Beagle Pup door
We took off shortly after that Pup and it was quite hot, we were slightly downwind and, with everything working as advertised in our Condor, you had to fly accurately to maintain any sort of climb rate and safely clear the trees.
I've never flown a Pup 100 but I imagine the extra drag and distraction of a door opening in those conditions would not be helpful.
Edited to say that this post should be No 3