Two types of tail dragger gear configurations, one in which the gears are mounted in the wings, the other where the landing gear is mounted on the fuselage ( 4*s, Extras, etc., etc. ). For relatively rough grass fields it`s been my experience that fuselage mounted gears are MUCH more forgiving than wing mounted when it comes to noseovers. Where I fly, I`d rather occasionally re-align the nose gear on my Avistar than pop a gear on my PT-19.