KH4 Trouble

[masteroff]

Hi everyone. Quick question, our Kh4 has a problem. It has developed an 'oscillation'? It feels very unstable in the hover like you are constantly chasing it with the cyclic in nil wind. I noticed on approach that it followed a constant cycle as if I was moving the cyclic in a circular pattern. Has anyone experienced this before?

[topendtorque]

1 Consult your engineer you say it is unusual, DO NOT FLY.

2 has there been any metal in the engine filter on the last two oil changes.

3 if you have an extra spin on filter did you cut it open and examine for any metal

4 recently a head and mast assembly fell off a KH4 causing it to descend quickly (surprise) from its luckily very low altitude.
5 no one but no one has talked about what must have been chronic filter contamination that time for at least the last two oil changes. in that case the tip is that the mast bearing let go after what must have been large amounts of evidence in the filter

6 in this case it could be that your spigot bearing in the xmon at the bottom of the mast has collapsed

7 it could also be that your mast has broken just above the spigot bearing in the xmon

I have seen both situations and in either it could be that metal has not yet accumulated in your filter,

8 check that your four gimbal bearings are not worn and particularly that the head is not being allowed to float from side to side i.e. longitudinally. also that the gimbal is not broken

8 (a) check that the trunnion is not broken off one end wear it goes into the gimbal

9 check that your sprag mounts (there are two on the KH4) at the bottom of the engine is secure on to the mainframe, and of course that the sprag rubbers are not broken

10 never but never fly with a deteriorating lateral. it could be a sign of a cracking mast. or other terrible things

11 make sure that the engine basket does not have a broken tube.

12 make sure that the power cylinders and control rods are all attached securely

13 it is imperative that you check that the stab bar, damper frame and damper clamps are not cracked or broken or that either damper is not broken on the shaft where the damper arm connects.

never but never fly with a US component anywhere near there. one broken damper makes it squashy, a completely disconnected damper assy means extremely scary and super sensitive over controlling of feedbacks. usually a crash will ensue.

14 in all of the above refer to RULE #1

[topendtorque]

Oh, and I should have said, please forgive me, it was eight hours bottle to throttle eh?

[masteroff]

Thanks TET. Lots of info there. Will check it out in the morning. Although these machines usually have some slop in certain parts, this is definitely not normal. Its all over the shop in the hover.
Thanks again, Masteroff

And I forgot to mention we did an oil change today and there was lots of 'curly type metal shards'. Looked more than usual to me.

[spinwing]

GROUND IT ....pending engineering action ... DEFINATELY make an entry in the A/C maintenance documentation to reflect the flight control snag AND the contamination found during the oil change.

:mad: :eek:

[masteroff]

Hi guys and girls, heres a couple of photos of the filter materail I cleaned yesterday. A/C is now grounded pending investigation.
http://i176.photobucket.com/albums/w186/mark_heli/Filtermaterial2.jpg
http://i176.photobucket.com/albums/w186/mark_heli/Filtermaterial-1.jpg
Let me know what you think.
Masteroff:eek:

[topendtorque]

You could either turn it into a tin mine or give the contaminants to your engineer.

he will see if it is magnetic and burn it to check what colour flame it gives of - which tells him what material it is and then usually he will know straight away where it came from.

In this case as it is coupled to bad flying characteristics and the look of the shards it may be that it is the cage of your spigot bearing has collapsed thus allowing the needle rollers to fall out.

For sure the mast will have to come out and for very sure even if it is only minor damage then the xmon will still have to come off to be stripped and cleaned as any material which may have lodged elsewhere will do more damage. expensive damage.

It doesn't appear that there is quite enough material there to have bypassed the pressure relief on the oil filter. if it has then the engine will also have to be stripped and cleaned, so to all of the oil lines and the oil cooler.

Had it bypassed you should have seen the oil pressure flicker then go straightaways to about 32 to 35psi. The system is designed to maintain that pressure so that at least even though the engine will be rooted and pumping dirty oil, at least the cylinder skirt jets will still function at about their 28psi design pressure, if not blocked with metal.

This gives you a bit more time to notice the problem and land before it seizes as the oil stops your cylinders and piston walls from overheating and starting to get really serious about stripping metal off each other.

If it did bypass then its a complete overhaul and rebuild- about 35k or more I think the rate is.

if your spigot bearing did collapse i suggest that it is a symptom of another underlying problem

your sprag rubbers may be too hard and not allowing feedback vibrations to be cancelled out there where they should.
If the machine has been operating in cold weather for more than a year they usually go too hard.

Your pwr cylinders and next in line upwards control rods may not be in a straight line meaning that you can get an oil-canning effect which gives rise to a blade going out of track (commonly called the death rattles) which will overload the spigot and sprags if not arrested.

