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device) is to change the shape of the
type of wing required for high speed
flight into one suitable for low speed
flight, otherwise you would need
several miles of runway to get
Principles of Flight 11
airborne. Or land, in which case you
would need sturdier (and heavier)
undercarriages.
However, there is a point beyond
which the extra surface structure in
the airflow produces more drag than
lift, which is made use of when
deliberately trying to bring the speed
down, as with a short field landing,
or increase the angle of approach
without much sacrifice in speed.
Sometimes, the ailerons are made to
move in sympathy with flaps.
Various flap designs create different
effects (all try to reduce drag), but
the Fowler Flap is generally
considered to be the most efficient –
they do not just drop down from the
wing, but slide out from the back:
There is a maximum flap extension
speed, as they are not designed for
high speed flight. Lowering flaps will
generally force the nose down, as
they make the centre of pressure
move backwards, but sometimes
they affect the airflow over the
tailplane enough to go nose-up.
Once lowered, flaps should not
normally be raised until actually on
the ground. On a missed approach,
they should be raised after power
has been applied, in easy stages.
Other Wing Devices
Slats are small aerofoils that open
forward of the main one to smooth
out the airflow - when the angle of
attack is high, they do this
automatically (low pressure just
behind the leading edge sucks them
out. They are pushed back in by air
pressure when the angle is low).
They are usually found near the wing
tips on the leading edge to help with
lateral control.
Slots are openings a little bit back of
the leading edge of a wing that allow
high pressure air underneath the
wing to pass through them at high
angles of attack to the low pressure
area, to re-energise it and extend the
laminar flow by reducing eddies.
This reduces loss of lift and drag,
and increases the stalling angle of
attack. Slots may go across the whole
length of the wing, or just where the
ailerons are.
Manoeuvres
Taxi
Before you get to take off, you have
to get from where you are to the
runway, and return when you land.
The "roads" that get you there are
called taxiways, and they are usually
identified with letters, such as
12 Canadian Private Pilot Studies
Taxiway Alpha, or Taxiway Bravo, etc.
You will be told the sequence to use
when you first get clearance from
ATC to start moving. The clearance
may involve crossing a runway or
two to get to the one you want – you
should still check to see that nobody
is using them! Clearance to enter your
runway is entirely separate – taxi
clearance is only to get you there.
To get started, you may need what
seems like a lot of power, but this
will reduce to a very small amount
once the wheels start rolling. The
first thing you do then is test the
brakes with a small dab on the toe
pedals, and bring the machine to a
stop again.
Once under way, the machine will
want to head into wind – it is only
held straight by friction from the
tyres, but you can help by
positioning the controls. Moving the
control column into the wind
direction deflects the ailerons so that
they help control direction. A high
wing aircraft with the wind coming
from one of the rear quarters (SW,
SE, etc.) should also have its
elevators down (i.e. control column
forward), but this is also true to a
lesser extent for other aircraft. On a
rough surface, pull the control
column back.
It is usual to initiate a turn to the left
and right, if there is no opportunity
to do so anyway, to check the
instruments. The artificial horizon
should always be level, and the
compass and DGI increasing and
decreasing according to the turn.
The needle and ball (or turn
coordinator) should also indicate the
correct direction.
Try not to use the brakes to turn –
you should be able to use the rudder
pedals by themselves. Wearing out
the brakes costs money, and you
don't want to do this unnecessarily.
Use them smoothly at all times. It is
considered to be bad practice to use
high power to taxi, and use the
brakes to slow you down. A brisk
walking pace is recommended. If
you do use a brake to turn, the inside
　
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