods of Calculation" section near the end of this article.)
What is density altitude?
The density altitude is the altitude at which the density of the International Standard Atmosphere (ISA) is the same as the density of the air being evaluated. (The Standard Atmosphere is simply a mathematical model of the atmosphere which is standardized so that predictable calculations can be made.)
So, the basic idea of calculating density altitude is to calculate the actual density of the air, and then find the altitude at which that same air density occurs in the Standard Atmosphere.
In the following paragraphs, we'll go step by step through the process of calculating the actual density of the air, and then determining the corresponding density altitude.
And finally, at the very end of this article, we'll compare the accurate density altitude calculations with the results of a greatly simplified equation that ignores the effects due to water vapor in the air.
Some different meanings of the word "altitude":
An aircraft altimeter measures only air pressure... nothing else. If the air pressure changes, due to temperature or humidity, then an aircraft altimeter will of course change to indicate the actual air pressure. Nonetheless, the aircraft altimeter is simply measuring air pressure.
As odd as it may seem, an aircraft altimeter does not actually measure altitude, it only measures pressure. Hence, the name "pressure altitude" is properly applied to any aircraft altimeter reading.
For pilots, it is very important to understand that an aircraft altimeter only measures air pressure (not altitude). This point is especially important to understand with the advent and use of GPS. An aircraft flying at a specific pressure altitude (as indicated by an altimeter) may note some other altitude displayed on the GPS (which measures actual distance above mean sea level). In some cases this difference is small... but in some cases it could be enough to cause a mid-air collision if a pilot was flying on a GPS altitude rather than pressure altitude. (To solve that problem, some GPS units do include an air pressure sensor so that they can indicate pressure altitude.)
Therefore, it is crucial to always verify what is meant by "altitude", and differentiate a pressure-based measurement of "pressure altitude" from a distance-based measurement of actual altitude.
Density altitude is a concept based on solely on air density, and is neither "pressure altitude" nor "mean sea-level altitude", but is strictly "density altitude".
Now... on to Density Altitude.....
Density and Density Altitude:
Although the concept of density altitude is commonly used to help express the effects of aircraft performance, the really underlying property of interest is actually the air density.
For example, the lift of an aircraft wing, the aerodynamic drag and the thrust of a propeller blade are all directly proportional to the air density. The downforce of a racecar spoiler is also directly proportional to the air density. Similarly, the horsepower output of an internal combustion engine is related to the air density. The correct size of a carburetor jet is related to the air density, and the pulse width command to an electronic fuel injection nozzle is also related to the air density.
Density altitude has been a convenient yardstick for pilots to compare the performance of aircraft at various altitudes, but it is in fact the air density that is the fundamentally important quantity, and density altitude is simply one way to express the air density.
(Note: If you're just hunting for a simple, but not very accurate, approximation for density altitude, be sure to study the "Simpler Methods of Calculation" section near the end of this article.)
09-05-2007, 08:41 PM
#62
Juiecee read the article from the page I linked early, it will make everything clear. At least I hope it finally sinks in, here is a direct copy and paste for you.
What is density altitude?
The density altitude is the altitude at which the density of the International Standard Atmosphere (ISA) is the same as the density of the air being evaluated. (The Standard Atmosphere is simply a mathematical model of the atmosphere which is standardized so that predictable calculations can be made.)
So, the basic idea of calculating density altitude is to calculate the actual density of the air, and then find the altitude at which that same air density occurs in the Standard Atmosphere.
In the following paragraphs, we'll go step by step through the process of calculating the actual density of the air, and then determining the corresponding density altitude.
And finally, at the very end of this article, we'll compare the accurate density altitude calculations with the results of a greatly simplified equation that ignores the effects due to water vapor in the air.
Some different meanings of the word "altitude":
An aircraft altimeter measures only air pressure... nothing else. If the air pressure changes, due to temperature or humidity, then an aircraft altimeter will of course change to indicate the actual air pressure. Nonetheless, the aircraft altimeter is simply measuring air pressure.
