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 6th Dec 2018, 22:31
  #981 (permalink)  

Avoid imitations
 
Join Date: Nov 2000
Location: Wandering the FIR and cyberspace often at highly unsociable times
Posts: 12,195
Originally Posted by n5296s View Post
I'm curious how this could possibly be recovered given any amount of height/speed. As I understand, even entering autorotation wouldn't help - the TR is in full right pitch and you'll just rotate all the way down. I suppose with an infinite amount of good luck it MIGHT be possible to flare and touch the ground with this going on and survive, if the cabin integrity remained. But who could realistically fly an auto while rotating at what, once every couple of seconds?
As I wrote earlier, once the aircraft fuselage begins spinning in yaw, the original trimmed position datum for the cyclic no longer exists because it (the fixed swashplate) is also rotating.
ShyTorque is offline  
Old 7th Dec 2018, 04:48
  #982 (permalink)  
 
Join Date: Mar 2008
Location: England... what's left of it...
Posts: 161
" Year by year, the AAIB reports get to the point with diligence and logic whether the object of the investigation is a dinged gyrocopter or something very much more significant. How long shall we be provided with such a service ? "


In an age of replacing technical excellence and genuine quality with mitigation and perception management (for both financial and political "Gain") across much of business and life, I understand and share your concern.
Overdrive is offline  
Old 7th Dec 2018, 05:07
  #983 (permalink)  
 
Join Date: Feb 2015
Location: space
Posts: 20

This made me think that with the right software and servo's you can fly down a helicopter without a working tail rotor . Biggest problem will be for the soft to select the place to land or allow some form of human input , but from a technical point of view what i seen above means automation can fly a TR-less heli indefinitely
Ahernar is offline  
Old 7th Dec 2018, 06:30
  #984 (permalink)  
 
Join Date: Apr 2000
Location: EGDC
Posts: 7,397
n5296s - it could be survivable from a low hover or a situation where you are so close to the ground that an immediate landing could be made (probably still roll over though).

In the high speed cruise it might not be so dramatic until you slow down so perhaps a very high speed running landing might be possible, drooping the Nr to reduce the TR power (again you are probably going to roll over)

Other than those two extremes I don't believe there is any solution - they were extremely unlucky.
crab@SAAvn.co.uk is offline  
Old 7th Dec 2018, 07:47
  #985 (permalink)  
 
Join Date: May 2016
Location: Middle England
Posts: 70
Originally Posted by Ahernar View Post
https://www.youtube.com/watch?v=9XMfhKxwo2c

This made me think that with the right software and servo's you can fly down a helicopter without a working tail rotor . Biggest problem will be for the soft to select the place to land or allow some form of human input , but from a technical point of view what i seen above means automation can fly a TR-less heli indefinitely
Ah, Iím a mechanical man, not a software guy, so youíll have to excuse my ignorance that software can now overcome the established laws of physics.

FlimsyFan is offline  
Old 7th Dec 2018, 08:24
  #986 (permalink)  
 
Join Date: Jul 2014
Location: South East Asia
Age: 50
Posts: 98
Software cannot overcome the laws of physics but it can
  • diagnose the problem in millisecond,
  • analyze 100s of possibilities in a few millisecond more,
  • apply the scenario that would maximize the chance of survival.
The key to that is more sensor distributed throughout the aircraft and a huge onboard database

Did you hear about the self recovery button on the cyclic of the H160 I think this a sign of things to come
Agile is offline  
Old 7th Dec 2018, 08:48
  #987 (permalink)  
 
Join Date: Nov 1999
Location: UK
Posts: 1,142
Originally Posted by Ahernar View Post
.....This made me think that with the right software and servo's you can fly down a helicopter without a working tail rotor . Biggest problem will be for the soft to select the place to land or allow some form of human input , but from a technical point of view what i seen above means automation can fly a TR-less heli indefinitely
You seem to be missing a fundamental point: A helicopter turns its main rotor by having an engine, (or engines), pushing round - via a small gear wheel - a large horizontal ring gear which is connected to the main vertical shaft that drives the main rotor.

