Propeller manufacture in OZ

[spacesailor]

Soleair,

 

I bought "Tassie oak" but was stunned to find it's really Pine, as the name "Tassie oak" is a registered trade name.

 

Now were to get real "OAK" from, only need one lamination in the center.

 

I've thought about using "Bamboo" lamination's, like the old fishing rods, it could be really springy.

 

spacesailor

 

 

[Bruce Tuncks]

I'm surprised too space... Is the Tassie oak you see at Bunnings really a pine too? It's a lot heavier and stronger than the pinus, maybe its something different again?

 

 

[Soleair]

'Tasmanian Oak' is actually a species of Eucalyptus: Eucalyptus regnans, Eucalyptus obliqua or Eucalyptus delegatensis, when it comes from Tassy.

 

In Victoria it is called 'Victorian Ash', and that is why I ordered it from a wood yard in Sydney. When I made propellors in UK, I often used alternate laminates of mahogany and ash, & I hoped my choice of maple & Victorian ash would give a similar prop.

 

This didn't really work out as I'd hoped. There isn't the contrast between the maple & Tassy oak as between mahogany & ash. And the Tassy oak is considerably heavier than the European ash I have used before. As I said, for my next prop I think I'll just use 3 laminates of maple: it is easy to from; it's fairly light, & has historically been used for aircraft propellors. My current prop is disappointingly heavy, with a correspondingly high moment of inertia - not good for gearboxes & bearings. I'll make another after flight trials.

 

Spacesailor, your idea of using bamboo for at least one laminate is interesting. If you could find a piece long enough with straight grain, it might well work. I don't know where you'd start looking though. But bamboo is used as structural material in Indonesia - I've seen it used as scaffolding there. And bamboo bikes are quite common - in the US some are very expensive - $4000 or more!

 

 

 

[IBob]

"As I said, for my next prop I think I'll just use 3 laminates of maple: it is easy to from; it's fairly light, & has historically been used for aircraft propellors."

 

Briefly, I have never made a prop, but I have done a fair bit of cabinet work and my father was a chairmaker/cabinetmaker.

 

Different woods have hugely varying properties suiting them for different things: traditionally in Europe, yew for bows, ash for arrows and spears, hammer and axe handles, beech for furniture (though elm for a slab seat), seasoned oak for ships and houses, and so on. Nowadays this old knowledge is supplemented by good technical information on timbers.

 

I would be using all that info to select suitable timbers, rather than some stab in the dark empirical approach:

 

Edison improved the lightbulb (he did not invent it) by having his people try a whole range of materials: that is the empirical method, and the quivalent here would be to make props of all possible woods and test them.

 

Surely the more logical approach, now that the so much information is now freely available, is to use that information first?

 

 

[Soleair]

Yes, not all wood varieties are suitable for props. But many are. When considering the wood for the prop described here, I first looked for density. Followed by 'strength' (defined in various ways depending on the reference source); hardness (too hard & it's too hard to carve); suitability for gluing (not too oily); grain runout & knottiness.

 

Ideally I wood (geddit?) have chosen Hoop Pine, but I couldn't find a timber yard who could supply it by the time I need it. Hoop pine is very close to North American spruce, which makes an excellent, lightweight, stiff propellor. Douglas Fir would be up there too. Consideration should be taken of the fatigue strength & static rupture values - a good reason to go for a 'thicker' prop to keep the stiffness high enough to resist flutter.

 

The two species I chose were reasonable on most counts, although I knew the Victorian Ash/Tassy Oak was heavier than I would have liked. I arranged the laminates so there was more Maple than Tassy Oak.

 

Propellors have been successfully made from some types of Mahogany; Birch; Spruce; Douglas Fir; Western White Pine, & Parana Pine that I know of in European species. I am not as well up on antipodean breeds, but I'm learning. . .

 

The other major consideration in gummy woods is resin pockets, which is a good reason to lay up a larger number of thinner laminates: there is a better chance a pocket will be revealed in machining the blanks.

 

If I gave the impression that I had just taken a stab in the dark, that is not the case. It's my neck!

 

 

[Bruce Tuncks]

I would really like to "make " my own prop, except that the carving bit which I would like to have done by a computer machine.

 

So I would like to make the laminated blank and then send this off to some service which computer-carved the airfoil shape. Then I would do the final sanding and finishing.

 

Is this a silly idea?

 

 

[IBob]

Sorry, didn't mean to imply you were taking a stab in the dark. Obviously you've done a lot of work on this.

 

In NZ the (western) history is very short, so much less traditional information is available on what woods are good for what, with evidence of quite inappropriate woods sometimes used for building.

 

Also woods of apparently similar names are not related in any way to their northern cousins. For instance, there are a number of indigenous beech trees here, none of which bear any resemblance to European beech.

 

 

[Bruce Tuncks]

Yes IBob, when I was a kid in Alice Springs we had these street trees called "cedars"

 

I have since found that they are also called "Indian Bead Tree", "Persian Lilac" and "Chinaberry Tree"

 

The last 3 names are much more accurate.

 

 

[spacesailor]

IBOB

 

I wood really like a good straight piece of "yew", as the centre laminate of the next prop.

 

If I can make a "sabre" shaped prop it will have to have a bending tendency,

 

so a very springy wood is needed, mahogany is ok for cheeks to aid shaping.

 

Also it needs some weight to act as a fly-wheel as my MoslerMotor hasn't got one,

 

Bruce

 

There's lots of fun chopping lumps of wood away, to get a great prop, put lots of saw-cuts in then Hack the lumps out & watch the shape start to appear.

