To supply Sixth Army with 300 tons a day, the absolute minimum amount demanded by the army
(which really needed 500 tons) would necessitate an average of 150 fully laden Ju 52s landing in 
the pocket each day. (500 tons an average of 250 Ju 52s landing in the pocket, including loading,
unloading, losses, etc.  it would mean they needed 800 Ju 52s to realize 500 tons each day.)

Of the 7 airfields inside the Stalingrad pocket, only Pitomnik was properly equiped to handle
large-scale operations. It even had lights, flare paths and signal equipments for night operations.

This is not complete, I tried to add as much info as I found. If someone can help me to complete, 
please let me know. 

Ju 52 = Junker 52
He 111 = Heinkel 111