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Wood props, was: Re: wood resonance 912

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Dana

Joined: 13 Dec 2007
Posts: 1047
Location: Connecticut, USA

Posted: Tue Sep 09, 2008 1:37 pm Post subject: Wood props, was: Re: wood resonance 912

At 02:23 PM 9/9/2008, JetPilot wrote:



  	  Quote: 	
		  Wood props are very fragile, and are very likely to be broken by something coming off a pusher plane like a Kolb.   This is a very well known fact.



 If anyone out there is starting to wonder after reading Terrys very misleading post, read this:



 http://www.associatedcontent.com/article/418892/four_disadvantages_of_aircraft_propellers.html



 http://users.hunterlink.net.au/~dddj/Powershift.htm 	


 Mike,



 I don't agree.



 You can't make a blanket statement that "wood props are more fragile" or "composite props are better".  Wood is more susceptible to some kinds of damage and less susceptible to other kinds.  



 I have seen (especially in the PPG world) wood props in regular use with all kinds of damage, and they hold together.  I know one pilot whose headphones went through the [wood] prop right on takeoff.  He said it was vibrating so bad that he thought the engine mounts would snap, but he made it up and aro

 und for a safe landing.  OTOH I have seen composite props come completely apart due to what seemed a very minor nick, or even no visible damage at all.  Wood props are softer, so they're more likely to suffer abrasion damage (a major factor for seaplanes or airboats with water spray), but that very softness means that a nick is less likely to propagate into a major crack.



 Also not all composite props are the same.  The Warp Drive props, as I understand, are solid, rather heavy, and durable.  Powerfins, with their relatively thin skin and foam core, are much more easily damaged.  I don't know much about the Ivos.



 Wood has some other advantages as well as disadvantages.  A wood prop is easier to repair if it is damaged.  It can get out of balance, especially if damaged or neglected (but not because it's stored vertical, that's an old wives tale).  A composite or metal prop can be more efficient due to the thinner blades, but a wood prop is easier to modify or "tweak" if it's not quite right.  And wood is less expensive (I hesitate to say "cheaper").



 The websites you cited are both either misleading to this discussion or plain wrong.  I agree that a composite prop is probably better for an airboat, but only due to the specifics of their application.  OTOH, the associatedcontent site has mostly misleading statements:

   "If there is a small split on the propeller, it can easily travel up through the wood grain and get larger and cause the propeller to fail. You don't want this to happen in the air, so you need to make sure there are no cracks or splits before you takeoff."



  A small nick in an aluminum prop can also cause a crack to propagate, much more likely than a similar nick in a wood prop.

   "Propellers that are made from wood can warp over time. Changes in temperature and humidity can easily cause wood propellers to warp."



  I have never seen a wood prop warp, though I suppose it's possible if left out in the rain with badly worn finish.

   "Four stroke engines generally run smoother when used with heavier propellers. Unfortunately, most wood propellers are very lightweight. Therefore, they usually aren't suitable to use with four stroke engines."



  Tell that to the designers, builders, and owners of hundreds of thousands of 4-stroke powered aircraft with wood props.

   "The density of wood is not uniform. Therefore, two blades of a propeller that is made from wood may not balance with each other. This can be the cause even when the blades have identical shapes."



  That's not a problem so much as an issue that must be dealt with in manufacturing.  Careful attention to wood selection, final shaping, and finishing means any new wood prop you buy from a reputable manufacturer will balance properly.



 -Dana

 --

  People are more violently opposed to fur than leather because it's safer to pick on rich women than biker gangs.    [quote][b]

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russ(at)rkiphoto.com
Guest

Posted: Tue Sep 09, 2008 2:06 pm Post subject: Wood props, was: Re: wood resonance 912

I'm a little surprised at the recent wood-prop bashing that's appeared on  the List.Wood props, as had been said, have been  around forever and work VERY WELL. You can't argue with many many many years of good wood-prop service.

These two links cited are from  (1) a man who I doubt has much real wood-prop experience (he lists chess and music as two main activities), and (2) from  a manufacturer of composite props. So what would you expect? I'm not at all surprised at their comments

And I wonder how many hours 'jetpilot' has flown behind a wood prop? Didn't think they used them on jets.

do not archive



On Sep 9, 2008, at 5:33 PM, Dana Hague wrote:

[quote] At 02:23 PM 9/9/2008, JetPilot wrote:



  	  Quote: 	
		  Wood props are very fragile, and are very likely to be broken by something coming off a pusher plane like a Kolb.   This is a very well known fact.



 If anyone out there is starting to wonder after reading Terrys very misleading post, read this:



 http://www.associatedcontent.com/article/418892/four_disadvantages_of_aircraft_propellers.html



 http://users.hunterlink.net.au/~dddj/Powershift.htm 	


 Mike,



 I don't agree.



 You can't make a blanket statement that "wood props are more fragile" or "composite props are better".  Wood is more susceptible to some kinds of damage and less susceptible to other kinds.  



 I have seen (especially in the PPG world) wood props in regular use with all kinds of damage, and they hold together.  I know one pilot whose headphones went through the [wood] prop right on takeoff.  He said it was vibrating so bad that he thought the engine mounts would snap, but he made it up and aro

 und for a safe landing.  OTOH I have seen composite props come completely apart due to what seemed a very minor nick, or even no visible damage at all.  Wood props are softer, so they're more likely to suffer abrasion damage (a major factor for seaplanes or airboats with water spray), but that very softness means that a nick is less likely to propagate into a major crack.



