How Did MH370’s Flaperon Come Off?

In my last post, I reviewed Malaysia’s analysis of the MH370 debris its investigators have gathered. Not included in that study was the flaperon found on Réunion, as it is being held by the French. So today I’d like to look at what the damage patterns seen on the flaperon suggest about the crash, based on the work done by IG member Tom Kenyon and by a reader of this blog, @HB.

On February 3 of this year, Kenyon released an updated version of his report “MH370 Flaperon Failure Analysis” in which he gives an overview of the flaperon’s structure and how it was damaged. He notes that of the six main structural attachment points of the aircraft, the two biggest and most significant are the flaperon hinges (pictured above). They snapped in the middle:

The lesser attachment points failed in a similar way. That is to say, they did not rip away the flaperon structure to which they were attached.

Kenyon observes:

The location of the failure points of Flaperon hinges is consistent with a large singular lateral force or repetitive lateral (or torsional) movement of the hinges in the inboard/outboard direction. If Flaperon was separated from the Flaperon hinge with forces in forward/aft direction or by applying forces to the Flaperon in the extreme rotated up/down direction (beyond structural stops) then deformation of the Flaperon structure due to such forces would be evident. Significant and permanent deformation of the Flaperon structure does not appear to be present in photographs of the Flaperon.

Recall that two scenarios have been proposed for the flaperon coming off 9M-MRO: either the plane hit the water, or it came off as the result of flutter in a high-speed dive. Neither event could reasonably be expect to produce a primarily lateral (that is side-to-side) force on the flaperon of the kind Kenyon describes.

To raise the level of perplexity, Kenyon points out in other crashes involving 777s, failures didn’t occur at the hinges; rather, the hinges remained intact and the material to which they were attached broke. That is to say, hinges are stronger than the flaperon proper. Here’s an example from MH17:

Kenyon concludes that:

No significant evidence of secondary structural damage excludes a massive trailing edge strike and leads the author to conclude that the Flaperon separated from MH370 while in the air and did not separate from the wing due to striking water or land.

In other words, since the damage isn’t consistent with a crash into the sea, we can deduce that flaperon must have come off in the air. The only conceivable cause would be high-speed flutter. However, on closer inspection the evidence seems to rule out flutter, as well.

The reader who goes by the handle @HB is an expert in quantitative risk assessment in the transportation industry and has extensive experience with composite materials. In a comment to the last post, he observed:

For the flaperon… the lift/drag load is normally passed on the honeycomb panel over the exposed surface area then the primary stucture of the component (the aluminum frame of the flaperon) then the hinges then the primary aluminum stucture of the wing.

In a nut shell, those panels are not designed to sustain any in-plane loads either compressive or tensile. They are just designed to resist bending due to uniform lift load on the surface (top FRP layer in tension and bottom FRP layer in compression, the honeycomb is basically maintaining the distance between the layers without much strength).Those panels can arguably take a little bit of shear load due to drag forces on the top skin (top and bottom forces in opposite direction) but not much due to limits in the honeycomb strength.

The second thing to consider are the GRP properties. The GRP is very tough in tensile mode, much stronger than Steel. In compression mode, it buckles easily and only the honeycomb is preventing this. This is by far the weakest failure mode. If it fails, you will see fibres pulled out link strings on a rope failing under tension. For the skin under compression, you will see sign of compression on the honeycomb but the fibres will have to be pulled out as well. Also, a perfect manufacturing does not exist, there are always delamination (small bonding defects) between the honeycomb and the GRP skin to weaken further the compressive strength.

The hinges are usually much stronger as all the load is passing through them (analogy door hinges).

So you could imagine, if there is a large impact the hinges are expected to fail last. The part of the skin that will buckle is expected to fail first.

@HB here is agreeing with Kenyon: it is baffling that the flaperon came off the plane due to failure within the hinges. But @HB goes further, arguing that this type of damage is inconsistent with flutter:

I would tend to agree that the hinges have been subject to cyclic fatigue… the hinges appear to have been subject to cyclic lateral forces which are not expected in any accidental circumstances (take door hinges, for instance, and imagine the hinge fail after 50 times someone is trying to burst through – you can try at home but it is very unlikely to happen). This of course requires a closer look by experts to double confirm. I cannot think myself of any possible lateral force on this part in the first place but a lateral force that will fail the hinges and not the skin which is weaker is very hard to explain. Try with a wooden door and tell me if you manage.

