Spin recovery vs tail design

Ron Ogden wrote:
I would like to solicit comments on the question: Compared to a standard
tail configuration such as a 2-33 or Blanik L-13, does the initiation and
recovery from a spin vary substantially in T-tail (ASK-21 type),
all-flying (Phoebus) or V-tail (HP series) sailplanes? Really look forward
to reading and learning.


The main difference, to the extent that there is any generic difference,
might be that T-tails tend to end up rather more nose down after you've
stopped the spin. However, this may not be true for a particular model
of glider. Also, your timing of the spin recovery will alter this, and
other matters.

Of those I've spun:

K13 (low tail) - quite gentle, recovers into a dive but not a
particularly steep one.

K6cr (low tail) - ditto, though it all happen quicker than a K13.

Puchacz (mid tail) - recovery may be into a dive beyond the vertical and
substantial height loss per turn, but it does exactly what the manuals
say if you perform the recovery properly.

Astir CS (Grob 103, T-tail) - quite gentle, recovers into a steeper dive
than the K13

IS28 (T-tail) - like the Astir, but a bit slower all round.

Open Cirrus (mid tail) - fairly gentle, dive after recovery about as
steep as the Astir. However, you do need FULL rudder to stop the spin
(and the last inch requires a hard push; it feels like you're on the
stop but you're not).

I've read that some V-tails need full forward stick before they recover,
but haven't had the pleasure of flying any.

Of my list I'd say the most "extreme" attitudes on recovery are from the
Puchacz, so from my limited experience the difference in tail
configuration is not the most important factor.

Primary answer: Use the spin recovery technique which is described in
the AFM.

Secondary answer: All certificated modern gliders will recover with the
"standad procedure", it's a requirement for certification.

That said: Eric Müller was a, no, probably *the* spin expert. He
described the ins and outs of spins in detail in his book "flight
unlimited". According to him, most "conventional" tail designs recover
best when you keep holding the stick back until the rotation stops,
because pushing it forward will blank the rudder. With T-tails it's
exactly the other way: Pushing the stick generates more airflow on the
rudder to stop the rotation. V-Tails are a story by themselves. There
has been at least one fatal accident with a salto which spun into the
ground. Eric was the accident investigator for this case and examined
the spin behaviour of another salto. He found that the salto would only
recover with the stick pushed *fully* forward.

But again, this is the theory, in practice, do whatever the AFM recommends.

On Mon, 11 May 2009 21:53:53 +0200, John Smith
wrote:


Eric was the accident investigator for this case and examined
the spin behaviour of another salto. He found that the salto would only
recover with the stick pushed *fully* forward.

I've been doing some spins in the alto myself - the cause for this is
the poor (doenwards) deflection of the outside tail surface, the inner
having sufficient deflection but being blocked by the outer tail
surface.

But again, this is the theory, in practice, do whatever the AFM recommends.

Always a good advice.
By the way, it's pretty amazing how spin manners change with CG.



Bye
Andreas

On May 11, 5:00*pm, Ron Ogden wrote:
I would like to solicit comments on the question: Compared to a standard
tail configuration such as a 2-33 or Blanik L-13, does the initiation and
recovery from a spin vary substantially in *T-tail (ASK-21 type),
all-flying (Phoebus) or V-tail (HP series) sailplanes? Really look forward
to reading and learning.

If your glider is JAR 22 certified then it will respond to the
standard spin recovery - reverse rudder, stick centrally forwards
(e.g. ailerons neutral) until the spin stop, centralise the rudder and
pull out of the dive. Exactly how it responds depends on the type of
glider and probably the spin itself.

There are also several ways of getting a glider to spin, but AFAIK the
recover is the same for all. For check flights I slowly ease back on
the stick until the nose drops (or it mushes) and kick in with the
rudder. The wing drops, and I have to hold it in to start the spin
proper. I have heard of one club where three ways of getting a glider
(K13) to spin have to be demonstrated.

But, as someone else said, read the manual and talk to instructors.
And if you can get an ASK-21 to spin I suggest you check the cockpit
weights - I don't know anyone who has without the use of tail ballast.

On Mon, 11 May 2009 12:59:17 -0700 (PDT), Cats
wrote:

And if you can get an ASK-21 to spin I suggest you check the cockpit
weights - I don't know anyone who has without the use of tail ballast.

Raises his hand and yells "Here"

The 21 won't stay in the spin (will enter a spiral dive after 1.5
turns), but even enters a spin with pretty forward CG (up to 30%).

