Destruction due to turbulence when below Va - how?

"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.

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.)

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

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.

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/

"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