In a followup comment, @HB observes that even under very strong oscillation the flaperon should not be expected to disintegrate. “If hydraulic power is on, fluttering is unlikely to cause any disintegration. If off, fluttering forces are up and down and the hinges are free to move. Lateral forces, I think, would be small in comparison with the vertical forces and not be strong enough to cause fatigue on the hinges.”

Kenyon concludes his report with a list of six questions and issues generated from his analysis. While all are worthwhile, one stands out to me as particularly urgent:

• Why are the official investigators silent on releasing preliminary reports on their Flaperon analysis? Why would France’s Direction générale de l’armement / Techniques aéronautiques (DGA) release photographic data to ATSB and yet chose not to make Flaperon Analysis findings public after such a long period of elapsed time?

To sum up, a close examination of the flaperon’s breakage points does not yield any comprehensible explanation for how it came off the plane, commensurate with a terminal plunge into the southern Indian Ocean.

This is baffling but unsurprising. Every time we look at the debris data carefully, we find that it contradicts expectations. The barnacle distribution doesn’t match the flotation tests. The barnacle paleothermetry doesn’t match the drift modelling. The failure analysis doesn’t match the BFO data. And on and on.

Something is seriously amiss.

290 thoughts on “How Did MH370’s Flaperon Come Off?”

  1. @Eoghanf

    Essentially you have answered a fourth question to the affirmative that it was the hijackers original intent to spread 777 debris in the Western Indian Ocean. There is another possibility of course that on the 8th March 2014 they never thought in their wildest dreams they would end up having to “plant” debris in the WIO.

    That is of course is if 9M-MRO was a hijack, though this is looking increasingly likely.

    However the failure of the primary search zone at the beginning of this calendar year was a epochal moment in the 9M-MRO story. It effectively excludes the hypoxic pilot scenario.

    I accept the conscious pilot scenario is still alive. However I find it difficult to believe Captain Z flying a 777 for a number of hours with 238 recently deceased passengers and crew behind him. The shear practicality of it plus the psychology required in Captain Z (at odds with the discussion in this and other forums) is hard to comprehend.

    I also accept the recently expressed opinion of @Ge Rijn that the Captain may still be somehow responsible though this has receded with the developments over the last year.

  2. According to the ACARS Position Reports in the ‘Unredacted’ INMARSAT logs, the airplane on the preceding flight MH0371 from Beijing to Kuala Lumpur was descending through 3300 ft at 7:24:05 with 9780 kg fuel on board.

    The airplane reported “On Ground” at 7:28:20.

    According to “Factual Information” 8200 kg fuel remained after the preceding flight. Perhaps the difference of 1580 kg is normal fuel consumption for landing and taxi-in, it just seemed on the high side to me.

  3. @David

    Thanks. Nice piece of detailed work with good pictures.

    Some comments as a first reaction:

    To me it’s more obvious a series of strikes must have taken place.
    And the main blows must have been on the underside of the flap for several reasons;

    First; the widening big crack starting at the flaps underside running through the seal pan till the upper side (picture 9) is IMO a clear tension-crack caused by forces (series of strikes) on the underside of the flap.

    The crack at the opposit upper side starting with the inward dent (which the ATSB thinks is caused by the flaperons edge hitting there) is IMO clearly a compression-crack with buckling which forced the material to break inwards at the place of the dent.
    So I doubt if this dent and crack are caused by the flaperon hitting the flap (or visa versa). And remember the ATSB only thinks the flaperon hit the flap there. They did not stated it as proof.

    Second; the dents in the bottom-stiffener are much deeper than the one slight dent in the upper-stiffener. Indicated to me the upwards strikes on the flap were more forcefull than the downward ones.
    Indicating to me again the main forces (hits) were on the underside of the flap.