Newton’s third law states that ‘every action has an equal and opposite reaction’, so the turning force that the engine(s) are applying to turn the ring gear against the forces from the main rotor also pushes back on the engine(s). On the ground, this reaction force is not enough to move the helicopter when it is sitting on its skids/wheels, but in free air the reaction force pushes the engine(s), and therefore the helicopter to which they are bolted, in the opposite direction to the turning of the main rotor. The engines are effectively trying to ‘climb round the main ring gear - similar to a motorbike doing a wheelie.

To compensate for this, a tail rotor is fixed at the end of a long boom to apply a side force to oppose this reaction torque. The tail rotor has to produce a variable force to allow adjustment for varying main rotor torque, so it is made variable pitch, controlled via foot pedals. This also allows the pilot to yaw the aircraft when required, similar to the rudder of a conventional aircraft.

Having a tail rotor pushing sideways, will push the whole helicopter bodily sideways, (in the air), so the main rotor is usually offset sideways from the vertical by a small amount so a component of the lift force pushes in the opposite direction to the tail rotor, and stops the sideways drift.

When a helicopter loses its tail rotor drive, it will start turning in yaw due to the reaction to the engine torque on the main ring gear. If it has sufficient forward airflow past its tail fin, the heli will be able to fly straightish, but on slowing and landing, will yaw round and round. I am not a heli pilot but I understand the recovery is to idle the engine(s), which removes the turning torque, and gives the pilot a chance of an auto-rotation landing. This video of a ?Wessex lifting an air-con unit from a building roof and losing tail rotor drive illustrates all of this very clearly.

Uplinker is offline  
Old 7th Dec 2018, 08:53
  #988 (permalink)  
 
Join Date: Jun 2016
Location: Brantisvogan
Posts: 496
Originally Posted by Agile View Post
The key to that is more sensor distributed throughout the aircraft and a huge onboard database
Sensors can also provide bad data, to systems which will make the wrong decision as a result.
You can push a problem upstream, but it does not get rid of it.
If a servo doesn't know when it should stop, it doesn't matter whether it was someone's foot or a digital system that gave it the instruction to initially move.
You can't engineer out failures, the more underlying complexity, the more failure points are introduced.
Bell_ringer is offline  
Old 7th Dec 2018, 09:03
  #989 (permalink)  
 
Join Date: Jan 2011
Location: on the cusp
Age: 47
Posts: 217
Originally Posted by Agile View Post
Software cannot overcome the laws of physics but it can
  • diagnose the problem in millisecond,
  • analyze 100s of possibilities in a few millisecond more,
  • apply the scenario that would maximize the chance of survival.
The key to that is more sensor distributed throughout the aircraft and a huge onboard database

Did you hear about the self recovery button on the cyclic of the H160 I think this a sign of things to come
I'm a big proponent of the capabilities of avionics. But at this point it has lost a major effector. While the auto-stab may have a mode that can help level, it could also help relieve torque, but what would it use to counter a yaw forcing, possibly even beyond the design limits? I suspect nothing, at least nothing that would change the game significantly for the pilot.
dClbydalpha is offline  
Old 7th Dec 2018, 09:05
  #990 (permalink)  
 
Join Date: Aug 2005
Location: uk
Posts: 97
Originally Posted by Agile View Post
Software cannot overcome the laws of physics but it can
  • diagnose the problem in millisecond,
  • analyze 100s of possibilities in a few millisecond more,
  • apply the scenario that would maximize the chance of survival.
The key to that is more sensor distributed throughout the aircraft and a huge onboard database
One of the most recent heavy jet crashes had its root in a faulty AOA sensor being acted upon by automated systems. Something which has become very clear in recent years is that the interaction between automated systems decision making and pilot initiative is very complex, not least given the added factors of *multi-mode* automation and the cognitive barriers to a pilot avoiding being dangerously 'behind' an automated system. The decision tree in a comprehensive automated system would be dauntingly complex, subject to human error in its creation and subject to sensor malfunction in use: yet it would have to be significantly more robust and reliable than existing systems or would offer no net gain. Even then, pilots would need to defer instantly to the automation... unless the automation was malfunctioning, in which case the pilot would need to instantly fight or disable the automation. Which brings us full circle.

