Let's talk curves (Topic of the Week)

[bigD]

I'd like to second Bobby's recommendation of taking a physics course. Thermodynamics is indeed a physics subject, but a formal course of it requires a good working knowledge of PDE's, and that's not something that's taught in most high schools. Fortunately this kind of question doesn't require a formal thermodynamics course, and is generally covered in an entry level chemistry course as well.

If you really want to get hard core about the physics, take a fluids class. If you can, take one from the engineering department instead of the physics department - less math is required, and it's more applicable to real life situations. Then you won't have to spend all your time arguing with someone about what makes airplanes fly!

 

[100LL... Again!]

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If you really want to get hard core about the physics, take a fluids class.
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I did take a fluids class in college... down at the pub.
Nearly cost me a couple passing grades.

My thesis was in amber-colored carbonated fluids.

 

[bobbysamd]

School is (was) sooooo boring . . . . .

Where in tarnation were you 10 years ago?

If you really want to know, read some of my other posts. Also, in later years, wishing that (1) I had applied myself more in high school, especially regarding math and physics, although my teachers were essentially mediocre; and (2) wishing that I had taken a second B.S., in Aeronautical Science.

Of course, (2) is a whole 'nother subject that's been explored elsewhere.

 

[Timebuilder]

Amen, Bobby.

I think that what may be the easiest way to visualize what is going on here is this:

picture the airplane atop a column of air. If the air is cold, the column is shorter, because things contract when cold. If the air is warming, the column will become taller, because things expand (get longer or taller or wider) when they rise in temperature. The column height is representative of your actual height above the ground, while you altimeter indication remains the same for the same Kollsman window setting.

 

[midlifeflyer]

I did take a fluids class in college... down at the pub.
Nearly cost me a couple passing grades.

My thesis was in amber-colored carbonated fluids.

I didn't realize we went to school together!!

 

[uwochris]

CEO,

I had the exact same problems as you are having now... I would highly recommend you take a meteorology course at university (as I got to do) or read up on met in other books, especially those non-aviation related as they tend to get into more detail.

First off, colder air does not necessarily imply higher pressure than warmer air. It is possible to have an altimeter setting of 29.63 on a cold day, and the same setting on a warm day as well. Also, you can have a setting of 30.02 on a cold day, and on a hot day as well. Temperature is only one of variables to consider, there are others.

Second of all, the reason why your altimeter underreads in cold air has to do with the workings of the altimeter. You see, the altimeter is nothing more than an aneroid barometer that registers changes in height as the surrounding pressure changes. Now, since cold air tends to be more dense than warm air, the rate of pressure decrease with height is greater in cold air than it is in warm air, and so the constant pressure level at which you fly at (recall- since the altimeter is a barometer, pilots do not fly at constant altitudes, but at constant pressure levels) in colder air will be lower than it is in warmer air. It all has to do with the rate of pressure change with altitude, which in turn is affected by air densities, which in turn is affected by temperature (and other factors, such as moisture content).

I hope this helps a bit.

 

[ceo_of_the_sofa]

So, in the end, pressure remains the same despite the volume of a pressure level...and since the volume of a denser pressure level is smaller, it will effectively be closer to the ground...

Voila!

Hopefuly, this thread (if searched for, properly) will help someone with this issue...It has boggled CFIs and ATPs alike that I spoke too, and among other issues, I don't think enough time is being devoted to it in the classroom.

I am a SEL rated PP, but, even after passing the written and the checkride (to the FAA standards), I still feel that there's a lot more I had to have learned during the primary stage. It's kind of sad the FAA is so lax when it comes to stuff like this...

 

[Timebuilder]

It's kind of sad the FAA is so lax when it comes to stuff like this...

SHHH! They'll hear you!

You have the right idea, though. The PPL is the beginning of a continuous learning experience.