    Third: picture 7 shows the remainder of the pivot link. The breakline at the top (clear with enlarged view) this breakline is twisted with the inner ends curling inwards.
    Indicating the flap section first broke on the inboard side track, then rotating backwards and twisting the pivot link till it snapped.

    Like you say; I agree this sequence could not have been instant but took some time.
    A high speed nose first impact would not have this time-frame and would also have destroyed its leading edge.
    So IMO we can rule this scenario out.
    Aerodynamic flutter can also be ruled out by now IMO.

    This leaves aerodynamic overload stresses during a high speed pull-out or a ditching.

    For reasons I suggested before in lenght I believe the latter is the most probable.
    It would explain the series of strikes necessary, the time needed and the most forcefull strikes happening on the underside of the flap resulting in the tension and compression damage shown including the breaking of trailing edge pieces before the flap section seperated completely.

  4. @David

    I like to add; in picture 9 you can also see delamination of the upperskin around the dent-crack (enlarge picture).
    This also indicates compression damage on that side of the flap opposed to the tension crack starting on the other side and through the pan seal ending narrow at the upper skin.

  5. @Gysbreght
    Good point about the fuel remaining. I am under the impression that self-measurement of fuel once on the aircraft is less accurate. More accurate would be the direct measurement of the fuel flow as it is pumped on.

    The MH371 fuel data I noticed was the total fuel load for MH371 was relatively close to the MH370 take off weight, so that tends to the MH370 fuel load was about right. Of course, more data for other prior MH370 flights would be helpful.

  6. @David
    Thank you for the debris analysis. I have become more interested because it has flight path implications. Right now I am keeping open to pilot control after Arc5, and if so, I think the pilot probably did more than just impassively watch the plane dive uncontrollably from FL350. Unfort, who knows what the PIC had in mind? (if he was indeed at the controls)

  7. @Ge Rijn. Thanks for your first reaction.

    About the dent adjacent to the upper skin, you say, “…clearly a compression-crack with buckling which forced the material to break inwards at the place of the dent.
    So I doubt if this dent and crack are caused by the flaperon hitting the flap (or visa versa).”

    I do not follow. If it was a compression crack why would that not have been a consequence of flaperon spar penetration?

    “ …the dents in the bottom-stiffener are much deeper than the one slight dent in the upper-stiffener. Indicated to me the upwards strikes on the flap were more forcefull than the downward ones.”

    Yes they are but bear in mind that from a glance at the ATSB’s Fig 15, right hand upper diagram, the track free end had to flex beyond belief to reach the top stiffener when the carriage assembly was intact. Once that had broken the multiplying effect it had on the strike speed would be gone. The upward strike was probably then.

    You are seeing the cause of the crack and strikes as multiple whacks from beneath but I do not think that explains the dent.

    @TBill. The trouble is that while there remains reasonable doubt about the end being pilotless, if then a glide is seen as possible the basis for both old and new searches is shot. It is not just whether this is actually so but the effect on confidence while the doubt remains. That is why I had been hoping that an analysis like this might assist with that most important issue, though so far it hasn’t.
    A flaps up ditching remains on the table.

  8. @David
    …correct hopefully near 7th arc…I am not hoping for a long glide…maybe a cut back to an area he thought looked good for hiding crash rather than progressing foward to an unknown area near a unseen ship ahead or loss of cloud cover.

  9. @David

    On your comment:

    “You are seeing the cause of the crack and strikes as multiple whacks from beneath but I do not think that explains the dent.”

    I think it could. In picture 9 close up of the dented area you can see the ‘dent-in’ seal pan material did not crush through the fastener which it would have if it was pushed in by the flaperon or something else.
    The edge to the seal pan crack is completely clean and undamaged there. This can only mean the ‘dent-in’ part of the crack went OVER the fastener.

    IMO this could only have happened when the trailing edge of the flap was bend with great force upwards causing a tension crack through the underskin and through the seal pan and a compression crack on the upperside, buckling and delaminating the upperskin forcing it upwards and making room for the compression seal pan crack moving inwards OVER the fastener flexing back after the bend forces ended.

