Turbulence

"Gary Drescher" wrote in message
news:nCT9d.150772$wV.28126@attbi_s54...
for a given airspeed, lift=F is constant;

Sorry, I should have said: for a given airspeed, and at the maximum
coefficient of lift, lift=F is constant. (The limits Va and Vno are
calculated to be the airspeeds that offer protection even at the angle of
attack that achieves the maximum coefficient of lift.)

--Gary

"Chris W" wrote in message
news:a9T9d.5690$cJ3.3838@fed1read06...
Gary Drescher wrote:

Minor correction: the wings snap due to excessive lift (force), not due
to excessive Gs (acceleration).

What?!!! You can't have force with out acceleration and you can't have
acceleration with out force. The most basic formula in physics is:
F = MA or Force = Mass times Acceleration. A net force gives you
acceleration.

Yes, of course. But staying below Vno is what keeps the wings from snapping,
by keeping the lift (force) from being more than the wing can bear. Staying
below Va is what keeps the aircraft's acceleration from being more than
other components can bear.

The difference is important, because it explains why you have to scale Va
(but not Vno) in proportion to the square root of your gross weight. For a
given airspeed, weighing less obviously does not put greater lift force on
the wings. But (again for a given airspeed), weighing less does increase the
acceleration that the lift force causes (F=MA; for a given airspeed, lift=F
is constant; so less M implies more A). That's why Va becomes a stricter
limit at lower weight, whereas Vno is unchanged.

--Gary

Gary Drescher wrote:


Minor correction: the wings snap due to excessive lift (force), not due to
excessive Gs (acceleration).

What?!!! You can't have force with out acceleration and you can't have
acceleration with out force. The most basic formula in physics is:
F = MA or Force = Mass times Acceleration. A net force gives you
acceleration.


--
Chris W

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"Marco Rispoli" wrote in message
et...
One of the things that TERRIFIED me for the longest time was turbulence.

In fact, the very reason why my wife bought me a "Discovery Flight" at the
very beginning (and got me hooked to flying) was to get me to see that
there
was nothing to fear from planes, after me and her had a really bad (for
me)
flight back from Italy.

Ok ... after a little less than 100 hours of flight I have had my dose of
turbulence in flight ... while at the controls of a plane.

It is reccommended that if you encounter turbulence you slow down below Va
(manouvering speed), so if you encounter an especially stiff gust the
plane
will stall before pulling enough Gs to snap a wing. That's what the book
says ... and I used to follow it to the letter, to the point that even the
minimum turbulence would make me slow down to below Va.

I remember once, during a mock checkride with a senior instructor we
encountered some turbulence and I instinctively pulled the power to slow
the
plane below Va.

The intructor's reaction was instantaneous and unyelding:
"The hell are you doin'?" (Heavy Staten Island accent).
"Slowing the plane below manouvering speed" I say, my tone of voice like
that of a guy that has just been asked why the sun comes up in the
morning.
"Why?"
"Ah .. " I stammer surprised by the question ... isn't it obvious why?
"Because we are in turbulence?" it was supposed to be a statement but it
came out as a question ... a sheepish question at that.
The Instructor roars in laughter, for an instant louder than the engine.
"Dude, this is not turbulence. Put that power back in. I want to see that
needle at 2400 RPMs, in the RPM green arc." End of the argument.

It was light turbulence with occasional moderate. It was one of those cold
late winter days when winter is about to give up to spring but doesn't
quite
like the idea ...

To me it felt like we were getting slammed. To him this wasn't even a
tickle. Obviously our concepts of turbulence differed dramatically.

So, question to the more seasoned and weathered pilots out the

If I am clear air (VFR), and I am not close to mountains (so I don't have
to
worry about mountain waves), and I am flying around in my little cutie
Piper
Cherokee 180 do I even need to worry about turbulence?

I am just about done reading Rod Machado's IFR book and the bottom line is
that you need to be inside a thunderstorm in order to start worrying about
turbulence. In most conditions, just flying around VFR in your everyday
CAT
(Clear Air Turbulence) doesn't warrant fussing about it, and all you
really
have to do is just stay in the green arc. That's all.

