This is why I decided to post. This is very unusual for me.

I've been running RC aircraft since 1983 and I have never had a propeller fail, with only one exception: Probably 25 years ago I was running a Cox TD .051 powered hot-rod and the engine seized due to excess rpms. The prop unscrewed itself and shot across the sky (you could hear it).

I quite using Master Airscrew some time ago on high performance engines just because I had seen too many problems like yours.  I see two problems here: first, you are using too small a prop for those engines - you must really like to hear a high pitched whine.  Second, the GF prop is designed to give more thrust at low to mid RPM and will twist too much at high RPM.  If you want to stay with Master Airscrew then go for the higher performance props.  But on those engines you should use APC and increase the size to a 12x8.

When all else fails RTFM.

Turn the carb around and it'll be push-open/pull-close.

Here's what TFM says.

I went down a size (and increased the pitch from the suggested 12-7) due to ground clearance issues on the D-40. I don't have enough clearance in the grass for a 12 inch prop. I have no such excuse for the Curare.

I see no warnings or information on MAs site about using that prop on a .60. It says: "Acclaimed Sport Props. Made of Glass-filled Nylon for strength & durability"

I'm not saying that what I did is right, just showing how I got here.

"Turn the carb around and it'll be push-open/pull-close."

Thanks but that's not a suggestion I can use for already completed aircraft.

On a new aircraft, I'm not sure I could get used to having the needle on the wrong side. Old dog, new tricks = cut fingers.

Hi, Haven't seen a master Airscrew prop throw a blade. How ever that isn't saying it doesn't happen as in your case. Some rules about using molded props though including all types. always flex the prop before you buy it and every now and then flex the prop before flight just to be sure it hasen't been damaged. Do this by holding it buy each end and flex in both directions. When on the motor hold the spinner and flex each blade in both directions. Also make sure that the edge of any spinner installed does not contact the prop at all. There should be about 1/16" clearance all the way around the blade. Props especially moulded props flex a lot between idle speed and full throttle. If the prop blade it touching the spinner it will cause a fracture point at the hub. It also doesn't hurt to boil molded props this will expose any flaws inside the prop like air bubbles, if there is a falw it will fracture and boiling will also reintroduce moisture into old props.

What you experienced is a manufacturing defect. I had a similar experience many years ago and switched to wood. Send the props back to the manufacture and let them explain the cause.

Thirty years ago, noone used Master Airscrew props on pattern airplanes for two reasons. First they were known to have a tendency to throw blades and secondly, the blade shape was very inefficient and the blades flexed too much. I'm sure the materials used for Master Airscrew are much better now and less likely to fracture but I don't see much improvement on blade airfoil. We used mainly reworked Zingers and TF Power Props.
When APC props came along, they took over the pattern market by producing a safe and very effective product at a good price.

Boiling was to reduce stresses in early nylon props such as the Tornado and TopFlite. Later we were told to bake them rather than boil because the water weakened the prop. Not sure that boiling or baking will do anything for APC which are glass filled nylon resin props, which I assume the new Master Airscrews are as well.

A quote from APC to keep in mind
 <font size="2">"</font><font face="Verdana,Tahoma,Arial,Helvetica,Sans-serif,sans-serif" size="2">In summary, please abide by the safety practices recommended by propeller manufactures. This is especially important for high performance propellers. Assume that propellers can fail at any time, especially during full power adjustments on the ground. Never stand in or expose others to the plane of the propeller arc. </font><font size="2">"</font>

John

Something else to consider is use alum. type spinners. I have had two plastic spinners explode on run up. One was "BRAND NEW" and the other had been on my Top Flight Mustang 150 size using a Satio 4-stroke for about two years then one day it went ballistic. There have been others at our field that has had plastic spinners go bad so this is why I never use plastic any more, just VERY LUCKY myself or others close by were not injured. Just another thought on safety.

I have never in my 25 years of flying, never had a failure like that of Master Airscrew prop or any really. And I push my props with over powered engines.

I even fly with a prop that I ground strike and not balance. Just go up again.

BUT............................. I always expect any and all to fail. May never happen, may happen next time out.




Never trust high speed moving parts.

Steve

That's great but what about those who have.

This might sound ugly but with the same type of failure on tow different props that are NOT systematic of just "flying apart", this looks more like a "user error" than a material defect. 
We don't know if there is/was any stress during transport, storage, shipping, or handling. 
Also, knowledge of how that large missing section got there when the post leads us to believe the prop disintegrated in midair and should have been static/still at landing (dead stick)?
Do you hang the planes by the prop when not flying?  Is there any stress on the props at storage and are then stored indoors or in subfreeze garage conditions?
Just for heck of it, when you install new props, give them a light flex motion prior to startup just to check and see if that movement causes them to break?
Make sure your spinners are not biting into the prop?
Perhaps leave the glow plug OFF and give them a few normal starting attempts, then disassemble the spinner and closely examine the prop PLUS give them a good tug, pull, flex and see if they break  (I'm not saying bend them until they break)
Just a few suggestions and ideas.  Typically, one sees this type of failure due to prop strikes and I will venture to say that they just don't self destruct under normal usage.  

