Make your own wooden prop

[Bruce Tuncks]

I have used what Jabiru have provided but I can't see why it is so hard to do one for yourself. Here's what I would like to see...

A plan showing the laminations bandsawed and glued. Then you would send this off to a computer routing place, with the coordinate file.

On getting it back , there would be sanding and finishing and balancing. What am i missing here? why no kit props?

[spacesailor]

No kit props !.

Because  it,s SO easy to make it yourself, from buying a few planks of wood from Bunnings, glueing them together.

Length of prop ( from freinds plane ), PI times radius gives circumference, which is length of ' lofted ' layout, pitch is hight of one end of lofted length.

This gives angles from which you make pitch formers to chop the prop blank to shape.

EASY

And cheap !,

spacesailor

 

[APenNameAndThatA]

I know of someone who copied a prop. They had a cutting wheel and a guide wheel of the same diameter attached to something like a jig and used an existing prop to make a new prop. Kind of like a giant, 3D pantograph. At least that's what they said they did. 

[spacesailor]

Great if you can get a spare prop, And that machine !.

If you need a courser pitch that machine won,t work for you.  ( Just lift that lofted pitch up another notch, )

46 X 36 prop was quoted as $500 plus, $ 80 to make myself.

Why put that price so high for a simple wooden prop.

What price a Jabiru, must be very high !, near a $ thousand ld,e guess

[kasper]

Yes wooden props can be made and yea they are really not expensive materials wise even when you take account of the reject wood. I’ve made a few and built a manual  follower copier for a grinder to blank them myself based on the semi automated follower copier I saw in the USA at a prop factory - I flew a few hand made props made from scratch by Fred Byron on the flea and his were pieces of art that I could never replicate with a spoke shave so I built a jig to replicate existing blades.  
 

why so expensive to buy?   Price in your time.  Price in the workshop overheads. Price in a profit.  Factor in the very low volume of production. 
 
$100 of materials quickly becomes $500+ as a finished prop.  

[spacesailor]

All that is OK,

If your happy with the finished product !.

BUT

If it doesn,t hold up to your expectations, then you have to pay return postage, wait to see If they accept your version of Their fault.

If the First time you hand-prop your motor, the 'trailing edge ' comes off, Is it your fault OR their prop, as ordered for a hand started motor !.

Home made, was told by many to see if it is Strong enough,

So l put a band of metal around My prop to check If it would stop the motor before!  Selfdestructing.

Answer NO it was not That strong.

BUT

It saves your engine from damage.

That prop was a test prop,and not finished to a good standard, all joints held well, no joint failure at all using epoxy construction glue.

Next prop finished to a much higher standard than original shop bought propeller,

Better rpm , less vibration, and Accidently smashed to bits,

Still No motor damage,  ( and it cost $85, frg covered, ) better than the third prop !.

Now l must finnish the next one with it,s ' semi-scimitar ' shape, hopefully t, Better.

spacesailor

[Yenn]

A friend of mine made his own prop using the grinder and a guide wheel of the same diameter. He used a special Plywood which was mainly longitudinal plys with only a small amount of cross ply. He used to carve one blade of a prop and then copy it to both sides of his blank. His props worked OK I know they were used in a couple of Boorabees.

[Bruce Tuncks]

Yep, it is not that hard to make a duplicator yourself. There are some good examples on utube. That would be a good place to start I reckon.

And while I agree that the prop makers are not really ripping me off, I am just a hopeless diy guy.

[kasper]

you do not have to be great at stuff.  Fred made beautiful wooden airframes - pieces of art.  My airframes are at best adequate - they have held together and get me around  ... but nothing I make is perfect just functional.

 

And perfect is not actually critical - workmanlike is often good enough - I lost an exhaust stud on a pusher trike while flying over the Thames many years ago and it punched a hole straight through the prop blade and split that blade into three along its length ... I was just in cruise and I did not even notice the prop strike and there was no vibration ... I noticed the slight note change on the engine and when I landed about half an hour later it was all still working. 

[spacesailor]

Kasper 

A HummelBird , & pilot was Shot at when flying over a lake.

He felt something and had a vibration, so returned to the landing field, to discover a smattering of shotgun pellets in one of his prop blades. ( making it unbalanced )

the Sherriff was called, who promptly called for Every one, the State Troopers surrounded the lake. were the Duck hunters quickly gave the culprit over.