According to what the book is saying, only older planes really need to
worry
about Va in moderate turbulence. Modern planes (certified after 69) can
fly
right through it, as long as you stay in the green arc.

I don't plan to fly into thunderstorms any time soon ... so, do I even
need
to worry about manouvering speed if I am just flying in one of those gusty
fall or spring Northeast VFR days?

Is staying below the green arc good enough?

--
Marco Rispoli - NJ, USA / PP-ASEL
My on-line aviation community - http://www.thepilotlounge.com



I wonder what setting them pilots use when flying in to hurricane's now that
has to be unsane and very turbulent.

"Marco Rispoli" wrote in message
et...
[...]
If I am clear air (VFR), and I am not close to mountains (so I don't have
to
worry about mountain waves), and I am flying around in my little cutie
Piper
Cherokee 180 do I even need to worry about turbulence?

I guess you have to define "worry".

If the air is bumpy, it always potentially could exceed the design limits of
the airplane. For that matter, you could be flying along in completely
smooth air and experience sudden and severe turbulence.

In that respect, you should *always* worry about turbulence. It's always
potentially there, and always potentially greater than the limits of the
airplane.

However, as others have mentioned, pilots, especially relatively
inexperienced ones, typically overestimate the strength of turbulence. It's
probably true that general bumpiness out in the open, away from severe
weather (includes strong winds) and terrain is probably going to be safe at
any normal cruise airspeed.

That said, "away from" is an ambiguous term. Terrain can still be quite far
away and still cause strong turbulence (50-100 miles or more in some cases).
Similarly, strong winds can seem trouble-free for long distances, but due to
wind shear result in very significant, isolated clear-air turbulence as you
fly through an area where there's another fast-moving air mass going a
different direction.

I am just about done reading Rod Machado's IFR book and the bottom line is
that you need to be inside a thunderstorm in order to start worrying about
turbulence. In most conditions, just flying around VFR in your everyday
CAT
(Clear Air Turbulence) doesn't warrant fussing about it, and all you
really
have to do is just stay in the green arc. That's all.

According to what the book is saying, only older planes really need to
worry
about Va in moderate turbulence. Modern planes (certified after 69) can
fly
right through it, as long as you stay in the green arc.

I haven't read Machado's book, so I don't know what he says and what he
doesn't. I would disagree that there's never any turbulence outside of a
thunderstorm that you need to worry about, or that there's never any
moderate turbulence in which newer planes might have a concern. Those kinds
of absolutes seem troublesome to me.

I don't plan to fly into thunderstorms any time soon ... so, do I even
need
to worry about manouvering speed if I am just flying in one of those gusty
fall or spring Northeast VFR days?

I would say that it's true that most of the time. Just make sure you are
paying attention to winds aloft forecasts, especially comparing wind speed
and direction changes over the various altitudes. Strong winds, or
significant shear, can result in significant turbulence.

I guess to me the thing to keep in mind is that continuous turbulence is
unlikely to be the real issue. If you can stand the turbulence, the
airplane can. Regardless of when it was built. The problem is that you
could be flying along, tolerating the turbulence, and then run into
something more significant.

As Mike says, slowing down to match your comfort level is always a good
thing. There's nothing worse than an anxious pilot. Even if you know the
airplane can handle the turbulence, you need to be at ease. Even an older
airplane is likely to be able to handle stronger turbulence than you feel
comfortable with.

The real question is whether you are potentially going to hit some strong
turbulence without any warning. For this, the turbulence you're feeling now
is less important than things like current and forecast weather and pilot
reports.

Bottom line: it's true that most pilots rarely, if ever, experience
turbulence strong enough for Va to be a real issue. But it can happen, and
usually it happens without warning. Furthermore, for both pilot and
passenger comfort, it's helpful to slow down in turbulence, even if the
airplane is in no danger of being hurt. As with all aviation decision
making, being conservative is a fine thing with respect to flying at or
below Va.

