Date: November 22nd 04, 08:28 PM
From: Bob Chilcoat
Subject: Pinging Ron Wanttaja - "Unporting?"

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 (Chief Pilot, White Knuckle Airways)

Post 1:

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.


Post 2 in response to several replies that referred to unporting of fuel
tanks:

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.

Quote:

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

Date: November 23rd 04, 05:45 AM
From: Richard Isakson

"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