Go Back  PPRuNe Forums > Aircrew Forums > Rotorheads
Reload this Page >

Helicopter down outside Leicester City Football Club

Rotorheads A haven for helicopter professionals to discuss the things that affect them

Helicopter down outside Leicester City Football Club

Old 8th Nov 2018, 22:32
  #721 (permalink)  
 
Join Date: May 2005
Location: UK
Posts: 5
Originally Posted by sycamore View Post
Chronus, #3, loss of tail rotor blade ,followed milliseconds later by loss of other blade(s),and probably the gearbox.. The C of G of the a/c will move to somewhere beyond the nose of the a/c ....
How can CG be fwd of nose?
Blade Slap is offline  
Old 9th Nov 2018, 00:12
  #722 (permalink)  
 
Join Date: Jan 2008
Location: sweden
Age: 79
Posts: 12
As a former helicopter pilot I experienced three total engine failures in single engine helicopters and three lucky autorotations that saved the day for my pax, me and the company. Most of my helicopter time though is logged in twin engine helicopters, one of which also gave me an engine failure, but that was in level flight and therefore nothing of interest..

With Occam's razor in mind I got to my very own simplified conclusion that this accident started with a tail rotor failure that turned out catastrophic due to no visual recovery in the blurry video. The helicopter’s counter rotation and the engine sound made me think the helicopter descended with high power and high collective all the way to the ground.. The shape of the tail rotor blades on the downed helicopter made me also think that the helicopter hit the ground with the TR not spinning at all due to a TR drive failure… Why wasn’t the pilots able to lower the collective?
arizona is offline  
Old 9th Nov 2018, 02:49
  #723 (permalink)  
 
Join Date: May 2002
Location: "Deplorable but happy as a drunken Monkey!
Age: 70
Posts: 16,309
Slap,

Originally Posted by Blade Slap View Post
How can CG be fwd of nose?
That was some British understatement being used.

When you lose the Tail Rotor Blades, Gearbox, and associated items from the very rear of the helicopter....the CG shift is forward...and very significant....causing a strong pitching movement that might exceed the ability of the flight controls to compensate for and thus cause the loss of the aircraft.
SASless is offline  
Old 9th Nov 2018, 06:32
  #724 (permalink)  
 
Join Date: Jul 2013
Location: -
Posts: 59
Originally Posted by Pittsextra View Post
Yeah that would be fair but what evidence? The video footage was available almost instantly and so now evidence surely means physical evidence from the accident aircraft or of prior events that have been caught prior to an accident with other in service aircraft. It can't be the former if the narrative around the AD is faithful and if its the latter does that take a week to get out with the commitment of intelligent minds?

It would be incredible if this isn't off the back of something seen or suspected and so why it can't be said more plainly - or indeed co-ordinated via the AAIB goodness knows... Hey Ho.
It could be that during the preliminary investigation something was found that could or could't be the main cause so Leonardo as a precaution released the SB.

The investigation is probably far from over and as far as I know no one would release informations until all data has been analysed.
MitchStick is offline  
Old 9th Nov 2018, 19:03
  #725 (permalink)  
 
Join Date: Jan 2008
Location: Hotel Sheets, Downtown Plunketville
Age: 72
Posts: 687
Originally Posted by arizona View Post
As a former helicopter pilot I experienced three total engine failures in single engine helicopters and three lucky autorotations that saved the day for my pax, me and the company. Most of my helicopter time though is logged in twin engine helicopters, one of which also gave me an engine failure, but that was in level flight and therefore nothing of interest..

With Occam's razor in mind I got to my very own simplified conclusion that this accident started with a tail rotor failure that turned out catastrophic due to no visual recovery in the blurry video. The helicopterís counter rotation and the engine sound made me think the helicopter descended with high power and high collective all the way to the ground.. The shape of the tail rotor blades on the downed helicopter made me also think that the helicopter hit the ground with the TR not spinning at all due to a TR drive failureÖ Why wasnít the pilots able to lower the collective?