America of course, But it could have been Canada,   

spacesailor

[Markdun]

I have mostly used props I’ve made myself, but also commercial ones like Sweetapple and Sensenich.  Currently I have 4 props for Jab 2200, 1 for a VW 1835 and another for a half VW conversion.
I have the Sensenich 60x46 Jab ‘climb prop’ on my Cygnet and it spins up to 3200 at WOT at 65kts IAS and climb rate of 1000fpm and around 3000rpm cruise of 92kts.  A great prop. for this airframe/engine combination. And very smooth. But I think the Sensenich ‘pitch’ is per the chord line and is more like a 42 or 43” pitch as measured on the flat rear prop face.
I made a 4 lamination alpine ash (E.delegetenis) prop (60x47)  for the Corby after another Sensenich 60x44 gave great climb but crap cruise speed....exceed max rpm. Another great prop, but just not right for the airframe. The alpine ash is much stiffer than whatever Sensenich make their props from and being without fibreglass the ash is lighter.  This prop gives me 1500fpm climb at 70 kts or so at an rpm around 3100 and 110 kts cruise at 3200....still hits max rpm before Vne straight and level at WOT.  So I’ve whittled a third prop; this time from 3 laminations of plantation hoop pine; 57x48.  It’s a tad thicker (weaker and not as stiff as the euc) and has a wider blade area (hence the reduced diameter). I haven’t tried it yet as the current prop on the Corby is just too much fun as it is.  

On my props I find 3 coats of high modulus epoxy resin then 3 coats of polyurethane varnish (UV barrier) and a reasonably soft prop tape (from Spruce) on the LE works well.

It’s not hard to manufacture yourself with a good square, straight edge and profile gauge, hand saws, chisel and various sanders  The hardest thing is cutting the holes for the Jabiru spigots accurately. Tthe old VW conversions were easy by comparison because they were centred on a central mandrel.  I’ve thought of prop copiers but it seemed like a lot of trouble.  I think even really crap shaped props will work (assuming strength, balance tracking is ok).....it’s just the last few percentage points of efficiency that may not be achieved.  
The comments about the cost of doing it yourself are delusional.  The timber is around $150, epoxy glue to laminate say $60 (though you will need to buy at least double that amount), sanding consumables ($30), epoxy saturation resin (another $100), plus syringes, gloves, brushes etc, high quality UV blocking pu varnish ($50), and then there’s your time drawing plans and computing angles and airfoils, sourcing materials, doing the actual work, making a prop balancer.  If you can get below $500 per prop excluding your labour...good luck. But then if you make one, you’ll probably end up with making at least 3 before you are content to leave it be.  So my guess is, factor on spending about $1500 for making it yourself.

There are some negatives of making them yourself though.  It is easy to make a poor performing prop by making the blade area too big and the blade too thick because you don’t want it to be too weak.  For low HP motors those toothpick props that look ridiculously small seem however, to be the most efficient (some say a single bladed prop is more efficient..so maybe try cutting off one blade, replacing it with a counterbalance?).  But how much is too thin?   The bigger problem is that if you even consider your current prop is not ‘perfect’, you’ll end up having to make yet another one instead of reducing drag by replacing your gap tape, canopy seals, making strut fairings etc.

And if you make a prop for someone else, remember that any and all performance issues will be absolutely due to the prop you made , not due to the engine being 30 years old, well past its TBO, the carb not jetted correctly, the fuel 4 month old, the aircraft exceeding its MTOW by 20%. etc etc.  it’ll probably also be the source of noise in the intercom too.

[spacesailor]

I just used the cheaper Tasmania Oak, & Meranti,  cheaper  " Construction epoxy glue. Cheaper hairdresser's gloves, with throwaway $1,50 brushes. Seems to work for the Half VW motor, 

My problem, All the distractors telling me " it won't work & you'll kill yourself. LoL

The wood yard told me Tassie oak is not OAK but

" Tasmanian oak is the name used for three almost identical species of eucalypt hardwoods that are normally marketed collectively. E. delegatensis (alpine ash) occurs at higher altitudes, while E. regnans (mountain ash) is found in wetter sites; E. obliqua (messmate) has a wide distribution, occurring in wet forests but also extending into drier areas. "

" Mountain Ash - E. Regans
Messmate Stringybark - E. Obliqua
Alpine Ash - E. Delegatensis "
They have similar Charteris tics and are grouped together much in the same way as the imported timber Meranti which comprises a huge number of species.

