747 flight controls

[Eric Coffey]

Originally posted by Drago
They're turning left.

Downward deflection on left inboard aileron = right roll.

Tsk, tsk, YOU should now better!

Although, I haven't a clue what the explanation is either!

All I know is that in cruise (or flaps up) the outboard ailerons & spoilers are locked, and the inboard ailerons/spoilers work in concert to control roll.
The only thing that comes to mind is maybe the AP is compensating for a nasty crosswind (crabbing w/ right aileron + left rudder), and the spoiler is countering the rudder-induced yaw? Still that looks like a lot of deflection for trim. Are you sure you weren't in a gradual right turn? Even the wing vs. horizon in the picture kinda looks that way.

Also, since the spoiler is only slightly deflected, another explanation may be that it's cable needs to be re-tensioned and the extreme low pressure on the top side of the wing is "sucking" it up into airstream.

Ah, who knows...

[fingpilot]

Originally posted by zefsuper911
Fingpilot...there is no FE in a 747-400....

You are so right. Just noticed it is a -400. Same laws for the -400 as the earlier versions.

[fingpilot]

Originally posted by Eric Coffey



The only thing that comes to mind is maybe the AP is compensating for a nasty crosswind (crabbing w/ right aileron + left rudder), and the spoiler is countering the rudder-induced yaw? Still that looks like a lot of deflection for trim. Are you sure you weren't in a gradual right turn? Even the wing vs. horizon in the picture kinda looks that way.

No crabbing required in cruise. A crosswind once established on course is compensated for by ROLLING the A/C HEADING onto whatever offset is required to maintain COURSE, and then the plane is ROLLED level again. Autopilot is a wing leveller ONLY. No yawing possible.

In flight the wings flex upwards several FEET at the tip, and from the cabin, they appear as depicted in the photo.

No crosswind, COURSE and HEADING are the same. Crosswind makes HEADING diverge from COURSE in the direction that the crosswind is coming from. Autopilot doesn't care. It ROLLS A/C to new HEADING to maintain COURSE, and then levels wings again to keep zero error on COURSE.

[fingpilot]

Originally posted by Eric Coffey


Also, since the spoiler is only slightly deflected, another explanation may be that it's cable needs to be re-tensioned and the extreme low pressure on the top side of the wing is "sucking" it up into airstream.

Ah, who knows...

The spoilers are hydraulically driven, and sometimes cable actuated. Unless the several hydraulic systems driving the spoiler boards have failed, they are driven closed and open by 3000psi of hydraulic pressure. Failed hydraulics, and high angle of attack MIGHT get them to float, but they all would be floating.

Once again, this is probably a mis-rigged board, powered up out of stow slightly, making the aileron compensate.

We know from the report that the opposite wing had no such deflections of either kind.

[Drago]

Originally posted by Eric Coffey
Tsk, tsk, YOU should now better!

Hey, cut me some slack man...I'm a structures guy, not aero.

[450knotOffice]

Wow, guys. You're coming up with some pretty far reaching explanations. They are fun to read though. Fingpilot has it right as far as I can tell. He knows what he's talking about, obviously. The inboard spoiler panel is up slightly and shouldn't be (could be for any number of reasons, but for the purposes of this discussion it doesn't matter why). This induces a slight rolling tendency left wing down. The autopilot senses this rolling tendency and corrects it with an aileron deflection. Equilibrium is achieved and the autopilot is "happy". However, this does lead to a little more drag and would therefore decrease the range somewhat due to the fact that the autothrust system is set to hold a fixed mach number and would obviously need to counter the slight additional drag with slightly more thrust.

On a side note, are fingpilot and singpilot one and the same? Hmm.

[oldE]

"On a side note, are fingpilot and singpilot one and the same? Hmm."

I've been thinking of Singpilot as "Singapore Pilot", I think of "fingpilot" as "F___ing Pilot" I could be wrong.

And yes, I too enjoy the 'techie' aspects of the question.
(I am neither a pilot, nor flight systems engineer, nor do I play either on TV. I did not stay at a Holiday Inn, last night.) I just like gadgets.

Les

[Leland Pate]

Wow, guys. You're coming up with some pretty far reaching explanations.

What, you mean it isn't possible that the cockpit party was in need of more champagne???

[KevinP73]

Originally posted by 450knotOffice
On a side note, are fingpilot and singpilot one and the same? Hmm.

I think they're onto you ****pilot.
(Note to self upon entering "pilot witness protection plan" pick a name that doesn't rhyme with your original name.)

[id10t]

Well, as long as the otto pilot is happy....

[swa911]

Bad spoiler actuator causing the spoiler to "float".

[fingpilot]

Originally posted by swa911
Bad spoiler actuator causing the spoiler to "float".

I'd go for that, except a floating spoiler wouldn't need constant counter from the aileron. Cruise speeds would more likely keep a 'floating' spoiler conformal.

[swa911]

typical fingpilot......they know everything

[KevinP73]

Originally posted by swa911
typical fingpilot......they know everything

Speaking for those of us in the back rows, I kinda think thats a good thing! The last thing I want to hear is the pilot on the intercom asking for suggestions.

[swa911]

Sure, but speaking for those of us on the ground with the wrenches in our hands it's just another know-it-all button pusher telling us how to do our jobs.

[fingpilot]

Ah... now the true colors come out.

Clearly, this is a maintenance FUCUP and there are pics to prove it.

Dollars to donuts the maint reply to this writeup will be.... "Could not duplicate on ground", and the plane will cross three more oceans like this.

[Drew001]

This thread delivers!

[84porsche]

Originally posted by KevinP73
Speaking for those of us in the back rows, I kinda think thats a good thing! The last thing I want to hear is the pilot on the intercom asking for suggestions.

LMAO. Could not agree more. That would be quite scary if they were.

[450knotOffice]

"Could not duplicate." How many times have I seen that in 15 years as an airline pilot.

[Bob Goding]

I once had a pilot write up an ADF problem in the tech log thus---
"No 2 ADF off"----I had spoken with him after the days flying and he didnt mention it.
So I wrote it up as--

Re No2 ADF off--is it switched off, off heading, or does it just smell bad?

S---t hit the fan and I got hauled on the mat over it.
No sense of humour those flyboys ,ever since Captain Wilbur declared Orville as the dirty fingernail brigade!