As odd as it may seem, an aircraft altimeter does not actually measure altitude, it only measures pressure. Hence, the name "pressure altitude" is properly applied to any aircraft altimeter reading.
For pilots, it is very important to understand that an aircraft altimeter only measures air pressure (not altitude). This point is especially important to understand with the advent and use of GPS. An aircraft flying at a specific pressure altitude (as indicated by an altimeter) may note some other altitude displayed on the GPS (which measures actual distance above mean sea level). In some cases this difference is small... but in some cases it could be enough to cause a mid-air collision if a pilot was flying on a GPS altitude rather than pressure altitude. (To solve that problem, some GPS units do include an air pressure sensor so that they can indicate pressure altitude.)
Therefore, it is crucial to always verify what is meant by "altitude", and differentiate a pressure-based measurement of "pressure altitude" from a distance-based measurement of actual altitude.
Density altitude is a concept based on solely on air density, and is neither "pressure altitude" nor "mean sea-level altitude", but is strictly "density altitude".
Now... on to Density Altitude.....
Density and Density Altitude:
Although the concept of density altitude is commonly used to help express the effects of aircraft performance, the really underlying property of interest is actually the air density.
For example, the lift of an aircraft wing, the aerodynamic drag and the thrust of a propeller blade are all directly proportional to the air density. The downforce of a racecar spoiler is also directly proportional to the air density. Similarly, the horsepower output of an internal combustion engine is related to the air density. The correct size of a carburetor jet is related to the air density, and the pulse width command to an electronic fuel injection nozzle is also related to the air density.
Density altitude has been a convenient yardstick for pilots to compare the performance of aircraft at various altitudes, but it is in fact the air density that is the fundamentally important quantity, and density altitude is simply one way to express the air density.
(Note: If you're just hunting for a simple, but not very accurate, approximation for density altitude, be sure to study the "Simpler Methods of Calculation" section near the end of this article.)
What is density altitude?
The density altitude is the altitude at which the density of the International Standard Atmosphere (ISA) is the same as the density of the air being evaluated. (The Standard Atmosphere is simply a mathematical model of the atmosphere which is standardized so that predictable calculations can be made.)
So, the basic idea of calculating density altitude is to calculate the actual density of the air, and then find the altitude at which that same air density occurs in the Standard Atmosphere.
In the following paragraphs, we'll go step by step through the process of calculating the actual density of the air, and then determining the corresponding density altitude.
And finally, at the very end of this article, we'll compare the accurate density altitude calculations with the results of a greatly simplified equation that ignores the effects due to water vapor in the air.
Some different meanings of the word "altitude":
An aircraft altimeter measures only air pressure... nothing else. If the air pressure changes, due to temperature or humidity, then an aircraft altimeter will of course change to indicate the actual air pressure. Nonetheless, the aircraft altimeter is simply measuring air pressure.
As odd as it may seem, an aircraft altimeter does not actually measure altitude, it only measures pressure. Hence, the name "pressure altitude" is properly applied to any aircraft altimeter reading.
For pilots, it is very important to understand that an aircraft altimeter only measures air pressure (not altitude). This point is especially important to understand with the advent and use of GPS. An aircraft flying at a specific pressure altitude (as indicated by an altimeter) may note some other altitude displayed on the GPS (which measures actual distance above mean sea level). In some cases this difference is small... but in some cases it could be enough to cause a mid-air collision if a pilot was flying on a GPS altitude rather than pressure altitude. (To solve that problem, some GPS units do include an air pressure sensor so that they can indicate pressure altitude.)
Therefore, it is crucial to always verify what is meant by "altitude", and differentiate a pressure-based measurement of "pressure altitude" from a distance-based measurement of actual altitude.
Density altitude is a concept based on solely on air density, and is neither "pressure altitude" nor "mean sea-level altitude", but is strictly "density altitude".
Now... on to Density Altitude.....
Density and Density Altitude:
Although the concept of density altitude is commonly used to help express the effects of aircraft performance, the really underlying property of interest is actually the air density.
