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mSparks43 / 747-400

A Boeing 747-400 aircraft for X-Plane 11 & 12
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AP: Issue with the TOGA pitch FD #512

Closed oMrSmith closed 3 years ago

oMrSmith commented 3 years ago

This is the last major issue of my original list #463

The TOGA pitch FD is currently not showing pitch for the right speed. As a result it does not raise high enough, causing the plane to accelerate too early if you follow the FD during take off.

This is the reason why the MCP Speed has to be set to V2 before take off and not to V2+10. The AP will add 10 knots to whatever speed is set in the MCP.

This has lead to many confusion. To compare with the 737: You will not find one single video of flight deck to sim where he sets the MCP Speed to V2+15. Because if he did, the TOGA FD would in fact show pitch for V2+15+15, which can easily be proven by test:

(You can set the MCP speed to 180 knots in the Zibomod, the TOGA FD will show pitch for 195 knots.)

In the following video a real pilot sets the MCP SPD to V2 in the 747 by PMDG: https://youtu.be/9eRJP0ge_Uw?t=1504 (What can also be seen in the video is that arming VNAV will not set the MCP SPD to V2+10.)

PS: If it would cost too much effort to program this, I think it would be helpfull if the TOGA pitch FD would at least show the pitch for the speed which has been set up in the MCP panel. (Currently it's not linked to the MCP speed at all.)

mSparks43 commented 3 years ago

I'll use https://www.youtube.com/watch?v=j-MuS0N_0n0&t=268s as a reference, this will need TOGA pitch mode FD ripping out and replacing with one that matches actual boeing functionality. Might not be soon because its dependant on computing PLI #455

oMrSmith commented 3 years ago

Yeah. I suppose that's fairly complex to program and other things might be more important now - like the totalDistance ? ;) ...

PS: I think there is one little inaccuracy in the video: The reference is not V2 but the MCP speed which has to be set to V2. The difference is: In the first case it wouldn't actually matter which speed is set in the MCP panel, whereas in the second scenario it does, resulting in a false guidance, in case the pilot forgets to set the MCP speed to V2.

mSparks43 commented 3 years ago

I think there is one little inaccuracy in the video:

The video I just linked is an FAA approaved computer based training vid for the 744, sooo, if it disagrees with other sims, I go with that (and it wouldn't be the first time)

I might be able to mod the toga pitch setting to keep it below B747DR_airspeed_Vs, right now its set to 8 degrees and stays there until the AP is set by VNAV or the pilot to FLCH (at which point pitch targets MCP speed)

V2 is an FCC variable, if the PFD is showing no vspd I guess it just stays in the lower of 15' or below PLI

oMrSmith commented 3 years ago

Those trainings as well as the FCOM have one thing in comon. They are good in telling you what you should do and not so good in telling you why and how the system works. But that's just my humble opinion ;).

(I only question: If the TOGA pitch mode refers to the internal value of V2 which has been entered in the FMC, rather than refering to the MCP SPD, why do pilots still have to set up the MCP SPD to V2? I believe it is because it actually matters... Tested this a lot when Zibo was working hard to implement this in his Mod.)

mSparks43 commented 3 years ago

which has been entered in the FMC, then why would it matter to set up the MCP to V2?

well, a lot here is to do with climb rate rather than speed, if you need more acceleration the trade off is a slower climbrate.

Docs FMA review doesn't mention the 15' section https://www.youtube.com/watch?v=sDa1ukA3CUo&t=480s

but adds that it also varies if you lose an engine. you want the MCP speed to be more or less equal to what it comes out of TOGA pitch mode, else target pitch will change significantly when it does. Think we see that now in VNAV, with a sharp pitch up when VNAV SPD becomes active after it was targeting 8'

oMrSmith commented 3 years ago

Maybe we do not even disagree :D. I'll make a video soon to explain my point better...

(If you jump in the 737 from Zibo set the MCP SPD to a false value, let's say 180 knots, then take off with TOGA without VNAV armed and follow the FD accurately the resulting SPD will be 195 knots even if V2 in the FMC is 150 knots!)

PS: Yeah I think anything more than only 8' of initial pitch would be good as a first step!

oMrSmith commented 3 years ago

The transition from the pitch-mode TOGA to the pitch-mode VNAV SPD during take off with VNAV armed feels very flued now!