Discussion:
1956 Loss of Boeing 377 Caused By Mishandling of Cowl Flaps
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p***@hotmail.com
2019-08-22 05:36:20 UTC
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When reading about the Boeing 377 Stratocruiser I came across mention of a
disaster involving one of these aircraft in 1956. Northwest Airlines flight 2
took off from Seattle Tacoma at 8:00 AM Pacific standard time on April 2 1956
en route to New York with stops at Portland and Chicago. Wing flaps were at
25 degrees. As the crew reduced power to climb setting and retracted the flaps
at 145 knots and about 1,000 feet altitude the aircraft experienced severe
buffeting and full right aileron was needed to maintain level flight. The
captain interpreted this as due to an asymmetrical flap condition which would
have made turning very dangerous so he decided to continue to McChord Air Force
Base in Tacoma. The aircraft was unable to maintain altitude and ditched in
Puget Sound at about 8:10. The plane remained intact and all passengers and
crew got out, but water temperature was 42 degrees Fahrenheit and four
passengers and a flight attendant drowned from presumed hypothermia by the
time a Coast Guard boat arrived 30 minutes later.

The Civil Aviation Board report on the event is available here:

https://upload.wikimedia.org/wikipedia/commons/e/e9/CAB_Accident_Report%2C_Northwest_Airlines_Flight_2_%281956%29.pdf

According to the report the actual cause was the failure of the flight engineer
to set the cowl flaps to their proper position for takeoff. On the Boeing
377 Stratocruiser, at cruise speed the cowl flaps would be set at closed
position where they would form the outer wall of a convergent nozzle ejecting
the cooling air into the slipstream for minimum drag; the entire cowling
including the air intake and internal baffling was optimized for cruise
efficiency. At takeoff and climb out the speed of the intake air was much
less than at cruise and the cowl flaps would be opened part way to allow
adequate cooling airflow under these conditions. On the ground the cowl
flaps could be fully opened for better cooling at taxi speeds and run-up,
but if the cowl flaps were fully open in flight the resulting turbulence
would seriously interfere with airflow over the wing.

Was it common for aircraft with wing-mounted radial engines to have a
fully-open position for the cowl flaps that could be safely used only
on the ground? I believe the Stratocruiser had the same wing and
Pratt & Whitney R4350 engine installation as the KC-97 tankers and
B-50 bombers; did these aircraft ever have any problems involving open
cowl flaps in flight? How about the B-29: very similar wing but different
nacelles and Curtis-Wright R3350 engines?

My thanks in advance for any replies.

Peter Wezeman
anti-social Darwinist
Scott Kozel
2019-08-22 11:00:11 UTC
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Post by p***@hotmail.com
When reading about the Boeing 377 Stratocruiser I came across mention of a
disaster involving one of these aircraft in 1956. Northwest Airlines flight 2
took off from Seattle Tacoma at 8:00 AM Pacific standard time on April 2 1956
en route to New York with stops at Portland and Chicago. Wing flaps were at
25 degrees. As the crew reduced power to climb setting and retracted the flaps
at 145 knots and about 1,000 feet altitude the aircraft experienced severe
buffeting and full right aileron was needed to maintain level flight. The
captain interpreted this as due to an asymmetrical flap condition which would
have made turning very dangerous so he decided to continue to McChord Air Force
Base in Tacoma. The aircraft was unable to maintain altitude and ditched in
Puget Sound at about 8:10. The plane remained intact and all passengers and
crew got out, but water temperature was 42 degrees Fahrenheit and four
passengers and a flight attendant drowned from presumed hypothermia by the
time a Coast Guard boat arrived 30 minutes later.
I have wondered before why maintaining full power would cause dangerous levels
of buffeting, so much so that power had to be reduced to a level that would
not maintain altitude.
Jeff Crowell
2019-08-22 14:20:23 UTC
Permalink
Post by Scott Kozel
I have wondered before why maintaining full power would cause dangerous
levels of buffeting, so much so that power had to be reduced to a level
that would not maintain altitude.
Disturbed air is very disruptive--turbulent flow over the wing would
dramatically reduce lift (which depends on smooth airflow at all times), not to mention causing significant buffeting if it also impinged the tail surfaces. The left wing dropping badly enough to require full aileron makes me wonder if the cowl flap issue was only present on one side. You'd expect the problem to at least be symmetrical otherwise.

What I find odd is that the captain would refuse to add power as he was in the process of crashing due to insufficient altitude (smacks of the crash at Washington National in '82, when an iced-over EPR input caused the crew to take off at far below normal takeoff power, and they mushed into a highway bridge and died without ever mashing the throttles full forward. I mean, at that point, what do you have to lose?

Though in his defense, ditching under control beats rolling over at 50 feet due to the flaps being mismatched!


