Make your own wooden prop

[spacesailor]

A work college, died before 50 , mainly because of ' chain smoking '.

And not wearing a dust mask. ( couldn't smoke with it on  ).

BUT

At the same time l have witnessed More deaths by suicide than accident.

Bad years for the " silent generation ".

spacesailor

[meglin]

I'm sorry that I reminded you about this side of an absolutely beautiful production. I adore it myself - it is closest to art. But fewer and fewer people want to do this. The modest money that can be earned on this is given by hard work. I am very glad that we gave someone joy.

[Marty_d]

That's beautiful Vladimir.  

[meglin]

Mon opinion est la suivante: il est très utile d'essayer de concevoir et de fabriquer une hélice, alors vous saurez exactement ce que vous payez en commandant une nouvelle hélice.

[meglin]

Sorry, I didn't find how to delete unnecessary messages.

Edited July 9, 2022 by meglin

[meglin]

My opinion is this: it is very useful to try to design and manufacture a propeller, then you will know exactly what you are paying money for when ordering a new propeller.

[meglin]

My opinion is this: it is very useful to try to design and manufacture a propeller, then you will know exactly what you are paying money for when ordering a new propeller.

[meglin]

This is a decorative propeller for symbolic money:

[facthunter]

 That's a lot like a Sopwith Camel prop that used to be hung above Aero Club Bars. Big and slow revving.  Nev

[Ian]

I noticed a few people recommending epoxy as a lamination glue, there are better glues, epoxy has a poor record compared to other glues in relation to resisting de-lamination and glue-line failure. About all it has going for it is that its easy to use. Epoxy is good with fibreglass and carbon fibre but not wood. I'd be wary of a plane build with epoxy.

The gold standard for wood glue is resorcinol, it is the glue recommended in most plane building standards and is also in the Australian Standards for commercial exterior glumlam glues. Basically moisture penetration weakens the epoxy-wood bond permanently even after drying. Is your prop likely to ever get a stone chip and then get rained on or fly through a shower? Resorcinol is the glue used in marine ply and was also used in WW2 to fix the Mosquito delamination issues in tropical environments. One thing to note is that resorcinol doesn't have gap filling properties and requires a relatively high clamping pressure which shouldn't be a problem when making propeller glulam blanks. Some isocynanate and PU glue also have good results however results vary across manufacturers and formulations.

A lot of research has been done in this area I've attached one paper and the text from it is below. The research was looking at gluing acetylated wood, however the control was un-treated wood and the text relating to epoxy is pretty damming. An example of a primer is a resorcinol primer applied to the wood surface which chemically bonds with the wood surface and achieves a strong bond with the epoxy.

Quote

 

Epoxy bonds to wood are generally strong when tested in a dry condition, but they weaken drastically when subjected to water saturation and drying. If primers are used to increase adhesion, epoxy bonds can withstand
exterior environments. Poor exterior performance is probably caused by inadequate wetting and limited penetration of high molecular-weight adhesives into the wood. Epoxy-polyamide ( EP ) adhesive was diluted with 10% butyl glycidyl ether in an effort to increase its penetration, which helped somewhat. After examining failed bonds under the microscope, it was evident that the adhesive penetration was poor. Not only was there poor adhesion to the wood, as evidenced by failures in adhesion to the wood, but some cohesive failures were evident. Although the adhesive did bond well to the untreated controls, it was still negatively affected by the level of acetylation. as indicated by lowered dry shear strengths and wood failures (Table 1). Wet shear strengths were very low and wood failure was non-existent (Table 2). The lowered polarity of the acetylated wood probably contributed to the poorer wetting and penetration, hence the bond strengths, as the level of acetylation increased.

 

 

 

Australian woods are significantly stronger than their northern hemisphere counterparts, for example ironbark has a tensile strength about 2x that of english oak (famous for it's strength) however they are difficult to glue, however this strength provides the ability to create a thin strong prop which is appealing. Again resorcinol glue appears to be about the best adhesive in this regard according to research done by the Queensland Government which is about the only Government agency actively doing research in this area which is a pity as from an engineering perspective these timber have great structural potential.

 

Also if you're going to the trouble of building a propeller you can use the wonders of computer software to get an optimal design for a particular speed and generate a cad file and have a machine carve your blank. I think that I generated this using https://web.mit.edu/drela/Public/web/qprop/  but it was a while ago. Unless you have thousands of HP big paddle shaped things are far from optimal, thinner designs with an airfoil that goes towards a point will provide a significantly better outcome. Below is an airfoil generated to provide optimal thrust at about 160 knots with about 180 hp. 

