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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 |
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Bob Chilcoat wrote:
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. Before Ron provides you the right answer, let me offer what is probably a wrong one. This is what the internet is all about...wild ass guessing at it's finest. "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." I'm guessing that it has something to do with the flow of air between the top (high pressure) side of the elevator and the bottom through the gap between the fixed and movable pieces, which for certain geometries and separation can enter an unstable mode (flutter). How close am I? |
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On Mon, 22 Nov 2004 15:30:55 -0500, nafod40 wrote:
Bob Chilcoat wrote: 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. Before Ron provides you the right answer, let me offer what is probably a wrong one. This is what the internet is all about...wild ass guessing at it's finest. I'm guessing that it has something to do with the flow of air between the top (high pressure) side of the elevator and the bottom through the gap between the fixed and movable pieces, which for certain geometries and separation can enter an unstable mode (flutter). I'm afraid this one is well out of my area of expertise, but I think your explanation is what was going on. Perhaps the slight geometric change due to the missing bolt allowing air to leak from top to bottom and trigger flutter at an unexpected aerodynamic condition. But calling it "unporting"? I've always heard that term used to describe a condition where fuel inlets get the gas sloshed away so they suck air. My money's on Nauga to explain this one.... Ron Wanttaja |
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Bob Chilcoat asks;
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? I am an aeronautical engineer, and I've never heard that term other than in reference to fuel lines. Sounds to me like a load of hooey. ...Gann was not mechanical, and I was wondering if he got the term wrong. Sure sounds like 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..... This sounds like a very poor laymans interpretation of moving surface flutter. If a bolt was missing, then the surface (in this case, the elevator, apparently) could have more motion and less stiffness than it was designed for, and this could allow the flutter to begin at lower frequencies (speeds) than it normally would. But "unporting"??? ..... But if you had been the nervous type, if you slowed down, the center of gravity would have changed. The fact that someone thinks that the CG changes substantially with a change in speed indicates a poor understanding of both aerodynamics and terminology. People wandering around inside the plane to go to the bathroom will change the CG more than a couple of degree change in AOA. ..... 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." And what happened when the plane came in to land - it didn't slow down? They landed at cruising speed? The air density stayed the same at all altitudes that day? No change in aerodynamic inputs as the plane went from cruise to landing configuration? ..... 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." And if this could possibly be true, at all combinations of climb speeds and altitudes, cruise speed and altitude, and descent/approach speeds and altitudes, then the phrase "only possible combination" has very little meaning. If this passage is indicative of Mr. Gann's knowledge of aircraft, then I'm glad that I never read the book. -- Marc J. Zeitlin http://marc.zeitlin.home.comcast.net/ http://www.cozybuilders.org/ Copyright (c) 2004 |
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Marc J. Zeitlin wrote:
Bob Chilcoat asks; 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? I am an aeronautical engineer, and I've never heard that term other than in reference to fuel lines. Sounds to me like a load of hooey. ...Gann was not mechanical, and I was wondering if he got the term wrong. Sure sounds like 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..... This sounds like a very poor laymans interpretation of moving surface flutter. If a bolt was missing, then the surface (in this case, the elevator, apparently) could have more motion and less stiffness than it was designed for, and this could allow the flutter to begin at lower frequencies (speeds) than it normally would. But "unporting"??? ..... But if you had been the nervous type, if you slowed down, the center of gravity would have changed. The fact that someone thinks that the CG changes substantially with a change in speed indicates a poor understanding of both aerodynamics and terminology. People wandering around inside the plane to go to the bathroom will change the CG more than a couple of degree change in AOA. ..... 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." And what happened when the plane came in to land - it didn't slow down? They landed at cruising speed? The air density stayed the same at all altitudes that day? No change in aerodynamic inputs as the plane went from cruise to landing configuration? ..... 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." And if this could possibly be true, at all combinations of climb speeds and altitudes, cruise speed and altitude, and descent/approach speeds and altitudes, then the phrase "only possible combination" has very little meaning. If this passage is indicative of Mr. Gann's knowledge of aircraft, then I'm glad that I never read the book. Interesting passage on this topic. http://www.rwebs.net/avhistory/fate.htm Jerry |
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Ron Wanttaja wrote...
My money's on Nauga to explain this one.... Last time Bob asked this I think I wrote that he might have meant "uncorking," which is sometimes used to refer to a departure from controlled flight. Or maybe Gann just made something up. Somebody dig him up and ask him. Dave 'colloquial' Hyde |
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"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 |
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Richard Isakson wrote...
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." Cool answer. P&H is setting on a bookcase right behind me. Maybe I should've cracked it instead of looking for a shovel :-) Dave 'frise frame' Hyde |
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"Marc J. Zeitlin" wrote: If this passage is indicative of Mr. Gann's knowledge of aircraft, then I'm glad that I never read the book. ++++++++++++++++++++++++ Somebody needs to chill out. Barnyard BOb -- over 50 years of flight |
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Marc J. Zeitlin wrote:
If this passage is indicative of Mr. Gann's knowledge of aircraft, then I'm glad that I never read the book. Marc, I too am glad you've never read the book. It sucks. Not a single differential equation in the whole damn thing. |
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