 

If you stuff it up think of the postage from the US, and buy some more wood, its still cheaper.

 

spacesailor

 

 

[Soleair]

I would really like to "make " my own prop, except that the carving bit which I would like to have done by a computer machine.So I would like to make the laminated blank and then send this off to some service which computer-carved the airfoil shape. Then I would do the final sanding and finishing.

Is this a silly idea?

No. it's not a silly idea. I just don't know where you'd find a computer controlled machining facility. But really, once you've prepared the blank it isn't very difficult to finish it yourself. If you don't feel comfortable using spokeshaves & chisels, etc, you can do quite a lot of wood removal with a coarse rotary sanding disc, as others have suggested.

 

Why not go & buy some cheapo pine planks from Bunnings Aviation Dept, lay up 3 laminates, & have a go at a prop? You can put a clock in it afterwards & sell it on Fleabay & the whole exercise won't cost you a cent! You might find it's easier than you think.

 

 

[Bruce Tuncks]

Thanks guys, you are convincing me that having a go might be fun.

 

 

[spacesailor]

If you think you might use it, Use "epoxy construction" glue. it won't fall apart, in fact the wood fails before the glue-line.

 

spacesailor

 

 

[geoffreywh]

My Richard Sweetapple prop is made from "Victorian Ash" A species of gum tree, Nice to work and sands nicely, not prone to splitting. I would laminate at least 6 layers as the glue lines will help in carving....

 

 

[Bruce Tuncks]

How are the Jabiru props made? They look like quite soft pine type wood, stiffened up by quite a thick layer of what I think is polyester and glass cloth. The finish almost but not quite looks like a female mould. It is a better finish than I could get just applying the glass on top.

 

 

[geoffreywh]

Jab props are very light. They have to be a type of Pine mines weighs a considerable amount more

 

 

[Bruce Tuncks]

I was buying a circular saw on ebay and saw an ad for this...

 

www.diysmartsaw.com

 

well its in my price range... do you guys think it could be of use making a prop?

 

 

[spacesailor]

And the price?. $39. aus or us............. Got it $55.70 aus

 

spacesailor

 

 

[Yenn]

A lot of props are copies, rather than new designs carved out of timber.

 

That makes it much easier. You build a carving machine using an angle grinder with a wood working wheel. rather like a chain saw toothed wheel.

 

It is hooked up to a copying machine which resembles the key cutting machines you see in hardware stores. A circular plate same size as the cut off tool wheel follows the shape of an existing prop. Make one side then turn it around and do the other.

 

A friend of mine built several props and at least one of them was of manufactured plywood, specially made with most of the plies running in one direction. I think it was Tassie Oak.

 

 

[Bruce Tuncks]

I reckon the Jabiru props are made with such a machine as you describe Yenn, except that the wood becomes the core in a female mold.

 

So you lay up one or 2 layers of glass in the lower mold, then put in the wood core, then lay up again in the other mold and then join the lot together.

 

This is my guess, not having seen Jabiru props get made.

 

 

[spacesailor]

Has any-one got a design for the 100mm angle-grinder, copying machine that YENN is talking about, ( I saw one many years ago) that could be used by a lowly amateur.

 

Made a few props but having trouble getting both ends identical, After the prop is finished, balancing puts a different shape on one blade to make it lighter.

 

The blank looks great but 600grams heavy at one end, is too much to use weights in the hub area.

 

spacesailor

 

 

[acrofan]

Has any-one got a design for the 100mm angle-grinder, copying machine that YENN is talking about, ( I saw one many years ago) that could be used by a lowly amateur.Made a few props but having trouble getting both ends identical, After the prop is finished, balancing puts a different shape on one blade to make it lighter.

The blank looks great but 600grams heavy at one end, is too much to use weights in the hub area.

 

spacesailor

No. it's not a silly idea. I just don't know where you'd find a computer controlled machining facility. But really, once you've prepared the blank it isn't very difficult to finish it yourself. If you don't feel comfortable using spokeshaves & chisels, etc, you can do quite a lot of wood removal with a coarse rotary sanding disc, as others have suggested.Why not go & buy some cheapo pine planks from Bunnings Aviation Dept, lay up 3 laminates, & have a go at a prop? You can put a clock in it afterwards & sell it on Fleabay & the whole exercise won't cost you a cent! You might find it's easier than you think.

Wood in Australia by kr Bootle gives good info on various timbers,

 

 

[Yenn]

I don't have the design, but it wouldn't be too hard to make one. Will have to sit down and draw one up, but not today.

 

 

[Oscar]

I reckon the Jabiru props are made with such a machine as you describe Yenn, except that the wood becomes the core in a female mold.So you lay up one or 2 layers of glass in the lower mold, then put in the wood core, then lay up again in the other mold and then join the lot together.

This is my guess, not having seen Jabiru props get made.

Jab. wood props are made from plantation Hoop Pine. They used to be - but I am not sure of this for recent times - hand-shaped using a jig, then hand-laminated epoxy resin and light e-glass.

 

 

[Bruce Tuncks]

Thanks Oscar, I don't think that I have the skill to achieve a finish like that with a hand lay-up. I would love to see them being made.

 

My impression is that most of the strength comes from the glass and not the hoop-pine.

 

 

[geoffreywh]

To get even weight you have to get a large piece of timber and have it sawn into planks then laminate the planks reversing every other one. That evens out the density discrepances