Title: **For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**admin** on **February 17, 2011, 12:46:44 AM**

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Delved deep in the issue, Pejsa was not clear about it. However on page 76 in his book he stated that he adjusted his A function to equal the Mayevski a function at 2600fps.

this means that he uses the Ingalls conditions P=30inchHg, T=60F, humidity=67%.

The (ICAO air density)/(Ingals air density)=1.00371. Although the effects will be minor to the point of being neglible, I will adapt Pejsa's drag calculations in BfX to ICAO. Furthermore, I will add Mayevski Ingalls (under ICAO conditions) drag functions.

this means that he uses the Ingalls conditions P=30inchHg, T=60F, humidity=67%.

The (ICAO air density)/(Ingals air density)=1.00371. Although the effects will be minor to the point of being neglible, I will adapt Pejsa's drag calculations in BfX to ICAO. Furthermore, I will add Mayevski Ingalls (under ICAO conditions) drag functions.

Title: **Re: For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**ThunderDownUnder** on **February 17, 2011, 11:45:26 AM**

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Interesting research and all good news for BfX! Let us know when we need to update the add-in. I really think within 12 months your BfX functions will be in use by the sporting shooting community world wide. Your continuous improvements are much appreciated.

Ian

Ian

Title: **Re: For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**admin** on **February 21, 2011, 10:38:04 PM**

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I used several atmospheric density calculators on the net - they give different answers! It seemed that, in 2011, it is not clear how to compute the density of air! I know now also why people mention pressure, temperature and humidity and not density - it is not trivial to compute. I researched more and found an article called

"Revised formula for the density of moist air (CIPM-2007), Metrologia 45 (2008) 149–155"

I have a prototype implementation of it. Soon I will release a BfX function that calculates the air density and expand BfX_c to include humidity as an option. (humidity effects, however are very very small).

(CIPM = International Committee for Weights and Measures)

The calculations confirm the earlier calculations menitionned in this thread for the density for which Ingalls tables are valid, as well as its relative density to icao.

"Revised formula for the density of moist air (CIPM-2007), Metrologia 45 (2008) 149–155"

I have a prototype implementation of it. Soon I will release a BfX function that calculates the air density and expand BfX_c to include humidity as an option. (humidity effects, however are very very small).

(CIPM = International Committee for Weights and Measures)

The calculations confirm the earlier calculations menitionned in this thread for the density for which Ingalls tables are valid, as well as its relative density to icao.

Title: **Re: For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**ThunderDownUnder** on **February 26, 2011, 04:42:53 AM**

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Do you plan on adding atmospheric condition parameters to your 'Bullet Path and Elevation Functions', etc, (BfX_Zx and BfX_Ze)? I guess new function names would be needed e.g. BfX_Zxa, a for atmospheric. Thinking about this, it work make more sense to simply correct the ballistic coefficient by applying BfX_C to it within the existing functions.

I'm looking forward to making up a range chart using these functions when you have the update available and checking them against Berger Bullets ballistic calculator. I guess if humidity does not make much difference then the existing functions should be very accurate already. I'll make up some tables and check!

Ian

I'm looking forward to making up a range chart using these functions when you have the update available and checking them against Berger Bullets ballistic calculator. I guess if humidity does not make much difference then the existing functions should be very accurate already. I'll make up some tables and check!

Ian

Title: **Re: For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**admin** on **February 26, 2011, 09:08:59 AM**

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Indeed BfX_C is modified. I will put the update online immediately, then your weekend is still long enough to play with it.

Have also a look at gettingstarted. Furthermore look at bfx_ad.

I am in a hurry, one of the shooting friends is coming and we will go at a match at 10.00.

Have also a look at gettingstarted. Furthermore look at bfx_ad.

I am in a hurry, one of the shooting friends is coming and we will go at a match at 10.00.

Title: **Re: For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**admin** on **February 26, 2011, 09:33:30 AM**

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Quote from: ThunderDownUnder on February 26, 2011, 04:42:53 AM

I'm looking forward to making up a range chart using these functions when you have the update available and checking them against Berger Bullets ballistic calculator. I guess if humidity does not make much difference then the existing functions should be very accurate already. I'll make up some tables and check!

After the match, I will look!

Title: **Re: For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**ThunderDownUnder** on **February 26, 2011, 12:29:04 PM**

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I used your new BfX_C function in the calculation for trajectory, drift and velocity in a Range Chart application. I then checked it against Berger Bullets ballistic calculator (Bryan Litz designed program) and it is damn near perfect when using the same data including temp, pressure and humidity. Your BfX functions are really good, precise and accurate.

