When using JBM to figure out a drop chart, if I have a density altitude figure from using a Kestrel, do I plug that number into the altitude box, or does JBM automatically adjust for density altitude given the other values of input?
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- Thread starter Dark Horse
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Re: Density Altitude Question
The other atmospheric variables will tell JBM the same this as your density altitude number tells you. Put in your actual altitude and let it make the adjustment. If you were to put in your DA number, then plug in the other variables, it would change away from your DA. Does that make sense? DA is an adjusted altitude number based on the other variables, baro, temp, humidity...
The other atmospheric variables will tell JBM the same this as your density altitude number tells you. Put in your actual altitude and let it make the adjustment. If you were to put in your DA number, then plug in the other variables, it would change away from your DA. Does that make sense? DA is an adjusted altitude number based on the other variables, baro, temp, humidity...
Re: Density Altitude Question
So, if you put DA in the alt box and zero out all the variables you mention will you get good data?
So, if you put DA in the alt box and zero out all the variables you mention will you get good data?
Re: Density Altitude Question
No, you'd have to figure out the variables in such a way that they don't change your DA. If you don't have the measurement for your actual altitude, and you're trying to back figure it, you can look up one of the online calculators and plug in your numbers and play with it until you get what you need.
No, you'd have to figure out the variables in such a way that they don't change your DA. If you don't have the measurement for your actual altitude, and you're trying to back figure it, you can look up one of the online calculators and plug in your numbers and play with it until you get what you need.
Re: Density Altitude Question
There's another alternative, if you don't find one. As long as your variables produce the same DA, it doesn't matter what they actually are. DA is just a measure of air density, so however you get that density it will affect the ballistics the same.
In the past I have just plugged the numbers I know into a DA calculator and played around until I got the DA I wanted. Then just copy those input values into JBM and it will respond with ballistics equivalent to the DA value you are looking for.
Here's an example of a DA calc:
DA calculator
There's another alternative, if you don't find one. As long as your variables produce the same DA, it doesn't matter what they actually are. DA is just a measure of air density, so however you get that density it will affect the ballistics the same.
In the past I have just plugged the numbers I know into a DA calculator and played around until I got the DA I wanted. Then just copy those input values into JBM and it will respond with ballistics equivalent to the DA value you are looking for.
Here's an example of a DA calc:
DA calculator
Re: Density Altitude Question
DA is just an equivalent standard condition (15 celsius, 101.3 kPa, etc..) altitude to account for the variables at your position. ie, on a hot day at sea level DA might be 2000 ft to account for the lower air density due to the high temperature. In JBM enter your density altitude from your kestrel into the altitude box, then select std atmosphere at altitude further down the page.
DA is just an equivalent standard condition (15 celsius, 101.3 kPa, etc..) altitude to account for the variables at your position. ie, on a hot day at sea level DA might be 2000 ft to account for the lower air density due to the high temperature. In JBM enter your density altitude from your kestrel into the altitude box, then select std atmosphere at altitude further down the page.
Re: Density Altitude Question
I was always afraid to rely on that, so the standard atmosphere at altitude is their way of saying density altitude? Do you know if they use the same calculations? Sounds like a much easier route than mine!
I was always afraid to rely on that, so the standard atmosphere at altitude is their way of saying density altitude? Do you know if they use the same calculations? Sounds like a much easier route than mine!
Re: Density Altitude Question
Std. atmosphere at altitude is the definition of density altitude. Under ICAO standard atmospheric conditions density altitude is equal to actual elevation above sea level. (altitude) However, since conditions are almost never standard, density altitude is used to predict performance based on air density. Suppose your standing 1000 feet above sea and kestrel gives you a DA of 2000 feet. All its saying is that the air at your location has equivalent density to the air at 2000 ft on an ICAO standard day.
Cheers
Std. atmosphere at altitude is the definition of density altitude. Under ICAO standard atmospheric conditions density altitude is equal to actual elevation above sea level. (altitude) However, since conditions are almost never standard, density altitude is used to predict performance based on air density. Suppose your standing 1000 feet above sea and kestrel gives you a DA of 2000 feet. All its saying is that the air at your location has equivalent density to the air at 2000 ft on an ICAO standard day.
Cheers
Re: Density Altitude Question
What Charron said. Basically, DA is just a substitute for air density.
Life for ballistics program developers would be a litle easier if you could just type in air density, as that's the value that gets used in the calculations. But for various reasons, DA, temp, pressure, humidity, etc. are what people have access to. In the end the goal is always "how dense is the air?".
