Weird Windshear

jsmith wrote:
I cannot personally speak for the "a few hundred miles", but I have
experienced mountain wave within ten nm of the lee side of the
Appalachians in both North Carolina and Georgia.

Maybe I shouldn't say "mountain wave". There is a definite vertical component to
the air movement where I live, about 200-300 miles east of the Appalachians in
NC, when the wind blows perpendicular to the ridges. If you're flying east-west,
you are alternately pulling and pushing to maintain altitude as you pass from
crest to trough of the waves. I'm *guessing* the time from push to pull is a
minute or so, so that would make the wavelength about 5 nm at Mooney speeds.

[Before someone else says it, yes, I know, efficiency can be improved by
allowing altitude to vary and just staying trimmed for your airspeed.]

Dave


Dave Butler wrote:

Here in NC you can get mountain waves a few hundred miles downwind
from the Appalachians, though I've never experienced anything as
severe as the OP describes. I think St Simons is too far south for
Appalachian mountain waves, though.

On 28 Feb 2005 18:19:31 -0800, "Bravo8500"
wrote:

I thought this was interesting so I'll share it. I hit some unusual
windshear snip

By this time I've disengaged the ap and now am
allowing the airplane to drop to maintain around 80. I'm just about
to call ATC when we start picking up airspeed, slowly. Man, that was
weird.

Why were you going to call ATC? Declare an emergency?

For one, I was going to tell them I wasn't able to hold altitude, I was
already 200 below assigned. Also, I was thinking about turning around,
changing directions or something, I was kind of at a loss for what to
do next.

"Nathan Young" wrote

Why were you going to call ATC? Declare an emergency?

Naah. With stuff like that goin' on, I'd tell him I was gonna go ahead and
crash, and quit fightin' it! ;-)
--
Jim in NC

On 28 Feb 2005 18:19:31 -0800, "Bravo8500"
wrote:

This is just the way wind shear works. Yes, it's an extreme example,
but I've stalled in level flight at Va on a beautiful clear day.

The first clue to extreme shear conditions is the large change in
direction in a relatively small change in altitude. If you cruise at
165 into a 40 knot head wind and abruptly enter a 40 knot tail wind
you are going to lose 80 knots. If you have the altitude it will
eventually end up at the original cruise. OTOH if you went from a 40
knot tail wind to a 40 knot head wind abruptly, can you imagine what
that would do to the plane. You not only would have some extreme
turbulence, but would temporarily hit close to 240 knots which is well
above Vne.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

I thought this was interesting so I'll share it. I hit some unusual
windshear I suppose last night going into St. Simmon's Island, GA
(BQK) in an A36 Bonanza. Here we were, me flying and the non-pilot
owner (my brother-in-law) in the right seat cruising at 3000 over the
top of a broken layer about 25 south of the localizer to runway 7,
about 9:30 EST. We were in moderate to occasionally severe turbulance
and I had been warned by the FSS briefer about a windshear at 1000 agl
- I think it was the fact that there was a 180 degree diff in wind
direction between the surface and 1000 agl that was causing it. Oh
yeah, a big fat low pressure was sitting right on top of BQK, more or
less, as I could determine from the duats graphical current analysis in
the motel room an hour later. The pressure had been dropping since
Atlanta and the altimeter was down to 29.68 I believe. Anyway, here we
are in flat out cruise, I look up and notice I'm only indicating 140
or so when I should see 165, and dropping a couple of knots per second.
As the airspeed goes through 110, I bring in full RPM and manifold and
we continue to lose airspeed down to 80 knots. I'm wondering what the
heck is going on, we're now in a climb attitude and get one blip of
the stall warning. By this time I've disengaged the ap and now am
allowing the airplane to drop to maintain around 80. I'm just about
to call ATC when we start picking up airspeed, slowly. Man, that was
weird.