Both aircraft landed dead-stick.

I store my aircraft indoors.

I do not hang them by the prop.

I think the damage on the remaining blade from the Deception was due to the blade hitting either the detached blade or a piece of the cowl or spinner when the failure occurred.

Neither aircraft has had a prop-strike.

The Deception had probably ten flights, the Curare three with these props.

The spinner was discussed in previous posts.

MA props to flexable, have low pitch that stated and have a poor airfoil. good fow low rpm trainers and tow planes.

your 11x8 prop is close to a APC 11x6 prop in pitch and a 11X5 by flight performance.

I have done some Telemetry testing and the MA i had to go up 2-3 pitch sizes for the same flight speed.

I also found out that 17,000 on a apc 11" prop they start get that super sonic howl/zing to them. i would never run a MA past 12,000 on the ground in the 10-11" sizes 11,000 on the 12" props and so on.

Thank you. Technical information is much appreciated.

The Deception was screaming at the time of failure. The Curare, not so much, I'm sure the rpm was well below 12,000.

It sure looks to me like it's either a manufacturing defect (maybe they're both from the same batch?) or a failure related the inherent design of the blades...possibly combined with other factors that have already been discussed. As far as alternate brands go, I'll throw my two cents in for Graupner props. Grey reinforced resin, extremely rigid, yet durable. I've had many that have survived some pretty serious prop strikes, I think I've only actually had one or two break and that was under severe abuse. They're also the only props I've ever found that seem to perform as well as the old-timey Top Flite Super-M props. On various aircraft in my stable, they've proven themselves to perform as well or better than APC. Might want to give 'em a try, at any rate....good luck!

Will the Graupner fit in my Tru-turn 2 1/4 inch aluminum spinner without modifications? I don't think that the APC will. It will pain me greatly to take a grinding bit to such a pretty spinner.

I would use APC props on everything if they weren't so hideous. I don't mind the shape, but the color is awful. I like my planes to look nice as well as perform well. Maybe I should put APC props on them when I go to the field and wood props on them when they are displayed.

Back in the day, we used to boil the props in water for a minute or two to get rid of 'stress'. Haven't used that technique in decades.

The manufacturer website says 15,000 RPM max for their 11" props, based on dividing 165,000 by the prop diameter:

http://masterairscrew.com/manualinst...tructions2.pdf

They have a Formula 1 high-performance series that will probably hold up better, or try an APC. They rarely fail, and need little balancing. They have lots of flash and sharp edges though.

Balancing is a forgotten item until one has a failure such as yours. Really doesn't take that long, is good for the airframe and electronics also.

I always hold both sides of the prop when tightening, thumb on one trailing edge and one or two fingers on the other. Balancing and sanding flash is mandatory, especially with MA props. I agree they are poorly balanced (if at all) from the factory.

Thanks, I'll take a look at the high-performance series, they may fit in the spinner.

I have definitely learned my lesson about balance and sanding the flash. I always thought of the sanding as a safety measure, but now I see that it may eliminate a stress riser.

I've seen a lot of painted APC props. Not sure what was used but any fuel proof enamel should work. Black or white with contrasting tips looks much better than gray. Have to admit it improves the appearance a lot. But I would much rather have the performance than pretty though. The contasting tips are important though as the props disappear when turning.

John

I use Krylon when I paint my props, it holds up well to all fuels but you do need to let it set for a couple of days to cure and then re-check the balance.

I may try Rit dye on an APC. I already use it on car chassis parts and wheels, works good.

My two cents worth:

Both blade failures appear to be fatigue related, not overload per se. The breaks are clean, and there is evidence of crack propogation. High RPM caused final failure as the cracks spread. Fatigue is related to operating RPM - especially dangerous if you transition slowly through critical flex frequency of the blades, ESPECIALLY bad if critical frequency is at or near full operational speed. Relatively small root section vs. heavy blade (as in the case of both of these MA props) lowers critical frequency, putting more fatigue stress flex cycles on the blades as prop goes from idle to full load.

The section area at the breaks is relatively small when compared to other well designed glass reinforced props such as APC.

MA props are not very efficient aerodynamically. Propeller efficiency of any APC prop compared to "equivalent" MA is noticeably higher. I have compared them in the air, and the aircraft performance is noticeably better with the APC. This, along with the apparent danger associated with MA props should convince anyone to use APC, not MA.

MA props do have their place. I use mine for stirring paint and large batches of epoxy. Literally. I would not mount one on the crakshaft of a model engine any longer.

I'm willing to let that be the last word on this topic. I'm convinced.

Shall we let this thread fade away?

(that trick never works!)