Crankshaft failure data points - large bore continentals.

[Dave Taylor]

While at the Pecan Plantation fly-in yesterday, quite by happenstance I was seated next to a gentleman L-IV owner who told the group a story about having a crankshaft failure in his airplane last year over the Panhandle followed by a successful landing to a dirt road.
Because the exact same thing happened to me in 2020, I am always looking for similar stories and within those stories any information that can link our engines.
Both our engines were TSIO-550's assembled by Performance Engines.
P.E. has a previously well-described history on the chats regarding their products but I still had never heard of any work that they did which would explain a severed crankshaft.

Both ours broke in the space between cyls 1/2 and 3/4 - I forget the cheek number on mine right now.
Both of ours had a composite prop in use. I mention this because my first overhauler (who actually sat on the replacement engine for over a year) said he has seen crank and case failures in a disproportionately large number of 550s and 520s that had a composite prop and his theory (completely anecdotal, no supporting evidence) is that the lack of mass in the composite props was unable to absorb the acceleration/decelerations of each combustion event like a heavy metal prop would.

[J.C. Peterson]

Dave,

I believe this type of failure was really only seen on Performance Engine builds, and it occurred on a large percentage of them. If this was a problem fleet-wide on 550s there would almost guaranteed be an AD or advisory letter issued by a manufacturer or the FAA. As many Cirrus as there are flying with composite props of various manufacturers you would expect to see a lot more failures if the prop(s) were the cause.

Based on the data I’ve seen, some firsthand, the likely culprit is Ron Monson’s build techniques and/or parts used.

[Dave Taylor]

Thanks for your thoughts, J.C.
To prove that the problem was a Munson build error, I would love to hear an hypothesis or see photos of what was done in his shop to the case or crank that could cause this type of failure. I still have mine and might just send it off to a metallurgist some day. My understanding is that he did a lot of top end modifications, fuel system changes, turbo changes but I have not heard of case/crank/bearing changes. I called him when I bought mine in 2018 and that is what he told me as well.

[Chris Zavatson]

Dave,
Continental has a minimum inertia requirement for propellers. Hartzell isn’t able to supply a composite prop for the Legacy because the inertia requirement would make the diameter too large.
The regulatory side is a little fuzzier. There is nothing to stop you from installing a prop that doesn’t meet the Continental inertia requirement. I don’t know where the Cirrus installations fall with respect to the requirement. Nor do I know how good the Continental number is i.e. too conservative or not.

[Dave Taylor]

Thanks Chris, zackly what the concern is.
(If they have a number does it have a large enough safety margin…. And how did they come up with it - seems to me they had to test engines to failure, to get real world numbers.
I have to wonder how those engines failed.

The major overhauler I mentioned earlier, who knew of a large number of cracked cases & cranks…he did not seem to be the type to submit a SDR “oh well, another busted engine, let’s get in with fixing it”.

[Dave Taylor]

Poking around, found
This chat on bearhawk forums
And a Hartzell mention (search the document for “inertia”)

https://hartzellprop.com/EXP-AIRCRAFT/M ... Vol-02.pdf

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[J.C. Peterson]

The major overhauler I mentioned earlier, who knew of a large number of cracked cases & cranks…he did not seem to be the type to submit a SDR “oh well, another busted engine, let’s get in with fixing it”.

Dave,

I have a couple observations on all of this.

First, the engines that I know of that had failures from the overhauled you mentioned did not get sent back to the same facility for rebuilding. One big reason is that they were beyond repair, i.e. major damage to the crankcase. Another reason was owners being skittish about having the same facility build another engine for them after having the first fail in spectacular fashion.

In regards to the Bearhawk forum post, there seems to be some discrepancy from what is stated and what is being installed on aircraft. There are multiple STCs and original installations for composite props on 550-powered certified airplanes. I find it hard to believe that multiple manufacturers would completely disregard Continental’s engineering data when developing a prop and STC. Something tells me attorneys would have put a halt to that long before a prop went into production. That would seem to confute the post’s claim that “composite props are too light.”

Where the post may be correct is that there are no “experimental prop companies” that produce a prop of sufficient mass, material, etc. to properly dampen vibration on a 550. I flew a Whirlwind propeller on a TIO-540 experimental that was substantially lighter than an equivalent Hartzell composite prop, and that could be the case.

Hartzell has several statements regarding engine/prop combinations:
1. “The most critical factors when determining the compatibility are compression ratio, crankshaft counterweight configuration, and power and rotational speed ratings.”
2. “In general, if the propeller has been approved on a naturally aspirated Continental 520 or 550 engine, it can be deemed acceptable vibrationwise on other 520 and 550 series with the same compression ratio, crankshaft counterweight configuration, and the same or lower power and rotational speed ratings.”
3. “Approved propeller/engine combinations are listed in Note 9 on the propeller TCDS, approved for use on a certified aircraft installation, or are summarized in Manual 193, Vol. 1”

Performance Engines was well-known for delivering engines with higher compression ratios, higher horsepower (through multiple methods), and using higher RPM than factory engines. They also commonly did other modifications including different pistons and changes to crankshaft balance. Any of these could have put the engine prop combination outside of the design envelope that Continental and/or the prop manufacturer tested.

Interestingly, Hartzell states on their website the approved prop for the IV and IV-P as the PHC-H3YF-1RF/F7693DF. The engines shown are: “TSIO-550-B,-E 350 hp @ 2700 rpm, 10-550-G 280 hp @ 2500 rpm.” However, looking at the stated limits for that prop shows a maximum compression ratio of “8.5:1 or less” and a maximum engine rating of “310 HP at 2700 RPM.” Why would they approve a prop/engine combo that is outside of their own quoted design limits for the propeller if they thought it might be a problem? The answer to your overall question doesn’t seem quite as clear cut given all of this information.

I’ve attached photos from the manuals and website if you’re curious to review them further.

[Dave Taylor]

Thanks J.C. - a topic that will always interest me.