It flies like a champ with D engines!! I've had 3 flights with D engines and have yet to crack an egg. I haven't yet tried it with an E9 but plan to soon. This is a fun kit. Easy to build and fun to fly. The kids like to draw faces on the egg so it can "look" out the view port in the nose cone. Don't try to launch this rocket with anything under a D motor if you are lofting the egg. Even the slightest breeze makes the rocket weathercock with a C engine. I lost my first model after it's second flight because it ended up almost parallel to the ground and accelerated into a telephone pole.