Puchaz Spinning thread that might be of interest in light of the recent accident.

The behaviour described in a previous message as an "insipient spin" with
the ASH-25 seems to be a very simple early part of a stall.
If ailerons are used close to the Stall AOA, they might seem to work in
reverse, which is consistent with the description given in that message.
This is due to the fact that in the pre-stall, you're already close to the
Stall AOA.
The lowering Aileron (to pick up the low wing) will produce an increase in
the AOA in that part of the low wing, thus exceeding the Stall AOA and
essencially stalling that part (where the aileron is) of the low wing.
In other words : Pre-stall, left wing is low (for instance), right aileron
will stall the left wing tip thus increasing the bank angle and going to a
spiral, an apparent control reversal, easily corrected by :
The correct control input, which is to apply right rudder to pick it up, and
move the stick forward enough the reduce AOA.

This is the reason why instructors teach all students to pick up a low wing
during pre-stall by using Rudder (opposite rudder, for that matter), and not
by using coordinated controls as it is suggested, because the aileron will
work against the intended recovery.
Even if the glider wing was designed with some twist to lower the AOI at the
wingtips, they will still suffer from this reverse effect when in a
pre-stall condition.

All existing airplane and glider literature clearly recomends picking up a
low wing with opposite rudder during pre-stall, along with lowering the
nose.
I have never seen a manual suggesting to pick up a low wing at the pre-stall
with "coordinated controls", it would surprise me very much if the ASH-25
suggested something like that.

What it may be suggesting is that you always use coordinated controls (the
correct use) while thermalling, and if you sense the glider in a pre-stall
condition, lower the nose slightly and use coordinated controls to continue
the turn.

I wrote about this before : While thermalling, if you feel an inpending
stall, it may not be necessary to "dive like mad" to recover.
It may be a simple case of lowering the nose only slightly and maybe
applying some opposite rudder for a few seconds.
If you do it calmly, other gliders in the same thermal won't even notice
that you were about to stall.
Again, any experienced instructor can demonstrate this.

Happy flying.


"Chris OCallaghan" wrote in message
om...
I've noted that many 25s have wing extended wing tips, some factory,
some home built. The vertical stab was designed to some theoritical
maximum... This would be yet another aggrevating factor.

What fascinates me about these reports is the effect in the real world
of the designer's tradeoff between stability and controlability.
Bigger vertical stabs would reduce the likelihood of a spin, but at
the cost of much drag. Less drag is better, but you don't want a
sailplane so unstable that moderate turbulence can flick it into a
spin from a low speed turn. So if you want to give it a good low speed
roll rate, you have to depend on the pilot's proper use of the
powerful rudder he'll need to counteract adverse yaw. But pilots are
people, and we all make mistakes. So the conscientious designer must
needs put enough surface area back there to prevent autorotation so
long as the pilot neutralizes the controls at the first indication of
an insipient stall. Even if the stall progesses, so long as the
controls aren't crossed, it shouldn't lead to a spin.

Little modern gliders seem to reflect this philosophy. As bigger
gliders become more popular among lower time pilots, shouldn't we be
examining their characteristics more carefully? While manuals give
very precise instructions on how to recover from a fully developed
spin, they recommend coordinated use of ailerons and rudder
(accompanied by a forward motion of the stick) to pick up a dropping
wing during the initial phase of a stall, straight ahead or turning.
In other words, the designer is recommending picking up the low wing
so long as it is accompanied by a "firm easing of the control stick
forward." This procedure is recommended because it results in the
minimum loss of height. We were all taught, thouigh, that if the wing
begins drop during a stall, we neutralize the ailerons, ease the stick
forward, and kick opposite rudder. Given the number (I counted 4) of
over the top spin entries noted in another thread, I wonder if we
haven't been to aggressive in preventing the "insipient spin" with
spin recovery control motions.

And as a result, misinterpret any yawing of the nose during a stall to
be the preamble to a spin. I'm splitting hairs. And it's certainly not
the stuff for students to be pondering. They need a one size fits all
recovery. But I'm genuinely interested in just what is going on at the
stall and immediately after, and if our perceptions haven't been
altered by the necessity of the shortcuts we take during training to
get us quickly to the point where we can go teach urselves.
Robert Ehrlich wrote in message
...
Chris OCallaghan wrote:

This is an interesting case. I haven't really thought this through
since stalling is difficult in most properly balanced sailplanes at
high angles of bank. A long wingspan adds yet another aggrevator. But
your speed is higher in a steep turn, thus the vertical stabilizer is
more efficient. And right off hand I can think of several outcomes
that would look like spins, but are, in fact, something else. Think of
a wing over, for example. If you shot the initial 90 degrees of turn
after apex, it would look very much like a spin entry.

Nonetheless, I haven't tried a stall from a coordinated steep turn,
with controls crossed and the yaw string straight. And I won't have a
chance for another month or so...

Perhaps, for the time being, I need to ammend my position to say that
a spin is unlikely in most sailplanes if the ailerons and rudder are
neutralized.

In the meantime, if you have a chance to repeat, see if the instructor
will let the "spin" develop. I'm interested to see if it is really a
spin (I think the chances are good, though, if the controls stay
crossed). Try it again, but at entry, center the ailerons and rudder,
but leave the stick back. That is, add no further aggrevation after
the stall break and see what it does. By the way, how rapid was the
autorotation at stall break? How much change in direction did you
experience before rolling back to level? How much altitude did you
lose, if you took notice? And was there anything unusual about this
particular 25?


There was nothing unusual about this 25, only about myself. It was my
first flight in the ship, I had a very low experience at this time (
100
hours) and had only flown ASK21 and ASK23. This happened twice in the
day
at a low bank angle. There was almost no autorotation or change in
direction. It was rather the feeling that increasing outside stick could
no more counter the overbanking tendancy, but rather increased it,
that made me realize that the inner wing was stalled and the I had to
quickly release back pressure to avoid some mess, so nothing wrong
happened before immediate recovery. My propension to low speed flight
came from my familiarity with the ASK23 whose wing loading is much
lower,
and from the fact that it was a weak day where low speed rather than
high bank angles helps to remain close to the core of thermals, at least
in the ASK23 I was usually flying. It was my first attempt to make a
flight
longer than 5 hours, I felt it was better to try it first with an
instructor
behind me and in a glider in which this may be achieved even in
unfavorable
weather. This last point turned out to be true, all other gliders were
in the hangars when we landed at the end of the day and the duration was
effectively over 5 hours. However I had to wait another season before
getting my silver duration, but this is another story.

BTW I cannot try what you suggest since this 25 is no more in my club,
nor any other club 25 (but 2 private ones) and the instructor in such
a repeat attempt would probably be myself as I got this rating during
last September.