Tiger down off Straddie
F@rkwits
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On 16 December 2013, a de Havilland DH-82 (Tiger Moth) aircraft, registered VH-TSG, took-off from the operator’s airstrip at Pimpama, Queensland with a pilot and passenger on board.
my question is simple. what broke????
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if old experienced LAME's could do aeronautical calculations and be cognisant of loads in a structure then greg47's comment would be valid.
I suspect though that many LAME's could tell you whether a part had deteriorated from what a new one looked like but could not tell you the load in the structure or whether the part originally had adequate margins of strength.
a lot of guesswork is involved in maintenance.
the question remains. what broke?
I suspect though that many LAME's could tell you whether a part had deteriorated from what a new one looked like but could not tell you the load in the structure or whether the part originally had adequate margins of strength.
a lot of guesswork is involved in maintenance.
the question remains. what broke?
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JammedStab - The likelihood of any original casein glue still being in any certified aircraft in Australia is virtually zilch. This casein glue problem was identified by the late 1940's, and many a (nowadays-fabulous-antique) aircraft was scrapped in the late 1940's and early 1950's, due to the horrendous cost of replacing all the casein glue.
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Curious.
Reading some of the more reasoned posts got me curious (a curse). Apart from a couple of delightful hours, more years ago than I care to remember, I have no knowledge (zero) of Tiger operations – so indulge me here. I am curious as to the 'why' a wing 'broke', also which wing went first (top or t'uther).
For the sake of discussion, lets take a small risk and make some assumptions; (a) the aircraft was correctly maintained and 'in good order'; (b) the pilot was of 'average' competency, medically serviceable and could manage 'basic' aero's. The weather is a given. I believe we could almost ignore a bird strike as being a 'wing breaker'. So what else could possibly cause a sudden event??
Some will no doubt recognise their words in the quotes below; so my question – is it remotely possible that the deployment of leading edge slats, if unlocked could create enough additional load (twisting ?) on a 'weak' spot to create the break ?. Looking at the drawings creates a doubt, there's some pretty robust material to 'break' built in.
Just asking - ???
For the sake of discussion, lets take a small risk and make some assumptions; (a) the aircraft was correctly maintained and 'in good order'; (b) the pilot was of 'average' competency, medically serviceable and could manage 'basic' aero's. The weather is a given. I believe we could almost ignore a bird strike as being a 'wing breaker'. So what else could possibly cause a sudden event??
Some will no doubt recognise their words in the quotes below; so my question – is it remotely possible that the deployment of leading edge slats, if unlocked could create enough additional load (twisting ?) on a 'weak' spot to create the break ?. Looking at the drawings creates a doubt, there's some pretty robust material to 'break' built in.
It is important to lock the automatic slats (leading edge flaps) during aerobatic manoeuvres
Put simply, Auto slots (slats) work by the center of pressure moving forward until there is a lifting force on the slats rather them being held in position by slipstream. I think the reason for locking them is mainly to prevent them being damaged, after all, if it deployed on the wing about to stall that would delay the stall and hence reduce the likeyhood of a spin - though not significantly.
The slats on the Tiger's top wing can be locked shut, and indeed some are permanently wired shut. They are usually locked for aeros, as at high AoA one slat might deploy before the other. Indeed that might have been a factor in this accident, if he let the AoA get too high in the loop and one slat deployed and the other didn't, round you go into spin-land (unless you counter it with instant forward elevator and appropriate rudder, an instinctive reaction for an experienced aeros pilot,
The slats on the Tiger's top wing can be locked shut, and indeed some are permanently wired shut. They are usually locked for aeros, as at high AoA one slat might deploy before the other. Indeed that might have been a factor in this accident, if he let the AoA get too high in the loop and one slat deployed and the other didn't, round you go into spin-land (unless you counter it with instant forward elevator and appropriate rudder, an instinctive reaction for an experienced aeros pilot,
In a perfect world both slats deploy at exactly the same AoA and there is no delay in deployment. In the real world there will be a difference in the AoA that provoke deployment wing to wing, and then a delay (also variable wing to wing) from closed to open, which become significant in the sort of accelerated stall that happens if you pull back too hard while climbing steeply (loop entry). It's a flick really, so it all happens very quickly compared to a level stall.
