Wood Prop Broke While Running (UPDATE)

[Mike Griffin]

Just thought I would share this with you all.  A friend of mine in our club was running an engine on a test stand and had a 11 x 4 Wood Master Airscrew propeller on the engine.  He picked up his tach to see what the RPMs were and the prop literally broke and shattered and the flying debris from the prop cut three of his fingers so bad, he had to go to the emergency room to get sewed up.  One finger was cut to the bone but did not fracture it.

I have never heard of this happening but in this hobby, you can never be too careful.

Mike

[Rusty]

I am sorry to hear that.  I have had a APC on a 25 engine come off and stick in my arm.  It was my fault for not tightening the nut enough. My arm was in the outer radius of the prop arc because I was holding the plane with that hand. 

Was his hand in the outer radius of the prop arc?

[Dwayne Donnelly]

I saw the pics on FB    I've had a wood prop break once, luckily I was behind the plane when it broke. 

[Jim Hoffman]

Before the event, was the prop free of nicks and dents?  Any photos? 

[Mike Griffin]

I am sorry to hear that.  I have had a APC on a 25 engine come off and stick in my arm.  It was my fault for not tightening the nut enough. My arm was in the outer radius of the prop arc because I was holding the plane with that hand. 

Was his hand in the outer radius of the prop arc?

The way I understood it Rusty, Yes.

[Mike Griffin]

Before the event, was the prop free of nicks and dents?  Any photos?

Jim, I really dont know the answer to that.  From what Nick told me, It was a new prop and the thing just sort of disintegrated and broke and be was hit by the shrapnel.   Nothing hit the prop, it just came apart. 

Mike

[kenneth cook]

            The only wood prop I had explode was a Top Flite Power Point. For no apparent reason it just came apart and it too was a beech wood prop like Master Airscrew.

[Colin McRae]

I have a few wood props in my box but normally do not use them. Usually I use APC or MAS-GF. Now I think I won't use wood in the future.

Wood props do have an issue in that the wood compresses and the prop needs to be retightened often. I have often wondered if the continued tightening might eventually cause a crack at the hub area causing a safety issue.

I have a couple of MAS and Brodak BYO wood props. These are not of the highest quality in my opinion. As far as quality goes, XOAR wood props seem to be great.

In any event, I think I will shy away from using wood.

I am also very glad the author's friend (or any possible bystanders) did not lose an eye.

[Dave_Trible]

Wood props are usually the most safe props to use in this respect.  It’s the nylon/ plastic props you have to be careful about.  In 60 years I’ve only had one wood prop come apart.  That was a prop made in the 1940s- maybe pre-war that could have been almost petrified wood.  I would have to think your failed prop was damaged or cracked from a previous ground strike or simply a bad spot in the wood.

Dave

[Steve Dwyer]

I've never heard of this happening but in recent years I have become more careful not to look down at the blade for this very reason. Nor do I reach over the blade to adjust the NV I always get behind the engine. I have too many scars and don't need any more or a lost eye.

Steve

[Motorman]

Beech wood Master Airscrew props are junk.


MM

[Leonard Duke]

I knew there was a reason all the books told me to not put my face in line with the prop!

The same rule applies to Model A Fords that still have their original radiator fans. A lot of Model A hoods have dents in line with the fan.

[Air Ministry .]

Some turkeys wander around carrying the plane by the prop blade . a bad habit .

Think thisiswhy the 3 blade master ' went ' and a carbon Eather prop has a blade cracked across .

Load x moment etc . Specially at 80 ounces . 

[Dan McEntee]

