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drag to reduce adverse yaw. It also
produces a slot (i.e. a gap between it
and the rear of the wing) to smooth
out the airflow over it:
The controls will move the aircraft
in one of three axes – pitching (nose
up or down), rolling (wings up or
down) or yawing (nose left or right).
They do not move in isolation,
however – an adjustment in one
causes a secondary effect in another
and must be allowed for, as we shall
see in the discussions below. For
example, an uncontrolled yaw
eventually results in a roll, because
one wing will be moving faster and
will generate more lift on that side.
Your instructor will need to
demonstrate certain manoeuvres,
and there is a well established system
of establishing who has control of
the aircraft at any given time. The
person handing over the controls
will say "You have control", while
the person receiving them replies
with "I have control".
Trim
Depending on the net result of
power and control positions, it may
take more physical force to keep the
aircraft in a particular attitude. That
is to say, for any combination of
power and control position, they will
move freely with a certain range, but
take a lot of force to go outside of it.
These extra forces can be trimmed out
with a wheel or similar device which
operates a very small control surface
in the elevator (for example), so you
10 Canadian Private Pilot Studies
have a control surface within a
control surface. The wheel moves
the surface up or down in the
airflow, which moves the elevator
the opposite way and does the work
you would otherwise have to do to
keep it there. If the trim wheel is
moved forward, it forces the trim
surface upwards, which creates more
lift between it and the elevator,
which therefore is forced down,
creating more lift underneath the tail
which lifts and forces the nose
down. The thing to remember for
exams is that the control column,
when moved forward, moves the
elevator down, whereas the trim
wheel moves its attached surface up.
Power affects trim tabs, as more
airflow varies the sensitivity of the
controls. Reducing power makes the
nose pitch down because the trim
tab has become less effective and
cannot hold the nose in position.
Trim surfaces may also be found on
rudders, depending on the
complexity of the machine.
You may occasionally see a fixed trim
tab, which is there to provide a fixed
amount of trim to make the machine
fly true (it may be one wing low, for
example, from the factory). It must
only be altered by an engineer. Fixed
tabs are used on helicopter rotor
blades to make them fly higher and
lower with respect to each other,
with the goal of making them fly in
line, to reduce bouncing.
An anti-balance tab moves in the same
sense as the main surface, and is
there to increase the force required to
move the control. The further it is
deflected, the greater the force (the
angle of attack increases at a greater
rate on the tab). This prevents overcontrolling
and overstressing the
aircraft, especially where controls
have a low aerodynamic loading.
Balance
At high speeds, control surfaces may
flutter because of buffeting. To
prevent this, a streamlined balancing
weight (usually lead) is fitted forward
of the control surface's hinge. It may
be inside the control surface itself, or
fitted externally (Mass Balance).
Sometimes, part of the control
surface is placed forward of the
hinge line, so that airflow hitting it
will help the pilot move the controls
(known as aerodynamic balance).
Flaps
These are hinged devices on the
trailing edges of wings, inboard of
the ailerons, that temporarily
increase the lift producing areas for
certain modes of flight, like landing,
and sometimes takeoff (not in the
PA 31, or aircraft without enough
power to overcome the extra drag
that reduces acceleration), where you
might be going very much slower
than normal and need a boost – in
fact, flaps produce the same lift at
lower speed by increasing the upper
camber (exam question), and the
negative pressure underneath
because the chord line moves further
down at the rear and changes the
angle of attack against the relative
airflow (pushing the nose down
restores the original angle).
Thus, the reason for using flaps (or
any other low speed lift-producing
　
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