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Empennage

Observations & questions on thrust asymmetry, FBW, RAT, dual engine failure, use as an alarm clock, etc.

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Hey guys, just wanted to share some observations I've made while messing around in the PMDG 777.

 

First of all, let's start out with a scenario where an engine cuts out during rotation. The aircraft will be a 777F with full payload and short range fuel departing from PAFA's RW20R:

ravenfreight_boeing_777f_by_hyppthe-d6ry

 

A VR right engine cutout is programmed via the CDU menu...

pmdg_777_lrx_observations_by_hyppthe-d6r

 

Observations:

1. The Thrust Asymmetry Compensation system does its job well, it trims the rudder hard left to compensate for the rightboard engine failure. Apart from the rudder, the thrust asymmetry compensation doesn't touch anything else; a slight roll to the left is observed with the left engine on TO -10% power and the rudder trimmed to the left. The roll wasn't caused by me, but I do think it is one of the side effects of the rudder being trimmed to the left.

pmdg_777_lrx_observations_by_hyppthe-d6r

 

2. Even with one engine out, the 777 was able to climb away at ~1100fpm at a speed of ~240kts to ~12,000ft.

3. When the DEP/ARR button is pressed on the left side CDU, it automatically displays the arrival procedures for PAFA.

4. Apart from yaw, the pitch and roll handling of the 777 seems to be the same as with both engines running.

Good work, PMDG!

 

5. On another flight, I programmed a left engine flameout and disabled both the thrust asymmetry compensation and the FBW computers to see what will happen. Provided that the engine failure occured before the FBW functions are turned off, the rudder will remain trimmed in the direction of the failed engine. Once the rudder trim is returned to the normal position, all the usual symptoms of thrust asymmetry reappeared; the 777 yawed and rolled to the left with the left engine failed and the right engine on full power.

pmdg_777_lrx_observations_by_hyppthe-d6r

However, this is where I also encountered a weird problem. After programming a flameout in the left engine on the CDU menu, the engine went out for a moment and... seconds later... coughed back to life and spooled up to full power. How can this happen? The fuel control levers on the center console are left in the run position but I'm pretty sure the autostart button was left in the off position.

 

Back to the PAFA flight, after reaching 12,000 feet, I failed the left engine to see what will happen during a twin engine out scenario. Observations:

1. The RAT did not deploy automatically (I always thought the RAT deploys automatically whenever both engines lose power and the APU is not turned on). I'm not sure what happens on the real 777 but does the RAT deploy automatically or do you HAVE to press that RAT button on the overhead?

2. With the RAT deployed, the first officer's DUs and CDU remained off, though the primary flight computers still worked and the FLT CTRL MODE remained on NORMAL. There are no noticeable differences in control sensitivity apart from pitch up movements.

3. After ~2-3 minutes, all the electronics, hydraulics and air packs came back online. Somehow, the 777 has started the APU without me touching anything! Does the real 777 do that? (Even though the EICAS pages showed the APU was running, the APU off/run/start knob on the overhead was still in the off position. Weird...)

 

One final note to make:

On Oct 22, I was in the Pan Rong Village in the GuanXi province doing some menial work for the Habitat for Humanity project. That morning, my roomate has slept through 3 whole barrages from his phone's alarm clock and he only has a few minutes left before he will run out of time for brushing and grooming. So this was what I tried to wake him up:

https://www.youtube.com/watch?v=WbWGZ6MoQrg

YouTube Link

Observations:

1. With the MacBook's speakers at full blast, the 777's siren is LOUD! It will certainly slap any drowsy pilot out of his power nap in no time flat.

2. But my roomate slept on.

3. Other members attending the project said they could hear the 777's siren from two rooms away.

4. But my roomate still slept on.

 

One last question: I noticed that in the CDU's options menu, there is an option to make silencing the siren possible with just a push of the master warning button. Does the real 777 have that option?

 

Thank you for reading & answering.

