Woods for props

[Curare]

Hey all, I had an idea the other day when competing in the last stunt comp we had here, that my plane was flying a bit fast, and could probably use a little less pitch, and a bit more blade area. Rather than rework an existing prop (that I didn't have anyway) I borrowed a BY&O paddle prop from a friend, 3D scanned it and generated a copy for CNC milling.

I figure that once I have the correct shape and a known pitch I should (in theory) be able to modify the depth and thus create whatever pitch I need, and with a bit of remodelling I should be able to achieve what ever blade area I require.

The question then is material. I know that Beech is the industry standard for props, but I have seen cherry as well.

What woods make good props? What should I be looking for when selecting prop material?

Pic for attention

[Dan McEntee]

  I think Top Flite props , and maybe Rev-Up also, were made from hard maple. or maple wood of some kind. I have heard a story that Sid Axlerod , original owner of Top Flite, would watch for house and apartment buildings on fire, and then salvage the hardwood maple flooring that didn't get consumed in the fire!!The big factor is finding wood with consistent grain feature to it and getting the prop oriented to wood in the correct way. this will be a lot of work but props and how they work is a pretty interesting subject. I can just say that all props are not the same, even with the same diameter and pitch, and what works on one engine/model combination, might not work on the next model. That's why I have a lot of boxes with props in them!!
  Type at you later,
   Dan McEntee

[Lauri Malila]

Interesting, of course, but how about just some heating & tweaking for the existing prop..? L

[M Spencer]

Id do em six inches overlength , Grip the outer two inches , both ends ! .  Machine out past blades a inch ish .  So well supported and ACCURATE . Then last step is cut & finish ENDS

[M Spencer]

Ive had SPRUCE strips , with straight even grain the full length , some with the stripes the full length , 36 or 48 inch . 1 m.m. or less spacing .
Whereas somes all over the place , and none spaced even . and wandering . As a GUIDE of WHAT TO LOOK FOR .



FROM : https://www.enginehistory.org/Propellers/Rotol/rotol.shtml

theres a number of sites with Timber Prop info .
https://www.aeropp.co.nz/
https://www.bushaero.com.au/wooden-propellers

Think I put a Merlin prop bade link on , the other day .
https://www.historicpropellers.com/spitfire/
GOTTEM .

If you want light strong props , you may want to laminate say 2 m.m. vineer , and soak / impregnate the finished prop , before micro finishing .

https://www.historicpropellers.com/woodenpropeller-fokker/ heres a good one for youse fokkers . 

Compregnol & other trade names were for pressure laminated impregnated type stuff .  Berringer props were maybe six laminations . But horses for courses .
Youll see maybe half one of those 12 x 5 T F packs have resonable grain , matched side to side . the other halfs unmatched or wanders off .
Depends how much load you put on it , as theyll veer , under load . Which WAS one of the tricks of custom wood stunt props .
Could ' Fine Off ' under max. load to go uphill better .
Or some speed configured to shift steeper pitch under high rotational load . Blade center weight point vs root configuration ! . so There ! were a few articals on it in early 60s U.S. mags . 

[Dave Hull]

Eastern maple (not western or bigleaf maple), beech, yellow birch are top woods for props in my opinion. Close grained, and dense/hard for durability. Need to resist crushing from the mounting provisions.

I have made props from all three and like all of them. This is also borne out by looking at the material properties from the Forest Products Laboratory--Wood Handbook.

I just saw some BY&O props last weekend in the hobby shop made from oak. Not a good choice. Oak is ring-porous. I'd try the cherry or walnut before I'd mess with oak. Ash would be better than oak and I wouldn't waste the effort on any in this group.

[Curare]

Interesting, of course, but how about just some heating & tweaking for the existing prop..? L

Lauri, a great idea if all you want to do is reduce pitch, but adding blade area onto a skinny prop might be a problem!

I think I think you'll find some resonance: I Like to do things not because it's easy, but because I want to know if I can!