 Also not all composite props are the same.  The Warp Drive props, as I understand, are solid, rather heavy, and durable.  Powerfins, with their relatively thin skin and foam core, are much more easily damaged.  I don't know much about the Ivos.



 Wood has some other advantages as well as disadvantages.  A wood prop is easier to repair if it is damaged.  It can get out of balance, especially if damaged or neglected (but not because it's stored vertical, that's an old wives tale).  A composite or metal prop can be more efficient due to the thinner blades, but a wood prop is easier to modify or "tweak" if it's not quite right.  And wood is less expensive (I hesitate to say "cheaper").



 The websites you cited are both either misleading to this discussion or plain wrong.  I agree that a composite prop is probably better for an airboat, but only due to the specifics of their application.  OTOH, the associatedcontent site has mostly misleading statements:

  "If there is a small split on the propeller, it can easily travel up through the wood grain and get larger and cause the propeller to fail. You don't want this to happen in the air, so you need to make sure there are no cracks or splits before you takeoff."



 A small nick in an aluminum prop can also cause a crack to propagate, much more likely than a similar nick in a wood prop.

  "Propellers that are made from wood can warp over time. Changes in temperature and humidity can easily cause wood propellers to warp."



 I have never seen a wood prop warp, though I suppose it's possible if left out in the rain with badly worn finish.

  "Four stroke engines generally run smoother when used with heavier propellers. Unfortunately, most wood propellers are very lightweight. Therefore, they usually aren't suitable to use with four stroke engines."



 Tell that to the designers, builders, and owners of hundreds of thousands of 4-stroke powered aircraft with wood props.

  "The density of wood is not uniform. Therefore, two blades of a propeller that is made from wood may not balance with each other. This can be the cause even when the blades have identical shapes."



 That's not a problem so much as an issue that must be dealt with in manufacturing.  Careful attention to wood selection, final shaping, and finishing means any new wood prop you buy from a reputable manufacturer will balance properly.



 -Dana

 --

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lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Thu Sep 11, 2008 6:46 am Post subject: Re: Wood props, was: Re: wood resonance 912

 	  Dana wrote: 	
		  At 02:23 PM 9/9/2008, JetPilot wrote:



  	  Quote: 	
		  Wood props are very fragile, and are very likely to be broken by something coming off a pusher plane like a Kolb.   This is a very well known fact.



 If anyone out there is starting to wonder after reading Terrys very misleading post, read this:



 http://www.associatedcontent.com/article/418892/four_disadvantages_of_aircraft_propellers.html



 http://users.hunterlink.net.au/~dddj/Powershift.htm 	


 Mike,



 I don't agree.



 You can't make a blanket statement that "wood props are more fragile" or "composite props are better".  Wood is more susceptible to some kinds of damage and less susceptible to other kinds.  

	




I can't agree either. 

I've flown wood props on several of the planes I've owned and my experience has not been that they're overly fragile.



Most woodies, probably all of them in fact, are made from laminated blocks. Laminating wood in this fashion is a time-honored/well-known way to create a very strong, warp-free material for making props. 



The loosening bolt thing I would consider to be a non-argument, as loose prop bolts easily corrected with a torque wrench are more properly considered owner/operator error and not the fault of the prop. Laminated woodies don't suffer from this problem to a huge degree anyway.



Woodies also have the advantage of light weight, particularly as compared to metal props. This is important for us with our smaller motors that are more sensitive to moment-of-inertia affects.



Easy repairability of the woody is time-honored and pretty well understoond also.



The failure mode of a good woody is not generally a complete explosion. Highly laminated wood blocks don't generally fail that way, since the grains of the laminates don't all run in the same direction (to my knowledge).



I've never been a strong advocate of putting objects through spinning props anyway, tho, so I'm not too overly concerned about this particular aspect of it . But in case it does happen without my consent, and it has with one or two of my woodies in the past, the woodies seem to be very durable to me.



Would I run one on my 912s? In a heartbeat if there were one appropriate for my plane....



LS

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LS
Titan II SS

Steve Boetto

Joined: 11 Jan 2006
Posts: 364

Posted: Fri Sep 12, 2008 3:53 pm Post subject: Wood props, was: Re: wood resonance 912

In a message dated 9/9/2008 5:38:06 P.M. Eastern Daylight Time,  d-m-hague(at)comcast.net writes:

  	  Quote: 	
		  Wood    props are very fragile, and are very likely to be broken by something coming    off a pusher plane like a Kolb.   This is a very well known    fact.



If anyone out there is starting to wonder after reading Terrys    very misleading post, read this:

	
 Mike,  I do not agree.

 I sat in front of a Sensenich 64 x 79 all wood blade for over a 1000 hours  that was bolted to an 0-320 lyc.

 Even made trips to the Bahamas.  That same blade took my good friend  from Key West to Roatan and back. Non Stop both ways.    Over the  years I did have a few small screws from the cowl leave their mark but last time  I checked it had over 2k hrs.

  	  Quote: 	
		  I    suggest that you learn how to keep stuff from falling off your plane and not    rely on a blade not breaking no matter what it is made of. 	
 steve b

  	  Quote: 	
		  

 	


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