Mystery R44 Damage

[B47]

http://i301.photobucket.com/albums/nn65/mpatrickw/R44damage.jpg

To all engineers and R44 owners – ever seen anything like this?

The damage happened on a one hour flight from my home base and back – no field landings, rough surfaces or gravel.

The damage is just behind the port skid support and was clearly made by an object from inside, travelling outwards. The hole is in line with the alternator pulley (all cooling vanes intact) and the exhaust (all intact). The only thing with sufficient energy and centrifugal force to throw something hard at the panel from the inside is the main fan but the shroud is all fine. The main drive belts could possibly have thrown something like a washer if it fell into them from above, but it’s hard to imagine enough force to puncture the panel.

I’ve checked the whole engine bay on two occasions for half an hour each, panels off and from underneath and there is nothing missing or loose. I’ve flown her for four hours since the damage and all is fine.

I and my engineers are completely baffled!

There is a possible trajectory for an object that passes from a couple of inches below the identical starboard panel, rising up into the engine bay to the exit hole. Don’t want to be dramatic, but can any of you ex-mil types tell me if a bullet can make anything other than a round hole, especially in a curved panel?

If you have any experience of damage similar to this or have a sensible theory I’d be grateful to hear it. Regardless of the fact that machine is fine and safe, I hate not knowing what caused it.

P.S. If anyone is going to bother with Robbie knocking wisecracks, they better be HILARIOUS - this is serious!

[Jetscream 32]

have you spoken to mike or quentin smith from heli - air?

irrespective of how well you have looked at it - something that can punture the panel outbound is worth a full and frank investigation by expert Robbbie engineers - unless your autoration skills are red hot and very very current - i would err on the side of caution and spend 500 quid having experts looking at it.... slightest hint of a problem hit the ground floor button........ :ok:

[ShyTorque]

My immediate thought was a piece of the the generator cooling fan; I once had one let go on my Triumph Spitfire. It sounded like I had been shot at. It made a big dent outwards on the steel bonnet, very similar to that.

Have you taken pulley off and had a proper look?

I can't think of anything else rotating fast enough to send something out with so much force. If something has dropped into a fan, there will surely be some witness marks, somewhere.

If it was a bullet, there would have to be an entry point as well as an exit wound!

I wouldn't want to fly the machine until this was properly resolved.

[timex]

I would suggest a good look at all panels and attachments for missing screws, and also a good engineering check before getting airborne again..


Shaun

[effortless]

The hole is very washer shaped.

[B47]

Shytorque:

>>If it was a bullet, there would have to be an entry point as well as an exit wound!


The bottom of the rear engine bay on a R44 is open - no panel.

[206 jock]

Are you 100% sure this was something inside travelling out? The funny marks around it (bottom right) look like something COULD have been bashed against the metal from the outside, puncturing then peeling back the metal.

I'm no engineer or metalurgist, but I wouldn't have thought that something penetrating from the inside out, wouldn't have peeled it back like that, it would have made more of a puncture wound.

Small child armed with fencepost,or malicious git with a screwdriver? Followed by a less-than-perfect walkround? We've all done them!

[Lt.Fubar]

Don’t want to be dramatic, but can any of you ex-mil types tell me if a bullet can make anything other than a round hole, especially in a curved panel?If it not be the first thing a bullet would go through, you could get similar hole because some bullets tumble, and go out sideways. But the size and shape of it... I think you could rule out anything except the steel core of 7.62 AP ammo. And I don't think you have enemy's with AKs or SLRs and military surplus ammo ;)

So... if no other holes anywhere else, or deep scratch marks, than this is not a bullet exit hole.

[helimutt]

Not quite a hilarious reply but at least it gives you the chance to repaint it in a decent colour unlike the present awful colour it is now!! :ok::eek::E

ps, looks like a something about 1/2" long exited, are there any other witness marks on the inside of that little flappy bit which we can't see?

I'd get it all checked as, an imbalance due to a small piece being missing, could end up costly, in more ways than one.

[ShyTorque]

The bottom of the rear engine bay on a R44 is open - no panel.

OK, understood, but from the photo it looks like the trajectory was sideways and downwards. I would have thought for a bullet to come in from below and exit like that, and leaving other than a round hole it would have hit something elsewhere first, leaving some evidence in the bay.

I would rather suspect my first guess, or a screw came out and got pinged out at speed by a rapidly rotating component.