My guess would be because it was a time critical event.
Factors are : Height above ground coupled with the likelihood of occurence at critical moment of transit to forward flight, size of helicopter, twin engines, high rotation speed following TRFand location of site.
Any chance of succesful recovery would have entailed almost instant recognition of TRF, immediate power reduction and simultaneous pitch down for immediate descent and autorotation, which would involve a high ROD and require favourable terrain below. Might be survivable at low height but not so at the sort of height involved in this instance.
I would readily admit I know little about rotary wing, but I understand that they are far less forgiving than their fixed wing sisters. One thing in common must be that with the vertical stab gone on a fixed wing it also spells curtain time, but as in the cases of the JAL123 747 which managed slightly better than AA 587 they seem to keep going for a little longer before the inevitable. With rotary wing the equivalent of no TR means in no time at all the machine assumes the characteristics of a dandelion strung to a brick.
I really don`t think even the most accomplished pilot could have pulled it off. It would have been a far greater miracle than the Hudson one if they had, would be my humble view.
Chronus is offline  
Old 9th Nov 2018, 20:54
  #726 (permalink)  
 
Join Date: Sep 2015
Location: UK
Posts: 1
Originally Posted by Chronus View Post
One thing in common must be that with the vertical stab gone on a fixed wing it also spells curtain time, but as in the cases of the JAL123 747 which managed slightly better than AA 587 they seem to keep going for a little longer before the inevitable.
Chronus: Is this because of loss of yaw stability or the shift in CG?
Jagwar is offline  
Old 9th Nov 2018, 21:36
  #727 (permalink)  
 
Join Date: Jun 2002
Location: east ESSEX
Posts: 3,209
Jag,you will lose your stability in yaw,coupled with the C OF G change; you might be able to crowd pax into the back to restore/mitigate the CG PROBLEM.The a/c if disturbed in yaw or roll will probably start Dutch -rolling which will require a lot of handling skills,especially during any configuration changes,and approach/landing....or may not.. A B52 lost it`s fin/rudder and landed safely-see u-tube..

Slap,in my case of t/r and gearbox departure ,the change of CG was about 3" forward of the Fwd limit,`past my nose, anyway`!! The stick has reached the back-stop ,and the a/c has changed direction by about 50-60*;entering autorotation and chopped the engine leads to a further pitch down ,but there is a `pimple` of a hilltop with cleared scrub that we are pointing at.
To flare requires another quick fwd stick and back again with lever,as it`s also uphill,but at zero groundspeed.Landed upright,but burst a main tyre on a treestump.. ...There is a pic on `Rotorheads around the World-views from cockpit(not video) ,page 15....
sycamore is offline  
Old 10th Nov 2018, 13:38
  #728 (permalink)  
 
Join Date: May 2004
Location: Tax-land.
Posts: 865
Originally Posted by SASless View Post
Slap,



That was some British understatement being used.

When you lose the Tail Rotor Blades, Gearbox, and associated items from the very rear of the helicopter....the CG shift is forward...and very significant....causing a strong pitching movement that might exceed the ability of the flight controls to compensate for and thus cause the loss of the aircraft.
That is not always the case SAS, I agree on the forward shift, however actual CG position at time of accident is a big part of the equation.
You can PM me and we can talk the details.
tottigol is offline  
Old 10th Nov 2018, 14:57
  #729 (permalink)  
 
Join Date: Jan 2010
Location: South of France
Age: 63
Posts: 15
Why look for a TR failure ?

Statistically there are many more accidents due to unanticipated yaw -- so poorly named as LTE -- than due to TR failures. Looking at the initial yaw, there is no abrupt acceleration. If it is a TR failure, I guess you have to look for a very progressive failure...
AAIB investigations will say it.
AMDEC is offline  
Old 10th Nov 2018, 16:52
  #730 (permalink)  
 
Join Date: Aug 2000
Location: UK
Posts: 3,662
The reference datum is a reference plane that allows accurate, and uniform, measurements to any point on the aircraft. The location of the reference datum is established by the manufacturer and is defined in the aircraft flight manual. The horizontal reference datum is an imaginary vertical plane or point, placed along the longitudinal axis of the aircraft, from which all horizontal distances are measured for weight and balance purposes. There is no fixed rule for its location, and it may be located forward of the nose of the aircraft. For helicopters, it may be located at the rotor mast, the nose of the helicopter, or even at a point in space ahead of the helicopter. While the horizontal reference datum can be anywhere the manufacturer chooses, most small training helicopters have the horizontal reference datum 100 inches forward of the main rotor shaft centerline. This is to keep all the computed values positive. The lateral reference datum is usually located at the center of the helicopter.
.................................
Thomas coupling is offline  
Old 10th Nov 2018, 17:39
  #731 (permalink)  
 
