Bill
Actually, a bird has pretty good odds on getting to your air intake
without encountering a prop blade. The odds would be somewhere around 3 1/2 to 1
of success (although I'm sure that the bird wouldn't see it as successful)
depending on your speed, rpm and the size of the bird.
At 180 knots, you're traveling about 18,216 feet per minute. At 2500
rpm a blade is passing by the intake at the rate of 5,000 blades per minute (for
a two blade prop). That means that the airplane travels over 3 1/2 feet between
blade passes. A 1 foot long bird would have better than 3 to 1 chance
of getting through.
So what's it all mean, Mr. Natural? Uhhh, not much. Just that you
shouldn't count on your prop to mince avian airspace sharers into bite size
pieces.
That's a nice design, John. And good info from all of you.
I have the unfortunate experience of having been in the flight path of a
group of small birds. It occurred during takeoff at about 500' AGL out of
Salem, Oregon. One of them met its 'undoing' at my induction opening
of the bottom cowl. So, it did make it past the prop as Bill
discussed.
The flight went fine (I was not aware of the intake obstruction until
landing 1 hour later). My bird, that is, the one I sit in, has a
metal screen at the front of the carburetor air box which is about an inch in
from the cowl opening. There was a bird wing and some feathers stuck
in the screen. And there was a lot of 'goo' (bird parts) to clean up
around the intake opening on the bottom cowl. The souvenir feathers
are on the wall in my hanger. I am of the opinion that the intake
screen very well may have saved "my bacon".
I occasionally think about the possible forced landing at
an off-airport location in the city (Salem airport is at the south end
of the city and my heading was north) had the bird obstruction caused an
engine stoppage.
Gary Edwards
LNC2 N21SN
Medford, Oregon