I have had the thought of doing carbon props but I feel a carbon prop on an OTS model just wouldn't be right!

[Lauri Malila]

I fully agree, Greg. It's a very interesting technology and I'm looking forward to hear what is the precision of the scanned/milled product, compared to the original.
I think that wood is the best material for our props, especially when used together with modern CNC-technology. L

[Tom Luciano]

For some reason I have in my head that Top Fite also used Beech wood.

Tom

[Dwayne Donnelly]

For some reason I have in my head that Top Fite also used Beech wood.

Tom

They may have used other types of wood as well I don't know but yes Top Flite most definitely made props from beechwood. 

[Dave_Trible]

Top Flight Super Ms were obviously maple of some type.   I order sugar maple cabinet door planks and cut them up for motor mounts.  That stuff is very hard and would make good props.  I think beechwood is hard enough but a little lighter weight which could be a consideration.

Dave

[Al Ferraro]

 I know it would be cool to make your own prop. APC or MAS should have a prop that would work for your combination. What is your plane and power source?
Al

[Howard Rush]

Maple can split along the grain and separate. Cross-grain strength would be a good prop property. We went from Rev-Up 8-8s to Y&O 8-8s because the Rev-Ups would fly apart.

[M Spencer]

Are you after doing VOLUME production ? regarding materials , comercial quatities , or just a few for the locals , or justyou .

The Yat.have a aluminum Spacer / center - for the crank fitting . A lot of the old soft T F rounded blade props are soft as , and  C R U S H  if your needing to tightenem firm .




If youve got it right , the apperance each side should match , grain / the quatergrain look , etc . you can see a few of these the grain flows off . Good T F 12 x 5s are near matching ' patterns ' side to side .

A old Fox .35 or Max .35 isnt going to stress a prop like a VF or ST 51 / 60 or your Rojetts & P.A.'s . More Grunt & severe opperating conditions ( a bit of wind ' ) and them blades is working , All Right -
if the grains match all right . If the grains way mismatched the blade deflection under load will be missmatched .

so horses , or timbers , for corses .
dunno if the picture came out , but the old 50s / 60s Top Flite , some are way soft , a ST .46 Maybe , but a .51 up with the higher revs & output would be marginal if theyre less than perfect , perhaps .
soitonly onna Piped humdinger .

Like Balsa , the olde ' over the knee ' or both hands grip , a EVALUATION of the ridgidity - elasticity - durability - of the raw stock ( a sample ) would be amiss . See if the odd one snaps prematurely ,
if its for mega motors .

Traditionally , a pilot was acomplished when he stopped breaking timber props . Id think you could get the weight . inertia - of wood , lighter than C-F / Glass props . for a swifter 4-2 switch ,
so the lighter softer timber'd be more suited to the older type baffle piston motors & there recent clones , D.S. , Stalker etc .



From the Horses Mouth ! https://www.eaa.org/eaa/aircraft-building/builderresources/while-youre-building/building-articles/wood/building-with-wood-part-1

[Curare]

Well, if Jarrah were a viable prop material, I've got that down pat. Jarrah was used for home costruction here in perth right up until the 90's.  Not sure I'd trust it as a prop though, it's hard and has a tendency to splinter under stress.

[M Spencer]

Bob Gorrie was up Qld . There Gorries Hobbies ad's in the Old 60s aus. mags in R C Bookcase . quite humourous .
the Props are ' Mighty ' intelligent . One or two ads , he has ' mighty ' on the Brain. And in his Nats. report .

a catchword .  The PROPS of his I have , grey with decades age , but I furniture oiled two of the 10 x 4s ,

Theyre a STRAIGHT close grained hardwood , similar to Mahogany . Being Maiden Aus, IId assume its orstrawlian teomber .
Not grooty bush jarra tho .



Hurumph . Sun Deck Timber . SPLITS ? probly wasnt dried / seasoned wright . Tho'd vary . Good two decade old demo. stuff , if it addent split likely wouldnt .
Mine appear grianwise loike high grade close grained aircraft spruce . Dyed brown. and harder . so that there plank likely aint top grade . Being Australian .       

