Nimbus 4DT accident 31 July 2000 in Spain.

As long as a 26m glider is certified under JAR22, there is no issue of
control inputs versus speed other than for a 15m glider.

What changes drastically with a long wing is the entry into a spin or a
spiral dive. The long wing makes that you can have large discrepancies of
effective angle of attack along the wingspan (which can make the spin entry
under g-load quite interesting). Long wings also have much more angular
momentum once the spin/spiral dive is developped - it can be as much as 5
times the angular momentum of a 15m glider, and that makes that recovery
will take a certain time even if correct counter procedures are undertaken.
And during that time, the glider will accelerate like hell so that you are
likely to operate you final recovery well beyond what's written in the
flight manual.

I think that training of instant recovery of a spin entry (or spiral dive
entry) is mandatory if you want to fly a 25+m ship safely. But in contrary
to short wings, it would be plain stupid to train the recovery of a fully
developed spin/spiral dive in these ships (beyond fligh testing for
certification) and that's the reason that a flight manual will usually call
it illegal.

Been there, done it, and don't feel that I want to get there again.
--
Bert Willing

ASW20 "TW"


a écrit dans le message de news:
...
KC, yup.

I wonder at the thread though. Everyone discussing recognition of a
fully developed spin versus spiral dive.

Years ago, Al Blackburn pointed out to me that long span gliders need
to be treated gingerly at speed. His concern had to do with the
application of aileron during dive recovery. While he felt that most
pilots could manage the elevator to avoid structural damage, aileron
asymmetry (and the resulting squatcheloid assymetry) presented a
complicating factor. The longer the span, the more critical its
effects. Add a partial load of water, a yaw moment, and/or spoiler caps
deploying with wing bend and it's not hard to see how things might
quickly get to the breaking point.

Hmmm,

disagree in practice if not in principle. Bending and twisting moments
are much greater with increasing span. And a certain degree of symmetry
is assumed in measuring load limits. Contol inputs will significanly
change the lift distribution across the span (the squatcheloid). So
will twist in the wing. Al Blackburn's point, and I take it to heart,
is that design requirements don't look at failure modes under a variety
of assymetric lift distributions.

Consider the deployment of one spoiler cap during the spiral dive
recovery with deflected ailerons to recover from a steep bank.

The lesson I take away is to be very thoughful in applying the controls
under high load.