ASW 20 SPIN CHARACTERISTICS

Eric Greenwell wrote
Andy Durbin wrote:


I couldn't find the photos last night so I can't attempt any
measurements of wing deflection. The scenario I imagine is this. The
pilot makes an agressive contest finish pull up. The pull up starts
at over 100kts, the pilot continues to pull as the speed decays to say
60kts where the wing experiences an accelerated stall.

If he waits to 60 knots, he is well into a loop. Based on my contest
finishes, I'd guess he'd be back at 1 G before the speed decreases to
85-90 knots. The high G part of the pull-up is very short - just long
enough to get the glider aimed upward.

I've read most of these posts and now I'm thoroughly confused:
1. isn't it true that unless the pilot aggressively pushes over, the wings will unflex too slowly to cause a large AOA increase? And even then, the increase is relatively small - at most about 1 degree for realistic speeds of travel and rates of unflexure?

2. isn't it more likely that the pilot tried to initiate a low speed, initially low G turn, then as the load factor increased due to the increasing angle of bank the wing AOA went past the stalling angle and so the (then inevitable) spin became a fact?

3. everything I've ever read and learned about wing theory states that a stall results when the AOA is greater than the stalling angle - it doesn't matter what the G loading is or what the speed is.

Rgds,

Derrick Steed

On 15 Jul 2004 18:17:04 GMT, Derrick Steed
wrote:

Eric Greenwell wrote
Andy Durbin wrote:


I couldn't find the photos last night so I can't attempt any
measurements of wing deflection. The scenario I imagine is this. The
pilot makes an agressive contest finish pull up. The pull up starts
at over 100kts, the pilot continues to pull as the speed decays to say
60kts where the wing experiences an accelerated stall.

If he waits to 60 knots, he is well into a loop. Based on my contest
finishes, I'd guess he'd be back at 1 G before the speed decreases to
85-90 knots. The high G part of the pull-up is very short - just long
enough to get the glider aimed upward.

I've read most of these posts and now I'm thoroughly confused:
1. isn't it true that unless the pilot aggressively pushes over, the wings will unflex too slowly to cause a large AOA increase? And even then, the increase is relatively small - at most about 1 degree for realistic speeds of travel and rates of unflexure?

2. isn't it more likely that the pilot tried to initiate a low speed, initially low G turn, then as the load factor increased due to the increasing angle of bank the wing AOA went past the stalling angle and so the (then inevitable) spin became a fact?

3. everything I've ever read and learned about wing theory states that a stall results when the AOA is greater than the stalling angle - it doesn't matter what the G loading is or what the speed is.


I'm not certain any of us know enough detail about the accident to
make a sensible guess about its cause.

FWIW, on Tuesday evening I decided to investigate turning stall/spin
behaviour in my '20 at a sensible altitude. It was calm and with
little air movement under a high overcast. With the aircraft clean and
flaps at zero (setting 3) I flew some moderately steep turns - about
45 degrees of bank and at speeds ranging down to about 43 kts. This
was completely uneventful - no buffeting, burble or hints of
departure. In short, it flew like a pussycat. I'll try this again by
myself in a turbulent thermal next time because all that series of
turns told me was that in nearly still air my '20 can fly uneventful
turns at stupidly slow airspeeds. By comparison I typically fly at
48-50 kts for that steep a turn in zero flap during normal thermalling
turns.

--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

Martin Gregorie wrote in message . ..
On 15 Jul 2004 18:17:04 GMT, Derrick Steed
wrote:

FWIW, on Tuesday evening I decided to investigate turning stall/spin
behaviour in my '20 at a sensible altitude. It was calm and with
little air movement under a high overcast. With the aircraft clean and
flaps at zero (setting 3) I flew some moderately steep turns - about
45 degrees of bank and at speeds ranging down to about 43 kts. This
was completely uneventful - no buffeting, burble or hints of
departure. In short, it flew like a pussycat. I'll try this again by
myself in a turbulent thermal next time because all that series of
turns told me was that in nearly still air my '20 can fly uneventful
turns at stupidly slow airspeeds. By comparison I typically fly at
48-50 kts for that steep a turn in zero flap during normal thermalling
turns.

