RE: dirt in carb
Flying off a dirt runway can lead to problems whether or not you stick it in nose first. I use Bruline carb air filters whenever possible. Of course I also use muffler extensions. Both of these items will rob you of a few RPM's but you will be flying the engine for a long time. I never rotate an engine after a crash until it has been taken apart and cleaned. Voyager has suggested a good method of cleaning. I usually use a coffee can and fuel. Sounds costly but it's cheaper than a ruined engine.