Good test card Chris.

Thanks for the great info.

9B

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.