Two density altitude inputs.

Look at the link for a picture of my manual aviation computer. It has two
different places to put in pressure altitude and temp to get density
altitude and convert airspeeds. Can anyone explain the correct use of these
two similar functions?

http://flickr.com/photos/26467772@N05/2508589733/

On May 21, 4:55*am, "Danny Deger" wrote:
Look at the link for a picture of my manual aviation computer. *It has two
different places to put in pressure altitude and temp to get density
altitude and convert airspeeds. *Can anyone explain the correct use of these
two similar functions?

http://flickr.com/photos/26467772@N05/2508589733/


There is an instruction manual that comes with those things. Have you
ever tried to read it?

On Tue, 20 May 2008 13:55:43 -0500, "Danny Deger"
wrote:

Look at the link for a picture of my manual aviation computer. It has two
different places to put in pressure altitude and temp to get density
altitude and convert airspeeds. Can anyone explain the correct use of these
two similar functions?

http://flickr.com/photos/26467772@N05/2508589733/


Density altitude converts the current altitude to a "performance"
altitude, based on temperature and pressure.

For instance, if my local field (250 MSL) has the correct conditions
to create a 1250 MSL density altitude, I would use the performance
charts for 1250 ft. to predict my airplane's behavior and limits.

Here is the calculation:
http://en.wikipedia.org/wiki/Density_altitude

The airspeed conversion is used to convert indicated airspeed to true
airspeed by compensating for lower air density and temperature at
altitude.

http://en.wikipedia.org/wiki/True_airspeed


The instructions for the unit in the photo are actually printed on it.
Here's a link to a manual for a similar unit that may help better
explain:
http://www.asa2fly.com/files/support/E6B_Manual.pdf
Some aircraft have such converters built into the airspeed indicator.
http://en.wikipedia.org/wiki/Airspeed_indicator

The top photo has an instrument with rings allowing the pilot to set
the temperature and altitude, then the TAS is read from bottom of the
outside ring.

On Tue, 20 May 2008 13:55:43 -0500, "Danny Deger"
wrote:

Look at the link for a picture of my manual aviation computer. It has two
different places to put in pressure altitude and temp to get density
altitude and convert airspeeds. Can anyone explain the correct use of these
two similar functions?

http://flickr.com/photos/26467772@N05/2508589733/

Way too simple---read the print on the disk beneath the input windows
for each section--one place gives you density altitude as the product,
the other gives you airspeed and some other things listed which my
aging eyes could not make out in the picture.

Now, turn it over and figure out how to do a point-to-point using the
square grid in the bottom third of the slide on that side....

Drift and heading stuff using the back side of the disk is too easy.

Typical driver today probably never even gets one of those issued.

Ed Rasimus
Fighter Pilot (USAF-Ret)
"When Thunder Rolled"
"Palace Cobra"
www.thunderchief.org

In article ,
Ed Rasimus wrote:

Typical driver today probably never even gets one of those issued.

Yah. My first thought was that he'd found this one in the attic and
couldn't find the directions for it.

I use mine to calculate TAS once in a while. Sometimes I yank the
slide out because it's got mileage scales on the edges. That's
about it.

--
-Ed Falk,
http://thespamdiaries.blogspot.com/

"Mr.Smartypants" wrote in message
...
On May 21, 4:55 am, "Danny Deger" wrote:
Look at the link for a picture of my manual aviation computer. It has two
different places to put in pressure altitude and temp to get density
altitude and convert airspeeds. Can anyone explain the correct use of
these
two similar functions?

http://flickr.com/photos/26467772@N05/2508589733/


There is an instruction manual that comes with those things. Have you
ever tried to read it?

The one on the top/left is to correct indicated altitude to true altitude --
a function I have no use for. The one on the right is the one for density
altitude/airspeed correction -- a very useful function.

And mine didn't have a users manual. It was issued to me by the Air Force
and I was given training on how to use it. I didn't keep all of my training
material.

Danny Deger
Read my story, "Houston You Have a Problem" at
www.dannydeger.blogspot.com

In article ,
says...
On Tue, 20 May 2008 13:55:43 -0500, "Danny Deger"
wrote:

Look at the link for a picture of my manual aviation computer. It has two
different places to put in pressure altitude and temp to get density
altitude and convert airspeeds. Can anyone explain the correct use of these
two similar functions?

http://flickr.com/photos/26467772@N05/2508589733/

Way too simple---read the print on the disk beneath the input windows
for each section--one place gives you density altitude as the product,
the other gives you airspeed and some other things listed which my
aging eyes could not make out in the picture.

Now, turn it over and figure out how to do a point-to-point using the
square grid in the bottom third of the slide on that side....

Drift and heading stuff using the back side of the disk is too easy.

Typical driver today probably never even gets one of those issued.

geez, I've got one of those around here from my high school days..

--

"Oh Norman, listen! The loons are calling!"
- Katherine Hepburn, "On Golden Pond"