On Oct 31, 2:20*pm, Udo wrote:
Here are the data points for glider A:
starts at exactly 13 minutes and 42 seconds.
at 2349 ft with a speed of 50 kt

arrives at 20:22 at the finish line with an
altitude of 121 ft at 95 kt, a distance covered of 12.7 miles.

Glider B
starts at nearly the same location ( within 100 ft) at 13:56
at an altitude 2400 ft at 57 kt

arrives precisely at the same finish line at 20:02
at an altitude of 62 feet with a speed of 103 kt also covered the same
distance of 12.7 miles.

*The condition are the *same but for the second glider leaving 14
seconds later and arriving 20 seconds *early. The flight pass was
nearly identical but for the second glider passing the first
hal ways

What is the true difference between the two. It is clear there is not
much difference.

Thanks in advance for shedding light on this for me.
Udo

Udo,

I'm assuming the distance is quoted in statute miles and that the
gliders accelerated to their average speed over the distance at the
start of the glide and slowed to the finish speed at the end of the
glide. Glider A averaged 99.3 kts. Glider B averaged 108.6 kts.

The difference between starting and finishing energy for Glider A was
292 feet and for Glider B was 330 feet. If we subtract this energy
from the altitude difference for each over the glide we get 1,936 and
2,008 feet and L/D's of 34.6 and 33.4 respectively for Glider A and
Glider B. For a current generation 15M glider this is about the
performance you'd expect with zero wind and half a load of water.

The main anomaly is that for the same glider at the same wing loading
you'd expect 4-5 points lower L/D for the higher cruise speed versus
the 1.2 points in your example. This would indicate that either
Glider B was a higher performance design, was at a higher wing loading
or found more favorable conditions on the glide.

I'm not sure what you're trying to figure out, but that's how the
rough calculations come out for me.

9B