Nimbus 4DT accident 31 July 2000 in Spain.

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.

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.

"the resulting squatcheloid assymetry"?
What the heck is that?
Anything like the yeti dihedral?

wrote in message
ups.com...
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.

That would be sasquatcheloid assymetry, typically only encountered in
the high Sierra during the winter. It would be much more manageable (if
not entirely polite), if they hitched their rides in pairs.

Hi Chris-

Thanks for herding the discussion toward more science and less emotion.

I apologize to anyone that may have been offended by my comments above re
"clueless". One person wrote a nice note pointing out that the family is
grieving enough without that type of thing.

The point I was trying to make was that those of us that choose to fly these
very long winged aircraft need to be keenly aware of impending problems and
react to them immediately should they begin to develop. If you decide to
thermal in turbulent conditions at just above stall speed then you should be
on edge every second you are doing so and if a gust begins to push you into
a spin or spiral then you should execute your already planned out and
hopefully second nature, correction. If you haven't thought of this plan or
possibility then you have no business flying at those speeds in that
aircraft.

Will having a plan ALWAYS get you out of trouble? No. But as others have
pointed out, in these birds you only have a very short time before there is
not any amount of skill that will save the aircraft.

Sorry to digress Chris.....I'd still really like to hear more about the
aerodynamic reasons that things go awry.....can only help to formulate the
best plan of action!

Casey

On Wed, 22 Jun 2005 12:54:44 UTC, wrote:

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

Isn't it generally more useful to recognize the difference between a
just-developing spin and a just-developing spiral dive?

Which reminds me of Johnston's Test Question for BGA Instructors
Number Three:

"The offical recovery from a stall with wing drop is different from
the official recovery from a spin. At what point do you, personally,
transition from one to the other?"

Ian

--

"Ian Johnston" wrote in message
news:dzZo7CxomoOm-pn2-39ddFD9pBSKp@localhost...
On Wed, 22 Jun 2005 12:54:44 UTC, wrote:

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

Isn't it generally more useful to recognize the difference between a
just-developing spin and a just-developing spiral dive?

Which reminds me of Johnston's Test Question for BGA Instructors
Number Three:

"The offical recovery from a stall with wing drop is different from
the official recovery from a spin. At what point do you, personally,
transition from one to the other?"

Ian


As often happens, the BGA comes through with some useful wisdom. Thanks,
Ian.

As for the difference in sensations between an incipient spin and incipient
spiral, the former seems to me to be like an uncommanded yaw and the later
like an uncommanded roll. To me, at least, they clearly say that if the
situation is allowed to continue without intervention, the uncommanded yaw
will become a spin and the uncommanded roll will become a spiral.

I wish I could capture the sensations and record them. They would be very
useful in training.

As for a spinable trainer with similar characteristics, the venerable IS28b2
would do a creditable job of either spin or spiral and build up speed like
crazy in the ensuing dive. It had the requisite large inertia about all
axes. I found it taught me a lot about how to fly a Nimbus.

Bill Daniels

Bill Daniels writes
"The offical recovery from a stall with wing drop is different from
the official recovery from a spin. At what point do you, personally,
transition from one to the other?"

I'm curious. Although in practical terms I'm quite confident (through
practice) that I can tell one from the other and react and recover
accordingly, but how would you phrase the answer to that?

--
Bill Gribble
http://www.scapegoatsanon.demon.co.uk
- Learn from the mistakes of others.
- You won't live long enough to make all of them yourself.

Most important is recognition of prestall and initial departure. Since
the spin is a product of yaw moment at departure, you can prevent a
spin with coordinated controls alone. IE, modern aircraft must be
"helped" into the spin. (Put another way, the vertical stabilizer
creates enough yaw dampening to prevent autorotaion at stall so long no
pro spin control imputs are made. Since there are two yaw controls,
that would mean pro rudder or anti stick.) Thus, any prestall or
initial departure that is met with a release of back pressure and use
of coordinated controls to level the wings will produce the desired
effect before a spin or spiral dive can develop. Even if you choose not
to release back pressure, you shouldn't spin. Instead, you might find
yourself in a secondary stall. The longer it takes to apply these
simple actions, the less likely that it will produce an immediate
remedy, as the aircraft will continue into either a spin or spiral dive.