Date: 19 Dec 96 03:06:34
From: journali@sprynet.com
Organization: Sprynet News Service
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Two DC-9 aileron questions from a student pilot
Hello to all in group!
Took a trip this past weekend which saw me on a number of DC-9s -- a
couple of questions arose concerning this aircraft's aileron rigging, and
the use of the ailerons by one flight crew in particular. Hope you all can
help! Here are the questions:
(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.
(2) Also while on a DC-9 flight observed this unusual use of ailerons (at
least "unusual" to this student pilot -- I know you all will tell me if
this is a "usual" practice and it's just me who thought it a bit strange.)
Here's what happened: 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.
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?
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?
Would appreciate your answers to these puzzles. And please email your
replies to me if possible, for Sprynet's news server has a nasty way of
losing messages not long after they are posted. Email to:
journali@sprynet.com
Thanks to all!
Happy landings!
