Ep. 58: How an Altimeter Works | Inner Workings

In this video we'll take another look at one of our primary aircraft instruments (Altimeter) and how it works. We'll go over how adjusting the setting in the kollsman window affects the altimeter as well as how it is able to measure abient pressure.
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[@c2protect]

John thanks so much for breaking this all down. I'm working on my instruments and reinventing myself for the 4th time in 53 years. This helps greatly. We appreciate the the insight and effort you provide.

[@jeremymendoza4394]

What a great demonstration! I'm a visual person and that was much easier to understand than reading a book. Any thoughts on doing the same for the other 6-pack instruments? Thanks!

[@fly8ma.comflighttraining199]

I'd be happy to do it for the other instruments too! I do have a vid up on the turn coordinator, but would have to take some time asking around to find other extra instruments to chop up!

[@zeneyel]

Me too, but I do not understand, what is the concrete function of the kollsman window?

[@airwipe1639]

@@zeneyel you probably have your commercial by now but its where you set the barometric pressure

[@philippenguyen7339]

Oh yes I approve this comment, my god just imagine the genius that invented this

[@davidwallace5738]

Thank you sir for breaking it down in simple trems. Great job!

[@fly8ma.comflighttraining199]

Happy that it helped ya!

[@Pianist7137Gaming]

How have I never noticed that the "ALT" moves as well! Great video!

[@5tnguyen]

so cool that you added the tip of the checkers part of reading the altimeter near the end of this video, wish i knew this when I was learning my private pilot written.

[@francescocandian2708]

AWESOME! Thank you so much! Used these things for decades, always knew the theory, but never actually got to see the inside and the mechanics! This was extremely useful!

[@romeo16668]

I am an airline pilot with 8500 hrs of jet experience, and this is my first time seeing what is inside altimeter..thanks

[@iket7396]

Excellent! This is a great supplement to the 8083

[@TamilFlightSimmer]

Well explained appreciate it

[@maheralazzawi7814]

very good

[@sureshkm]

Very very helpful! Thanks

[@BK-it6te]

Excellent

[@peterweiss2925]

Great Stuff!!! Hope all my students are watching! I sure am!

[@theleetbeagle]

Excellent video.

[@Joel07zx6r]

Thats really cool. Ive been watching your videos all afternoon Geat job

[@fly8ma.comflighttraining199]

Thanks, Safe Flying!

[@spdmusicproductions3435]

That's really cool and great information Jon! Thanks.

[@fly8ma.comflighttraining199]

Glad it helps!

[@jtveg]

Thanks so much for sharing. 😎👌🏼

[@keepitsimple5982]

Very useful about what it is for and how pilots read the dials - but sorry, it is WRONG about the capsules/wafers in it. They are referred to as "aneroid" because it means without air. During the manufacture the air is pumped out, then sealed. They would collapse under the pressure from the air except that a flat spring holds them open. As the air pressure around the capsules varies the amount of pull on the spring changes and with that the spring moves; turning the gears etc. as described.

[@jamesmacneil1609]

Excellent video. Best one I've seen you do so fr. Was mesmerized watching it. Thank you. I'm in 5th week of ground school. J.B.

[@jjbird420]

Your awesome. Thanks dude.

[@fly8ma.comflighttraining199]

Much appreciated! I'm always happy to help

[@robertocarriero5728]

Muy bueno. Muchas gracias

[@avaitionlovr]

Very educational video thanks a lot

[@fly8ma.comflighttraining199]

Glad it helps! Check out some of the other instrument "take apart" vids on our channel too!

[@eddy4135]

Thanks

[@laerciosantos2728]

Very good explanation, thank you.

[@sethregan8734]

That is so cool

[@MrVineet32]

Fantastic explanation, Please make one for VSI

[@joerandom756]

It is probably safe to say I can't use this for my project, If it is fragile and needs replaced often.

[@DOLRED]

Thanks!

[@fly8ma.comflighttraining199]

Glad it helps! Share us with your friends on facebook and around the airport! Check out the new site at www.fly8ma.com !

[@diegosplendore6626]

Great video! Just a question: are you sure the capsule (wafer) contains any gas? I've always found the term "aneroid diaphragm" in several handbooks. That means "vacuum chamber" so an empty space into the wafer. Any gaseous element goes subject to expansion and contraction (pressure variation) due to temperature change. This is my understanding of the physics of gases. Thank you!

[@IdleIslander]

Diego, It has to contain some gas. The gas "expands" as the pressure outside the chamber decreases. If the chamber did not contain any gas, it would not expand. In this context, "vacuum chamber" probably refers to a low pressure environment. Also, the altimeter IS affected by temperature. The amount of error depends on the height above sea level and the temperature. When it is hotter, the indicated altitude shows you are lower than you actually are, which isn't generally a problem. However, when it is colder than standard(15 C) you are lower than indicated which puts you closer to terrain and obstacles. That's why some airports are cold weather restricted.

[@karhukivi]

@@IdleIslander Not correct. There is a vacuum, not perfect of course, but the aneroid capsule will change as the external pressure squeezes it against the spring which keeps it open. The effect of temperature is calculated as density altitude by the pilot and the altimeter does not correct itself for temperature changes.

[@adolfconrad5176]

Thank you for this brother, it gave me an idea of how an altimeter works. May you always follow GOD's guidance.

[@capatangoa2006]

Very helpful Thanks

[@arod1pilot]

Loved it. Ty

[@fly8ma.comflighttraining199]

Glad it helps! Share us on Facebook and around the airport with your friends!

[@澳门威尼斯人-y8j]

how does it compensate for temperature change?

[@bartekokot1]

Good stuff. Thanks a lot

[@samfoster1664]

Thanks for the videos.

