Analog technique to Calculate DA

[fujam]

Hello,
I'm looking for an analog way of converting my atomosphric inputs to determine the DA. I have found online converters but I'm looking for something that works independent of electronics and avoids long hand math. Are there paper charts or practical analog calcultors out there that anyone knows of? I've spent sometime looking for them here and elsewhere but I've been unsuccesful in digging them out. I figure they must exist given much of aviation's history predates modern electronics. Thanks for the help!

 

[_Windrider_]

 

[_Windrider_]

take your temp and enter the chart there. Go up to your elevation and then go left to read DA. You can ignore the conversion factor on the right unless you are super anal about getting exact numbers, pulse it’s a correction from barometric pressure not station pressure.
the in your head method is to remember DA is standard pressure corrected for non standard temperature. DA increases 1000’ for roughly every 15 degrees Fahrenheit above standard. So using sea level as an example if it was 89 degrees, DA would be 2000’ approximately.

 

[fujam]

awesome thank you @TacticalDillhole
That is exactly what I was looking for. Super simple and fast. However how much of a factor is humidity? I know it affects air density but also way less than pressure and temp.

 

[308pirate]

However how much of a factor is humidity?

Not important unless you're doing ELR

 

[308pirate]

View attachment 7478833

Beat me to it

DA is old news in aviation

 

[_Windrider_]

awesome thank you @TacticalDillhole
That is exactly what I was looking for. Super simple and fast. However how much of a factor is humidity? I know it affects air density but also way less than pressure and temp.

It’s no factor really. I ignore it, unless doing ELR. But you can see what it does easily by messing with any ballistic calculator. Most of us just set it at 50% and never change it. That way at worst you’ve cut any error by 50%. But the difference between 0 and 100% RH is like 300 feet. DA for most applications needs to be to closest 1000 ft increment.
if you are shooting ELR, you are going to measuring everything anyway.

 

[fujam]

Makes sense, just to see the influence of RH I input some numbers in JBM using a 300 gr Scenar going 2800 fps and the deference at a mile from 0-100% for a DA of 3500 was only .2mils so like you say using 50% RH cuts the maximum error in half and at most puts it at a tenth of a mil. Thanks for the attachment, and advice / guidance!!

 

[_Windrider_]

Makes sense, just to see the influence of RH I input some numbers in JBM using a 300 gr Scenar going 2800 fps and the deference at a mile from 0-100% for a DA of 3500 was only .2mils so like you say using 50% RH cuts the maximum error in half and at most puts it at a tenth of a mil. Thanks for the attachment, and advice / guidance!!

Somewhere along the line I got this. This isn’t my work, but the person is credited in the image.

 

[fujam]

Surprising how much heat thins the air. Kind of explains, in part, why hiking on a really hot day is more difficult than on a nice cool one.

 

[one shot ST]

Hello,
I'm looking for an analog way of converting my atomosphric inputs to determine the DA. I have found online converters but I'm looking for something that works independent of electronics and avoids long hand math. Are there paper charts or practical analog calcultors out there that anyone knows of? I've spent sometime looking for them here and elsewhere but I've been unsuccesful in digging them out. I figure they must exist given much of aviation's history predates modern electronics. Thanks for the help!

hello, I use this device, is an altimeter with absolut pressure, there is also a little temperature indicator and a compass.
you can have data to use with a table.
no difference with a kestrel
data are in metric, this table are from Field Firing Solution, there is a function to create and export DA table in excel format.

 

[fujam]

hello, I use this device, is an altimeter with absolut pressure, there is also a little temperature indicator and a compass.
you can have data to use with a table.
no difference with a kestrel
data are in metric, this table are from Field Firing Solution, there is a function to create and export DA table in excel format.

Thank you for sharing, this is an awesome solution! Completely analog from Sensors to determining DA. I like the tables you created using FFS. Might you mind sharing the excel table file? I ask because I use metric too and this table is perfect for my uses.

 

[one shot ST]

for other people, here the file for DA chart