Thanks BG and all who have posted information.
I am currently building up my 2nd D-2500 with many of the improvement mods. My 1st one was totally destroyed (including battery, ESC, Rx, motor, fues) when the elevator servo wire shorted out on the sharp edge of the vertical fin tube. This was a 45 deg. full speed give straight in. If I had thought fast enough to exted the flaps this would have greatly reduced the damage. Most of the servos survived and the carbon wing joiner was not damaged. The square steel tube spars were bowed but the carbon rod/tube was extracted and showed no sign of damage.
I would say the wing joiner rod is necessary to stiffen the spar which measures 35.5 inches long in each wing for a total of 71 inches. The stock aluminum pipe is 33.5 inches which almost extends to 1/2 the spar length. When I straightened out the bowed wings without the carbon joiner installed the square steel spar was very easy to bend indicating to me that the steel spar needs to be reinforced with the joiner rod. The carbon tube is much stiffer than the aluminum pipe which will bend in a crash.
Regarding the carbon tube joiner rod from Goodwinds purchased Jan 2012
(product number 020979) I measured it at (32.375 x 0.467 OD x 0.356 ID inches) and 59.0g. Goodwinds lists the O.D. at 0.4720 inches which is 11.99 mm. This is however not what I measured (0.467” = 11.86 mm). Not sure who is the original manufacture of if there was a change. The 11.86 mm carbon tube is a perfect fit without sanding in both my old and new wings, so no change has been made in the square steel tube spar. What I did find is square tube opening in both the older and newer wing is deformed making the opening smaller. This is most likely the result of being cut with an abrasive cutoff wheel. I used a very fine steel file to file down the deformed opening and the carbon tube fits snug with zero clearance.
What I was disappointed about in the new D-2500 is the wing root joint has a 1/16” offset and will not come together without being in a bad bind as was reported by Barry2020. The problem is the result of the spar being mounted into the foam wing with some offset for some reason in the current production run. The fix is to rempve the 1/16” plywood wing root reinforcement which is easily pulled off both wings and replaced with 1/32” plywood, aluminum or carbon. I used epoxy glue which is much stronger than whatever the origional glue was with lots of small holes punched into the foam surface for the epoxy to have a better grip.
The D-2500 flies very nice and has more power than necessary on 4S battery (200 M climb in less than 20 sec). It is surving my goal of improving pilot skill with cheep full house glider before investing in a expensive high performance glider...Mark