You have to look hard , for the good stuff . It dosnt grow on trees , you know .        not many , anyway . It needs to be a superior tree with superior milling dring seasoning and dressing .
not a modern plastic one .

[M Spencer]

Thought one or two people MIGHT be intrested . Watts 2 Blade prop . Hurricane & Spitfire . Way longer take of distance than variable pitch .





And you think youve got it tough , hand starting it . the COWL is bigger diameter than the prop hub , so all the leaky oil gets blown out the back . 



Wtd. ' Good keen men ' . Givin a 1.000 horsepower flying ' sports car ' , why not .

[Istvan Travnik]

For non-industrial use (no milling, just grinding+sanding), the hornbeam was the classical material by us.
Far harder / stronger than beechwood, or red (Canadian) maple, and not heavier. 

[Dave Hull]

Interesting. You can't find hornbeam lumber here (USA West Coast) although it can grow across most of the USA. It is not a commercial wood. It is not listed in the Forest Products Laboratory--Wood Handbook. But when I compare data from The Wood Database (another good sourcebook) to the other woods, hornbeam is significantly heavier than eastern maple, yellow birch or beechwood when all are kiln-dried to 12% moisture content. There's a reason it is also known as "ironwood." That said, for a model propeller, it may well be lighter than a molded plastic prop. Hornbeam's bending stiffness is not quite as good as eastern maple or yellow birch, and yet is certainly better than some other woods that have been used to make propellers! While I can't confirm that the crush strength data is taken the same way, hornbeam is likely right near the top of the list with eastern maple. I don't have a comparable number for ramin, another wood used for modeling--but not in the USA so we don't have experience with it. The one place I believe I have seen hornbeam used in modeling is for the tiny blocks used in model ship rigging. It has very fine grain and seems to be the wood of choice...?

[Istvan Travnik]

I know that tablemakers do not like hornbeam.
They say: "it is good for bottom plate of a planner but nothing else..."
But, a modeller is not a tablemaker.
Always it's in my mind, how our classic "great dinosaurs" grind on sandpaper covered 12" spinning disc the bottom of a prop, in one movement...   

[M Spencer]

RAMIN .
https://www.mytropicaltimber.org/en/products/80/ramin
Botanical names : Gonystylus spp.
Specific gravity (at 12% of wood moisture) :   660
Class of resistance to fungi :   Class 5 - not durable
Resistance to marin borer :   No- cannot be used in marine environment or in brackish water
Stability :   Poorly stable - Moderately stable
Finishing :   Good
Average longitudinal modulus of elasticity (moisture at 12%) :   19020
Color :   Light yellow
Origin :   Asia, Oceania

looks like Balsa Wood ! ?

[M Spencer]

What is hornbeam wood used for
Image result for what is hornbeam wood used for
Hornbeam timber is a pale, creamy white with a flecked grain. It is extremely hard; in fact it has the hardest wood of any tree in Europe. Nowadays, it's mainly used for furniture, flooring and wood turning, but traditionally the wood was made into ox yokes which were used to join a team of ploughing oxen together.

However, this wood is resistant to crushing and ending, and is often used for wooden skittles, lead dressing hammers and windmills. Due to it's incredible resistance to repeated blows, Hornbeam is also suited to drumsticks, butchers blocks and impact-resistant flooring.

Crikey , it looks like Balsa Wood too . !
TAWA .
What is the use of Tawa timber?
MAIN USES: Typically used in flooring, panelling, furniture and cabinetmaking, interior joinery, turnery and dowel manufacture. WORKING PROPERTIES: Tawa machines and finishes extremely well and has excellent turning properties.

Structural.
Flooring.
Furniture.
Glue Laminated Timber (Glulam)
Decking.
Panelling.
Cladding.
Sleepers.