Dear Martin, In your next flight-test-experiment with the ASW-20, try
a climbing turn stall at good altitude. Bank into a right turn at
60-65 knots and as the right wing goes down pull back fairly hard and
steadily on the stick to make the glider go up and slow down. Keep
pulling back and wow! you will stall over the top and quickly too. I
think that this has been the cause of more than one low altitude
glider crash. I tried this in my '20 when Walt Cannon and I were
having a similar discussion about stalling in the ASW-20. Let me
know how it works and what you think. Rudy Allemann

On 17 Jul 2004 23:50:41 -0700, (Rudy Allemann)
wrote:

Martin Gregorie wrote in message . ..
On 15 Jul 2004 18:17:04 GMT, Derrick Steed
wrote:

FWIW, on Tuesday evening I decided to investigate turning stall/spin
behaviour in my '20 at a sensible altitude. It was calm and with
little air movement under a high overcast. With the aircraft clean and
flaps at zero (setting 3) I flew some moderately steep turns - about
45 degrees of bank and at speeds ranging down to about 43 kts. This
was completely uneventful - no buffeting, burble or hints of
departure. In short, it flew like a pussycat. I'll try this again by
myself in a turbulent thermal next time because all that series of
turns told me was that in nearly still air my '20 can fly uneventful
turns at stupidly slow airspeeds. By comparison I typically fly at
48-50 kts for that steep a turn in zero flap during normal thermalling
turns.

Dear Martin, In your next flight-test-experiment with the ASW-20, try
a climbing turn stall at good altitude. Bank into a right turn at
60-65 knots and as the right wing goes down pull back fairly hard and
steadily on the stick to make the glider go up and slow down. Keep
pulling back and wow! you will stall over the top and quickly too. I
think that this has been the cause of more than one low altitude
glider crash. I tried this in my '20 when Walt Cannon and I were
having a similar discussion about stalling in the ASW-20. Let me
know how it works and what you think. Rudy Allemann

Any particular reason you picked a right turn? Mine tends to drop the
left wing in a stall.

Your suggestion sounds like a good exercise to try: normally I don't
go below 50 kts at the top of a fast pull-up. Maybe Monday or
Tuesday....

--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

Any particular reason you picked a right turn? Mine tends to drop the
left wing in a stall.

Your suggestion sounds like a good exercise to try: normally I don't
go below 50 kts at the top of a fast pull-up. Maybe Monday or
Tuesday....

Dear Martin, No particular reason...just describing the manuever. It
will work either way. Rudy

I have never tried to spin my ASW20 in this way but I have done the =
exercise in a K13 at low level too. The results were a very fast stall =
and wingdrop, which is what I expected and is how I would I expect most =
gliders to behave. I what way does the ASW20 behave differently?? =
Bearing in mind that in a accidental spin flaps have to be moved to =
negative as well as the usual recovery, the glider will pick up speed =
that much faster any spin at 500ft is going to be irrecoverable.
Pulling up into a thermal, and slowing down as you turn attention must =
be paid to air speed as the load comes back onto the wings.
This is explained in the flight manual at .5G and 0 flap minimum speed =
is 30kts at 1g it is 42kts at 2g it is 68kts and add 5 kts to all those =
with ballast. Based on those speeds when thermaling in turbulent air =
lack of control response will be felt easily and either more speed or =
less bank will be needed. In 3 years I have found that my ASW20 gives =
plenty of warning that speed is too low or indeed that speed is too high =
for the flap setting selected.
A pilot with 100+hours solo that has read and understood the manual =
should have no problems, it is not a novice glider. It can be flown =
level or in gentle turns at less than 40 kts but do not try it in rough =
conditions the airflow will break away unpredictably.

David Smith

"David Smith" wrote...
I have never tried to spin my ASW20 in this way but I have done the =
exercise in a K13 at low level too. The results were a very fast stall =
and wingdrop, which is what I expected and is how I would I expect most =
gliders to behave. I what way does the ASW20 behave differently?? =

The ASW20s I've flown will do both normal spin entries (inner wing drops)
and over the top spin entries (outer wing drops) from a turn, depending on
how the glider is handled. Spin entry is also more abrupt than the typical
training glider. Those who have trained in something other than a K13 or a
Puchacz will not have experienced this type of spin behavior.

A pilot with 100+hours solo that has read and understood the manual =
should have no problems, it is not a novice glider. It can be flown =
level or in gentle turns at less than 40 kts but do not try it in rough =
conditions the airflow will break away unpredictably.

100+ hour pilots vary greatly in level of training and experience. I've
know 100 hour pilots who could safely fly just about any glider. I've also
known 1000 hour pilots who barely survive flying Grob Twins...

Marc

Marc
Do any other single seaters spin over the top in the same way and just =
how do deliberately make the glider do it. I certainly have done a left =
hand spin off a right hand turn in a Puchacz but I think you are =
describing different behavior.

David Smith