How to reproduce this:
- Start turn in a 15 degrees bank at 130 kp/h
- raise nose 10 degrees over the horizon and keep this attitude. Speed
is going to bleed off
- at 80-82 kph IAS enter full rudder into the direction of the turn
and start to pull back the stick fully to raise pitch attitude slowly
- once the 21 starts to rotate, apply full adverse aileron
- Keep full rudder, adverse aileron and full elevator

Voila - the 21 starts to spin immediately.
You'll find your self in a genuine spin and can practice recovery
techniques. After 1.5 turns it will recover itself into a very steep
spiral dive. Neutralizing the controls will end the spin immediately.





Bye
Andreas

I would like to solicit comments on the question: Compared to a standard
tail configuration such as a 2-33 or Blanik L-13, does the initiation and
recovery from a spin vary substantially in *T-tail (ASK-21 type),
all-flying (Phoebus) or V-tail (HP series) sailplanes? Really look forward
to reading and learning.

Center of Gravity is critically important when considering spin
characteristics. The same 'docile' ship with a forward CofG can bite
your head off quite easily with an aft CofG, regardless of tail
type... which in my book this is the single most important reason to
fully understand and fully respect the G/G specs for whatever ship you
are in.

Now up to $0.04 on the subject,
-Paul

sisu1a schrieb:

Center of Gravity is critically important when considering spin
characteristics. The same 'docile' ship with a forward CofG can bite

C of G ist critical for spin entry, but for recovering from a sustained
spin, mass distribution is far more important. (The rudder force must
overcome the angular momentum.)

Of course, C of G and mass distribution are somehow related.

On Mon, 11 May 2009 23:19:26 +0200, John Smith
wrote:

C of G ist critical for spin entry, but for recovering from a sustained
spin, mass distribution is far more important. (The rudder force must
overcome the angular momentum.)

Interesting noone has mentiond flap setting yet - setting the flaps to
negative is by far the best way to quicken up the spin recovery.

I guess pretty many pilots here have flown the ASW-20 - recovering it
with setting 4 (zhermal setting) with a medium to rearward CG ca take
up to 2 turns, but with flaps 1 (fully negative) recovery takes at
maximum 0.75 turns.


Bye
Andreas

On May 11, 3:19*pm, Andreas Maurer wrote:
On Mon, 11 May 2009 23:19:26 +0200, John Smith

wrote:
C of G ist critical for spin entry, but for recovering from a sustained
spin, mass distribution is far more important. (The rudder force must
overcome the angular momentum.)

Interesting noone has mentiond flap setting yet - setting the flaps to
negative is by far the best way to quicken up the spin recovery.

I guess pretty many pilots here have flown the ASW-20 - recovering it
with setting 4 (zhermal setting) with a medium to rearward CG ca take
up to 2 turns, but with flaps 1 (fully negative) recovery takes at
maximum 0.75 turns.

Bye
Andreas

Not surprising at all - it would surprise me if anybody really wants
to teach this. Lets see -

- A desire to teach a standardized recovery
- Don't distract people with grabbing for a handle while under stress
(or if not stress just physically being thrown around a little)
- Likelyhood of grabbing the wrong handle (esp. if transitioning from
another ship) and just moving it (i.e. opening full spoilers)
- With full negative flap what happens to increased likelihood of
entering another/reverse spin if the pilot recovers too "hard"?

Darryl

On Mon, 11 May 2009 15:28:18 -0700 (PDT), Darryl Ramm
wrote:

Not surprising at all - it would surprise me if anybody really wants
to teach this. Lets see -

- A desire to teach a standardized recovery
- Don't distract people with grabbing for a handle while under stress
(or if not stress just physically being thrown around a little)
- Likelyhood of grabbing the wrong handle (esp. if transitioning from
another ship) and just moving it (i.e. opening full spoilers)
- With full negative flap what happens to increased likelihood of
entering another/reverse spin if the pilot recovers too "hard"?

All of your points are right on the spot.
However, I really teach this.

The command is simple: "Push the flap lever forward".
The other levers on the left side of the cockpit (gear and airbrakes)
cannot be pushed forward, so no harm can be done by grabbing the wrong
lever.

Apart from the quicker recovery in negative flaps, there's one much
more important point why it's absolutely necessary (in my opinion!) to
move the flap lever forward as standard part of the spin recovery
procedu

In nost gliders (certainly all Schleicher ones), it is nearly
impossible with positive flaps NOT to exceed the Vne for this flap
setting during the recovery.

And pulling significant G with too-positive flap setting is the best
way to induce extremely high torsional load on the wing... with all
its consequences.

At the speeds during the recovery even the most negative flap setting
won't lead to a secondary stall.




Bye
Andreas