[B47]

Helimutt,

You're in a minority there. I get loads of unprompted compliments on the colour scheme (metallic blue and yellow - Astro scheme). But - each to their own!


But, back to the thread...

No ground damage outside flying time was possible. My machine is kept in my own locked hanger. No kids, no sharp objects, no opportunity for malicious damage or accidents.

Thanks to everyone for the suggestions - keep them coming. I'll take another look at the alternator pulley tonight. I've torquesealed marks to the ring gear and rotated it carefully to make sure every single tooth is OK, but I'll treble check the alternator pulley.

[Overdrive]

Strange. Comparing it to your thumb nail, it does look washer sized/shaped as someone said, but... I'd be surprised if anything but a very thick, heavy washer could do that, even at high speed. If a washer's gone from the ship, then a nut or bolt has gone; surely you'd've spotted that in an hour of checking.

No chance a tool was left somewhere that got fired at the panel then bounced out of the open section?

[Pink Panther]

Are the scorch (arcing) like marks around the damaged area connected in any way? :confused:

[irc1804]

From the marks on the bottom of the split, the projectile might not have exited through the panel, just split it and rebounded internally, and looks like it might have been bolt shaped or round (ball bearing)



Looking at the discolouration to the paint work, to the right of the hole .....are these oil spots ???

just my 2 pennies worth

[gizmocat]

http://www.boxoffrogs.org.uk/web/r44damageref.jpg

Just a hypothesis, not a theory, and thinking 'bolt-shaped object'.
Using the above pic for reference to the original, judging by the deformation, the initial point of impact looks like "A". Possible witness marks appear at "B" when the object spun sideways.
I'd look for something missing about "C" long.

[B47]

The marks around the hole are only oil spray - not significant, just a small spill while filling and it then works its way out of the panel where it joins the skid skin. I'd wiped down the panel to take the photo and this is the part I didn't touch to make sure I didn't rip my fingers..

[helicopter-redeye]

I'm not sure which way the moving parts on the 540 engine rotate - clock or anti clockwise, but if anti then any loose item could have been picked up[ by the fan, alt or belt drive (or the V belts) and been thrown to the lower left with great force. The engines do shed the pot cover screws (big grey ones/ 3 per cap) quite regularly, so if one got loose it could have gone that way with some force if thrown by a belt or fan - see if any are missing towards the back - take the side inspection panel off to check.

h-r;)

[helicfii]

Maybe a washer fell into your drive belt and got fired into the cowling? I don't think so.

How many hours since maintenance was performed? Might have been a screwdriver or other tool left in the engine compartment that hit the fan belt, punctured the cowling, then fell out somewhere...

More than likely it was a tool left in there. Something pointy with a handle! :eek:

[Cyclic Hotline]

Judging from the forensic work of gizmocat, I would have to say;

Colonel Mustard, in the Engine Room, with the washer!

The colour of the aircraft is the give away clue! :8

[Capt Hollywood]

I'm no engineer or metalurgist, but I wouldn't have thought that something penetrating from the inside out, wouldn't have peeled it back like that, it would have made more of a puncture wound.

Here are a couple of pics of shrapnel damage after the Kaflex shaft let go on a Jetranger we were operating, very similar effect to the picture above. Must be something to do with yellow aircraft!

CH :cool:

http://i112.photobucket.com/albums/n197/danodwyer/Bell%20206/shrapneldamage.jpg

http://i112.photobucket.com/albums/n197/danodwyer/Bell%20206/Shrapnel.jpg

[gizmocat]

Colonel Mustard, in the Engine Room, with the washer!

Yeah, OK CH. Like I said, just a hypothesis (and I am an engineer), but would add, I think that the weapon was wrong. "Colonel Mustard , In the Engine Room... but I hypothesise a "pointy thing" :O ( Damn, why is there not a smiley to signify 'Please don't take any offense, i was just adding to the discussion' ?)

[Kenneth]

I know you have said you have checked the alternator/generator cooling veins, but i have seen a near identical puncture mark cause by a cooling vein letting go in a 44.
Might pay to pull it off and have a real good look.

[helofixer]

I know you said you looked closely at the engine, but perhaps a fan balance weight (which if you dont know is an AN3 bolt nut and perhaps some large area washers.) Seems you would have heard that racket and Im sure it would have had to have gone thru the fiberglass fan shroud first.

[helicfii]

If the object that caused the puncture was spinning at the moment that it hit the cowling (a wrench, a screwdriver, etc..), it could cause a hole just like that.

