Rusty, forget grass and dirt strips. Next time you go to the airport you can set a good example by sweeping a portion of the runway. Anything you can sweep up could also end up in your engine if you don't have a filter. If you are third or fourth to take off, imagine the crap still in the air when its your turn. This is kind of a weird topic to me as I can't think of any reason to not protect the engine with a filter. I would like to see a photo of you sweeping the runway :) Jerry
On Tuesday, April 12, 2005, at 12:48 PM, Russell Duffy wrote:

"Conventional wisdom" is - every engine should have a filter to keep sand (and other hard parts) out of engine.

 
I think the key phrase is conventional wisdom.  There's no doubt that dirt and such will eventually wear out an engine, all evidence suggests that it's going to take a long time to do that on a rotary in our application.  As you likely know, Tracy has never had a filter, and flies off a grass strip.   I can't think of anyone who's verified damage from anything that came from outside the engine, though it can certainly happen.   
 
On the other hand, there have been plenty of engines damaged by items that came from somewhere within the engine itself (intake, TB, etc).  If anything, I think I'd like to have a screen between the intake and side housings, except that I'd be worried about the screen itself eventually breaking and getting ingested.  
 
I do agree that the best plan (space permitting) would be to have two air sources, filtered, and unfiltered.  
 
Rusty (unfiltered, unshaven, unwashed... )