Looking at all these , Id hink selection regarding cut & grian direction & straghtness through ' the blank ' Would be the prime considrations .
Id done a few props from radiata pine . Used on a HP 40 . The chief advantage was low weight . Wouldnt want to clip the deck with one ,
but seemed ridgid within THOSE working loads . Wasnt a knife thin thing , and was actually designed to layer air rather than cut through it.

Thing thought was if it was stiff enough to stay straight , it wouldnt get all askew and overload itself / fly apart . So NOT on a Rossi 40 for pylon ! .

[Dave Hull]

AirMin,

I've seen ramin called out for high stress areas on old F2C plans. Leading edges and the like. No marine borers there. If I had of had some I would have tried it!

[Curare]

We used to see ramin here in australia reasonably regularly, most of our dowels and other mouldings were sometimes made from ramin. These days it's all clear pine and Tasmanian oak.

You guys have given me some food for thought in terms of alternative woods, and I may have to get *somewhat* creative as there are a number of timbers that are mentioned here that might be ubiqutous and cheap in the US, but are like rockinghorse sh*t here in Australia (And even moreso Western Australia).

I could reel off a number of timbers that are available but they all have interesting names, and are probably unknown outside australia.

I did however think that we might look at desirable properties from existing woods and then find something local as an alternative.

The wood database filter can be used to select woods by their mechanical properties https://www.wood-database.com/wood-filter/

The only question I have is what would be a decent starting point?

Beech?
Maple?
Hornbeam?
Cardboard?

[Dave Hull]

I'd try using some Aussy woolybutt. I don't know if it would make a good prop or not, but you could always tell people you wanted to try some woolybutt, and see what that.... Well, maybe not.

The eucalyptus here is hard and a bit splintery, from what I've seen. But it would likely work. No idea if your woolybutt is similar.

I'd stay away from ring-porous woods. Just my opinion.

One advantage of jarrah is that if the prop bites you, you won't see the blood on the prop. Seems like it has multiple properties that would be suitable?

Don't forget about yellow birch. It is a great choice too.

If you are going to CNC mill, the harder the better!

[Steve Helmick]

My recollection is that early-type TF paddle blades and "Power Props" were Gum. The fact that Gum is easily stained to look exactly like Black Walnut made the price shoot up to unreachable levels for mere propellers for model aeroplanes.

I used almost 100% TF Speed Props when I flew speed. They were maple, and I had zero problems with them throwing blades or splintering, and they were very narrow and thin. I've not used many Rev-Up propellers and don't have any solid guesses about what wood they used.

When first reading this thread, I wondered about laminating bamboo. The bamboo chopsticks in my stash seem to be pretty tough stuff, not for engine mounts, but for sure some structural purposes and perhaps propellers.  Steve 

[M Spencer]

Speaking of which ,
these things were the Bees Knees , for F A I & ' A ' Team race , and ' B' .

The Tornado Nylon props seem to be eye dentical . Bartels glass copy I have is way scrawiner , tho labled as 7 x 8 tornado .

Pit Men belting the snot out of disels , to start / restart  . So wernt totally hopeless . Superceeded by F Glass for durability . catching .

[Steve Helmick]

Regarding Tornado/Grish Bros. "Presswood" props...I was once told they were balsa impregnated with an early type of resin. The color of them made me suspect the resin was Phenolic. It would be nice to know. I think it makes sense. What other sort of wood could be smashed into shape like that?

Early in my speed flying years, I tried flying my FAI-sized "A" speed model on 80-20 fuel, and the propeller I used was a clipped & sanded Tornado Presswood. I don't remember whether it was 7" or 8" pitch, but it was clipped down to 6-5/8" or something like that. It was timed at 132 mph on the standard AMA A speed line size (Monoline) of the time, which was a pretty decent speed for a box stock G.15 with no pipe. I think the US team guys were in the 143 mph range that year, and I think they were still monoline, but smaller wire size. Shorter meetric length lines also? IDK    Steve