Full scale question
 

I flew aboard American and Delta airlines this past weekend and noticed something while walking through the terminal.

When the planes are sitting on the tarmac I noticed the elevators are split. One side was in the up position and the other side was in a lower position. Also, on the one that was rasied, the trim tabs were raised even more? Why is this???

RE: Full scale question
 

Cruz, I take it you were looking at MD-80 series aircraft?

RE: Full scale question
 

Yes, sorry, it was the MD-80. Why do the elevators rest like that when sitting on the tarmac?

RE: Full scale question
 

Not exactly sure why, I know on the J32 (I know apples to oranges) once the engines shutdown the flaps would slowly start to lower till they were fully down. Pretty typical on the MD80 though as Falcons suggests

RE: Full scale question
 

MD-80 elevators are powered by servo (boost) tabs and aren't connected to each other, which allows them to just trail when there's no airflow over them. Kind of a strange sight but they do seem to work.

RE: Full scale question
 

diver, I see, but these were the elevators. I see how they could droop down with their weight as some of our planes do with the weight of the control surfaces on our servos, but on these planes, one side of the elevator was raised and the other was lowered. Also, on the side that was raised, it had its trim tabs raised even higher.

RE: Full scale question
 

The raised 'trim tab' is the (boost) servo tab, probably in the up position when the yoke is in a relaxed foward position. Also my bet is that the elevators are counter balanced, they can flop to any position. MD80s also look funny when they taxi. The elevators do not behave themselves untill about 40 knots.
Watch the ailerons in flight, they are servo tab controlled too.

RE: Full scale question
 

Someone told me they fly like they have bungees on the controls.

RE: Full scale question
 

The MD 80 series and before that the DC-9s primary flight controls are cable driven and flown with Control Tabs. (The rudder is normally hyd powered though.) They look like trim tabs. the Elev actually has a control tab, geared tab and an anti-float tab. Only the control tabs are connected to the control wheel. Moving the aileron on preflight does not move the control wheel in the cockpit, as well as the elev if you could reach it. If the elev goes up the tab goes down, and the aircraft is flown by tabs to move the larger control surface. During windy days the elevators usually bang against the stops before takeoff, but no movement is noted in the control wheel. Usually on takeoff full down is momentarily commanded to align the elevs. The geared tab on the elev assist the control tab. The anti-float tab is used should the aircraft get in a stall and only then does a small hydraulic pump start to move the elev full down with full down elev commanded. Works well and with total hyd failure the plane flys the same. hope this helps

Jack

RE: Full scale question
 

The Bae 146 is the same. It is also pretty common to see airbusses with their elevators split at the gate. When hyd power is applied they will line up again.