DC-9 split elevator

[9GClub]

Saw a cool pic of a NWA powerback on airliners.net (ID # 975772) and was reminded of a question I've had for awhile.... what's the deal with the split elevator on DC-9 series jets? Why aren't they aligned during taxi, etc.? This phenomenon seems unique to these jets from what I've seen, at least during ground ops. Any -9 pilots want to chip in with a systems rundown..... Thanks in advance.

 

[enigma]

Saw a cool pic of a NWA powerback on airliners.net (ID # 975772) and was reminded of a question I've had for awhile.... what's the deal with the split elevator on DC-9 series jets? Why aren't they aligned during taxi, etc.? This phenomenon seems unique to these jets from what I've seen, at least during ground ops. Any -9 pilots want to chip in with a systems rundown..... Thanks in advance.

The pitch and roll controls of a DC9/MD80 are all tab actuated. I.E., the yoke isn't connected to the ailerons and elevators, it is only connected to the control tabs. The ailerons are bussed together so that they always operate opposite of each other in order to allow one tab to operate both ailerons. (in case one control column gets jammed, etc)
Since the elevators always work in concert, the engineers who designed the system obviously saw no need to add the complexity and weight necessary to ensure that the elevators are connected.

The reason you sometimes see split elevators during taxi out is that wind gusts acted differently on the surfaces while the airplane was sitting, and one was moved more than the other.

Once airspeed rises during the takeoff roll, the elevators will align themselves to the relative wind.

regards.
enigma

 

[NuGuy]

9G,

The elevators on the -9 are not interconnected, nor are they directly connected to the flight controls. The yoke is only connected to the control tab on the trailing edge. On the ground, you can push/pull all you want, and all you do is move the control tab. The elevators are free to float or hang in any position, and are often opposite to each other.

In flight, this control tab, along with a geared tab, moves the elevator, which then alters pitch. Works great, but gives the DC-9 the feeling that you are flying it via rubber bands.

There is a back-up hydraulic actuator that is directly connected to the elevators, but this only operates at the extreme forward travel of the yoke (technically, it's looking for more than 10 degrees nose down command between the elevator and control tab).

Hope this helps,

Nu

 

[9GClub]

Enigma and NuGuy,

Ok cool, thanks guys.

 

[AA717driver]

Thanks for the free recurrant. I'm now current and qualified on the DC9 again. Anyone hiring? TC

 

[LarryinTN]

Thanks for the free recurrant. I'm now current and qualified on the DC9 again.

No not yet. First you'll have to have a dicussion about what systems are powered by DC Transfer.