On 9/1/2011 6:12 PM, Bill D wrote:
On Sep 1, 4:49 pm, jim wrote:
On Sep 1, 2:44 pm, Bill wrote:









On Sep 1, 12:25 pm, Frank wrote:

On Sep 1, 9:35 am, Judy wrote:

At 07:50 01 September 2011, Michael Vickery wrote:

Hi
I wonder if there may be an alternative interpretation for this accident?

Some conjecture in this thread seems to center on wind gradient as a
possible contributing cause. Here's an excerpt from the NTSB preliminary
report:

"A witness was located midfield under an awning on the east verge of the
north-south runway. He was seated, and facing northwest when he heard the
pilot report on the common traffic advisory frequency that he was inbound
for landing. A few minutes later, his attention was drawn to a glider
flying past the awning in level flight, heading north along the runway at
an altitude of about 75 feet above ground level (agl). He did not see the
glider prior to that moment, and while he could not accurately judge its
airspeed, he surmised that it was traveling at a "fast clip." He was
startled, and expressed considerable alarm at the glider's location.

"The glider continued to the end of the runway, and then began a smooth
pitch-up maneuver. During the initial climb, the right wing dropped
slightly, and the glider proceeded to bank smoothly to the left. The turn
continued until its heading had diverged by about 40 degrees, at which
point the airspeed had decreased significantly. It reached an apex of about
300 feet agl, and then began a spin to the left in a near vertical,
nose-down attitude. It completed one full rotation before disappearing out
of his view behind trees. The flaps did not appear to be deployed at any
point during the flight, and he estimated that winds were about 12 to 15
knots out of the south.

"Multiple witnesses recounted similar observations, all reporting tailwinds
for the downwind phase of between 10 and 20 knots. At the time of the
accident, an annual Fly-In was underway at the airport. The pilot had
arrived earlier in the week. Airfield records indicated that he flew the
glider one time prior, 3 days before the accident. Associates of the pilot
reported that he purchased the glider in 2006, and the fly-in was the first
time he had flown it since purchase."

-- Judy

Naturally, I presumed he'd turned nearer 180 degrees, but the report
indicates only 40 degrees, so most of his climb was with a tail wind
component. Vegetation and development is a bit spare in the area, so
the gradient between the described winds at the surface and 100 meters
is probably not too extreme, though the variability would suggest some
turbulence also. In any event, I suspect he was climbing into an
increasing tail wind component. The described wind would also
exaggerate his apparent speed to the ground observers and his
perceived speed across the ground. I doubt it would have had an
affect on aileron effectiveness unless he also transited a boundary
shear into another wind direction.

http://en.wikipedia.org/wiki/Wind_gradient

Our gliderport is also 5500MSL and when driving the winch, I've often
observed gliders during the launch transiting two wind 'shears'. The
first appears to be about 400ft agl, the second between 1100-1400ft
agl. Glider pitch and yaw are both affected. (The pilots notice it
too) The person who built our gliderport had started nearly five
miles closer to the foot hills. I once asked him why he moved it. He
mentioned, among other reasons, the difficulty in soloing new pilots
due to the wind anomalies nearer the hills. Of course, this often
puts our operation further from the convergence zone, which can mean
later starts when the zone develops strongly as it draws cooler air
from the South Platte and Poudre River valleys causing trigger
temperature to be reached later, if at all some days. This surface
layer can be 60 to 180 degrees out from the forecasted winds and is a
'local' effect.

Our minimum pattern speed is 55knots.

Frank Whiteley

This is yet another case where an angle of attack indicator with stall
warning stick vibrator would have saved a life. Tiny cellphone/pager
vibrator motors embedded in the stick grip would be an excellent stall
warning.- Hide quoted text -

- Show quoted text -

I respectfully disagree. Not attempting a high speed pass in a slow
glider might have saved a life. Flying THAT glider more frequently may
have saved a life. I don't think having the stick buzz a second before
the stall/spin would have helped given the pilot's lack of experience
in THAT glider.

Shoving the stick forward one second before a stall break will prevent
it in any glider.
The commuter plane that crashed in Buffalo last year had a stick shaker
and it didn't seem to help them. More gadgets won't compensate for a
lack of basic airmanship.

--
Mike Schumann