The Scenario:

After takeoff with VNAV SPD as the engaged pitch mode, a Boeing 747-400 has reached the acceleration height and the nose is lowered to pick up airspeed prior to flap retraction

My questions:

1.  What is the airspeed governing the commanded pitch on the Flight Director bar?
2. is it the retraction speed for the next flap setting, or the maximum speed restriction below FL100 (in come countries)?

My understanding of PID control systems logic is that generally rather than approach a target at a rate proportional to the difference between the current value and target value, a fixed rate is used to avoid overshoots, until with a zone of convergence, so I'm inclined to believe that the actual governing criterion right at the acceleration height would be a fixed acceleration, but I'm not familiar with the specific logic in the above context.

@jon b Care to add your experience here?

The question is which 744 version do you have and what sim are you using.

I'm asking this because PMDG and IFLY has that simulated correct.

As to the real airplane after lift-off pitch command target speed is v2+10 limited up to v2+25 by APFD logic while at accelerate height, will pitch for speed to 5 KTS below max flaps speed of the commanded flap position. During this transition it will lower the nose based on configuration (weight, altitude, OAT).

After flaps is up VNAV will target APFD to climb speed which will be approximate +20 KTS above flap maneuvering speed (clean speed) regardless of 250 KTS  below 10,000 FT pr FL100. At light weights will do 250 KTS but most of the time we climb "clean" between 260 up to 280 KTS. Now, certain SIDS at certain WPTS have speed restrictions that are honored by FMC DBASE otherwise we will accelerate to min clean speed whatever that speed it is or adjust to ATC requests. That 250 below 10K is not applicable for heavy, super or fighters as a rule when minimum clean speed is higher than that. As a curtesy to ATC we advise them that "due to operations limitations our minimum clean speed is...." 

@F737NG I couldn’t have made a more thorough reply than LRBS has.

All I remember is it accelerates and climbs, and it can do both of those at once, something the new wonder jet isn’t too good at.

53 minutes ago, jon b said:

All I remember is it accelerates and climbs, and it can do both of those at once, something the new wonder jet isn’t too good at.

Just did a dirty calculation for a power-to-weight ratio, which showed the 744 is the better performer.
Ah well, turns out the good ol' days really were in some respects!

Thanks LRBS and JonB,

that certainly answers my question. As for your question regarding version and sim, the answer is none, actually! I'm just in the process of putting together an an analytical model of the Boeing 747-400 flight mechanics based on published data, flight ops manuals, and simulator documentation  - a sort of reverse engineering exercise, if you will. As to why - purely for my entertainment and edification. I'm getting some nice results so far, but want to fine tune some details. I wish I could include a few snapshots from the graphics module of my home-grown "simulator", but will have to find a way to upload them to a URL first.

I agree that the phasing of of the 747s is a travesty. There will NEVER be another bird as magnificent as the Boeing Quad jet.