Destruction due to turbulence when below Va - how?

Peter wrote:
I think I understand the reasoning behind Va, the max maneuvering
speed, being that the wing will stall (and thus dispose of the
loading) before it breaks. This is why Va falls as the weight falls,
because at any given IAS a higher weight takes the aircraft closer to
stall already.
So, how is it possible to have aircraft destruction due to weather,
e.g. flying into a strong updraught in a CB, if flying below Va?
A DOWNdraught would do it more easily because most aircraft designs
have a lower design limit for negative G.

Find a copy of "FLYING THE BEECH BONANZA", by John C Eckalbar.
There is a section in the book expressly dealing with this topic.

"Peter" wrote in message
...

I think I understand the reasoning behind Va, the max maneuvering
speed, being that the wing will stall (and thus dispose of the
loading) before it breaks. This is why Va falls as the weight falls,
because at any given IAS a higher weight takes the aircraft closer to
stall already.

So, how is it possible to have aircraft destruction due to weather,
e.g. flying into a strong updraught in a CB, if flying below Va?


Flying into an updraught (updraft) in a CB can cause destruction for other
reasons that just the consideration of Va.

The windshear may put the aircraft into an unusual attitude from which
recovery may be impossible before, say, Vne is exceeded.

Turbulence is gusts which change the airspeed. I recall reading one account
of a thunderstorm accident where the plane encountered a 80kt vertical gust.
In the Sierra Wave Project loads of +16G and -20G were encountered in a
rotor cloud at below Va..

I think it should be understood that these are extreme examples i.e. flying
into the worst part of the worst thunderstorm at the worst time. A one in a
million event. The usual breakup story is loss of control followed by an
overspeed were the pilot pulls the wings off in the recovery.

Mike
MU-2

"Peter" wrote in message
...

I think I understand the reasoning behind Va, the max maneuvering
speed, being that the wing will stall (and thus dispose of the
loading) before it breaks. This is why Va falls as the weight falls,
because at any given IAS a higher weight takes the aircraft closer to
stall already.

So, how is it possible to have aircraft destruction due to weather,
e.g. flying into a strong updraught in a CB, if flying below Va?

A DOWNdraught would do it more easily because most aircraft designs
have a lower design limit for negative G.


Peter.
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The design limit is not really lower for negative G. Remember that you are
starting at +1G so, if the limits are +3.8G and -1.8G, the limits are both
2.0g away from steady state flight.

Mike
MU-2

"Peter" wrote in message
...

I think I understand the reasoning behind Va, the max maneuvering
speed, being that the wing will stall (and thus dispose of the
loading) before it breaks. This is why Va falls as the weight falls,
because at any given IAS a higher weight takes the aircraft closer to
stall already.

So, how is it possible to have aircraft destruction due to weather,
e.g. flying into a strong updraught in a CB, if flying below Va?

A DOWNdraught would do it more easily because most aircraft designs
have a lower design limit for negative G.


Peter.
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E-mail replies to but remove the X and the Y.
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Mike Rapoport wrote:

Turbulence is gusts which change the airspeed. I recall reading one account
of a thunderstorm accident where the plane encountered a 80kt vertical gust.
In the Sierra Wave Project loads of +16G and -20G were encountered in a
rotor cloud at below Va..

I think it should be understood that these are extreme examples i.e. flying
into the worst part of the worst thunderstorm at the worst time. A one in a
million event. The usual breakup story is loss of control followed by an
overspeed were the pilot pulls the wings off in the recovery.

Mike
MU-2

"Peter" wrote in message
...

I think I understand the reasoning behind Va, the max maneuvering
speed, being that the wing will stall (and thus dispose of the
loading) before it breaks. This is why Va falls as the weight falls,
because at any given IAS a higher weight takes the aircraft closer to
stall already.

So, how is it possible to have aircraft destruction due to weather,
e.g. flying into a strong updraught in a CB, if flying below Va?

A DOWNdraught would do it more easily because most aircraft designs
have a lower design limit for negative G.


Peter.
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Is it the tail or the wings that get snapped off. Hauling back on the
yoke loads up the elevator. The wings are near the center of gravity so
they don't get stressed as much.

Mike Rapoport wrote:
The design limit is not really lower for negative G. Remember that you are
starting at +1G so, if the limits are +3.8G and -1.8G, the limits are both
2.0g away from steady state flight.

Mike has the idea. You need to look at a V-g/V-n diagram for your
aircraft to see where the load limits lie for a given airspeed. This is
how Eckalbar explains it.

"Peter" wrote in message
...