  I think I saw some photos of this elsewhere and I have to ask the painful, obvious questions here, seriously.  You mention the prop was a wood Master Airscrew 11-4, but you do not mention what kind or size of engine. With an 11-4, I would think stunt engine in the .40 to .46 size range. I'm curious as to what this detail is. I have been doing this stuff a long time, and have never had nor seen a wooden prop just explode as described. I have seen blades thrown on a precious few occasions, but have not had it happen to me flying stunt with any size stunt engine. When a blade gets tossed, it goes out away from the engine in the path of the prop arc. The few times I have witnessed this, it has been the same way, and luckily, no one was hit. I have to ask the next question, in all seriousness, did he maybe stick the tach into the prop some how? Did you witness the incident?  In my mind, if he was in front of or behind the prop arc, that is the only way his hand could have been in the way of anything coming off that prop. Sticking a semi solid object like fingers of a tach could cause a prop to fracture like that and cause the described type of injury. And to injure three fingers that badly?  Did he slip and put the tach and related fingers into the prop? What does the tach look like now?  Slip and fall while getting ready to do this? Again, I am asking these questions out of concern and in all seriousness and not trying to make fun of the poor guy or anyone else.  I have seen on other rare occasions where guys get too close too a prop with a tach and put it into the prop slightly, but they were behind the prop and that tends to bat things back and away and nothing really happened.  I hope the gentleman recovers fully but this just sounds so freaky and that is why I had to post this. I know, as I am getting older, I am more conscious and extra purposeful in how I do things around a running engine. It's easy to get complacent.
  Type at you later,
   Dan McEntee

[Brett Buck]

  I think I saw some photos of this elsewhere and I have to ask the painful, obvious questions here, seriously.  You mention the prop was a wood Master Airscrew 11-4, but you do not mention what kind or size of engine. With an 11-4, I would think stunt engine in the .40 to .46 size range. I'm curious as to what this detail is. I have been doing this stuff a long time, and have never had nor seen a wooden prop just explode as described. I have seen blades thrown on a precious few occasions, but have not had it happen to me flying stunt with any size stunt engine.

   I would have to agree, short of something getting into the prop, or prior damage, I have never seen a wood prop on any stunt engine just fly apart from loads. And most of the Master Airscrew wood props I have see are very sturdy with very thick hubs.

    I would be a little nervous about a MA "electric" wood prop, due to the torque spikes you get when it fires.

     I am not saying it couldn't happen, but my bet would be on some unnoticed damage, or something getting into the prop that no one saw.

      Brett

[Mike Griffin]

  I think I saw some photos of this elsewhere and I have to ask the painful, obvious questions here, seriously.  You mention the prop was a wood Master Airscrew 11-4, but you do not mention what kind or size of engine. With an 11-4, I would think stunt engine in the .40 to .46 size range. I'm curious as to what this detail is. I have been doing this stuff a long time, and have never had nor seen a wooden prop just explode as described. I have seen blades thrown on a precious few occasions, but have not had it happen to me flying stunt with any size stunt engine. When a blade gets tossed, it goes out away from the engine in the path of the prop arc. The few times I have witnessed this, it has been the same way, and luckily, no one was hit. I have to ask the next question, in all seriousness, did he maybe stick the tach into the prop some how? Did you witness the incident?  In my mind, if he was in front of or behind the prop arc, that is the only way his hand could have been in the way of anything coming off that prop. Sticking a semi solid object like fingers of a tach could cause a prop to fracture like that and cause the described type of injury. And to injure three fingers that badly?  Did he slip and put the tach and related fingers into the prop? What does the tach look like now?  Slip and fall while getting ready to do this? Again, I am asking these questions out of concern and in all seriousness and not trying to make fun of the poor guy or anyone else.  I have seen on other rare occasions where guys get too close too a prop with a tach and put it into the prop slightly, but they were behind the prop and that tends to bat things back and away and nothing really happened.  I hope the gentleman recovers fully but this just sounds so freaky and that is why I had to post this. I know, as I am getting older, I am more conscious and extra purposeful in how I do things around a running engine. It's easy to get complacent.
  Type at you later,
   Dan McEntee

Dan,

I was not there when this happened.  Nick Liuzza is a personal friend of mine and a member of our club here in New Orleans.  He posted this in the Control Line Flying group page on facebook of which you are a member also.  I do not have the answers you are seeking so I would suggest that you find the thread on facebook and ask Nick Directly the answer to your questions.  All I know is that he said it was brand new prop.   I did call Nick tonight because I was concerned about the injury and his well being and I did not ask him a lot of questions but he did say he did not hit the prop with the tach meter and that the prop just broke and the flying pieces or piece cut three of his fingers badly.   I take Nick at his word.

He will be more than happy to answer the questions you have and they are valid questions.

Mike

[Brett Buck]

I take Nick at his word.

   Please understand that no one, certainly not me, is saying he is making it up. If it was "brand new", it could have been cracked in shipping, or something like that.

    Brett

[kevin king]

Had a similar experience happen when i was tightening a wood prop. Its like it fell apart in my hand. It was an old prop, but i suspect it absorbed oil or fuel.

