Inside the gas-engined model plane a tiny parachute soldier is waiting to make his jump. The plane buzzes up into the air, and as it levels off in full flight a timer suddenly cuts off the motor. At the same instant the timer presses a lever on the side of the fuselage to the point where it releases a wire, and the hinged trap door in the floor of the plane drops open. Out plunges the two-and-one- half ounce soldier, to drift down by parachute as his plane floats to earth, The plane and its parachutist were built by a young Syracuse, N. Y., mechanic, who has been a model-plane fam 2 hood. Copied after a popular high-wing monoplane, the model weighs three and one-half pounds; its silk parachute is three feet in diameter.