Coordinated turning stall and spins

Excellent post, I do have a couple of questions.
Did the glider start to recover from the spin with
positive flap selected? My understanding is that in
a flapped glider the first action is to zero the flaps.
Do you think that by selecting a negative flap setting
this accelerated the glider to a greater velocity than
selecting zero flap would have done? (I do not know
offhand the limiting speed for a Ventus in zero flap)

You quote figures of 475ft and 750ft for the fully
developed spiins. Do you have any figures for the spiral
dives off the co-ordinated turns? (I do note that you
delayed recovery for 3 seconds) It seems to me that
any stall in the final turn will result in hitting
the ground before recovery can be completed which bears
out what I have always said, teaching people to recognise
the approach of a stall and/or spin, and take appropriate
preventive action, is more important than teaching
spin recovery.

One final question, if a spin is entered at 300 feet
should recovery even be attempted? Are the chances
of survival greater if the glider hits the ground spinning
than if it is part recovered and 'tent pegged'? Interesting
what?


At 00:00 12 November 2003, Chris Ocallaghan wrote:
Posted this to the discussion on spinning Blaniks from
a coordinated turning stall.

November 9, 2003
Turning Stalls and Insipient Spins

As promised, apropos to this discussion on spin entry
from coordinated
turning stalls, I took a tow this morning to 5000 feet
agl and
performed a series of coordinated and cross control
turning stalls.

The aircraft used was a Ventus 2bx, delivered this
year. I have
approximately 75 hours in this aircraft and about 525
hours total in
the model. I flew the glider at approximately 70% of
the aft cg limit.
Wing loading was 7.8 lbs per square foot. All stalls
were entered in
the first positive flap position.

My intention was as follows: to perform a series of
turning stalls,
both coordinated and cross controlled, to determine
the departure and
post departure characteristics of a modern fiberglass
sailplane.
Stalls were entered gently and in a shallow bank (lower
wingtip on
horizon). Whether coordinated or cross controlled,
I fixed the
controls in the pre-departure position for three full
seconds after
departure (that is, no attempt was made to recover
immediately after
the stall break).

Once off tow I completed two clearing turns, then stalled
the glider
wings level twice to establish attitude. I then entered
a coordinated
shallow left turn and gently eased back on the stick.
The stall broke
cleanly. The glider initially yawed about 30 degrees
to the left,
dropped its nose through the horizon, then began to
increase its bank
angle and gain speed. G forces accumulated and I recovered
from the
spiral dive at about 80 knots and roughly 70 degrees
of bank. (As
noted above, the elevator was held firmly aft and aileron
and rudder
neutral until recovery was initiated.

I repeated the same maneuver to the right. The stall
break was less
clean (more mushy). Development of the ensuing spiral
dive was slower,
but airspeed and bank angle both accumulated until
I released the
controls and initiated a recovery.

I repeated this sequence with like results.

I then entered a shallow bank turning stall (left)
while skidding
slightly. As the low wing began to drop, I applied
about ½ stick
travel to the right, ostensibly to raise the dropping
wing. Entry into
the spin was immediate and dramatic. The glider yawed
approximately
ninety degrees while dropping it nose to about 60 degrees
below the
horizon. I left the controls in this position for a
count of three
(one one thousand, two one thousand…) The glider completed
approximately 1.25 rotations before I initiated a recovery
(stick
forward, ailerons neutral, opposite rudder, pull up
from dive).

I repeated this process to the right. However, this
time, I gently
accelerated the stall (achieving a slightly higher
nose attitude
before departure). Once again, I skidded the turn (10
to 20 degrees),
and tried to pick up the low wing as it stalled, this
time with full
deflection of the aileron. The ensuing spin entry was
even more
dramatic. I was unable to measure rotation rate (even
roughly) because
the glider's nose went immediately past vertical. As
I lost the
horizon I became disoriented, until I looked out at
the wingtip and
found the horizon again. I nonetheless fixed the controls
for a count
of three. There was no noticeable g build up until
I initiated a spin
recovery. Max speed during the dive was just above
120 knots, about 20
knots more than I typically see for a recovery from
a fully developed
spin.

