Mach speed vs IAS - Flight Sim X question
06-16-2009, 06:29 AM
#11
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So in a jet - at high altitude... Mach number determines Vne...(right?) My problem is that in FSX, if my autopilot is set to mach .82 (which is the max speed on an A321) every once in a while it jumps to overspeed and starts clicking at me. Then I have to turn it back down to .81 and back again if I want to "recalibrate" the bug on the speed tape... In real life, if autopilot is set to Mach mode, does it constantly 'update' the bug on the tape if it were changing? (say during a climb or a descent?)
06-16-2009, 07:47 AM
#12
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Transport jets don't have Vne. they use Vmo/Mmo. The mo is Maximum Operating. And most people don't run their plane at barber pole.
If you're in Mach Hold it'll try to keep whatever mach number you've set. At some point coming down a cruise mach number will exceed Vmo. I don't use the speed hold functions much so I can't say for sure what would happen. I'm willing to bet most transport jets won't hold .8 at pattern atitude unless they're going straight down so I think the experiment would be short lived.
If you're in Mach Hold it'll try to keep whatever mach number you've set. At some point coming down a cruise mach number will exceed Vmo. I don't use the speed hold functions much so I can't say for sure what would happen. I'm willing to bet most transport jets won't hold .8 at pattern atitude unless they're going straight down so I think the experiment would be short lived.
06-16-2009, 08:05 AM
#13
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Dan, I really don't know anything about MFS. I also don't know what you're referring to by "the bug on the tape" in mach mode. If you tell the aircraft to hold .82 mach it should try the best it can to hold .82.
You might want to ask somebody who is an expert at MFS because I think the differences between that program and the real thing probably out weigh the similarities. If you want to fly your sim like people fly the real 321 don't fly it right at it's critical mach in the real world that would be called dangerous
You might want to ask somebody who is an expert at MFS because I think the differences between that program and the real thing probably out weigh the similarities. If you want to fly your sim like people fly the real 321 don't fly it right at it's critical mach in the real world that would be called dangerous
06-16-2009, 08:42 AM
#14
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Originally Posted by GRDHound
Dan, I really don't know anything about MFS. I also don't know what you're referring to by "the bug on the tape" in mach mode. If you tell the aircraft to hold .82 mach it should try the best it can to hold .82.
You might want to ask somebody who is an expert at MFS because I think the differences between that program and the real thing probably out weigh the similarities. If you want to fly your sim like people fly the real 321 don't fly it right at it's critical mach in the real world that would be called dangerous
You might want to ask somebody who is an expert at MFS because I think the differences between that program and the real thing probably out weigh the similarities. If you want to fly your sim like people fly the real 321 don't fly it right at it's critical mach in the real world that would be called dangerous
Anyway the bug on the tape is the reference for the autopilot. When you select mach .80 or something on the autopilot and you are at fl350, it will 'reference' 272 kias on the airspeed tape. (Airspeed Tape is the left strip that tells your KIAS on a PFD in a glass cockpit)
06-20-2009, 04:03 AM
#15
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Just cruise slower, I don't know for sure but I would think the 320 "normal" cruise would be more like .77 or so. In the citation 650 MMO was .85, we never "cruised" up there, usually depending on temp altitude and weight was anywhere from .77 to .81 .
06-21-2009, 05:53 AM
#16
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Originally Posted by Dan64456
I
Anyway the bug on the tape is the reference for the autopilot. When you select mach .80 or something on the autopilot and you are at fl350, it will 'reference' 272 kias on the airspeed tape. (Airspeed Tape is the left strip that tells your KIAS on a PFD in a glass cockpit)
Anyway the bug on the tape is the reference for the autopilot. When you select mach .80 or something on the autopilot and you are at fl350, it will 'reference' 272 kias on the airspeed tape. (Airspeed Tape is the left strip that tells your KIAS on a PFD in a glass cockpit)
The Speed knob on the bus has a mach/ias selection. When in Mach the airplane attempt to maintain that mach. This works basically above about FL310 where the transition on the way down is from Mach to IAS. If you set .82 in the speed window the bug should follow on the airspeed scale. As you descend the bug will move on the scale reference to where .82 is and at around FL310 it will stop moving and be at the edge of the red on the speed tape.
Often in flight if you are flying at MMO (.82) and hit a bump in turbulence you can trigger an overspped warning. When I was flying 320's we used to use .80 as our planned speed. I understand they have backed off a bit now to save fuel.
L
06-21-2009, 05:52 PM
#17
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Originally Posted by Dan64456
It's more of a matter of understanding for me. I like to know how things work, and why they work the way they do work. I should say I NEED to know. Because I never rest until I feel I undestand it completely. So basically, it's not like i care about the 3 or 5 extra knots per hour in a game... Point being I even get overspeed warnings at .80 (normal cruise) unless I 'reset' it...
Anyway the bug on the tape is the reference for the autopilot. When you select mach .80 or something on the autopilot and you are at fl350, it will 'reference' 272 kias on the airspeed tape. (Airspeed Tape is the left strip that tells your KIAS on a PFD in a glass cockpit)
Anyway the bug on the tape is the reference for the autopilot. When you select mach .80 or something on the autopilot and you are at fl350, it will 'reference' 272 kias on the airspeed tape. (Airspeed Tape is the left strip that tells your KIAS on a PFD in a glass cockpit)
So in short, I don't see how anyone could know the answer to your problem since we have no idea how realistic MFS is ... or how it has been programmed.
In the real world, flying an aircraft near its barberpole isn't exactly safe. If you hit turbulence or a gust of wind, you can and most likely will overspeed it because you can't get the power off the engines fast enough.
So, either MFS is behaving like a real airplane, or it isn't. Either way, I don't see how we can determine this.
06-25-2009, 12:17 AM
#18
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There is a "brick wall effect" within MSFS. If you use "real-world weather", or any WX program...you will experience a sudden change in variables, that is not realistic.
MSFS atmosphere is not truly dynamic in change. On the software level, you simply fly from one grid, to another.
Yes, I have responded to Overspeed Warnings in cruise, (the tick you refer to?) But in the the real world, most airlines do not fly at VMo in the A320, or any other transport category aircraft, so you have a performance margin to work with, above planned speed (as determined by a fleet/flight/operational CI and GW/ZFW on most Boeing/Airbus aircraft) before you get a Master Warning/Overspeed condition.
MSFS atmosphere is not truly dynamic in change. On the software level, you simply fly from one grid, to another.
Yes, I have responded to Overspeed Warnings in cruise, (the tick you refer to?) But in the the real world, most airlines do not fly at VMo in the A320, or any other transport category aircraft, so you have a performance margin to work with, above planned speed (as determined by a fleet/flight/operational CI and GW/ZFW on most Boeing/Airbus aircraft) before you get a Master Warning/Overspeed condition.
Last edited by TurnAndBurn; 06-25-2009 at 12:38 AM.
06-25-2009, 10:25 AM
#20
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Originally Posted by Dan64456
In this example - I usually fly an A321... If I'm cruising at constant flight level 360, and use mach .81 as the speed reference the bug on the speed tape would be for example 275kts... Sometimes I have to change from .81 to .80 to .81 again to "reset" the speed so it doesn't go overspeed on me... sometimes comes back with a number different than 275. Almost as if the plane doesn't constantly calculate mach speed until you change it again. Is it this way in real life or just flight sim x? And just so I understand right, mach speed depends on temp?
Thanks all... let me know if the question needs clarifying.
Thanks all... let me know if the question needs clarifying.
WW
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