 In 1930 Hirth took "Musterle" to the US National Championships held at Harris Hill, New York equipped with a variometer, an instrument unknown outside Germany and previously only used by Robert Kronfeld in the RRG Professor two years earlier.On 5 October he flew a cross country, blue sky thermal flight for the first time.The following spring, on 10 March 1931, he flew over New York using ridge lift from the Hudson River until signalled to come down by police because he was causing a traffic hazard.