 

glue-comparison-strength.pdf

[Bruce Tuncks]

Thanks Ian...   You have got me wondering , all my life I reckoned that resourcinol was inferior to epoxy because of its lack of gap-filling properties, but as you say, in glued laminations, this should not be a problem.

I'd like your comments about the Australian ww2 Mosquito bombers. My understanding was that they were not built well enough to cope with non-gap-filling glues.

Epoxy was only invented after ww2 I also think.

[facthunter]

I think the Mosquitos used Casein which is not gap filling to any great extent. A lecturer I had for woodwork way back at Newcastle Tech College built  wooden components for the Mosquito. His name was Claude Lamb from memory.. I never heard of any issues with build quality. You hear these things from time to time but anther instance proven wrong with time was the alleged superiority of the Gipsy 1c.Dehavilland original crankcases to the GMH produced ones made here. In later years the Local ones were considered superior with the passage of time and experience and the best choice for engines being rebuilt later on.  Nev.

[Bruce Tuncks]

Thanks Nev. I had read that a pommy inspector came out and condemned all the australian mossies. Except for the first one, which broke up and killed its test crew.

I thought then that the glue joints were the problem...  I didn't know for sure it was casein, so thanks for that.

[Bruce Tuncks]

Unlike the UK, Australia did not have thousands of woodworking craftsmen...  that was also part of the story.

[facthunter]

Most of the organisations here were furniture makers but furniture was a lot better designed and made THEN than NOW. We had plenty of PLY timber and boat builders though. New Zealand has built Mosquitoes from the ground up.  Glue failures grounded most wooden planes here in the 50's and THEY weren't built here except the Wacket trainer.  Glued Wooden spar. RNAC had two I never got to fly. Lucky? I think the wing came off one.   Nev

[Markdun]

I definitely don’t agree with the view that resorcinol is a better glue than epoxy; but a lot depends on the epoxy- there are hundreds of different sorts of epoxy, of widely difference strength and hardness as there is widely different additives/fillers.  So it all depends.  Timber boats are almost universally glued together with epoxy, including laminated veneers, double diagonal plywood, strip-plank, laminated beams. Similarly nearly all timber aircraft built now are out together with epoxy glues, including laminated wing spars, wing ribs etc etc.  In most cases the glue join failure when subject to sheer or tension is of the wood fibres either side of the epoxy, not the epoxy itself.  An epoxy glue used for a wood propeller should have a similar hardness as the timber used and use an appropriate filler, like cotton fibres.  I’d suggest a System Three or T88, ir even Bote Coat ‘Poxy Glue’ with a 1:1 mix ratio (harder to get wrong). These glues can be used in high humidity, unlike some others, eg WEST’s. The one draw back off epoxy is that it not UV resistant.

 

 It’s incorrect that resorcinol is used in the manufacture of plywood, marine or otherwise. Almost exclusively used are thermosetting glues such as phenol formaldehyde. The veneers and glue are layered in a press and then subject to microwaves to set the glue.  It’s not worth ply manufacturers to stuff around changing glues.... they are nearly all the same. The difference between marine ply and others are that in marine ply the veneers are the same thickness and the sheet will bend the same when stressed lengthways or sideways. ‘Structural grades’ may have lower quality veneers and/or achieve the same bending length vs widthways by having inner veneers thicker.

 

 Any comment about Australian timber being stronger is just coddswallop. We have over 500 species of eucalypts and other hardwoods and around 100 or so species of softwoods/conifers.  The variability between species and even within species is enormous. Like epoxy, when it comes to timber its horses for courses.  If one wants to generalise one could say that the softwoods/conifers (gymnosperms) have stronger wood because in general the wood cells are longer and have overlapping tapered ends (toilet paper), compared to the hardwoods (angiosperms) where the wood cells/fibres are more like cylinders (the Australian newspaper).  But it ‘all depends’.  I try to use E.delegatensis (Alpine ash) for props, but this comes with densities from 300kg/m3 to 900 kg/m3.  Or one of our gymnosperms, like Aurucaria cunninghamii (hoop pine) which is a bit soft for a prop (not so with 3 coats of epoxy), but also highly variable in grain characteristics .... some samples I’ve seen you would not build a box with it.  Some ‘Ironbark’ species might be exceptionally strong, but they are also exceptionally heavy, frequently with densities greater than 1000kg/m3, ie they sink in water. Sitka is not strong, but it is light and stiff, which makes it suitable for aircraft building.  If you milled up a piece of ironbark to be of equivalent strength as spruce it would be lots smaller, probably a bit heavier, but it would be really bendy.... totally unsuitable.

