On Dec 8, 2009, at 9:09 PM, William Beaty wrote:
On Tue, 8 Dec 2009, Horace Heffner wrote:
Titanium dust oxidizing.
http://en.wikipedia.org/wiki/Helicopter_rotor
"When operating in sandy environments, sand hitting the moving rotor
blades erodes their surface. This can damage the rotors; the erosion
also presents serious and costly maintenance problems.[9]"
I'd have to track down the article and see if it's speculation. Or in
other words, if we use a sandblaster on titanium, do we get the glow?
Perhaps.
Maybe the eyewitness report was wrong about the glow extinquishing
when
the copter ramp hit ground.
I doubt the eyewitness report was wrong, nor that it was
inconsistent. As the copter nears the ground the vortex flattens out
and the radius widens. The air flow hugs the ground and carries the
sand outward. The amount of heavy grains of sand or rocks returning
to the blades diminishes. Also, tip speed drops after landing.
"The abrasion strips on helicopter rotor blades are made of titanium,
which is very hard, but less hard than sand; so when a helicopter is
flown near to the ground in desert environments abrasion occurs, and
at night there is a visible corona or halo around the rotor blades,
caused by the sand hitting the titanium and causing it to spark and
oxidize.[10] [11]"
Sounds like they're assuming the light is from oxidation... without
doing
anything to verify the speculation.
Here's one possibility. If you create a plasma in air, it's very
dim and
purple, but if you inject NaCl dust, it becomes yellow and very
bright.
Perhaps the light is from high voltage air glow with various kinds
of dust
injecting other ions which produce more light.
The light depends on the rotor surface material. If the color were
from dust material ionization it wouldn't go away when some other
metal is used.
The telling experiment
would be whether titanium gives light when sandblasted, even if
electrically connected to earth.
You would need a nearly supersonic sand blaster. The tips of
helicopter rotors run at near supersonic speeds. Note from the web
pictures that only the tips light up, and from the first reference
photos that the erosion is at the blade tips.
Best regards,
Horace Heffner
http://www.mtaonline.net/~hheffner/
