Wood type for wood prop?

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Mike von S.

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I am exploring the possibility of carving my own prop for my Flitzer Goblin project. Power will be flywheel-drive 2110 VW. I would start with 64.5" x 34", based on empirical results of AeroVee 2180s on Flitzer Z-21s, expecting to reduce the diameter a bit dependent on static rpm. Shape would be redolent of a TN-212, which would be period-correct for a Flitzer, but with somewhat reduced scimitar, blade width, and hub depth (likely 3-3 1/8" vs 4 1/4" for a similar prop diameter).

My question is: what's the latest thinking on wood types?

According to Weick's 1925 (original) and 1960 (EAA revisit), selection of wood type should be based on prop dia x rpm: below 170,000 spruce is acceptable, from there to 210,000 rpm walnut, mahogany, or white oak, 210,000-240,000 birch or hickory. No mention is made of hard maple.

208,000 is likely to be my max.

Al Schubert used oak, hickory, ponderosa pine, white pine, fir, mahogany, and yellow pine. He notes that many commercial props are made of birch.

Culver Props say they use hard maple and birch.

Dan Helsper tried ash, and switched to hard maple.

Eric Clutton says many woods are suitable, with mahogany a favorite choice (with a few varieties not suitable). Birch, Spruce or any wood of sufficient strength, not too oily to glue, is O.K., with Beech and Walnut being for the masochists among us as they tend to be much harder to work. Western White Pine or Douglas Fir are quite suitable. He often used a center lamination of mahogany with outer laminations of Parana Pine.

My plan is to follow Helsper's Propeller Carving - The All Power Tool Method, so the hardness of the wood is not terribly important (I'm no masochist).

Current thinking?
 

Mike von S.

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Feb 4, 2021
Messages
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I
I am exploring the possibility of carving my own prop for my Flitzer Goblin project. Power will be flywheel-drive 2110 VW. I would start with 64.5" x 34", based on empirical results of AeroVee 2180s on Flitzer Z-21s, expecting to reduce the diameter a bit dependent on static rpm. Shape would be redolent of a TN-212, which would be period-correct for a Flitzer, but with somewhat reduced scimitar, blade width, and hub depth (likely 3-3 1/8" vs 4 1/4" for a similar prop diameter).

My question is: what's the latest thinking on wood types?

According to Weick's 1925 (original) and 1960 (EAA revisit), selection of wood type should be based on prop dia x rpm: below 170,000 spruce is acceptable, from there to 210,000 rpm walnut, mahogany, or white oak, 210,000-240,000 birch or hickory. No mention is made of hard maple.

208,000 is likely to be my max.

Al Schubert used oak, hickory, ponderosa pine, white pine, fir, mahogany, and yellow pine. He notes that many commercial props are made of birch.

Culver Props say they use hard maple and birch.

Dan Helsper tried ash, and switched to hard maple.

Eric Clutton says many woods are suitable, with mahogany a favorite choice (with a few varieties not suitable). Birch, Spruce or any wood of sufficient strength, not too oily to glue, is O.K., with Beech and Walnut being for the masochists among us as they tend to be much harder to work. Western White Pine or Douglas Fir are quite suitable. He often used a center lamination of mahogany with outer laminations of Parana Pine.

My plan is to follow Helsper's Propeller Carving - The All Power Tool Method, so the hardness of the wood is not terribly important (I'm no masochist).

Current thinking?
I should mention the majors: Sensenich uses birch (still). Hartzell, which was in the walnut business until Orville convinced George to expand into propeller manufacturing, used...walnut.
 

TFF

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The person who use to demonstrate prop carving at Oshkosh, demonstrated on red oak from Home Depot. Prop was intended for an O-200.
Hard maple is still just maple. It’s just some is denser than others. Mahogany, maple, and birch are the traditional woods. Each brand has their favorites and mixes. You don’t want it too flexible. Wood that has the weights close end to end is the hardest to deal with.
 

Marc W

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Doug fir is a strong wood but it splits easily. You have to pay close attention to grain direction when you work it. Birch would be my choice based on strength and workability.
 

PMD

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In our airboat days I built from Birch - found a bunch of farmers with wood aged/dried for decades. We actually did test props in spruce, but meant for one use only (not dimensionally stable). Usually 5 ply using Resorcinol in those days.
 

Mike von S.

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In our airboat days I built from Birch - found a bunch of farmers with wood aged/dried for decades. We actually did test props in spruce, but meant for one use only (not dimensionally stable). Usually 5 ply using Resorcinol in those days.
I'm planning to use urea formadahyde (like DAP Weldwood Plastic Resin, but from a different supplier). Not totally moisture impervious like Resorcinol, but more foregiving of (small) gaps, meanng less pressure is necessary, and a bit more tolent of temperature (70 deg + is ideal for both, but UF cures ok down to 65.
 

TFF

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Weldwood likes warm temperatures and pressure. Something with a lot of surface area is deceptive with getting enough pressure. You want it warm too. I would build a warm
box and get the temp to 90-100F while it cures.
 

