By Tommy H. Thomason
Monday, February 26, 2018
F-111A vs B - What Drove the Weight?
It is true that carrier-basing imposes a weight penalty. The FJ-2 Fury weighed approximately 1,000 lbs more than the F-86 on which it was based, resulting it being underpowered with the Sabre's engine. (That was solved by putting an engine with more thrust in the FJ-3.)
It's not clear which service was responsible for the side-by-side seating arrangement. It is true that the Navy's two-seat jet night fighters, the F3D and the stillborn F6D had side-by-side seating, in part because shortness is a virtue on a carrier and their radar antennas were humongous. However, I've seen no documented evidence that the Navy required side-by-side seating, other than stipulating a maximum length, which the Grumman F-14 accommodated with tandem seating. On the other hand, the Air Force insisted on a heavy and complicated escape capsule that the Navy had no use for. It was best accommodated with side-by-side seating.
The Air Force also insisted on a bomb bay for nuclear stores and its unprepared field requirement (look up California bearing ratio at your leisure) dictated really big, low-pressure tires. Both of those features resulted in big compartments in the airframe that added empty (no pun intended) weight.
However, the biggest Air Force weight penalty was probably imposed by the Mach 1, low-level ingress on a nuclear strike. That results in the need to design for a very high "q" (dynamic pressure) and gust loading of the structure, neither of which were a requirement for a Navy missile-truck loitering on a Combat Air Patrol station at altitude and then dashing off toward an incoming raid. Moreover, given that the Navy's F-111B was not a true fighter, it probably could have been designed for a load factor of 4 rather than 6.5, further saving weight.
It should be noted that one reason for the F-14 being somewhat lighter than the F-111B was that it didn't have any of those Air Force features other than the variable-sweep wing and moreover, the weight of the big Phoenix missiles over and above that of Sparrows was considered an overload from a structural strength standpoint.