0-375 throwing blade tips

Hi All,
A few months ago a blade tip flew off while flying behind my 0-375 powered cub (with 10-1 compression). The propeller was a 1P235 84" (Pawnee prop)(prop had 400 hours on it, and about half of those were done behind the stroker engine). About six inches came off. It's a very strange feeling when that happens. You would not believe the shake and vibration through the airplane. I pulled the mixture within about two seconds of it happening and deadsticked it down on a beach. Luckily this happened on the skeleton coast in Namibia where I had hundreds of miles of beach in front of me to land. It could of been a very different outcome should the terrain have been different below.
It vibrated so much the engine case hit the engine mount in a few areas around the rubber mounts.
We ended up sawing off the other blade tip to the same length and kept flying.

So at the time I did not think anything of it. You hear about these things happening even though they are uncommon. Usually it is attributed to a manufacturing flaw in the blade.

Then i got speaking to a few other people and have heard of another 0-375 cub having a hard time keeping blades on. On that cub, the tip flew off an MT constant speed prop after less than ten hours. They replaced it, and it cracked the next one after a few hours as well. They changed to a Catto prop with metal leading edge, and it flew a blade as well. Then they swapped to a Catto without the metal leading edge, and it has held up for now.

Apparently they may be some harmonic created by the 0-375 engines which is really hard on props. I am sure other things in the engine affect that harmonic as well, such as compression ratios. I spoke to Catto about this and he confirmed that there are some nasty harmonics on this engine. ECI apparently also warned some customers about the likelihood of blades cracking.

To all other members running 0-375's, how are your props doing? How many hours do you have on them? What prop are you running? Have you heard of anyone else having issues with this engine and their props?
I am starting to believe that it was not a coincidence or a manufacturing flaw, and that there might be some nasty harmonics with these engines. Losing a blade tip is the same as having your engine fail, you're going down. I'm almost considering going back to a stock engine after this experience and hearing all this. More power is great, but not at the expense of safety.

best,
Alec

Aerosport 0-375 low comp 8.5 : 1
Borer 84/44
180 hours
Nil incidents
Seems to run very sweet but I have nothing to compare it to.

Alec,
I suggest that you read NOTE 9: http://rgl.faa.gov/Regulatory_and_G...ce4689ef4ac398625726d006193be/$FILE/P12EA.pdf

This is the approved type certificate for your prop. As you can see, there apparently has been no testing done on your engine. This suggests that what happened to you, could happen.

You were lucky. The whole engine could have come off of the airplane.

skywagon8a said:

Alec,
I suggest that you read NOTE 9: http://rgl.faa.gov/Regulatory_and_G...ce4689ef4ac398625726d006193be/$FILE/P12EA.pdf

This is the approved type certificate for your prop. As you can see, there apparently has been no testing done on your engine. This suggests that what happened to you, could happen.

You were lucky. The whole engine could have come off of the airplane.

Click to expand...

Hi skywagon, thanks for this. I am aware that no testing has ever been done on this prop with an 0-360 let alone an 0-375. That said, I have succesfully been running this prop for many years on a stock 0-360 with no issues. I also know of several other cubs running this prop on stock 0-360 for several thousand hours with no issues. I swapped to a 0-375 and after about two hundred hours this happened. Really would not of thought anything of it, had I not heard of similar problems on other 0-375's. then add to that the warning from Catto and ECI (who make the parts for the 0-375), and all this is starting to look like too much evidence for just a coincidence. The fact that the 0-375 seems to do this with several different prop makes and models lend me to think that the issue is with the engine itself rather than the specific prop model.

on a side note, the cub that I fly in Alaska, also has a 0-375 on it, with the same prop. It has held up for over 500 hours with no issues. But engine is 11-1 compression instead of 10-1 like on the cub that broke the blade. There might be different harmonics that come into play depending on compression ratios. Both engines sure vibrate differently inside the cockpit. The one that flew the blade is by far the smoothest engine of the two.

And yes, as you mention I was lucky that engine stayed attached to the plane, as I have heard some reports of engines being ripped off the frame following a blade failure. In my case it was an easy decision to shutdown the engine immediately since below me was a nice landing spot.

cgoldy, thanks for your feedback. I might be mistaken, but I remember hearing that ECI thought that the harmonics were a lot better with compression of 8.5-1 and might not be an issue.

Alec,
It could be something as simple as the 10-1 compression instead of the 11-1 which is on your Alaska airplane. Harmonics generated by various combinations of parts can cause strange results. It could also be something which has nothing to do with the engine and prop. Other than the compression ratio, is there any thing else that is different between your two Cubs?

