How important is an aircleaner to say a .46 airplane motor?

Depends on where you live.
IN the western midwest and south west, it is a good idea.
IN the eastern midwest and south east, it is not necessary.

Depends on where you're flying. I usually fly off of a clean paved runway so I don't
use one. If your exposed to dirt and dust it can save your engine. They do rob a little
power but not very much.

tommy s

I just got an air cleaner,fine for mine and I really like it. If nothing else it gives me some peace of mind thinking about sucking stuff into the bearings.

I'd only use one flying off of dirt or dried grass.

I use the coarse BruLine filters and neither me, nor my tach, can see any difference in RPM's.

I use a fine wire mesh air filter (Tettra) on most of my engines with no ill effects. I started doing this after one of my ABC engines ingested a grain of sand that ruined the cylinder. One positive side effect is that there is almost no fuel spray from the carburettor.
If you are operating from a grass field the air filter is not that important.

/Red B.