Crankshaft Failure Analysis - Rotax 912 Engine, 30km NW Goulburn, NSW, 6 January 2007

[Wilfred]

Crankshaft Failure Analysis - Rotax 912 Engine, 30km NW Goulburn, NSW, 6 January 2007, 24-3770, TL-2000 Sting Sport Ultralight

 

http://www.atsb.gov.au/publications/investigation_reports/2007/AAIR/aair200700054.aspx

 

ATSB Transport Safety Investigation Report 200700054, (technical analysis investigation) into the crankshaft failure analysis of a Rotax 912 engine relating to the fatal accident involving a TL-2000 Sting Sport ultralight aircraft, registered 24-3770, which occurred 30 kms north-west of Goulburn, New South Wales on 6 January 2007.

 

 

[facthunter]

Inconclusive.

 

Something to ponder on, there. The rotax is unusual in having a pressed-up crankshaft. There is no speculation as to whether the interference fit , (pin to web) may have contributed. Impossible to check it once a piece of the web has broken out. N...

 

 

[Yenn]

I couldn't believe that a 4 cylinder 4 stroke would have a pressed crankshaft, but a look in my book of words confirms it.They have a good reputation, so their workmanship must be really good. Just imagine one of the other aircraft engines, if it had to replace a crankshaft and con rods, whenever there was a problem with one bearing.

 

I still like to be able to replace a bearing if necessary for a reasonable price.

 

 

[hiperlight]

Of course one or more siezed pistons may have contributed to the crankshaft failure. Built up crankshafts have been used successfully for many decades. Porsche 356 Super and Carrera engines in the 1950's are good examples. The cranks were made by Hirth.

 

In my humble opinion the Rotax 912/914 motors are solid, and virtually bullet proof, if they have proper lubrication and cooling.

 

Bruce

 

 

[Captain]

It might have been worthwhile if the report had mention the hours that were on that engine.

 

 

 

And whether there was any sign of a piston seizing.

 

 

 

I guess that not making any reference to signs of piston or barrel troubles, it all looked good in the top end, and maybe the hours will be in the final report.

 

 

 

Pressed cranks are still used without issues in bikes and other racing engines with red lines 3 times that of the 912.

 

 

 

[facthunter]

comment.

 

Most built-up cranks are constructed that way to permit the use of roller bearings, as the journal has to be extremely hard to permit the rollers to run on it without damage. This is pretty much confined to 2-strokes these days, although it is not general practice in outboards. I don't accept that pressed cranks are used without issues in bikes, as the Z1 kawasaki was generally modified by welding to keep it in alignment under racing conditions, as one example. Even most V-twins are one piece now, (except the traditional Harley Davidson, which retains an extensively redesigned version of early practice). ALL built-up assemblies are inherently weaker than the one piece equivalents, as they rely on an interference fit for alignment and structural integrity.

 

..... Redline RPM figures used as a comparison, don't have much validity unless the stroke ( and hence piston speed) are taken into consideration as well. High RPM motors have very short strokes, to permit the use of high revs. The design should suit the use to which it is put. One of the most expensive pre-war Mercedes racing engines only had a design life of 3000 miles, probably more than adequate. Nev

 

 

[hiperlight]

Looking at the traumatic damage to crankshaft makes one wonder whether it was due to a prop. strike with power on.

 

Bruce

 

 

[facthunter]

Possibility.

 

Anything is possible. I believe that rotax, in the event of a prop strike require/ suggest a gearbox and drive flange runout check. I suppose that if this proves OK, that the rest of the engine etc. will be OK. There can be a certain logic to this ( if it is in fact the case) & this is the way that a " Heavy Landing" event is handled. The sequence of items inspected being "most susceptable" first, The first item not damaged in the list, limits the inspection process by confining the damage to the weaker items .

 

...... If a prop strike (under power, as you say), was combined with an engine overspeed, you could have an entirely different outcome.

 

...... Bear in mind that these cracks (at least the one in the crank web) progressed over a period of time (operation) from an originating point, till the remaining section is too weak to take the load. The only symptom/warning MAY have been an increase in vibration. NEV..

 

 

[gregrobertson]

The 912 ULS is fitted with with a slipper clutch as standard equipment. It is a preloaded multi plate arrangement similar to thoes fitted to motor cycles. It is designed to slip in the event of a prop strike to protect the engine. Rotax recomend, as you say that in the event of a prop strike the gear box should be examined.

 

It would have been nice if they had found a reason for the failure. Just makes you a little more cautious.

 

Regards

 

Greg