I witnessed and participated in a vibration test on an airplane once upon a time which resulted in reducing the VNE of the airplane. The change was the addition of de-icer boots on the wings. As it turned out the vibration limits of this particular airplane were very critical as to which pieces of optional equipment were installed. My participation in these tests were very eye opening. Lots of repeated tests were done on this particular airplane with various installed components. One other thing which effected the harmonics of this plane was the installation of an oxygen bottle in the fuselage behind the baggage compartment. The parts which failed on this plane were the stabilators. They were prone to bending in half at high speed. The speed at which this happened varied with installed equipment.

Be extremely careful when you explore the unknown. Harmonics which cause breakage, can often not be felt by the pilot.

We have a pawnee prop in our shop with the same 6 inches off one tip. It was on a Pa-25-235 pulling a glider.

Does Namibia have many airports fuel? hows the local faa? On the prop that not good no counter weights like 360 get a mc and bend it down why did you pick that one? to thin outboard.

I talked with Catto about this issue last year and they redesigned there prop, it seems there is a harmonics at certain RPMs that will transfer to the blade tip this has been known for some time about the metal props. CC was having the same problem with the first generation Catto my understanding is the new blade design from Catto resolved this issue.

I'd like to hear about any other experiences on this issue also as well. Indeed we've add some issues on one of our R&D birds with an O-375. Ours has 10:0-1 pistons also, we will be installing 8:3-1 pistons here shortly in an attempt to keep a prop on it. One seemingly sure solution would be go to with a counterweighted crank, but that would add about 7 lbs IIRC.

If you do have a tip depart, do a REALLY thorough inspection prior to flight. I had a prop tip break on an O320 cub, shut it down right quick and landed. One leg of the engine mount was broken and another was cracked. That failure was due to a stress riser fromarockdamage, apparently.

After that experience,I have no interest in being a test pilot. I wouldn't fly any prop/engine combo that hasn't had a vibration survey. A number of years ago,folks were hanging Hartzell 84 inch props on C170 for floats. That prop wasn't approved. An AI there got concerned and talked Hartzell into doing a vibration survey on the combination. Turned up a couple of destructive harmonics I the combo. Hartzell cut the prop back to 80 inches and installed a harmonic damper assy, and it passed muster.

prop harmonics are nothing to mess with, IMHO, specially if you're flying the wilds of Kenya...

FWIW.

MTV

Mike, you said the key words... "vibration survey". Indeed we are all test pilots without. We work closely with Craig Catto and he has come a long ways in this regard. He is developing his own data acquisition system (DAQ) that is wireless and lets him record inflight data for analysis. All of the props we currently offer have been through this, and he did indeed find some resonant nodes in the process that he fixed by changing the layup schedule.

mvivion said:

If you do have a tip depart, do a REALLY thorough inspection prior to flight. I had a prop tip break on an O320 cub, shut it down right quick and landed. One leg of the engine mount was broken and another was cracked. That failure was due to a stress riser from a rock damage, apparently.

MTV

Click to expand...

There was no damage visible to the engine mount in the case that Randy L is talking about but we did change the engine mount and all of the engine mount bolts both holding the mount to the engine and the mount to the fuselage just to be on the safe side.

Pete D

Is Aerosport the only builder of the O-375?

Not to change topic, you need to sell those cubs get a 172, they can land without a engine attached to the airframe! Yes I did not believe either it when I heard this, the engine went By By, As in separated from airframe!

This is a interesting one that a plane will not fly with a engine attatched! I bought this 172 after the mid air, insurance bid buyout. It had no engine, a slice in the left boot cowl from the prop hit plus left wing strut almost cut in half, otherwise fuselage was in good shape other than the brown streaks on pilot & co-pilot seats!. I had it rebuilt ,float kit, LR fuel, 180hp pen yan conversion, new floats, it resides MN on floats now.


