Witnesses in the pub and impact speed
 

Agree, geebee50: from reports at the time, I recall:

There was a bang, loud enough to stop the band playing.
Someone had time to quip (and be heard saying) that the band had brought the ceiling down.
Then a helicopter came through the roof.

That's probably not the signature of a 3-ton helicopter smashing straight in vertically at 200mph. Not unless the roof absorbed all that energy - equivalent to that of a 40-ton truck at highway speeds - held together for a couple of seconds more, and then gave way.

I still believe there would be no recognisable helicopter left if the drop had been very significant . Also I believe it would have been very unlikely to hit the roof the right way up . These things all point to a workable auto to a level not much more than 50ft or so , in my view . How do you explain the first impact that brought some ceiling down prior to the main impact some seconds later ??

Nigelh.

I agree. Tail then main fuselage perhaps?

Folk here posted some excellent YouTube videos of crashes, some 'real' and some trials. Helicopters are remarkably resilient, it seems, and if they land on the skids, those open up absorbing energy, then the fuselage crumples, again absorbing energy. In this tragedy, the roof also gave way and that would also have absorbed energy...the eggshell effect. From the description given by a builder, earlier in this thread, who explained something of the probable structure of the roof, I think it'd be very hard to estimate the consequences of any particular impact velocity but from the photo evidence a lot of energy went into the structure of the building, not the airframe.

Are you trying to contradict Newton?
1. Forces are an interaction between objects.
2. Object A pushes on object B the same as object B pushes on object A.
3. A force on an object changes it’s momentum where momentum = mass x velocity.

JimEli,

I don't think Lemain is trying to contradict Newton. The falling craft has a certain energy, and the resulting damage depends on how that energy is shared between deforming the hull and deforming the roof.

If it had landed on a stack of mattresses it might have come out unscathed, as the energy would all have been dissipated in the bedding.

On the other hand, if it had impacted a roadway, for example, it might look a lot worse.

Which Newton did you have in mind? Certainly not Sir Isaac Newton. Force = Mass x Acceleration.

When estimating the damage to structures and objects on impact we use energy. The total kinetic energy is dissipated during the deceleration - think of crumple zones on vehicles - and the forces on the structures, objects and in this case passengers depend on the deceleration. If the vehicle and the structure 'crumple' over a long-ish period absorbing energy then the deceleration is lower, the forces are lower and the survivability is better - unless objects are forced into passenger spaces or the passenger compartment is so distorted that the occupants are harmed.

It might be easier to imagine the difference between a crash onto a table of granite versus a crash onto a massive eiderdown, or even trampoline (e.g. as used by fire rescue services). The difference between granite and the other two is deformability, with the deformation absorbing the energy.

Edit: Roseland, our posts crossed, we are saying the same thing

Police helicopter crashes onto Glasgow pub
 

A 40 ton truck hitting that roof at 70mph would have resulted in more than a bang. I think penetration and collapse would have, in that case been more immediate. No doubt the roof did absorb a huge amount of energy as did deformation if the cab. However, I do not subscribe to the theory that it stopped and dropped from normal flight. More likely control was lost at a point near the bar roof after something else occurred. The toppling described by one eye witness reminded me of a piper tommohawk when fully stalled. Presumably, stationary main rotor blades would still provide some resistance to airflow and /or if turning very slowly result in a tumbling/ bobbing motion?

It was a tough roof.

A 3-ton helicopter hitting at 30mph would be two cars hitting head on in a crash on the sidewalk outside. Enough to stop the band.

Munnyspinner,

I agree, I think there was a serious problem, probably involving controllability, during which height was lost and then Nr decayed rapidly and it became a brick. At what height, I wouldn't even begin to guess, but certainly high enough that it punched through that quite substantial roof.

I don't hold with the 2 stage collapse.....I think it went straight through followed by progressive collapse of internal structures. From the pictures it appears the left side of the craft is more severely disrupted than the right, born out by the damage to the left engine from which the AAIB weren't able to prove the drive train.

Why no fire?????

Why would there be a fire? They only blow up in Hollywood

A lot to do with the design in some part but not all.

Why no fire? Because if, as Back at NH suggests, controllability was lost, he might have pulled the engines in the hope that they landed on something soft (trees?), and wanted to minimise the subsequent fire risk.

One of the many things that is baffling me about this is the witness account of the helicopter "tumbling". Anyone else struggling with this?

Catch21,

Not if control was lost, and the rotors slowed. Particularly if there was some rotation (yaw) before control was lost, such as would happen if the Fenestron failed in some way.

And before anyone jumps at me, I'm not saying this is what happened, it's just one of a number of possibles.

Catch 21
The 'tumbling' description reminds me strongly of an eyewitness to the Asiana SFO crash, who described the 777 as 'cartwheeling'. But when the video was closely examined, it became clear that the aircraft had reached a high level of bank and was turning/yawing accordingly. But to the eyewitness in real time, and perhaps shocked by what she was seeing, it was seemingly obvious that the aircraft was cartwheeling.

And that was in daylight.

Perhaps a high bank angle, as well as yaw, might have been part of the sequence of events with the helicopter? Seen at night, such a manoeuvre sequence could easily have been misinterpreted.

airsound

Not to speculate, but stuck object under collective could be the reason why a highly experienced pilot didn´t make it in the auto. Especially if it only takes 2 sec from norm rpm to stalled condition like some of you stated in your calculation.

Tech info;
The ELT I belive has a 10 G switch, ref early post stating it was sending.
Low on fuel puts this ac around 2.3t in pd config.
The ldg gear is constructed to absorb vs of 600´ ft/m.
Knowing this, zero fwd speed and roof absorbing some of the energy we would assume the blades stalled out at considerable height.

Q; from earlier picture, it shows dual controls. Is this correct?

Very simple. The bar below the impact point and the stage area with the band are separated from each other, the impact was essentially atomic and the sequenced ceiling collapse was at the edge of the hole or even further away which explains the time taken for people who couldn't see the wreckage to realise what had transpired.

I asked this before and saw no response, but does the EC135 have a fuel system crash switch to cut off fuel to the engines in the event of a heavy impact? If so, what g level is required to trigger it?