For example, the lift of an aircraft wing, the aerodynamic drag and the thrust of a propeller blade are all directly proportional to the air density. The downforce of a racecar spoiler is also directly proportional to the air density. Similarly, the horsepower output of an internal combustion engine is related to the air density. The correct size of a carburetor jet is related to the air density, and the pulse width command to an electronic fuel injection nozzle is also related to the air density.
Density altitude has been a convenient yardstick for pilots to compare the performance of aircraft at various altitudes, but it is in fact the air density that is the fundamentally important quantity, and density altitude is simply one way to express the air density.
(Note: If you're just hunting for a simple, but not very accurate, approximation for density altitude, be sure to study the "Simpler Methods of Calculation" section near the end of this article.)
.......interesting. The Juice has backed himself so far into a corner on this that you are not likely to get him to reverse himself.
.......what I find a bit amusing is how one can use a calculator to determine how fast his cars is, and be serious about it. Others simply race their cars and publish the slip. The Juice implies that those that don't use a calculator are not intellectual enough, because according to him it "requires too much thought." Maybe they just have faster cars.
...........since this is cause celeb for the Juice, it will be interesting to see anywhere else he published his famous calculations prior to owning an E63. It looks like when you take delivery of an E63, the dealer hands you complimentary calculator and weather station. Most people will gladly give up the calculator and the weather station for a low 12sec car.
........Having said that, the calculations obviously exist for a reason. Most car enthusiasts use them for their own personal information to tell them potentially how fast their cars can be. Wearing the calculated numbers on your chest as a badge of honor appears to be an activity solely practiced by those with E63's.
Ted
09-05-2007, 09:24 PM
#63
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E55
As fun as it is,just lighten up on ol Juicee.Give him credit for atleast taking his car to the track,not many 63 owners are at the track as often as Juicee is,or at all for that matter.So what if he wants to use DA correction as his basis for comparison's,he knows that in a heads up race,the guy out front wins,and theres no calculator for the outcome.
09-05-2007, 09:29 PM
#64
MBWorld Fanatic!
.......interesting. The Juice has backed himself so far into a corner on this that you are not likely to get him to reverse himself.
.......what I find a bit amusing is how one can use a calculator to determine how fast his cars is, and be serious about it. Others simply race their cars and publish the slip. The Juice implies that those that don't use a calculator are not intellectual enough, because according to him it "requires too much thought." Maybe they just have faster cars.
...........since this is cause celeb for the Juice, it will be interesting to see anywhere else he published his famous calculations prior to owning an E63. It looks like when you take delivery of an E63, the dealer hands you complimentary calculator and weather station. Most people will gladly give up the calculator and the weather station for a low 12sec car.
........Having said that, the calculations obviously exist for a reason. Most car enthusiasts use them for their own personal information to tell them potentially how fast their cars can be. Wearing the calculated numbers on your chest as a badge of honor appears to be an activity solely practiced by those with E63's.
Ted
.......what I find a bit amusing is how one can use a calculator to determine how fast his cars is, and be serious about it. Others simply race their cars and publish the slip. The Juice implies that those that don't use a calculator are not intellectual enough, because according to him it "requires too much thought." Maybe they just have faster cars.
...........since this is cause celeb for the Juice, it will be interesting to see anywhere else he published his famous calculations prior to owning an E63. It looks like when you take delivery of an E63, the dealer hands you complimentary calculator and weather station. Most people will gladly give up the calculator and the weather station for a low 12sec car.
........Having said that, the calculations obviously exist for a reason. Most car enthusiasts use them for their own personal information to tell them potentially how fast their cars can be. Wearing the calculated numbers on your chest as a badge of honor appears to be an activity solely practiced by those with E63's.
Ted
I think Juicee is honestly trying to figure out a methodology that will allow cars that run at high altitude to be compared to cars that run at lower altitude.
I think Juicee may be confused about what is considered acceptable by the NHRA and most racers I know. He may be confused about the difference between altitude as the NHRA views it, and density altitude as it is utilized by racers.
I can't believe that Juicee hopes or is even trying to create a racer revolution where everyone starts playing with a website that makes DA adjustments and considers those to be real times.