It should be noted that my glider has a flap redline
of 80 knots. In
all cases, if airspeed exceeded 80 knots, I moved the
flap handle to
the first negative position.

My interpretation: while the glider exhibited a yawing
motion during
the coordinated turning stall, it did not auto rotate,
nor did it show
any such propensity. Some pilots may find the dropping
wing, yaw
motion, and reduced g force of a coordinated turning
stall
disquieting, but when compared in sequence to an actual
autorotation
leading to a fully developed spin, the prior is patently
docile.
Height loss after an immediate recovery from a coordinated
turning
stall using a release of back pressure and coordinated
ailerons and
rudder could be measured in 10s of feet. The spin,
however, from entry
to the bottom of the dive recovery was measured in
hundreds. Loss of
height for the first spin, from entry, through development,
to the
bottom of the recovery dive was 475 feet. The second:
750 feet.

Conclusions: draw your own.

My resosponses in-line below...

Don Johnstone wrote in message ...
Excellent post, I do have a couple of questions.
Did the glider start to recover from the spin with
positive flap selected? My understanding is that in
a flapped glider the first action is to zero the flaps.
Do you think that by selecting a negative flap setting
this accelerated the glider to a greater velocity than
selecting zero flap would have done? (I do not know
offhand the limiting speed for a Ventus in zero flap)

Correct, I should have added that as part of spin recovery I moved the
flap to the first negative position. Though this is not expressly
dictated in the flight manual, the ensuing dive will certainly exceed
the flap redline (including 0 degrees). And, of course, dumping the
flap will immediately decrease AOA.


You quote figures of 475ft and 750ft for the fully
developed spiins. Do you have any figures for the spiral
dives off the co-ordinated turns? (I do note that you
delayed recovery for 3 seconds) It seems to me that
any stall in the final turn will result in hitting
the ground before recovery can be completed which bears
out what I have always said, teaching people to recognise
the approach of a stall and/or spin, and take appropriate
preventive action, is more important than teaching
spin recovery.


Approximately 200 to 250 feet, including the 3 second delay prior to
recovery. Unfortunately, my trace from the flight is not particularly
instructive. My FR was set at 4s intervals, so it doesn't show much
detail. Height loss is interpolated from the pressure altitude trace
as rendered in SeeYou.


One final question, if a spin is entered at 300 feet
should recovery even be attempted? Are the chances
of survival greater if the glider hits the ground spinning
than if it is part recovered and 'tent pegged'? Interesting
what?


That's a tough one to answer. I see your point: better to hit the
ground at 70 knots than 100 knots. In either case I suspect the
results will be the same. I suppose it a matter of whether you expire
at the scene or several hours later in an ICU. To that end, I'd always
try to recover -- your chances of survival going from miniscule to
maybe.



At 00:00 12 November 2003, Chris Ocallaghan wrote:
Posted this to the discussion on spinning Blaniks from
a coordinated turning stall.

November 9, 2003
Turning Stalls and Insipient Spins

As promised, apropos to this discussion on spin entry
from coordinated
turning stalls, I took a tow this morning to 5000 feet
agl and
performed a series of coordinated and cross control
turning stalls.

The aircraft used was a Ventus 2bx, delivered this
year. I have
approximately 75 hours in this aircraft and about 525
hours total in
the model. I flew the glider at approximately 70% of
the aft cg limit.
Wing loading was 7.8 lbs per square foot. All stalls
were entered in
the first positive flap position.

My intention was as follows: to perform a series of
turning stalls,
both coordinated and cross controlled, to determine
the departure and
post departure characteristics of a modern fiberglass
sailplane.
Stalls were entered gently and in a shallow bank (lower
wingtip on
horizon). Whether coordinated or cross controlled,
I fixed the
controls in the pre-departure position for three full
seconds after
departure (that is, no attempt was made to recover
immediately after
the stall break).