    Both cracks (upper and underskin) start at the end spar of the flap trailing edge.
    At that point the seal pan makes also a distinct curve inwards which IOM further could explain the inward crack at the seal pan upperskin region.

  10. @MH:
    “…likely it was done by a aircraft wrecking machine like these in this video…”

    Thanks for an interesting movie, MH, but perhaps overkill if you want to just bruise, rather than obliterate, when fake wreckage as part of the MH370 poof!

    Meanwhile this looked to be a very scary event…

    “AirAsia flight returns to Perth due to ‘technical issue’, passenger says ‘blade came off turbine'”

    http://www.abc.net.au/news/2017-06-25/airasia-flight-forced-to-turn-back-to-perth-technical-issue/8649990

    Interestingly, AirAsia was born out the wreckage of Malaysia Airlines and sold for a song. Curiously Richard Branson has a piece of the action, along with other western business magnates. Is it just me, but is the name a take on Air America, that well known CIA owned covert drugs and arms smuggling outfit?

  11. Boris: It might be that they decided to break up MH370 without Consideration for debris. But lucky for them the flaperon piece and a few more very small pieces were selected to be planted once it became apparent the independent investigators questioned why no debris. Then a year late it shows up. Some pieces had unexpected oil and flame damage (ie- cutting torch)

  12. It took me a few days to develop a working model to determine whether flutter occurred at high speed or not. Basically based on the best knowledge of the component geometry and material spec, it appears not.
    Note that the geometry is coarse and the exact structure of the honeycomb is not known but typical values were used.
    I did not check the individual components in case of delamination but no sign of delamination.

    Degree of freedom Free Free Free Free for Flaperon:
    Natural Frequency is 8.3kHz
    Mach required to achieve flutter: 186
    Flutter occurred: No

    Degree of freedom Fixed Free Free Free for Flapron:
    Natural Frequency is 8352 Hz
    Mach required to achieve flutter: 186
    Flutter occurred: No

    Degree of freedom Fixed Free Free Free for Flapron:
    Natural Frequency is 641 Hz
    Mach required to achieve flutter: 21.9
    Flutter occurred: No

    Degree of freedom Fixed Free Free Free for wing (no engine):
    Natural Frequency is 1.4 Hz
    Mach required to achieve flutter: 1.76
    Flutter occurred: No

    Degree of freedom Fixed Free Free Free for wing (with engine):
    Natural Frequency is 1.2 kHz
    Mach required to achieve flutter: 1.2
    Flutter occurred: No

    Please let me have your comments, I am also interested to plug in the most accurate geometry.

    So basically this indicates that flutter did not likely occur and consequently that there is no explainable mechanism for the damage of the trailing edge. An FEA on a 3d model with the actual geometry from the investigation team would be of course highly appreciated.

    https://drive.google.com/file/d/0B20K9OJG7RiLYU9wUDNOcXdfZDA/view?usp=sharing

  13. I feel I reached a dead end regarding my interpretation of the engine data in the unredacted INMARSAT logs for flight MH371. I’ve updated the spreadsheet posted on June 22 at 2:44 PM with what I’ve got so far.

    The spreadsheet includes a copy of sk999’s summary of ACARS Position Reports, but with slightly different fuel data. After correcting the anomalous GWT values, the Zero Fuel Weight (ZFW) is determined as 17250 kg, and the fuel quantity is then calculated from FWcorr = GWT – ZFW.

  14. @Ge Rijn. Your, “Both cracks (upper and underskin) start at the end spar of the flap trailing edge.” The cracks in the web and the bottom skin, as distinct from those at the dent, were well forward of the rear spar. Perhaps I misunderstand you.

    However if this had been a compressive failure at the top there should have been distress from tension in the bottom skin and web, directly under the ‘dent’.

    Also:
    • 13, shows top and rear tears to the second, rear, tongue. Those, particularly that at the rear, do not look to be due to compression.
    • 22 shows the extent the forward tongue was forced a way inwards and its double tear. The rear spar discolouration may be from buckling in compression. Both indicate side load.
    • These tears and that of the top skin at 27 with its deflection (seen too at 13) do not look compressive either.