NTSB Identification: FTW90FA151A.
The docket is stored on NTSB microfiche number 44583.
Accident occurred Tuesday, August 07, 1990 in ELMENDORF, TX
Probable Cause Approval Date: 5/3/1993
Aircraft: CESSNA 172M, registration: N1466V
Injuries: 1 Minor, 3 Uninjured.
A USAF T-38 & A CESSNA 172 COLLIDED AT 4200' MSL. DRG IMPACT, THE VERTICAL STABILIZER OF THE T-38 STRUCK THE RGT SIDE OF THE 172'S ENG. THE ENG SEPD & THE 172 PLTS LNDD ON A ROAD. THE T-38 DSCNDD OUT OF CTL, BUT THE T-38 PLTS EJECTED SAFELY. BFR IMPACT, THE STUDENT IN THE 172 (WITH A VISION RESTRICTING DEVICE) & HIS INSTRUCTOR (CFI) WERE PRACTICING AIR WORK MNVRS. THE TANDEM SEAT T-38A (WITH AN INSTRUCTOR PLT IN THE BACK SEAT & A RATED PLT IN THE FNT SEAT) WERE BEING VECTORED FOR AN ILS RWY 33 APCH TO KELLY AFB. THE T-38'S SPD WAS ABOUT 330 KTS; THE SPD LIMITATION OF 250 KTS HAD BEEN WAIVED FOR T-38 ACFT, DUE TO THE ACFT'S LACK OF CONTROLLABILITY AT THE LOWER SPD. THE 172 WAS EQUIPPED WITH A TRANSPONDER, BUT IT WAS NOT EQUIPPED WITH MODE C. THE T-38 WAS EQUIPPED WITH A MODE C TRANSPONDER. BOTH ACFT WERE IN RADIO CTC WITH THE SAN ANTONIO SOUTH DEP CTLR, BUT ABT 3 MIN BFR THE COLLISION, RADAR SVC WITH THE 172 HAD BEEN TRMTD.

Hi Skywagon, both those cubs are equipped almost identically. It is interesting to know that other components on the plane can affect the harmonics. In this particular case my gut feeling tells me the issue is not in the difference of components, mainly due to similar experiences by other operators of the same engine, as well as warnings from people who know a lot more than I do about the matter.

RAC cubs, yes Namibia is a great place to fly. Cheap airport fees, avgas is available, and the country is the least populated in Africa. The reason I run this prop is because it is the best metal prop I have found for an 0-360, and I have tried many different ones.

DW, my understanding is the issue is not resolved yet on the 0-375 engines. Am I missing some info?
Don't get me wrong, I am certainly not putting down Catto's props, I have the utmost respect for him, and believe if anyone can help resolve this issue, he is better placed and more willing to help than anyone else.

cgoldy, not sure if others build the 0-375. All of mine have come from Aerosport.

Randy, what made you decide to lower the compression back down to 8.3-1 from 10-1? Did ECI do any testing with the lower compression which gave favorable results, which made you take this decision? Or is it just trial and error?
Have you been able to use Catto's data acquisition system on the 0-375 engine yet?

Who else is running 0-375?

Alec,
To be fair, all of the harmonic troubles in that particular airplane were airframe related. The engine and prop were not part of the trouble. Just imagine doing a dive test at well over 200 mph with both props feathered.

Yes, It is likely that your situation is the propeller/engine combination. My point is only to expand the thought processes of our fellow SC.org folks on the subject of potential harmonic troubles.

Is it possible that you had a stone nick in the leading edge?

The engines that have had problems. Do they have solid crankshafts?

I ordered mine with a solid crank so I did not have to abide by any RPM limitation. Maybe this is something to consider.

Alec----I have a 0-375 with 9-1 pistons on my SQ-2. I have 200 hours on a 90" McCauley which was very smooth running. The 90" has a very thick blade tip and at the time was asking around about puting it on a diet. Catto figured my 90" tip was above the speed of sound at the RPM I was turning. I now run the Whirlwind ground adjustable prop with no problems as of yet. I set my Whirlwind to get a maximum of 2700 RPM either in the climb or in the cruise.

The few 1P235s I have seen have a very thin tip which bothered me alittle but maybe they had been worked on. I ran the 1P235 on a 0-320 which was the best of all in performance.

Harold

I have an 0-375 ,the prop is a prince.I have yet to fly my aircraft,but this news concerns me as the prince has very thin Q tips that would seem to make it vulnerable maybe?

ron said:

I have an 0-375 ,the prop is a prince.I have yet to fly my aircraft,but this news concerns me as the prince has very thin Q tips that would seem to make it vulnerable maybe?

Click to expand...

I doubt that appearances mean much with regard to detection of potential destructive harmonics. Otherwise, there'd be little need for vibration testing.

MTV

When they test engine / prop combinations, what do they do? And who does it. The engine manufacturer or the prop manufacturer?

KenyaCub said:

Hi skywagon, thanks for this. I am aware that no testing has ever been done on this prop with an 0-360 let alone an 0-375. That said, I have succesfully been running this prop for many years on a stock 0-360 with no issues. I also know of several other cubs running this prop on stock 0-360 for several thousand hours with no issues. prop makes and models lend me to think that the issue is with the engine itself rather than the specific prop model.

