If a helicopter landed on my roof… I would either expect the roof to
collapse straight away or to stay up. In the case of the Glasgow pub,
the roof stayed up for several seconds after the impact, and then it
collapsed. (It stayed up long enough for the band to make a joke about it.)

Can anybody explain the mechanism whereby that would happen like that?

GB expressed precisely :
If a helicopter landed on my roof€¦ I would either expect the roof to collapse
straight away or to stay up. In the case of the Glasgow pub, the roof stayed
up for several seconds after the impact, and then it collapsed. (It stayed
up long enough for the band to make a joke about it.)

Can anybody explain the mechanism whereby that would happen like that?

Obviously, it was just margininally too weak to support the load and
developing weaaknesses suddenly let go. Try bending a thick twig, it
will begin to crack and then sudenly let go completely if the same
strain is maintained.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

On Sun, 01 Dec 2013 18:13:16 +0000, GB wrote:

If a helicopter landed on my roof€¦ I would either expect the roof to
collapse straight away or to stay up. In the case of the Glasgow pub,
the roof stayed up for several seconds after the impact, and then it
collapsed. (It stayed up long enough for the band to make a joke about
it.)

Can anybody explain the mechanism whereby that would happen like that?

The lift from the rotors reduces as they slow to a stop.

Personally, I think it's great that the Gov't has such a golden
opportunity to save a fortune. They can disband the AAIB and spend a
fraction of the money on propping Usenet up. Win-Win.

On 01/12/2013 18:13, GB wrote:
If a helicopter landed on my roof… I would either expect the roof to
collapse straight away or to stay up. In the case of the Glasgow pub,
the roof stayed up for several seconds after the impact, and then it
collapsed. (It stayed up long enough for the band to make a joke about
it.)

Can anybody explain the mechanism whereby that would happen like that?

I believe it crashed, rather then landed, but that doesn't invalidate
the question.

The force on the roof was probably not enough to cause immediate
fracture of all the structural components but enough to overstress them,
or perhaps fracture some over stressing the remainder, such that there
was a progressive failure resulting in ultimate collapse.

--
Old Codger
e-mail use reply to field

What matters in politics is not what happens, but what you can make
people believe has happened. [Janet Daley 27/8/2003]

---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com

[quote='Old Codger[_4_];3158683']On 01/12/2013 18:13, GB wrote:
If a helicopter landed on my roof… I would either expect the roof to
collapse straight away or to stay up. In the case of the Glasgow pub,
the roof stayed up for several seconds after the impact, and then it
collapsed. (It stayed up long enough for the band to make a joke about
it.)

Can anybody explain the mechanism whereby that would happen like that?

I believe it crashed, rather then landed, but that doesn't invalidate
the question.

The force on the roof was probably not enough to cause immediate
fracture of all the structural components but enough to overstress them,
or perhaps fracture some over stressing the remainder, such that there
was a progressive failure resulting in ultimate collapse.

--
Having been in that bar, both to listen to Music and early evening for a Coffee, I think that the copper-chopper landed on top of the central "gantry" that would give some but limited support to the imposed load, that is the roof and via the gantry the floor were for a time taking the load imposed by the Chopper thus we have impact, load spread floor failure and instantly followed by Gantry and roof collapse.

This Pub [had] a horseshoe shaped bar area two, left and right sections to the public area with the bar roughly centralised between the two circulation spaces with the bar Gantry serving both sides of the bar.

It appears [to me] because of lack of detonation of the choppers Kerosene that fuel had been cut to the two engines prior to impact? no heat source hot enough to ignite the choppers fuel load?

Only time will tell, and over a considerably longer time [may] slowly heal the hurt experienced by so many.

ken

On 01/12/2013 18:50, Adrian wrote:
On Sun, 01 Dec 2013 18:13:16 +0000, GB wrote:

If a helicopter landed on my roof€¦ I would either expect the roof to
collapse straight away or to stay up. In the case of the Glasgow pub,
the roof stayed up for several seconds after the impact, and then it
collapsed. (It stayed up long enough for the band to make a joke about
it.)

Can anybody explain the mechanism whereby that would happen like that?