 

 My experience has been in successfully building the Jim Maupin designed Carbon Dragon which was almost exclusively Sitka Spruce, with carbon fibre tows laminated into grooves milled in the Spruce

(including the 6mm square wing rib stock which had a 2.5mm channel routed which was subsequently filled with carbon fibre and epoxy). I have also built the timber Minimax made from Hoop pine, Pinus radiata, Douglas fir and various types of plywood. I also have Cygnet I built in the 1990s with epoxy laminated Douglas fir wing spars and hoop pine geodesic lattice top and bottom of the wings. Now over 20 years and 1000 hours without an epoxy glue join failure. I have also refurbished a Corby Starlet with resorcinol glue joints. Several wing ribs and some plywood resorcinol joints had to be repaired (with epoxy).  I also have built several boats; the latest an 11m ocean sailing catamaran: all critical glue joints are epoxy except the strip planks which are powalina, of similar density and strength as balsa. This is glued with the moisture cured polyurethane expanding foam glue.  Some of my deck beams are from our rot resistant cypress pine glued with epoxy, but as this wood is extremely oily you must wash it with acetone before gluing.

 

Mark. BSc(Forestry)

[facthunter]

Every piece of wood used for structural parts of an aeroplane must be carefully inspected for "shakes" Knots and grain direction and where it's cut from in the log section. The darker part is the truewood and the lighter coloured is the sapwood and the properties differ a lot with some timbers. From the designers point of view it's difficult to determine the physical properties of a particular timber because there are so many variables. I think you would have to  do some destructive sample testing and apply a large safety  factor. You are also supposed to test the glued join the same way and keep  the samples. As stated the Joint shouldn't fail in the glue line. I used to use wood Araldite in speed models, in the 50's

[Ian]

6 hours ago, Bruce Tuncks said:

Thanks Ian...   You have got me wondering , all my life I reckoned that resourcinol was inferior to epoxy because of its lack of gap-filling properties, but as you say, in glued laminations, this should not be a problem.

I'd like your comments about the Australian ww2 Mosquito bombers. My understanding was that they were not built well enough to cope with non-gap-filling glues.

Epoxy was only invented after ww2 I also think.

Resorcinol penetrates and chemically bonds with the wood, this is one of the things which makes it's bond so durable. Very early Mosquito's were built with casein and later versions with urea formaldehyde. https://en.wikipedia.org/wiki/De_Havilland_Mosquito#Fuselage . Problems were found (often due to loss of aircraft) when these aircraft were deployed in tropical environments.

 

Urea Formaldehyde while strong is not as weatherproof as resorcinol. My understanding is that later Mosquitos and some of the Australian Mosquitos were built with resorcinol which mitigated many of these issues. Not saying that the build quality was high on the Australian planes but the glue was better.

 

 

[Old Koreelah]

I was glad to discover that the most important parts of my Jodel were glued together with resorcinol by builders with far more skill and precision than I can muster- which is the only way to use it.
The extra, less critical bits I’ve attached with epoxy, well-braced and bolted.

[Ian]

Sorry for the long post but while you may have studied forestry you didn't study engineering. 😉

The key here is repeatable research rather than belief and proclamations from on high. Epoxy glues are fantastic however they shouldn't be used blindly and their limitations should be well understood, especially when using them in things which can cause you harm.

I'm not saying that resorcinol is an easy glue to use, it's harder than epoxy to use however used correctly creates a better bond.

 

1 hour ago, Markdun said:

I definitely don’t agree with the view that resorcinol is a better glue than epoxy; but a lot depends on the epoxy- there are hundreds of different sorts of epoxy,

I know that there are a lot of opinions in this area however the rigorous studies all point to poor bonding qualities with timber when exposed to moisture. While there are lots of different epoxy formulations chemically they're very similar and the bonding results are the same. Happy for you to demonstrate the error of my ways however I haven't come across any testing programs where epoxy bonds in wood exposed to testing have survived standard de-lamination testing methodologies except where a primer such as resorcinol is used on the wood surface.

Epoxy is gap filling, easy to use and readily available. You just need to be very careful when using it as a bonding agent for timber, especially in harsh environmental conditions. 

 

Attached is the appendix of Classic Boat which provides a professional boat builders opinion, also attached another study which tested both wet and dry wood failure on four different glue types including epoxy. In the conclusion epoxy actually bond more effectively to acetylated wood, but not unmodified wood.

Quote

On the other hand, only the RF gave good wet bonds bonds to the acetylated wood. Modification to make the wood less polar improved the wet performance of the epoxy adhesive.

