747 flight controls
 

Woke up after sleeping on a 12 hour flight last month and opened the window shade to see this. aircraft in steady cruise,35000ft, spoiler in conflict with the inboard aileron?
I went and had a look at the other side and all was OK.
Any experts have an explanation? 747-400.
http://forums.pelicanparts.com/uploa...1166341699.jpg

Did the co-pilot come stumbling from the cockpt, half dressed, screaming at an attendent for more champagne????


...I dunno.

Hyd lock in the actuator or a bad rigging of that spoiler...It's surely induce a lot of drag for that wing at 450 mph...!

Interesting, I have seen this many times on the 747 and 767, so will be interested in what the pilots have to say.

Is Boeing's way of balancing ying and yang.

Is a tease for all the engineers on board.

Is a way of balancing out all the fuel savings in the 777 program.

They're turning left. ;)

Subscribe

Also curious

I am sure that title will attract the attention of some Pooshey drivers in the pacific northwest.

Probably trim.

But Jeff, that's the funny part. They are cancelling each other out.

Also subscribed.

I've noticed this on flights as well. Is this a way of bleeding off pressure/thermal expansion related? I initially thought it was an aux. trim feature as well.

Another shot of a 747 wing.. Truly amazing machine

http://forums.pelicanparts.com/uploa...1166382696.jpg

No they are not. They are both reducing lift on the wing.

It is not a trim purpose...Too much induced drag = fuel waste

uhhhhhhh.... beg to differ.

The raised spoiler panel is doing just that. Spoiling lift (result.. left roll).

The deflected (downwards) inboard aileron is generating a little addidtional lift (result.. right roll). In this case (since no turn is in progress), cancelling the spoiler's efforts.

The outboard ailerons are locked out when wing is clean until substancial input is entered. Normally, all you'll ever see is the inboard aileron moving to maintain lateral trim. Spoilers would deploy assymetrically next to bolster the inboard aileron. Even then, the spoilers would open from inboard to outboard, then finally the outboard aileron as well.

In reality, this is probably a misrigged or jammed spoiler panel. The aileron is responding to the spoiler. If it were the other way around, the opposite wing aileron would also be responding, in the opposite direction, of course.

You are correct. Is why I made the crack about the 777.....

Not an expert on the 747, but I'll propose the following for thought: The downward-deflected control surface is deflected downwards to increase camber (and lift) on the left wing, trimming for wings-level versus a left-wing-low condition in an untrimmed condition. The upward-deflected surface (spoiler) is deflected upwards in lieu of rudder trim to trim YAW - i.e. dragging the left wing back and trimming against a nose-right untrimmed condition.

Possible? Dunno.

Jeff;

In a perfect world, that might pencil out. The autopilot only looks to keep the wings level, all other things being equal (on course).

If the fuel was imbalanced (possible if the FE and the rest of the crew was asleep) would still be seen by the autopilot as a wing low situation, and it would apply ROLL corrections in the flight control programmed order for the present flight configuration.

A yaw out of trim situation would be seen by the autopilot as a deviation from course centerline effort, and would apply ROLL to correct for this. Even a really bad yaw (mistrim of the rudder, or engine out) would produce a constant ROLL correction by the autopilot, deflecting the inboard aileron, and perhaps the opposite wing spoilers only. There was a close call a couple of years ago of a 747 on departure from SFO that lost an engine at MaxGrossWeight on takeoff, and the pilot applied aileron to couteract the yaw and roll from the dead engine. The resulting spoilers destroyed much needed lift, and the airplane sank back to the ground below the horizon from the tower. Someone remembered basic systems, and got on the rudder, neutralized the aileron input and managed to get flying again. The tower had already pushed the crash alarm.

The autopilot has no yaw input other than the yaw damping function.

The picture is of an unusual situation. It should not be that way, but obviously was on this flight.

Suprising thing was , as I mentioned ,the stbd wing was was normal i.e. all spoilers flush and the r/h inboard aileron was at neutral.

Bob

Exactly; The control laws allow that. Only one inboard aileron can be slightly deflected without the other one responding as well. The aerodynamicists would accept the slightly downward deflected inboard rather than an upward deflected one.

Those sure are purty clouds.

Fingpilot...there is no FE in a 747-400....

Downward deflection on left inboard aileron = right roll.

Tsk, tsk, YOU should now better! :D :p

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

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...

SmileWavy

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

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.

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.

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

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. ;)

"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

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

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.)

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

http://www.bgu.ac.il/noar/students/i...plane/otto.jpg

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.

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.

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.

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.

This thread delivers!

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

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

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!