I feel a bit bad that I may have started this by asking that people consider the implication of using "uncorrected" to describe a real time and "corrected" to describe a calculator-generated and imprecise print-out.
Because I am paid to be curious, I couldn't help but try to understand better the methodology that was being utilized and whether its applicability was generally accepted. I thought that maybe because I have the luxury of being a resident of the Garden State (don't hear that often), that maybe there was a racing world out there that I had missed in my 19 years of hitting the strip. So I opened up a can of worms and put poor Juicee in a bad position. Sorry, Juicee.
If nothing else, it has led to an interestingly new appreciation of atmospheric conditions. And I have now come to understand that an adjustment for pure altitude is based on a sanctioned process. I have also come to realize that being able to carry a DA correction to the third decimal point does not make it accurate.
I said it once and I will say it again - I want the E63 to be a quicker and faster car than the E55. Why? Because I could decide tomorrow to sell my car. And if I have seller's regret six months later, I want to know that I can call my dealer and get myself a car that is still as fast. And soon enough, E63's are going to be all over E-town, Atco, MIR and any of "our" other fast tracks. We'll have plenty of data that will help answer the question of which is ultimately faster - if there is any difference at all.
And dammit if Venom and I don't line up one of these nights for a few runs.
09-05-2007, 09:55 PM
#65
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old daily driver '07 E63(gone); new dd '14 750xi; 2013 Viper GTS
Enzom, Will be there Friday if you can get out of work early. Won't be that cool though, they say 80's and humid. Doesn't matter, last 3 times at E-town I had to peal my pants from the seat with the heat. You know me...will still run anyway.
09-05-2007, 10:08 PM
#66
MBWorld Fanatic!
As fun as it is,just lighten up on ol Juicee.Give him credit for atleast taking his car to the track,not many 63 owners are at the track as often as Juicee is,or at all for that matter.So what if he wants to use DA correction as his basis for comparison's,he knows that in a heads up race,the guy out front wins,and theres no calculator for the outcome.
09-06-2007, 03:44 AM
#67
MBWorld Fanatic!
Thread Starter
.......interesting. The Juice has backed himself so far into a corner on this that you are not likely to get him to reverse himself.
.......what I find a bit amusing is how one can use a calculator to determine how fast his cars is, and be serious about it. Others simply race their cars and publish the slip. The Juice implies that those that don't use a calculator are not intellectual enough, because according to him it "requires too much thought." Maybe they just have faster cars.
...........since this is cause celeb for the Juice, it will be interesting to see anywhere else he published his famous calculations prior to owning an E63. It looks like when you take delivery of an E63, the dealer hands you complimentary calculator and weather station. Most people will gladly give up the calculator and the weather station for a low 12sec car.
........Having said that, the calculations obviously exist for a reason. Most car enthusiasts use them for their own personal information to tell them potentially how fast their cars can be. Wearing the calculated numbers on your chest as a badge of honor appears to be an activity solely practiced by those with E63's.
Ted
.......what I find a bit amusing is how one can use a calculator to determine how fast his cars is, and be serious about it. Others simply race their cars and publish the slip. The Juice implies that those that don't use a calculator are not intellectual enough, because according to him it "requires too much thought." Maybe they just have faster cars.
...........since this is cause celeb for the Juice, it will be interesting to see anywhere else he published his famous calculations prior to owning an E63. It looks like when you take delivery of an E63, the dealer hands you complimentary calculator and weather station. Most people will gladly give up the calculator and the weather station for a low 12sec car.
........Having said that, the calculations obviously exist for a reason. Most car enthusiasts use them for their own personal information to tell them potentially how fast their cars can be. Wearing the calculated numbers on your chest as a badge of honor appears to be an activity solely practiced by those with E63's.
Ted
For Godsakes pay attention, I DO NOT OWN AN E63!!!
I use DA correction because it is more accurate than altitude. Weather effects the run in some cases to a greater extent than the altitude at which the run began.
what you guys are missing and it seems you continue to miss it.
