Bamboo Propellers

"Stealth Pilot" wrote

well when that prop was shattered in a wheels up landing of the
sidlinger hurricane it was on, not one part of the curly grain had let
go. no glue breaks in the curly grain. no breaks of any type in the
curly grain area. all the breaks were in the adjoining straight
grained sections at radiuses either side of the wrong grained wood.


If the curly wood is in the middle of the prop blank, or carved section of the
blade, it is only taking up the centripetal forces (I know, they don't exist)
and not any bending load. It is only serving to hold the outer sections away
from each other, like the web in an I beam.
--
Jim in NC

On Thu, 4 Jun 2009 20:32:31 -0400, "Morgans"
wrote:


"Stealth Pilot" wrote

well when that prop was shattered in a wheels up landing of the
sidlinger hurricane it was on, not one part of the curly grain had let
go. no glue breaks in the curly grain. no breaks of any type in the
curly grain area. all the breaks were in the adjoining straight
grained sections at radiuses either side of the wrong grained wood.


If the curly wood is in the middle of the prop blank, or carved section of the
blade, it is only taking up the centripetal forces (I know, they don't exist)
and not any bending load. It is only serving to hold the outer sections away
from each other, like the web in an I beam.

centripetal forces exist.
it is centrifugal forces that dont.
Stealth Pilot

Charles Vincent wrote:
Stealth Pilot wrote:
On Mon, 25 May 2009 12:32:15 -0500, Charles Vincent
wrote:
I know the British preferred mahogany for their propellers, but as I
recall, mahogany had some serious knocks as prop material. I can't
bring them to mind at the moment though.

Charles

mahogany was used by the brits, to quote lattimer-needhams engineering
text,
"mahogany is largely employed in the manufacture of airscrews, and the
variety that grows in honduras is favoured for that class of work. The
suitability of honduras timber is due chiefly to the fact that its
liability to shrink (after efficient seasoning) is only very slight
and that it possesses particularly satisfactory glue retaining
qualities. it is a strong, hard, straight grained wood and is not
difficult to work."

I found the reference. It was in Martin Hollman's Modern Propellor and
Duct Design book. It just notes that mahogany tends to splinter easily
and is therefore not a good choice. In any event, mahogany doesn't
grow here in Texas, at least anywhere near me. Bois dArc does though
and has ridiculous strength in compression - double mahogany (I have a
house built on Bois D Arc stumps, the tree is so ugly, termites won't
touch it) I have the compressive strength numbers since it is a common
foundation material, but do not have the normal engineering values for
the rest. I need to find them.

Charles


Surely you've seen some native Indian bows (old ones) the wood is split
from a tree so that the heart (dark wood) and the lighter (outside,sap
wood ) both appear in the bow..The dark is placed on the inside of the
curve because it is much higher in compressive strength..The back side
is the sap wood which is much higher in tensile strength.

Pore old uneducated indians--didn't know much did they G --also
Bois= wood d'Arc= of the arc or bow. Jerry--(used to live on
Bois d'Arc in ElPaso.)

On Wed, 27 May 2009 03:54:38 GMT, Jerry Wass
wrote:



Surely you've seen some native Indian bows (old ones) the wood is split
from a tree so that the heart (dark wood) and the lighter (outside,sap
wood ) both appear in the bow..The dark is placed on the inside of the
curve because it is much higher in compressive strength..The back side
is the sap wood which is much higher in tensile strength.

Pore old uneducated indians--didn't know much did they G --also
Bois= wood d'Arc= of the arc or bow. Jerry--(used to live on
Bois d'Arc in ElPaso.)

the actual examples of english longbows that remain were recovered
from the holds of the Mary Rose. no other *actual* medieval english
longbows existed. the making of them was pretty well lost to hearsay.
they are made from Yew wood exactly as you describe for the american
indians.
most are apparently roughly shaped but I think that that was so that
the wood behaved as needed.
Stealth Pilot