There is surely a case for more intelligent and intuitive safety systems, but this accident seems to have arisen from an unforeseen failure mode leading to a malfunction which in all likelihood was simply not recoverable. You can’t automate 'thinking of what you haven’t thought of' nor program a computer to fix in real time any catastrophe which sets the laws of physics in fundamental opposition to accident survivability.
robdean is offline  
Old 7th Dec 2018, 09:33
  #991 (permalink)  
 
Join Date: Feb 2015
Location: space
Posts: 20
Not going to argue much around this but there are no laws of physics preventing tailles rotor flight . You have to equalise the rotor drag with drag from the body of the aircraft . If this requires 130 rpm , 130 rpm will be necessary ,if that's not humanly pilotable does not mean some autostab will find it impossible too .Most problems will be around oscilations and vibrations in the rotor disk but for an emergency descent it should work
Ahernar is offline  
Old 7th Dec 2018, 10:09
  #992 (permalink)  
 
Join Date: Oct 2018
Location: UK
Posts: 7
Well, EASA EAD 2018-0250-E back on 19 November required inspection of the duplex bearing on both 169s and 189s before they flew again. So hopefully there are no duff duplex bearings in service anymore.

I’d dearly like to know what the inspection was specifically looking for, as that would shed light on why the bearing failed. Knowing that would probably require access to Leonardo AMPs. Anyone know?
Slowclimb is offline  
Old 7th Dec 2018, 11:20
  #993 (permalink)  

Avoid imitations
 
Join Date: Nov 2000
Location: Wandering the FIR and cyberspace often at highly unsociable times
Posts: 12,195
Looking at the photo evidence in post#983 above, a thought that crossed my mind - would a simple left handed thread on the shaft have prevented this tragedy?

Having recently changed a rear wheel bearing, even my old car has a left handed thread on the left hand side stub axle, to prevent the hub nut coming loose in service.
ShyTorque is offline  
Old 7th Dec 2018, 12:25
  #994 (permalink)  
 
Join Date: Feb 2001
Location: Europe
Posts: 505
For those with a good engineering understanding of this failure, would the tail rotor have been harder to turn by hand than normal, pre-flight, given the breakdown of this bearing? Obviously not easy to reach on a 169, but is on most smaller types.
rotorspeed is offline  
Old 7th Dec 2018, 12:39
  #995 (permalink)  

Avoid imitations
 
Join Date: Nov 2000
Location: Wandering the FIR and cyberspace often at highly unsociable times
Posts: 12,195
Originally Posted by Ahernar View Post
Not going to argue much around this but there are no laws of physics preventing tailles rotor flight . You have to equalise the rotor drag with drag from the body of the aircraft . If this requires 130 rpm , 130 rpm will be necessary ,if that's not humanly pilotable does not mean some autostab will find it impossible too .Most problems will be around oscilations and vibrations in the rotor disk but for an emergency descent it should work
130 rpm (Nr) is well below the normal operating range of modern helicopters. Most run around 275 - 350 or even higher for smaller machines, with a minimum in flight of 90% of that figure for aerodynamic reasons. Going lower would cause the blades to stall and loss of control of the rotor disc.
ShyTorque is offline  
Old 7th Dec 2018, 12:46
  #996 (permalink)  
 