Just because the hole is small, does not mean that the object was small. As I said earlier, it may not have exited through the hole that it created.

[VfrpilotPB/2]

Mine could be in the minority but<... your thought about the bullet or some other sort of missile, ask your self this, How high were you flying, what speed were you doing,, and what was the terrain, dont ask me why but a .22 Long solid high Velocity bullet makes an entry wound on a car very similar to your picture BUT the lead bullet leaves a trail of fragments and bits stuck to the exit wound area, and this is in all cases, so get a Mag Glass and have a careful scan of the ripped edges of the tear and see if you can see any smudge or trace of lead, if there is nothing at all, then it deffo is not a lead bullet, if it had been a jacketed round that too would have left tell tale copper marks. But like the other member I would say you have not been shot because the projectile would have to have hit somthing else to start it tumbling and come out sideways, in hitting somthing else it would have left some residue of its body either a lump of lead or copper.

I hope you find its a washer or fan bit, otherwise change your route!

VfrpilotPB/2

Peter R-B

[Graviman]

B47,

It looks like if you were to fold the metal back on itself there is a circular piece missing? There also seems to be a triangular section missing near the back? It looks to me like the object was travelling upwards and forwards, as well as outwards through the port panel. You can tell this because the forward flap is only bent, while the rearward flap is torn out.

If you fly over wilderness i might be tempted to think of a misdirected airgun pellet. But the other possibility is a stone was somehow bounced off the pulley from below (clockwise rotation when seen from rear?) and given a nice increase in momentum. I would inspect the belt and fan for impact damage. Wouldn't hurt to change the belt...

[nigelh]

come on ....nobody is going to waste a bullet on a robbo :rolleyes:

[HELOFAN]

IT kinda looks like a object got hammered through sideways with the head being to the right as that point does look wider but I would expect that a small impression of the thread being left behind on the peice peeling outward.
Especially near the impact point on the left.

If you cant find any bolts, pins, washers, etc missing, find out from the mechs if from the last MTCE inspection ( or last few) if anything was removed or replaced.

Even though nothing is missing , it may have been a spare as mechs usually take a few extra over just incase one is dropped or broken etc.

It reminds me of the ice bullet theory.

It may have been a stone that has an irregular shape and got picked up by the fan or a skid touching the ground on landing and pinching it up to the fan or pulley and it was fired into the side panel.

The stone may have been destroyed on impact or shot through and very little evidence of what it was is left behid.

Maybe a little grit or sand on the inside.

Look at all fast rotating surfaces, fan cooling, alternator pulley/fan for signs of an impact, dents, nicks fresh shiny steel spots.

If you were shot at , that hole would have to be an entry hole and the metal is bending in not out.

If its an exit hole then there should be an entry hole on the other side or you were at a fantastic banking angle as that is pointing down so look high for the entry hole.
It really doesnt look like a tumbling bullet hole no copper, lead and edges of the hole are torn and jegged not smooth.

I doubt its a split pin as I would be surprised it would have the mass to sustain enough enertia punch that hole as it isnt very long or wide.

Maybe a cotter pin? solid and uneven shaped.... short though..hmm.

Doubt its a washer as the impact mark would be in the center of the tear not to one side and the washer would have folded from the initial impact also so wound would not be so narrow.

It has torn the steel from right to left, so the object was tumbling and hit unevenly at a slight angle.
If it hit square, it would have left a more even wound and the steel would not have torn the skin as much as stretched it thin till it exited.

I have seen similar on engine cowlings, either from a pin/bolt or a stones.
Thats my 3 best guess's

I rule out the 2nd shooter from the grassy nolle theory.

Keep us updated.

HF
Thats my 3 best guess's.

More pics?:confused:

[500e]

I've torque sealed marks to the ring gear and rotated it carefully to make sure every single tooth is OK, but I'll treble check the alternator pulley.
What about starter bits

[B47]

http://i301.photobucket.com/albums/nn65/mpatrickw/Alternatorcoolingvanes2.jpg

Mystery solved! Missing alternator pulley vane.

Firstly, thanks Nigel! I won a bet with a flying mate that you wouldn’t be able to resist a pop at Robbos with this thread! I’m £20 up! Anybody going to feel sorry for me with a great 110kt machine in a hanger at the end of my own garden that only I fly, when I want, at any time? – keep your Squirrel bills! Look forward to seeing you at Breighton soon.