Join Date: Aug 2001
Location: Shropshire
Posts: 592
Thatís the datum TC, not the C of G.
Cheers
TeeS

Just realised that was a quote but canít find where it was from, sorry if I misunderstood the point of your post.
TeeS is offline  
Old 11th Nov 2018, 04:53
  #732 (permalink)  
 
Join Date: Oct 2016
Location: NW
Posts: 78
You will not have "CG move in front of the nose" even you lose the TR while keeping the H stab. Thats BS unless helicopter had been loaded nose heavy anyways. Most of the weight are lining up with the MGB and the moment of inertial will hard to overcome. FM says it all.
Mee3 is offline  
Old 11th Nov 2018, 08:37
  #733 (permalink)  
 
Join Date: Jan 2008
Location: Herts, UK
Posts: 729
Originally Posted by MurphyWasRight View Post
From the picture it seems improbable that both locking means were missing/misinstalled.
There is a more subtle issue of the effects of the washer (140) either missing or on the wrong side. This would not jump out on a visual inspection like missing locking means would.

Not discernible from the drawing but appears that the shoulder the washer sits on is probably just a bit larger than the hole in the hinge bracket (90). Lack of washer would allow the system to operate normally but might cause high stress on the hinge bracket leading to a fracture. Even without a fracture it could dig a hole in the hinge bracket resulting in play that could cause other issues such as the nut being loose which in turn could cause other damage.
MWR ... If you are in any way correct, this implies a really poor original design... a prime goal in mechanical components design just as important as stessing and robustness is clarity of assembly whilst minimising potential for mis-assembly...
e.g. all bolts in a locality doing much the same job being of the same length, usually arranged by say stepping a casting thickness .. EVEN IF IT COSTS WEIGHT..
HarryMann is offline  
Old 11th Nov 2018, 11:57
  #734 (permalink)  
 
Join Date: May 2004
Location: Tax-land.
Posts: 865
Originally Posted by Mee3 View Post
You will not have "CG move in front of the nose" even you lose the TR while keeping the H stab. Thats BS unless helicopter had been loaded nose heavy anyways. Most of the weight are lining up with the MGB and the moment of inertial will hard to overcome. FM says it all.
Nailed it!
tottigol is offline  
Old 11th Nov 2018, 12:23
  #735 (permalink)  
 
Join Date: Dec 2006
Location: UK and MALTA
Age: 56
Posts: 1,188
Originally Posted by tottigol View Post
Nailed it!
He has not really "Nailed" it. the "Unless" statement is still hogwash.

To have the CG in front of the nose of the helicopter, you would need a MRB sticking over nose, the portion beyond the nose, weighing more than the entire helicopter behind it.

To keep this sensible and simple, The Helicopter CG should be directly under the Main Rotor Mast centroid both Longitudinally and Laterally. That's the optimum ideal position giving 100% MR flight control in all directions.

However, practically speaking, there has to be some loading of the helicopter which would cause the CG to move around the rotor centroid. It cannot move that much. Even in a large helicopter like an EC225 it can only move 0.5m longitudinally.

There are limits to how far the CG can move away from the rotor centroid before effective flight control is compromised.

If the TRGBX and its blades depart the airframe, the CG will make a significant move forward. It is highly likely in ALL helicopters that this will result in a significant compromise of the forward CG limit and effective aft cyclic to counter the forward movement of the CG will reach the aft stop before the pitch moment forward can be cancelled. The results.....well not pretty.

The Datum, as someone has already posted, is simply a point in space to facilitate all calculations to be in the positive range. Usually it is quite a way out in front of the helicopter nose to facilitate the fitment of long PITOT probes during certification. For simplicity, it remains there. Therefore, the limits for longitudinal CG are expressed in positive numbers and to keep the theme at the EC225 4.4m to 4.9m. This actually means, behind the datum. Not in front of the rotor centroid.

