HE-111 is a glider

[Furio]

I was writing this post, but then jf1981 beat me.

Saying it respectfully, we all could make an effort in better understandings what we are talking about (and correct me if I’m mistaken). For example, it’s not correct to say that the He111 “should glide well” because of its big wing area. Wing area has to do with minimum sink rate, but does very little for efficiency (lift over drag). For example, a Boeing 707 has an excellent glide ratio, in the order of 20:1, roughly twice the average light plane (and the He, probably). However, it has also a high wing loading, and its best glide speed is measured in mach numbers. For this same reason, modern sailplanes use water ballast. At higher weight, they have a higher best l:d speed.
Now, how should we measure the efficiency of any bird? First of all, we should know both the best glide and minimum sink speeds. If we don’t know them, we can guess the better glide at 1.3 times the clean stall speed (that varies with weight, of course), while minimum sink is a little slower. If we are flying at higher speed, some time will be needed to lose excess speed before starting descent. Once trimmed for better glide, we can easily made a rough estimates by just looking at a stopwatch for a couple of minutes, noting speed and altimeter readings. No particular precision is needed, but we must keep speed very carefully. Then some simple math can give us useful numbers. But beware: making the test away from best glide speed will give very different results. Above a certain speed, we’ll measure dive speeds.

Now, jg1981 made some reasonable tests. If you look at them, you’ll notice he found an l.d. of “around” 10 for all types, which is consistent with my guess above (comparing He111 to the B707), and is consistent with the average aspect ratio of WWII wings. With some allowance, we can say that CoD is accurate for all the type tested.