Prompted by the excellent advice of all who responded, I took all the panels off last night and checked again. Previously I’d checked the alternator pulley fan wheel from underneath by counting vanes round each side. Difficult to reach the top and the missing one must have been top dead centre. But last night managed to revolve the pulley slightly with the rear panel off and there was the answer. Still hard to imagine one vane giving way by itself, so I think something must have hit it. So we’ll never know if it was the vane (most likely) or possibly a stone that punctured the panel after hitting the vane.

Many thanks for all the advice – prizes go to Shytorque and Kenneth – spot on. Also gizmocat for such carefully worked advice – the missing vane piece is exactly the dimensions you calculated.

PPRuNe at it’s best!

[VfrpilotPB/2]

B47,


Good, you have found that Lee Harvey aint after you ,... however if you take a careful look at the break on the pressed metal, you will see that it has an almost straight break or even could be described as a cut, the thickness of the steel looks to be about 1.6 to 2.0mm thick and whilst the bend radius of the actual fan blade is very generous it seem the break has occured in the flat area as is evident from the blade that we can all see in the top of the picture, so the lobe has failed not the actual bend to the small paddle,.... the thickness of the material is obviously its main strength and if any sharp edges or small nicks occur whilst in manufacture that will be the starting point of any failure, the steel used I would guess would be Hot Rolled acid treated to remove any mill scale then punched out and the paddles formed almost in two ops, the fact that this type of steel is NOT stress relieved means that by putting it under quiet large and constant centrifugal forces ( Ie spinning in action)this will pick out any weakness at all, .. grain structure is not critcal in the manufacture of what is a commercial everyday steel such as this( it cannot be compared to Tool steel) so if you look at the bottom paddle in the picture you will see there is what can only be described as a nick running across the thickness of the material that forms the paddle, this is the start of a problem for that particular paddle and that would almost certainly have failed if you carried on using this alternator.

Sorry to have gone on a bit but steel gets into your brain when youve been in it for many years!

Glad you have found your problem though.

Peter R-B

Vfrpilotpb

[ShyTorque]

B47,

You're welcome - glad you found the problem. ;)

[nigelh]

so that will be a tenner you owe me then :ok: I take your point about the squirrel bills though:eek: But just like you it sits in my hangar in the garden and i LOVE it:ok: Anyway glad to see you have found out what it was :D

[topendtorque]

Firstly, thanks Nigel!


I also really appreciate your sense of humour, BTW are all of your exhaust gaskets secure?
tet

[bugdevheli]

I said to my wife, i swear that dent in my bonnet looks like it was caused by a broken alternator blade off a 44. She said dont be riduculous:D

[helicfii]

I'm sticking with my screwdriver theory.:}

[HELOFAN]

Great job finding it.

Like I say it could have been a stone hitting it and breaking it off but those fans do flex a lot at operating speeds.

Hard to imagine but get it up spinning at operating speeds ( around 4000-5000 RPM) and get up close and personal :ouch:

The plate at the back is to resist the flex but it still happens.

Eventually they will bust off after a very long period but tends to be when they are re used often.
Unless its a low RPM alt, I dont re use them on a rebuild.

You should see how far they flex out when they are not supported.
If you get a chance to see one on a test bed..well you tend to stand to the side of the shrapnel area.

Scary thought of one departing in a different direction from underneath eh!!

There is a cast fan that can be found rather than the pressed tin design.

And no it couldnt have been a starter motor tooth as they only spin up just above idle. With out a load it spins up faster somewhat but engaged only maybe if wasnt engageing nicely...bad mesh .... unlikely though.

Cheers

HF

Any sort of coverage/warrenty for a piece breaking off your 110k robby and making a hole where there shouldnt be a hole in your shiny robby that is parked in your hangar ...... not flying cause it has a hole in it and a busted alternator? LOL

[gizmocat]

So it was "Colonel Mustard, in the Engine Room, with the Alternator Pulley Vane" !!

Glad you found it mate :ok:

[topendtorque]

are all of your exhaust gaskets secure?



Have you yet worked out where all the exhaust residue on the top of your alternator is coming from?

[mini]

Automotive alternators typically spin at three times engine speed - ie up to 15,000 - 18,000 rpm. Pressed fan is std fitment - albeit internal - with no problems.

Metallurgical examination if you want an answer to this one IMHO.

I would strongly recommend you get the bearings replaced with the fan.