I think I understand the reasoning behind Va, the max maneuvering
speed, being that the wing will stall (and thus dispose of the
loading) before it breaks. This is why Va falls as the weight falls,
because at any given IAS a higher weight takes the aircraft closer to
stall already.

There was a long thread in January, "Va and turbulent air
penetration speed" which you ought to be able to find
on Google.

The short answer is that flying below Va (even at max
weight) doesn't guarantee that the wing will stall before
exceeding the load factor. Va is defined in terms of
what control surfaces can handle, not when the wings
will fall off; see for example FAR 23.423 and 23.335.

In article MwxLc.67$eM2.51@attbi_s51,
"William W. Plummer" wrote:

Mike Rapoport wrote:

Turbulence is gusts which change the airspeed. I recall reading one account
of a thunderstorm accident where the plane encountered a 80kt vertical gust.
In the Sierra Wave Project loads of +16G and -20G were encountered in a
rotor cloud at below Va..

I think it should be understood that these are extreme examples i.e. flying
into the worst part of the worst thunderstorm at the worst time. A one in a
million event. The usual breakup story is loss of control followed by an
overspeed were the pilot pulls the wings off in the recovery.

Mike
MU-2

"Peter" wrote in message
...

I think I understand the reasoning behind Va, the max maneuvering
speed, being that the wing will stall (and thus dispose of the
loading) before it breaks. This is why Va falls as the weight falls,
because at any given IAS a higher weight takes the aircraft closer to
stall already.

So, how is it possible to have aircraft destruction due to weather,
e.g. flying into a strong updraught in a CB, if flying below Va?

A DOWNdraught would do it more easily because most aircraft designs
have a lower design limit for negative G.


Peter.
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Is it the tail or the wings that get snapped off. Hauling back on the
yoke loads up the elevator. The wings are near the center of gravity so
they don't get stressed as much.


Sometimes it is aircraft components -- engine mounts, baggage
compartments, etc. that fail.

"William W. Plummer" wrote in message
news:MwxLc.67$eM2.51@attbi_s51...
Mike Rapoport wrote:

Turbulence is gusts which change the airspeed. I recall reading one
account
of a thunderstorm accident where the plane encountered a 80kt vertical
gust.
In the Sierra Wave Project loads of +16G and -20G were encountered in a
rotor cloud at below Va..

I think it should be understood that these are extreme examples i.e.
flying
into the worst part of the worst thunderstorm at the worst time. A one
in a
million event. The usual breakup story is loss of control followed by
an
overspeed were the pilot pulls the wings off in the recovery.

Mike
MU-2

"Peter" wrote in message
...

I think I understand the reasoning behind Va, the max maneuvering
speed, being that the wing will stall (and thus dispose of the
loading) before it breaks. This is why Va falls as the weight falls,
because at any given IAS a higher weight takes the aircraft closer to
stall already.

So, how is it possible to have aircraft destruction due to weather,
e.g. flying into a strong updraught in a CB, if flying below Va?

A DOWNdraught would do it more easily because most aircraft designs
have a lower design limit for negative G.


Peter.
--
Return address is invalid to help stop junk mail.
E-mail replies to but remove the X and the
Y.
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Is it the tail or the wings that get snapped off. Hauling back on the
yoke loads up the elevator. The wings are near the center of gravity so
they don't get stressed as much.



I guess I don't understand what you are trying to say. If you pull back on
the yoke, the wing supports the weight of the airplane plus the load on the
tail multiplied by the load factor.

Mike
MU-2

"William W. Plummer" wrote in message Is it the tail or the wings that
get snapped off. Hauling back on the
yoke loads up the elevator. The wings are near the center of gravity so
they don't get stressed as much.

It depends on the structure. The T-28 Trojan was used by the South
Vietnamese in their conflict for ground attack roles. The pilots were
pulling the wings off much too often and the engineers couldn't understand
because those wings should support a battleship. It turns out that the
horizontal stabilizer was actually the first component to fail. After it
failed, the plane would pitch over with enough force to break the wings off.
This happens in less than a second. Once the engineers understood the
problem and strenghtened the horizontal stabilizer, the problem went away.

Other planes break apart in different ways. The T-34 has been in the news
quite a bit lately because of wings falling off. It appears that the tail
isn't breaking. The cause is attributed to metal fatigue from repeated large
stresses. A C-130 water bomber was videotaped as the wings came off. The
cause has been determined to be undetected cracks in the bottom wing skins
that were hidden by doublers. An airworthiness directive was recently aimed
at the Cessna 400 series because of a wing seperation. It turns out that the
causal factors of the seperation were damage during building by the
manufacturer and repeated overstressing during years of abuse in Alaska.

D.