The lift from the rotors reduces as they slow to a stop....

Given that it was a twin engine helicopter, with an experienced pilot, I
suspect they stopped some time before it hit the pub.

Colin Bignell

On 02/12/13 02:15, Nightjar wrote:
On 01/12/2013 18:50, Adrian wrote:
On Sun, 01 Dec 2013 18:13:16 +0000, GB wrote:

If a helicopter landed on my roof€¦ I would either expect the roof to
collapse straight away or to stay up. In the case of the Glasgow pub,
the roof stayed up for several seconds after the impact, and then it
collapsed. (It stayed up long enough for the band to make a joke about
it.)

Can anybody explain the mechanism whereby that would happen like that?

The lift from the rotors reduces as they slow to a stop....

Given that it was a twin engine helicopter, with an experienced pilot, I
suspect they stopped some time before it hit the pub.

Colin Bignell
Google autorotate

it shouldn't have come down *that* way.

investigation will discover why.


--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On 01/12/2013 19:43, Apprentice 65 wrote:
....
It appears [to me] because of lack of detonation of the choppers
Kerosene that fuel had been cut to the two engines prior to impact? no
heat source hot enough to ignite the choppers fuel load?...

AVTUR has a minimum flash point of 37.8C, although the median of a large
number of samples tested by the FAA following the loss of TWA flight 800
in July 1996, was 53C. It also has a relatively small range of fuel to
air ratios between the lower flammability limit and the upper
flammability limit. The result is that it is not very easy to set fire
to it, even if you are trying. You have to get fuel temperature, vapour
pressure and ignition energy all within the right ranges.

Colin Bignell

On 02/12/2013 02:50, The Natural Philosopher wrote:
On 02/12/13 02:15, Nightjar wrote:
On 01/12/2013 18:50, Adrian wrote:
On Sun, 01 Dec 2013 18:13:16 +0000, GB wrote:

If a helicopter landed on my roof€¦ I would either expect the roof to
collapse straight away or to stay up. In the case of the Glasgow pub,
the roof stayed up for several seconds after the impact, and then it
collapsed. (It stayed up long enough for the band to make a joke about
it.)

Can anybody explain the mechanism whereby that would happen like that?

The lift from the rotors reduces as they slow to a stop....

Given that it was a twin engine helicopter, with an experienced pilot, I
suspect they stopped some time before it hit the pub.


Google autorotate

The fact that it appears to have crashed, rather than making a hard but
controlled landing suggests that it was not in auto rotation, hence my
comment.

it shouldn't have come down *that* way.

Exactly. It suggests some sort of catastrophic failure.

investigation will discover why.

The AAIB are good, but not omniscient. There is a slight chance that
they may never be able to say for certain.

Colin Bignell

On Mon, 02 Dec 2013 03:48:27 +0000, Nightjar wrote:

Given that it was a twin engine helicopter, with an experienced
pilot,
I suspect they stopped some time before it hit the pub.

Google autorotate

The fact that it appears to have crashed, rather than making a hard but
controlled landing suggests that it was not in auto rotation, hence my
comment.

Hum, IMHO if had "crashed" it would have gone straight through the
roof in one hit. It doesn't appear to have done that, it rather hard
and damaged the roof enough for it to then collapse a number of
seconds later. The pub is also right next to the river, the pilot may
have be trying to put ditch it there but didn't have suffcient
control/time. You need a significant amount of height to switch a
helicopter from powered to autogyro flight.

Exactly. It suggests some sort of catastrophic failure.

It does seem very odd for a twin engined helicopter to "just fall out
of the sky". There has been very little reported from eye witness
reports but I guess it was dark. Some mention of tail rotor failure
and Eurocopter do have some what of a reputation when it comes to
gearboxes...

Do these small civilian aircraft have data and voice recorders?

--
Cheers
Dave.

Dave Liquorice wrote:

Do these small civilian aircraft have data and voice recorders?

I heard someone (who sounded like he knew what he was talking about) on
the radio say they don't have 'black' box recorders, but the engines do
have some lower form of data recorders, also it would have radio contact
with the police control room which would have call recording, as well at
air traffic control.

