beta bracket failure

[chevron]

This bracket has failed on my beta 50 i guess it supports the oil cooler for the prm 500 gearbox. Find it strange that such a thick bracket has failed and as to why. 

[john.k]

Vibration fatigue,and maybe a stress raiser where the steel was sheared ........quick weld ,good as new ..........Id add a gusset ,provided there is clearance.

[Ken X]

Hi Chevron,

 

Please excuse this being my first post but these things interest me.  What you have there is a rather lovely classic fatique failure.  I surmise the horizontal plate is firmly bolted down and the vertical plate carries the cooler.  The bracket experienced vibration and possibly resonation which was at its maximum at the left hand end.  This vibration traveled down the bracket to the sharp change of direction in the bottom edge where the bracket became suddenly more rigid and initiated a crack.  The crack has travelled diagonally up the plate over time and you should see a row of lines or striations in the crack face, to where the light gray area begins, as each movement of the bracket increased the crack size.  This light gray area is where the remaining material became unable to support the load and failed catastrophically.  If you get a new bracket, or repair this one, a large radius at the point of crack initiation rather that a sharp change of direction will help prevent reoccurance.

[Chris G]

Yes the fatigue crack started from the stress raiser at the sharp bend.  Be very carful with a welded repair: the fatigue strength of welds is much lower than that of plain plate!

[Jen-in-Wellies]

How many hours has the engine done? The bracket will be a Beta designed one, not part of the base engine. Worth sending the pics to Beta. Helps them build up a file on the weak spots in their marine conversion. They may have seen this before and might even send you a new bracket if they've changed the design. You never know!

Edited August 4, 2022 by Jen-in-Wellies

[Ken X]

I agree entirely with Chris G, if a new bracket is not available, or prohibitively expensive, then renewing the complete vertical element would be a better repair.  It also gives you the opportunity to smooth out all the edge direction changes if clearances allow.  Nice little apprentice project if such people exist these days.

[Tracy D'arth]

Drill lots of tiny holes all along where it fractured last time and it will never break again.

 

How do I know this?   Perforated paper never tears along the perforations!

[chevron]

1 hour ago, Jen-in-Wellies said:

How many hours has the engine done? The bracket will be a Beta designed one, not part of the base engine. Worth sending the pics to Beta. Helps them build up a file on the weak spots in their marine conversion. They may have seen this before and might even send you a new bracket if they've changed the design. You never know!

Engine has done quite a lot of hours (hour meter had failed) had a replacement. What I hope has caused this is the boat has a Prm 500 gearbox which used to go into gear very fiercely with a real bang and a shake that’s now cured completely by putting a soft shift on a few months ago. Think this bracket had started to fail a long time ago as a result of that hopefully.

[BEngo]

21 hours ago, Tracy D'arth said:

Drill lots of tiny holes all along where it fractured last time and it will never break again.

 

How do I know this?   Perforated paper never tears along the perforations!

WaY back when, one of the American jet engine makers had trouble with cracking in  turbine discs at the roots of the fir tree shaped holes where the blades fitted.  Eventually one of the cracks would reach the centre, causing some expensive aeronautical inconvenience.

 

The solution  was to drill a hole just under each blade root.  The cracks still started, but grew to the hole, and   were then stopped.

 

N

[Tracy D'arth]

3 minutes ago, BEngo said:

WaY back when, one of the American jet engine makers had trouble with cracking in  turbine discs at the roots of the fir tree shaped holes where the blades fitted.  Eventually one of the cracks would reach the centre, causing some expensive aeronautical inconvenience.

 

The solution  was to drill a hole just under each blade root.  The cracks still started, but grew to the hole, and   were then stopped.

 

N

That is why anti resonance slits in circular sawblades have a hole at the end.  Pistons too if the skirts are slotted. Good engineering practice. 

[Chris G]

1 hour ago, BEngo said:

WaY back when, one of the American jet engine makers had trouble with cracking in  turbine discs at the roots of the fir tree shaped holes where the blades fitted.  Eventually one of the cracks would reach the centre, causing some expensive aeronautical inconvenience.

 

The solution  was to drill a hole just under each blade root.  The cracks still started, but grew to the hole, and   were then stopped.

 

N

That's how they stopped the crack in Big Ben.

[Tonka]

12 minutes ago, Chris G said:

That's how they stopped the crack in Big Ben.

I thought Boris smoked it all at a party

[Cheshire cat]

It's useful in the bicycle world too. Seat posts come in a variety of diameters to suit the bicycle frame they are meant for. 

 

Trying to persuade one of the wrong size to fit will result in a split in the seat tube. Drilling a small hole stops the crack growing.

[Bee]

Watched a helicopter hovering today. No way would I stand under that clattering, highly stressed barely flyable thing which must be full of brackets and nuts and bolts right on the edge of falling apart.

[BEngo]

Heliocopeters are Full of things that go round,  things that go upsy-downsy , things that flap and things that make noises as well as brackets and nuts and bolts and lots of other things.  All of  which regularly get looked at by people who are trained to know, to make sure they don't  fall apart.

 

Most bits are designed to be nowhere near failure, in normal operation, with a typical factor of safety of at least two to allow some room for abnormal operation.    BCAR, or its modern equivalent, has some very specific design rules just for helicopters, to ensure that things are not over stressed.  The CAA then works hard to see that those in the driving seat are trained to not take the machine outside its design limits and to do the right things if other things goq pear-shaped.

 

As for barely flyable, well, yes, helicopter aerodynamics are complicated.  Ask  Nick Norman for details.  I think he once managed to get paid for flying helos.   He will probably  even be able to explain inflow roll and flapback!😊   

 

Generally though you just learn to move one or more of the stick, lever and pedals in the right directions whilst keeping the throttle in the right position, and looking out of the windows.    If you can pat your head, rub your tummy, kick a ball and drink beer at the same time as reading the football results you have the basics sorted.  Fancy electronics may make it easier, but they are not always there, or on your side, so you should  first  do it the hard way.

 

Finally, remember that ther are old pilots, and there are bold pilots.  There are not many old, bold pilots.

 

N