Apologies if this has been said before, but I recently watched a program featuring the construction of the glider built in Colditz in WW2 by the British POWS.
The program went ahead and built a full size replica of the glider, stuffed a dummy in the cockpit and some remote controls and 'pinged it' off the roof of the actual Castle using the weighted bath as a catapult launch just as the original escapers had planned.
Spoiler alert - Don't read more if you don't want to know....
Bit of dip at first, which might have had a very high 'pucker' factor for the pilots at take off, but as the speed got up, the lift improved and it comfortably sailed around 2 miles and landed safely out side the castle. They had less room to make a landing because of modern buildings encroaching, but they answered the question. So would the glider built from matresses in the attic actually have flown? Yes. Definitely.