uwochris
Flightinfo's sexiest user
- Joined
- Dec 21, 2001
- Posts
- 381
Hey guys,
I am very confused with a few concepts, and I hope some people can help clarify the situation for me and explain some issues in a very simple manner. The first deals with the relationship between air pressure, density and flight performance, while the second concern deals with pressure altitude.
First off, I read in my flight manual that air density is dependant upon air temperature and air pressure. I realize that warmer air is less dense than cool air- no problem here; however, does air density increase as air pressure increases, or is it the other way around- air pressure increases as air density increases? Does it even make a difference how the relationship is stated (ie. higher pressure causes higher density VERSUS higher density causes higher pressure). I know the gas law is stated in terms of pressure.
Now... how does all this affect flight performance? I get confused because I know that different air pressures can affect the instruments, but can the pressure differentiation directly affect flight performance? ...... this is what I am assuming- higher air pressure causes the air density to increase because more molecules are getting compressed. This increase in air density (caused by a higher air pressure) increases performance because of the extra force exerted during downwash and by the extra thrust created by the engine. Am I right? Does a higher air pressure (ie. 30.00' versus 28.00') give better aircraft performance by affecting air density, or am I completely mistaken? Perhaps air pressure and performance aren't even directly related??
Now on to my other concern... pressure altitude. I just hope someone can provide a very simple, easy to understand definition of what pressure altitude is. I know that it is "indicated altitude corrected for non-standard pressure." The problem for me is that I always assumed that indicated altitude already compensated for non-standard pressure (ie. when you use the altimeter setting, aren't you directly correcting your altitude for non-standard pressures? Another explanation I received is that PA is "the altitude the aircraft THINKS it is flying at, assuming standard temperature. Is this correct? If so, I assume that a higher air pressure gives a lower pressure altitude, and thus, implies better performance (because flight performance diminishes with increases in elevation).
Well, I really appreciate all the opinions and truly hope someone can help clarify these issues for me.
Thanks a lot.
I am very confused with a few concepts, and I hope some people can help clarify the situation for me and explain some issues in a very simple manner. The first deals with the relationship between air pressure, density and flight performance, while the second concern deals with pressure altitude.
First off, I read in my flight manual that air density is dependant upon air temperature and air pressure. I realize that warmer air is less dense than cool air- no problem here; however, does air density increase as air pressure increases, or is it the other way around- air pressure increases as air density increases? Does it even make a difference how the relationship is stated (ie. higher pressure causes higher density VERSUS higher density causes higher pressure). I know the gas law is stated in terms of pressure.
Now... how does all this affect flight performance? I get confused because I know that different air pressures can affect the instruments, but can the pressure differentiation directly affect flight performance? ...... this is what I am assuming- higher air pressure causes the air density to increase because more molecules are getting compressed. This increase in air density (caused by a higher air pressure) increases performance because of the extra force exerted during downwash and by the extra thrust created by the engine. Am I right? Does a higher air pressure (ie. 30.00' versus 28.00') give better aircraft performance by affecting air density, or am I completely mistaken? Perhaps air pressure and performance aren't even directly related??
Now on to my other concern... pressure altitude. I just hope someone can provide a very simple, easy to understand definition of what pressure altitude is. I know that it is "indicated altitude corrected for non-standard pressure." The problem for me is that I always assumed that indicated altitude already compensated for non-standard pressure (ie. when you use the altimeter setting, aren't you directly correcting your altitude for non-standard pressures? Another explanation I received is that PA is "the altitude the aircraft THINKS it is flying at, assuming standard temperature. Is this correct? If so, I assume that a higher air pressure gives a lower pressure altitude, and thus, implies better performance (because flight performance diminishes with increases in elevation).
Well, I really appreciate all the opinions and truly hope someone can help clarify these issues for me.
Thanks a lot.