Carson1934
If I understand you correctly only the winner of the current challenge is entitled to make the next move.
That is correct.
And what happens if the challenge is not accepted and nobody knows what the submitted item is?
There is no time limit if after a day or so there have been no takers or nobody is getting near the answer the challenger provides a clue if it is obvious that the challenge is going no where the challenger "shows his cards" as did one11 at Post #1791 and declares open house.
Incidently was I correct regarding your aircraft? I am sure it is the plans of the Miles Hawk Speed Six G-ACTE that took part in the Spanish Civil War with bombs fitted?