Have fun, i suggest knock off for the day and have a beer and speak nicely to your engineer, especially if it out in the hot sun somewhere hard to get at.

[masteroff]

And I forgot to mention the engines done about 90hrs since new!!!

[topendtorque]

i've obviously made your day, :) if it's that bad.

i suggest before you go past go, buy your engineer a carton of his favourite syrup,

we'd all like to hear what you find, it may help others.
tet

[Reefdog]

masteroff

Mate cant see any part # on the metal so it should be right!!! just kidding mate

GROUND the heap of JUNK

Just as a matter of interest is this machine near Katherine?????????
havent flown a KH4 for 20 years now I remember why

[masteroff]

No mate, nowhere near Katherine. About 2000 miles....
I'll keep you all posted on develpments. Thanks.

[rotorque]

Hi MO,

As people have said already, you need to get clarification from the engineers regarding the metal.... I am sure you already know this.

I would be confident to say that the control feedback has little to do with the metal found in the engine, it is most likely a 'happy' coincidense.

I think TET may have mentioned the sprag mounts already. I am pretty sure that they are the culprit for introduceing an oscillation. These are the four rubber mounts under the engine that connect the dry sump to the frame. when these rubbers change composition over time (which they always do) we get some pretty impressive changes to the overall feel of the aircraft. Remember, any movement at this attachment point will be directly transmitted to the rotor head as all the components are connected and pivot around the basket mounts. A move of around 10mm at the bottom will be exaggerated by a factor of 4 by the time it reaches the head.

If the lateral sprags find a frequency that is unstable then we will feel the aircraft 'shunt'. Feels like the machine has just been kicked in the rear... a very disconcerting change but easily recognised. If the longtitudinal sprags are stuffed then we get a lateral bounce in the machine. An interesting one is when either both sets play up or the resonance of one set interferes with the other...... we then get all sorts of wobbles..... This is what I think you are experinceing.

Get them checked while you are there. If you are out in the field, engineers can just change the torque on the bolts holding the sprags. This in turn changes the resonance of the sprags allowing you to see which ones are playing up.

Anyway, I am sure you are going to follow through with the engine prob so we look forward to hearing what has happened to the old girl. I would be interested to hear if it has anything to do with the control feed back.......

Last thing, the 47 and KH4's are a wonderful aircraft. Sure they have problems as any older airframe is expected too, but not once in my career operating them did they not 'tell' me there was something wrong..... It sounds like you have listened to yours as well MO... good one.

Cheers

[topendtorque]

but not once in my career operating them did they not 'tell' me there was something wrong..... It sounds like you have listened to yours as well MO... good one.


Well rotorque I've heard of horse whisperers, but this one takes a bit of beating. Your comments do reflect some KH4 and Bell 47 experience.

Perhaps in the text below which refers to an incident at xmas time you'd like to relay what the, ah, whisperin' was all about. Or, was the operators in need of a set of hearing aids?

4 recently a head and mast assembly fell off a KH4 causing it to descend quickly (surprise) from its luckily very low altitude.
5 no one but no one has talked about what must have been chronic filter contamination that time for at least the last two oil changes. in that case the tip is that the mast bearing let go after what must have been large amounts of evidence in the filter


all the best sunshine
tet

[rotorque]

Hi TET,

Your probably right, it does sound a little dickie. I made the assumption that MasterOff is a young fella who deserves a pat on the back for taking notice of what his aircraft is doing. So much for subtle compliments.

TET, you obviously have a 'bee in your bonnet' about that KH4.

I can't help you in your witch hunt. You have made numerous assumptions and accusations that honestly make me wonder what the connection is with you and the operator. You deleted the last thread you started about the incident, I was hoping it was because you thought better of the comments or found out what actually happened...... Obviously not.

I don't know what happened to that KH4.... I 'horse wisper', I don't 'cross over'.

:ok:

[topendtorque]

TET, you obviously have a 'bee in your bonnet' about that KH4.

I can't help you in your witch hunt. You have made numerous assumptions and accusations that honestly make me wonder what the connection is with you and the operator. You deleted the last thread you started about the incident, I was hoping it was because you thought better of the comments or found out what actually happened...... Obviously not.

I don't know what happened to that KH4.... I 'horse wisper', I don't 'cross over'.


Well rotorque, I misjudged you, I did think that you may have known something about it.

I guess we can rest easy now that some time has elapsed and our erstwhile ATSB friends have not made a song and dance about any “conditions found that would make for unsafe flight in identical models.”

That is where I was coming from. I mean if someone told you that a so far very reliable type had all of a sudden had the f’n head fall off and no reason was forthcoming, wouldn’t you nearly spill your brew. Some of your mates might have even been in mortal danger?

I guess that we can just assume that the mast bearing was wearing out – UNNOTICED – and then fell off. Mighty strange that, if that’s what you say.