Peter Huang

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After programming a flameout in the left engine on the CDU menu, the engine went out for a moment and... seconds later... coughed back to life and spooled up to full power. How can this happen?

 

Flameout just means the engine lost its flame for combustion.  The default position for the autostart is ON, so unless you're sure you turned it off, the plane is going to try to restart the engine on its own.  The 777 is highly automated.

 

 

 


The RAT did not deploy automatically (I always thought the RAT deploys automatically whenever both engines lose power and the APU is not turned on). I'm not sure what happens on the real 777 but does the RAT deploy automatically or do you HAVE to press that RAT button on the overhead?

 

It will, but not instantaneously.

 

 

 


One last question: I noticed that in the CDU's options menu, there is an option to make silencing the siren possible with just a push of the master warning button. Does the real 777 have that option?

 

Yes.

 

 

 

No offense, but PMDG really does know what they're doing, so there's really no point in playing stump the chump.  There are real 777 pilots and experts on the Tech Team that validated and verified all of these behaviors.  I verified the flameout scenario myself numerous times in the beta stage.

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Regarding the APU, According to the manuals, it does automatically start on the real plane when both engines are failed in flight.

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The RAT will deploy automatically when hydraulic pressure is lost, engines shutting down does not cause a loss of pressure. The electric and bleed pumps hyd are still working.

 

The APU does autostart when there is no AC source, standby bus holds it all together until the APU takes over.

 

 

From my own testing (I test pretty much everything on every new PMDG plane I get) I didn't notice much help from the TAC, the most help I noticed was from the PFC which does a great job. I leave the PFC on but turn of the TAC and it continues to do a great job dynamically trimming the rudder. Turn both off however and you really get to feel the result of those big engines.

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Flameout just means the engine lost its flame for combustion.  The default position for the autostart is ON, so unless you're sure you turned it off, the plane is going to try to restart the engine on its own.  The 777 is highly automated.

 

 

 

 

It will, but not instantaneously.

 

 

 

 

Yes.

 

 

 

No offense, but PMDG really does know what they're doing, so there's really no point in playing stump the chump.  There are real 777 pilots and experts on the Tech Team that validated and verified all of these behaviors.  I verified the flameout scenario myself numerous times in the beta stage.

Thanks for the answer. And now that you've made me realize it; yes, I guess I should trust the pros' work. After all, PMDG did promise absolute realism with that 90USD price tag and ~18 months of development work...

 

Regarding the APU, According to the manuals, it does automatically start on the real plane when both engines are failed in flight.

Ah... The manuals... I admit I am not an avid manual reader but I did try searching for the answer in the FCTM and the FCOMs (the furthest I got was in chapter 8.7 of the FCTM, gave up after I couldn't find anything regarding APU autostarts); I really admire you guys who have seemingly next to no problems with reading and digesting entire 30mb pdfs. All that aside, thanks for pointing it out. :)

 

The APU does have an autostart feature. The overhead switch will remain off.

Thanks for the answer!

 

The RAT will deploy automatically when hydraulic pressure is lost, engines shutting down does not cause a loss of pressure. The electric and bleed pumps hyd are still working.

 

The APU does autostart when there is no AC source, standby bus holds it all together until the APU takes over.

 

 

From my own testing (I test pretty much everything on every new PMDG plane I get) I didn't notice much help from the TAC, the most help I noticed was from the PFC which does a great job. I leave the PFC on but turn of the TAC and it continues to do a great job dynamically trimming the rudder. Turn both off however and you really get to feel the result of those big engines.

Thanks for the answer and sharing your observations!

 

Thanks guys! Really appreciate your answers; they're very helpful in helping me understand the 777's intricate (if that isn't an understatement) systems.

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The RAT will deploy automatically when hydraulic pressure is lost, engines shutting down does not cause a loss of pressure. The electric and bleed pumps hyd are still working.

 

Not quite. The RAT will deploy under the following conditions IIRC:

 

  • Power to both transfer buses are lost.
  • All three hydraulic system pressures are low.
  • Both engines are shut down, and centre pressure is low.

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