Re: Two DC-9 aileron questions from a student pilot

Date:         27 Dec 96 04:41:05 
From:         dc8ray@airmail.net* (Ray Clawson)
Organization: INTERNET AMERICA
References:   1
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I at one time flew the DC9, so my memory is a little vauge on the
subject.  Also, my training was in the "Baby 9" the -15.  I don't know
if what I learned about the baby 9 applys to all 9's.  I'm suspect its
close because all 9's are a common type rating, including the MD80
(not sure about the MD88, but it probably is.

Here we go.........(article snipped where needed)


On 19 Dec 96 03:06:34 , journali@sprynet.com wrote:


>(1) Noticed that no matter what DC-9 I was on, the ailerons seemed to be
>rigged for a slow left roll at ALL TIMES. Even in level flight, the left
>aileron was "up" (relative to the rest of the wing) by about 1 inch, while
>the right aileron was "down" by the same amount. Sometimes when the pilot
>wanted a slow right roll or a minor roll correction to the right, the
>ailerons on both wings simply went to a totally NEUTRAL position and the
>airplane would roll right. Does this mean the DC-9 design has an inherent
>tendency to roll right, which must be corrected with a built-in left roll
>compensation in the rigging? I saw this on several different DC-9s, and
>observed this in all phases of flight  -- landing, takeoff, climb,
>descent, level flight, etc.

I'm not sure why the ailerons appeared that way.  The 9 does not have
a tendency to roll to the left.

>When I boarded the aircraft I noticed that the
>ailerons were in a fully deflected (or nearly fully deflected) position of
>about 25 to 30 degrees deflection. The left aileron was down, and the
>right was up. For what it's worth, this was an early morning flight and
>the aircraft had been parked at this airport overnight -- don't know if
>the ailerons were left like this overnight for some reason, or if the
>flight crew moved them to this position prior to the passengers boarding.
>
>Okay, so now it's time to head out of the gate. We fire up, back out and
>head for the active runway. During the start-up and entire taxi the
>ailerons never moved from their fully-deflected positions. I saw the
>spoilers cycle briefly during the taxi (as I expected to see), and of
>course the flaps extended to their takeoff position. But still no movement
>on the ailerons -- just hanging out there for a major amount of right
>roll. By the way, there was almost no wind ( I dare say nearly calm), so
>the aileron position had nothing to do with taxiing in a crosswind --
>besides, no matter which way the airplane was turned relative to any wind
>there might have been, the ailerons remined in the same postion.)
>
>Okay, we make the 180 from the taxi way onto the active and come in with
>full power for the takeoff. Ailerons still fully deflected. We're rolling
>and still full deflection. I'm beginning to wonder how long the pilot is
>going to hold full right roll control input, and imagining the headlines
>if we actually break ground with full aileron deflection, when finally the
>ailerons begin to return smoothly to their neutral position. I guess we
>were proably doing about 30-50 mph when they started to neutralize -- took
>about 3 seconds or so.

The ailerons on the 9 are free moving control surfaces.  They are
moved in flight by the "servo tabs" or "flying tabs"  These are small
trim tabs that move in response to movement of the yoke in the
airplane.  For example, in flight, if you want a right wing down, you
move the control yoke to the right (clock wise).  In response, the
flying tab on the right aileron moves down which causes an air loading
and moves the aileron up.  On the left aileron., the opposite happens.
The left and right ailerons are connected with cables.  On the ground
if you push the left aileron up, the right aileron will move down.  On
the ground the ailerons are supposed to be held in the netural
position by "viscous dampning" which (I think) is an oil filled piston
attached to the ailerons in the center position.

FYI, the elevators are the same way, they just flap in the breeze,
except the are not connected.  Its common during a walkaround to see
one elevator up and the other down

>So what was happening here? Do airline crews check for "controls free and
>correct" like C-152 students do? Why the taxi with the control yoke turned
>all the way toward the right? I know it doesn't matter in a no-wind taxi
>which way the yoke is turned, but isn't it natural to neutralize the
>controls at some point during start-up or taxi? Why wait until the takeoff
>roll to do this?

Yes, there is a control check, but depending on the airplane, you are
checking different things.(On most large ac, you cannot see the wings)
On the DC8(the ac I fly now), you are checking spoiler pressure
fluxuation to make sure the flight spoilers are operating,  rudder
preasure movement, and movement of the EPI (elevator position guage).
But it is different on different ac.

>One more question: I know DC-9 ailerons are hydraulically assisted, but is
>there any direct physical link between the ailerons and the control yoke?
>I mean, would it be possible for the yoke to be in the neutral position,
>but the ailerons to be deflected, and the pilot not know about it?

See above, there is no hydraulic power to the ailerons on the Baby 9

Ray Clawson

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