747 flight controls

[Bob Goding]

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.

[Leland Pate]

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


...I dunno.

[Zef]

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...!

[1973911s]

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

[fingpilot]

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.

[Drago]

They're turning left.

[rick-l]

Subscribe

Also curious

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

[Porsche-O-Phile]

Probably trim.

[fingpilot]

Originally posted by Porsche-O-Phile
Probably trim.

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

[Nostril Cheese]

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

[rick-l]

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

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

[Zef]

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

[fingpilot]

Originally posted by rick-l
No they are not. They are both reducing lift on the wing.

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.

[fingpilot]

Originally posted by zefsuper911
It is not a trim purpose...Too much induced drag = fuel waste

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

[Porsche-O-Phile]

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.

[fingpilot]

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.

[Bob Goding]

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

[fingpilot]

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.

[motion]

Those sure are purty clouds.

[Zef]

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