Unporting?

[Bob Chilcoat]

I was reading Gann's "Fate is the Hunter" again the other day, and was
curious about the incident in the last chapter where he unintentionally and
naively avoided disaster by NOT slowing down when the DC-4 he was flying
from Hawaii to Burbank developed an unexplained occasional vibrational
"shudder". Later an engineer called him a very lucky pilot, and described
to him a scenario that he called "unporting" which was an uncontrolled dive
caused by lose of "balance" between the fixed and movable parts of the
stabilizer, which could not be recovered from. His plane had a missing
hinge bolt in the stabilizer, and had he reduced power, which was the
natural reaction to an unknown vibration, this "unporting" would have
occurred. Another plane on the same day crashed from the same phenomenon,
and all DC-4's were grounded worldwide immediately afterwards once this
phenomenon was understood.

My interest is the word "unporting". It doesn't sound right. I'm an
engineer (biomedical), but not an aeronautical engineer. You aerospace
engineers out there, is this the right term? Gann was not mechanical, and I
was wondering if he got the term wrong. If not, can someone explain how the
term is (or was, back then) used in aeronautical engineering? What is the
"port" it refers to? I'm curious.

--
Bob (Chief Pilot, White Knuckle Airways)

I don't have to like Bush and Cheney (Or Kerry, for that matter) to love
America

[Aardvark]

Bob Chilcoat wrote:

> I was reading Gann's "Fate is the Hunter" again the other day, and was
> curious about the incident in the last chapter where he unintentionally and
> naively avoided disaster by NOT slowing down when the DC-4 he was flying
> from Hawaii to Burbank developed an unexplained occasional vibrational
> "shudder". Later an engineer called him a very lucky pilot, and described
> to him a scenario that he called "unporting" which was an uncontrolled dive
> caused by lose of "balance" between the fixed and movable parts of the
> stabilizer, which could not be recovered from. His plane had a missing
> hinge bolt in the stabilizer, and had he reduced power, which was the
> natural reaction to an unknown vibration, this "unporting" would have
> occurred. Another plane on the same day crashed from the same phenomenon,
> and all DC-4's were grounded worldwide immediately afterwards once this
> phenomenon was understood.
>
> My interest is the word "unporting". It doesn't sound right. I'm an
> engineer (biomedical), but not an aeronautical engineer. You aerospace
> engineers out there, is this the right term? Gann was not mechanical, and I
> was wondering if he got the term wrong. If not, can someone explain how the
> term is (or was, back then) used in aeronautical engineering? What is the
> "port" it refers to? I'm curious.
>
> --
> Bob (Chief Pilot, White Knuckle Airways)
>
> I don't have to like Bush and Cheney (Or Kerry, for that matter) to love
> America
>
>

Here is a page about that book ... no answer but an ok read.
http://rwebs.net/avhistory/fate.htm

On other pages I found this ....

"The tank design is such that the fuel will feed into the sumps in all
flight attitudes. The only known condition which would tend to favor an
unporting is in a prolonged = descent with just a few gallons in the tank."

"A very good feature of the fuel system is that the tanks incorporate a
'slosh bay', which precludes the possibility of the fuel pick-up
unporting should the aircraft be held in a prolonged sideslip."

ww

[Don Tuite]

On Tue, 16 Nov 2004 23:47:15 -0500, Aardvark
> wrote:

