Hello,

 

I just saw something different from real 777. As we know 777's Vne speed is 0.87 mach, some sources says 0.89 too, which is correct?

 

Anyway, there is a contradiction about real Vne speed and simulator's Vne speed, as you can see in this picture, same flight level on simulation, we can reach max 0.80 mach.

 

 

 

I make a test, when i pass this Vne speed, FSX's OVERSPEED warning comes after +20 knots after i pass the Vne speed on the PFD ( OVERSPEED warning comes at 350 knots)

 

As you can see in this picture plane can reach 0.844 mach and 350 knots indicated.

 

 

Is this a known bug or something? How can i equalize this Vne speed with real 777? If this is a known bug, it will be fixed?

 

Thanks and sorry for my bad English, have nice flights!

Here's a hint - I am enroute right now  WSSS - EDDP  My mach is .844 & my indicated is 330 (FL280)

Most of my flights are cruising around Mach 0.84

Yes guys you can reach mach .844 at high altitudes but as you can see you cant reach mach .844 at FL270 on PMDG, but 777 can reach. This is what i want to explain.

According to this type certificate data sheet, the Boeing 777 airspeed limits are 330 KIAS or Mach 0.87. So it would essentially be the lower of the two. In your screenshot, your maximum is 330 knots. As you get to higher altitudes, that'll change.

 

http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/8f760532478d923286257c6a00631141/$FILE/T00001SE_Rev_34.pdf

Yes guys you can reach mach .844 at high altitudes but as you can see you cant reach mach .844 at FL270 on PMDG, but 777 can reach. This is what i want to explain.

 I am at FL280 at mach .84   

 

Vne on the barber pole is related to IAS

 

IAS is not exclusively related to altitude

 

Probably best to get a comment from PMDG, I would be surprised if they managed to code the whole flight envelope to behave exactly like the real thing

According to this type certificate data sheet, the Boeing 777 airspeed limits are 330 KIAS or Mach 0.87. So it would essentially be the lower of the two. In your screenshot, your maximum is 330 knots. As you get to higher altitudes, that'll change.

 

http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/8f760532478d923286257c6a00631141/$FILE/T00001SE_Rev_34.pdf

But i am still in trouble about how This plane flies 340 knots at FL270?

Edit - Got my books out & was about to type a long post, way past my bed time. Will post some links in the morning.

 

Take a look at the TAS & GS in the pic you posted

But i am still in trouble about how This plane flies 340 knots at FL270?

I couldn't tell you, man. I'm just pointing out what the FAA type certificate data sheet says, so not really sure why it would be higher in the one picture. However, I would like to make a correction to an earlier statement I made. The Mach 0.87 is the maximum for the 777-200 and 777-200ER. For the 777-300, 777-300ER, 777-200LR, and the 777F, it is Mach 0.89, so to answer your original question, it's Mach 0.89 on everything, except the -200 and -200ER. For those two, it's Mach 0.87.

I am at FL280 at mach .84

 

Vne on the barber pole is related to IAS

 

IAS is not exclusively related to altitude

 

Probably best to get a comment from PMDG, I would be surprised if they managed to code the whole flight envelope to behave exactly like the real thing

The barber pole on the PFD speed tape shows Vmo/Mmo. That's not the same as Vne.

 

PMDG have not got this wrong. The aircraft may not behave exactly like the real thing over the whole flight envelope, no sim can, but the Vmo/Mmo limit can easily be made exactly right for all conditions. For most airliners it's one airspeed and one Mach number (for which you need to calculate the corresponding airspeed on the speed tape).

 

 

Sent from my iPhone using Tapatalk

The bottom of the "Barber Pole" on the speed tape is Vmo in IAS or Mmo in Mach number ( Max operating speed ). Vne is the never exceed speed which if exceeded the airplane would likely suffer structural damage. Vmo/Mmo however if minor excursion occured during flight, although requires a maintenance check, the airplane should not suffer any permenant damage. And the AP allows roughly an excursion of 20kts after Vmo for overspeed recovery ( by pitch the nose up, if A/T is enagaged the THR will go idle ) in extreme condition so that it would not introduce excessive G load to the airframe.

For the 777-200 Vmo is 330kts transition to M.87, 777-300 is 330/M.89, the 300ER is 330kts at sea level then goes up ( sort of linearly ) to 350kts at around 28000ft then transition to M.89. 

That's why on the real 777 cockpit pic you see 350kts Vmo. Because they were cruising at around 28000ft (Looks like they were flying over southern china based on the name of the waypoints on the ND and at with metric levels as well)

In the PMDG picture you posted, yes the Vmo is a bit low if its a 300ER. Since i dont know anyone who flies the 200LR, I am not sure if they are the same. However that speed in FS you posted would be correct for a normal 777-200/300 which is 330kts till 30000ft/32000ft then .87/.89.

 

Perhaps some 200LR experts can shade some light on it.

Hope it helps, cheers.

Hi,

 

Maybe I'm wrong, but it seems to me that the Vmo/Mmo might depend also on the weight/altitude.

I have the impression that if you climb close to your maximum altitude for some given weight constant mach number, your margin to Mmo is reduced and increase when you burn fuel.

I will check again during my next flights. Could domebody confirm that?

Vmo and Mmo does not depend on weight. It's not the same as Vmms or stall speed which is weight dependent. One can always make a dive at any weight to exceed your Vmo or Mmo. It's more of a limit from a structural point of view. The only outside factor I can think of its the temperature which may affect the transition altitude from Vmo to Mmo however the effect shouldn't be significant.

 

In FCOM3 there's a graph showing Altitude on the Y axis and speed (IAS) on the X axis. And it draws out the max speed envelope of the airplane as a function or Altitude.

Hi,

 

Maybe I'm wrong, but it seems to me that the Vmo/Mmo might depend also on the weight/altitude.

I have the impression that if you climb close to your maximum altitude for some given weight constant mach number, your margin to Mmo is reduced and increase when you burn fuel.

I will check again during my next flights. Could domebody confirm that?

What changes with weight is your margin to the Mach buffet boundary, shown as a yellow line extending below the barber pole at high altitudes. The heavier you are the lower this buffet speed is.

 

 

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Yep,

 

I have just noticed I was wrong when I have loaded a new flight. 

Sorry for my misleading post and thanks for having corrected me.