Hi everyone. 

 

I realized that there is a Vmo and mmo contradiction between pmdg 777 and the real one. 

 

I performed a test fligth to see this clearly and the results shows it.  The Vmo is 330 IAS and the mmo is .81 at FL270

 

 

And as you can see below , there is a huge difference between the parameters. The VMO is 350 IAS and the mmo is .87

 

 

in addition , 

 

Every single thing was the same with the real flight. such as temperature , track , grossweight , wind factor. Nobody believes that 600 fts of level difference can make this kinda huge difference between the parameters.  

Absolutely i have same problem, tried changing parameters like TAT, OAT, SAT, FL but doesn't work at it all!

 

Regards,

 

ANAN.

Hi everyone.

 

I realized that there is a Vmo and mmo contradiction between pmdg 777 and the real one.

 

I performed a test fligth to see this clearly and the results shows it. The Vmo is 330 IAS and the mmo is .81 at FL270

 

 

And as you can see below , there is a huge difference between the parameters. The VMO is 350 IAS and the mmo is .87

 

 

in addition ,

 

Every single thing was the same with the real flight. such as temperature , track , grossweight , wind factor. Nobody believes that 600 fts of level difference can make this kinda huge difference between the parameters.

 

Vmo and Mmo are not calculated......they are not 330kt and M.81 at FL270.......they are (for the B777200) 330kt and M.87 period.

They are fixed limits no matter what altitude you are at!

 

Boeing has determained that the airplane will safely operate up untill 330kt and up untill M.87.

Those two speeds are entered in the system and shown as a red bar.

When you are low and temperatures are higher, your mach number will be quite low, so the limiter factor becomes the 330kt. So the red bar is drawn at 330kt.

When you are higher and temps get lower then your Mach number increases at the same IAS and at some point (altitude) your Mach number becomes limiting. At that point the red bar is drawn at M.87.

 

So in the PMDG777 pic above you are seeing Mmo is the limiting factor.

The red bar is thus drawn at 330kt.

At the ambient temparature this happens to result in Mach.797

 

Could it be that in the other pic you are looking at a different model 777 (777300?) with a different Mmo limit of 350kt?

(I dont know limits of other type 777 cause I only fly the B777200ER)

Anyway since they are still low enough, Vmo is the limiting factor, so the red bar is drawn at 350kt.

At the current speed of 341kt and the ambient conditions that happens to result in M.847

 

 

Does that make any sence or am I missing what you mean completely?

Vmo and Mmo are not calculated......they are not 330kt and M.81 at FL270.......they are (for the B777200) 330kt and M.87 period.

They are fixed limits no matter what altitude you are at!

 

Boeing has determained that the airplane will safely operate up untill 330kt and up untill M.87.

Those two speeds are entered in the system and shown as a red bar.

When you are low and temperatures are higher, your mach number will be quite low, so the limiter factor becomes the 330kt. So the red bar is drawn at 330kt.

When you are higher and temps get lower then your Mach number increases at the same IAS and at some point (altitude) your Mach number becomes limiting. At that point the red bar is drawn at M.87.

 

So in the PMDG777 pic above you are seeing Mmo is the limiting factor.

The red bar is thus drawn at 330kt.

At the ambient temparature this happens to result in Mach.797

 

Could it be that in the other pic you are looking at a different model 777 (777300?) with a different Mmo limit of 350kt?

(I dont know limits of other type 777 cause I only fly the B777200ER)

Anyway since they are still low enough for Mmo to be the limiting factor, the red bar is drawn at 350kt.

At the current speed of 341kt and the ambient conditions that happens to result in M.847

 

 

Does that make any sence or am I missing what you mean completely?

 

D-AALB is a 777-200F, the one pictured in the OP's display picture. Hope that helps.

 

 

Does that make any sence or am I missing what you mean completely?

 

Makes sense to me. Didn't even know that. Thanks!

 

 

D-AALB is a 777-200F, the one pictured in the OP's display picture. Hope that helps.

 

haha - totally missed the reg plate. Good catch.

D-AALB is a 777-200F, the one pictured in the OP's display picture. Hope that helps.

yes, I googled around and found that out as well.....but I cant find its Mmo and Vmo yet.

Just want to note that TAS of 508 (on ND) seems a little high -- shouldn't it be more like 490?

 

Mike

Makes sense to me. Didn't even know that. Thanks!

Sure, anytime.....but what did you not know? That different 777 can have different limits?

Just want to note that TAS of 508 (on ND) seems a little high -- shouldn't it be more like 490?

 

Mike

Not sure what you have used to calculate this, but I have tried with the sportys digital E6B and arrived at different numbers too.

 

I also read in a document somewhere that the method of calculating Mach was changed between the B777200ER and LR resulting in higher mach numbers for the LR in some flight regimes.

Dont ask me about the details.....that is all I got.....but it demonstrates there are different ways to calculate the various speeds.

 

Interesting and weird right?!

 

 

but what did you not know?

 

The details behind the variable beginning of the red bricks.

 

 

sportys digital E6B

 

That sounds like a nice Christmas present.... I'm still using a 40-yr old aluminum E6B, well worn but wind window still intact.

 

 

I'm still using a 40-yr old aluminum E6B

 

I still keep one in my flight bag (which is kept in a passenger seat, unless one's occupied), just in case [stuff] hits the fan.

 

Otherwise, I'm all digital up front (though I do still fly steam most of the time - no need to pay a higher hourly for glass if I don't need it).

Mike777, on 22 Dec 2014 - 4:11 PM, said:

 

Just want to note that TAS of 508 (on ND) seems a little high -- shouldn't it be more like 490?

 

Mike

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

Not sure what you have used to calculate this, but I have tried with the sportys digital E6B and arrived at different numbers too.

The 490 knot number is just what I've noticed at cruise altitude c. Mach.84.

 

I found this table:

 

http://www.aerospaceweb.org/question/atmosphere/q0112.shtml

 

So at 25,000 ft Mach 1 = 602 knots, Mach .84 = 505.68 - not very far from what is showing in the O.P.'s post at 27,000 ft. At 35,000 ft, Mach 1 = 576.5 knot, Mach .84 = 484.2 knots.

 

One thing I never realized before is that the aircraft actually must slow down slightly to maintain Mach .84, as it climbs. But I suppose the difference in speed is negligible in relation to the fuel saving.

 

Mike

That sounds like a nice Christmas present.... I'm still using a 40-yr old aluminum E6B, well worn but wind window still intact.

Gotcha Dan,

 

I've still got my CPU-26A/P from 1969. :-))

 

Billy Bluestar

Mmmm...it looks like there is a difference between 772ER and 772LR when it comes to Vmo.

 

As far as I know in the ER Vmo is fixed....allway 330kt (I have never noticed it being somewhere else but I will take a closer look whenI get a chance.

 

The 772LR seems to have a variable Vmo as is also discussed here:

http://forum.avsim.net/topic/458015-bug-report-b777-300er-vmo/

 

(if only these very similar threads would have been merged....sigh).

 

I guess that is what my document meant when it stated that Mmo can be faster for the LR then the ER in some flight regimes.

 

Anyway....maybe PMDG just took the fixed 772ER speed (330kt) for Mmo.

In that case only a support ticket will make them aware of the difference (if they dont know already anyway).

This is what Boeiing says about Vmo/Mmo - and it should know!

 

http://www.recreationalflying.com/tutorials/groundschool/VMO_MMO_Limitations_Review.pdf