1. WeedWhacker

    WeedWhacker Senior Member

    No, that also is not flutter. Mach buffet.
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  2. Keith Beachy

    Keith Beachy Active Member

    Playing the Vd definition by a journalist card, which is not based on the real definition is not good for much. Using a journalistic piece as an expert is not going to hack it.

    1.2Vd is the design 767 was under. Thus the fake Vg diagram fails, since the curves are not for a 767. And there is no structural failure speed for a 767. Never will produce a source from Boeing for the structural failure zone you made up in the fake Vg diagrams for a 767.

    Can you explain the Gish Gallop, "in equivalent airspeed at both constant Mach number and constant altitude", and why this only means a lack of aeronautical engineering knowledge? A detailed explanation is in order.

    Who can supply proof a 767 was not designed to meet the 1.2 Vd specification as required? It looks like the OP is right, and has supporting evidence, with real requirements.
    Last edited by a moderator: Apr 7, 2014
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  3. jaydeehess

    jaydeehess Senior Member

    A piece of the aircraft did come loose. However, that was the test flight AND it was redesigned to address that problem. The production model, after test flight certification, would not do the same thing.

    Note also that 0.96M +15% would be above 1.0 M so that would not apply.

    However, we have also seen a 727 hit 0.96M WITH one slat extended and still manage to land despite this being well over Vd for a 727 let alone for one so oddly configured.
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  4. WeedWhacker

    WeedWhacker Senior Member

    Yes, I know. A fairing on the fuselage. Not a structural component (as "SpaceCowboy" would seem to have inferred). And as you said, it was addressed so that in production, the problem would not re-cur (not that the full production fleet were ever expected to achieve those Mach speeds anyway, in normal use).

    While on the subject of "structural damage" (the term so often touted) this seems to have been a moving goalposts sort of concept, for the PfT. For airplanes, "structure" is specifically designated when determining whether any extant damage to an airplane (aircraft) is an "Incident" or an "Accident", by definition.

    For instance, ding the wingtip? "Incident". An inspection panel that is improperly secured, and comes off in flight? "Incident". These items are part of the over-all 'structure', yes...but NOT critical STRUCTURE.

    For reference, there are (U.S.) NTSB definitions (49 CFR Part 830)

    A narrative explanation (emphasis added):

    And, specifics:
    There are various other criteria that immediately trigger the term "Accident", even if there is no aircraft damage related...such as the death or severe injury to a person.

    But, those other criteria are not the question, here.
    • Informative Informative x 1
  5. jaydeehess

    jaydeehess Senior Member

    I stated:
    The regs as applies to the Airbus: ( bolding mine)
    Last edited: Apr 7, 2014
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  6. deirdre

    deirdre Moderator Staff Member

    the whole pft concept is silly anyway. theres no point in building a specially strong plane to crash into a building when it's easier to just teach the kamikaze pilot how to fly the plane properly.
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  7. jaydeehess

    jaydeehess Senior Member

    Wasn't an F-4 Phantom a subsonic fighter but quite capable of going above Mach 1 in a dive? Doesn't apply to thread but seems to me I read that when I was a kid( which at my present age, means some time before I hit 30)
  8. jaydeehess

    jaydeehess Senior Member

    Further to that, PfT makes the claim it was done so in order to get the plane to NYC before the interceptors. However flight 175 slowed down after being hijacked. They could have avoided having to modify an aircraft by simply pushing to max cruise speed and staying there until lined up with WTC 2.