    All the same I would like to see photos of the damaged flaperon rear spar from better angles than in the ATSB report. The best I can find is not very helpful:
    http://reho.st/www.clicanoo.re/IMG/jpg/-18777.jpg.
    However it does show the bottom of the web behind the flaperon rear spar to be missing, raising how this came to be. Collision with the flap?

    Oddly more fasteners show at 20 than 5 and 9. However because 5 has the carrier installed I take it that is the earlier and 20 is the result of poking or moving the flap part about.

    As to the skin being lifted up and over, I think I can see discolouration on one of them, possibly due to abrasion. In 13 there is a mark on the inside of the front tongue showing it was dragged over. I think the tongue was twisted and slid across.

  15. @David

    Figure 13 from the ATSB report shows the ~10cm crack in the upperskin just after the end-spar where the trailing edge begins.
    You can see it cracked around the fastener there and the upperskin was pushed up there through the fastener
    Figure 20 shows this more clearly. The upperskin is lifted up and you see two fasteners that moved over the dent-in material.
    This has IMO all signs of compression damage.

    Also the damage on the flaperon point that is supposed to have hit the flap there shows severe cruch damage; figure 21.
    But the dent-in area on the seal pan shows no sign of impact like this at all imo. Not even a scratch.

    In your figure 9 (from your paper) you can see a crack in the seal pan near the underskin which starts wide and than runs narrow towards the leading edge stopping near the vertical big crack through the seal pan.
    This indicates a clear tension crack opposed to the direct opposit side where the dent-in crack and the up-lifted upperskin show clear compression damage Imo.

    Then finally the big vertical crack through the seal pan also starts wide at the underskin and ends narrow at the upperskin.
    Typically a tension crack that started at the underskin.
    The place where this crack started is Imo exactly the area where you would expect a crack to start as the center of the highest bending momentum in case of a huge bending force upwards between the trailing edge and the hinges.
    It’s like bending a bow against its curve; it will crack inside out near the center of the bow.

    I think the tongue was forced inwards during compression while the upperskin was lifted upwards during compression and then when the compression forces ended the upperskin flexed back leaving the fasteners in front of the tongue.

  16. @David

    A correction. I confused it with the clear tension crack running through the seal pan from the underskin to the inspection door in the seal pan towards the leading edge.
    The crack running through the seal pan along the underskin starting at the end spar of the trailing edge seems also a compression crack to me. The upper edge of this crack seems to have been pressed over its under edge around the end-spar and a rivet has been sheared off and is missing.

  17. @David

    Something else that caught my eye is the crushed point where the flaperon is supposed to have delved into the flap seal pan.
    (ATSB report figure 21).
    This crushed point is about ~15cm away from the original edge of the flaperon there.
    This part of the underskin is almost completely missing as you can see in the smaller overview picture.

    This means the crushed point would have been ~15cm away from the flap seal pan with ~15cm of material in between them.
    I think this is another indication this crushed point could not have penetrated the seal pan. It is just too far away from the seal pan surface. And it leaves unexplained what happened to the material (flaperon underskin) in between.

  18. @HB

    Even within the limits of your modelling this is still a significant contribution. That flutter can explain the state of the flaperon has receded.

    Essentially the mechanism of the missing trailing edge of the flaperon is ‘unknown’. Or better expressed there doesn’t appear to a natural cause.

    One presumes the French have had a look at the Kenyon report and your Google spreadsheets.

  19. @HB

    I also think you make a significant contribution. You seem to provide scientific proof flutter could not have been the cause of damage and seperation of the wing/surfuce control related pieces.

    I hope other experts will take a close look at your findings and will be willing to comment here.

  20. @Steve Barratt

    On your comment:

    ‘Essentially the mechanism of the missing trailing edge of the flaperon is ‘unknown’. Or better expressed there doesn’t appear to a natural cause.’