THE NHRA TABLE is a density of air correction. The Altitude is calculated from AIR PRESSURE not by any other method.
You cannot have an altitude correction factor underived from DENSITY.
The relationship between barometric pressure and altitude is not the same over the whole surface of the globe. Because of the warming of the atmosphere by the sun near the Equator, the column of air is higher there, and therefore the barometric pressure at any given altitude is higher than at the poles. These differences are important to the mountain climber. For example, it can be shown that if Mt. Everest were at the latitude of Mt. McKinley (Denali) in Alaska, which is 60° N, the summit would in effect be over 950 metres (3000 feet) higher because the barometric pressure at high altitude at latitudes far from the Equator is so much lower. This would make it impossible to climb the mountain without supplementary oxygen. On the other hand, the use of the International Civil Aviation Organization (ICAO) Standard Atmosphere (often used to calibrate altimeters) considerably underestimates the barometric pressure on the summit of Everest: the severity of hypoxia was therefore overestimated in some predictions based on this method in the past.
You must take the measurements to accurately predict a sea level run which for those not following is at STANDARD ATMOSPHERIC PRESSURE.
Its a very useful tool.
I know my car better than anyone , and I know everytime what my car will do based on what the measured DA is, end of story.
To pick a DIAL TIME w/o taking a DA measurement is absolutely IDIOTIC.
I have run my car over 700 times appx 7000 of my 11000 miles are from driving to and running up and down and around tracks. , I know exactly where I can get to and where I cannot. what slows me down? Not spinning not mechanical probs, not even a BAD TRACK, its the air, I can make adjustments for the others but I cannot CHANGE THE ATMOSPHERE. Forget the EGO bullshi* Ted, the correction is not to suggest my car is faster than yours or anyone elses, it is simply to accurately predict what run in my car was the best. MY 13 second pass was faster than my 12.6, I know it because my 60ft time was .3 better, it was in a high DA and I do not care that you say , "uh nope uh 12.6 is FASTER", its not to me. That 13 second run tells me I can get to a 12.36 on a day with GOOD AIR. I will bet you MILLIONS that is what the car will do at a DA of 0 or Negative like you folks enjoy at MIR. The NHRA does not use ANY corrected times to proclaim winners or fastest cars or records , that table is a T O O L.
09-06-2007, 04:47 AM
#69
MBWorld Fanatic!
Thread Starter
Juicee - for the love of Pete (whoever he is), we are knocking skulls over a point that should not be the subject of dispute. It really shouldn't be.
As everyone knows, DA's change from moment to moment. That is not because altitudes change. That is because temperature, humidity and barometric pressures change.
The NHRA chart - however the heck it is put together by the NHRA - provides a constant calculation. Run at 2,700 ft above sea level - the NHRA says you multiply your e.t. and speed by a pre-set number. If you run at 2,700 ft on a 90 degree day or you run at 2,700 ft on a 45 degree day, you use that same constant multiplier - it doesn't change. Whether or not weather factors were taken into consideration by the NHRA in determining how to create the multipliers is besides the point. The multiplier is fixed.
What you are doing, I think, is making ADDITIONAL calculations based on weather conditions. The NHRA does not recognize weather related modifications as valid. And there is good reason for that.
If you want to argue that the DA-specific calculation is better than what the NHRA recognizes, then you can argue that. I am just trying to figure out if it is your view that there is room in the NHRA calculation for weather-related modifications.
Help a brother out, will ya?
P.S. - I changed my sig for you guys.
As everyone knows, DA's change from moment to moment. That is not because altitudes change. That is because temperature, humidity and barometric pressures change.
The NHRA chart - however the heck it is put together by the NHRA - provides a constant calculation. Run at 2,700 ft above sea level - the NHRA says you multiply your e.t. and speed by a pre-set number. If you run at 2,700 ft on a 90 degree day or you run at 2,700 ft on a 45 degree day, you use that same constant multiplier - it doesn't change. Whether or not weather factors were taken into consideration by the NHRA in determining how to create the multipliers is besides the point. The multiplier is fixed.