    Just more ridiculousness from the pilots for truth
  9. WeedWhacker

    WeedWhacker Senior Member

    Really? I had not yet seen that latest stretch of the truth. Just making it up as 'they' go along, huh? :rolleyes:
  10. jaydeehess

    jaydeehess Senior Member

    It was a while ago, let me see if I can find it again. I'm at home with a bad cold so I have time on my hands and daytime TV sucks.
  11. Jazzy

    Jazzy Closed Account

    Certainly not. http://en.wikipedia.org/wiki/McDonnell_Douglas_F-4_Phantom_II
  12. WeedWhacker

    WeedWhacker Senior Member

    "Jerry! Jerry! Jerry!"
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  13. jaydeehess

    jaydeehess Senior Member

    Not an ice pellet's chance in a well known hot place that I would allow my TV to go there :)
    • Funny Funny x 1
  14. jaydeehess

    jaydeehess Senior Member

    OK, in the video "9/11 Intercepted" at time approx 20:20 the narrator asks "Was this aircraft modified to beat Otis fighters to its target..."
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  15. Mick West

    Mick West Administrator Staff Member

    Just added the following to the OP:
    Does Vd vary with altitude?

    Yes, however the Vd limit of 420 Knots is the Calibrated Airspeed (essentially the same as the indicated airspeed) , which is the same as the true airspeed at sea level. The FAA certification document says:

    Note that Vd is a certification speed, not an actual operating limit, so it does not show up in the 767 flight manual. However the lower speed Vmo does:

    closer in for clarity:


    Notice the Vmo is a constant indicated airspeed below 26,000 feet. This means that the Vmo of a 767 is 360 knots at sea level. The same applies to Vd, meaning Vd of a 767 is 420 knots at sea level.
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  16. WeedWhacker

    WeedWhacker Senior Member

    Yes, for large commercial airliners (in my experience) there is always a pressure altitude where some parameters switch from Vxx to Mxx (the 'xx' as a placeholder for any appropriate designation).

    Although the chart (great find, BTW!! Man, I've hunted to no avail to find online sources!) is labelled for the -300 variant, there should be no differences at all between the -200 and it, in terms of that graphed chart. (Except of course, for any MZFW or MTOW references**).

    (** 'MZFW' = "Max. Zero Fuel Weight" 'MTOW' = "Max. TakeOff Weight")

    (Keep in mind that we see a LOT of such charts when related to large commercial airplanes {{and of course, they are biased towards pounds, etc...which I am used to. Other operators who purchase airplanes receive data already in metric units, for their convenience}}. As compared to relatively less complicated smaller airplanes that a student pilot might encounter early in his/her training. However, the principles in displaying data are the same, even if the variables become more complicated.)
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  17. jaydeehess

    jaydeehess Senior Member

    Given that this is a forum that sets out to address scientific and technical claims , and this thread concerns the claimed by Pilots for 9/11 Truth wrt flight 175 and aircraft exceeding their Vd;
    Given that no PfT member is willing to detail , on this forum, their claim or adequately address issues raised here;

    What is being said in the PfT forum that could be considered response to these issues?

    From a discussion on that forum;
    Another poster also has an opinion concerning Vd and Balsamo again responds :
    Had SpaceC replied to the issue as above, agreeing with the first poster that the shallow dive and increasing speed of AA175 negate the flight certification standard, (which i personally indicated in this forum, appeared to be the stance of pft) and stating that while a new aircraft may need to meet such criteria, it cannot be said to still apply to a 20 year old in service aircraft, that I expect would have not been diverted to the Rambles thread.

    So, debate may now move to these claims.
  18. jaydeehess

    jaydeehess Senior Member

    My take on flutter as a resonance phenomena:
    We have seen discussion that refers to damping and excitation but how to explain these concepts?

    Let's take a simpler set up:
    Imagine a long rope hanging plumb and anchored at the ground. It is under no tension or load, other than its own weight generating a tension in the rope. A slight wind is applied and the rope will respond with a slight deflection. Keep that wind steady and the deflection will remain constant. Slowly and steadily increase that wind and a greater lateral force will cause greater deflection and no fluttering will be likely to develop until a very high wind is being applied.

    However, now do this again but at regular intervals "pluck" the rope. This is an excitation. Similarly you could have a wind gust apply the excitation. This excitation itself would have various parameters, amplitude, rapidity of onset(akin to frequency) and location of excitation along the rope.
    There will be combinations of excitation states and lateral load that will introduce a resonant fluttering of the rope.

    Now alter the set up by putting a tension load on the rope and repeat all of the above.
    This will reduce the combinations that result in flutter. The loading has introduced another damping effect.

