MT prop leading protective edge letting go.

[African Bear]

Hi All,
Has anyone had experience of the leading protective edge coming loose on a composite MT prop.
I had recently moved my Bearhawk to the coast and have been enjoying performance that I have never had before. I normally fly at DA 8500 and above.
Today I flew from one airport to another to get fuel and then was going to start the next leg. Powered up gradually on a long Tar runway and lifted off, great takeoff and at about 80ft a sudden really loud whistling, screaming noise. Cut the throttle, nose down and managed to land, not the most ceremonius landing but it worked on what was left of the runway. Anway, told tower that i was stuck and got out to assess the situation, to find that the protective leading edge on one blade has almost let go. Luckily not completely as there would have been a lot of vibration.
Attached is a pic of the blade
By the way, there was no propstrike or birdstrike.
Best
Andrew

[Battson]

When I was selecting my new prop, I decided to do some market research.

Choosing a composite constant speed propellor, suitably sized for the Bearhawk's usual horsepower range, MT and Hartzell were the frontrunners. Hartzell was the newcomer, this was around seven years ago.

I reached out to the Backcountry Pilot community, as MT props were prevalent in that community - and probably still are. I received some interesting feedback, particularly in private messages. Privately, people disclosed concerning issues with their MT props including photos (like the above). Information came from commercial and private operators, mostly in North America. Others chose to comment publicly, albeit with much less detail.

The reported issues included exactly what you've posted above, leading edge separation. Annoying to see it's still happening all these years later.
The reports also included blades deforming in extremely dry environments i.e. blades developing wrinkles in the "skin" and similar issues.

The issues appeared to be isolated and/or related to environmental factors, but there were clear repeated themes.
In some cases, MT said the issues with wrinkles were expected, and did not present a risk. In extreme cases, I think the blades may have been repaired / replaced, I can't recall.


Opinion...

Even if the risk was small, I didn't like the amount of hassle involved to sort out such an issue, if it occurred - especially living on the 'edge of the map' down here in New Zealand, when shipping costs are so high.

Personally, just based on pure gut-feel... I think the MT prop's wooden core, complex sandwich of different materials, and overlaid leading edge are inferior design choices. I am sure each material has slightly different coefficients of expansion, perhaps extremes of temperature cause internal stress for that reason. I am sure the engineers at MT know exactly what's happening, and I am sure we will never know for sure.

A solid nickel leading edge and inert foam / synthetic core seems more sensible to me, again just based on opinion. I believe the Hartzell has a foam core, and a solid leading edge from what I can see at the tips of my blades.

[alaskabearhawk]

FWIW, I showed the photo to a local mechanic friend. He just said: "Typical MT quality". He hadn't seen damage to that extent before, but he did say that delamination of the nickel LE usually only happens after significant rock strikes. He's guessing that may be the case here.

[marcusofcotton]

Zooming in on the photo, it surely does look like significant rock strikes are there.

[kestrel]

It looks to me (...what do I know?) like that prop was poorly repaired. There are voids in some sort of adhesive/filler under the leading edge and dents in the leading edge that are inconsistent with just de-laminating but do look like rock strikes. Maybe there is a different explanation for the dents and maybe that is stock MT workmanship in the adhesive. ...but I doubt it.

[Bissetg]

Well done on getting on the ground safely.

Do you know the history of the prop? Was it new on the aircraft or second hand??? Has it been repaired or overhauled before?

I have no experience with MT props and I’m not qualified in composites however the deformation in the cap and subsurface look to indicate some sort of impact damage.

What sort of prop clearance do you have? I notice it doesn’t look like standard Bearhawk gear legs?

It’s possible to pick up damage taxiing or starting with the wind behind you over fine gravel. I’ve witnessed it with Maules particularly as the standard gear and small wheels don’t give great prop clearance.

It takes surprisingly little tailwind to develop a little vortex that sucks crap up and typically damages the outer section of the blade…about where that deformity appears to be.

If it was me I would be contacting MT directly, give them as much info and detailed pictures as you can and see what they say.

Trailblazers are popular over here and to date I haven’t heard of anything like this happening with them.

[paulodonnell]

I would be sending that photo to MT in Germany for comment... I have owned several aerobatic aircraft (Extra 200 /300 and currently a CAP232) over the years all with one thing in common...MT props, 2/3/and 4 blade versions. Also a Husky A1B with a very similar two blade MT...We have never seen anything like that and certainly always considered MT very top quality, and I have never heard anything like the mechanics quote 'typical MT quality' ??. These being certified aircraft, we send those props back for rebuild every three years. That one looks like it sure had some abuse!

