Complex sentence: It was realised that the machines that resulted from the 1923 and 1924 light aircraft trials were too low-powered for serious use, the Daily Mail sponsored a similar competition in September 1926, this time allowing the use of heavier and more powerful engines.
Split into simpler sentences: It was realised that the machines that resulted from the 1923 and 1924 light aircraft trials were too low-powered for serious use. The Daily Mail sponsored a similar competition in September 1926, this time allowing the use of heavier and more powerful engines.