As glider pilots there are many things we do which are familiar to
us, we deal with these events very quickly, the so called muscle
memory. If we are prudent we practise, on a regular basis so
emergency situations, such as launch failures and every one we
practise increases the chance of recognition and proper recovery
action.

As regards spinning we may practise in a glider cleared for
intentional spinning but we seldom if ever practise a spiral dive
which is uncontrolled, we have no experience of such an event. We
may have been told that it can happen, briefed on the symptoms
and warned of the consequences but never actually seen it and
recovered unless we are one of the very few test pilots.

The difference between a spiral dive and a spin may be bleedin
obvious to a few but for most of us it is a situation which requires
the processing of information which is completely unfamiliar.

Some gliders are prohibited from deliberate spinning so we never
have the opportunity to practice, it is likely therefore that the first
time we see an event be it spinning or spiral dive is when it occurs
unintentionally. One of the symptoms which distinguishes a spiral
dive from a spin is the already high and increasing airspeed. To
recognise the difference you have to see it. The problem is that the
increase in airspeed, the acceleration, is very high, maybe
approaching 18kts per second per second (32fps/ps). If we take
just 3 seconds to see that the speed is in fact increasing we will
have added 57kts and we still have to decide how to correct that
and take the appropriate action. If we take a further 3 seconds to
decide on and start to carry out the appropriate recovery we are
already through VA, approaching or exceeding VNE and headed for
the scene of the accident. It has been said that recovery will result
in uncommanded airbrake deployment which transfers and
increased load to the outer wing panels, which are likely to fail.

When a test pilot carries out his tests he deliberately does so, he
knows what to expect and has already decided on his recovery
action, his recovery is likely to be close to optimum. He is likely to
guard the airbrake control. I would suggest that anyone, including
our test pilot might have difficulty if the event was completely
unexpected.

Even if the acceleration is only 90% of the maximun in a Nimbus
4DM, the speed will increase by 100kts in the 6 seconds. Assuming
we started with 50kts the recovery will go through VNE (177kts).
Max manouvering speed (VA) for a Nimbus 4 is 100kts, so full
control deflection is not available after 3 seconds. It seems to me
that if it happens unexpectedly it is not going to end well however
lighting fast our reactions might be.