So I think it's time to announce the winners of the challenge.
First of all, a kind of foreword. The idea of this challenge came to my head quite long ago, in the times when there were no fancy parts in the game, like gyroscopes. So quite naturally, when I finally decided to start the competition, I totally forgot about them and how they can affect the possible length of the flyable plane. I think I should have banned gyroscopes together with xml editing and scaling, it would have made it much more challenging.
Okay, and now on to the winners.
THE FIRST PLACE goes to @Supernovaboss504 and one of his clever wingless planes. Not sure which one though, I think the shortest one in appearance is #3, but according to figures, it isn't. Apparently the RCN nozzles look much shorter than they really are! But hey, are they needed there at all? It could be even shorter (one block length!) without them. Anyway, being 2.9 feet long, the Supernovaboss504's #2 is the shortest plane in the challenge, congratulations! Get ready for some upvotes and spotlights!
THE SECOND PLACE goes to @Chancey21 and his second shortest plane that is 3.8 ft long. I think I almost got nausea when I first tried to fly it, but once it gains speed, it is pretty stable. You get 12 upvotes, congratulations!
Aaaaand, THE THIRD PLACE! Goes to @Viper3000ad and his Flying Wing. Yes, I know it isn't really short (but it's not the longest one!), but I just LOVE how perfectly it flies! It is almost too good to be true with the length of 7.7 feet and no gyroscopes! You have 7 upvotes, my friend, congratulations!