I am avoiding answering this in the AMCA thread for I get singled out again (even though I don't know what prompted the last mention). If the main thrust of your question is that do the 5GFA have to be designed to 4th generation maneuverability requirements then the answer is no. The F-35 itself blows the socks off of many of the individual attributes on the F-16, F-18 or Harriers it is replacing. Similarly, the F-22 performs better than the F-15 in many areas. I don't think, I ever argued around that. What I argued was that a clean 5th generation aircraft carries the IWB penalty (it can still perform better despite of that), the RCS optimization penalty, and the large internal fuel capacity penalty. Those constraints do not apply to clean 4th generation fighters and HENCE a direct drag comparison, without factoring in the DI is inappropriate. So a raw statistical comparison of a slick F-15 and a laden F-22 or a F-35 is of no meaningful use hence most modeling is done with a particular mission and DI in mind for reference.Indranil wrote:I think you evaded the main the thrust of my questions. The question is “Does the stealth vs. aerodynamics compromise mandate that a fifth generation fighter be sub (or at best at) par to fourth generation aircraft in aerodynamics? I strongly believe that the answer is no. People try to justify otherwise citing the F-35 which is wrong in my opinion. Your rebuttal to making F-22 a truly multirole aircraft is also based along the same lines. If F-22 was being designed today, its bays would have been suitably designed to carry the bombs and missiles required. That would not have affected its shape (and hence its aerodynamic prowess) significantly.
Now, let me argue that if designers were given the sole task of designing a CTOL (or even a CATOBAR) multirole aircraft, the design would go differently from the F35. Aircrafts are designed around engines. And the F35 program was designed to use the same engine for all three variants, including the STOVL variant. This (almost) mandated a single engine fighter. The drive train for the lift fan is a design marvel (and a maintenance headache) in itself. If that had to accommodate power from two engines, it would have been a nightmare. But, there is only so much power that one can derive out a single low bypass engine, and the 119 is up there! So that limits the thrust available. But, then on the other variants, you also have to live with this power and yet provide the extraordinary hangtimes on internal fuel!
You are also mistaken about the F-35 program. The single engine requirement was not - to make it common across three variants - it emerged and was set in place even before the three services got together on one program. The USAF had a hard single engine requirement, because its entire expeditionary logistical support was developed around the F-16 which is a single engine fighter. In the early 1990's, the USAF had a plan for a new Multi role fighter which would have been the "low" to the ATF. It was expected to cost 1/2 as less than the ATF and be a single engine, single seat aircraft. Around the mid 90's or so, the budget outlook and the pressures to curtail or even terminate the ATF was enough to convince the Pentagon that the USAF could not afford such an aircraft if it pursued it as a service program. Meanwhile, other programs were also in S&T phases which looked at STOVL fighter concepts for USMC and UK. The US Navy was actually a observer on both (AF program and the DON funded Joint ASTOVL program) and it was rightly decided to aggregate this demand so that each service would end up with an aircraft that was higher performing and more affordable than what they could have gotten if they pursued 2 or 3 separate programs. It is wrong to assume that a twin engine trade space was ever open for the USAF.
Also, if one is only interested in an academic exercise then yes, if one were to focus on just one requirement the end product is going to be different. That is not how requirements are framed though and as I mentioned, if Lockheed was tasked with just building something for the USAF, the program, its risk and budget appetite and performance would have been severely degraded. In fact, the USAF would have done well to get something as good as the Rafale. The program survived the post FSU environ because it was a joint program and hence everyone concerned was able to get a higher performing aircaft than what they would have individually gotten. If you think similar hard and soft constraints also do not apply to every other program out there then you are highly mistaken. All requirements are framed in, and all designs represent, some sort of constraint. In this case the decision was to either pursue something that was agreeable to most (not all) or buy duper hornets and F-16 U/F-15E's. The US defense budget (inflation adjusted) decreased by >33% between the peak of the Reagan build up (85-86) and the bottom of the Clinton cuts (97). Successive Republican and Democrat administrations (late Reagan, all of HW Bush, and all of Clinton) had cut defense spending in relative terms and the civilian and military leadership had seen the writing on the wall. The individual service plans like the MRF, or the ASTOVL went no where. They pooled their demand and pursued a DOD wide program.
Aircraft are designed to a requirement. Requirements are framed with performance, need, threat, and a cost in mind. The F-22 does not carry the features required for it to be as capable a strike fighter as the F-35 because doing so, without reducing some other requirement would have impacted program risk, complexity and cost and as such it would have probably not survived even the initial few requirements scrubs as the team would have been sent back to the drawing board after deeming the entire effort too expensive. As it is, the baseline F-22A was too expensive to justify beyond an "insurance" fleet size post FSU collapse. There has been a lot of research done around the impact of performance requirements on aircraft design and production cost. Every aircraft is designed within certain requirements for fleet size in mind. If something has to be produced in massive quantities then affordability is important. The F-22A requirements were high end because it was never meant to be a "mass fighter", even in the cold-war force structure (relatively speaking). It would have had a companion "low end" component. In fact, if the F-22A was to be re-designed, knowing what we know today (how much the Congress was willing to pay for it) it would have likely shed some of its performance in favor of a lower cost to buy and operate.Indranil wrote:Your rebuttal to making F-22 a truly multirole aircraft is also based along the same lines. If F-22 was being designed today, its bays would have been suitably designed to carry the bombs and missiles required. That would not have affected its shape (and hence its aerodynamic prowess) significantly.