What you are doing, I think, is making ADDITIONAL calculations based on weather conditions. The NHRA does not recognize weather related modifications as valid. And there is good reason for that.
If you want to argue that the DA-specific calculation is better than what the NHRA recognizes, then you can argue that. I am just trying to figure out if it is your view that there is room in the NHRA calculation for weather-related modifications.
Help a brother out, will ya?
P.S. - I changed my sig for you guys.
You seem to understand now.
The NHRA correction factors are FIXED and based on the know appx elevation of the tracks. This makes this correction factor far less accurate IMHO.
The Density of the Air as you point out CHANGES and the elevation does not. The track starts out at a Standard Air Pressure , a constant a known # to which the corretion factor is set. As the temp rises or falls Air Pressure changes and so does the Altitude. The density of the Atmosphere as measured by a weatherstation is far closer to actual altitude than the altitude calculated from standard air pressure.The NHRA table is a STANDARD CORRECTION TABLE and does not account for temperature. It is a table that assumes standard atmospheric pressure. 59 degrees , so a 90 degree temp is going to change the ATMOSPHERIC PRESSURE and the air less favorable. The 5800 ft track is now equivalant to air pressure at 9000 ft.
So the DA calculation is much more accurate than the standard correction factor.
09-06-2007, 04:54 AM
#70
MBWorld Fanatic!
Thread Starter
Juiecee read the article from the page I linked early, it will make everything clear. At least I hope it finally sinks in, here is a direct copy and paste for you.
What is density altitude?
The density altitude is the altitude at which the density of the International Standard Atmosphere (ISA) is the same as the density of the air being evaluated. (The Standard Atmosphere is simply a mathematical model of the atmosphere which is standardized so that predictable calculations can be made.)
So, the basic idea of calculating density altitude is to calculate the actual density of the air, and then find the altitude at which that same air density occurs in the Standard Atmosphere.
In the following paragraphs, we'll go step by step through the process of calculating the actual density of the air, and then determining the corresponding density altitude.
And finally, at the very end of this article, we'll compare the accurate density altitude calculations with the results of a greatly simplified equation that ignores the effects due to water vapor in the air.
Some different meanings of the word "altitude":
An aircraft altimeter measures only air pressure... nothing else. If the air pressure changes, due to temperature or humidity, then an aircraft altimeter will of course change to indicate the actual air pressure. Nonetheless, the aircraft altimeter is simply measuring air pressure.
As odd as it may seem, an aircraft altimeter does not actually measure altitude, it only measures pressure. Hence, the name "pressure altitude" is properly applied to any aircraft altimeter reading.
For pilots, it is very important to understand that an aircraft altimeter only measures air pressure (not altitude). This point is especially important to understand with the advent and use of GPS. An aircraft flying at a specific pressure altitude (as indicated by an altimeter) may note some other altitude displayed on the GPS (which measures actual distance above mean sea level). In some cases this difference is small... but in some cases it could be enough to cause a mid-air collision if a pilot was flying on a GPS altitude rather than pressure altitude. (To solve that problem, some GPS units do include an air pressure sensor so that they can indicate pressure altitude.)
Therefore, it is crucial to always verify what is meant by "altitude", and differentiate a pressure-based measurement of "pressure altitude" from a distance-based measurement of actual altitude.
Density altitude is a concept based on solely on air density, and is neither "pressure altitude" nor "mean sea-level altitude", but is strictly "density altitude".
Now... on to Density Altitude.....
Density and Density Altitude:
Although the concept of density altitude is commonly used to help express the effects of aircraft performance, the really underlying property of interest is actually the air density.
For example, the lift of an aircraft wing, the aerodynamic drag and the thrust of a propeller blade are all directly proportional to the air density. The downforce of a racecar spoiler is also directly proportional to the air density. Similarly, the horsepower output of an internal combustion engine is related to the air density. The correct size of a carburetor jet is related to the air density, and the pulse width command to an electronic fuel injection nozzle is also related to the air density.
