Blade carving

[wdyasq]

Some time ago I was asked about carving blades/airfoils by hand and how one could get the proper 'twist' from '2 by' material. It is difficult to describe things with words at times so I suggested I post in a diary and all might benefit.

A simple CAD drawing shows one can get over 40 degrees twist if one just properly positions the twist in the blank. The 'face' won't be a place to register the airfoil. One can imagine the complaining at this time. Get over it. Make wedges to create the proper attack angle or make the blade adapter with an angle.

The strongest and most stable woods are 'Vertical Grain'. Ideally the airfoil should be 'VG' at all points for strength and stability. With '40 degrees of twist' it would be difficult, if not impossible, to get a chunk of wood to conform to vertical grain at all points on the airfoil. It is doubtful a piece of wood with 40 degrees twist in a few feet would be stable. The best blanks will be clear vertical grain material. It is hard to find. The first question asked is usually 'Can I laminate up a blank.' . The proper answer is, 'I have no idea'. Many can. Many have no idea of selection of the wood to make a  carving blank or that the annular rings should alternate with each added piece. Get good clear wood, avoid the 'heart', orient the grain properly, make good tight joints, use the proper adhesives, cure them at the proper temperatures and it should be fine.

Wood species: Use what is available. Preferably one can find a light, rot resistant wood that is basically clear or small tight knots. One can dream of Sitka Spruce, 50 growth rings per inch and no knots on a 40 foot long, 24" square timber. Well, dream on, it is no longer common. Many species were once 'certified for aircraft spars'. 'Atlantic white Cedar', Douglas Fir, Eastern white pine and many other species were used and certified for aircraft work. Early Gibson and Martin guitars were built with 'Spruce' from local lumberyards. Basswood, walnut, butternut, cherry, ash, yellow pine and even oak would make a decent prop although oak will be a bit heavy and others are more valuable as a furniture wood than as a turbine blade.

Ron

[ruddycrazy]

Eh Ron I have some mahogany wood planks here but the are only about 3 foot long. My late father used the wood for making grandfather clock cases so it wont have any knots and that idea of your does look plausable. This weekend I'll see if they are suitable and it would be heaps of fun trying to carve out the right profile. Ya never know mate if they turn out they could blow your smelly *arts out of the irc forever.

Cheers Bryan

[jmk]

 Yellow pine will change its shape for sure. It likes to cup, twist, and bow. Other than that it is a strong pine. In the housing industry we have a real hard time with it staying true. Even the plywood goes bad in no time at all. Truss co. like to use it for certain members of the trusses, but even those don't stay all that straight.

[wdyasq]

"Yellow pine will change its shape for sure. It likes to cup, twist, and bow."

Last I checked (and I am not prone to check this stuff) there were four viable commercial species of Yellow Pine. They are Longleaf, shortleaf, loblolly and slash pine. The two dominate 'construction species' are slash and loblolly. Both species grow fast and are harvested 'young' and will have a high percentage of non-heart wood as well as transitional grain from knots. This stuff is processed quickly and harshly kiln dried. Loblolly has a natural 'crook' in the top and has little rot resistance.

I can get 'bent out of shape' easily and haven been treated near that rough.

Rather than blame the wood or tree, one should consider the harvesting methods and treatment as well as the one selecting a board for converting into a project. I pay quite a bit more for my materials than 'framing contractors'. However, I expect my land based work to last for centuries as opposed to a generation.

Dynamic projects such as boats, airplanes, automobiles and wind turbines will eventually destroy themselves if used. 'Hanger Queens' and 'Garage Princesses' are not subject to this fact.

Ron

[winston]

Douglas Fir is very nearly as strong as Sitka Spruce and is very stable

a good source is old bleacher seats  --but you'll have to scrape the gum off them first LOL

My BIL has made many aircraft props from laminated douglas fir including one for a 180 HP Lycoming with excellent results