747 Directional Stability in the climb phase

[B2N2]

Clean climb through FL230 experienced some light yawing in alternating directions, climb speed in the *270-280* kts range probably 15 tons below MTOW at this stage.
According to the check airman there is a Boeing paper on this phenomena.
Anybody familiar with this or is it hogwash?
He couldn’t tell me if this also occurred with the BCF/ERF with the extended upper deck.
My reasoning is that at a particular weight at a particular climb speed there is a aerodynamic effect from the upper deck hump that causes some yawing that is not sufficiently dampened by the yaw dampers.

[RandomPerson8008]

That's abnormally slow to climb that jet. Normally you're almost always 300+ knots indicated until crossover even at light weights at most cost indices. 10 tonnes below MTOW? You should be climbing much faster, at least 320 kias even at low cost index. In other words, I don't know, because I'm pretty sure I've never flown at those altitudes at those speeds on climbout.

[BBK]

B2N2

Boeing did put out a memo regarding this. From memory experienced it at least once as a gentle wing rock. Seemed to recall going to speed intervention and reducing the speed slightly stopped it. Wasn’t a big deal and don’t recall the crew even noticing it.

BBK

[B2N2]

Originally Posted by RandomPerson8008

That's abnormally slow to climb that jet. Normally you're almost always 300+ knots indicated until crossover even at light weights at most cost indices. 10 tonnes below MTOW? You should be climbing much faster, at least 320 kias even at low cost index. In other words, I don't know, because I'm pretty sure I've never flown at those altitudes at those speeds on climbout.

I had that speed wrong as that is indeed slower then normal.
Lets rephrase that to normal climb speed.
Same question applies, can the paper be found anywhere and what exactly causes it.
Thanks BBK.

[fdr]

Originally Posted by B2N2

... My reasoning is that at a particular weight at a particular climb speed there is a aerodynamic effect from the upper deck hump that causes some yawing that is not sufficiently dampened by the yaw dampers.

Not a phenomenon from the fuselage. This is a 744? Winglet flow is sensitive to AOA, would think that increasing to proper climb schedule would remove the yaw. Next time, set up a printout of roll and yaw, and the aileron and rudder positions. The lower rudder position will give an idea if the YD is part of the issue. The upper deck length didn't make much difference to the flow, but the extended upper deck was a slightly lower drag but added some weight. The winglets do reduce lateral directional stability, but nothing much to speak of. The plane has a very gentle phugoid, overall, an amazingly nice plane to fly.

[Le Flaneur]

The B744 has a structural mode that is suppressed by the yaw dampers. It is not an issue with directional stability.

[Coastrider26]

We have one BCF in our company which displays this behaviour as well. After a lot of troubleshooting the engineers came to the conclusion that one of the wires of the upper yaw damper was corroded. For roughly two years did indeed fixed the problem but it is coming back now at times. Today at 300 kts and roughly FL230 - FL 250 the rudder output on the CMC display page did not show any unusual fluctuations.

Just getting more and more mysterious about this Boeing papers around this phenomena if they exist