[Lauri Malila]

Without knowing the details,I just say that it's always a good idea to seal the center hole with epoxy, otherwise the oil will eventually come out from tips. also, drill 4-5x 2mm holes around the hole and fill them with hardwood dowels & epoxy. That will help against compression. L

[Steve Dwyer]

Mother nature cannot guarantee wood to be a perfect medium, flaws are always imminent.

[Peter in Fairfax, VA]

>  i was tightening a wood prop. ... it fell apart in my hand.

I had the same recent experience with my go-to prop, a Rev-Up 12x5 cut down to 11.25 on an LA 46.

[Mike Griffin]

   Please understand that no one, certainly not me, is saying he is making it up. If it was "brand new", it could have been cracked in shipping, or something like that.

    Brett

That thought had never crossed my mind Brett.  When I see Nick next time, I will ask him how it happened and share the details with everyone.  I had never heard of anything like this happening either. 

Mike

[Dan McEntee]

Without knowing the details,I just say that it's always a good idea to seal the center hole with epoxy, otherwise the oil will eventually come out from tips. also, drill 4-5x 2mm holes around the hole and fill them with hardwood dowels & epoxy. That will help against compression. L

      Charlie Reeves showed me a prop with some aluminum pins added into the hub of a .60 size prop years ago, and I thought that was a good idea. I asked Jim Lee to make a fixture for me with 4 equal spaced 1/8" holes and a 1/4" stub for the crankshaft hole. I drill the first hole, then drop a pin in to locate that, then drill the rest in a drill press. I started out using 1/8" aluminum pins but decided to try wood dowels to see how the did, and have used then ever since. I drill the hole just a few thousandths small, then chamfer the wood dowel and press that in, using the drill press again as an arbor press. A dab of glue in the hole before pressing the dowel in , just for giggles and grins. When you draw down on the prop nut to tighten it against the washer and prop hub, it feels like you are tightening it against solid steel!! The nut just stops, because it can't compress the wood dowels. Compression of the wood in the prop is a concern when using them, but even on older wood props that I have used and seen, I never saw any signs of stress fractures or anything that might lead me to think to prop would come apart. The wood grain goes through the hub, and you are just compressing the wood grain. Having a rounded edge on the washer would keep it from digging in sharply. Could the prop in question have had a void or some other internal flaw?  Maybe, but would be hard to tell now, but I would still like to see the remains of the prop. But whether using beechwood or maple props, I don't think the loads on a prop are enough to cause a prop to explode as described. Think about how many wood props that have been produced over time, and how many hours they have in the air? I certainly don't think that this one incident should ward anyone off from using a wood prop in normal conditions and used properly (read that as balanced and such, with no splits, cracks or nicks.)
  Type at you later,
   Dan McEntee

[Dan McEntee]

   I would have to agree, short of something getting into the prop, or prior damage, I have never seen a wood prop on any stunt engine just fly apart from loads. And most of the Master Airscrew wood props I have see are very sturdy with very thick hubs.

    I would be a little nervous about a MA "electric" wood prop, due to the torque spikes you get when it fires.

     I am not saying it couldn't happen, but my bet would be on some unnoticed damage, or something getting into the prop that no one saw.

      Brett

    I was going to bring up the MA wood prop tendency to have really thick hubs in my first response. I have only ever tried one or two of these, and out of all the boxes of props I have accumulated, that is probably all the MA wood props you would find in my inventory, for that reason. I always seem to run out of crank shaft threads when using these, and I won't use anything that won't take the full threads of the nut. I always wondered how Rev-Up and BY&O could make such nicely shaped hubs and Windsor propeller could not??
   Type at you later,
   Dan McEntee

[Mike Griffin]

In order to get you all some better details, I called Nick this morning and here is what he told me happened:

The engine was an Evolution 36 and was mounted on a test stand.  The prop was a brand new, never been mounted, Master Airscrew 11/4 wood prop.  He hand flipped the engine and it started right away.  He used his tach to check the RPMs and it was turning 9000 rpms.  He laid the tach down and right after he did this, one side of the prop broke off at the hub and his hand was close enough that when the broke half of the prop came off, it caught three of his fingers and cut them badly.  NOTHING touched the prop.