The new "GettingStarted" spreadsheet is now so much better and easier to understand. The use of the functions and the units can be easily understood in the well displayed example spreadsheets. It is amazing how many different units can be converted within the functions. This is a big update and really needs the new add-in and spreadsheet to be downloaded by all who are using it.

My spreadsheet tables can be downloaded here: http://www.safclass.com.au/Spreadsheets/Range%20Chart%20Using%20BfX_C.xls

Ian

The new "GettingStarted" spreadsheet is now so much better and easier to understand. The use of the functions and the units can be easily understood in the well displayed example spreadsheets. It is amazing how many different units can be converted within the functions. This is a big update and really needs the new add-in and spreadsheet to be downloaded by all who are using it.

My spreadsheet tables can be downloaded here: http://www.safclass.com.au/Spreadsheets/Range%20Chart%20Using%20BfX_C.xls

Ian

Title: **Re: For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**admin** on **February 26, 2011, 09:12:21 PM**

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Thx, I am flattered!

I saw your spreadsheet and found the formula =BfX_Zx("moa";$B$9;"fps";$B$12;"in";0;D5;"m";$B$13;"m";$B$10*BfX_C($B$5;$B$6;"inHg";$B$7/100);"g7")

In there you used BfX_C($B$5;$B$6;"inHg";$B$7/100)

This formula contains $B$7/100 because you expressed the humidity in %, for instance 50 and by default BfX_C expects a number from zero to 1. Hence you divided 50 by 100. However, I am not sure if you saw the "%H" qualifier that would have allowed you to write BfX_C($B$5;$B$6;"inHg";$B$7;"%H")

Robert.

I saw your spreadsheet and found the formula =BfX_Zx("moa";$B$9;"fps";$B$12;"in";0;D5;"m";$B$13;"m";$B$10*BfX_C($B$5;$B$6;"inHg";$B$7/100);"g7")

In there you used BfX_C($B$5;$B$6;"inHg";$B$7/100)

This formula contains $B$7/100 because you expressed the humidity in %, for instance 50 and by default BfX_C expects a number from zero to 1. Hence you divided 50 by 100. However, I am not sure if you saw the "%H" qualifier that would have allowed you to write BfX_C($B$5;$B$6;"inHg";$B$7;"%H")

Robert.

Title: **Re: For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**ThunderDownUnder** on **February 27, 2011, 10:18:13 AM**

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I added "%H" as suggested for use in the spreadsheet and its been uploaded to the website. Thanks for the suggestion, I seem to have overlooked the functions ability to convert to almost anything. BfX functions have great versatility with unit conversion, a much appreciated quality that you have included for no extra cost :)

When I get time I will explore the BfX_AD function and see if I can use it somewhere!

Ian

When I get time I will explore the BfX_AD function and see if I can use it somewhere!

Ian

Title: **Re: For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**ThunderDownUnder** on **March 05, 2011, 01:15:23 AM**

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Improved the Range Chart spreadsheet.

Download from here: http://www.safclass.com.au/Spreadsheets/Range%20Chart%20Using%20New%20BfX_R2.xls

Ian

Download from here: http://www.safclass.com.au/Spreadsheets/Range%20Chart%20Using%20New%20BfX_R2.xls

Ian

Title: **Re: For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**admin** on **March 05, 2011, 08:22:58 AM**

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Thanks for putting some life in this forum!

After the match (60 shots; 100m small bore 30x and 30x big bore), this evening I will have a better look. With BfX_U you can use the unit also as input parameter - your ballistic calculator becomes unit independent.

After the match (60 shots; 100m small bore 30x and 30x big bore), this evening I will have a better look. With BfX_U you can use the unit also as input parameter - your ballistic calculator becomes unit independent.

Title: **Re: For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**ThunderDownUnder** on **March 05, 2011, 10:23:28 AM**

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Quote from: admin on March 05, 2011, 08:22:58 AM

Thanks for putting some life in this forum!

After the match (60 shots; 100m small bore 30x and 30x big bore), this evening I will have a better look. With BfX_U you can use the unit also as input parameter - your ballistic calculator becomes unit independent.

I really think that that once people realise how useful and easy BfX functions are to use we will see many spreadsheets posted here to share. All the thanks goes to you Robert, for your ballistic add-on!

"With BfX_U you can use the unit also as input parameter - your ballistic calculator becomes unit independent." If you get a chance could you put up a sample use of this concept?

Ian

Title: **Re: For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**ThunderDownUnder** on **March 05, 2011, 10:49:03 PM**

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Thank you for the email with attached example spreadsheet. Whats the famous cliche? "its easy when you know how" I will use the name method of applying different units of measure in all my future spreadsheets.