Density altitude has been a convenient yardstick for pilots to compare the performance of aircraft at various altitudes, but it is in fact the air density that is the fundamentally important quantity, and density altitude is simply one way to express the air density.
(Note: If you're just hunting for a simple, but not very accurate, approximation for density altitude, be sure to study the "Simpler Methods of Calculation" section near the end of this article.)
What is density altitude?
The density altitude is the altitude at which the density of the International Standard Atmosphere (ISA) is the same as the density of the air being evaluated. (The Standard Atmosphere is simply a mathematical model of the atmosphere which is standardized so that predictable calculations can be made.)
So, the basic idea of calculating density altitude is to calculate the actual density of the air, and then find the altitude at which that same air density occurs in the Standard Atmosphere.
In the following paragraphs, we'll go step by step through the process of calculating the actual density of the air, and then determining the corresponding density altitude.
And finally, at the very end of this article, we'll compare the accurate density altitude calculations with the results of a greatly simplified equation that ignores the effects due to water vapor in the air.
Some different meanings of the word "altitude":
An aircraft altimeter measures only air pressure... nothing else. If the air pressure changes, due to temperature or humidity, then an aircraft altimeter will of course change to indicate the actual air pressure. Nonetheless, the aircraft altimeter is simply measuring air pressure.
As odd as it may seem, an aircraft altimeter does not actually measure altitude, it only measures pressure. Hence, the name "pressure altitude" is properly applied to any aircraft altimeter reading.
For pilots, it is very important to understand that an aircraft altimeter only measures air pressure (not altitude). This point is especially important to understand with the advent and use of GPS. An aircraft flying at a specific pressure altitude (as indicated by an altimeter) may note some other altitude displayed on the GPS (which measures actual distance above mean sea level). In some cases this difference is small... but in some cases it could be enough to cause a mid-air collision if a pilot was flying on a GPS altitude rather than pressure altitude. (To solve that problem, some GPS units do include an air pressure sensor so that they can indicate pressure altitude.)
Therefore, it is crucial to always verify what is meant by "altitude", and differentiate a pressure-based measurement of "pressure altitude" from a distance-based measurement of actual altitude.
Density altitude is a concept based on solely on air density, and is neither "pressure altitude" nor "mean sea-level altitude", but is strictly "density altitude".
Now... on to Density Altitude.....
Density and Density Altitude:
Although the concept of density altitude is commonly used to help express the effects of aircraft performance, the really underlying property of interest is actually the air density.
For example, the lift of an aircraft wing, the aerodynamic drag and the thrust of a propeller blade are all directly proportional to the air density. The downforce of a racecar spoiler is also directly proportional to the air density. Similarly, the horsepower output of an internal combustion engine is related to the air density. The correct size of a carburetor jet is related to the air density, and the pulse width command to an electronic fuel injection nozzle is also related to the air density.
Density altitude has been a convenient yardstick for pilots to compare the performance of aircraft at various altitudes, but it is in fact the air density that is the fundamentally important quantity, and density altitude is simply one way to express the air density.
(Note: If you're just hunting for a simple, but not very accurate, approximation for density altitude, be sure to study the "Simpler Methods of Calculation" section near the end of this article.)
Great post , you run NITROUS so no correction allowed!!
09-06-2007, 08:20 AM
#71
MBWorld Fanatic!
Doubt that I can get down there Friday, assuming I feel better. This weather is nuts, but in three weeks, we will see 60 degree nights. I am currently scheduled to be off from work on the 19th. Let's see how that looks as we get close to it.
09-06-2007, 08:36 AM
#72
MBWorld Fanatic!
You seem to understand now.
The NHRA correction factors are FIXED and based on the know appx elevation of the tracks. This makes this correction factor far less accurate IMHO.
The Density of the Air as you point out CHANGES and the elevation does not. The track starts out at a Standard Air Pressure , a constant a known # to which the corretion factor is set. As the temp rises or falls Air Pressure changes and so does the Altitude. The density of the Atmosphere as measured by a weatherstation is far closer to actual altitude than the altitude calculated from standard air pressure.The NHRA table is a STANDARD CORRECTION TABLE and does not account for temperature. It is a table that assumes standard atmospheric pressure. 59 degrees , so a 90 degree temp is going to change the ATMOSPHERIC PRESSURE and the air less favorable. The 5800 ft track is now equivalant to air pressure at 9000 ft.