He called Master Airscrew to report what happened and the first person he talked to said they did not make props for Model Airplanes.  Yes, you read that right.  He then asked to talk to someone who knew what they were talking about and got someone else on the phone and they immediately went into the defense mode saying they were not responsible for restitution of the medical bills.  Nick explained he did not want restitution, he just wanted them to know what happened.

I hope this answers the questions about what actually happened.  I guess you can draw your own conclusions about why it happened.

Mike

[Steve Dwyer]

It certainly makes you wonder if they are outsourcing their wood props. Wherever they are made, is there control in place to monitor the quality of the wood being used? Perhaps a call to Sensenich to have a discussion would be revealing as well. What methods do they use to analyze a failure in the wood?

Steve

[Colin McRae]

It certainly makes you wonder if they are outsourcing their wood props. Wherever they are made, is there control in place to monitor the quality of the wood being used? Perhaps a call to Sensenich to have a discussion would be revealing as well. What methods do they use to analyze a failure in the wood?

Steve

I don't know about the origin of MAS wood props, but I do know that Brodak BYO wood props 'can' come from China.

Brodak told me that they used to source from China and still have some in stock, but now do their BYO props in-house. I have some Brodak wood props that look very different from one another. A few have a finish that looks as good as ones I have from XOAR. But others have a crappy looking finish, probably the ones sourced from China.

[Rusty]

Mike, thank you for the update.  Is it possible you could get a picture of the broken prop and pieces? 

Thanks

[Mike Griffin]

Mike, thank you for the update.  Is it possible you could get a picture of the broken prop and pieces? 

Thanks

Rusty I will check with Nick and see if he still has them. 

Mike

[John Carrodus]

Probably a mute point. Is there a photo of the prop remains? Did it break at the hub or further out towards the tip. Had the prop been worked on? ( I think there was mention of this? )
A worrying event.
Hope injuries heal quickly.
......Just an afterthought from the outside...Has anyone blamed Trump yet?

[Steve Helmick]

I don't know about the origin of MAS wood props, but I do know that Brodak BYO wood props 'can' come from China.

Brodak told me that they used to source from China and still have some in stock, but now do their BYO props in-house. I have some Brodak wood props that look very different from one another. A few have a finish that looks as good as ones I have from XOAR. But others have a crappy looking finish, probably the ones sourced from China.

My bet would be ($5) that the ones from China are the ones with the nice finish...like the XOAR, which are made in China.
  Steve

[Air Ministry .]

Timber is a bit like steel . You Pull Test your lines . Omit at your peril . IF you pull them , up to the ' stretch ' point , plus a bit , you see theyre ELSTIC . Like Wood .

Therefore , a carefulll grip , one hand on each blade , symetricish , outer palm depressing near ends , you can ' twist ' ( a bit of flex ) and  ' bow '  , as Timbers Elastic .

Unless its mega dryed out . Beyond seasoned . Tho that could be used to stiffen & britilise them ! . Theres many timbers , Beech , Ash , etc etc used , with each having their own properties . But those MASTER props are generally hard old seasoned heart timber , rather than / pulp ;/ pith ,  from further out the tree .


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The POINT BEING , if it snaps at minimum deflection in a ' grip ' , it would fail anyway . ANY decent grained timber will ' talk to you ' if your sympathetic .
Yatsenko Props I think are Beech . I sanded a few white ones and saw filler & poor grain symetry . But they were ancient ones and I belive theyre better
disposed as to timber selection  nowadays . Like the Balsa suppliers - not all are the same quality care & expertiese , in growing selecting & milling .

SO , some maybe 1/4 up n down total at the tips is sufficent , on some its maximum . But the ' feel ' off the bowing will have some spring and resitance ,
on the weightier props , Real Light ones youd be more carefull .

