Newps wrote:


Jim Logajan wrote:

Newps wrote:

How are stones going to defy the laws of physics? The plane is moving
forward. Rocks don't leap off the ground and jump into the prop.



I believe there is a low-pressure area in front of the prop which
causes an inflow of air from the area forward of the prop to
compensate for the air that is being directed aft. Combine that with
the usual preferential headwind takeoffs and it seems likely stuff on
the ground can be wind blown and/or sucked off the ground and into a
prop.


There is a short video that you can see that shows a Cessna running its
engine up while parked in a puddle. The water is maybe an inch deep,
hard to tell. The prop will create a little tornado directly beneath
its lowest point. This is what causes prop damage. Get the plane
moving just slightly and this effect is lost. Any air being sucked in
from the front, and I don't believe there is, is not strong enough to
pick up rocks.

I still wouldn't rule out getting a small pebble or stone into the prop
if you are sliding the wheels to a stop in gravel. The propwash might
sling a small stone into the nosewheel where it could bounce forward
into the prop. Similarly, if the nosewheel is pushing through gravel at
any rate of speed, stones could bounce forward off the nosewheel.

Rocks certainly won't leap off the ground into the prop, but they could
bounce off the nose wheel.

Matt