Join Date: Jan 2013
Location: Midlands
Posts: 127
Originally Posted by rotorspeed View Post
For those with a good engineering understanding of this failure, would the tail rotor have been harder to turn by hand than normal, pre-flight, given the breakdown of this bearing? Obviously not easy to reach on a 169, but is on most smaller types.
With the length of the blade and the weight of the rotor, I think it would be very difficult to detect any tightness or "grittiness".
Pozidrive is offline  
Old 7th Dec 2018, 12:58
  #997 (permalink)  
 
Join Date: Jan 2013
Location: Midlands
Posts: 127
Originally Posted by ShyTorque View Post
Looking at the photo evidence in post#983 above, a thought that crossed my mind - would a simple left handed thread on the shaft have prevented this tragedy?

Having recently changed a rear wheel bearing, even my old car has a left handed thread on the left hand side stub axle, to prevent the hub nut coming loose in service.
Interesting, but your hub nut still has a split pin? It was once the practice to use LH threads on the left of vehicles, including wheel nuts. I think it was all a bit theoretical and the fact it isn't done any more suggests it wasn't really necessary.

I don't know which way this tail rotor turns relative to the control shaft, but with similar threads the nut at one end would tend to loosen and the other would tighten. One LH and one RH would both try to tighten, or loosen - depending on the rotation.
Pozidrive is offline  
Old 7th Dec 2018, 13:08
  #998 (permalink)  
 
Join Date: Nov 2006
Location: After all, what’s more important than proving to someone on the internet that they’re wrong? - Manson
Posts: 1,492
# I will let you work out the rest for what happens if the bearing fails and what could possibly happen to the nut.
Apparently so - it will be interesting to see how the design complies with CS-29.

I am surprised that the attachment of the lever mechanism to the control shaft relies purely on clamp up with the nut. No key or index?

Maybe there should be a weak point in the shaft so that the integrity of the feedback is maintained so the servo does not go to full travel?

I am amazed that things like this can still develop in this day and age. Somehow folk have lost sight of the details.
RVDT is offline  
Old 7th Dec 2018, 13:24
  #999 (permalink)  
 
Join Date: Mar 2007
Location: UK
Posts: 321
Originally Posted by ShyTorque View Post
Looking at the photo evidence in post#983 above, a thought that crossed my mind - would a simple left handed thread on the shaft have prevented this tragedy?

Having recently changed a rear wheel bearing, even my old car has a left handed thread on the left hand side stub axle, to prevent the hub nut coming loose in service.
I'm not sure that it would have done. The smaller nut would have tightened up against its cotter pin and still possibly spun with the pitch rod. It may have still welded itself to the pin carrier. It wouldn't unwind, but could strip the threads or break the pin carrier if the turning force was great enough. If the pin carrier failed and detached from the servo feedback link (as it did on VSKP- according to the report, it was found detached and lying in the TRGB cowling), the resulting loss of TR control would be the same.
Or, the tightening of both nuts on each end may increase the clamping effect on the rod and stop it from spinning, despite the failed bearing. Difficult to say really, and one for the design engineers.
nodrama is offline  
Old 7th Dec 2018, 13:29
  #1000 (permalink)  
 
Join Date: May 2002
Location: "Deplorable but happy as a drunken Monkey!
Age: 70
Posts: 16,309
Uplinker,

In your video....that was a Sikorsky S-58T that had the tail rotor drive failure.

The Pilot controlled the aircraft and was maneuvering towards a safe landing area.

He maintained power until he thought he could make an authoritative landing and cut the throttles to Flight Idle.

After the accident I had the opportunity to talk with him about the crash....and he was very bothered that he was unable to land the aircraft safely.

He did his best....but the odds were against him...but he flew the machine all the way to the ground and did not give up trying to land it.

The failure we see in the 169 under discussion was a very different kind and far more critical than that shown in your video.

It was a loss of thrust in the video and just the opposite (apparently) in the 169 crash.

The 58T was a drive shaft failure.....where the 169 was far more complicated a failure.
SASless 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.