>Bob Chilcoat wrote:
>
>> I was reading Gann's "Fate is the Hunter" again the other day, and was
>> curious about the incident in the last chapter where he unintentionally and
>> naively avoided disaster by NOT slowing down when the DC-4 he was flying
>> from Hawaii to Burbank developed an unexplained occasional vibrational
>> "shudder". Later an engineer called him a very lucky pilot, and described
>> to him a scenario that he called "unporting" which was an uncontrolled dive
>> caused by lose of "balance" between the fixed and movable parts of the
>> stabilizer, which could not be recovered from. His plane had a missing
>> hinge bolt in the stabilizer, and had he reduced power, which was the
>> natural reaction to an unknown vibration, this "unporting" would have
>> occurred. Another plane on the same day crashed from the same phenomenon,
>> and all DC-4's were grounded worldwide immediately afterwards once this
>> phenomenon was understood.
>>
>> My interest is the word "unporting". It doesn't sound right. I'm an
>> engineer (biomedical), but not an aeronautical engineer. You aerospace
>> engineers out there, is this the right term? Gann was not mechanical, and I
>> was wondering if he got the term wrong. If not, can someone explain how the
>> term is (or was, back then) used in aeronautical engineering? What is the
>> "port" it refers to? I'm curious.
>>
>> --
>> Bob (Chief Pilot, White Knuckle Airways)
>>
>> I don't have to like Bush and Cheney (Or Kerry, for that matter) to love
>> America
>>
>>
>
>Here is a page about that book ... no answer but an ok read.
>http://rwebs.net/avhistory/fate.htm
>
>On other pages I found this ....
>
>"The tank design is such that the fuel will feed into the sumps in all
>flight attitudes. The only known condition which would tend to favor an
>unporting is in a prolonged = descent with just a few gallons in the tank."
>
>"A very good feature of the fuel system is that the tanks incorporate a
>'slosh bay', which precludes the possibility of the fuel pick-up
>unporting should the aircraft be held in a prolonged sideslip."
>
>ww
I understand that the Luscombe 8A, with the fuselage tank behind the
cabin was placarded for all takeoffs with carb heat on. The reason
was to reduce engine power to prevent too steep a pitch angle on
climb-out, which would unport the fuel outlet in the tank.

I got the story from a guy I knew at the FBO, a LA motorcycle cop who
knew a fellew officer who'd been killed taking off from Agua Dulce in
a departure stall that the NTSB said was caused by such a chain of
events. We talked about it because my friend was a part-time CFI and
because the FBO had an 8E.

Don

[Bob Chilcoat]

I'm well aware of the use of the term "unporting" to describe loss of fuel
flow from a tank because of low quantity, perhaps coupled with a slip or
high angle of attack.

The use of the term I was curious about was to describe an aerodynamic
condition at the stabilizer that caused loss of control. See the quote from
the book below.

--
Bob (Chief Pilot, White Knuckle Airways)

Then he sat beside me and drew out a pencil. And while he talked, he made
notations and diagrams on the tablecloth, each line and figure neatly set
down after his hands had flown their interpretation. He began by saying
that my written report on the suspected vibration had been a masterpiece of
innocence. He stated flatly that if I had any training as an engineer, I
would never have had the opportunity to write it. It seemed that only a
most remarkable series of causes and effects had kept us from duplicating
the catastrophe of Bainbridge. The aura of fantasy was compounded when we
considered both had occurred on the same day.

"Did You know we grounded every DC-4 in the world because of you?" he asked.

"I've been sailing."

"Never giving a thought to vibration, of course."

"No."

"Thank you for completing my picture of blessed ignorance." He frowned and
his hands fluttered uncertainly. "But I will never understand your
nonchalance. Listen to me very carefully. I've spent too much time on this
investigation to miss the finale."

It soon became obvious that Howard's detective work had included my personal
anticipations. Even what I had said to the crew and passengers had been
remembered and considered.

"Although we can never be absolutely certain, we now believe the Eastern
Airline crash at Bainbridge was caused by unporting. Do you know what that
is?"

I confessed that I had never heard of it.

"Unporting is the balance destruction of the elevators by aerodynamic force.
I won't confuse you with theory, but if enough separation between the fixed
and the balance portion of your elevators occurs, your airplane will go
into a vertical dive or even beyond the vertical, and no two men in the
world are strong enough to bring it out. This can be caused by a missing
hinge bolt."

He sighed heavily and drew wavelike lines on the table, then an airplane
diving for the lines. He sketched another airplane more precisely and
marked its approximate center of gravity:: slow down when you first noticed
the vibration? You did not because you had no fear of it. But if you had
been the nervous type, if you slowed down, the center of gravity would have
changed. That would have been quite enough to complete the process of which
had partially begun."

"The vibration really wasn't very bad."

"It doesn't take much. But let us assume another pilot would have
reacted in the same way. It would only have postponed the inevitable. As
soon as the time came for a normal power reduction and it was accomplished,
unporting would begin. But not you. In the past you had lost all four
engines so many times, the prospect of losing one gave you relatively little
concern. So you sat there, fat, dumb, and happy, and you cancelled all
power reductions. This brilliant decision saved your life the first time
that day."

I could think of nothing to say but a series of well. well's.

