Severe (or more) turbulence... how common?

"John Harper" wrote in message
news:1075755778.686463@sj-nntpcache-5...
Yes, that's pretty much what my math came up with too. But for sure
I lost 2000' (I couldn't believe it when I looked at the altimeter after
recovering the plane - I'd been pretty focussed on the ASI since I
was close to redline). And I don't think the whole thing lasted more
than 10 seconds, although of course I wasn't timing it. Maybe it
was longer, but usually these things seem to last longer than they
really do, not less.

The terrain there is a bit special - there's a first ridgeline which is
at 6000-7500', then after a couple of miles there's a lower ridge
at around 4000', with a valley in between at about 2000'. I think
the only reason I recovered (much though I'd like to take credit for
my excellent airmanship :-) ) is that we flew through the downdraft.

I don't know whether this was "severe turbulence" according to
the definition. It was actually quite smooth, except that we were
going down at something around -1G. I did keep the plane under
control - my main concern being to avoid hitting Vne. We came out
about 30 degrees off heading. My wife says we did bank quite
steeply - she was looking out of the windshield, I was focussed on
the instruments. Whether it was "severe" or not, it was certainly quite
an experience, one I'm not in a big hurry to repeat.

John


If its smooth, its not turbulence. When you are flying roughly
perpendicular to a ridgeline and encounter a rotor there is a very strong
updraft and then an equally strong downdraft (of course the order is
reversed if you are going the other way). The terrain sounds like a good
setup for a wave if the air is stable and the wind is perpendicular to the
ridges and increases with height.

The numbers don't really match up with the reported conditions. To get
2000' of altitude loss in 10 seconds would require winds of well over 100kts
since the vertical speed is going to average 120kts. If you are interested
in mountain waves you should read the book "Exploring the Monster" which is
about the Sierra Wave Project which studied the very powerful wave systems
on the east side of the Sierra Nevada near Bishop. The Owens Valley is an
ideal wave generator being 10,000' deep, perpendicular to the jetstream and
about one wavelength wide. Gliders regularly reach 40,000' there and in the
Carson Valley farther north.

Mike
MU-2

flying out along the coast,
headed to Half Moon Bay Airport to practice some t/o & landings at another
airport.

same thing happened to me with 2 friends doing a Bay tour last week.
Beautiful calm and unlimited visibility with no bumps whatsoever.
Then we're flying down the coast just north of Half Moon Bay just
outside the 7nm ring of the SFO Class B and a couple of miles (?)
out over the ocean when we hit a medium bump. Just a quick
short one but it came from no where.

then also into 20 hours or so of my flying life near OSI VOR,
plan dropped quite hard, engine paused for a second and everything
continued.

That stuff is scary for a few minutes.


Where was the rotor (?) that you experienced between LA and SF?

Gerald

If you ever experience truely *severe* turbulence you will never have
any doubt as to what *severe* really means.

The air is not smooth, it is not just an uncommanded altitude
excursion. It is something to behold.

I only hit severe once and fortunately had slowed to Va. The plane
stalled in level flight at Va. That is one whale of a ride!

Now, I've been in moderate (things not secured tend to fly around the
cockpit) a good many times and it's not a lot of fun, but severe is
memorable.

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

In article .net,
Gerald Sylvester wrote:
flying out along the coast,
headed to Half Moon Bay Airport to practice some t/o & landings at another
airport.

same thing happened to me with 2 friends doing a Bay tour last week.
Beautiful calm and unlimited visibility with no bumps whatsoever.
Then we're flying down the coast just north of Half Moon Bay just
outside the 7nm ring of the SFO Class B and a couple of miles (?)
out over the ocean when we hit a medium bump. Just a quick
short one but it came from no where.

In that area, it is quite possibly wake turbulence from planes
departing SFO. A friend cracked his head on the ceiling after a
wake turbulence encounter. He saw the plane's path, and was above
it, but the wind was out of the west, and the wake turbulence blew
into his flight path.

John
--
John Clear - http://www.panix.com/~jac