Consider pulling up into a loop, pulling too hard near the top, and one slat pops out. Both wings were near the stall and flow breakaway was starting, but now the slatted wing fully recovers so there is a roll component towards the unslatted wing which increases the AoA of that (downgoing) wing by quite a lot and it fully stalls. Of course its slat will then deploy but by then, assuming the pilot keeps pulling as the speed continues to decay, the damage is done and the aeroplane has flicked into a spin.
That is precisely why they should be locked before aeros!
Consider pulling up into a loop, pulling too hard near the top, and one slat pops out. Both wings were near the stall and flow breakaway was starting, but now the slatted wing fully recovers so there is a roll component towards the unslatted wing which increases the AoA of that (downgoing) wing by quite a lot and it fully stalls. Of course its slat will then deploy but by then, assuming the pilot keeps pulling as the speed continues to decay, the damage is done and the aeroplane has flicked into a spin.
That is precisely why they should be locked before aeros!
As a commercial Tiger Moth Pilot, I can tell you that the slats are a real pain. The cables used to operate them stretch over time, especially if one is doing a lot of aeros allowing the slats to 'float'. This stresses both the slat mechanism and the wing, leading to all manner of maintenance headaches. We remove the slats as a matter of routine whenever we are having wings rebuilt.
Thanks for replies so far. asw 28-866 - If the slat cables stretched over time and caused the "floating" you describe, this suggests routine maintenance of the cables was lacking - not faulty cables. Most components, if not serviced to manufacturer's specified time limits will inevitably cause problems down the line. While the IAS stalling speed difference may be negligable, the CAS stalling speed is what counts. There is no doubt the slats act as an effective stall warning device.
Removal of a component for reason of servicing costs can lead to undesirable results. In 1992, a Tiger Moth spun in during the execution of a simulated engine failure shortly after take off at 300 ft. One pilot was killed. The accident investigation board criticised the operator for locking the slats in the permanently closed position (to save the bother and costs of servicing). Litigation quickly followed.
The Board of Inquiry stated the accident might have been avoided if the slats had been operating as they served as an effective signal of stall warning and a slower stall speed.
Removal of a component for reason of servicing costs can lead to undesirable results. In 1992, a Tiger Moth spun in during the execution of a simulated engine failure shortly after take off at 300 ft. One pilot was killed. The accident investigation board criticised the operator for locking the slats in the permanently closed position (to save the bother and costs of servicing). Litigation quickly followed.
The Board of Inquiry stated the accident might have been avoided if the slats had been operating as they served as an effective signal of stall warning and a slower stall speed.
Last edited by Kharon; 23rd Dec 2013 at 19:07. Reason: My bolding of the bit that caught the Mk I EB.
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Dh164,
your comment on slats are "pain for no gain" has me a bit perplexed.
just so we know, what is your total command experience on Dh82/a/c's ?
mine is a lowly 774.4 ,and last flew one 3 days ago, and I think they are very worthwhile, as they helped me during a forced landing into a rather small field a few years ago, to keep SA on speed.
but to be fair, yes, they should be checked locked for aero's, by doing the old HASEL checks....but a pain...never.
b/regards
Arawa
your comment on slats are "pain for no gain" has me a bit perplexed.
just so we know, what is your total command experience on Dh82/a/c's ?
mine is a lowly 774.4 ,and last flew one 3 days ago, and I think they are very worthwhile, as they helped me during a forced landing into a rather small field a few years ago, to keep SA on speed.
but to be fair, yes, they should be checked locked for aero's, by doing the old HASEL checks....but a pain...never.
b/regards
Arawa
Agree with Arawa,
The slats are a Fantastic aid to speed awareness. They are a visiual and audible sign as to the wings AoA.
I would never render my slats useless. They are there to help!
The slats are a Fantastic aid to speed awareness. They are a visiual and audible sign as to the wings AoA.
I would never render my slats useless. They are there to help!