"This was not enough," he said, and I saw that he was exasperated. "You
landed at Burbank and disembarked twenty-one passengers. God alone knows
why, but you took on just enough fuel to make up the difference in losing
their weight. Even so your center of gravity would have changed enough so
that unporting was more likely than not. But."

He moved a third finger up beside the others.

"You were in a hurry to reach Oakland so you could go about your silly
sailing. As a result, and don't deny it because the figures are in the
logbook, you used full gross weight cruising power all the way and your
speed was correspondingly high." He paused, touched at his moustache, and
stared at me incredulously. Then he spoke very slowly, clipping off each
word as if he intended to impress them on my memory forever. "I would look
at you quite differently if I thought you had planned what we eventually
discovered. We had some long sessions with our slide rules and we found, my
friend, that you had arranged the only possible combination of power, speed
and weight which would blockade the chances of unporting."

Later, when the wine had mellowed us both, I asked Howard if his slide
rule could measure the fate of one man against another's.



Fate is the Hunter

Ernest K. Gann

1961

[John Galban]

"Bob Chilcoat" > wrote in message >...
>
> My interest is the word "unporting". It doesn't sound right. I'm an
> engineer (biomedical), but not an aeronautical engineer. You aerospace
> engineers out there, is this the right term? Gann was not mechanical, and I
> was wondering if he got the term wrong. If not, can someone explain how the
> term is (or was, back then) used in aeronautical engineering? What is the
> "port" it refers to? I'm curious.

I'm stumped. The only references to "unporting" that I know of are
conditions in a fuel or oil system when the plane's attitude causes
the port or pickup to be exposed to air. Never heard of an airframe
reference like that. Looking over the description, it sound more
like he was describing "flutter" of a control surface.

John Galban=====>N4BQ (PA28-180)

[Morgans]

"John Galban" > wrote

> I'm stumped. The only references to "unporting" that I know of are
> conditions in a fuel or oil system when the plane's attitude causes
> the port or pickup to be exposed to air. Never heard of an airframe
> reference like that. Looking over the description, it sound more
> like he was describing "flutter" of a control surface.
>
> John Galban=====>N4BQ (PA28-180)

Sounds more like blaketing? to me, when the surface is in an area that is
not receiving flow, because of a surface blocking the flow before it.
--
Jim in NC


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[Bob Chilcoat]

FYI, I posted this question over on RAH, and got this explanation. Sounds
right.

--
Bob (Chief Pilot, White Knuckle Airways)


Subject: Re: Pinging Ron Wanttaja - "Unporting?"
"Richard Isakson" > wrote in message
...
> "Bob Chilcoat" wrote in message ...
> > Ron,
> >
> > I posted this over on RAP but apparently managed to stump everyone. I
> > thought that perhaps some of your contacts at Boeing might know if this
> > word, "unporting" was misused by Gann, or is an old term that is no
longer
> > used. It just doesn't sound right to me.
>
> Bob,
>
> The term was properly used. In this context, unporting means moving the
> leading edge of an elevator counter weight from behind the horizontal
> stabalizer into the free stream. Think of a frise style aileron. Most of
> the Cessnas have them. They have a sharp leading edge placed down at the
> bottom of the surface. As soon as you move the wheel to deflect the
> aileron up the leading edge deflects down (unports) into the flow off the
> bottom of the wing.
>
> From Perkins and Hage "Airplane Performance Stability and Control": "The
> pure frise type aileron is characterized by an asymetrical sharp nose
> located on the airfoil lower surface so that it will unport as soon as the
> control is deflected upward."
>
> In Gann's case, the elevator must have had a part of the elevator leading
> edge that was ahead of the rest of the leading edge. This would be both
for
> static and aerodynamic balance. Normally, in high speed flight the tail
is
> loaded so that it is not deflected very much. The balance would be hiding
> behind the stabilizer and wouldn't cause much of a load on the tail. Had
> Gann slowed down it would have been necessary to increase the deflection
of
> the elevator to keep the airplane balanced. Eventually the balance would
> have unported causing a large load on the elevator. With the bolt gone,
the
> elevator would have bent causing an even greater download on the tail and
so
> on until either the surface failed or the airplane departed from
controlled
> flight.
>
> Rich
>
>

[Greg Esres]

<<FYI, I posted this question over on RAH, and got this explanation.
Sounds right.>>

Except that the poster confused the counterweight with the aerodynamic
balance.

The counterweights are there to prevent flutter, not to make the
controls easier to move.