Jeff
--
Old soldiers never die. Young ones do.
Scott Kozel
2019-08-22 19:06:50 UTC
Permalink
Post by Jeff Crowell
Post by Scott Kozel
I have wondered before why maintaining full power would cause dangerous
levels of buffeting, so much so that power had to be reduced to a level
that would not maintain altitude.
Disturbed air is very disruptive--turbulent flow over the wing would
dramatically reduce lift (which depends on smooth airflow at all times), not
to mention causing significant buffeting if it also impinged the tail
surfaces. The left wing dropping badly enough to require full aileron makes me
wonder if the cowl flap issue was only present on one side. You'd expect the
problem to at least be symmetrical otherwise.
What I find odd is that the captain would refuse to add power as he was in the
process of crashing due to insufficient altitude (smacks of the crash at
Washington National in '82, when an iced-over EPR input caused the crew to
take off at far below normal takeoff power, and they mushed into a highway
bridge and died without ever mashing the throttles full forward. I mean, at
that point, what do you have to lose?
The NTSB report has a diagram that shows an about 20 degree nose up attitude
while the stickshaker was activating. Would adding full power make the pitchup
even worse and add to the tendency to stall?
Post by Jeff Crowell
Though in his defense, ditching under control beats rolling over at 50 feet
due to the flaps being mismatched!
The CAB report says that the flight engineer basically mismanaged the cowl flap
settings thruout the short flight, and while the captain and first officer
could have seen them thru the windows, that they were busy and trusted what
the flight engineer was telling them.

Also, quote, "The captain was faced with a series of adverse conditions, such as
low ceiling and unfavorable terrain, and it was his belief and decision that
ditching was the safest action since he was convinced that any attempt to
continue flight would result in complete loss of control of the aircraft."

I got a B-377 book at the USAF museum recently, and it discussed how
incredibly complicated were those large 4-engine piston aircraft, and how the
B-707 as introduced in the 1950s had less than 1/2 of the engine instruments
on the FE panel as compared to the B-377.

Also I didn't realize how large the flight crew was on the B-377. In addition
to the two pilots and FE, a navigator and radio operator as well.
Scott Kozel
2019-08-22 19:08:20 UTC
Permalink
NWA 2
https://upload.wikimedia.org/wikipedia/commons/e/e9/CAB_Accident_Report%2C_Northwest_Airlines_Flight_2_%281956%29.pdf

AF 90
https://www.ntsb.gov/investigations/AccidentReports/Reports/AAR8208.pdf
p***@hotmail.com
2019-08-24 05:03:09 UTC
Permalink
Post by Scott Kozel
Post by p***@hotmail.com
When reading about the Boeing 377 Stratocruiser I came across mention of a
disaster involving one of these aircraft in 1956. Northwest Airlines flight 2
took off from Seattle Tacoma at 8:00 AM Pacific standard time on April 2 1956
en route to New York with stops at Portland and Chicago. Wing flaps were at
25 degrees. As the crew reduced power to climb setting and retracted the flaps
at 145 knots and about 1,000 feet altitude the aircraft experienced severe
buffeting and full right aileron was needed to maintain level flight. The
captain interpreted this as due to an asymmetrical flap condition which would
have made turning very dangerous so he decided to continue to McChord Air Force
Base in Tacoma. The aircraft was unable to maintain altitude and ditched in
Puget Sound at about 8:10. The plane remained intact and all passengers and
crew got out, but water temperature was 42 degrees Fahrenheit and four
passengers and a flight attendant drowned from presumed hypothermia by the
time a Coast Guard boat arrived 30 minutes later.
I have wondered before why maintaining full power would cause dangerous levels
of buffeting, so much so that power had to be reduced to a level that would
not maintain altitude.
As I understand it, the buffeting on the Boeing Stratocruiser and I suspect
on the KC-97 occurs when the wing flaps are retracted and the engine cowl
flaps are open to an extent that was not intended to be used in flight.
It would seem that the cowl flaps act as spoilers to initiate flow
separation which spreads downstream along the surface of the wing.
Here is the third paragraph of the CAB report:

"Takeoff was made on runway 20 and the flight climbed to an altitude of 1,000
to 1,200 feet. At this time power was reduced and the wing flaps, which had
been set at the normal takeoff position of 25-degrees, were retracted at an
airspeed of 145 knots. Immediately the crew became aware of severe buffeting
and a strong tendency of the aircraft to roll to the left. Because the
buffeting began immediately after the flaps were retracted, the captain
believed that it was due to a split flap condition, i.e., the wing flaps on
one side being retracted while the flaps on the other side remained partially
or fully down. Power was reduced momentarily in an attempt to alleviate the
buffeting but this was not effective and maximum continuous power was again
restored. After being cleared by the Seattle tower for return, the pilot
decided not to turn the aircraft because of control difficulty and advised
that he would proceed to McChord Air Force Base at Tacoma. Thereafter, the
captain testified the trouble became worse and the aircraft continued to lose
altitude. The captain elected to ditch and did so at approximately 0810."

From this, it appears that they tried reducing power to see if this would
reduce the buffeting, but it didn't and they quickly returned the throttles
to maximum continuous power and maintained that setting until touchdown,

I wonder if ground effect might have allowed the aircraft to continue flying
as it descended to within a half wing span of the water. During World War 2
in the Pacific badly damaged American bombers were sometimes able return to
allied territory by flying in ground effect when the combination of lost
engines and drag from battle damage prevented them from flying at altitude.
A good flight simulator could determine if this was possible.

Peter Wezeman
anti-social Darwinist

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