Go around thrust logic?

[tcas_climb 45]

Let us know the response when you get one.

[Michael Moe 495]

 

I have erased all panel states, all flights, FSUIPC.ini and used the original Aircraft.cfg, but nothing works...

 

Now I am reading this on the 777 Introduction pdf file (page 0.00.53):

 

"I’m seeing erratic changing fuel loads and autopilot issues.

There is an issue with the BIOS/UEFI clock and high precision event timer on certain recent Asus motherboards at the time of this writing. The timer becomes erratic or stops completely and causes issues with the aircraft systems. We use these timing functions extensively and they must be working correctly for proper operation of the airplane. Check with Asus for a firmware update and consider replacing the CMOS battery on your motherboard if you experience these issues. The problem is not specific to PMDG or to FSX and has been widely reported on the big hardware forums around the Internet. If you are building a new PC for FSX, we recommend staying away from Asus motherboards until this issue is confirmed to be resolved."

 

I have an ASUS Z87 Plus motherboard, purchased Sep 2014. I hope the problem is not related to it, otherwise I am really in big troubles. How can I check that? Further, why should I change the CMOS battery?

 

 

 

I have the Z87 Pro and have changed the CMOS batteri like 5-8 times. Latest BIOS has not got the problem totally away but now it holds 3 months or so. You will crash and the Microsoft windows watch/calender will reset to 01.01 .12.00 and there is nothing to do in the 777 or NGX other than you will crash

 

Michael Moe

[jgoggi 65]

there is nothing to do in the 777 or NGX other than you will crash

 

Sorry, but I don't understand what you mean with "you will crash". Could you please be more specific? My computer works perfectly, I never crash and have no problems with the 777 going crazy whatsoever, except the one I'm talking about here and the overspeed during early VNAV descent, but I start thinking that such problems are of the airplane and not of the computer, since I can reproduce them with another computer at work, that has another type of motherboard. Therefore I am really not convinced at all that the guilty is my Z87 (Plus, not Pro) motherboard...  Unless you show me with a video that, with a "working" motherboard, you get THR REF every time you press the TOGA twice during go around... 

[Michael Moe 495]

Sorry, but I don't understand what you mean with "you will crash". Could you please be more specific? My computer works perfectly, I never crash and have no problems with the 777 going crazy whatsoever, except the one I'm talking about here and the overspeed during early VNAV descent, but I start thinking that such problems are of the airplane and not of the computer, since I can reproduce them with another computer at work, that has another type of motherboard. Therefore I am really not convinced at all that the guilty is my Z87 (Plus, not Pro) motherboard... Unless you show me with a video that, with a "working" motherboard, you get THR REF every time you press the TOGA twice during go around...

I think you misunderstood. I dont think either that you have the issue with Asus but as i wrote i know i am. And everytime all systems fails and rudder and aileron gets jammed and then you cant control the plane at all. Also it reset the time to 01.01 12.00 when i had this Asus problem.

 

Michael

[jgoggi 65]

 

 

I think you misunderstood.

 

Aha, sorry Michael, now I get what you meant. That's too bad that you got those problems, but your experience even more gives me a confirmation that my motherboard should be ok.

[777simmer 117]

Thank you, Romain. I think there is something not working correctly. I tried at least 15 go around and only once, like you, after retracting gear and flaps, I had THR REF, all the other times only THR and, above all, never THR REF after pressing the button twice. Maybe it's something for the developers to look into....

I just did three automatic approaches followed by a go around.

 

The system works just fine but you are correct that the THRUST LIMIT indication does not change to THR REF as it should.

 

Just so we are all talking about the same thing first:

 

- The THRUST LIMIT indication is what the autothrottle will use maximum.

The green line at the end of the N1 dial will show you at what N1 this maximum/limit will be reached.

 

(Do not confuse this with the N1 redline limit by the way.

The red line is a real limit beyond which structural damage can occur.

The green thrust limits are just calculated limits that extend engine life just like reduced TO thrust does. You can exceed the green limits (safely) by disengaged the AT and pushing the AT full forward if you need that much thrust.)

 

- So, if the thrust limit says CLB, then the AT will not use more than the calculated CLIMB thrust limit and the green line is set at an N1 speed that defines this climb thrust limit (under the current atmospheric conditions).

- If it says GA then the green line will be a bit higher up the dial at the N1 setting that defines Go Around thrust (under the current atmospheric conditions).

 

But that does not mean the AT will use all that thrust available. The AT can use less than the limit (green line), but not more.

 

So the Green line in the N1 dial and the corresponding CLB/CRZ/TO/GA indication just show a safe limit.....this has nothing to do with what the AT is actually doing.

 

What the AT is doing, is displayed on the FMA (on top of the PFD over on the left). In SPD mode for example, the AT will advance and retard to keep the target speed. The AT is smart though and it will add/retard as much as is required to keep the speed. It will not just go back and forth between idle N1  and full CLB or CRZ or GA thrust limit (green line).

