How does Lord Redgrave prove the Astronef is capable of flight to skeptical onlookers?

Lord Redgrave proves the Astronef's flight capabilities to skeptical onlookers through several demonstrations. Initially, he brings the Astronef alongside the American liner St. Louis, then makes it 'leap a couple of thousand feet into the air, swept round to the westward in a magnificent curve, and vanished into the gloom of the upper mists'^[1].

Later, he publicly demonstrates its speed and maneuverability by flying 'rings round' the German liner Deutschland^[1]. In Washington, the Astronef rises from the ground and signals 'Vote for sound men and sound money!' using its searchlight, visible to a 'huge crowd'^[1]. He also takes guests on a trip to Niagara Falls, showing its ability to 'leap up into the clouds, dropped again, and took a slanting course for Washington at a speed incredible'^[1].