I shot in 300 metre F-Open yesterday using my 22BR (90gr Berger VLD's @ 3160fps) in light wind with many direction reversals and velocity changes. The wind changes were probably at max 1 moa. Out of a possible score of 60 (USA 100) in the second round I scored 58.7X (USA 98.7X). The little 22BR in a 10Kg rifle has very little recoil and with slightly better ballistics than a 6BR. Couple that with my much improved understanding of ballistics I still could not manage better than two points off of 60.

In long distance shooting once you have ballistics covered it all comes down to wind reading. It seems the challenge of wind reading and conditions is the one variable that will never be able to be dropped into a spreadsheet and I wouldn't have it any other way.

Ian

I shot in 300 metre F-Open yesterday using my 22BR (90gr Berger VLD's @ 3160fps) in light wind with many direction reversals and velocity changes. The wind changes were probably at max 1 moa. Out of a possible score of 60 (USA 100) in the second round I scored 58.7X (USA 98.7X). The little 22BR in a 10Kg rifle has very little recoil and with slightly better ballistics than a 6BR. Couple that with my much improved understanding of ballistics I still could not manage better than two points off of 60.

In long distance shooting once you have ballistics covered it all comes down to wind reading. It seems the challenge of wind reading and conditions is the one variable that will never be able to be dropped into a spreadsheet and I wouldn't have it any other way.

Ian

Title: **Re: For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**admin** on **March 05, 2011, 11:42:16 PM**

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I was't happy with my own match. I shot a mere 567 of 600. 30 shots with small bore, 30 with a big bore, both at 100m indoor, iron sights, shooting jacket. I am still puzzled how that could happen - a too busy week, causing a dimnished sharpness? My friend shot 585 - that is better.

Next week I'll shoot my service rifle - outdoors 100m, iron sight shooting jacket. Wind is no problem but the light is.

Next week I'll shoot my service rifle - outdoors 100m, iron sight shooting jacket. Wind is no problem but the light is.

Title: **Re: For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**mman** on **May 08, 2011, 08:23:02 PM**

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Quote from: admin on February 21, 2011, 10:38:04 PM

I used several atmospheric density calculators on the net - they give different answers! It seemed that, in 2011, it is not clear how to compute the density of air! I know now also why people mention pressure, temperature and humidity and not density - it is not trivial to compute. I researched more and found an article called

"Revised formula for the density of moist air (CIPM-2007), Metrologia 45 (2008) 149–155"

I have a prototype implementation of it. Soon I will release a BfX function that calculates the air density and expand BfX_c to include humidity as an option. (humidity effects, however are very very small).

(CIPM = International Committee for Weights and Measures)

The calculations confirm the earlier calculations menitionned in this thread for the density for which Ingalls tables are valid, as well as its relative density to icao.

This air density issue is interesting.. I compared my own air density calculator results to bfx results. There seems to be some differences.. Error between these results is highest when temperature and humidity are high. Actually difference can be as much as few percents... I've always thought that air density for ICAO conditions is 1.225 but with your new formulas it seems to be 1.226. I don't know what is right but my calculator is in line with quick target 3.2 and very close to litz's PMBS.

Here is direct comparison in excel file:

http://dl.dropbox.com/u/12618884/Air%20density%20calculation.xlsx

Title: **Re: For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**admin** on **May 08, 2011, 09:52:09 PM**

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well, it proves the point that it is not trivial to compute.

I stick with my implementation of "Revised formula for the density of moist air (CIPM-2007), Metrologia 45 (2008) 149–155".

Back to QT. I have no clue how the radar measurements are done and interpreted. I have the following issue.

Under which elevations the bullets are fired? How does one know the air density corrections?

(and How does one know the properties for v0 close to 0?

If one fires a bullet at various v0, how does one correct for various yaw related effects on bc?)

I stick with my implementation of "Revised formula for the density of moist air (CIPM-2007), Metrologia 45 (2008) 149–155".

Back to QT. I have no clue how the radar measurements are done and interpreted. I have the following issue.

Under which elevations the bullets are fired? How does one know the air density corrections?

(and How does one know the properties for v0 close to 0?

If one fires a bullet at various v0, how does one correct for various yaw related effects on bc?)

Title: **Re: For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**mman** on **May 09, 2011, 08:44:44 AM**

Post by:

Quote from: admin on May 08, 2011, 09:52:09 PM

well, it proves the point that it is not trivial to compute.

I stick with my implementation of "Revised formula for the density of moist air (CIPM-2007), Metrologia 45 (2008) 149–155".

