B717, MD-88, DC-9 elevator

C

Chris Barnes

Well-Known Member
Chris Barnes said:
When I see these aircraft taxing (or even at the gate) I have noticed that their elevators are in the full up position. And one side of the elevator is sometimes higher than the other. why is this?

http://www.airliners.net/photo/Boeing-717-2BL/1623699/L/

http://www.airliners.net/photo/Quantum-Air/Boeing-717-2CM/1635922/L/

http://www.airliners.net/photo/AirTran/Boeing-717-231/1614794/L/

http://www.airliners.net/photo/AirTran/Boeing-717-231/1614795/L/
Click to expand...

It's because they're not interconnected. What controls the elevator movement is a trim tab.

Any type-rated pilots on here can give you a much better answer, but that's the way I understood it.
 
Technically, it's a control tab that 'flies' the surface of the elevator.

SFCC/UND, it's a legit question and I'd have been more than happy to answer it!
 
Chris Barnes said:
When I see these aircraft taxing (or even at the gate) I have noticed that their elevators are in the full up position. And one side of the elevator is sometimes higher than the other. why is this?

http://www.airliners.net/photo/Boeing-717-2BL/1623699/L/

http://www.airliners.net/photo/Quantum-Air/Boeing-717-2CM/1635922/L/

http://www.airliners.net/photo/AirTran/Boeing-717-231/1614794/L/

http://www.airliners.net/photo/AirTran/Boeing-717-231/1614795/L/
Click to expand...

When you are taxiing out behind them you'll see one side full up and the other full down. Kind of funny looking sometimes. The servo tabs and thus the elevators don't become active until you start to get airflow over them during the takeoff roll.

This is obviously different from a hydraulically powered system that positions the surfaces with PCU's (power control units which are little pistons/actuators). Those will always match up as long as the two control yokes are not disconnected from each other.
 
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