I do hope that someone says a prayer for the pilot, a very, very lucky boy.

Who ever forgot to look at the filter evidence, well they need their backsides kicked until their nose bleeds.

I’ll be very happy to retract that if it is proven that the head fell off without prior long term metal in filter evidence.

As far as the operator is concerned, I don’t know him or ever had a beef with him. If the above scenario is true and he contributed in any way then I suggest that the Gestapo will kick his backside and save us all the trouble. Don’t you agree?

And for your info, no I did not delete the thread. That was done by head office I believe. The technical reasons for which I did ask, but so far have not received an answer. That bit, I thought, was not quite cricket!

Not a witch hunt mate ~ a truth hunt. So, how are your nags going? You should talk to ‘inthetin’, it’s a fair bet that he’s forgotten more about them than I ever learnt.
tet

[NorthSeaTiger]

So what happened ? A head and Mast just let go and flew off on its own with no prior warning ? No metal on mag plugs or filters ? Just went bye-bye ?

NST

[topendtorque]

So what happened ? A head and Mast just let go and flew off on its own with no prior warning ? No metal on mag plugs or filters ? Just went bye-bye ?


Yep, see below.





Occurrence Details Occurrence Number:200607687Location:5NM northeast Mt GambierOccurrence Date:20 December 2006 State:SAOccurrence Time:1430 ESuTHighest Injury Level:NoneOccurrence Category:AccidentInvestigation Type:Occurrence InvestigationOccurrence Class:OperationalInvestigation Status:ActiveOccurrence Type:CollisionRelease Date:
Aircraft Details Aircraft Manufacturer:Kawasaki Heavy IndustriesAircraft Model:47G3B-KH4Aircraft Registration:VH-LFKSerial Number:2133Type of Operation:Other Aerial WorkDamage to Aircraft:DestroyedDeparture Point:Mingbool, SADeparture Time:nkDestination:Mingbool, SACrew Details:RoleClass of LicenceHours on TypeHours Total Pilot-in-CommandCommercialnknk


Abstract (http://www.atsb.gov.au/publications/investigation_reports/2006/AAIR/aair200607687.aspx#tab_abstract)
During aerial spraying at 20 ft AGL, the pilot reported a loud bang followed by a loss of collective control. The helicopter landed heavily and the main rotor detached from the fuselage.
The investigation is continuing.

[ericferret]

Many years since I worked on one of this breed. I seem to remember that the fitting on the bottom of the engine which attaches to the sprag mount assy goes into a bush which when it wears can cause this problem. Can be checked by shaking the mast while someone underneath inspects the bearing.

ericferret

[masteroff]

Hi guys, had some dramas with the dampeners and got that sorted. Ran the engine again but the evidence remains. Separated the Gearbox from engine and looked at the clutch and all seems fine. Next step I'm told is to delve deeper into the engine to find out. The metal is not magnetic so hopefully rules out bearings somewhat. I'll keep you's posted.

Masteroff

[ericferret]

Big end bearings, piston/ piston pin caps, chrome ring material, camshaft bearing surface,

It's not a plastic type material is it? As I seem to remember that some of the main gearbox bearings had plastic in them.


ericferret

[topendtorque]

I think you are entitled to change your handle to 'master coming on'.:)

Unlike your endorsing instructor on type who evidently didn't brief you well enough for you to be aware of Damper clamp problems so that you would be ahead of problems that would cause the below spontaneous statement.:{ If it was only a problem in the damper area that caused it that is.

It feels very unstable in the hover like you are constantly chasing it with the cyclic in nil wind.

The plastic ef talks about could be the spacers in the xmon planetary gear roller bearings, which should have been coupled to a small quantity of tiny steel slivers as the rollers tumble and break up.

Or maybe its a piece of the red o ring out of the starter drive adapter assy. That should have been coupled with lower oil pressure indication as well. I'd pull that before i pulled the engine out. But I don't know where the other material would be from in that event.

If its magnesium, we once found the accessory gear box drive gear bearing support - so chewed out that the gear was all set to disengage. But there were vast quantities of ground up magnesium in the filter very quickly.

The other test that ef talks about of rocking the mast for movement of the sprag rod ends, should be followed with the same test only checking for excess movement between the collective sleeve and the top of the inner ring of the swash plate.

I assume that you did pull the mast out before you pulled the xmon off? and also that you checked for absolutely no material of any sort sitting in the usual muck in the inner portion of the xmon drive gear on top of the engine?

[masteroff]

Thankyou for your comments. You obviously know more about me than I do. The non ferrous metal in the filter is still a mystery but have got the engineer working on a saturday so thats a good start.
Will let you know the outcome. :hmm:

[ericferret]

The more we look at this the more I realise that you really needed to know your stuff on these older aircraft.


ericferret