That would be really uncomfortable!

 

 

The same is true for a go around.

The go around thrust limit (GA) is shown on top of the N1 dial and the green line sits high up the dial showing you that IF you wanted maximum GA thrust....that green line is where you would have to set your N1

.

The whole final approach you will see that GA is your thrust limit, but neither you nor the AT if engaged will require that much power under normal circumstances.

During approach the AT is in SPD mode and varies thrust to keep the target speed.

 

And during a go around (single TOGA click) the AT will switch from SPD to THR mode.

The PMDG777 does this correctly.

With the AT in THR mode, +2000ft/min is the go around target for the AFDS (Auto pilot Flight Director Sytem).

 

Note that the GA thrust limit does not change.....you still have GA as your limit and the same green line as during the approach.

The AT could use up to that GA limit green line, but usually is will require much less than that to reach a vertical speed of +2000ft/min.

 

The AP and FD will pitch up to maintain speed at Vref+5 to25kt (pitch for speed) and the AT in THR mode will add thrust as required to keep those +2000ft/min.

During my go arounds N1 advance to around 81%.....on a hot day or at heavier weights more N1 will be required to keep the same +2000ft/min.

THR is telling you that go around thrust is set variably.

Wind shifts can also require the AT to advance more....and it will do so up to the GA thrust limit if required.

 

A second click of the TOGA switches should engage the AT in THR REF mode.

It does so correctly in the PMDG777.....I could clearly see on each go around how N1 went up from those initial 81% to the GA thrust limit green line!

But on the PMDG777 the AT mode indication still says THR.....it should be saying THR REF.

So the system does work....but the AT mode annunciation (FMA) is not changing correctly with what the AT is actually doing.

Not a big deal.....but a small bug that should be reported yes.

 

The videos you have posted where the PMDG777 simply stays in SPD mode after pressing TOGA is something else completely.

That is just all wrong but I dont know what happened there.

If you still have that problem as well then I would suspect a corrupt install since you have already tried deleting the FSUIPC.ini and you are no longer using a saved panel state or saved flight.

[jgoggi 65]

Thank you, Rob, for your detailed explanation, it gave me a confirmation on the way thrust limits work. Yes, in the end the only "bug" is that THR doesn't turn into THR REF, even if once I tried a sequence of 2 go arounds and the first time SPD became correctly THR, the second time (after realigning on the ILS) it didn't change and the plane did not climb. 

[777simmer 117]

the second time (after realigning on the ILS) it didn't change and the plane did not climb.

 

So we have established something is wrong at your end.

And since you also have that weird Vnav dive problem it is either the PMDG777 install itself that has an error, or a weather app or something else is interacting with the PMDG777.

 

By the way.....probably not gonna help........but make sure you have the latest Ops Center version (after I updated that, I could swear performance was better).

[jgoggi 65]

 

And since you also have that weird Vnav dive problem it is either the PMDG777 install itself that has an error, or a weather app or something else is interacting with the PMDG777.

 

The problem is that I have exactly the same behaviour at home and at work, two different systems, two different installations, no points in common between the two systems. At work I have just FSX, FSUIPC and the 777, no hardware controls, no other addons.

 

 

 

By the way.....probably not gonna help........but make sure you have the latest Ops Center version (after I updated that, I could swear performance was better).

 

I will check that (I am at work, now).

[777simmer 117]

 

I will check that (I am at work, now).

Cant wait for us to get internet on board ;-)

[jgoggi 65]

 

 

A second click of the TOGA switches should engage the AT in THR REF mode.
It does so correctly in the PMDG777.....I could clearly see on each go around how N1 went up from those initial 81% to the GA thrust limit green line!
But on the PMDG777 the AT mode indication still says THR.....it should be saying THR REF.

 

Anyway I encourage the developers to correct this bug. In a delicate moment as the go around is, it's important for the pilots to distinguish between THR and THR REF, to have clear if they pushed TOGA once or twice and if the A/T is applying the maximum thrust (for the go around) or not...

[777simmer 117]

Anyway I encourage the developers to correct this bug. In a delicate moment as the go around is, it's important for the pilots to distinguish between THR and THR REF, to have clear if they pushed TOGA once or twice and if the A/T is applying the maximum thrust (for the go around) or not...

Absolutely. I plan on submitting a support ticket as well but I would like to do a few more flights/Go Arounds to make sure.

[Sam 68]

Very informative Rob as always..

[777simmer 117]

Thanks :-)

[jgoggi 65]

Rob, very strange, I did some more tests and, if the aircraft has touched the ground before performing the go around (therefore not starting the flight from the air), I manage to get THR REF during go around when pressing TOGA twice. The same happened with the other problem of SPD not turning into THR at go around. Did you test any further?