On 02/12/2013 08:44, Dave Liquorice wrote:
On Mon, 02 Dec 2013 03:48:27 +0000, Nightjar wrote:

Given that it was a twin engine helicopter, with an experienced
pilot,
I suspect they stopped some time before it hit the pub.

Google autorotate

The fact that it appears to have crashed, rather than making a hard but
controlled landing suggests that it was not in auto rotation, hence my
comment.

Hum, IMHO if had "crashed" it would have gone straight through the
roof in one hit. It doesn't appear to have done that, it rather hard
and damaged the roof enough for it to then collapse a number of
seconds later. The pub is also right next to the river, the pilot may
have be trying to put ditch it there but didn't have suffcient
control/time. You need a significant amount of height to switch a
helicopter from powered to autogyro flight.

Exactly. It suggests some sort of catastrophic failure.

It does seem very odd for a twin engined helicopter to "just fall out
of the sky". There has been very little reported from eye witness
reports but I guess it was dark. Some mention of tail rotor failure
and Eurocopter do have some what of a reputation when it comes to
gearboxes...

Do these small civilian aircraft have data and voice recorders?

They are not mandatory if the aircraft weighs less than 3000kg. However,
some data is likely to be recoverable from the electronic systems. The
previous Eurocopter gearbox problems have been cured by retro fitting
parts AFAIK.


--
Peter Crosland

Well, if its wood, it tends to splinter and not always straight away.
I'm not sure whether this is the question we should be asking though, more
so, why do the Police as they were Saturday night around here, flying so
low over a built up area for so long?
One knows from all the progs on the Telly that they use thermal imaging and
night vision devices etc, but one has always supposed that their twin
engined craft were safe. OK its only one machine, but considering they are
porbably all using similar craft, and as nobody knows the cause, it might
have been prudent to at least ground them for a confidence check?

Brian

--
From the Sofa of Brian Gaff Reply address is active
"GB" wrote in message
...
If a helicopter landed on my roof… I would either expect the roof to
collapse straight away or to stay up. In the case of the Glasgow pub, the
roof stayed up for several seconds after the impact, and then it
collapsed. (It stayed up long enough for the band to make a joke about
it.)

Can anybody explain the mechanism whereby that would happen like that?

On 02/12/2013 08:44, Dave Liquorice wrote:
On Mon, 02 Dec 2013 03:48:27 +0000, Nightjar wrote:

Given that it was a twin engine helicopter, with an experienced
pilot,
I suspect they stopped some time before it hit the pub.

Google autorotate

The fact that it appears to have crashed, rather than making a hard but
controlled landing suggests that it was not in auto rotation, hence my
comment.

Hum, IMHO if had "crashed" it would have gone straight through the
roof in one hit. It doesn't appear to have done that, it rather hard
and damaged the roof enough for it to then collapse a number of
seconds later.

The occupants should have survived a controlled landing. It is reported
as coming down fast and without the rotors turning.

The pub is also right next to the river, the pilot may
have be trying to put ditch it there but didn't have suffcient
control/time. You need a significant amount of height to switch a
helicopter from powered to autogyro flight.

Unless it was at the scene of an incident, which does not appear to be
the case, I would expect the helicopter to have been near the river
because it was flying along it. Rivers are usually helicopter routes
through cities, because it minimises the risk to people on the ground if
there is a failure.

Exactly. It suggests some sort of catastrophic failure.

It does seem very odd for a twin engined helicopter to "just fall out
of the sky". There has been very little reported from eye witness
reports but I guess it was dark. Some mention of tail rotor failure

If the tail rotor failed, then the response would be to put the
helicopter into auto rotation, which removes the engine torque. That
should not result in a crash like this.

and Eurocopter do have some what of a reputation when it comes to
gearboxes...

This particular model does not, although there was a recent
Airworthiness Directive, after cracks were found on a hub flange in
France. SFAIK, only a couple of others have come down, one due to pilot
error and one where the AAIB were unable to find any cause.

Do these small civilian aircraft have data and voice recorders?

BBC reports say it is not thought this helicopter was fitted with a
flight recorder. However, there would be both aviation and Police radios
aboard. If they were not used, it suggests a very sudden event. If they
were they would have been recorded and the recording passed to the AAIB.