Mike von S.

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Weldwood likes warm temperatures and pressure. Something with a lot of surface area is deceptive with getting enough pressure. You want it warm too. I would build a warm
box and get the temp to 90-100F while it cures.
Thanks for the tip.
What did you mean earlier by "weights close end to end is the hardest to deal with"?
 

TFF

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I guess I should have said match densities with the woods you pick, to mitigate having a heavy blade.
 

challenger_II

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Fisher County, Tx. USA
Might I recommend Cascophen?

CASCOPHEN | Aircraft Spruce

I'm planning to use urea formadahyde (like DAP Weldwood Plastic Resin, but from a different supplier). Not totally moisture impervious like Resorcinol, but more foregiving of (small) gaps, meanng less pressure is necessary, and a bit more tolent of temperature (70 deg + is ideal for both, but UF cures ok down to 65.
 

TFF

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What kind of gap filling are you looking at needing? The wood will need a planed smooth surface. That’s not too hard. You are not going to pull down a cupped board and hope glue fills it in. Flat and normal grain is what you need. Lots of glue before you clamp, brushed on both sides. Epoxy is really the only gap fill glue because it wants to be relatively thick.
 

Mike von S.

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What kind of gap filling are you looking at needing? The wood will need a planed smooth surface. That’s not too hard. You are not going to pull down a cupped board and hope glue fills it in. Flat and normal grain is what you need. Lots of glue before you clamp, brushed on both sides. Epoxy is really the only gap fill glue because it wants to be relatively thick.
I am not speaking from experience. What I know is what I've read. Most of what I've read about these glues is from the prop makers I mentioned earlier, from boatbuilders forums, and from the manufacturers' websites.

Both resorcinol (phenol-formaldehyde) and plastic resin (urea-formaldehyde) glues are picky about cure temperature, assembly time, and glue line thickness (resulting from wood prepping technique and clamping pressure). Resorcinol is said to be very picky about shelf life.

It is said that resorcinol cure temp MUST be at least 70 deg F. Plastic resin glue has the same spec, but apparently cures ok down to 65 deg. Both have tight assembly times, particularly "open" assembly times (before the surfaces are mated). The spec sheets for both call for clamping pressure for hardwoods of 150 - 250 psi.

The ideal glue line thickness for resorcinol is said to be .003" (3 thousandths). Plastic resin glue is said (by commentators, not by the manufacturers, as far as I can tell) to gap fill up to .02" (2 hundredths).

For resorcinol, Al Schubert describes using at least 25 x 1/2", or 50 x 3/8" machine bolts as cross clamps for a 6' prop, which he tightens progressively three times, the last time pulling as hard as he can on a 12" wrench. That's a lot of pressure. Eric Clutton, who preferred plastic resin glue, recommends 28 x 3/8" threaded rods (configured as 14 cross clamps) tightened by hand with butterfly nuts. That's a lot less pressure.

Unless you are building for water immersion (say the keel of a boat), plastic resin glue (urea-formaldehyde) sounds to me like the better choice.
 

WonderousMountain

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Clatsop, Or
You may want to pick a couple heat lamps up.
My experiance with Wood glue is none too great.
An enclosed space can get toasty with heat transfer
held to a modicrum. They're costly to run without a
reason, but simpler to use than open oven coils.
 

Mike von S.

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Feb 4, 2021
Messages
100
I am not speaking from experience. What I know is what I've read. Most of what I've read about these glues is from the prop makers I mentioned earlier, from boatbuilders forums, and from the manufacturers' websites.

Both resorcinol (phenol-formaldehyde) and plastic resin (urea-formaldehyde) glues are picky about cure temperature, assembly time, and glue line thickness (resulting from wood prepping technique and clamping pressure). Resorcinol is said to be very picky about shelf life.

It is said that resorcinol cure temp MUST be at least 70 deg F. Plastic resin glue has the same spec, but apparently cures ok down to 65 deg. Both have tight assembly times, particularly "open" assembly times (before the surfaces are mated). The spec sheets for both call for clamping pressure for hardwoods of 150 - 250 psi.

The ideal glue line thickness for resorcinol is said to be .003" (3 thousandths). Plastic resin glue is said (by commentators, not by the manufacturers, as far as I can tell) to gap fill up to .02" (2 hundredths).

For resorcinol, Al Schubert describes using at least 25 x 1/2", or 50 x 3/8" machine bolts as cross clamps for a 6' prop, which he tightens progressively three times, the last time pulling as hard as he can on a 12" wrench. That's a lot of pressure. Eric Clutton, who preferred plastic resin glue, recommends 28 x 3/8" threaded rods (configured as 14 cross clamps) tightened by hand with butterfly nuts. That's a lot less pressure.

Unless you are building for water immersion (say the keel of a boat), plastic resin glue (urea-formaldehyde) sounds to me like the better choice.
But I've never used either of these glues, much less built a prop, so I am eager to hear your views.
Thanks
 
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