Make your own wooden prop

[facthunter]

 I'd regard it as primarily giving some protection to it but adding mass more than strength unless you get into carbon fibre which is another story. Great in tension. Nev

[Bill]

Questions please: Old Koreehla - what brand of epoxy did you coat your prop with & what brand - type did you spray (aeorosol?) it with? And Markdun - what brand of epoxy did you use to glue the laminates. Thanks,  Bill

[danny_galaga]

This is what they do at P prop by the way:

 

http://www.p-propeller.co.za/propeller-manufacturing/

[Old Koreelah]

4 hours ago, Bill said:

Questions please: Old Koreehla - what brand of epoxy did you coat your prop with & what brand - type did you spray (aeorosol?) it with? And Markdun - what brand of epoxy did you use to glue the laminates. Thanks,  Bill

Can’t recall, Bill, but the same epoxy brand I’ve been using for yonks; the spray cans recommended by Jabiru.

[Markdun]

For glueing, I use the System Three one to one ratio glue.....the same as I use on my wing spars, ribs, and on structural beams on my 11m yacht.  I’m told it’s the same as one of tge approved epoxies for certified aircraft....and good for gluing in high humidity (some epoxies aren’t).  When cured it is only a tad harder than E.delegatensis and pretty resilient (ie. not brittle).  For coating I just use a local Qld made epoxy that is fairly high modulus, ie. hard and waterproof, but will chip more. Some epoxies are softer (eg. BoteCote) which have characteristics more like lower density wood used in boatbuilding like WRC and are better in that use.  I tried these softer types thinking they would be better for leading edge protection, along with Kevlar woven tape....not worth the effort. I now use hard epoxies for coating and prop tape for leading edge protection.  If I was making the prop out of low density timber like hoop pine, now I’d probably use the single pot expanding urethane glue.  Not as tough as epoxy, but the urethane glue joins are stronger than the wood if the wood is soft.   Lots of laminated beams and plywood in my sloop held together with urethane, and it’s over 10 years in the water with a few thousand blue water ocean miles under its hulls....and no glue joins have failed.

[Aero28]

This is how I do it ,I haven't flown behind one yet but this is an easy way to carve them.

[Bruce Tuncks]

I was there when a Jabiru lost most of its fiberglass prop covering. It made a thump noise followed soon after by an engine shut-down. Apparently the out-of-balance forces were feeling like the engine would be ripped out. The air had ripped the glass off.

The pilot handled the situation ( engine failure at 300 feet, not enough runway straight ahead) very well and I was first on the scene to congratulate him. No damage.

Those old jab props had the fiberglass covering routed off at the leading edge and replaced with a butt-jointed rubber shaped bit. This works ok as long as the prop tape is in good order, but in this case the prop tape had been removed by our then maintenance guy.

[facthunter]

Loss of a prop blade ripped the motor from a Chipmunk over lake Macquarie many years ago. It was so tail heavy it could not be controlled and spun but the RoD was much less than in a normal spin due less weight so was survivable.  The prop was a metal l Fairey Reed that failed near the centre . Wood props are pretty free from blade failures in flight  Some earlier Chipmunks had wooden props. Nev

Edited June 19, 2021 by facthunter

[Old Koreelah]

1 hour ago, facthunter said:

Loss of a prop blade ripped the motor from a Chipmunk over lake Macquarie many years ago…

A fearful situation, Nev. Rotax engines seem to have in-built protection against the engine being ripped out by massive out of balance situations- their carbs are not clamped on and just fall off, stopping the engine pretty quickly. I have a rough approximation of that: a cable around my carb designed to rip it off if the engine moves too much. Might work.

 

1 hour ago, facthunter said:

Wood props are pretty free from blade failures in flight…

Nice to know.

[Thruster88]

The propeller disintegrated on my Skycraft Scout just after takeoff, only ever found the one blade. Found it in the shed just now, it is smaller than I remembered. There is almost no thru grain because the prop hub bearings were inside the prop.

 

 

[facthunter]

That's something to watch out for and a trap with wood. Some timber s are fissile (split easily). Nev

[Old Koreelah]

I guess that’s why several laminates are normally used.

[Marty_d]

That one doesn't look laminated at all.  Was it carved from a single piece @Thruster88?

[Thruster88]

9 hours ago, Marty_d said:

That one doesn't look laminated at all.  Was it carved from a single piece @Thruster88?

Yes it is laminated, you can see one just above my hand. The wood is very soft, similar to the wood used for skirting boards.

[facthunter]

The holes in the hub give it no chance of doing the job. Sheet carbon fibre between the laminates in the hub area? Nev

[spacesailor]

Wooden props have served us well, even through a couple of wars !.