    On an aircraft there are numerous and various parts on the air frame that will respond independently to the air flow , excitations and have differing types of damping. In level flight at constant Mach number with all expected excitations, the aircraft must not experience flutter at least until Vd plus 15% ( 20% was in effect at the time of flight certification of the 767).
    So, what of increasing speed and decreasing altitude?
    Descent removes loading and decreases damping.
    Increasing speed however increases loading thus increasing damping

    What of manoeuvering?
    Thus increases loading and damping but also alters air flow over varying surfaces.
    So any particular surface sees a constantly changing set of parameters, loading, and air flow speed and direction. Any particular surface may experience conditions that would introduce destructive resonances but with changing conditions may rapidly move out of those conditions.
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  19. jaydeehess

    jaydeehess Senior Member

    Now, what about the effect of age on an airframe?

    Mr. Balsamo seems to forget that aircraft must undergo constant checks to ensure no adverse structural effects. This year Boeing 727s were required to increase frequency of inspections of their wing components to ensure that micro fractures have not developed.
    These are not private passenger automobiles, "beaters" ready to drop parts or break down due to age. There are still DC-3s, and Norseman aircraft flying that are as old or older than I am and still in very good shape( wish I could say the same for me). Those that aren't have been removed from commercial operations.

    So, we must accept that if an aircraft is in passenger carriage, commercial operation, it also meets continuing flight certifications and is at least close to the new aircraft pristine condition it was in when it rolled out of the Boeing plant.

    Is it still good to Vd +20%? Quite possibly not.
    Vd of the 767, 420 knots was it?
    20% = 84 knots
    10% = 42 knots
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  20. jaydeehess

    jaydeehess Senior Member

    Seems to me that some PfT members had things to say about twa841 as well. Perhaps I'll look for that as well since all SpaceC could do was flatly deny what I said about the NTSB report and the data on the fdr, was true.

    Incidentally this is by far the most time I have spent viewing PfT forums for many years. Robby gets one of his wishes, my visits are increasing his traffic stats incrementally.:(
  21. Keith Beachy

    Keith Beachy Active Member

    "in equivalent airspeed at both constant Mach number and constant altitude"

    Posting this, and they are unable to explain. Then post the airbus test in a dive, and self-debunk. Making up silly claims based on nonsense.

    To say an aircraft built to specifications can't live up to the specifications later is nonsense.
    To say the specifications don't apply to a real aircraft flying is extra credit nonsense.
    Last edited: Apr 8, 2014
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  22. Mick West

    Mick West Administrator Staff Member

    It's interesting that that while the regs for Flutter and divergence prevention say "at both constant Mach number and constant altitude", the flutter testing is actually done in a shallow dive, and with the speed gradually increasing.

    Of course you can't actually just magically fly a plane at Vd, you need to accelerate up to that speed. Nor can you instantly fly a plane at Vd+20%. So a plane being safe up to Vd+20% must logically encompass the process of actually getting to that speed. The only way of doing this would be to accelerate, possibly in a shallow dive.

    These are additional details though. The basic claim of Vd being a hard limit with no safety margin has been debunked. I really don't think we want to waste too much time debunking "claims" that we have to infer from passing comments on other boards. Especially on page 3, which very few people will read.
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  23. Keith Beachy

    Keith Beachy Active Member

    The constant stuff is what you see in aeronautical engineering. This will not be explained by pilots for truth, they avoid reality based sources.

    When you find technical work on flying, the charts are done for constant altitude and constant mach. They make little sense to pilots for truth, and doubt they read technical aeronautical engineering work. This anti-intellectual approach is reflected in the fake 767 Vg diagram.
    No need to study pilots for truth forum for knowledge on flying. What can you learn visiting pftf, someone was projecting the term ghost town.
    • Agree Agree x 2
  24. jaydeehess

    jaydeehess Senior Member

    I see that a possible confusion was set up in my first line of post 98.
    It should have read:
    . The following three paragraphs being simple demonstrations of resonance, which is a concept far from exclusive to aircraft, and I thought might be better envisioned in a simpler scenario.