I even went to the extreme of making a half circle " prop smasher " to see for myself if my prop was strong enough, then accidently smashed the replacement prop !. and a " spoke shave, to save on sanding.

spacesailor

Edited April 19, 2021 by spacesailor
added more

[Markdun]

Spacey, you will find a huge variation in the wood of any of the three eucalyptus species you mention.  And I would doubt many people could tell the difference between the wood of one and the other without reference material and a good microscope.  I wouldn’t be keen on meranti....too soft despite being a hardwood.  I’m sure people could make a functional prop from knotty, tangentially sawn Pinus radiata....probably strong enough, but would it hold its shape, twist and withstand the odd collision with gravel and insects?
 I’m not sure of the point you are making regarding the broken prop?  Did you break it on purpose, and what was that purpose?
I would suggest you might want to consider your crankshaft.  I had a very minor incident with a half VW powered Minimax with an idle prop strike (landing in long grass)...only a nick and crack on one blade from tip inboard about 10cm.  5 flight hours later total crankshaft breakage at 4500asl with uneventful out landing.

[Bruce Tuncks]

The existing Jabiru prop is made from a type of pine ( not radiata) with quite a thick fibreglass covering. In fact. the fiberglass covering is so thick that it may have been done in a mould. Does anybody know just how these props are ( were) made?

I like the idea of the Tasmanian mountain ash, especially if it is lighter.

About being too thin... the loads are quite calculable and so the prop should be able to be tested by proofloading I reckon. Has anybody done this?

Apart from spacy, but I have to say that markdun seems more right about a deliberate prop-strike not being the best idea.

I have in mind clamping the prop hub in a vice and pulling forward on a prop tip with a spring balance.

 

[Bruce Tuncks]

In Spacy's defence , I noticed that  Russian trainers used wooden props because they protected the crankshaft in the event of a prop strike.

But maybe those Russians just had a relaxed attitude about trainees dying.

[facthunter]

I think Meranti is also known as Pacific maple and is quite soft. I wouldn't consider Radiata. You put the work into a prop and don't waste it with something that varies so much between sapwood and truwood and splits and twists when seasoning as well as getting a fungus/mould problem. If someone's getting rid of Pinoak it's a real oak and quite good for uniformity.. Season any wood carefully and protect the ends from drying out too quickly.  I had a clinker built Boat made of mountain ash that was quite good timber. Might split a bit easier than Pin Oak. Sorry I don't know the botanical name but it's becoming a common roadside tree. in many parts of Australia that's elevated or southern. Nev

[spacesailor]

In my defence !.

Lots of people said a home chopped prop would be No good and, dangerous.

So l made a circular band that fitted the prop, then l pulled the band onto the prop slowly, thus reducing the revs.

Thats when the prop  broke !, very pleased it broke uniformly, then l killed the ignition, with my salary switch.

The replacement prop Was a different kettle of fish ! In that a 'deck-chair stand l put away was facing the wrong way.

and it fell into the prop, as per picture.

Checked hub runout & seems l got away with only a busted prop & Pride.

Harder wood in the center with easily worked Maple on outer for all that shaping. Light covering of glass

Finnishes the job.

spacesailor

Edited April 20, 2021 by spacesailor
Added more

[Markdun]

‘Quercus’ is the genus for the old world oaks down in the northern hemisphere.  I’m not sure of the species for ‘pin oak’.  The Quercus’ is often used in furniture and was used in boat structure.  It has quite obvious ray parenchyma cells which grow out radially...this gives the wood grain an interesting look as well as making it more difficult to split, if I remember correctly from the several subjects Idid at uni last century.  It’s also is hard and holds an edge well and resists denting, like our eucalyptus oaks...hence good for furniture. Unfortunately, unlike Huon pine, western red cedar and meranti, it is not dimensionally stable with changes in water content. It will warp with changes in moisture content....so not so good for doors, windows or external.

Generally, I think a solid wooden prop would be difficult to make insufficiently strong if you have a reasonable airfoil ie. breaking from flight loads (thrust) or centrifugal forces.  The issue are: (a) stiffness.  Bending out of shape with rpm and thrust forces).  Some shapes are designed so some bending changes the pitch...eg ‘scimitar’ shaped props;  (b) robustness, that is, able to take the rough and tumble of a propellor for more than a week or two; and (c) not changing shape much with changes in moisture content.

