The FAA says glide ratio doesn't change, regardless of weight, here on page 5-7.
Glide ratio is not affected by weight because, while a heavier glider sinks faster, it does so at a greater airspeed. The glider descends faster, but covers the same horizontal distance (at a higher speed) as a lighter glider with the same glide ratio and starting altitude.
However, a friend suggested to me that this is BS, and if you overload a craft above its operational limits, its glide ratio will plummet. In fact, he's confident that there's a sharp decline in glide-ratio from the point of going over the maximum weight limit. I don't know if this is true, but am interested to learn.
The question is, quite simply, is the FAA inaccurate/wrong on this point? Can you reduce glide ratio by increasing the wingloading of a craft, as my friend suggested?
My Attempts at Research
I tried to look for polar curves that show the performance of overloaded craft, but couldn't find any' only curves within operational limits. I have no intention of testing something so dangerous myself, of course, but I do want to know the answer. I have heard anecdotes of people going well above the safety limits of their craft, for things such as world records.
I'm hoping wise people here can teach me a bit about the facts, and whether the FAA's statement is technically wrong as was suggested.
He pointed out cargo planes have extremely severe limitations, where exceeding their weight limits will often be catastrophic.
There was a world record flight, I forget the plane and pilot, but I recall it was apparently loaded up to almost twice it maximum weight with fuel tanks.
Glider weight limits I saw seemed more related to landing and taking off than to concerns about performance in the air.
I've seen a couple of people state that glide ratio will only improve with a higher weight (very slightly), up till the point where A, the materials break from being overloaded, or B, the optimum speed will reach the Vne and become disabled for that fact.
Notably, even if glide ratio does remain consistent with more weight, landings, takeoffs, and manoeuvring become more difficult. It's also harder to make use of thermals.