For what it's worth, I think the chances of the wings falling off are the
least of one's worries. More of an issue are all the other parts in the
airplane that are important to a successful flight. It would still require
some heavy turbulence to cause a problem, and I don't think this difference
should mean that pilots should be braver in the face of turbulence. It's
just an interesting academic aspect to the issue, IMHO.

Pete

"Peter Duniho" wrote

If the air is bumpy, it always potentially could exceed the design
limits of the airplane. For that matter, you could be flying along in
completely smooth air and experience sudden and severe turbulence.
I haven't read Machado's book, so I don't know what he says and what
he doesn't. I would disagree that there's never any turbulence
outside of a thunderstorm that you need to worry about, or that
there's never any moderate turbulence in which newer planes might have
a concern. Those kinds of absolutes seem troublesome to me.

Quoted from Aerodynamics for Naval Aviators:

"The loads imposed on an aircraft in flight are the result of
maneuvers and gusts."
"As a general requirement, all airplanes must be capable of
withstanding an approximate effective +/- 30 foot per second
gust when at maximum level flight speed for normal rated power.
Such a gust intensity has relatively low frequency of occurrence
in ordinary flying operations."

BTW, the aircraft must withstand the 30 fps gust at Vno (top of
the green arc) even if the aircraft cannot attain Vno at maximum
power.
Weather induced gust loading establishes Vno, pilot induced
maneuver loads establishes Va.

Bob Moore

On Sat, 09 Oct 2004 00:04:33 GMT, Bob Moore
wrote in ::

Quoted from Aerodynamics for Naval Aviators:

"The loads imposed on an aircraft in flight are the result of
maneuvers and gusts."

There's some information on the subject he
http://ecfr.gpoaccess.gov/cgi/t/text...3.70.8&idno=14
§ 23.333 Flight envelope
(c) Gust envelope. (1) The airplane is assumed to be subjected to
symmetrical vertical gusts in level flight. The resulting limit load
factors must correspond to the conditions determined as follows:

(i) Positive (up) and negative (down) gusts of 50 f.p.s. at VC must be
considered at altitudes between sea level and 20,000 feet. The gust
velocity may be reduced linearly from 50 f.p.s. at 20,000 feet to 25
f.p.s. at 50,000 feet.

(ii) Positive and negative gusts of 25 f.p.s. at VD must be considered
at altitudes between sea level and 20,000 feet. The gust velocity may
be reduced linearly from 25 f.p.s. at 20,000 feet to 12.5 f.p.s. at
50,000 feet.

On Sat, 09 Oct 2004 00:04:33 GMT, Bob Moore
wrote in ::

Quoted from Aerodynamics for Naval Aviators:

"The loads imposed on an aircraft in flight are the result of
maneuvers and gusts."

There's some information on the subject he
http://ecfr.gpoaccess.gov/cgi/t/text...3.70.8&idno=14
§ 23.333 Flight envelope
(c) Gust envelope. (1) The airplane is assumed to be subjected to
symmetrical vertical gusts in level flight. The resulting limit load
factors must correspond to the conditions determined as follows:

(i) Positive (up) and negative (down) gusts of 50 f.p.s. at VC must be
considered at altitudes between sea level and 20,000 feet. The gust
velocity may be reduced linearly from 50 f.p.s. at 20,000 feet to 25
f.p.s. at 50,000 feet.

(ii) Positive and negative gusts of 25 f.p.s. at VD must be considered
at altitudes between sea level and 20,000 feet. The gust velocity may
be reduced linearly from 25 f.p.s. at 20,000 feet to 12.5 f.p.s. at
50,000 feet.

Marco Rispoli wrote:

If I am clear air (VFR), and I am not close to mountains (so I don't have to
worry about mountain waves), and I am flying around in my little cutie Piper
Cherokee 180 do I even need to worry about turbulence?

First, mountain waves cause up and downdrafts, but they are as smooth as
you can imagine. What you mean is rotor. Well, if you really want to
know how turbulence really feels, go to your friendly glider operator
somewhere in the mountains when there is wave and ask for a ride into a
rotor. As a side effect, you will also learn what a "steep turn" is.

