The pilot was taking off from an unimproved grass airstrip to the west during the late afternoon. As the airplane crested a rise in the runway the pilot lost visual reference with the ground due to the sun being in his eyes. The pilot could not maintain directional control and struck a rut in the ground. The landing gear collapsed and the airplane came to rest on its belly, substantially damaging the firewall. The pilot did not indicate there were any mechanical problems with the airplane prior to the accident.