Yeah, I haven't read the article yet, but it may even be the best formula so far. Still this arises questions about the accuracy of trajectory calculations. If we can't even calculate air density more accurate than that, how one can except that bcs are measured for the accuracy of 1 %. For example Litz claims that his measurements are in those limits. I'll look into this when I have more time.

Quote from: admin on May 08, 2011, 09:52:09 PM

Back to QT. I have no clue how the radar measurements are done and interpreted. I have the following issue.

Under which elevations the bullets are fired? How does one know the air density corrections?

I'm not sure if I got your point... Is it that you are concerned about the accuracy of measurements or something else? If I'm not wrong it seems to be that most error in air density happens when humidity changes a lot. This is a weakness of ICAO standard. If measured bcs are corrected to ICAO conditions, there is always a huge variation in humidity. When in ICAO condition's humidity is 0%, in real world it is nearly always much higher. I think the pressure isn't so much of a problem. It can be directly measured and that counts out the elevation issue, at least if trajectory isn't very high. It also turns out that those equations pretty much agree in pressure effect to air density.

Quote from: admin on May 08, 2011, 09:52:09 PMYaw effect to drag is insignificant.. And when it isn't aerodynamic jump or unstability will destroy the groups anyways..

(and How does one know the properties for v0 close to 0?

If one fires a bullet at various v0, how does one correct for various yaw related effects on bc?)

Title: **Re: For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**admin** on **May 10, 2011, 02:42:11 PM**

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the radar measurement... if the bullet went up a few kilometres, how do you know the conditions.... balloons?

Title: **Re: For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**mman** on **May 10, 2011, 07:06:46 PM**

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Aa okay... That's a good point. Lapua's ballisticians do not make very much noise about what they do, they might still answer if someone would ask them..

Title: **Re: For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**RidderMare** on **July 09, 2011, 02:59:43 PM**

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Dear Robert,

The real beauty of the Pejsa model is that you can model your own dragfunction, tailored to your own data.

Do I understand it correctly that your Pejsa function is fixed to the retardation coefficient rate of 0.5?

If that is the case, it is not possible to model your own drag function any more.

Would it be possible to modify the retardation coefficient rate in Bfx, and if not, would it be possible to incorporate that in the code? I would be much appreciated if you could.

Best regards,

AL

The real beauty of the Pejsa model is that you can model your own dragfunction, tailored to your own data.

Do I understand it correctly that your Pejsa function is fixed to the retardation coefficient rate of 0.5?

If that is the case, it is not possible to model your own drag function any more.

Would it be possible to modify the retardation coefficient rate in Bfx, and if not, would it be possible to incorporate that in the code? I would be much appreciated if you could.

Best regards,

AL

Title: **Re: For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**admin** on **July 09, 2011, 08:45:55 PM**

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Al,

The retardation coeficient is not used in BfX. I use Pejsa's drag function, what Pejsa calls in his book "a far superior drag function". What a retardation coeficient and slope factor allows is to create your own drag function. During my holidays I will see how I could allow users of BfX to supply their own drag functions/tables.

In the mean time you might consider adapting the ballistic coefficient. If you give me your data I will show you how to do it. On the otherhand you can follow a procedure I have published in one of the downloads to do so.

Robert

The retardation coeficient is not used in BfX. I use Pejsa's drag function, what Pejsa calls in his book "a far superior drag function". What a retardation coeficient and slope factor allows is to create your own drag function. During my holidays I will see how I could allow users of BfX to supply their own drag functions/tables.

In the mean time you might consider adapting the ballistic coefficient. If you give me your data I will show you how to do it. On the otherhand you can follow a procedure I have published in one of the downloads to do so.

Robert

Title: **Re: For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**RidderMare** on **July 10, 2011, 10:28:20 PM**

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Dear Robert,

Thanks for your offer. However I know how to use the Pejsa model and know how to use the retardation coefficient, but it will be great if it can be used with BfX. For me it will most certainly add value (and maybe for a few others as well ;-)).

Al

Thanks for your offer. However I know how to use the Pejsa model and know how to use the retardation coefficient, but it will be great if it can be used with BfX. For me it will most certainly add value (and maybe for a few others as well ;-)).

Al

Title: **Re: For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**admin** on **July 11, 2011, 12:33:07 PM**

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... nevertheless I am quite curious now, can you give me an example of what you are doing?

Title: **Re: For which atmospheric conditions did Pejsa derive his drag functions**

Post by:**RidderMare** on **August 06, 2011, 03:39:33 PM**

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Dear Robert,

I will post an example later this month. Its holiday season here in Belgium and my kids don't allow me to sit behind the computer a lot.

Regards,

AL

I will post an example later this month. Its holiday season here in Belgium and my kids don't allow me to sit behind the computer a lot.

Regards,

AL