KOXR Mooney blade failure

[MikeOH]

51 minutes ago, EricJ said:

I had an injector clog at full throttle just after takeoff and I thought the engine was going to come off the airplane it shook so hard.  Four-cylinder motors aren't happy when a cylinder stops making power but still has full compression.  I had to keep it at full throttle to maintain about 100 fpm climb to get around the pattern and land, so it did that for a lot more than a few seconds.   I've put over 900 hours on it since then.     

THAT does not sound like fun! But seems all the rotating ‘stuff’ was still in balance in your situation. I’m just thinking missing a large chunk of prop is going to be much worse. BWTHDIK

[A64Pilot]

5 minutes ago, MikeOH said:

THAT does not sound like fun! But seems all the rotating ‘stuff’ was still in balance in your situation. I’m just thinking missing a large chunk of prop is going to be much worse. BWTHDIK

It is. Sometimes essentially ripping the engine off its mounts. The attached report from memory rendered the aircraft unable to maintain altitude because the engine was mostly ripped loose and hanging down or sideways maybe but whatever it created a large amount of drag.

 https://asn.flightsafety.org/wikibase/36677

The cause of this prop failure was traced to “reactionless mode” and I think this high profile accident is what caused it to be addressed, essentially reactionless mode is a harmonic that causes extreme stress and therefore blade fatigue, what’s so bad about this mode is when it occurring there is no vibration felt, it’s actually very smooth, hence the name reactionless, but it’s why yiu hear some Pratt four and five bladed aircraft with such high ground idle speeds so high they sound like Garrett’s.

I dealt with it by having the MVP-50T flash yellow if you were in the range instead of turning the idle up real high.

https://hartzellprop.com/FAA/NE-06-13.pdf

[bluehighwayflyer]

Didn’t they used to chain or strap Formula One racer’s engines to their mounts, just in case?  I think I remember that.  Maybe they still do.  

[EricJ]

48 minutes ago, bluehighwayflyer said:

Didn’t they used to chain or strap Formula One racer’s engines to their mounts, just in case?  I think I remember that.  Maybe they still do.  

Drag racers used to do that sometimes, and offroad people as well.   Sometimes it was just to limit engine travel relative to the chassis due to torque.

[Hank]

53 minutes ago, bluehighwayflyer said:

Didn’t they used to chain or strap Formula One racer’s engines to their mounts, just in case?  I think I remember that.  Maybe they still do.  

I've heard of airboats doing that, but wasn't sure if it was due to operational reasons or theft prevention.

[EricJ]

11 hours ago, MikeOH said:

THAT does not sound like fun! But seems all the rotating ‘stuff’ was still in balance in your situation. I’m just thinking missing a large chunk of prop is going to be much worse. BWTHDIK

Both create severe vibrations, both stress the crank and the case and the mounts and a bunch of other stuff.   Yes, they're different, but everything is. 
 

[Pinecone]

10 hours ago, bluehighwayflyer said:

Didn’t they used to chain or strap Formula One racer’s engines to their mounts, just in case?  I think I remember that.  Maybe they still do.  

Yes.

FYI for others, he is talking about Formula One AIR racers.  Not F1 cars.

How to go over 200 MPH on an O-200

https://en.wikipedia.org/wiki/Formula_One_Air_Racing

[A64Pilot]

On 3/11/2025 at 11:32 PM, EricJ said:

Drag racers used to do that sometimes, and offroad people as well.   Sometimes it was just to limit engine travel relative to the chassis due to torque.

Believe it or not but a few of us did on long distance cruising sailboats. Reasoning was that God forbid but the weather was so bad that the boat rolled you didn’t want the engine coming loose in the cabin.

What could you chain it to in an airplane though? It’s not just the rubber that breaks on an aircraft, it’s the tubular engine mount itself. 

We did it only on the left side of drag cars if memory serves because torque pulls the L side up.

[DXB]

This anxiety-provoking thread makes me wonder if I should have formally overhauled my prop rather than IRAN’d/resealed it recently.  It’s a 12 year old Top Prop with ~1500hrs that was slinging a modest amount of grease on one blade. It had a few nicks and chips over the years.  The engine was getting overhauled so it was a good time to do it.  They made it look brand new for less than half the cost of a prop overhaul, and it runs very smooth now even before dynamic balancing.   But I wonder if I would hsve gotten much more peace of mind from the careful dye penetrant testing that’s included with overhaul…

…and I would love to know what the metallurgy of this failure was….

[takair]

I wonder if this STC possibly missed some harmonic resonance of this combination airframe (Porsche legacy) , engine, prop?  Is this exact combination on many other airframes? 

I would be curious to hear from a metallurgist if and how calendar time in service can play into this type of fatigue failure. I don’t believe it does. Formal NDT may have caught it, but it seems to me that flight time in service is a better indicator of cycle related stress than calendar time. Even then it seems like there is a missing link to this failure. 

I also have a theory that the annual lube interval and amount adds up to an overfilled and leaking hub in about 12 years.  I would again be curious how many, if any, leaking props come back underlubricated. Hard to say what the alternative is since it is hard to determine that there is adequate grease through the hub, but I am coming to my own conclusion that the leakage and 12 year interval may not be entirely coincidental and may not be purely due to the orings. I wish there was a better way to asses grease condition and dispersal than to just add grease as the various iterations of the service manual have suggested. 

Edit:  I am venting my frustrations of my Hartzell props with regard to the grease. Likely not appropriate for this thread…apologies. 

[Shadrach]

On 3/10/2025 at 7:32 AM, DXB said:

I imagine this requires crank  inspection like a prop strike?  The asymmetric loads must be enormous 

It might require a prop inspection, but I’d like to see the data behind that requirement.  If you think about it, there are many asymmetric loads within a reciprocating engine. Think about the asymmetric loads on a piston pin given, the piston is reversing direction every 180°.  It’s pretty amazing to consider how much pressure it takes to disrupt the hydrodynamic plane.

 

this is a long video, but it’s very well done and conveys a lot of information that most of us don’t think about in terms of the physics of multi cylinder, reciprocating engines.