    I agree the causes are still unknown but there are two or three natural causes left.
    The most obvious to me is a ditching scenario. It could explain the missing flaperon trailing edge but also the right wing flap section trailing edge, the left wing flap trailing edge piece, the right wing aileron trailing edge piece, the left and right wing flaperon fixed panels, the left and right wing flap fairing pieces, the engine cowling pieces and even probably the nose gear door piece.
    And it could explain the overwhelming amount of tension induced damage reported.

    A near vertical belly impact like AF447 could also be a possibility. But then a huge amount of floating debris should have occured from all over the plane.
    With AF447 the found ~700 plane pieces floating. After more then 3 years we have only around 30 MH370 pieces.

    The final possibility is Imo a pull-out from a high speed dive like in ChinaAir 006.
    But in that incident no wing related pieces (thus trailing edges) seperated.
    MH370 must have exceeded those speeds and +5G forces that ChinaAir 006 endured to possibly cause damage like seen with MH370.
    It seems very unlikely to me but it cann’t be ruled out ( by me at least..).

    The other possibility at which you, Jeff Wise and others are pointing to; deliberate mechanically removing and mutulating parts, can not at all explain the kind of consistent damage seen in all of the pieces.

  21. Yes flutter calculations are standard checks in aircraft investigation i found. ATSB have done such calculations for other aircraft crashes using FEA and it is a mystery why it was not done here, especially given the high profile of this case. Such reports are in public domain.

  22. @HB, As I believe I mentioned in an earlier post, I spoke with someone who was privy to the debris examination part of the official examination, and he did not feel that flutter was a plausible explanation for the separation of the flaperon.

  23. @Ge Rijn. Closing of the gap would have been during flaperon separation as I explained in the paper. The external skin around the flaperon spar extension would have been snapped off in an upward hit.

    I think better pictures of that flaperon spar extension would be decisive though I retain little doubt there was a penetration.

    We are not getting far with that so best put it aside.

    The flap also was forced outboard, which I have attributed to flaperon impact in that direction. What is your explanation?

  24. @Ge Rijn. Second last line should read, “….direction, or possibly shock from a wing break.”

  25. Whether debris have been planted or not, the plant has hit FL0 one way or another. It is still important to understand how.

    I think, as explained below, the scenario of “no one in control” can be definitely ruled out.

    @Jeff, if my understanding is correct, effectivelly the only two links that led to conclude that the plane was in “high speed descent with no pilot on board” was the
    (1) guiderail damage but here it is obvious from most of the knowledgeable people in this forum that the debris damage are not consistent with high speed impact with no prior part detachment.
    (2) the possibility of flutter at high speed which could have potentially explained prior part detachment but it is now ruled out.

    The only two other possiblilities for high speed descent with no pilot on board, desintegration in mid air (in this case flutter is possible on wing components) and high 5G+ pull out.
    (a) desintegration in mid air (in that case, it will have to be a desintegration that detach the wings to lead to flutter and subsequent part detachement – ie very unlikely to be a cabin sudden depresurisation causing this) and inconsistent with no debris and inconsistent with the pattern of many debris
    (b) 5G+ pull out. @Ge Rijn, for me this could be ruled out. 5G is not conceivable without a pilot, ie control surfaces will follow the path of least resitance and a scenario like the one modelled by Victor I is more likely. That simulation did not show 5G+.

    @David, Ge Rijn: could you consider the case of ditching whether the engines do not separate which could inturn lead to deformation of the aluminum frame. The crashworthiness principles on most aircrafts is to design the engine mounts to such that engines to not cause fire hazards if detached. I am still bother by the lack of damage from the engine (being detached first) in case of the ditch scenario.

  26. @David, thanks for your paper. Very interesting. All sequences make sense.

    I am not sure if the PCUs will be free to move in case of power failure to the hydraulic system. We need to check whether flaperon PCUs are hydraulic locked or not ie pressure is maintained even in case of power loss to allow a couples of actuations (this is standard design in hydraulic systems but not sure if those PCUs are hydraulic locked). If it is, the flaperon tilt up would be hard to explain and high speed pullout could be ruled out entirely and the bottom up force could only be explained by low AOA impact at FL0?

  27. @David @HB

    On your question:

    ‘The flap also was forced outboard, which I have attributed to flaperon impact in that direction. What is your explanation?.’

