Pressure Altitude

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jesse

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Jesse
Is pressure altitude of any value to a pilot other than for determining density altitude?

I ask because I'm building an e6b and started to wonder if there were a point in having separate functions for pressure altitude and density altitude. It seems like it'd be easier to just have it be one function.
 
Isn't it pressure altitude that you need for setting the true air speed indicator? I don't remember.
 
From an E6B standpoint, how would you redesign so it was only one function if you still need pressure altitude to calculate density altitude?
 
Pressure altitude is often used to calculate performance numbers where temperature is omitted or in the case of a tabulated performance chart, located in a separate column/row.
 
jesse said:
Is pressure altitude of any value to a pilot other than for determining density altitude?
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It's what you fly in the flight levels. I know you know that.... but I can't see how you need to calculate PA... just set 29.92 in the Kollsman window and fly it...

-Skip
 
I'm assuming this is a web based thingy. If so, I suggest you output both. Pressure altitude as far as I know is only used as Jason said when the performance tables are in alt and temp.

Are you going to calculate aviation density altitude, or take into account humidity and get real DA?

Joe
In case you haven't done it yet I do have something to calculate wind correction angle and GS, you're welcome to.

Joe
 
midlifeflyer said:
From an E6B standpoint, how would you redesign so it was only one function if you still need pressure altitude to calculate density altitude?
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You just wouldn't ask for pressure altitude on the density altitude calculation. Instead you'd ask for indicated altitude and pressure. The more I think about it though - the more sense it makes to do it like it's always been done. As you might have a more accurate pressure altitude.
 
Areeda said:
I'm assuming this is a web based thingy. If so, I suggest you output both. Pressure altitude as far as I know is only used as Jason said when the performance tables are in alt and temp.

Are you going to calculate aviation density altitude, or take into account humidity and get real DA?
Click to expand...
It's not a web based thing - but it's unlikely the pilot would know the humidity nor would most understand why its needed. SO it'll be aviation density altitude.

JesseWeather's density altitude graph is a little better and does take into account humidity.
 
jesse said:
It's not a web based thing - but it's unlikely the pilot would know the humidity nor would most understand why its needed. SO it'll be aviation density altitude.

JesseWeather's density altitude graph is a little better and does take into account humidity.
Click to expand...
Please tell me it's a reasonable priced Android app. I want one of those.

Joe
 
jesse said:
You just wouldn't ask for pressure altitude on the density altitude calculation. Instead you'd ask for indicated altitude and pressure. The more I think about it though - the more sense it makes to do it like it's always been done. As you might have a more accurate pressure altitude.
Click to expand...

Indicated altitude, pressure altitude, and altimeter setting are three variables in a two state equation. IOW if you know any two, you can calculate the third. If your real goal is air density (or it's cousin "density altitude") you also need air temperature (and humidity, water content, or dew point if you want to be precise) but pressure altitude or static air pressure is all that's needed in addition to temp and humidity to get density.

For a pilot flying below the flight levels, the combination of indicated altitude and altimeter setting is easiest since those are always available on the face of the altimeter without moving anything. In my airplane, pressure altitude is also available on the face of the transponder.
 
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gismo said:
Indicated altitude, pressure altitude, and altimeter setting are three variables in a two state equation. IOW if you know any two, you can calculate the third. If your real goal is air density (or it's cousin "density altitude") you also need air temperature (and humidity, water content, or dew point if you want to be precise) but pressure altitude or static air pressure is all that's needed in addition to temp and humidity to get density.

For a pilot flying below the flight levels, the combination of indicated altitude and altimeter setting is easiest since those are always available on the face of the altimeter without moving anything. In my airplane, pressure altitude is also available on the face of the transponder.
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Understand that. I was thinking in the sense of traditional e6bs. Generally the work flow for the pilot, if they were standing in the FBO, would be to first determine pressure altitude by using field elevation and pressure from the ASOS. From there they would take that pressure altitude and apply that to the density altitude calculation. I was thinking about merging that all into one step instead of having two separate workflows.

I realize that a truly accurate density altitude would require more information but I'm not trying to determine precise density altitude - I'm trying to provide an e6b similar to all the other ones out there.
 
jesse said:
Understand that. I was thinking in the sense of traditional e6bs. Generally the work flow for the pilot, if they were standing in the FBO, would be to first determine pressure altitude by using field elevation and pressure from the ASOS. From there they would take that pressure altitude and apply that to the density altitude calculation. I was thinking about merging that all into one step instead of having two separate workflows.

I realize that a truly accurate density altitude would require more information but I'm not trying to determine precise density altitude - I'm trying to provide an e6b similar to all the other ones out there.
Click to expand...

I see no problem having the user enter indicated (or field) elevation and the local altimeter setting along with OAT to arrive at DA in one step rather than making it a two step process with pressure alt as an intermediate result, if that's what you're asking.
 
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