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Flying wires
Having read most of the posts re this accident, I find it strange that no one has mentioned the integrity f the flying wires or should I say their attachment points.
My own experience is limited to~500 hrs on DH82 and Stampes, some 40 odd years ago but due one fortunate ground incident, a/c tied down securely overnight caught in a squall and ended up inverted on top of a Cessna. The rope was still secured to the a/c tiedown fitting but the bolt either 3/8" or lighter had corroded away out of sight holding on by one thread. On further examination most of the other similar fittings were also well corroded. Including the ends of the flying wires.
The interplane struts and their fittings must be the weakest points as most connect through a single bolt (from memory) the video will hopefully show the moment of disintegration.
My condolences to the families. SW.
My own experience is limited to~500 hrs on DH82 and Stampes, some 40 odd years ago but due one fortunate ground incident, a/c tied down securely overnight caught in a squall and ended up inverted on top of a Cessna. The rope was still secured to the a/c tiedown fitting but the bolt either 3/8" or lighter had corroded away out of sight holding on by one thread. On further examination most of the other similar fittings were also well corroded. Including the ends of the flying wires.
The interplane struts and their fittings must be the weakest points as most connect through a single bolt (from memory) the video will hopefully show the moment of disintegration.
My condolences to the families. SW.
your comment on slats are "pain for no gain" has me a bit perplexed.
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If you want to pull yourself over your xxx POINT FOUR! hours in a Moth thats fine by me. I haven't totalled mine but maybe 3 figures both in slats and without slats. So you maybe stall 2 knots less with slats, big whoop. They're just another unnecessary item to maintain.
I also need slats to tell me how much energy I've got over my wings.
They are a visiual and audible sign as to the wings AoA
Mcoates might like to re read that part of the report.
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They (ATSB) have changed the report and the general details, it originally said Albatros Airfield Coomera as their base and departure point!
I am glad the ATSB read PPRUNE and can be alerted to their errors.
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They (ATSB) have changed the report and the general details, it originally said Albatros Airfield Coomera as their base and departure point!
I am glad the ATSB read PPRUNE and can be alerted to their errors.
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Funny you should mention the ATSB reading pprune because I can confirm at times that they do. Those of us that make bold comments about crashes and operator past history may find a nice message waiting in their inbox. My experience in this happening was around being able to offer photos for the report and also a rogue GPS experience that relevance to a recent fatal crash.
Stan My thoughts exactly... im no expert on anything but as far as i have seen the tiger moth is constructed with a tube steel fuselage with wood wings and tail surfaces. The wings are constructed using SINGLE piece wood spars routed into an I beam shape attached at the root and interplane struts with bolted metal fittings (steel?) and wood ribs glued to the spars.
A catastrophic wing failure such as this suggests to me that the failure occurred in either the spar, root attachment or interplane strut attachment. The slats themselves would probably fail long before the wing would and flicking into a spin as Kharon described would have been a fairly regular occurrence back in the days when the tiger was the back bone of flight training.
Also im wary of statements such as
i dont have my original tiger moth pilots notes or DH service manuals handy but im fairly certain it makes no mention of G limits (none of the other DH manuals i have do - indeed the leopard moth one i have in front of me doesn't even list a VNE). stress analysis of individual components may indicate load factors as high as 5 or 7.5 but this may be a case of applying modern ideas of structural analysis to older aircraft designs.
Although both wood and steel do not fatigue in the same way aluminium structures do any structure where you have joints consisting of different materials with different stiffnesses will suffer from a kind of fatigue particularly if they are subjected high loads. Im fairly certain the tiger was not designed with anything other than gentle loops rolls and spins in mind...
anyway this is a terrible tragedy and my sincerest condolences to those affected
A catastrophic wing failure such as this suggests to me that the failure occurred in either the spar, root attachment or interplane strut attachment. The slats themselves would probably fail long before the wing would and flicking into a spin as Kharon described would have been a fairly regular occurrence back in the days when the tiger was the back bone of flight training.
