How the F-15 avoided a disastrous design

Here is a part of Jack Neufeld’s history of the F-15 development, “The F-15 Eagle: Origins and Development 1964 – 1972.”

Indeed, the emphasis on the multi-purpose features of the F-X dominated ASD’s parametric studies…

 

To accommodate multi-purpose requirements, the four study-contractors agreed that the F-X needed avionics comparable to the F-111’s Mark II system. Moreover, the understood that multi-purpose meant the use of a variable sweep wing design for the F-X and that a high bypass-ratio turbofan engine seemed preferable to a low-bypass engine. As for armaments, they called for considerable air-to-ground ordnance.

 

… what emerged was a proposed F-X weighing more than 60,000 pounds (to accommodate all the avionics and armaments packages). The aircraft would have a 110-pound per square foot wing loading, a thrust-to-weight ratio of .75, and a 2.2 bypass turbofan engine…

 

By the spring of 1967, through the efforts of Boyd and others, a 40,000-pound F-X aircraft was “popped out.” Its proposed engine bypass had been lowered to 1.5, thrust-to-weight increased to .97… [Boyd’s] calculations of these tradeoffs pointed to 0.6 as the “best” engine bypass ratio and to a 60 to 65 pounds/ft² wing loading. The design studies incorporated into the final F-15 configuration confirmed these values.

HT: Ryan Fishel. The wing-loading was cut nearly in half, engine bypass cut by two-thirds, thrust-to-weight increased by a third, and the sweep-wing design abandoned for a fixed wing design. In other words, the F-15 we know and are buying new models of nearly 50 years later was completely different from the most likely outcome — where John Boyd and others did not amend the design through sheer doggedness.

Another interesting point is that the government released a design RFP to 13 contractors, 8 returned proposals, and 3 were selected for contracts (with Grumman entering for free — or based on excess funds from the flailing F-111 program they owned). Of the four contractors, all agreed to sweep wing design and other major parameters that proved disastrous in the F-111. How could such conformity have resulted without a degenerative culture in the broader fighter airframing ecosystem?

Here’s another part elaborated by Chuck Myers, another fighter mafioso:

… air-to-air missiles had severe limitations. For example, an F-4 pilot first had to close with his target for positive enemy identification and then drop back far enough to launch his Sparrow missile effectively.