| Although
most unintentional stalls occur from flying too slowly, it is useful to show one
or two very steep stalls with the nose up 60 to 70°. In this case, the complete
wing stalls together and the nose drops into a steep dive. The glider then gains
speed so quickly that it can be levelled out almost immediately with a remarkably
small loss of height. This is an excellent opportunity to emphasise the total
lack of control while the nose is dropping, which is often the only obvious symptom
by which a stall can be recognised once it has happened. A similar situation can
occur with a cable break during the full climb on a ground launch. Ground
launch failures With winch and car launching the heavier
and faster gliders, there have been many stall/spin accidents after launch failures.
Usually following a cable break in the full climb, the nose of the glider is pulled
up very steeply as the pull from the cable stops and the heavy cable falls away.
By the time the pilot has realised what has happened and moves forward
on the stick to get the nose down into the normal gliding attitude, the glider
is at a very low speed, often well below the usual stalling speed. It may seem
from the noise of the airflow that the speed has increased and that a full recovery
has been made. When the pilot has put the nose down to the normal gliding attitude
or lower and makes a move to start a turn, the glider will flick into a violent
spin without warning. This is so sudden and unexpected that the pilot may
be too confused or disorientated to make a normal recovery. The reason for the
rapid entry is that at this moment both wings can be well past their normal stalling
angle. After recovering from the nose high position to a normal approach
attitude does not mean it is safe to turn. It takes much longer than you might
expect to regain a safe speed, probably 10-12 seconds. As the noise of the airflow
increases, it is easy to believe it is safe to make a turn and this can be fatal.
You can only be certain by checking the speed by the ASI. The same situation
can even occur following a rope break on aerotow, particularly if the glider is
pulling up from being too low when the rope breaks. Unless a positive nose down
movement is made to regain speed, the glider may be semi-stalled and at risk of
spinning if a turn is started. At low heights, it is absolutely vital to check
the actual indicated airspeed before making any turn and particularly following
a launch failure. Demonstrating a
simulated winch launch failure This demonstration may
even be possible in some docile two-seaters but it takes practice to make it work
satisfactorily. You need to start high enough to try it two or three times to
determine the best moment to push over the nose down into the normal gliding attitude. First
the glider is put into a dive to obtain at least 80kts before pulling up into
the very steep climb, simulating a winch launch. As the speed falls close
to the stalling speed, the nose is pushed down quickly into the normal gliding
attitude and held there. At this time the airspeed should still be wel |
