Prop failures
 

I'm going to give facts here, you can draw your own conclusions.

Last week, I was flying my OS .55 AX powered Deception 40 and in a down-line with the engine turning very high rpms, the prop let go. The firewall was ripped from the plane and the cowling was trashed. I brought her back dead-stick and landed with the engine, firewall, and what was left of the cowl hanging from the throttle cable.

I thought I just pushed it too far.

Today, I was flying my new Curare. At the time, I was just flying straight and level at around half power. There was a loud vibration, the canopy flew off, and the engine shut down. Another dead stick landing. Checking the plane revealed that the prop had failed at the root of the right blade in an identical manner as the one on the D-40. This caused my engine mount to fail. Fortunately, there was very little damage to the plane.

Both props were purchased at the same time from my lhs. They are both Master Airscrew G/F 3 Series 11-8.

RE: Prop failures
 

Here's a better pic of the fracture faces.

Additional info: the Curare is powered by a OS 61 FX.

RE: Prop failures
 

Wow, that's kind of scary! I used to use Master Airscrew props all the time years ago and never had this happen. They were always great props.

Just a thought here......Any chance that you were using aluminum spinners and the failed blades were rubbing on the metal? Maybe the electric starter spun the cone against the prop? That could cause a stress point on the blade and possibly failure.

RG

RE: Prop failures
 

I was using a plastic spinner on the Deception and an aluminum one on the Curare. I can see a very slight mark made by the spinner on the blade that is still there from the Curare, but there's no material loss, just a shiny mark. I don't see any type of cut or step on the top of the fracture face.

RE: Prop failures
 

At some point I switched from plastic to wood props because I was afraid the the plastic ones would fail flying in cold weather. It gets a bit nippy here in PA this time of year. Was it very cold on the days they failed? Most plastics get brittle if they get cold enough.

RG

RE: Prop failures
 

Nope, we had a beautiful day today, it was 53 degrees and sunny. It wasn't particularly cold when the Deception failure occurred either.

I would like to find an answer to this that doesn't point to the manufacture of the prop too. I have been a loyal Master Airscrew customer for many, many years. I'm not seeking any type of justice, nobody was hurt, and the damage is easily fixed.

So here's a little confession: I didn't balance either prop. I never do, and I've never had a failure like this.

I think I'll pick up a good balancer tomorrow. Just in case.

I will also NOT mount another MA G/F 3 on these planes.

RE: Prop failures
 

I always made sure I balanced the Master Airscrew props. Actually I balance all my props, but the MA props seemed to be the most out of balance of all the different props that I've used. They are great props, but not very well balanced from the factory.

But I would think that if your props were out of balance enough to cause failure you would have probably noticed a fairly severe vibration on the ground.

RG

RE: Prop failures
 

I didn't notice any unusual vibration on the ground.

Looking closer at the failed props, there is a "crease", or a transition between the hub and the blade. The failure is exactly on that crease. The failure is not located where the spinner would contact the blade.

RE: Prop failures
 

Hello,

Looking at the blades it seems that in both instances, the same blade failed. This would seem a little unusual. Out of curiosity, do you know which blade you hold on to while tightening the prop nut? The reason why I ask this is that I noticed some crazing on my APC-E props (which are pretty thin) and it always seemed to be the same blade regardless of prop. Then I realized that the blade showing the damage was the one which I normally hold while tightening the nut. I am much more careful when I tighten the nut now and the problem seems to have goen away. I must have been lucky since I have never had a blade fail.

Teo

RE: Prop failures
 

Can you post a close up photo of the crease. I'd be interested in seeing that. It wouldn't be a mold mark, would it?

RG

RE: Prop failures
 

That's a very good point!

RG

RE: Prop failures
 

This is a theory that has merit. I don't pick a particular blade to hold onto, I just grab the one that is convenient to the way I am holding the wrench. But since it's always the same hand, and the same wrench...

I could see that procedure putting alot of load on the blade. But how can you lower this load? Is there a procedure that minimizes it?

RE: Prop failures
 

Wow, taking this pic made me realize that there is a crack in the crease of the other blade on the one that came from the Curare.