    I don’t see why and how the flap would have been forced outboard actualy.
    This outboard flap is massive and near ~10 meters in lenght.
    IF the flaperon hit the flap seal pan and caused that small dent the impact force needed to cause that dent would be much to small to have any sideways (outboard direction) effect on the outboard flap.
    The seal pan is also fiberglass. This material has little resistence for puncture.

    As said before I explain the dent by compression forces that caused the seal pan to break there and force the dented material inwards and lifted the upperskin upwards which also broke by compression forces at the upperskin fastener that pulled through.

    @HB

    I don’t know but I assume those big 777 engines sheared off in case of a ditch-like scenario. Especially when it has been a flaps retracted ditch which requires a higher speed. Regarding the two rather big engine cowling pieces found I can imagine pieces of the engines could have hit the outboard flaps and flaperons trailing edges and other parts of the plane particularry leading edges from the tail section.

    Regarding the right wing flaperon PCU’s it was established before that the outboard PCU is actuated under RAT and the inboard PCU is in bypass. The left wing flaperon would have both PCU’s in bypass under RAT. Which would mean the left wing flaperon was free floating and the right wing aileron fixed in a position.
    Are you doubting this and why?

  28. @HB. Having had a glance at your work, thanks, I have some queries if you would help with those.

    Control surface flutter is an amalgam of aerodynamic stimulation, torsional stiffness and inertia yet you seem to have no aerodynamic energy input and I see no sign of torsional stiffness or for that matter, damping. The reference you give is about a cantilever mounted thin plate without curvature, hit with a hammer, akin to a tuning fork. Would you describe how you get from estimating such a natural frequency to equating that to Broadbent criteria please and let us have a reference to the Broadbent underpinnings, their derivation and on what the criteria these are based (eg empirical, theoretical divergence)?

    Perhaps this will tell us why you are concerned about skin flutter?

    I think you are treating the flaperon as a flat plate about 8” thick across the whole chord which surely would be unrealistic as to its natural frequency. Also I do not think they are filled with Nomex from top to bottom: just the skins are.

    More generally while you have gone to this trouble I doubt the ATSB or Malaysians would invest much effort into it. A very high speed descent, which flutter outside the boundary would represent, is consistent with the ATSB search width and there is no indication at all that flutter caused the aircraft’s loss. Hence I am unclear that your further work is warranted.

    Responding to your most recent, yes there are hydraulic accumulators, with nominally no usage, thus extending pressurisation of actuators, duration unknown. Furthermore the engines windmilling might provide hydraulics, particularly at high speed. From memory the RAT is not selected down for 15 secs after centre system hydraulics fall beneath pressure and both engines are beneath flight idle so there is potentially a total gap there. It is also possible that there would be electrical supplies to some other actuators, including one of the left flaperon’s, so a complex scene.

    Still if the flaperon actuators were active I do not see that there could not have been overstress during a high speed spiral or pull out

  29. @Ge Rijn.”I don’t see why and how the flap would have been forced outboard actually.”

    Well the physical evidence indicates the auxiliary support track was swung hard outboard and I do not see how that could have been without the movement my paper describes. What else could have caused that evidence?

  30. @David @others

    I think it could be usefull if the ATSB did a bending test on the inboard side of the flaperon between the trailing edge and the leading edge undersides.
    And then see where and what kind of cracks and damage appear and at which level of bending-forces.
    If similar or other damage appears we would have valuable answers.

    Should be possible for they still have an original flaperon to perform this kind of stess-tests on.

  31. Another correction.. didn’t sleep that well..
    I mean the flap not the flaperon. They still have the original flap section but also an original flaperon which I didn’t had in mind with this suggestion.

  32. @David

    I rather think that after a few major blows on the flaps (trailing edge) underside the rail guide support broke off and the guide rail had then more or less free movement to the left and right.

    And on my ‘test-comment’; the ATSB would ofcourse also need an original other outboard flap section like the flaperon Boeing provided. Probably Boeing could perform a test like that also.

  33. @Ge Rijn. The damage by the track outboard was forcefully down and to the outboard side. If the carriage assembly had failed before that the forces, speed and reach of that free end would have been much the less.

