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Mean Aerodynamic Chord

Cruising Speed Question

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Okay, when I go on FlightAware and look up a route, the cruising speeds always seem incredibly high.

 

For example, AAL1607 here: http://flightaware.com/live/flight/AAL1607

 

It says they are cruising at 481 knots. Where do I input this information on the FMC? It can't be the CRZ page, because when I put 481, it says INVALID ENTRY or sometimes MAX 340 or something like that. I'm a little confused on this section.


i7-6700K @ 4.5 GHz, 16 GB DDR4-2400 MHz, GTX 1070 8GB

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That is not indicated airspeed. That is either the TAS or the ground speed. You can input speeds on the LEGS, CLB, CRZ, or DES pages.


Kenny Lee
"Keep climbing"
pmdg_trijet.jpg

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Kenny thanks for your reply, I didn't see it until now. :smile:

 

 

Is there a way to only use ground speed or what?

 

No, because the ground speed will always be changing based on the winds aloft. You could be going 400 knots one minute, and 600 the next.


Jared Listinsky

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No, because the ground speed will always be changing based on the winds aloft. You could be going 400 knots one minute, and 600 the next.

Jared than how is cruising speed determined? :unknw:


i7-6700K @ 4.5 GHz, 16 GB DDR4-2400 MHz, GTX 1070 8GB

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Look up True Airspeed, and I'm sure you can find good stuff about it on the net. With airliners, dispatch software takes into account cost index, winds aloft, temperature, cruising altitude, and some other stuff to calculate the flights TAS. When PFPX comes out, I'm sure you'll have an accurate route TAS calculator to use.

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In short,

 

the airplane measures speed by measuring the difference between static pressure, and dynamic pressure, in other words, it measures how much air passes by it. This makes sense, because the amount of air determines things like lift, drag, stall speeds etc.

 

But, as you know, there is less air up high, so if the airplane needs same amount of air to pass it, so it has same airspeed, as down low, it will have to travel faster relative to the air. That is called True AirSpeed = TAS, and you can find some nice quick ways to calculate it, even if it will not be completely precise. For this reason, if you take for ex. 300kts on your indicator, it will be 300KTS true airspeed on sea level, but on FL380 it will be almost or about 500knots TAS.

 

If you add wind, you can get even higher numbers, so sometimes, speed shown on flightaware and such, can be more than twice as much as shown on your speed indicator.


--Peter Fabian 
RTFM.jpg

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I’m a bit cranky today - PMDG and all other high end developers should include a basic Cessna in the download package, no one is able to unlock the complex jet until they get the basics in the Cessna.

 

Children of the magenta line… Can program a RNAV approach with there eyes closed but don’t understand the simple basics of flying…


Rob Prest

 

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I’m a bit cranky today - PMDG and all other high end developers should include a basic Cessna in the download package, no one is able to unlock the complex jet until they get the basics in the Cessna.

 

Children of the magenta line… Can program a RNAV approach with there eyes closed but don’t understand the simple basics of flying…

 

Partly agree, but it's a sim and people like it cause they don't have to take like 5 different ratings to be able to fly the big ones, even if they're as complex as PMDG.

 

Guess it's a matter of personal preference how realistic each one wants to be and as long as they pay with their own money and not mine I do not mind how they use their addons.

 

However once you get into flight simming it's very probable that at some point you'll want to learn more... At least that's what happened with me!

 

:Peace:


George Golas

----------------------

I hate gravity!

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I’m a bit cranky today - PMDG and all other high end developers should include a basic Cessna in the download package, no one is able to unlock the complex jet until they get the basics in the Cessna.

 

Children of the magenta line… Can program a RNAV approach with there eyes closed but don’t understand the simple basics of flying…

I thought this was an ok question. It's the ones like, "Where's the auto-takeoff button?" that make me want to smack whatever generation is in school right now. GenZ? GenGimme?

Matt Cee

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I can't really tell if anyone has answered the original question though...and frankly I'm a little confused by it. To the OP: why are you trying to "Input this information into the FMC?" The FMC calculates all the speeds for you as long as you enter a cruise altitude, cost index, etc on the PERF INIT page. You shouldn't have to enter the actual performace data yourself; the FMC will calculate everything based on the parameters you set. You should give the #1 tutorial pages 12 - 45 a look.

 

And if you still want to muck around with the speeds the FMC calculates, you can do this from the CLB, CRZ, and DES pages (keys on CDU). There you can modify the speeds the FMC is following for each flight regime. Keep in mind that modifying those values is most definitely not SOP.


Adam Hill

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I thought this was an ok question. It's the ones like, "Where's the auto-takeoff button?" that make me want to smack whatever generation is in school right now. GenZ? GenGimme?

We're not all like this. I'm in high school (16 years old) and i'm that type of guy ''no autopilot below 5000ft ;-)

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To the OP: why are you trying to "Input this information into the FMC?"

I imagine when he sees a B737 doing 481kts, he wants to, too, not realizing that's it's two different speeds.

Matt Cee

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I can't really tell if anyone has answered the original question though...and frankly I'm a little confused by it. To the OP: why are you trying to "Input this information into the FMC?" The FMC calculates all the speeds for you as long as you enter a cruise altitude, cost index, etc on the PERF INIT page. You shouldn't have to enter the actual performace data yourself; the FMC will calculate everything based on the parameters you set. You should give the #1 tutorial pages 12 - 45 a look.

 

And if you still want to muck around with the speeds the FMC calculates, you can do this from the CLB, CRZ, and DES pages (keys on CDU). There you can modify the speeds the FMC is following for each flight regime. Keep in mind that modifying those values is most definitely not SOP.

 

I understand now, thanks! I was just confused because on VATSIM for example, aren't you supposed to enter a cruising speed on your flight plan?


i7-6700K @ 4.5 GHz, 16 GB DDR4-2400 MHz, GTX 1070 8GB

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