The use of FRG , has been used a few times but is much better on the Outside, doing a good Finnishing job when there,s a rough surface to hide.

But laminating CF betweem wood is something else.

Has any one tried it, to check the finished strength,  ?.

spacesailor

[facthunter]

It's been done with  fibreglass. Nev

[spacesailor]

Yes glass between the wood is good, ( Don  )

BUT

Carbonfibre is a lot harder to get that perfect ' glue line ' to which, means, will it be safe ,.

spacesailor

[facthunter]

fibreglass and carbon fibre. Carbon fibre is (relatively) poor in compression..Nev

[Markdun]

Spacey, that’s an excellent idea.  My Jim Maupin designed Carbon Dragon had lots of wood-cf composite construction.  The wing main spars (full cantilever wing 44’ wing span) had caps of spruce and carbon fibre.  The spruce was in the shape of a ‘U’ that tapered towards the wing tips. The carbon was ‘tows’; a specified number went full length and then there was progressive less full length. You had to make a jig for the carbon to roll off a roll, down through an epoxy bath, up to be squeezed to get rid of excess resin, then along the length of the spar cap.  The wing ribs were also made with 1/4x1/4” spruce strips with a 3/32” groove routed down the centre (another jig), and carbon tows were laminated into that groove (similar jigging as for the wing spar caps).  These made exceptionally light and very rigid and tough wing ribs.

CF has good compression strength, unlike Kevlar, but in most work the compression forces are handled by the resin.  But this is why cf laminations are very stiff, again unlike the floppy nature of Kevlar laminations.  The problem with cf is that with such a low modulus of elasticity it bends only a very little and then fails completely.....it’s brittle.  The combination with wood as a composite in the Carbon Dragon seemed to work well.  However, Kevlar was the main tension load bearing material from the wing spar (and anti drag) attachment points to the fuselage.

Back to prop building, the question would be what are you trying to achieve by laminating cf between the wood?  It would make it much stiffer, which could make the prop more efficient, but it would also make it less resilient and perhaps less forgiving to engine power pulses say.  I’d also give a warning from my experience...cf is not easy on tools...if you intend to do any shaping, cutting, sanding etc...good luck.

 

[Markdun]

I forgot to mention.  Laminations are used because wood shrinks and expands with changes in moisture content, and this doesn’t occur evenly.  Laminating makes the plank/propeller dimensionally stable with changes in moisture content. Length wise, along the grain, wood moves little ~1% or so.  Radially (imagine a line from the centre of the tree going outwards horizontally) ~5% or so.  Tangentially (also horizontal, but parallel to the growth rings ~ 8-10%.  This is why many timber boards twist cup and split.  Of-course, some timber’s are pretty dimensional stable with moisture content, eg western red cedar, and this is why this wood is often used in windows and boat building despite being soft (it’s also toxic and doesn’t rot).  And if you purchase radially sawn timber (the yanks call it ‘quarter sawn’) as you ought to for aircraft, then you minimise twisting, cupping and splitting, but you don’t get rid of it; laminating does.  Also laminating overcomes small defects, like knots, gum pockets, grain misdirection etc.

[Old Koreelah]

A neat laminated prop:

 

 

[meglin]

This is a very difficult production.

Dust, noise, toxic fumes.

Hard wood varieties are very difficult to process. We usually use beech, oak, ash. Oak forms small needles that dig into the skin. At the finish, we must paste over fiberglass to exclude the influence of humidity. The blade edge is necessarily protected by a stainless steel strip. The quality depends on the hands of the master, on the wood, on the temperature in the room and the humidity of the wood, on the quality of the adhesives. We use only epoxy glue with maximum strength. All this increases the cost of the final product, but allows you not to worry in harsh operating conditions at temperatures from -50 to +50 degrees Celsius.

For Jabiru engines, we have produced many samples of propellers with a diameter from 49 to 59". And we have achieved good performance indicators. But there is a factor that completely cuts off this business. At the request of the EU, our post office has limited the dimensions of parcels to 41'. 

Only very expensive courier services remain. For remote countries, there is only one way out - the use of composite propellers with especially strong carbon blades. The saber-shaped shape of the blades significantly reduces noise and allows the use of propellers with a diameter of 63.8". The thrust increases, vibrations decrease, there are no deformations of the blades from temperature and humidity changes. They are placed in a small box and can be delivered for a reasonable fee by regular air mail.

[meglin]

In our entire history, we have never encountered a rupture of a wooden propeller. This is physically impossible, because the margin of safety is huge. There may be a longitudinal stratification due to poor-quality gluing of layers, such cases can be 1 out of 1000. But transverse destruction - never. 

Perhaps the propeller was intended for scenery, like these?

[Old Koreelah]

A work colleague recently died of emphasima, decades after a working life breathing wood dust.