Once off tow I completed two clearing turns, then stalled
the glider
wings level twice to establish attitude. I then entered
a coordinated
shallow left turn and gently eased back on the stick.
The stall broke
cleanly. The glider initially yawed about 30 degrees
to the left,
dropped its nose through the horizon, then began to
increase its bank
angle and gain speed. G forces accumulated and I recovered
from the
spiral dive at about 80 knots and roughly 70 degrees
of bank. (As
noted above, the elevator was held firmly aft and aileron
and rudder
neutral until recovery was initiated.

I repeated the same maneuver to the right. The stall
break was less
clean (more mushy). Development of the ensuing spiral
dive was slower,
but airspeed and bank angle both accumulated until
I released the
controls and initiated a recovery.

I repeated this sequence with like results.

I then entered a shallow bank turning stall (left)
while skidding
slightly. As the low wing began to drop, I applied
about ½ stick
travel to the right, ostensibly to raise the dropping
wing. Entry into
the spin was immediate and dramatic. The glider yawed
approximately
ninety degrees while dropping it nose to about 60 degrees
below the
horizon. I left the controls in this position for a
count of three
(one one thousand, two one thousand?) The glider completed
approximately 1.25 rotations before I initiated a recovery
(stick
forward, ailerons neutral, opposite rudder, pull up
from dive).

I repeated this process to the right. However, this
time, I gently
accelerated the stall (achieving a slightly higher
nose attitude
before departure). Once again, I skidded the turn (10
to 20 degrees),
and tried to pick up the low wing as it stalled, this
time with full
deflection of the aileron. The ensuing spin entry was
even more
dramatic. I was unable to measure rotation rate (even
roughly) because
the glider's nose went immediately past vertical. As
I lost the
horizon I became disoriented, until I looked out at
the wingtip and
found the horizon again. I nonetheless fixed the controls
for a count
of three. There was no noticeable g build up until
I initiated a spin
recovery. Max speed during the dive was just above
120 knots, about 20
knots more than I typically see for a recovery from
a fully developed
spin.

It should be noted that my glider has a flap redline
of 80 knots. In
all cases, if airspeed exceeded 80 knots, I moved the
flap handle to
the first negative position.

My interpretation: while the glider exhibited a yawing
motion during
the coordinated turning stall, it did not auto rotate,
nor did it show
any such propensity. Some pilots may find the dropping
wing, yaw
motion, and reduced g force of a coordinated turning
stall
disquieting, but when compared in sequence to an actual
autorotation
leading to a fully developed spin, the prior is patently
docile.
Height loss after an immediate recovery from a coordinated
turning
stall using a release of back pressure and coordinated
ailerons and
rudder could be measured in 10s of feet. The spin,
however, from entry
to the bottom of the dive recovery was measured in
hundreds. Loss of
height for the first spin, from entry, through development,
to the
bottom of the recovery dive was 475 feet. The second:
750 feet.

Conclusions: draw your own.

"Don Johnstone" wrote in
message ...

One final question, if a spin is entered at 300 feet
should recovery even be attempted? Are the chances
of survival greater if the glider hits the ground spinning
than if it is part recovered and 'tent pegged'? Interesting
what?


As a matter of interest in this subject let me provide the following.
In the early 1960s I rebuilt a Pratt-Read glider. This glider was used by
the USA Navy during early WW 2 (1941-42?) for flight training. During the
rebuild I obtained an original Navy Flight Manual for the glider. In the
manual, in bold print, was a sentence that stated " If entering a spin below
1000 feet DO NOT attempt recovery."
The reason for this was that the Pratt-Read tended to spin flat. Recovery
from a spin was near vertical for several hundred feet at a speed of more
than 100 mph. Vertical speed in the flat spin was something like 500
ft/min. Therefore it was deemed safer to hit the ground in a flat spin
rather that nose down in a vertical dive.
I would think that most (all??) modern gliders will not spin flat.
Therefore, whether one allows the spin to continue or attempts recovery, the
attitude of the glider will be nose down. With a recovery attempt there is
at least a chance of survival.

Duane