Turbulence

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

Marco Rispoli wrote:

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

To folks that haven't experienced a lot of turbulence, a little can seem
like a lot. I gave a ride to a COZY builder who had never been in a
small plane - he asked whether we were in moderate to severe turbulence
when I hadn't really even noticed that we had hit a tiny burble.

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?

Not really. I fly in the NE, like you do, and while I've experienced
mild to moderate turbulence down low on VFR days, I've never really
gotten hammered. Even when it __feels__ like I'm getting hammered, it's
still considered moderate - go look up the definition of severe
turbulence - basically, you can't control the plane.

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?

Nope. If you can keep the plane upright, there's no issue.

Is staying below the green arc good enough?

You mean red? Below the green arc, I don't think the plane will stay in
the air :-). On my COZY (admittedly a homebuilt, but the concept is the
same) the red arc begins at 220 mph IAS and the yellow arc begins at 140
mph IAS. Va is 140 mph, but I NEVER fly that slow - usually I'm
cruising at about 175 - 180 mph IAS, no matter what the turbulence level
(I'm VFR only). The only thing I slow down for in cruise is if the
visibility sucks.

--
Marc J. Zeitlin
http://marc.zeitlin.home.comcast.net/
http://www.cozybuilders.org/
Copyright (c) 2004

You mean red? Below the green arc, I don't think the plane will stay in
the air :-).

Yea sorry. I meant below the yellow arc. Not below the green arc, but IN the
green arc.

Typo.

Thanks for the info!

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

If I am in an area where moderate or greater turbulence can be expected (or
is possible) like desending to an airport in mountainous terrain with the
wind howling, I slow down whether I am currently experiencing any turbulence
or not. If I am flying along below small cumulus and experiencing some
bumps, I don't slow down.

There is nothing wrong with slowing down if you are uncomfortable. I would
try to keep everything in the green arcs as much as possible though.

Mike
MU-2


"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

"Marco Rispoli" wrote in message
et...
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.

Minor correction: the wings snap due to excessive lift (force), not due to
excessive Gs (acceleration). Staying below Vne keeps the force from being
excessive; staying below Va keeps the acceleration from being excessive. Vne
does not vary with weight; Va varies in proportion to the square root of
gross weight, becoming a stricter limit when weight is lower. That's because
the less mass you have, the more acceleration is produced by a given force.

If you don't feel more than 2G upward acceleration (or 1G downward) in
turbulence, you're well within the acceleration design limits for a
normal-category airplane.

--Gary

"Gary Drescher" wrote in message
news:T_z9d.436094$8_6.136539@attbi_s04...
Minor correction: the wings snap due to excessive lift (force), not due to
excessive Gs (acceleration). Staying below Vne keeps the force from being
excessive; staying below Va keeps the acceleration from being excessive.
Vne does not vary with weight; Va varies in proportion to the square root
of gross weight, becoming a stricter limit when weight is lower. That's
because the less mass you have, the more acceleration is produced by a
given force.

IMHO, you are making things more confusing, not less.

Yes, what will break the structure is force. But when we talk about "G's",
typically we are describing a *factor* multiplied with the weight of the
airplane, not "acceleration due to gravity". In that context, all "G's"
means is "a factor increasing the nominal 1G force experienced by the
airplane".

For example, in a bank, lift needs to be increased in order to maintain
vertical speed (i.e. prevent up or down acceleration), usually at zero. At
a high enough bank angle (much higher than any normal operation would
require), the "G's" exceed the certification limit. Those "G's" would be a
static state, not due to acceleration of the airplane (if allowed to turn,
the airplane would also be accelerating, but this acceleration isn't
directly related to the "G's" experienced...if you could somehow counteract
the lateral force caused by the increase in lift, the wings would still
experience increased "G's", but the airplane would track straight ahead).

Vne is not typically related to lifting force at all, but rather to other
things like flight control flutter and longitudinal strength of airframe
structures (e.g. drag pulling the wings backwards). In level flight, at any
airspeed, the wing is generating exactly as much lift as there is weight of
the airplane. The force (lift) is constant.

Va, on the other hand, is related to a variety of other things. In the
sense that those things have to do with rapid changes in airfoil loading,
they are related to acceleration. But ultimately, those limits still have
to do forces imposed on structure. The acceleration is relevant -- higher
acceleration results in higher G forces on structure -- but the reason that
Va changes due to weight has less to do with the distinction between
"force", "G's", and "acceleration" and more to do with the fact that there
are internal structures carrying loads that don't change with total gross
weight of the airplane.

It's true that "the less mass you have, the more acceleration is produced by
a given force", but the reason this is relevant here is not because
acceleration is the problem per se. Rather, it's because there are
components in the airplane with a fixed load that, with the increase in
total acceleration of the airplane, could experience loads higher than
designed for. Because of these, the acceleration limit of the entire
airframe needs to be held constant. If it weren't for that, increased
acceleration would not be a problem, because the total load (force) at lower
weights would be the same, and it's force that breaks things, not
acceleration.

As this relates to the original statement, Va is the only airspeed related
to "keeping the force from being excessive". You can fly above Va and below
Vne, and still create out-of-limit *force* on the airframe, enough to damage
or even break the structure, simply by exerting too rapid a control movement
(on the elevator, for example). Vne does nothing to prevent this; only Va
does (and it's not perfect either...there exist gusts in nature than can
still exceed the structural limits at or below Va).

IMHO, arguing that Vne is only about force and Va is only about acceleration
is misleading and only serves to confuse the issue. Ultimately, they are
*both* about force imposed on various parts of the airframe structure; they
just happen to be addressing different *force-related* issues.

Pete

Oops, major slip: I meant to say Vno, not Vne.

--Gary

"Gary Drescher" wrote in message
news:T_z9d.436094$8_6.136539@attbi_s04...
"Marco Rispoli" wrote in message
et...
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.

Minor correction: the wings snap due to excessive lift (force), not due to
excessive Gs (acceleration). Staying below Vne keeps the force from being
excessive; staying below Va keeps the acceleration from being excessive.
Vne does not vary with weight; Va varies in proportion to the square root
of gross weight, becoming a stricter limit when weight is lower. That's
because the less mass you have, the more acceleration is produced by a
given force.

If you don't feel more than 2G upward acceleration (or 1G downward) in
turbulence, you're well within the acceleration design limits for a
normal-category airplane.

--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

Bring Back the HP 15C
http://hp15c.org

Not getting the gifts you want? The Wish Zone can help.
http://thewishzone.com

"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 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