I’m with Spacey in that one can go way overboard on tge different types of wood.  Epoxy glues, laminating, and epoxy moisture barrier and hardening coats can overcome a lot of issues. I’m sure an engineer could work out the forces, but empirically we know wood props work.
Another, generality though is that the softwoods like Araucaria (hoop pine), Pinus, Douglas Fir tend to be stronger and stiffer than hardwoods (weight for weight)..this is because the wood cell fibres are longer and have tapering ends compared to hardwoods which tend to have shorter wood cells shaped like plain cylinders.....this is the reason toilet paper is made of softwood fibres (harder to tear) and newsprint (sorry, I mean propaganda print) can have a lot of hardwood fibre.  I wouldn’t have a problem with using radiata pine or Douglas fir for a prop....as long as I could get clear straight grained planks radially sawn and I used several laminations and a good epoxy barrier coat.  But both of them would be a right bastard to shape....neither sand well as the ‘late wood’ (dark growth rings) is very much harder than the lighter coloured ‘early wood’, so any sanding gives one big hills and deep valleys.  Definitely spoke shave shaping.
I mentioned stability in moisture content.  All wood changes size with the seasons due to moisture content changes.  This is why one has to frequently re-do prop bolt tensions with a wood prop.  Some wood is better than others.  Those Taswegian eucalypts sure have a nice look varnished, but they do shrink and grow.  Unfortunately the shrinking and growing with moisture content changes is very uneven.  Along the grain (longitudinally) there may be a change of less than 1%.  From the centre of a tree trunk in a radial line outwards it’s likely to be 3-5%.  Still not much.  But tangentially, ie. along the growth rings, it can be 10%. So it matters quite a lot how the log is sawn into planks, or more likely, which planks you select.  A plank with the growth rings parallel to the longer dimension  (when looking at the ends) and with a nice flame pattern on the larger flat surface will warp and cup much more than a plank where the growth rings are perpendicular to the longer dimension.  The Douglas fir main wing spars in my Cygnet  (6”x1”x15’) are laminated because I could not source radially sawn planks.

The other thing about those tassie eucalyptus (and many from the north island) is their density is highly variable.  I think it was E.regnans that has a wood density ranging from 250 to 900kg per metre cubed.

Spacey, I can’t see any significant benefit of the fibreglass.  It just adds another failure possibility, ie de-laminating in flight, as well as weight, particularly if you have a hardwood prop. I know from boat building that most fibreglass sheathing really only ensures a minimum thickness barrier coating for abrasion resistance and moisture ingress, not structural strength.

[facthunter]

You might do what some wood model plane props did. Pull a vacuum and  saturate with plastic. Radiata is carroty and weak. Oregon has the hard growth rings you speak of. Laminated  say 5 piece with todays glues should be fine. Wooden props have a different feel in flight. Sort of quieter and less rumby/harsh if that makes sense. You are possibly 5% less efficient than a metal one but no problems with lifed prop and cracks from nicks. Don't usually chuck blades. Don't fly in rain. Nev

Edited April 20, 2021 by facthunter

[spacesailor]

Agreed, not structural, but for water ingress And great looks, as in the picture hard to tell it,s glassed over,  and not  varnished. very fine modeling fiberglass, with a hard epoxy leading edge.

spacesailor

[Bruce Tuncks]

Gosh it’s harder than I thought. I think jab props were made out of hoop pine.

it makes sense to me that wood is easier on the rest of the engine , and so a small loss of efficiency is a small price to pay for more reliability.

If you cover a wood prop with glass, surely this adds to the strength?

[Markdun]

Bruce, adding a 175x75x2.4 gal steel C beam to your wing spar will make your wing stronger, but I wouldn’t think that a good thing.  The glass covering is mostly about ensuring a thickness of the coating for moisture and abrasion.  I think the strength claims are marketing spin mainly. My guess is the glass will also increase the moment of inertia and diminish one of tge benefits of a wood prop.   But its swings and roundabouts....I don’t think there’s much in it to worry about.

[facthunter]

Hoop Pine (from what I know) would be fine. The hub is going to be heated and spin dried so will come loose  a bit but it's proven safe and good for the engine Nev.

[Old Koreelah]

I recently repaired my standard Jab hoop pine prop after it copped some minor surface damage.

Very easy to gently sand the glass layer and add a coating of epoxy, sand that smooth then apply a few coats from a can to get a good, silky finish. Static balancing might be time consuming, but it’s easy and the prop is smoother than it ever was.

 

Must agree with Bruce that despite their lesser efficiency, I prefer the simplicity and reliability of the wood.

 

[danny_galaga]

My prop ( http://www.p-propeller.co.za/ ) is glass covered. I would imagine (but I didn't ask) that allowances would be made for the extra  thickness and weight of the glass when designing and building the prop. 

Edited April 26, 2021 by danny_galaga