On 8/30/2012 12:33 PM, Duster wrote:

Major snip...

Since we have Bruno's video and comments for a "real-life" spin
(albeit at altitude), it looks like he was successful in getting out
of the spin solely by moving flaps either from positive to negative,
or from neutral to negative (you can see the flap handle position; are
they positive before the spin?). From what I gather, no opposite
rudder was inititated and he even went more opposite aileron after the
spin begins. What impresses me is that once the spin was recognized,
there was no hesitation in immediately reaching for the flap handle.
Why? Like he said, it was the most effective control input for
recovery based on his experience. I will try this in my own flap-only
ship to see if it works; however at low altitude I'm not inclined to
dump my flaps as the ship would settle and the stall speed goes up.

Indeed, assuming no other changes/inputs, reducing flap deflection reduces
lift, the glider will settle (increasing the AoA, as - thanks to gravity and
trim forces - the plane/wing tries to regenerate the lost lift and return to a
non-changing-acceleration state), and the stall speed (assuming no change in G
load) increases. Kinda makes for a strong argument to not put oneself in the
position of NEEDing to dump flaps (reducing the wing's camber and effective
AoA) to prevent a spin when close to the ground, eh? :-)
- - - - - -

My
question is on the ASW-20, which I've never flown, aren't the flaps
and ailerons interconnected to increase effectiveness? So, as the
flaps go to negative, lift decreases, correct?,

A partial response to the first question is, "tip-to-tip" interconnection is
generally done hoping to remain as close to the ideal (lowest induced drag)
lift distribution as possible, in the absence of roll-inducing aileron inputs.
"Roll interconnection" gets into additional aerodynamic reasoning...

To the 2nd question: "Yes"...ignoring short-time-constant changes that begin
the instant wing profile is changed. That said, "at speed" and away from any
ground reference, Joe Pilot will likely not be able to detect anything more
than a (fairly rapid/"short time constant") change in pitch attitude and
(possibly) a brief sensation (assuming he holds the same stick position) of
settling. In the real world, few pilots probably change ONLY the T.E. flap
setting; I'd bet most simultaneously are tweaking their stick position, too,
even if they don't realize it.
- - - - - -

but aileron
effectiveness becomes less also, right?

Now THAT's a seemingly simple question...having considerable complexity in its
answer(s)! Rather than attempting a direct response, I'll toss out a few
related questions...

So why do many flap-equipped drivers start their T.O. rolls with negative
flaps? (Hint: the answer has to do with better low-speed aileron effectiveness
in T.O. configuration/attitude...easily tested in a reasonably steady ground
breeze with a friendly wingtip holder's brief assistance.)

Are every ships' ailerons rigged with the same (if any) differential?

Have you measured 45-to-45 rolls in your ship at (say) the same (thermalling)
speed in your ship, at different flap/aileron settings?
- - - - - -

Doesn't this effectively help
neutralize aileron effectiveness w/o moving the ailerons, yet be
sufficient to unspin it? Would the same technique be used at a more
critical altitude?

I'm not sure I understand the first question, but at its essence, "unspinning"
a glider "merely" requires re-achieving flight. Most "unspinning instructions"
for fully-developed-spins presume rudder input will be desirable, along with
reduced AoA, but simply unstalling the wing will be sufficient. Reason for the
rudder input is (most likely - this is why they pay test pilots!) to minimize
subsequent altitude loss.

As to the "same technique" question, never forget the key to unstalling a wing
is reducing AoA. Someone will surely point out that unloading the wing will
also reduce the stall speed to zero, which is correct, but "unloading the
wing" is really a specific flavor of reduced AoA, and, is something Joe Pilot
has limited ability to do at thermalling speeds (though gravity is always
willing to help if he's out of elevator authority!). Trailing edge flaps
somewhat complicate (add to) the means of reducing AoA, compared to unflapped
wings.

Also, never forget that SOMEthing has to also initiate rotation; simply
stalling a wing symmetrically (if possible) won't by itself achieve rotation.
Possible initiators of rotation: non-symmetrical rudder input; untimely gust;
unbalanced bug accumulation (leading to unbalanced/asymmetric flow
separation/lifting forces); heavy wing; use your imagination...

If you feel OK betting your life on always achieving symmetrical flow
separation across your ship's span, then thermal away as low as you'd like,
while maintaining a hair trigger on forward stick motion! :-)
- - - - - -

Bruno's obviously a skilled pilot who knows his
ship; he even had the presence of mind to keep turning in the thermal.
I wish the Soaring Safety Foundation would consider archiving white
papers on flying characteristics of the different glider models, as
one recipe doesn't fit them all. A lot of good stuff gets lost in the
blogosphere. Gliderpedia anyone?
.
One lesson I learned from a master CFIG (Burt Compton) during a
simulated rope break was to avoid looking immediately back at the
airport. His point was that some stall-spins might be due to pilots
inadvertently pulling the stick back as they pivot their heads around.


Kids, can you spell "John Denver"? (Meaning, Burt is almost certainly right in
this particular surmise...)

Bob W.