Someone whop wont be mentioned mentions stripping ALL props bare wuith thinner , 320 sanding , with a stick , evenly . ( thats me ) and then with a foam block ,
like say 2 x 1 x 8 inch or so . With THAT dressed FLAT on 100 Wt .( give or take ) Sanding with this / these , you get a ' FEEL ' of the timber & its durability .
Then it gets a rat tail or Sq Bstd. file to grip & spinit . Two Strokes aft , spin . ditto . so about ten strokes a face . Duplicolour clear . Or can ends , for phycadelic props .
The pale gold was so good the Goodyear got the rest of the can .
The IDEA ios to keep the OIL OUT .So a test or two with enough for that for a bit , and you can go atit as you go , if you fine tuning to a model / engine  .
( aft thickness , high point % , Flat or hollowed under / rear face , L E radius & hight , tighter under or full radius , L E top surfave curve . Like a wing section )
FINE TUNING .  Depithing outer or cleaning up inner inward ti inside of spinner . So its ALL BLADE ( working Blade ) outside the spinner  . If its there in the air
it may as well be doing something

Ive done the props to suit the spinner cut outs , and so as the slide in , it slides on  . Rather than butcher an aluminum spinner  , wich Ill give say 3 mm total ( 1/16th say )
clearance fitted . LOCKED ! .  The Brodak Backplates bow back , with the nosecone pulled down a way . So can push the cutouts back . Really wants a ' fill ' on B plate
so as the cone caint ro tate , just nipped down . AND I whittle the inner edge of the cutouts further . Or say dress inner edge parrallel to prop rathe than tangental -at a sector

A favoiurite was a twenty year old thinned and shaved or shaved thinner Master 12 x 6 . The dressing down the thickness means it loads the motor with a lot less drag .
SO DONT LET RISSOLES CARRY YA PLANE BY DA PROP BLADE < OR IT'LL BE MOIDA, or youll getit in the eye . And it wasd sucha noice prop to . Now THATS explained. ALSO .
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And a good selected grain master , or Zinger ( which it mayve been , thinking aboutit now ) are pretty good .

But IF one sat aroound for twenty years ( not uncommon )  under a hot tin roof , or in the sun , it could dry out beyond wots goodforit .
Some olde Gorrie Mi - T ( Mighty ! ) undercambered ! Full L E Rad , or generous ) ffropm the 60s I used Timber Oil on two of the 10 4's . to FEED EM . for flexibility .
The 12 4  Gorrie is a way better prop for stunt than any off the shelf thing from these wonderous times .

The pitchas a proper timber SEASONING storage set up , with pickets? betweenem so as they CAN BREATHE .
A truckload coming in the Air was Blue till the Job was Done RIGHT , Mahogany teak sapali oregon cetra & so on .

Were all guilty of throwing them places . Cool Dark  Dry on a voiticle dowle 'd be a start , for ya timberprops .
One Bloke has a Towell / apron ( n o mentioning names  ) for atthefield , lines of pockets , rolls up . foratthe field .

[Steve Dwyer]

The craftsmen at the worlds first propeller company, Chauvière, were first in the business of making toilet seats. Switching to propellers came naturally. Laminating helps to control the density of the wood planks and makes it easier to cut out imperfections, so laminated propellers are better balanced and will be 25% lighter because less allowance has to be made to account for imperfections.

[Tim Wescott]

I'd love to see a close-up picture of the remains.  In addition to being cracked during handling, if Master Airscrew is making wooden props without actually realizing that they make wooden props, they may also not realize that the grain actually needs to run the length of the prop, or close to it.  If there was a significant bend in the grain right at the hub of the prop when Master Airscrew was accidentally making propellers, then the prop would have been significantly weaker than one that was accidentally manufactured from straight-grained wood.

[Steve Helmick]

Also consider "wind checks" (which often show up in balsa) supposedly caused by wind flexing the tree prior to harvesting, or perhaps when it falls to the ground and lands roughly on other fallen trees or stumps. I think the latter is most likely to cause the wind checks, but I didn't name these flaws. Could wind checks have been present in the wood before it was ever carved into the propeller? Seems like QC problem, both before and after the carving is done. It would take a sharp eye.

A few years ago, I found a wood prop in my stock that had a horizontal split in one blade. I finished it off and threw it into the yard waste bin. There was a very short lived thought to put some CA in there, but common sense won. Steve

[Mike Griffin]

I'd love to see a close-up picture of the remains.  In addition to being cracked during handling, if Master Airscrew is making wooden props without actually realizing that they make wooden props, they may also not realize that the grain actually needs to run the length of the prop, or close to it.  If there was a significant bend in the grain right at the hub of the prop when Master Airscrew was accidentally making propellers, then the prop would have been significantly weaker than one that was accidentally manufactured from straight-grained wood.

Tim I have no idea if Nick threw it away or not.  If he did not, I will try and get a picture of it for everyone.

Mike