"Roger" wrote in message
...
On 28 Feb 2005 18:19:31 -0800, "Bravo8500"
wrote:

This is just the way wind shear works. Yes, it's an extreme example,
but I've stalled in level flight at Va on a beautiful clear day.

The first clue to extreme shear conditions is the large change in
direction in a relatively small change in altitude. If you cruise at
165 into a 40 knot head wind and abruptly enter a 40 knot tail wind
you are going to lose 80 knots. If you have the altitude it will
eventually end up at the original cruise. OTOH if you went from a 40
knot tail wind to a 40 knot head wind abruptly, can you imagine what
that would do to the plane. You not only would have some extreme
turbulence, but would temporarily hit close to 240 knots which is well
above Vne.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

Roger, your experience and mine are pretty much the same, but reversed.
I dropped through the turbulence of the shear from a 40+ tailwind into calm
air in just a matter of a few seconds. The result was an almost instant
increase in airspeed. The increased lift jammed me back up through the
shear -- It was almost like I had bounced off of something. The plane didn't
stall when it went back to the upper level, but thinking back it could have,
if I'd've lost enough forward speed. In any case it was a hell of a ride
for a bit.
I still had to go through the shear to get down to pattern altitude. On
the next trip down, I throttled back to just above stall. When I went
through the shear, I shoved the nose down and cut the throttle all the way
back -- then recovered into normal flight when things settled down.
What I should have paid more attention to was when my whiz-wheel told me
I had a ground speed of 155 knots. In a C-150. I dismissed it at the time as
manipulating the dials wrong.
I wasn't going to quarrel with the original poster over his assessment
of his conditions, but his was more like flying into a severe sink than into
a shear. Especially with his description of the airspeed bleeding off over
minutes while the autopilot tried to compensate. He did a good job of coping
with it in any case. I'm just picking on calling it a shear.

Casey Wilson
Freelance Writer and Photographer

Felt like a sink, but I've never heard that term, only windshear.

"Bravo8500" wrote in message
oups.com...
Felt like a sink, but I've never heard that term, only windshear.

We use it mostly in gliders -- sometimes referred to as a downdraft
by power pilots. Glider guiders call updrafts "lift." Typically measured on
a vario(meter) in fps or knots. The only difference between a vario and an
VSI is the vario usually beeps. The pitch and period of the beeps sort of
indicate the velocity. Lift and sink work together -- somewhere in the
vicinity there was a rising volume of air. You were unlucky enough to fly
into the negative half.
Sorry if that seems patronizing or pedantic.
That brings up an autopilot question you might answer for me. If you
had not disconnected the autopilot, could it have taken you into a stall?

Downdraft, shear, microburst - bad! The ap I use (kfc200) only knows to
hold altitude, it doesn't care about airspeed, so it will gladly stall
it for you.

On Fri, 04 Mar 2005 01:53:44 GMT, "Casey Wilson" N2310D @ gmail.com
wrote:


"Bravo8500" wrote in message
roups.com...
Felt like a sink, but I've never heard that term, only windshear.

We use it mostly in gliders -- sometimes referred to as a downdraft
by power pilots. Glider guiders call updrafts "lift." Typically measured on
a vario(meter) in fps or knots. The only difference between a vario and an
VSI is the vario usually beeps. The pitch and period of the beeps sort of
indicate the velocity. Lift and sink work together -- somewhere in the
vicinity there was a rising volume of air. You were unlucky enough to fly
into the negative half.
Sorry if that seems patronizing or pedantic.
That brings up an autopilot question you might answer for me. If you
had not disconnected the autopilot, could it have taken you into a stall?

That depends on the AP, but mine (IF set to altitude hold) will just
keep pulling the nose up until it quits flying. That means you need
to know your power settings when doing a step down approach,.Altitude
hold off, power back (by the numbers), gear down (depends), flaps
(maybe), lead the altitude with power, with the power back to the
proper setting for the approach, turn the altutude hold back on.

BTW, the FAA defines wind shear as *any* abrupt change in wind
direction or speed. That includes up and down.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com