(SelwayKid) wrote in message . com...
Philip Sondericker wrote in message ...
in article fT27d.3595$mS1.2578@fed1read05, BTIZ at
wrote on 9/30/04 7:00 PM:

that would be one heck of a thermal ride... if it weren't for the rocks...
and "cough cough" the ash..

BT

I was thinking about this recently, and I was trying to determine exactly
what the effects would be on a small plane flying into an ash cloud. How
long would it take for the air filter to become completely clogged? And at
that point, assuming the plane had a carburetor, what would be the effect on
the engine? Would the plugs become fouled? Would they fire at all?

I'm a new pilot and relatively ignorant of engine operations, so I'm curious
to hear the answers.
Phillip
If you were unlucky enough, or foolish enough to fly into a volcanic
ash cloud, your engine would probably quit within minutes. That is if
the turbulence, or heat, or other potential trash like huge boulders
isn't in there to get you first!
The ash would quickly plug the air filter choking out the airflow. The
ash would most likely corrode your windscreen to an opaque as well as
take off paint from the leading edges. The engine may quit entirely or
just run weakly. there are reports of jet aircraft that sucked up ash
cloud and destroyed the engines from the abrasive pumice they
ingested. Many people to the east of St Helens had some expensive
repairs to their vehicles after all the ash had settled. It was a
couple of feet deep in many places as far away as 90-100 miles in the
Columbia Basin and Moses Lake area.

Jet engines have almost no sliding parts exposed to incoming air.
Piston engines have many sliding parts, and ash or any other grit gets
between pistons and rings and cylinder walls and destroys them in
minutes. Grit will get past the piston and rings and foul the oil,
plugging the oil filter and causing the bypass to open, feeding gritty
oil to the pump and every bearing and gear. Alternator brushes and
vented mags would be in big trouble.
Tests on auto engines in the '80s by a piston ring manufacturer
found that a teaspoon of grit fed into a Chev 350 carb while running
near max power on a dyno would trash the engine in 5 minutes. No
compression, bearings gone, rattling madly. Anyone who deliberately
flies a lightplane into any ash cloud could be suspected of being
ignorant or insane.

A friend of mine was crop dusting east of St Helens in the Palouse
area, a day after it exploded, when he said the ash entered the
cockpit of the spray plane and he couldn't even see the panel! Only
many thousands of hours of experience saved him from crashing.

If the cockpit fills with ash, the central vacuum filter will plug
up quick, and there's no bypass to open. You'd lose all vacuum-powered
gyros; not the ideal situation in IMC.

Dan