New Way to Think About Pressure & Density Altitude | Aircraft Performance Explained

Do you know how what pressure and density altitude are? It's a weak area on many checkrides. Here is a new method of understanding it, which will help you conceptualize and calculate it.
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[@space1commander]

I did my ground School in 1998 and whether, pressure, and density altitude was the hardest topic to understand to me. I could only wish that FlightInsight had this type of video on KZbin back in the days. But, now after watching this beautifully explained Videos by Dan I think I got it now.

[@A_Mongey]

I'd like to add to this just in case there is anyone like me who will ask why something is the way it is down to the smallest detail, and if it was explained in the video, I must've missed it. But the reason pressure alt is multiplied by 1,000 is because there is a 1,000ft difference for each inch of mercury and density alt is multiplied by 120 because there is 120ft difference between each degree of temp(C).

[@charlesli4012]

But isn't the standard lapse rate of 1000ft for 2 degree of temp(C)?

[@nabilelyousofy9318]

I will look into to this comment the moment i understand the concept of this subject as it is not an easy one to actually comprehend by heart easily..but thank you

[@glennwatson]

For those interested, for countries that use hPA and feet, standard atmosphere = 1013.2hPa, expected change per hPa to feet is 30 feet, so therefore, Pressure Altitude = (1013 - (current qnh)) * 30. The density altitude calculation is the same as the video.

[@nadifhadien8297]

where is the 120 come from in density altitude calculation?

[@glennwatson]

@@nadifhadien8297 the expected change in altitude per degree celcius. So 120 feet per degree of celcius.

[@glennwatson]

@@nadifhadien8297 basically a number they figured out from gas law in physics.

[@nadifhadien8297]

@@glennwatson i see, thank you!

[@aviatortrucker6285]

I remember when I used to fly overseas in a military arrow club. They would always report the altimeter setting in millibars . It was always referred to as QNH. Both steam gauge alters have a second Kohlsman window on the left that has the millibar numbers.

[@khrdina]

A couple of times toward the end of the video (at 4:58 and at 6:00) you called out the pressure as 30.25" rather than 30.22". I think having the temperature as 25 distracted you! :D This was a really good explanation, especially having the sliding scales on-screen while you spoke.

[@kam1583]

Very nicely explained, my ground school was in 1975, and I used to calculate it with my circular slide rule

[@refness3108]

Pressure Altitude = Field Elevation + (1013.25-local QNH setting)) * 27 or 30feet While Density altitude is the pressure Altitude plus (OAT-ISA Temp)) * 120 Off course E6b can be more useful and easier to get both values

[@chrisbautista827]

Nicely explained!

[@EmberHarrington]

Excellent Video!! Thank you so much!

[@jrmiller43015]

This is wonderful, I finally understand this thing... thanks SO MUCH!

[@gerry602]

what i would really love to understand more is the relationship between the changes in density, pressure, and temperature. i keep trying to understand a chart that basically says temperature affects density a lot alow altitudes but as you go up, that's no longer true and it affects pressure more..i think.. but i know density affects temperature too? and pressure, and ...well.. it's too confusing at that point

[@bartoszskowronski]

how much moisture (dewpoint) interact with density altitude and engine performance? (one gram of H2O vapor takes more space than one gram of air). For wings moisture will have less effect then on engine because you can fly on water vapor, but you can not burn fuel with water instead oxygen.

[@nicksantos1042]

cool vid!

[@iliegotca1049]

Privet from Moldova!!!! You the best

[@user-kx9im1oo1i]

Zdarova blyat 👍

[@Everythingisgonna_beok]

Where did the number 120 come from when calculating DA?

[@austinbrace6765]

So a question I haven't been able to get answered is why we subtract our pressure variance(not sure what its called) on our performance charts. So what I mean is if the local altimeter is saying 30.02 and I plan on flying at a cruise alt of 5500 and my field elevation is 628. I would use performance numbers for 5400' for my cruise alt and 528 for my takeoff performance. I'm having a hard time following why we do this. When we adjust our altimeter aren't we flying at that pressure altitude? What makes sense to me is to adjust or landing and take-off performance because we cant change what elevation we are taking off and land at. On the other hand when it comes to like engine performance at 5500 why do i use 5400, am I not flying at 5500?

[@EmberHarrington]

So when you establish your pressure and density altitude pragmatically how do you fly differently? There are needless to say different factors as well ie clouds, flight path etc? Thanks much.

[@nicholasotero5532]

When calculating the standard temperature for use in the density altitude equation, do you use True Altitude or Pressure Altitude?

[@charlesprenaveau4969]

Pressure Alt.

[@fzakrzewski]

Density Altitude (in Feet) = Pressure Altitude (in Feet) + (120 x (OAT°C - ISA Temperature °C)) Where: DA = Density Altitude (ft), PA = Pressure Altitude (ft), (the two values below for your actual flight you look for on the Winds Aloft chart on aviation weather website - Google "wind/temps aviation weather" - first url; at least for me!) OAT = Outside Air Temperature (Celsius), ISA = Standard Temperature (Celsius) Equation: DA = PA + (120 x (OAT - ISA))

[@jimallen8186]

Show a water tower preferable old school wooden barrel like cylinder water tower. Highlight how the rings or metal bands about the tower are more closely spaced near the bottom of the tower. Then go into this discussion.

[@manuelgugger7056]

what simulator are you using? I want to buy one too for my IFR training

[@jacksongriggs1468]

MSFS 2020, highly recommend. Sim flying made my IFR ride so much less stressful!

[@lil_will23]

Where did that expression 120 come from I got my test tomorrow morning 😢

[@CashMoney5280]

120feet… 120 feet because there is difference between each degree of temp (C).

[@SoloRenegade]

the best way to teach Denisty Altitude, is for someone to fly out of a high DA airport. it never makes as much sense as after having experienced it.

[@NikolaB93]

If Airplanes have poor preformance at high altitudes why airlanes struggle so much to get higher flight levels??

[@aviatortrucker6285]

That calculation is a lot more accurate than trying to use an E6B. The numbers in between the tick marks are so hard to use. It is better to use an electronic E6B or do it on paper. I can only imagine trying to figure that out while you are in the airplane.

[@Saml01]

You don't figure it out when you are in the plane. You figure that out on the ground before you leave the house by either doing the math by hand or using foreflight forecast. If you're at the field, just call the asos/awos.

[@patrick5372]

The dumb thought that unlocked me being able to reason about DA is that “high” describes altitude, not density.

[@A_Mongey]

Same! When I realized high density altitude actually meant low density, it made way more sense to me.

[@AllegeK]

High pressure is not always cool. Low pressure is not always warm. Totally wrong

[@SoloRenegade]

relative to one another, they are. other factors can flip that, if the temps are close enough together to offset the temp difference by other factors. But if all you're comparing is temp differences of otherwise identical locations, cooler air is more dense. But if you think you know better, prove it. give an example scenario to explain your claim that anything said in this video was wrong.