Click to expand...

FYI

A few year back I researched the possibility of getting an STC for installing the P235 prop on O-360 certified PA-18's.

In my quest, I talked to an engineer at McCauley about running a P235 on an O-360. He told me that they had done tests and found that at 1700 RPM the O-360 induced a destructive harmonic vibration that could lead to prop failure. He also said they had gotten wind of a number of these props installed on Cubs via 337 in Alaska and had requested that the FAA put a stop to this. Which they did.

So anyway, there have been tests done with this prop on the O-360. The O-375, no. Looks like you're doing the testing. Good thing you were not half way across Cook Inlet when it failed.

Take care,

Greg

cgoldy said:

When they test engine / prop combinations, what do they do? And who does it. The engine manufacturer or the prop manufacturer?

Click to expand...

I had an acquaintance who lost his life in the ensuing forced landing after loosing part of a propeller blade. The aircraft was an RV-6A fitted with an originally new factory O-360 and a Hartzell constant speed prop. The installation of that prop was approved by Hartzell on the O-360 in the RV-6. From what I have read of literature that has come out of Vans is the prop manufacturers come out to Vans and vibration test the prop.

However my acquaintance had fitted electronic ignition, and the theory put forward by the accident investigators is that the electronic ignition changed the harmonic of the engine and made it destructive to the propeller. I have read, associated with Vans, that the big manufacturers like Hartzell and Sensenich state that their approvals are for factory standard engines and once higher compression pistons or electronic ignition are fitted, all bets are off and their approval is null and void.

To answer your question, from what I recall, the prop manufacturers strain gauge their props all down the length of the prop. The data is fed via a slip ring arrangement at the prop hub to some sort of data acquisition unit, probably a lap top now days, and they just go and fly the aeroplane. They fly at all imaginable speeds and power settings, which is why it takes so long (read expensive). After flying they analyse the data and if the strain recorded indicates that the fatigue limit of the material has been exceeded that is a operating mode that will be destructive to the propeller. That is how I recall what I have read and I do not have the article handy to verify my memory, so please don't shoot me if my account it not fully accurate. For the purposes of this discussion, I believe that I have conveyed the information that is relevant. Vibration testing a prop is no simple matter, eye-balling the propeller is as much good as dancing in front of it and it is truly an empirical process. Also a vibration that is destructive to the prop may not be felt at all by the pilot.

Even the experts get it wrong. On the RV series the Sensenich metal prop designed specifically for the RV's and the O-320 has a vibration mode that resulted in them limiting the redline RPM to 2600. Now what good is a prop that you can't go to 2700 on bolted to a Lycoming?

I hope this helps.

Crash's sage comment about sums it up.

Andrew.

skywagon, this prop did not have any visible nicks or dents.


cgoldy, i would have to ask Bart to be sure, but I believe I have the hollow crank in my engines.


harold, good to hear from you. Been a long time. How does that whirlwind compare to the 90 for performance?

Greg, thanks for sharing. Interesting info.
from what I recall, even certified props have some bandwidth issues. I remember when I used to run the Sensenich prop on the cub, there was a band between 2250-2350 that was not meant to operate in for extended periods of time. I suppose they found some harmonics in that power setting. But they still approved the prop?
As you mentioned, there are a number of cubs flying with this prop in AK on field approvals. Have you ever heard of any issues any of them had?

Andrew, thanks for sharing the info.

I would be really interested to hear more from randy/cubcrafters on their experience. When I saw Jim at JC this year he mentioned that they were working closely with ECI and Catto on this issue. Did ECI believe that the lower compression would solve the issue? i would lower my compression in a heartbeat if I knew that would solve any potential issue.

KenyaCub said:

Then i got speaking to a few other people and have heard of another 0-375 cub having a hard time keeping blades on. On that cub, the tip flew off an MT constant speed prop after less than ten hours. They replaced it, and it cracked the next one after a few hours as well. They changed to a Catto prop with metal leading edge, and it flew a blade as well. Then they swapped to a Catto without the metal leading edge, and it has held up for now.

Apparently they may be some harmonic created by the 0-375 engines which is really hard on props. I am sure other things in the engine affect that harmonic as well, such as compression ratios. I spoke to Catto about this and he confirmed that there are some nasty harmonics on this engine. ECI apparently also warned some customers about the likelihood of blades cracking.

Click to expand...

