A clarification...

When I ask did you let the spin fully develop, I mean through one or
more full turns, ie, to the point where it is easily differentiated
from a spiral. The initial turning stall very often self-recovers
within a quarter turn (yaw stability). If the stick is not moved
forward, the glider will continue to turn in a steepening bank and
accelerate. Most pilots instinctively recover long before they can
tell the difference between a stall -- recovery -- spiral dive
scenario and a stall -- spin. This often causes confusion about which
is which. I'm quibbling a little here, but there is a difference in
recovery times and altitude loss between the two. Your underlying
message, "Don't trust the yaw string alone to prevent a spin" is a
good one. Airspeed/AOA is the primary concern. A straight yaw string a
close second.

There is some value in understanding that a straight yaw string helps
a sailplane resist spinning. If we can be certain of this, low
altitude stalls can be more confidently addressed with greater control
and less loss of altitude. I'm thinking principally of wind shear
while turning base to low final. If the pilot doesn't detect the loss
of airspeed, he will certainly notice that the nose pitches down
(position of the elevator will try to return the glider to the lower
angle of attack) and may respond, initially, by trying to raise the
nose, aggrevating the situation. If a stall develops a quick glance
at the yaw string can help determine appropriate action, that is,
release back pressure and raise the lower wing using coordinated stick
and rudder, versus ailerons neutral, stick aggressively forward and
hard-over opposite rudder, then recovery from the ensuing dive.



(Chris OCallaghan) wrote in message . com...
Eric,

Point of interest: did you let the spin fully develop after the
coordinated turning stall? There is an aerodynamic tipping point --
that is the self-righting tendency of the tail that would typically
favor a spiral over a spin assuming that the only deflected control
surface was the elevator. Of course a wing drops when in a turning
stall, but without aileron deflection generating drag my guess would
be that designed yaw stability would prevent spin development.

There is a significant difference in the assymetric drag profile with
and without aileron deflection. Remember that most modern aircraft
begin their stall at the root. That means less torque and less
disposition to overpower yaw stability and enter a spin. Slapping an
aileron down to pick up the low wing adds significat drag at the tip.
Add some rudder (cross-controls), and now you have a greater
disposition to get the aircraft spinning rather than spiralling.

I'll give this a try over the weekend -- that is, making no recovery
to a coordinated turning stall to see how it develops. My Ventus spins
happily if aggrevated. It should prove a good test bed.

Eric Greenwell wrote in message ...
Ian Forbes wrote:

On Thu, 06 Nov 2003 00:02:30 +0000, Colin wrote:


- Spins occur when you stall and the glider is not "co-ordinated" ie
either slipping or skidding.

I used to think this, but I soon discovered our club Blanik would
happily spin from a coordinated turn by using a shallow bank and simply
reducing the airspeed. Since then, I've done this with other gliders.

A coordinated turn doesn't prevent the inner wing from flying at a
higher angle of attack than the outer wing, which is why it stalls
first, and a spin can begin. I haven't experimented with it enough to be
certain, but I suspect a slipping turn would reduce the tendency for the
inner wing to stall first.