What Charron said. Basically, DA is just a substitute for air density.
Life for ballistics program developers would be a litle easier if you could just type in air density, as that's the value that gets used in the calculations. But for various reasons, DA, temp, pressure, humidity, etc. are what people have access to. In the end the goal is always "how dense is the air?".
Re: Density Altitude Question
Yep. I even say that in the posts above, it's just a measure of air density. What I wanted to confirm is that JBM ignores the other variables if you check standard atmosphere at altitude. If that's the case then we can forget about the whole DA calculator thing and just plug DA into JBM directly. Thanks
Yep. I even say that in the posts above, it's just a measure of air density. What I wanted to confirm is that JBM ignores the other variables if you check standard atmosphere at altitude. If that's the case then we can forget about the whole DA calculator thing and just plug DA into JBM directly. Thanks
Re: Density Altitude Question
Mash the big button on phone...
Hit the settings icon
Scroll down to and click on the FTE Icon
Click on JBM Computer
under Atmosphere change it to Density Altitude
Reboot the phone
Now you can enter D/A instead of all that other shit.
Mash the big button on phone...
Hit the settings icon
Scroll down to and click on the FTE Icon
Click on JBM Computer
under Atmosphere change it to Density Altitude
Reboot the phone
Now you can enter D/A instead of all that other shit.
Re: Density Altitude Question
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ~Ace~</div><div class="ubbcode-body">Mash the big button on phone...
Hit the settings icon
Scroll down to and click on the FTE Icon
Click on JBM Computer
under Atmosphere change it to Density Altitude
Reboot the phone
Now you can enter D/A instead of all that other shit. </div></div>
Smartass....
I'm just jealous. I have a Blackberry and my contract is almost up, soon I will have the cool toys...
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ~Ace~</div><div class="ubbcode-body">Mash the big button on phone...
Hit the settings icon
Scroll down to and click on the FTE Icon
Click on JBM Computer
under Atmosphere change it to Density Altitude
Reboot the phone
Now you can enter D/A instead of all that other shit. </div></div>
Smartass....
I'm just jealous. I have a Blackberry and my contract is almost up, soon I will have the cool toys...
Re: Density Altitude Question
There are a boat load of guys using DA even though it is purely based on "standard" atmosphere. I'd like to hear them chime in on how accurate it is.
There are a boat load of guys using DA even though it is purely based on "standard" atmosphere. I'd like to hear them chime in on how accurate it is.
Re: Density Altitude Question
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: coues7</div><div class="ubbcode-body">There are a boat load of guys using DA even though it is purely based on "standard" atmosphere. I'd like to hear them chime in on how accurate it is. </div></div>
It's perfectly accurate. Density altitude is simply the standard altitude that matches the actual air density at your current location. It's another way of saying "air density".
What can be less accurate is converting the (corrected) pressures from the local news (which are useful for weather prediction) into the absolute pressures we need for ballistic calculations. DA doesn't suffer from that problem.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: coues7</div><div class="ubbcode-body">There are a boat load of guys using DA even though it is purely based on "standard" atmosphere. I'd like to hear them chime in on how accurate it is. </div></div>
It's perfectly accurate. Density altitude is simply the standard altitude that matches the actual air density at your current location. It's another way of saying "air density".
What can be less accurate is converting the (corrected) pressures from the local news (which are useful for weather prediction) into the absolute pressures we need for ballistic calculations. DA doesn't suffer from that problem.
Re: Density Altitude Question
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SSSamurai</div><div class="ubbcode-body">No, you'd have to figure out the variables in such a way that they don't change your DA. If you don't have the measurement for your actual altitude, and you're trying to back figure it, you can look up one of the online calculators and plug in your numbers and play with it until you get what you need.
</div></div>
Sorry I'm a little late posting here but I think I should add this in case somebody else stumbles onto this thread. You don't have to guess what the inputs would be to get the correct Density Altitude (DA) you use standard values for Temperature (59), and air pressure(29.53 in hg) for all those inputs and then just enter the DA in the altitude field. Not all programs use these same standard valuse but most do. And, you only have to enter these standard values if your program doesn't have a DA only field.
DA is standard altitude that matches the actual air density at your current location taking into account temperature and humidity.
The great thing about Density Altitude is that it you don't have to know anything about anything to get great results, the Kestrel does it all you, just have to turn it on and let it settle.