Colin Bignell

On Mon, 02 Dec 2013 08:44:40 +0000, Dave Liquorice wrote:

It does seem very odd for a twin engined helicopter to "just fall out of
the sky". There has been very little reported from eye witness reports
but I guess it was dark. Some mention of tail rotor failure and
Eurocopter do have some what of a reputation when it comes to
gearboxes...

Except if it had been a tail rotor failure, would it not have corkscrewed
down rapidly?

The lack of damage to both main and tail rotors suggests neither was
doing very much.

On 01/12/2013 18:13, GB wrote:
If a helicopter landed on my roof… I would either expect the roof to
collapse straight away or to stay up. In the case of the Glasgow pub,
the roof stayed up for several seconds after the impact, and then it
collapsed. (It stayed up long enough for the band to make a joke about
it.)

Can anybody explain the mechanism whereby that would happen like that?

It is called progressive structural failure. One part fails, which
increases the load on other parts. Ductile parts, such as steel bolts,
may then slowly yield under the higher load before finally failing
completely.

Colin Bignell

"Dave Liquorice" wrote in message
ll.co.uk...
On Mon, 02 Dec 2013 03:48:27 +0000, Nightjar wrote:

Given that it was a twin engine helicopter, with an experienced
pilot,
I suspect they stopped some time before it hit the pub.

Google autorotate

The fact that it appears to have crashed, rather than making a hard but
controlled landing suggests that it was not in auto rotation, hence my
comment.

Hum, IMHO if had "crashed" it would have gone straight through the
roof in one hit. It doesn't appear to have done that, it rather hard
and damaged the roof enough for it to then collapse a number of
seconds later. The pub is also right next to the river, the pilot may
have be trying to put ditch it there but didn't have suffcient
control/time. You need a significant amount of height to switch a
helicopter from powered to autogyro flight.


The engine automatically disconnects on power failure.
It takes a significant amout of hieght to get sufficient speed on the rotor
to make a soft landing,
So if they were low they might not have had enough for a soft landing.
The other possiblity is gearbox/rotor/transmission failure.

On 02/12/2013 10:01, Nightjar wrote:
On 01/12/2013 18:13, GB wrote:
If a helicopter landed on my roof… I would either expect the roof to
collapse straight away or to stay up. In the case of the Glasgow pub,
the roof stayed up for several seconds after the impact, and then it
collapsed. (It stayed up long enough for the band to make a joke about
it.)

Can anybody explain the mechanism whereby that would happen like that?

It is called progressive structural failure. One part fails, which
increases the load on other parts. Ductile parts, such as steel bolts,
may then slowly yield under the higher load before finally failing
completely.

Colin Bignell

I understand the concept, but I was expecting the time interval to be
short between one part failing and the next, milliseconds rather than
seconds.

On Mon, 02 Dec 2013 08:44:40 +0000 (GMT), "Dave Liquorice"
wrote:

Do these small civilian aircraft have data and voice recorders?

It was originally certified a few kg, 10kg iirc under the limit for FDR's, but
lots of info can be retrieved from engine controls and navigation equipment.

A mark 1 eyeball is usually the most useful tool
--

On Mon, 2 Dec 2013 10:33:37 -0000, "harryagain"
wrote:


The engine automatically disconnects on power failure.
It takes a significant amout of hieght to get sufficient speed on the rotor
to make a soft landing,
So if they were low they might not have had enough for a soft landing.
The other possiblity is gearbox/rotor/transmission failure.

Which bit of twin engined helicopter do you not understand?


--

On Mon, 02 Dec 2013 12:17:44 +0000, The Other Mike
wrote:

On Mon, 2 Dec 2013 10:33:37 -0000, "harryagain"
wrote:


The engine automatically disconnects on power failure.
It takes a significant amout of hieght to get sufficient speed on the rotor
to make a soft landing,
So if they were low they might not have had enough for a soft landing.
The other possiblity is gearbox/rotor/transmission failure.

Which bit of twin engined helicopter do you not understand?