    The next paragraphs was my attempt to bring it back to airframe application and my intent was to illustrate that there are many factors involved in the effects on an airframe at such high speeds.
    In fact of course, this even applies to slower speeds as demonstrated by one aircraft suffering a catastrophic loss of vertical stabilizer on take off due to pilot commands that generated huge forces on that component.

    The regs seek to simplify conditions. While there is no guarantee that an aircraft will survive Vd+20% under complex conditions of flight, it is to survive under the specific conditions set out in the regulations and thus to offer some level of certainty of airworthiness at the edges of the normal flight envelope.

    As Mick states, Vd is not published in the pilot's manuals from Boeing. Pilots are not supposed to fly in that realm. That is not to say they cannot, only that they do not have the blessing of Boeing nor the legal permissions of their license, to do so.

    Two scenarios can cause an aircraft to enter this realm though; first and most common is by accident such as was the case for TWA841 (although the accident was very possibly caused by flight crew actions)
    ; the second is a pilot who has decided to ignore the stipulations of flight rules, as in the case of EA990 or all four Sept. 11/01 aircraft.

    The certification regs offer some level of certainty, but no guarantee, that an aircraft at Vd or Vd+20% will survive, but it is also erroneous to state that an aircraft definitely will not survive that single condition within the context of the complex conditions of real life situations.

    In my simple illustration of resonance effects I did not intend to imply that manoeuvering or a shallow dive would or should impart better airframe survivability. It would be great folly to rely on such a principle. However a combination of relatively slowly changing flight conditions could ( not "would", not "should") in fact aid in keeping it intact over a short period of time.
    The 9/11 terrorist pilots had no concern with the stipulations of commercial pilots license, nor did they have much concern in the continued airworthiness of the aircraft. What concern they did have wrt the later, would decrease the closer to the target they got.
    They had no intention of trying a go around, hitting well off center....good enough,,, having the plane tear apart in the last ten seconds while trying to manouver on target at full power,,,, good enough,,, deliberately pounding into the Earth in order to not allow passengers into the cockpit,,,, good enough.
    Last edited: Apr 10, 2014
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  25. TWCobra

    TWCobra Senior Member

    My take on it is that it the margins must apply till the end of the designated "fatigue life" of the airframe. Typically this life is defined as a maximum number of hours and flight cycles.

    This would infer some significant over-engineering by the manufacturer in order to achieve this; something that appears to be the case in the examples we have looked at.

    It is interesting to note the margin between VMO and Vd for the A330. VMO is 330 and Vd is 365 KEAS. Only 35 knots compared to 60 for the slightly smaller 767.

    The question I would pose to P4T is that; does this reduced margin on the Airbus mean that Airbus build much weaker airframes than Boeing, or does it represent the result of changed requirements for the regulatory calculation of Vd due to the advent of Fly-by-wire control systems?
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  26. WeedWhacker

    WeedWhacker Senior Member

    There is STILL an open invitation for member "BlindIdiots" to return and post, here, and respond.

    Much information has been presented here, freely and accurately.
  27. inam56

    inam56 New Member

    The FAA 25.629 Figure 1A for SpaceC/Balsamo

    [...] the design dive speed (VD) and design dive Mach number (MD) versus altitude envelope enlarged at all points by an increase of 15 percent in equivalent airspeed at both constant Mach number and constant altitude. Figure I A represents a typical design envelope expanded to the required aeroelastic stability envelope.
    • Agree Agree x 2
  28. Efftup

    Efftup Senior Member

    I know this is an old comment but I just saw it. An F4 Phantom was capable of Mach 2.2.
    But there was probably at least one plane that WAS exactly as you described. a spitfire would get reasonably close,(one got to 0.92 mach once although the propeller did break off in the process)

    you were probably thinking of something like the F86 Sabre. That would seem to fit the bill quite well.
    • Agree Agree x 1
  29. jaydeehess

    jaydeehess Senior Member

    Yeah possibly the F86 I was conflating with the F4 for some odd reason.
  30. inam56

    inam56 New Member

    Yes, you admit that VD is not a structural limit "at constant mach and altitude" and that the FAA certification includes a check of zero flutter at 1.2VD in this case ?

