The
pilot of a Lazair ultralight aircraft had taken off to practice
touch and go's. He was proceeding on a wide left-hand circuit downwind
for landing. He had been sequenced number one and as he turned base,
witnesses heard both engines stop. The aircraft continued on what
looked like a power-off glide back to the airport.
The Lazair
ultralight aircraft is equipped with two small 185 cc Rotax engines
mounted forward of the leading edge of the wing, and the pilot sits
underneath the wing. As the aircraft approached final, the wings
were seen to rock from side to side. The aircraft then nosed over to
about a 90° angle and the pilot was unable to recover from the dive,
even though the altitude from which it was begun was reported to be
close to 500 ft. The pilot lost his life.
Each year stalls account
for a high number of mishaps and many deaths. They often occur in
the pattern, after takeoff or when coming in for landing. Flying low
and tight circles over a friend's house has also claimed the lives
of many pilots. Stalls are often related to a sudden engine failure,
poor take-off or landing techniques, and the failure to recognize
the onset of a stall.
A review of the theory of flight and the
stalling characteristics of your airplane with an experienced
instructor should help you stay out of trouble, especially if you
train regularly. No one is immune to the danger of a stall, as it
claims lives indiscriminately.
Stalls
can be prevented. The warning sign is usually an unmistakable buffet
or shaking of the airplane. The buffeting is the result of the
airflow separating from the top of the wing. It can occur very
quickly depending on the angle of attack, angle of bank and the
gross weight of the aircraft. It needs your immediate attention. To
recover from the stall, reduce the angle of attack by gently
lowering the nose of the airplane with the elevator control.
Once
the angle of attack is less than its critical angle, the air
molecules will flow smoothly over the top of the wing again and the
production of lift will resume. It's as easy as that. Remember that
you must apply all available power to accelerate the airplane
and
attack
is usually close to 18°. When you are flying at or close to this
angle, the air molecules racing over the top of the wing cannot
provide a uniform, highvelocity, laminated airflow, and the wing
stalls.
Remember
that at the moment the wing stops flying, it creates stress in your
mind and you may have a tendency to do the opposite of that which is
required to regain lift. As the airplane pitches nose down, many
will have the instinct to pull back on the elevator control. Don't.
Release back pressure on the controls and apply power.
You must
realize that airplanes can be stalled at any altitude or at any
airspeed. It will occur when an airplane exceeds its critical angle
of attack, independent of attitude and airspeed.
In
most cases, there are five warning signs.
1-
The unmistakable buffet or shaking that is usually felt in the
airplane and on the flight controls.
2- Flight control response
diminishes when the airplane approaches the stall. Controls may feel
mushy and less effective.
3-
The airspeed indicator approaches the beginning of the white or
green arc.
4-
A distinctive difference in sound occurs as wind noise diminishes
considerably.
5-
A stall warning horn will be heard (if the aircraft is equipped with
one).
There
is a sixth sign that will be felt depending on your perception of
subtle differences in your weight against the seat cushion; this is
a certain weightlessness as you gravitate upward while the aircraft
wants to proceed downward.
Aviation Safety Letter from Transport Canada. 02.2004
stall angle described above) and attempting to prevent the plane from
descending by applying increasing up elevator control input. When an
aeroplane approaches the stall speed it has already adopted an
extremely nose-high attitude, and the pilot will notice the controls
have become less responsive. The pilot may also notice some buffeting,
an aerodynamic vibration caused by the airflow starting to detach from
the wing surface. 