[@bkembley]

They say a picture is worth a thousand words--this video should be mandatory viewing in flight school. I can't tell you how many texts I read that left me asking, but how does it actually work?! This video put it to bed.

[@Hearthglow]

Thanks millions for this. I also encourage viewers to watch "How It works Altimeter" by shidifu111, because it is a great graphic vid that shows what you can't see well in the real altimeter. Also, I see some discussion of aneroid wafers the PHAK says "A stack of sealed aneroid wafers comprise the main component of the altimeter. An aneroid wafer is a sealed wafer that is evacuated to an internal pressure of 29.92 inches of mercury ("Hg)." There are some misleading ideas here. "evacuated " seems to indicate that all the air is removed. BUT it then says "to an internal pressure of 29.92 in Hg", which is not a vacuum. Maybe they used the term aneroid, which I take to mean no air, because the static tube goes to the altimeter, not the aneroid wafers.

[@Edelweiss-uv5xi]

How much more petrol do you burn flying without doors like that? I cannot imagine the drag that'd cause.

[@Rubenefer1]

AMAZING TBH WOW. :)

[@fly8ma.comflighttraining199]

Always happy to help!!

[@desireercortez]

John thank you for sharing this video! Where can I buy an Altimeter like this one for my CFI lessons?

[@kadriislami8018]

Can you make video cabin differential pressure altimeter

[@Dr._Spamy]

Do this altimeters somehow compensate for athmospheric pressure changes ?

[@carollevine9423]

Great video!

[@fly8ma.comflighttraining199]

Thanks, Safe Flying!

[@sourabhjain9075]

What is the purpose of leaf spring in altimeter ?

[@wrefakis]

Question: is the front face of the dial completely sealed off from rest of the internals? For instance, could radium dust fall off the dial numbers and into the rear chamber where the wafers are?

[@officergregorystevens5765]

If you have say a 50 or 80 foot deviation and your altimeter are you allowed to adjust for it and have a different barometric pressure to correct four versus the pressure you're given from ATC? Is that some kind of FAA violation?

[@jimstanley_49]

The AIM (7-4-3) recommends having the altimeter serviced if the error is on the order of ±75'. 14 CFR 91.205 requires an altimeter for an aircraft to be issued an airworthiness certificate for day VFR and all other flight rules, and 14 CFR 91.213 (d) 2. states you may only take off in an aircraft with a faulty instrument if that instrument was not required for the airworthiness certificate, unless you get special permission.

[@peyton_1524]

I would like to take an old altimeter and turn it into a clock. Is that possible?

[@frederf3227]

I'm stumped about the altimeter Kollsman adjustment. The altimeter is essentially height readings as a function of various supplied pressures. When set QNE the table is the ISA relationship (ignoring everything but pressure as a factor). When set other than QNE is it biasing all of the pressures (independent variable) by a set amount or is it biasing all of the altitudes (dependent variable) by a set amount? E.g. if your altimeter was showing 1,000' too high and you cranked the Kollsman to subtract 1,000' would you be taking a constant 1,000' off each reading or would you be adding a constant P pressure?

[@FerralVideo]

It's a mechanical adjustment that rotates the entire mechanism by, using your example, 1000 feet. It doesn't influence the pressure sensing linkage at all. Therefore, climb 1000 feet and it'll indicate a 1000 foot climb, regardless of the Kollsman adjustment. In other words, it adjusts the "zero point" of the instrument.

[@777matthewv]

Hi there, do you know if the adjustment knob adjusts the hands and pressure indicators only, or does it also influence the compression of the bellows. My impression from the video and from some schematics I've been looking at is that it does not affect the bellows hence the rotation of the entire rear of the module.

[@ShawnMorel]

great video. One correction, at around 3:00 standard pressure is 29.92 not 29.90

[@fly8ma.comflighttraining199]

It wasn't intended to be set to standard pressure there, just using 29.90 as a random setting to yield an altimeter reading to compare it to an imaginary "field elevation". Almost nice catch though! Safe Flying!

[@yashpatel4676]

you said something wrong at 3:27. It will expand as an aircraft ascends, not another way.

[@carlcrutchfield6502]

❤❤❤❤❤❤❤❤❤❤❤❤❤

[@gauravkakkar8228]

whats the pressure inside the aneroid wafer

[@fly8ma.comflighttraining199]

Basically "neutral" or standard 14.7psi to start, then of course it varies relative to the pressure surrounding it.

[@gauravkakkar8228]

Thanks😉

[@mrkhan2983]

altimeter are always confusing .. what happens when we put pressure altitude ? how much difference we expect in the reading ?

[@anzahkhan5715]

Pretty helpful but it was 11,000 ft not 10,000 ft @ 5:13 ☺

[@marcfeyzeau]

no he was right on 10,000 ft

[@guest2007]

9 apr 2020 6:52 pm edt:thanks 9 apr 2020 7:52 pm edt: 3:59 altimeter-maximum-operating-altitude 20,000 feet. 10 apr 2020 12:25 pm edt: 2:37 maybe barometer-altimeter for high altitude, has thick-aneroid-waffer. barometer-altimeter for low altitude, has thin-aneroid-waffer. 42,000 feet is maximum-flying-altitude. [source:'Flights travelling around the world often fly at an average height of 35,000 feet', 'While there is no official maximum altitude for flying from aviation authorities, aircraft carriers have their own maximum heights that they are capable of flying. Private planes and commercial jets can go up to 42,000 feet, while smaller aircraft often stay around 10,000 feet.'' in www.express.co.uk/travel/articles/1020729/flight-secrets-plane-flying-too-high-maximum-altitude from google (aircraft maximum altitude)]

[@maheralazzawi7814]

very good