The paper Hydroxymethylated_resorcinol_coupling_agent_for_en.pdfHydroxymethylated_resorcinol_coupling_agent_for_en.pdfHydroxymethylated_resorcinol_coupling_agent_for_en.pdfHydroxymethylated_resorcinol_coupling_agent_for_en.pdf

Starts with the following quote which is relevant for anyone considering using epoxy for externally exposed structural purposes.

Quote

Epoxy adhesives can develop bonds to wood that are as strong as the wood itself, but only if the bonds remain dry. Once exposed to repeated water soaking and severe stresses from drying, epoxy bonds delaminate and fail to meet requirements for structural wood adhesives intended for exterior exposure.

 

3 hours ago, Markdun said:

It’s incorrect that resorcinol is used in the manufacture of plywood, marine or otherwise.

Resorcinol Formaldehyde can be set at room temperature or can be heat set. Phenol Formaldehyde PF is a very similar adhesive to RF and is often mixed with RF to create RPF adhesives which can also set at room temperature. Australian Standards specifies Type A adhesives for marine ply, both RF and PF are classed as Type A. RF is more reactive than PF and in some cases will bond with timbers more successfully than PF. The main reason to use PF rather than RF is price. RF is more expensive hence its limited use in this role. Actually RF is classed as a phenolic compound, it just has more reactive groups enabling lower temperature reactions.

3 hours ago, Markdun said:

It’s not worth ply manufacturers to stuff around changing glues.... they are nearly all the same. The difference between marine ply and others are that in marine ply the veneers are the same thickness and the sheet will bend the same when stressed lengthways or sideways. ‘Structural grades’ may have lower quality veneers and/or achieve the same bending length vs widthways by having inner veneers thicker.

The main reason for changing glues is price and ease of use. This page give a good overview

https://www.matildaveneer.com.au/stuck-on-you-plywood-glue-bonds/

 

Type A (A-Bond)
This is the strongest bond and is also waterproof. It’s produced from a phenol formaldehyde resin that is set under heat and pressure. The result is a permanent bond that can be exposed to heat, cold or wet conditions for a long time without deteriorating. This glue bond is used for structural, exterior and marine plywoods.

Type B (B-Bond)
Less durable than Type A, a Type B glue bond is waterproof but will deteriorate after several years being exposed continuously to weather. It is usually produced from a Melamine-urea-formaldehyde (MUF) resin. Plywood with a B-Bond is best used in situations of limited weather exposure, e.g. exterior doorskins and concrete formwork.

Type C (C-Bond)
This glue bond can only withstand occasional exposure to dampness and as such is most suitable for general internal uses. It should not be used for structural applications or wet/damp areas. This glue bond is usually produced from urea formaldehyde (UF) resin.

Type D (D-Bond)
Similar to Type C, Type D is also made from urea formaldehyde (UF) resin. D-Bond Plywood is best suited to internal uses where it is completely protected from wetness or dampness. It should never be used for structural applications.

 

 

3 hours ago, Markdun said:

Any comment about Australian timber being stronger is just coddswallop. We have over 500 species of eucalypts and other hardwoods and around 100 or so species of softwoods/conifers.  The variability between species and even within species is enormous. Like epoxy, when it comes to timber its horses for courses.  If one wants to generalise one could say that the softwoods/conifers (gymnosperms) have stronger wood because in general the wood cells are longer and have overlapping tapered ends (toilet paper), compared to the hardwoods (angiosperms) where the wood cells/fibres are more like cylinders (the Australian newspaper).  But it ‘all depends’.

Australian structural hardwood timbers are significantly stronger on average than softwoods and hardwood species used in the northern hemisphere, using standards methods of testing strength which is measure in force per unit area. I'll list a few of the accepted timber strengths.

Grey Ironbark Modulus of Rupture 185MPa

Spotted Gum Modulus of Rupture 142MPa

Rose Gum Modulus of Rupture 119MPa

Hoop Pine MoR 90MPa

Norway Spruce MoR 63.0MPa

Sitka Spruce MoR 70.0MPa

Radiata Pine MoR 81.MPa

 

I could go on but you get the drift. Happy for you to add your own figure with published Module of Rupture figures.

 

You can also get an idea of the timber strengths from the following link which shows European glulam beam strength vs Australia standard strengths https://ash.com.au/blog/gl-au-nz-vs-europe/ . The main reason for the difference is the fundamental difference in strength of the base material, Australian hardwoods being stronger lead to significantly higher engineered wood ratings.