RE: Prop failures
 

http://i1203.photobucket.com/albums/...Picture010.jpg

RE: Prop failures
 

Hope you contact Master Airscrew (Windsor Propeller) and relay your double failure issue.

RE: Prop failures
 

Looking a little closer at the fractured ends it looks like both props may have been cracked for awhile. The light gray areas in the photo are where the blades were still connected and the darker areas are where the cracks were. The reason they are darker is because the cracks allowed oil to seep into them. I've seen this type of failure in metal quite a bit and it looks very similar to your props. I doubt that this is a manufacturing flaw. I think the blades were stressed somehow.

RG

RE: Prop failures
 

I think that you are correct that the dark areas are areas that the crack existed prior to the failure and the light areas are the areas that failed when the blades separated. I don't think that the dark color is oil soak, it's just a different type of crack surface.

My new theory: I did not sand the flashing off of these props. I think that the sharp edge of the prop, combined with the stress riser of the crease, combined with loads due to holding a blade while wrenching on the prop-nut, caused a crack in the blade at the crease.

This crack grew during operation and then failed.

(I know, technically composites don't fatigue. It's just a theory.)

RE: Prop failures
 

Sounds like a reasonable theory to me! It's good that they failed in flight and not on the ground where someone could have gotten hurt!

RG

RE: Prop failures
 

Yes, it really reinforces the habit of not letting anyone stand in line with the propeller.

RE: Prop failures
 

You never said what the prop size was you are using for the 55ax and what rpm's were you turning on the ground. A friend of mine and myself has Kaos's and he has a 55ax and I have a 45fx and we both use APC props and both turn ( on ground ) around 11,500rpm's and have no problems. So I am wondering if it was cold and you were turning high rpm's like we do and those master airscrew props flex a lot they could have broken from flex fatigue. Just a thought! :eek:

RE: Prop failures
 

Sorry to hear of your prop problems. I have used Master Airscrew and APC props for a long time and have never experienced a failure in flight. Can't imagine what is causing you to tear up all your stuff.

RE: Prop failures
 

Nothing new here really......

MA props are known to throw blades....thats why APC props should be used.
I've seen several blades tossed over the years and they have always been MA.

The last one I saw was a local friend running up a 3 blade on the ground just before takeoff.
One blade came off, the engine ripped the entire nose off the airplane and the fish head went zooming over the clubhouse, hit someone's mother in law in the tail feathers, then went on down the parking lot and the engine needle valve got stuck in the sidewall tire of an Edsel.

Fortunately, no one was hurt....
Spend more money for a good prop and this will never happen again.

RE: Prop failures
 

Well I'm glad you posted about your Master Airscrew problems cause my local hobby store is no longer going to carry the Topflight line of props.

I setup my Utter Chaos with a 50FSR with a Macs tuned pipe turning a TF 11 x 6wood and theyaren't going to restock the TF's. So my thoughtswhere to try the Master airscrews. I guess I try to find find the TF's on line.

The real pain is I'll have to retune the pipe if I can't find the TF 11 x 6's. I would really hate to have toretune the pipe as I'm gettin 14400rpm with that 11 x 6 on the ground running rich. It really unloads in the air and I've been really enjoying boring holes through the sky.http://www.rcuniverse.com/forum/js/f...sn/biggrin.gif

RE: Prop failures
 

Both props were 11x8. Unknown on the rpm. It was 53 degrees when the Curare had the prop failure. I did run it last weekend with the same prop in cold weather, it was around 36 degrees.

RE: Prop failures
 

In both cases the engine shut down immediately because a pull on the throttle closes the carb. This is a very good thing.

I wonder what would happen on one of my fourstokes (magnum .91 and Saito 100)? The throttles work the other way. A pull on the throttle cable results in a fully open carb. Why did they do this???

And yes, I'll spend more money on a better prop. I've learned my lesson. It's not worth saving a buck on something that you don't have to replace often but has the potential to destroy the aircraft (or worse!!!).

Mother in laws have tail feathers? Mine just clucks like a chicken.