I find this part of the discussion fascinating and disturbing, as I have not heard of wooden propellers shedding blade parts due to a vibration harmonic problem. The MT, Catto and Prince are all made of wood. Wood is a very absorbent materiel and is generally considered to be able to withstand the harmonics which are so destructive to various metal propellers. And, from a maintenance point of view, there is not as much concern with nicks which would cause crack propagation.

Are these 0-375 engines certified? Or are they just a hopped up engine for experimental airplanes? It seems that perhaps they are the problem more than the propeller. The propeller is just the victim.

I am using a 77" Whirlwind ground adjustable prop on my IO-360. It is smooth, powerful and I can change the pitch to suit my desires of the moment in a couple of minutes. The blades are made of a hollow carbon fiber layup. My only objection is the fact that I can not change the blade angle in flight. Perhaps most would not care, but I have found that my plane's performance would be greatly enhanced if I could.

Alec----Hope we can get together someday. I really like the whirlwind. It leaves as hard on takeoff as the 90" and I can cruise 10 to 12 MPH faster. It being only 77" dia., I don't cut any tall grass like I did with the 90"--Harold

cgoldy, i would have to ask Bart to be sure, but I believe I have the hollow crank in my engines.

Kenya Cub,

Did you ever find out for sure if your engine has a hollow crank?

Goldy

Harold, thanks. Sounds like a nice prop.
Cgoldy, I confirmed mine is a hollow crank.

Randy/Cubcrafters, anything more you can tell us on your decision to lower the compression on the engine that was throwing blades? Would be interesting to know as you've probably done more research than most on the matter.

KenyaCub said:

Hi All,
A few months ago a blade tip flew off while flying behind my 0-375 powered cub (with 10-1 compression). The propeller was a 1P235 84" (Pawnee prop)(prop had 400 hours on it, and about half of those were done behind the stroker engine). About six inches came off. It's a very strange feeling when that happens. You would not believe the shake and vibration through the airplane. I pulled the mixture within about two seconds of it happening and deadsticked it down on a beach. Luckily this happened on the skeleton coast in Namibia where I had hundreds of miles of beach in front of me to land. It could of been a very different outcome should the terrain have been different below.
It vibrated so much the engine case hit the engine mount in a few areas around the rubber mounts.
We ended up sawing off the other blade tip to the same length and kept flying.

So at the time I did not think anything of it. You hear about these things happening even though they are uncommon. Usually it is attributed to a manufacturing flaw in the blade.

Then i got speaking to a few other people and have heard of another 0-375 cub having a hard time keeping blades on. On that cub, the tip flew off an MT constant speed prop after less than ten hours. They replaced it, and it cracked the next one after a few hours as well. They changed to a Catto prop with metal leading edge, and it flew a blade as well. Then they swapped to a Catto without the metal leading edge, and it has held up for now.

Apparently they may be some harmonic created by the 0-375 engines which is really hard on props. I am sure other things in the engine affect that harmonic as well, such as compression ratios. I spoke to Catto about this and he confirmed that there are some nasty harmonics on this engine. ECI apparently also warned some customers about the likelihood of blades cracking.

To all other members running 0-375's, how are your props doing? How many hours do you have on them? What prop are you running? Have you heard of anyone else having issues with this engine and their props?
I am starting to believe that it was not a coincidence or a manufacturing flaw, and that there might be some nasty harmonics with these engines. Losing a blade tip is the same as having your engine fail, you're going down. I'm almost considering going back to a stock engine after this experience and hearing all this. More power is great, but not at the expense of safety.

best,
Alec

Click to expand...

Correction of the quote above, we never lost any part of a Catto prop. That airplane flew from 0 hours TT to 6 or 8 hours with a used MT prop that we had previously had on a PA18 for some testing some years before. We then noticed a small crack forming in the metal LE on one blade about 8" in from the tip. The prop was removed and sent in for service. It came back with (new? maybe refurbished) blades that were a couple of cm shorter. At around 12 or 14 hours TT is when the MT lost around 10" of one blade.

When we next put it back into service we converted it to fixed pitch and put a early version of a Catto NLE prop on. I don't remember how many hours exactly, but somewhere around 20 hours on that prop we found a crack forming in the NLE, again around 6-8" in from the tip. At no time did any part of the Catto prop depart the airplane.

Since then we have had an 86" NLE Catto climb prop (86-40, wow, what amazing climb rate!) and now for the last 60-70 hours we have had a 80" non-NLE Catto prop on it with no issues at all on either of those.

I have helped Catto with a little bit of set up to test some props on our CC340 engine with the data acquisition system he is/has developed, its pretty cool. Eliminates the slip-rings etc and records it all on an SD card.