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  Derek On Instructing  
  By Derek Piggott
Issue 8/2004

 
 

In this very worthwhile series Derek writes some more about spins and spiral dives and makes the observation "contrary to the advice given in some books on aerobatics, always keep the full opposite rudder on until the spin stops". There is much sound advice in this article so read on

 

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