曝光台 注意防骗
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the aerofoil breaks up badly, making
it unable to create enough lift, as
well as creating large amounts of
drag. The speed at which an aircraft
stalls, however, varies according to
circumstance (remember that an
aircraft with a high stalling speed is
easier to stall).
For one thing, a thick wing will
produce a lower stalling speed than a
thin one, as will one with a larger
wing area against a smaller one. Also,
as air density decreases, the stalling
speed will increase until it reaches
the cruise speed and you won't get
any faster (although the indicated
airspeed remains the same).
Turning has a similar effect, too,
because you are artificially increasing
the wing loading – the steeper the
turn, the greater the increase in
stalling speed.
Because of the above variables, the
quoted stalling speed in the flight
manual is the "clean" speed, which
occurs in a straight and level glide at
maximum weight with no gear and
flaps down.
As an exercise, it's the point at which
the nose drops down when the
elevator is pulled all the way back to
the stops. Since you stall the aircraft
onto the ground every time you land,
practice gained here can only serve
to improve subsequent arrivals on
the runway.
To perform the exercise in straight
and level flight, do the HASELL
check, place the carb air into hot,
and reduce power to zero. Keep the
nose level with the horizon, and be
prepared for the controls to become
mushy and ineffective. Do not use
rudder, except very sparingly to keep
straight, or you might end up in a
spin, and you don't learn to get out
of those until the next lesson.
Allowing it to yaw is just as bad as
using too much rudder, so don't use
Principles of Flight 19
aileron, either, because yaw is a
secondary effect of roll. In addition,
aileron drag will only make the
situation worse.
Keep pulling the elevator back, in
attempt to maintain height. About 5-
10 kts before the proper stall, you
might hear the stall warning going (if
you've got one), or feel a little
buffeting in the controls. This is the
aircraft protesting that it can't stay
up in the air, and that it is reaching
the critical angle of attack –
turbulent air is hitting the elevator
and other controls.
At the stall, the nose will pitch
down, usually just after the elevator
reaches its full limit of travel
backwards. The dropping could be
relatively mild, or quite severe,
depending on the design of the
aircraft (sometimes, you don't even
notice it!).
The point to realise is that, in
dropping the nose, the angle of
attack improves enough to get lift
again, and the aircraft starts flying,
even if you keep the control column
back, but we want to recover, so
relax the back pressure, and note
how much height is lost during the
exercise, once you recover the cruise
attitude. It will be around 350 feet,
quite critical near the ground, so
applying power just after relaxing the
back pressure will reduce this to a
minimum, sometimes down to
below 100 feet.
Spinning
When spinning, the aircraft is out of
control in all three axes of flight. It
results from uneven stalling. A spin
is basically a stall that is not straight.
That is, you are turning and
descending with one wing (the
downgoing one) in a permanent stall,
hence the spin. The effect is a
continuous roll, which causes yaw.
Left to itself, the aircraft will not
recover, as long as the one wing
remains stalled.
You can't use aileron to get out of a
spin, because of aileron drag making
the condition worse, but rudder is
available, so you shove in a bootful
in the opposite direction to the turn,
until the yaw stops. Then relax the
back pressure on the elevator to
pitch the nose down and reduce the
angle of attack on the stalled wing
(this may be done at the same time,
depending on the machine). Do not
use ailerons, and pull out of the dive
once you have some airspeed. Then
apply power as necessary.
The aircraft must stall first, so if you
avoid stalling you won't get into a
spin. To start a spin deliberately,
shove in a bootful of rudder at the
point of the stall.
Before performing any manoeuvres,
however, you should do:
The HASELL Checks
Remember these well, as they are
useful throughout your flying,
particularly with steep turns:
· Height – are you high enough to
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