In fact there is growing interest internationally in using Eucalypts originally grown for pulp, for engineered wood due to its high strength. The main species grown in this manner is Eucalyptus Globulus which is also known as southern blue gum.  An articles on this are below.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7078706/

 

I suspect that you've become confused by the concept of strength to weight ratio which is a related concept, which is relevant to airplanes but is a derived measurement based upon strength in MPa. Aluminium is not as strong as steel as it has and ultimate tensile strength of 90MPa in the unalloyed form and up to 690 MPa with special heat treated alloys whereas special steels have a UTS of up to 2690. However on a strength for weight basis they're pretty equivalent.

 

But the point which is missed is that you can make a propeller from ironbark which is thinner and more efficient than one made from spruce while still retaining the strength properties in tension which is where most failures occur. Due to the increased Modulus of elasticity the propeller can also maintain greater stiffness with a thinner section. In fact based on the figures above you can have a stiffer propeller with half the thickness.

ClassicBoatAppendix.pdf glue-comparison-strength2021.pdf

[Ian]

This file didn't appear to attach however it shows a mechanism to reduce the degree of delamination which epoxy often suffers. Hydroxymethylated_resorcinol_coupling_agent_for_en.pdfHydroxymethylated_resorcinol_coupling_agent_for_en.pdf

 

[Markdun]

So Ian you know just how much engineering is involved in a forestry degree do you?  Obviously not.

 

And I might add ignoring the human element (the skill required to affect a good resorcinol joint) and assuming little variability in timber physical characteristics  of published mean values is not uncommon.

 

 To be clear, balsa wood is not very strong (layman’s term) but is an exceptionally good timber for lightweight structures. It too has high variability in stiffness, strength and density. Ditto for spruce.

 

 Even in bolts, a high MPa bolt maybe not ‘better’ than a lower yield bolt that is more malleable and resilient to repeated bending/loads. It all depends on what you need.
 

And yes there are various Type A to C or D bonds in plywood, but in my experience even in Bunnings, they are all type A.  Even some crappy interior lining ply I bought had type A bond.

 

 I’ve absolutely no idea of what species of timber you refer to as ‘ironbark’.  Most likely it covers several species, quite divergent botanically and in physical properties, so who knows what?  As I’ve said before, I and others, have crafted workable props from E.delegatensis (Alpine Ash) that is light (meaning less density if you select your planks carefully), and reasonably dimensionally stable with changes in moisture content (radially and tangentially) & hard & strong enough. A closely related species E.viminalis can have similar physical properties, but the timber of some trees of this species when milled are completely useless for any structural purpose. B. marginata, an Australian hardwood, is also totally useless for any structural purposes. I would not use any of the eucalyptus species in a wing spar, but I would and have used Douglas fir (close grained radially sawn), hoop pine, and I have even used clear close grained radially sawn radiata pine in tail spars. Although I have used eucalyptus as spar caps (tension and compression parts) in large roofing beams. I’ve never used, nor have I heard of anyone else using, ‘ironbark’ for props. My inclination is that that timber probably would be better suited for building stumps, wharf piles, or the edges of snow skis.
 

So we disagree. i don’t really care. Resorcinol glue has its place in history, just as casein glue derived from bovine milk proteins was a technological advance providing a waterproof glue that enabled the Vikings to expand their empire via boats. It may still have its place, but is limited.  As for timber, I’d suggest readers look to what is available and make informed decisions on it. As another contributor noted the presence of knots, the orientation of the grain, growth ring spacing etc and the individual density of each plank are likely to be as important or more so than the species.

 

As an aside, I did wonder about worrying about delamination with high moisture content wood. Are we talking about timber props made from unseasoned timber or timber not fully encapsulated in a waterproof polymer like epoxy and polyurethane, & this subject to dimensional changes with moisture content changes?

 

 

[Bruce Tuncks]

Is casein susceptible to going rotten? I think I have heard of casein "remembering" it was made from milk and reverting with heat and humidity....

But it may be animal glue I am thinking of..  that stuff stank like hell even when it was done properly.

 

 

[facthunter]

 Stressed steel has a memory till it's annealed. I think Casein was subject to some mould or other. So is Pinus Radiata and that's a wood that rots easily and is pretty Carroty, that I would not recommend.. (even though I have 1,000's of tons of it) Animal glue is applied HOT out of a fairly large pot with a brush and was a popular glue for indoor applications that don't get wet like good furniture. You get used to it's smell.. Nev

[Yenn]

There are at least 5 types of ironbark used in Qld, all very similar, heavy and hard.

Resorcinol was used for years for boat building, especially for double diagonal planked hulls. I built one and was amazed at how tough the hull was. I used epoxy for building my Corby and it has had no problems over 22 years of flying.

The use of carbon with a wooden frame in an aircraft would have to be very thoroughly designed. The timber part would not get any loads until the carbon yielded, then it would take all the load.