uncle joe,
It doesnt matter what is under the seat if the engine fails! RPM is what makes a helicopter fly. The R22 will autorotate at any speed between zero and max range speed but you will die if you are relying only on how heavy it is. PLEASE practise with an instructor on board.
The odds of an actual engine failure in an R22 are infinitessimal compared with the odds of you cocking up a solo auto.