Mystery R44 Damage

[B47]

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........

[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!!

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 hangar. 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?

[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]

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!

[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!

[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