    We are talking about VD, the FAR 25.629 certification of VD and aeroelastic stability, not the 9/11 planes.
    The debate first concerns your lies about : VD is a structural limit.
    You are trying to confuse us about the 767 VD certification in 1982 and the 9/11 events !

    So, after recognizing that VD is not a structural limit "at constant mach and altitude", can you explain us the figure 1A of the FAR 65.269 posted above (#107), the sea level line and C' value ?
  31. jaydeehess

    jaydeehess Senior Member

    While he may very well read posts on this forum, SpaceCowboy no longer posts here after having his derriere handed to him. (though he would probably characterize it as an inability to convince his detractors that they are all stupid)

    His avatar shows his status as "banned"
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  32. Mick West

    Mick West Administrator Staff Member

  33. inam56

    inam56 New Member

    Hi Mick

    My posts here are still read by Balsamo !

    And it's link metabunk to his forum and shows he always answer the same thing to any question : constant mach and altitude .. and the A380 flutter video.

    i'll create a login on his forum.
  34. WeedWhacker

    WeedWhacker Senior Member

    He still posts that? I used to also....except when he posts it he claims it shows "structural damage". It doesn't. The piece that breaks in the first part of that vid is a fairing, not a structural member. It merely needed to be re-designed to provide a more smooth airflow, so that in subsequent flutter tests it doesn't....flutter.

    But of course, P4T mis-represents (as usual).
  35. jaydeehess

    jaydeehess Senior Member

    I referred to the roll through 360 degrees, of this a/c, as a barrel roll. I see lately that this is not specifically accurate. It more resembles an aileron roll though in both cases that would imply starting and finishing at the same altitude.
  36. WeedWhacker

    WeedWhacker Senior Member

    A "barrel roll" is (typically, when done correctly and intentionally) is a constant positive (+) 1-G maneuver.

    An "aileron roll" can have negative (-) G forces at the inverted stage of the maneuver.
  37. jaydeehess

    jaydeehess Senior Member

    The 727 did more of an uncontrolled, diving, stuck slat roll. Probably not something anyone would care to repeat.
  38. WeedWhacker

    WeedWhacker Senior Member

    Yes, indeed. You are correct, here. HOWEVER, the other claims that you have made remain: That airplane greatly EXCEEDED any design "specs" (and of course the "aerobatics" were unintentional....I can explain the circumstances that led up to these "gyrations", but in another thread, perhaps).

    POINT is....multiple G-force excursions, well beyond typical FAA (or ICAO) certification "standards". Yet?? Airframe stayed intact.

    This was a B727...there is NO reason to presume that a B757 or B767 would be constructed to a "lesser" standard.

    It is NOW up to the so-called "P4T" to suggest, and then "prove" otherwise.
  39. inam56

    inam56 New Member

    I can't post on the P4T forum ? My new account is not valided by Balsamo ?

    In his first response to my posts here, Balsamo says :
    In other words, flutter prevention is only "at both constant ..." and not in conditions which would induce flutter ?

    Fultter, one of the most dangerous events that can occur in flight, does not require flight test ?

    Don't worry about FAR 25.629, it's only theorical calculation, speed over VD can't by free of flutter ?

    If VD is a structural limit, why the FAR 25.629 require a verification above VD ? (at constant ... :))
    [EDIT: * and even a litlle above 1.15VD by control of damping ratio (and 1.2VD for the 767 in 1982)]

    An overview of Flight flutter testing/in flight modal analysis from Boeing :
    [EDIT: * FAA AC25-629]
    No significant mode, such as curves (2) or (4), should cross the g=O line below VD or the g=0.03 line below 1. 15 VD.
    Last edited: Aug 28, 2014
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  40. Keith Beachy

    Keith Beachy Active Member

    "at both constant Mach number and constant altitude" - Balsamo had no idea what this meant. Will he understand why he was wrong, will he understand the graph.