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ctruong

777-200 Cruise Speed/Mach

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Hello all,

 

I have been running PDMG 777-200 for a few months.

I have noticed when cruising, eventhough you have set the cruise mach number is, say, 0.92, when in cruise, the aircraft can only do 0.875.

 

Is there a way to increase it to 0.92?

 

Cheers,

ctruong.

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The cruise speed is between M0.83 and M0.85

The MAX speed is M0.92

You don't want to cruise faster than M0.85.

 

Regards

Trevor

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M0.92 is excessive. They don't cruise at that speed unless they're falling from the sky.

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Wow! If you want to do M0.92 you might want to switch to a different sim like DCS  :lol:

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The cruise speed is between M0.83 and M0.85

The MAX speed is M0.92

You don't want to cruise faster than M0.85.

Type certificate data sheet shows 0.89 for the 777-200LR. 777-200ER would be 0.87.

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Type certificate data sheet shows 0.89 for the 777-200LR. 777-200ER would be 0.87.

Once again, those are maximum speeds.

Typical crz speeds are 0.83 to 0.85

 

Trevor

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You should be able to cruise at M.92. I haven't tried it myself but the LR engines should have enough power to overspeed the airplane in level flight at medium weight.

 

First you need to disconnect the Autothrottle as it prevents speed from increasing above Vmo/Mmo - 5kts for overspeed protection. Then applymfull thrust, passing M.89 you will get an overspeed warning, which you can silent it by pressing the Overspeed warning cancel button located next to the EICAS event button below the lower left corner of the lower MFD ( the lower middle screen ), I am not sure if there's a time limit as to how long it inhibits the overspeed warning, just press it again if it ever it comes up again.

 

However I don't think it is a safe and sensible way to fly the airplane. If you simply want to get from A to B as quick as possible just put 9999 as cost index on the Perf Initial page. And accept whatever cruising speed you get from the FM.

 

Cheers.

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Didn't a 747SP exceed MACH1  after the crew lost control during an engine out in cruise?  I remember reading the report years ago.

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Once again, those are maximum speeds.

Typical crz speeds are 0.83 to 0.85

Yes, I know that, however, that was a correction to your initial post since you said the maximum was 0.92. My apologies for not making that clear.

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You should be able to cruise at M.92. I haven't tried it myself but the LR engines should have enough power to overspeed the airplane in level flight at medium weight.

 

First you need to disconnect the Autothrottle as it prevents speed from increasing above Vmo/Mmo - 5kts for overspeed protection. Then applymfull thrust, passing M.89 you will get an overspeed warning, which you can silent it by pressing the Overspeed warning cancel button located next to the EICAS event button below the lower left corner of the lower MFD ( the lower middle screen ), I am not sure if there's a time limit as to how long it inhibits the overspeed warning, just press it again if it ever it comes up again.

 

However I don't think it is a safe and sensible way to fly the airplane. If you simply want to get from A to B as quick as possible just put 9999 as cost index on the Perf Initial page. And accept whatever cruising speed you get from the FM.

 

Cheers.

 

No, you wouldn't be able to cruise that fast. Your airplane would simply brake apart before it reaches this speed!

 

Vmo/Mmo is the maximum it can fly before it will brake up. There is no "safety margin" from these speeds in which you could overspeed the plane.

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.87 is MMO, anything above this is logged as an overspeed, and anything above .92 will require conditonal inspections in the real world.

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No, you wouldn't be able to cruise that fast. Your airplane would simply brake apart before it reaches this speed!

 

Vmo/Mmo is the maximum it can fly before it will brake up. There is no "safety margin" from these speeds in which you could overspeed the plane.

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the airplane holds up quite well all the way to Max Dive speed which was proved in flight test during flutter testing which the test pilot basically dive the airplane to which the design max speed of the airplane. In fact the autopilot allows quite a a bit of Overspeed before it recovers at about Vmo +15 to 20kts to avoid excessive G load. So don't worry the wings won't just shear off when you hear the Overspeed warning. Sometimes especially on high speed descent into a strong headwind or riding the mountain waves it is very possible to Exceed Mmo if not careful.

 

Whilst I don't know the actual Max Dive on the 777, I would believe its sits around .92 to .98 based on the A380 and 747 figures.

 

Btw I forgot to mention the Autopilot will tried to recover the airplane by pitch the nose up at some point to try to recover.

 

I never tried to test the envelope protection of the PMDG 777. Those who are interested should have a look. Overspeed and stall recovery is part of the flight crew training course.

 

Cheers

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No, you wouldn't be able to cruise that fast. Your airplane would simply brake apart before it reaches this speed!

 

Vmo/Mmo is the maximum it can fly before it will brake up. There is no "safety margin" from these speeds in which you could overspeed the plane.

 

That's not quite true.  I'm not sure who told you that, but I'd suggest taking a little more of a look into aircraft design before simply repeating those assertions.

 

While it's true that you're taking a significant risk by operating outside of the published limits of the aircaft, it's not quite true that the aircraft will suddenly begin to break apart at those limits.  There are - in some cases significant - safety margins built into the various limit speeds of the aircraft.  Additionally, some of these values are highly theoretical.  Granted, they're theoretical with a huge backing in mathematics and fluid dynamics, but they're not proven practically.  What I mean by that is, in order to prove them practically, you'd have to subject the airframe to the actual conditions, and no person in their right mind is going to take a 777 up and overspeed it to the point that it begins to break apart.  Why waste the money and risk life?  Instead, why not take the theoretical limit, apply a safety margin to that calculation, and then take the aircraft up to ensure that it flies safely up to that theoretical limit?  That option is much safer, but it doesn't prove where, exactly, the aircraft will fail beyond that theoretical limit.

 

A lot of what you "grow up with" in PPL training is very overly parental.  CFIs and ground instructors try to drill safety into PPL students because as soon as they get their license, they "graduate into" the highest risk time of their piloting career (one author calls it "The Killing Zone" - oddly enough, the first edition of the book featured my home airport on the cover above the 'N' in 'killing').  As such, there are quite a few stories out there that the limits are absolute, and if you break them, you might immediately turn the aircraft into a heap of scrap.  If you think about it, though, for most of the training fleet out there, it's better to keep yourself off of the limits.  As the aircraft age, the metal fatigues, and that safety margin above the published figures may be significantly reduced.

 

TL;DR:

The aircraft isn't going to immediately (or even partially) come apart, but limits are there to help you avoid the potential of that type of situation.

 

Source:

Went to school here, and spent all of my waking hours around my roommate and residence hall mates, most of which were majors in this.

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Didn't a 747SP exceed MACH1  after the crew lost control during an engine out in cruise?  I remember reading the report years ago.

 

            

 

Exactly, Rob, on the topic of Boeings and safety margins, take a look at the safety margin, concerning G-loads here:

 

http://aviation-safety.net/database/record.php?id=19850219-0

 

According to official/published/certified G-limits, this plane could never have landed in one piece. (Well, a couple of parts had fallen off the plane, for sure.)

 

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