  34. @David

    Lets resume theoretically: the first or following blow(s) on the flap’s underside caused the deep dent right in the middle of the underside stiffener.
    Probably this blow(s) broke also the guide rail support/carriage assembly which left the guide rail free moving left and right in a violently moving flap section.

    I just don’t think the guide rail track could have caused the major damage and cracks in the seal pan at that location. It maybe could have helped to create a weak spot where the main crack through the seal pan starts but Imo it could not have been the cause.
    Imo the cause of the damage seen must have been mainly due to tension and compression forces after several forcefull hits at the underside of the flap mainly on its trailing edge.

    When the flap section seperated from the wing the guide rail with its carriage was pulled through the leading edge and remained on the wing spar Imo.

  35. @Ge Rijn,

    Yes i would like more info on the bypass mode. If this is a damped bypass mode, there should be no free floating. See typical design here.

    http://www.daerospace.com/HydraulicSystems/PowerControlUnitDesc.php

    @David: i did not put all the references yet, but this is the standard approach for calculating natural frequency on honeycomb pannels. The purpose is to check whether the excitation by the airflow fluctuation reaches the natural frequency of the system (ie flutter). If so, this could have been a mechanism of failure leading to mid air detachment at high speed and possible explanation of high speed descent with no one in control. This is necessary step to assess the “no one in control” scenario.

    This approach is the common approach to calculate the natural frequency for plates or pannels including honeycomb pannels.
    The thickness of the honeycomb is accounted for in the bending stiffness. Not as accurate as a 3D FEA but it is relatively accurate.

    Piscane V L, Fundamental of Space Systems, 2005, 2nd Edition, ISBN 9780195162059
    http://www.vibrationdata.com/honeycomb.htm
    https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660024166.pdf
    and many other references.

    For flutter criteria used by ATSB, refer to:
    https://www.atsb.gov.au/publications/investigation_reports/1976/aair/pdf/197603014.pdf

    The assumption of Nomex is not very sensitive. It is just to estimate the overall weight of the core, which here matches the overal weight of the component. The most sensitive parameters are the geometry and the skin properties.

  36. @HB

    From earlier comments on this subject I learned that the flaperon PCU’s don’t have a damped mode. Only bypass or actuated.
    And the right wing flaperon would be actuated with one PCU when only under RAT. The left wing flaperon should be in complete bypass and free floating under RAT.
    I would be suprised if you found something different for this is also important for the left bank the plane is supposed to have made after second engine flame out.

  37. Just going back to “drift” issues.
    The link below goes to a site that apparently maps the amount of floating plastic in the oceans. The maximum density of floating plastic in the Indian Ocean is concentrated well to the south, and seems to “pool, or “collect” there, and it is WAY south of where MH370 debris has been found.
    http://app.dumpark.com/seas-of-plastic-2/#oceans/IO

  38. @HB

    BTW ‘free floating’ would be relative. There always will be some considerable damping by the hydraulic oil that has to be pressed through tiny holes in the PCU system in both directions.

  39. I’m sure I’ll get dogpiled, but I just don’t buy it. The structural integrity of the honeycomb surely would fail before the hinge or rivets would, right? This, to me, looks like a mechanically separated piece of decomissioned scrap.

  40. @Tex

    The structural strenght is not by the honeycomb alone but by its combination of being glued between two skins of carbon or/and fibreglass laminates.
    The tension resistance of those kind of laminates is far greater then steel or alu-alloys.
    So before those honeycomb laminates would fail under tension the metal parts will fail first.

  41. @Tex, I don’t think you’re going to get dogpiled.

    @Ge Rijn, You’ve got it backwards. As @HB has argued, and as Tom Kenyon demonstrated with his pictures of MH17 debris, the metal hinges are stronger than the composite structures to which they are attached.

  42. Perhaps someday someone can point out the differences between a flaperon and a wooden door.

  43. @Tex as per “This, to me, looks like a mechanically separated piece of decomissioned scrap.”

    Totally in agreement mh370 was taken apart mechanically.

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