WHILE ATTMPTING TO TAKE OFF FROM A GRASS AIRSTRIP ON A 90 DEGREE DAY, THE ACFT WOULD NOT ACCELERATE OUT OF GROUND EFFECT. THE LANDING GEAR COLLIDED WITH AN EMBANKMENT AT THE END OF THE RWY CAUSING THE ACFT TO NOSE OVER. THE ACFT CAME TO REST INVERTED IN A POND ADJACENT TO THE EMBANKMENT. THE PLT STATED THAT THERE WAS NO ENG FAILURE OR MALFUNCTION.