[alaskabearhawk]

My friend maintains aircraft for air taxi operators in Alaska and as such the aircraft are subject to a lot of wear and tear. The MT props just don't hold up under this kind of use as well as others. That having been said, the pilots generally like the performance and just replace them...passing on the cost to their clients as part of doing business.

[African Bear]

Thank you all for your comments, that prop was overhauled 90 hrs ago and about 20 hrs ago had to go and have the grease "o" rings and wear sleeves changed about 20 hrs ago. It has had a small stone impact about an inch or so in from the tip. The LE strip loosened at the end and I had to do a bush repair with epoxy 2 pack plastic metal. (as advised by MT) as I was in the middle of nowhere. I've kept a very close eye on it every time I fly and it has showed no cracking at all until this incident. I am a little nervous as to how a small dent has now, after quite some time escalated into quite an instant failure. Some people around here are saying that the composite props are not for Africa's harsh environment. ( I know stones are unreasonable to include in that statement) . The whole incident is being relayed to MT in germany and hopefully I'll get up and running soon.
I am a bit wary about the prop now. Any advice from anybody as to what Ally prop may be an equal performer as a replacement. It,s mounted on an IO390 lycoming.
Best
Andrew
Battson what type of prop did you go for in the end? I,d prefer to file a small dent on an Ally prop than go through this whole story .
Bissetg The prop has good clearance with the the tail on the ground, and when in flying attitude the tip is 11 inches off the ground. The prop has been overhauled about 90 hrs ago , but there is no record of it having been repaired before.

[Battson]

I went with the Hartzell Trailblazer 2-blade 83" constant speed prop, which has proved a popular choice for the Bearhawk 4-place. I think it has a solid nickel leading edge, so I hope it would survive a stone impact.... I hope.... I mean - that's what it is designed to do!

[kestrel]

It has had a small stone impact about an inch or so in from the tip. The LE strip loosened at the end and I had to do a bush repair with epoxy 2 pack plastic metal. (as advised by MT) as I was in the middle of nowhere. I've kept a very close eye on it every time I fly and it has showed no cracking at all until this incident. I am a little nervous as to how a small dent has now, after quite some time escalated into quite an instant failure.

I'm still not an expert and I haven't stayed at a Holiday Inn Express, but now that the leading edge has peeled off and we can see it, it looks like the field repair wasn't good enough to be a long term solution. There may be something to question about how tolerant of abuse various props are, and we need to be careful out looking at one event and passing judgement. Different props may have different weaknesses.

This doesn't look like a failure of a "good prop". We have the advantage of seeing what the repair looked like under the leading edge. You couldn't see that before it came off, but my take is that the field repair was sufficient to get home, but the blade should have been better overhauled once home. It is certain that some of that leading edge was not bonded to the blade after the repair.

I don't see reason here to feel that a good MT prop will fail, but my eyes are opened to the ways they may fail after rock damage.

[African Bear]

Ok guys, asking for comments again,
Since my prop, the MT mentioned above is taking time and probably lots more to rebuild. I have found a 3 blade Hartzell CS prop off a Mooney. It was mounted on a 200hp Lycoming. In theory it is a bolt on job. I like the idea of a metal prop as a backup but would like to know if anyone has experience of doing something like this on a Bearhawk. I see there is a very pertinent discussion going on already called "props vs Crankshaft"

[Battson]

I understand that different models of 2-blade and 3-blade Hartzell metal props require different counterweights to be installed on the crankshaft, in order to avoid vibration modes which can damage the engine / prop.

The requirement for counterweights and the model of counterweights varies, depending on the exact metal prop. You would need to contact Hartzell for advice, with your exact engine and prop make and model details.

I had the 72801 counterweights installed when Bob made my engine, at practically no cost, to give me some options in future should I want to change propellors.

[African Bear]

Battson thanks for your insight. I will definitely contact Hartzell.
Do you know if the same applies if I move from MT prop to Hartzell trailblazer, or does this apply to metal props only
Best
Andrew

[Battson]

I understand it applies more critically to metal props. A metal prop is literally a large "tuning fork" bolted directly to the crankshaft, reflecting the combustion vibrations from the motor right back into it. The natural frequencies are the main concern.

I understand the natural frequencies of carbon props are so different to the engine, that the issue of vibration interactions between the engine and the propellor is not such a significant concern. But you'll really need to ask the manufacturer, this is complex engineering - only they can answer definitively.

[African Bear]

At Last with a lot of comms. the zero timed prop and new blades are mounted. The new nickel leading edge blades look considerably more robust , fingers crossed WhatsApp Image 2024-04-06 at 17.21.56.jpg