MD80 Series control surfaces

[ajmitch]

Can someone answer this for me please. I understand that conventionally, aircraft have a horizontal stabilizer with elevator. Some aircraft have that replaced by a stabilator in which the whole wing pivots, but what is this on the MD80 series?
In the photos that I've found, it can clearly be seen that there are several movable surfaces.
In pictures 1 and 3 the front part of the wing is almost horizontal and the elevator raised.
In pictures 2 and 4 the front part is angled down - so it also pivots like stabilator.
But then as seen in pictures 5 and 6 we have the trim tabs, but they are split and operating in opposite directions - which appears to give a total of four separate movable surfaces on each side.
Also in pictures 5 and 6 - I thought that both sides were supposed to move together - but these are clearly operating differently.
What sort of system is this?

http://www.flightsim.com/dcforum/Use...d915778c43.jpg

[Armitage_Shanks]

When the WHOLE elevator moves, thats usually trim. When the entire BACK surface moves, thats yoke imput. I think the smaller tabs on the rear are also trim tabs, like on Cessnas.

[Jimjam]

>When the WHOLE elevator moves, thats usually trim. When the
>entire BACK surface moves, thats yoke imput. I think the
>smaller tabs on the rear are also trim tabs, like on
>Cessnas.

you sure?

i thought that the trim tab was the little bit on the back and when you moved it it just eased the required input on the yoke to keep it in the neutral position so that you wernt fighting with it for the entire flight and thus it eases fatigue on the pilot...

as for the pics above... looks odd to me

[KathyPilot]

Hi:
I'll confine the answer to photo #5 because this shot shows the parts the best.

First, the entire surface (the horizontal stabilizer) moves for pitch trim. Many aircraft use this method. Now to the individual tabs and surfaces.
There is a elevator surface on the rear of the stab the runs the entire length of the stab. Attached to the trailing edge of that are three control tabs. Going from the rudder out these control tabs are elevator control, elevator gear, and the elevator anti-float tab.

Each of the elevator control tabs are connected to their respective yokes - Pilot and FO(yes they are seperate systems but connected by a torque tube - there is a reason for this..think about it). When these control tabs are moved by the pilot this in turn moves the entire elevator surface by aerodynamic force.

The next control tab, elevator gear, is geared (duh) to the elevator movement and assist the control tab.

Lastly, the anti-float tab. This one is geared to the horiz stab and is used to help stability during a greater than 10 deg nose up landing.
Now, as to your question about them being in different positions. This is due to the fact that they are on the ground and no airflow exists to streamline them. They are all flying control surfaces.

Hope this helps.

** Born to Fly **
Kathy

[Cannikin73]

Thats my favorite!

[ajmitch]

Thank you very much Kathy, for taking the trouble to give me such a detailed explanation. I had no idea that control surfaces had become that complex. Now I have to go and eat some humble pie and apologise to a group of guys to whom I complained when I thought they had modelled the horizontal stabilizer wrongly.

Thanks again.

[positiveg]

How do you guys know this? How do you people come up with this knowledge. Do you read a whole bunch of stuff about aivation and try to understand? I want to be a pilot and an aeronautical engineer and I feel that I need to know all this.

[flyinggriffin]

When it comes to the real world pilots, good ones read a lot on aviation. Besides the fact we love flying and reading about it when we don't fly, knowledge is power. If you are smart you don't stop learning about weather, systems and airspace when you get to be a pilot.

[lnuss]

Between reading everything you can get your hands on and discussions with a wide variety of pilots (hangar flying), you can accumulate a lot of information over a period of years. A natural curiosity helps, too.

Flying magazine, AOPA Pilot, Plane and Pilot, EAA's Sport Aviation,and other periodicals, along with novels about aviation and numerous non-fiction books about aviation will, over time, cover much of the principals of aviation, mechanical workings of aircraft, a ton about avionics, numerous areas of flying procedures and much else.

Some abstruse piece of information may save your life some day, too, so there's a practical side to this. Chuck Yeager attributed his success as a test pilot partly to his desire to know everything about the aircraft he was flying, not just how to fly it. He gave a number of instances where that knowledge saved his life. I've had a few of those myself, though I've never been in the kind of demanding situations that were almost routine for him.

As Bob says above, good pilots never stop learning. You can't get it all at once, and the willingness to listen to others, to think about what they say, to evaluate who is blowing smoke and who is feeding you the straight skinny, will help you eventually to gain a tremendous amount of information. Reading everything you can get your hands on and asking questions (as you are doing) will also help add to your knowledge.

If you want to be an aeronautical engineer, you'll get a lot of good information from your schooling, a good background to start really learning about how to design aircraft. If you want to be a good pilot, the flight training gets you to the point you can start learning more. The Private, Commercial and even the ATP are really just licences to learn.

No one knows it all. Everyone can learn from someone else. Even after 30+ years of flying, and teaching flying, I still find more things to learn -- I've even learned some things from these forums, things to add to what I've picked up from many, many other sources over the years.

And I know 30,000+ hour pilots who tell me they are still learning.

[lnuss]

Good explanation, Kathy. Even the Piper Cub uses a movable horizontal stabilizer for pitch trim. An excellent point, too, about what airflow (or the lack thereof) does to control surfaces. Many folks seem to forget (or not be aware) that there is a LOT of force generated by the relative airflow, and aircraft are designed to work in that environment, often in non-intuitive ways.

I might mention to Tony, though, that the horizontal tail surfaces are not a wing. Collectively they, along with the vertical tail surfaces, are called the empennage. The term wing generally refers to the main lifting surfaces, and the tail surfaces don't actually provide lift, in the sense of supporting the weight of the aircraft, although they are airfoils and do provide aerodynamic forces in the same way as a wing. But these forces are aimed downward, to help balance the aircraft, although elevators (or the movement of stabilators) do modify that force.