Back to your question: There is no point in demonstrating how brave you
are. If you feel uncomfortable, slow down to Va. there is nothing wrong
in staying on the safe side.

Stefan

Marco
Be careful doing what others say to do, one day it may cause problems for you.
Some people who fly only go by rules they make up for their airplane .. ie ..
they see nothing wrong with flying thorugh clouds while VFR, put tape over gas
tank filler hole because they lost their gas cap, perform an instrument
approaoch in IMC with a handheld GPS and no approach plates, fly into known
icing and so on.

Personally, If I expect turbulence I will slow down a bit or as I got in the
habit of doing at this mountain near kingman, I would pass the mountain on the
upwind side to avoid the turbulence it causes. I have been in what I called
severe before, when I got done bouncing I was pointed 90 degrees off course, it
was just bone jarring bumps, felt like a hundred of them in a matter of a few
seconds.

My suggestion is to fly the way your used to flying, as you get more time, you
get used to the bumps and will start to tell when you may experience them and if
they are an issue. If you want to slow down, slow down, nothing wrong with it,
its your flight. Its better to slow down then assume some type of turbulence is
less then it is and cause damage to your plane or make your passangers not want
to fly with you again.


Marco Rispoli wrote:

One of the things that TERRIFIED me for the longest time was turbulence.

In fact, the very reason why my wife bought me a "Discovery Flight" at the
very beginning (and got me hooked to flying) was to get me to see that there
was nothing to fear from planes, after me and her had a really bad (for me)
flight back from Italy.

Ok ... after a little less than 100 hours of flight I have had my dose of
turbulence in flight ... while at the controls of a plane.

It is reccommended that if you encounter turbulence you slow down below Va
(manouvering speed), so if you encounter an especially stiff gust the plane
will stall before pulling enough Gs to snap a wing. That's what the book
says ... and I used to follow it to the letter, to the point that even the
minimum turbulence would make me slow down to below Va.

I remember once, during a mock checkride with a senior instructor we
encountered some turbulence and I instinctively pulled the power to slow the
plane below Va.

The intructor's reaction was instantaneous and unyelding:
"The hell are you doin'?" (Heavy Staten Island accent).
"Slowing the plane below manouvering speed" I say, my tone of voice like
that of a guy that has just been asked why the sun comes up in the morning.
"Why?"
"Ah .. " I stammer surprised by the question ... isn't it obvious why?
"Because we are in turbulence?" it was supposed to be a statement but it
came out as a question ... a sheepish question at that.
The Instructor roars in laughter, for an instant louder than the engine.
"Dude, this is not turbulence. Put that power back in. I want to see that
needle at 2400 RPMs, in the RPM green arc." End of the argument.

It was light turbulence with occasional moderate. It was one of those cold
late winter days when winter is about to give up to spring but doesn't quite
like the idea ...

To me it felt like we were getting slammed. To him this wasn't even a
tickle. Obviously our concepts of turbulence differed dramatically.

So, question to the more seasoned and weathered pilots out the

If I am clear air (VFR), and I am not close to mountains (so I don't have to
worry about mountain waves), and I am flying around in my little cutie Piper
Cherokee 180 do I even need to worry about turbulence?

I am just about done reading Rod Machado's IFR book and the bottom line is
that you need to be inside a thunderstorm in order to start worrying about
turbulence. In most conditions, just flying around VFR in your everyday CAT
(Clear Air Turbulence) doesn't warrant fussing about it, and all you really
have to do is just stay in the green arc. That's all.

According to what the book is saying, only older planes really need to worry
about Va in moderate turbulence. Modern planes (certified after 69) can fly
right through it, as long as you stay in the green arc.

I don't plan to fly into thunderstorms any time soon ... so, do I even need
to worry about manouvering speed if I am just flying in one of those gusty
fall or spring Northeast VFR days?

Is staying below the green arc good enough?

--
Marco Rispoli - NJ, USA / PP-ASEL
My on-line aviation community - http://www.thepilotlounge.com