(in relation to all but the last line)


--

On 02/12/2013 10:46, GB wrote:
On 02/12/2013 10:01, Nightjar wrote:
On 01/12/2013 18:13, GB wrote:
If a helicopter landed on my roof… I would either expect the roof to
collapse straight away or to stay up. In the case of the Glasgow pub,
the roof stayed up for several seconds after the impact, and then it
collapsed. (It stayed up long enough for the band to make a joke about
it.)

Can anybody explain the mechanism whereby that would happen like that?

It is called progressive structural failure. One part fails, which
increases the load on other parts. Ductile parts, such as steel bolts,
may then slowly yield under the higher load before finally failing
completely.

Colin Bignell

I understand the concept, but I was expecting the time interval to be
short between one part failing and the next, milliseconds rather than
seconds.

It will depend upon how near the strength limits the excess load is. If
you have several minutes to spare, you can watch a piece of steel being
stretched until it fails here, followed by a piece of precipitation
hardened aluminium:

http://www.youtube.com/watch?v=D8U4G5kcpcM

Colin Bignell

On 02/12/2013 09:42, Adrian wrote:
On Mon, 02 Dec 2013 08:44:40 +0000, Dave Liquorice wrote:

It does seem very odd for a twin engined helicopter to "just fall out of
the sky". There has been very little reported from eye witness reports
but I guess it was dark. Some mention of tail rotor failure and
Eurocopter do have some what of a reputation when it comes to
gearboxes...

Except if it had been a tail rotor failure, would it not have corkscrewed
down rapidly?

The lack of damage to both main and tail rotors suggests neither was
doing very much.


So gearbox failed stopping the tail rotor?
But why guess when the experts will tell us in a month or two?

On 02/12/13 18:08, dennis@home wrote:
On 02/12/2013 09:42, Adrian wrote:
On Mon, 02 Dec 2013 08:44:40 +0000, Dave Liquorice wrote:

It does seem very odd for a twin engined helicopter to "just fall out of
the sky". There has been very little reported from eye witness reports
but I guess it was dark. Some mention of tail rotor failure and
Eurocopter do have some what of a reputation when it comes to
gearboxes...

Except if it had been a tail rotor failure, would it not have corkscrewed
down rapidly?

The lack of damage to both main and tail rotors suggests neither was
doing very much.


So gearbox failed stopping the tail rotor?
But why guess when the experts will tell us in a month or two?

Doesn't add up. First thing to do is chop power on main rotor and
autorotate down.


--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

"dennis@home" posted
So gearbox failed stopping the tail rotor?
But why guess when the experts will tell us in a month or two?


You're forgetting that this was a *police* helicopter, so the experts
will tell us in a decade or three.

--
Les

On 02/12/13 18:33, Big Les Wade wrote:
"dennis@home" posted
So gearbox failed stopping the tail rotor?
But why guess when the experts will tell us in a month or two?


You're forgetting that this was a *police* helicopter, so the experts
will tell us in a decade or three.

NO it was a helicopter CHARTERED by the police or at least run
independently of them. They cannot obstruct the AAIB in any way at all.

The answers will probably not make the MSM and 'helicopter crash down to
corrosion and failure in bearing 357 in association with cracked hub
part G696 is not 'Yuman Intrest' and so they think humans wont be
interested.



--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On 02/12/2013 18:08, dennis@home wrote:
On 02/12/2013 09:42, Adrian wrote:
On Mon, 02 Dec 2013 08:44:40 +0000, Dave Liquorice wrote:

It does seem very odd for a twin engined helicopter to "just fall out of
the sky". There has been very little reported from eye witness reports
but I guess it was dark. Some mention of tail rotor failure and
Eurocopter do have some what of a reputation when it comes to
gearboxes...

Except if it had been a tail rotor failure, would it not have corkscrewed
down rapidly?

The lack of damage to both main and tail rotors suggests neither was
doing very much.


So gearbox failed stopping the tail rotor?
But why guess when the experts will tell us in a month or two?

Realistically, a year or two is more probable. There may be an earlier
interim report, if there was something very obvious, but most AAIB field
reports (ones where they are directly involved) generally take that long.

Colin Bignell