Suddenly, as the plane rose at a sharper slant, she began to roll. Ned shouted to ask his chum what had happened, for the windows were open on the sides of the prow and the drumming of the wings and the rush of the air engendered a noise that was almost deafening. “I don’t know,” admitted Tom, shaking his head. “Remember, this is my first trip in the thing as well as yours. Why should _I_ be supposed to know all about it?” and he grinned cheerfully as he looked at his chum. But in a moment the car took another roll. Ned thought it was about to turn turtle. It was no laughing matter. “Did you make her so she would fly just as well upside down as on even keel?” he demanded, having closed the windows. Tom looked serious. His hand was on the steering levers, or controls. He knew that this rolling motion must wrench the framework of the plane enormously. They heard the beams groan, and somewhere a cable snapped. “Listen to that, will you?” exclaimed Ned. The plane kept on even keel for a few moments longer. They had been in peril, as Tom well knew. Were they now safe? He lifted the nose of the craft a bit more and again the wings dipped sideways and the boat rolled “upon her beam ends,” as would have been said of a seagoing craft. “Stop her, Tom! Stop her!” shouted Ned, scrambling up from the floor, where he had fallen when the craft rolled. But Tom knew that to shut off power and “stop” the flying boat would court greater disaster. For some unknown reason the craft had lost her balance, and when she rolled over the other way it seemed to the young inventor as though she must go completely over, her wings be wrenched away, and the great craft fall to the earth in a tremendous crash! CHAPTER XIII A SECOND TEST After his second shout of alarm Ned Newton remained quiet. After all, he did not lack either physical or moral courage. He had not entered into this test of the flying boat without knowing very well that something might go wrong and that a fatal disaster for all was possible. How the mechanicians were affected, the inventor and Ned did not know just then. The members of the crew in the tail of the boat made no comment through the speaking tube. As for comments by anybody on the earth that might be watching the careening plane, Tom Swift had made no provision for receiving such a communication. There was radio on board the _Winged Arrow_, but it was not in use during this test. Nor could any advice, even from Mr. Barton Swift, have aided the young inventor in this serious emergency. Something was wrong with the balance of the seaplane. Just what it was, Tom had not yet the first idea. He was as much puzzled as anybody else could have been. The rolling of the huge structure continued. Had it not been put together with such care, the plane would never have withstood the second roll.