[ACE-OF-ACES]

Maximum allowable gross weight. All up weight with fuel and payload. Another reason for the removal of the remote stations was it allowed them to incorporate another fuel bladder in aft bomb bay so they had a little more cushion to account for winds aloft. And of course they probably had to deal with some density altitude problems though I do not know what average temps are on the island. I was fortunate enough to spend time with most of the Enola Gay crew on several occasions and spoke quite a bit about this mission. Most of my reference comes from NASM as I worked there for 30 years. of which 13 were spent with the Enola Gay. You can find any number of different ceilings from 31,500 to 36,000 ft most likely as the maximum allowable gross weight was increased to over 140,000 lbs the ceiling was derated.

Very cool

Than you understand very what what I am alluding to..

That being the payload affects the top speed, total range, and max altitude (ceiling) that can be reached..

Put another way, less bombs more fuel, more distance..

And here is a quote that reflects that truth..

It was able to fly at 30,000 feet and to carry a 2000 lb bomb load 5,000 miles. However, on smaller distances, the B29 was capable of carrying sixteen 500lb bombs in its after bomb bay and another sixteen 500lb bombs in its forward bomb bay. [ref 1]

Note they point out that the distance will be affected by a heavier bomb load, in this example a 2,000lb vs 16,000lb (2x16x500lb) payload, The quote makes no mention of how the ceiling is affect but we know that it would be..

here is a example of the B-29 general stats..

Empty Weight: 7,0140lb
Max. Weight: 12,4000lb
Speed: 357mph
Ceiling: 31,857ft
Range: 3,250miles

As I pointed out 'stat's can be very misleading in that that they don't indicate if each value listed is a best case value or some average configuration value.
By best case I mean the max speed, range, and ceiling was obtained at the min weight, not max.

Combat range: 3,250 mi (2,820 nmi, 5,230 km) a little more than the distance from Tinian to Hiroshima.

Actually Tinian to Hiroshima was ~3,405 miles round trip.. [ref 2]

Which is more than the listed Combat Range of 3,250miles..

And goes back to my initial point as to why they lighted up the B-29 (removed guns, etc) to carry the 8900lb Little Boy and or 10,000lb Fatman payloads that far, that high, and that fast

ref 1: http://www.fighter-planes.com/info/b29.htm
ref 2: http://serv.peace.hiroshima-cu.ac.jp/En ... ne2302.pdf