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OK, so. In very short words. Also, I am going to lie to you, but it's for your benefit. As you learn more, you will realize how wrong what I wrote below is, but that's OK.

The speed you are seeing on the PFD (left screen) is something called indicated airspeed (IAS; or knots indicated airspeed: KIAS). While we call it speed, it actually measures differential pressure between static input (a hole on the side of airplane), and dynamic pressure (a hole in front which sucks up air as the plane is moving forward). What this differential pressure shows is dependent on the density of the surrounding air. As you probably know, there is more air closer to the ground you are. As you go higher, there is fewer air, therefore the amount of pressure that air can exert is lesser. This is why you are seeing "low speed". What you are *really* seeing is "low pressure".

So, this is why we have things like TAS (true airspeed; which is important, but you "don't care" about it), or the indicated speed adjusted for pressure and temperature. The speed the aircraft is moving when compared to the ground is called "ground speed", or GS. You can see it indicated in the upper left corner of your second screen from the left. This speed is the combination of TAS and wind, and is the speed you seem to care about.

As you learn more, you will realize that it's really just CAS (calibrated airspeed) you care about, but that gets even more complicated ;-).

Oh, and one more thing. Please note that this is PMDG support forum. Their rules require you to sign all messages with your full name. Please, do that. Thanks!

Edited by icemarkom
Minor typo fixes.
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Have you got the doodah in the "on" position? Also, make sure that the thingamabob is set to "active", or else you'll find yourself on an inclined plane wrapped helically around an axis. :P

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42 minutes ago, martino2706 said:

whats that? i just start flying on pmdg before i used just basic plane so iam just learning

 

Start with the Tutorial.  If you are new to aviation this is all but mandatory.  Also, get a copy of the FAA Airman Information Manual (AIM), which will be your bible as you learn the basics, free here: https://www.faa.gov/air_traffic/publications/

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56 minutes ago, martino2706 said:

hi. why is mine max crz speed only 280?

Hi Martino2706.  Welcome to the PMDG forums.

Please read through this thread, and try to ignore the smart-alecky stuff.  There's some useful information on your question here:

Also, PMDG wants you to sign your full, real name in its forums.

Mike

 

 

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Any time. Also, please try to ignore smartassery in the forum. Folks are rather mean to newcomers here for some reason. I suppose they were all born knowing everything about aviation.

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To be fair, there was only one unhelpful reply. Most were trying to help.

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48 minutes ago, icemarkom said:

Any time. Also, please try to ignore smartassery in the forum. Folks are rather mean to newcomers here for some reason. I suppose they were all born knowing everything about aviation.

I'm not really too sure what was wrong with my post. All I asked was what his Mach speed was. Knowing that goes a long way to knowing whether there's actually an issue or not.

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2 hours ago, Captain Kevin said:

I'm not really too sure what was wrong with my post. All I asked was what his Mach speed was. Knowing that goes a long way to knowing whether there's actually an issue or not.

I think it was the fact that you asked what his Mach speed was when he didn't even know what IAS was. It could come off as rude asking that when he didn't even know the basics with absolutely no chance of him knowing what it means, let alone where to find it on the PFD.

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15 hours ago, martino2706 said:

thanks to all of you

I read the above, sorry if I missed it - but I didn't see the layman explanation. Marko's explanation makes perfect sense, but its still pretty technical.

martino2706 - if you're at 35,000 and the "speed" in your cockpit is showing 280 (or 298 in the photo below), for a variety of reasons (explained above) you are actually travelling much much faster. If you had a car following you on the ground, it would be traveling about 420.

You can see this in your cockpit. The speed on the "tape" is the IAS, the one that seems low to you. If you look right can see the actual ground speed (the speed at which the car on the ground following would have to be going in order to keep up with you). That speed is shown in the upper left of the navigation display (window to the right).

I would encourage you to research the internet over time to gain knowledge about flight dynamics. Not sure how old you are, but if you are still very young a lot of the concepts will go right over your head until you've had a chance to take physics in high school - and maybe if you go to college some fluid dynamics will clear things up. Otherwise, if you're just dinking around with the flight sim and want answers now, hopefully this clears things up.

x3jzTFu.jpg

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Also, in the above screenshot, the Mach speed is what you want to look for, which in this case is Mach 0.850. As long as you're doing that speed, you're fine.

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25 minutes ago, NJ_Flyer said:

M0.85 in a NG? Bit behind schedule were we? 

Funny!  But Kevin was referring to the screen shot just above his post.  I don't think we know which aircraft the OP is flying, and it doesn't matter for his question.

 

On 8/1/2017 at 5:40 PM, Captain Kevin said:

I'm not really too sure what was wrong with my post. All I asked was what his Mach speed was. Knowing that goes a long way to knowing whether there's actually an issue or not.

Kevin, I don't think anyone was referring to your post.

Mike

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13 hours ago, NJ_Flyer said:

M0.85 in a NG? Bit behind schedule were we? 

Gave me a good chuckle but Nick's image is the 777 I believe.

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A proper layman's answer is that you need a certain amount of air to pass over (and under) your wings to keep flying. At sea level, that is the same as the amount you get flying at 280 knots. As you go higher, the air gets thinner but the clever thing about the way they measure IAS is that it will still say 280 when you have the same amount of air, no matter how thin it gets.  That is why they measure it that way.

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