Also im wary of statements such as
But, I found this interesting quote from an earlier report link, "The aircraft was stressed to withstand maximum loads of approximately 7.5g (acceleration due to earth gravity). Information from the manufacturer indicated that even with the reinforcing doubler delaminated and ineffective, the aircraft was designed to withstand manoeuvre loads of about 5g."
Although both wood and steel do not fatigue in the same way aluminium structures do any structure where you have joints consisting of different materials with different stiffnesses will suffer from a kind of fatigue particularly if they are subjected high loads. Im fairly certain the tiger was not designed with anything other than gentle loops rolls and spins in mind...
anyway this is a terrible tragedy and my sincerest condolences to those affected
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lets see dh164,
a civil question was met with a sarcastic answer.
plus you say in your last line that you now NEED the slats .
I thought they were a pain ?
If I have to lower myself to your level, I will, but for just a second, but maybe the location from where you come from shows your flying style/skill...like chopping meat.
this forum was to try and work out possibly what happened ,and find any answers to the sad loss of two young lives.
That is what is most important, and Im sure the moderator will agree.
a civil question was met with a sarcastic answer.
plus you say in your last line that you now NEED the slats .
I thought they were a pain ?
If I have to lower myself to your level, I will, but for just a second, but maybe the location from where you come from shows your flying style/skill...like chopping meat.
this forum was to try and work out possibly what happened ,and find any answers to the sad loss of two young lives.
That is what is most important, and Im sure the moderator will agree.
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Arawa,
How would you like me to respond to the dense question of "just so we know, what is your total command experience on Dh82/a/c's ?"
This is the internet, trying to waive your genitals around to attempt to give yourself some sort of credibility is laughable. I'll take the 'sarcasm' out of it. I don't see the benefit of slats because all they do is lower your stall speed by 2 knots at a maximum.
No, now that was sarcasm.
But then the same old sods come out and say 'Oh my god hurr durr you cant speculate on the cause of the accident, just wait till the ATSB come out with their findings, have some respect for the victims and their faimiles'.
Brown nose that hard and it will soon become red.
a civil question was met with a sarcastic answer.
This is the internet, trying to waive your genitals around to attempt to give yourself some sort of credibility is laughable. I'll take the 'sarcasm' out of it. I don't see the benefit of slats because all they do is lower your stall speed by 2 knots at a maximum.
plus you say in your last line that you now NEED the slats .
I thought they were a pain ?
I thought they were a pain ?
this forum was to try and work out possibly what happened ,and find any answers to the sad loss of two young lives.
That is what is most important, and Im sure the moderator will agree.
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interesting mcoats isn't it :-)
the DH82 obviously wasn't designed to the loads of FAR23.
It was probably designed to one of the early english standards.
what were the loads requirements the DH82 was designed to?
the DH82 obviously wasn't designed to the loads of FAR23.
It was probably designed to one of the early english standards.
what were the loads requirements the DH82 was designed to?
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arawa
Quote:
this forum was to try and work out possibly what happened ,and find any answers to the sad loss of two young lives.
That is what is most important, and Im sure the moderator will agree.
The ATSB is there to work out what happened. So far all I have seen in this forum are four pages of speculation.
this forum was to try and work out possibly what happened ,and find any answers to the sad loss of two young lives.
That is what is most important, and Im sure the moderator will agree.
The ATSB is there to work out what happened. So far all I have seen in this forum are four pages of speculation.
DH164, without any respect I think you have a problem:
You were merely being asked what qualifications you had to make the statements you made, but what we get back is heavy sarcasm because Arawa clearly has a lot more Tiger Moth expertise/experience than you do.
Or are you embarrassed at the contradiction in your statements about the value of slats in your various postings.
Please take the time to re-read the last two paras of Arawas last post; I happen to agree with these and there's no way they deserve your petty, unhelpful and spiteful response.
If you want to pull yourself over your xxx POINT FOUR! hours in a Moth thats fine by me.
Or are you embarrassed at the contradiction in your statements about the value of slats in your various postings.
Please take the time to re-read the last two paras of Arawas last post; I happen to agree with these and there's no way they deserve your petty, unhelpful and spiteful response.