So the DA calculation is much more accurate than the standard correction factor.
The NHRA correction factors are FIXED and based on the know appx elevation of the tracks. This makes this correction factor far less accurate IMHO.
The Density of the Air as you point out CHANGES and the elevation does not. The track starts out at a Standard Air Pressure , a constant a known # to which the corretion factor is set. As the temp rises or falls Air Pressure changes and so does the Altitude. The density of the Atmosphere as measured by a weatherstation is far closer to actual altitude than the altitude calculated from standard air pressure.The NHRA table is a STANDARD CORRECTION TABLE and does not account for temperature. It is a table that assumes standard atmospheric pressure. 59 degrees , so a 90 degree temp is going to change the ATMOSPHERIC PRESSURE and the air less favorable. The 5800 ft track is now equivalant to air pressure at 9000 ft.
So the DA calculation is much more accurate than the standard correction factor.
But if it were more accurate, then the NHRA would have adopted it. The key is that you will NEVER, NEVER, NEVER, NEVER get an accurate measurement of the actual temp, humidity, and barometric pressure for the DA from a website. That is what you don't seem to accept. If the info is not exact, the calculation cannot possibly ever, ever, ever, ever by "accurate". It won't be.
And shouldn't we ALL then be correcting for weather when we run, regardless of the altitude? Could you imagine what would happen if everyone started doing that? There are probably a dozen DA conversion calculators out there that will give you a dozen different times. Which one is correct?
Look - you can keep correcting your times - but you should continue to expect people to frown on it. And I give you just props that you go through all of this to run your car. You make us all proud by hitting the strip in your E63 (I know
) Keep up the running.
09-06-2007, 08:53 AM
#74
MBWorld Fanatic!
09-06-2007, 10:33 AM
#75
MBWorld Fanatic!
Thread Starter
Hey enzom ,
How accurate do you need to be?
Your car , you could run 50,000 times MIR, it will be faster all 50,000 times at MIR than if you ran 50,000 times at LACR.
The calculation is entirely spot on, I can prove it to you easily.
I can predict your car relatively close, what it will run at ten degree intervals, likely to the tenth.
So on a 90 degree day, and a 60 degree day without EVER seeing a time slip I can tell what you ran. Its a great predictor. Funny even the Corvette forum is SPLIT on this despite me never even getting to VOTE :-(
The calculation simply takes known air density at altitudes up to 12000 feet and round it to the nearest 100 feet , EXACTLY WHAT THE NHRA TABLE DOES!!!!!!!! EXACTLY
Are there any Engineers in this forum that can explain that this table is a derivative of AIR DENSITY?
When I drove 1800 miles RT to SAC 3 times, I had a number in my head. The first time ever sub 13 , and it happened on every run. On 300 plus runs at LACR my car never went sub 13 even with a 1.69 60 ft time. The car simply produces more power at STANDARD ATMOSPHERIC PRESSURE tham it can when at Altitude. As temps rise so does altitude at which the air pressure corresponds.
Here is why taking altitude correction alone is not accurate.
What if it is 42 degrees F at Palmdale instead of 59.9?
No longer does the car run as if it was at 2700 feet, it will run like 1700 feet so do you now use the 1600 ft elevation correction? I would LOL...
In the end you guys should GIVE MORE INFO, at least note the DA on the slip? or the temp and let folks that feel so inclined do a correction. Temp is critical to note IMHO.
If I raced you heads up at MIR and I may just to prove my point do you think you would win by .8?
You should certainly win ..
I just contacted NHRA technical dept.
I will als o call , I will be very suprised if they have the same opinion of DA correction as you. If they do , pop goes the weasel , I will never again correct a slip , k?
Last edited by juicee63; 09-06-2007 at 10:44 AM.
