Complex sentence: This should have competed in the Second Polish Glider Contest, held in August 1923 and was there but was badly damaged in a pre-launch accident and though it was repaired before the end of the competition a lack of wind kept it on the ground.
Split into simpler sentences: This should have competed in the Second Polish Glider Contest, held in August 1923. It attended but was badly damaged in the run-up to its first launch and though it was repaired before the end of the competition a lack of wind kept it on the ground.