The density altitude measurement does not rely on the reference values in the altitude or barometric pressure screens. The density altitude is a function of temperature, relative humidity and pressure. Only the altitude and barometric pressure measurements rely on a reference.
Density altitude takes station pressure into account instead of barometric pressure, there's no need to set a reference for an accurate density altitude reading. (Station pressure is the actual pressure reading, and barometric pressure is the pressure reading adjusted to your geographic altitude.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SSSamurai</div><div class="ubbcode-body">No, you'd have to figure out the variables in such a way that they don't change your DA. If you don't have the measurement for your actual altitude, and you're trying to back figure it, you can look up one of the online calculators and plug in your numbers and play with it until you get what you need.
</div></div>
Sorry I'm a little late posting here but I think I should add this in case somebody else stumbles onto this thread. You don't have to guess what the inputs would be to get the correct Density Altitude (DA) you use standard values for Temperature (59), and air pressure(29.53 in hg) for all those inputs and then just enter the DA in the altitude field. Not all programs use these same standard valuse but most do. And, you only have to enter these standard values if your program doesn't have a DA only field.
DA is standard altitude that matches the actual air density at your current location taking into account temperature and humidity.
The great thing about Density Altitude is that it you don't have to know anything about anything to get great results, the Kestrel does it all you, just have to turn it on and let it settle.
The density altitude measurement does not rely on the reference values in the altitude or barometric pressure screens. The density altitude is a function of temperature, relative humidity and pressure. Only the altitude and barometric pressure measurements rely on a reference.
Density altitude takes station pressure into account instead of barometric pressure, there's no need to set a reference for an accurate density altitude reading. (Station pressure is the actual pressure reading, and barometric pressure is the pressure reading adjusted to your geographic altitude.
Re: Density Altitude Question
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: CTressler</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SSSamurai</div><div class="ubbcode-body">No, you'd have to figure out the variables in such a way that they don't change your DA. If you don't have the measurement for your actual altitude, and you're trying to back figure it, you can look up one of the online calculators and plug in your numbers and play with it until you get what you need.</div></div>
Sorry I'm a little late posting here but I think I should add this in case somebody else stumbles onto this thread. You don't have to guess what the inputs would be to get the correct Density Altitude (DA); you use standard values for Temperature (59) and air Pressure (29.53 in hg) for all those inputs and then just enter the DA in the altitude field. Not all programs use these same standard values, but most do. And you only have to enter these standard values if your program doesn't have a DA only field.
DA is standard altitude that matches the actual air density at your current location, taking into account temperature and humidity.
The great thing about Density Altitude is that you don't have to know anything about anything to get great results, the Kestrel does it all you, just have to turn it on and let it settle.
The density altitude measurement does not rely on the reference values in the altitude or barometric pressure screens. The density altitude is a function of temperature, relative humidity and pressure. Only the altitude and barometric pressure measurements rely on a reference.
Density altitude takes station pressure into account instead of barometric pressure; there's no need to set a reference for an accurate density altitude reading. (Station pressure is the actual pressure reading, and barometric pressure is the pressure reading adjusted to your geographic altitude.</div></div>
thanks
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: CTressler</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SSSamurai</div><div class="ubbcode-body">No, you'd have to figure out the variables in such a way that they don't change your DA. If you don't have the measurement for your actual altitude, and you're trying to back figure it, you can look up one of the online calculators and plug in your numbers and play with it until you get what you need.</div></div>
Sorry I'm a little late posting here but I think I should add this in case somebody else stumbles onto this thread. You don't have to guess what the inputs would be to get the correct Density Altitude (DA); you use standard values for Temperature (59) and air Pressure (29.53 in hg) for all those inputs and then just enter the DA in the altitude field. Not all programs use these same standard values, but most do. And you only have to enter these standard values if your program doesn't have a DA only field.
DA is standard altitude that matches the actual air density at your current location, taking into account temperature and humidity.
The great thing about Density Altitude is that you don't have to know anything about anything to get great results, the Kestrel does it all you, just have to turn it on and let it settle.
The density altitude measurement does not rely on the reference values in the altitude or barometric pressure screens. The density altitude is a function of temperature, relative humidity and pressure. Only the altitude and barometric pressure measurements rely on a reference.
Density altitude takes station pressure into account instead of barometric pressure; there's no need to set a reference for an accurate density altitude reading. (Station pressure is the actual pressure reading, and barometric pressure is the pressure reading adjusted to your geographic altitude.</div></div>
thanks
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