I know 99% of Rotor heads know this but to clear up the incessant garbage postings by the odd individual who seems confused....enjoy!
DOUBLE BOGEY is offline  
Old 11th Nov 2018, 14:03
  #736 (permalink)  
 
Join Date: Oct 2006
Location: UK
Posts: 4,570
The only occasion I know off where the main door departed into and then removed the tail rotor assembly resulted to a massive pitch down which the pilot tried to correct with aft cyclic. The caused the main rotor, in sympathy with the pitch up of the tail boom to slice off the boom just aft of the mounting point.

The ensuing pandemonium resulted in the aircraft descending almost vertical and killing everybody on board.
Fareastdriver is offline  
Old 11th Nov 2018, 14:08
  #737 (permalink)  
 
Join Date: May 2002
Location: "Deplorable but happy as a drunken Monkey!
Age: 70
Posts: 16,309
Bristow lost a 412 in Nigeria and the evidence showed a Cabin Door had come into contact with the Tail Rotor.

The flight was at night in IMC weather.

The aircraft and occupants were not recovered as I recall.....just some odd bits and pieces.

A ROV was lost on the first dive and the search was called off afterwards.
SASless is offline  
Old 11th Nov 2018, 16:00
  #738 (permalink)  
 
Join Date: Dec 2007
Location: devon
Age: 80
Posts: 364
Bristow lost a 212 in the Sumatran jungle when the T/R departed in the cruise with half of the 90 box. The T/R was not found within a few hundred yards of the crash site. It later found by some Indonesians who were paid a lot of rupiahs, the distance from the locus could not be determined. The rotor was examined by the AAIB and it was determined that it had been hit by an oil cooler duct. The aircraft had caught fire and the port side was burnt out but the starboard panel was still attached. It was assumed that a faulty catch on the panel had failed and the panel had flown over the tail boom and hit the rotor.
Oldlae is online now  
Old 11th Nov 2018, 16:20
  #739 (permalink)  
 
Join Date: Jun 2002
Location: east ESSEX
Posts: 3,209
For; Blade Slap,totti,M3- perhaps I should have put the phrase about the CG` beyond the nose`` in italics/commas,or a couple of smilies.It was meant to imply that the loss of a tail-rotor and gearbox will have a very significant FWD C o G change,irrespective of where it was originally,and if it was FWD AT THE TIME you will get a significant NOSE DOWN pitch.
In my case ,I had 2 engineers at the front of the cabin,looking at the rear of the engine and reduction g.box checking for oil leaks,as we had just done an engine out,change a component /pipe on the back of the gearbox,, engine back in,and RTB.,so my CoG was well Fwd anyway.
I might suggest if you are pilots or gingerbeers that you go ,find the appropriate tech manual which shows all the weights for tailrotor ,g/box,etc and work out the resultant change of C o G ,if they should depart,......
SAS,DB, thanks....
sycamore is offline  
Old 11th Nov 2018, 19:03
  #740 (permalink)  
 
Join Date: May 2004
Location: Tax-land.
Posts: 865
Originally Posted by sycamore View Post
For; Blade Slap,totti,M3- perhaps I should have put the phrase about the CG` beyond the nose`` in italics/commas,or a couple of smilies.It was meant to imply that the loss of a tail-rotor and gearbox will have a very significant FWD C o G change,irrespective of where it was originally,and if it was FWD AT THE TIME you will get a significant NOSE DOWN pitch.
In my case ,I had 2 engineers at the front of the cabin,looking at the rear of the engine and reduction g.box checking for oil leaks,as we had just done an engine out,change a component /pipe on the back of the gearbox,, engine back in,and RTB.,so my CoG was well Fwd anyway.
I might suggest if you are pilots or gingerbeers that you go ,find the appropriate tech manual which shows all the weights for tailrotor ,g/box,etc and work out the resultant change of C o G ,if they should depart,......
SAS,DB, thanks....
Not all aircraft are affected the same, it seems that the 212/412, perhaps the H-1 series and civilian counterparts suffer the most.
I am aware of more than one 407 TRGB and a portion of tailboom departures back in '98/2000 where a successful autorotation was made at least once to the water (PHI GoM 1998 or '99) with a full load of passengers, the pilot reported no excessive pitch down moment.
As far as consulting the appropriate tech manuals, I have access to a couple of types (which I cannot disclose) and we ran calculations confirming that the loss of the TRGB and the TR blades does not move the CG forward to a catastrophic unrecoverable value.
HTH
tottigol is offline  

Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.