Re: Destruction due to turbulence when below Va - how?

[Roger Long]

It's not complete protection, it just loads the odds a bit more in your
favor.

The aircraft is as likely to be broken by a panicked response by the pilot
or a botched attempt to recover from an unusual attitude and being at Va
will reduce that probability significantly.
--

Roger Long



"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.
> Please do NOT copy usenet posts to email - it is NOT necessary.

[john smith]

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.

[Icebound]

"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.

[Mike Rapoport]

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.
> Please do NOT copy usenet posts to email - it is NOT necessary.

[Mike Rapoport]

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.
> --
> Return address is invalid to help stop junk mail.
> E-mail replies to but remove the X and the Y.
> Please do NOT copy usenet posts to email - it is NOT necessary.

[William W. Plummer]

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.
>>Please do NOT copy usenet posts to email - it is NOT necessary.
>
>
>
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.

[john smith]

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.

[Tony Cox]

"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.

[Orval Fairbairn]

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.
> >>--
> >>Return address is invalid to help stop junk mail.
> >>E-mail replies to but remove the X and the Y.
> >>Please do NOT copy usenet posts to email - it is NOT necessary.
> >
> >
> >
> 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.

[Mike Rapoport]

"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.
> >>Please do NOT copy usenet posts to email - it is NOT necessary.
> >
> >
> >
> 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

[Capt.Doug]

>"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.

[john smith]

Capt.Doug wrote:
> 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.

T-28 breaking point occurs at 428 kts. (As related to me by a retired
North American engineer many years ago.)

[Pooh Bear]

Tony Cox wrote:

> "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.

Can I suggest that avoiding turbulent air is simply the most pragmatic
approach?

It's broken enough airliners for starters !


Graham

[William W. Plummer]

Capt.Doug wrote:
>>"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.
>
>
Metal fatigue, cracks and construction defects are not caused by
turbulence although turbulence may be the straw that breaks the camel's
back when those problems exist.

IIRC the Convair Electra was the first plane that metal fatigue was
determined to be the cause of its wings coming off. And, it took
years. What caused the fatigue? Gyroscopic motion of the wings.

[Michael Houghton]

Howdy!

In article <01PLc.162096$XM6.47385@attbi_s53>,
William W. Plummer > wrote:
>Capt.Doug wrote:
[snip]
>>
>> 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

No. I've seen discussion that suggests the problem is operator error. Rolling
pullups can, apparently, generate excessive g-loads with remarkable ease.

[snip]
>>
>Metal fatigue, cracks and construction defects are not caused by
>turbulence although turbulence may be the straw that breaks the camel's
>back when those problems exist.
>
>IIRC the Convair Electra was the first plane that metal fatigue was
>determined to be the cause of its wings coming off. And, it took
>years. What caused the fatigue? Gyroscopic motion of the wings.

Not quite. Damage to engine mounts would lead to whirl mode oscillation of
the engines, which would resonate with the wing, inducing flutter, leading
to wing coming off.

yours,
Michael


--
Michael and MJ Houghton | Herveus d'Ormonde and Megan O'Donnelly
| White Wolf and the Phoenix
Bowie, MD, USA | Tablet and Inkle bands, and other stuff
| http://www.radix.net/~herveus/

[Bob Moore]

"William W. Plummer" wrote

> Metal fatigue, cracks and construction defects are not caused by
> turbulence although turbulence may be the straw that breaks the
> camel's back when those problems exist.
>
> IIRC the Convair Electra was the first plane that metal fatigue was
> determined to be the cause of its wings coming off. And, it took
> years. What caused the fatigue? Gyroscopic motion of the wings.

Turbulence most certainly is the cause of fatigue in the wing
structure of aircraft. I would suggest that you read FAR Part 25
to understand how the nature of the Standard Atmosphere and the
cruise speed is used in designing a "fatigue life" in transport
category aircraft.

"Convair Electra"??? No way...my Electra time was flown in a
Lockheed Electra..L-188 and it's US Navy derivitive the P-3 Orion.

The civilian L-188s failed early in their service life, Braniff's
Flight 542 crashed in 1959, only two months after it's delivery
from Lockheed. The Northwest Flight 710 crashed in 1960 after
only one year in service.

It was not "gyroscopic motion of the wings" nor "fatigue".......

"On May 12, 1960, Lockeed President Bob Gross announced that both
airliners broke-up due to an undampened propeller whirl mode that
produced destructive flutter of the wing."

This from the "Great Airliners Series, Volume Five, Lockheed 188
Electra" by David G. Powers.

You disappoint me William.

Bob Moore
Air Florida L-188 1973
VP-46 P-3B 1965-67