Spin recovery vs tail design

Thanks to all who have contributed to answering my original question. I
am especially interested in the comments about the ASK-21, especially in
reference to changes in how it behaves as the spin continues through more
than one or two turns.

The short answer is: With all legal loading it recovers by the book from
as many turns as your or your student's wallet allows.

The somewhat longer answer is that usually it recovers in less than half
a turn, but in certain special circumstances recovery may take up to two
turns. This will frighten you if you aren't prepared, but the ASK *will*
eventually recover. Some people will tell you that the ASK may bite you;
actually, it will not, but probably those people have experienced a
longer than expected recovery delay. (Or more probably have been told
the story from somebody who knows somebody who knows somebody...)

The longest answer is that a long time ago there has been a spin
accident with a cadet of the USAF academy. Subsequently the USAF topk
the ASK 21 through a thorough spin test program, in which they found
what I wrote above. Schleicher will probably send you a copy of the 120
page report if you kindly ask them.


One more thing: Outward ailerons will flatten the spin considerably
which doesn't help on recovery. I've never tried whether it will recover
at all from that flat attitude.

"One more thing: Outward ailerons will flatten the spin considerably which
doesn't help on recovery."


What does that mean?



At 07:44 12 May 2009, John Smith wrote:
Thanks to all who have contributed to answering my original question.
I
am especially interested in the comments about the ASK-21, especially
in
reference to changes in how it behaves as the spin continues through
more
than one or two turns.

The short answer is: With all legal loading it recovers by the book from

as many turns as your or your student's wallet allows.

The somewhat longer answer is that usually it recovers in less than half

a turn, but in certain special circumstances recovery may take up to two

turns. This will frighten you if you aren't prepared, but the ASK *will*

eventually recover. Some people will tell you that the ASK may bite you;

actually, it will not, but probably those people have experienced a
longer than expected recovery delay. (Or more probably have been told
the story from somebody who knows somebody who knows somebody...)

The longest answer is that a long time ago there has been a spin
accident with a cadet of the USAF academy. Subsequently the USAF topk
the ASK 21 through a thorough spin test program, in which they found
what I wrote above. Schleicher will probably send you a copy of the 120
page report if you kindly ask them.


One more thing: Outward ailerons will flatten the spin considerably
which doesn't help on recovery. I've never tried whether it will
recover
at all from that flat attitude.

Nyal Williams wrote:

"One more thing: Outward ailerons will flatten the spin considerably which
doesn't help on recovery."

What does that mean?

First it probably means bad terminology. Second, it means that the pitch
attitude of the ASK in the spin depends on aileron position. Play enough
with the ailerons and you will find yourself in something like a flat
spin which may be reluctant to recovery. But you can always continue to
play with the ailerons until you'll find yourself in a normal spin again.

I've never tried this, but I have wondered whether adding downward
deflected aileron on the outside wing during a spin might 1) add drag that
would slow the rotation, stall that wing and further reduce the asymmetric
lift, and thus aid in stopping the spin.

Comments, anyone?

At 12:25 12 May 2009, John Smith wrote:
Nyal Williams wrote:

"One more thing: Outward ailerons will flatten the spin considerably
which
doesn't help on recovery."

What does that mean?

First it probably means bad terminology. Second, it means that the pitch

attitude of the ASK in the spin depends on aileron position. Play enough

with the ailerons and you will find yourself in something like a flat
spin which may be reluctant to recovery. But you can always continue to
play with the ailerons until you'll find yourself in a normal spin
again.

Nyal Williams wrote:

I've never tried this, but I have wondered whether adding downward
deflected aileron on the outside wing during a spin might 1) add drag that
would slow the rotation, stall that wing and further reduce the asymmetric
lift, and thus aid in stopping the spin.

Spins are aerodynamically extremely complex and each aircraft type
reacts differently.

At 13:56 12 May 2009, John Smith wrote:
Nyal Williams wrote:

I've never tried this, but I have wondered whether adding downward
deflected aileron on the outside wing during a spin might 1) add drag
that
would slow the rotation, stall that wing and further reduce the
asymmetric
lift, and thus aid in stopping the spin.

Spins are aerodynamically extremely complex and each aircraft type
reacts differently.


No question; that's why it's important to read the POH.

To answer your question: Outside aileron often flattens the spin because
it increases the drag on the inner wing, this accelerates the rotation,
which increases the centrifugal forces and therefore flattens the spin.
The consequence is twofold: The angular momentum increases while the
rudder becomes less effective to the point that the rotation cannot be
stopped anymore.

John Smith wrote:
To answer your question: Outside aileron often flattens the spin because
it increases the drag on the inner wing, this accelerates the rotation,
which increases the centrifugal forces and therefore flattens the spin.
The consequence is twofold: The angular momentum increases while the
rudder becomes less effective to the point that the rotation cannot be
stopped anymore.

By "outside aileron", I assume you mean "the aileron motion achieved by
moving the stick towards the outside of the turn/spin". Sometimes that
is called "top aileron", as when you are in a turn, and the outside wing
is the high wing.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* Sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

John Smith wrote:

Spins are aerodynamically extremely complex and each aircraft type
reacts differently.


"Spins are a normal mode of flight, unsuitable for landing".
Unknown British aerodynamicist (sp?).

Tony V.

At 13:56 12 May 2009, John Smith wrote:

Spins are aerodynamically extremely complex and each aircraft type
reacts differently.

One too many words in that statement, delete the word type.