How well did F-22 meet the original ATF objectives?

[Roscoe]

First off, IR signature wasn't a thing back then (we weren't even capable of measuring it worth a damn given it's dependance to atmospheric conditions and background "clutter") so I firmly doubt that was a differentiator.

With all due respect, didn’t they use the Airborne Turret Infrared Measurement System III (ATIMS III) and Threat Infrared Generic Emulation Radiometer (TIGER) pod to measure F-22 infrared signature back then?

True, but those systems measure the IR signature "Up close and personal" mostly for end-game survivability (i.e. missiles). Long range IR signature measurement and modeling back then was essentially non-existent. The F-22 in blower can be seen from Mars...never made a lot of sense to try and reduce IR signature when the motors reveal your presence well beyond missile range. I state with confidence that IR signature reduction was not a source selection differentiator.

edit: You guys can speculate all you want, but I have significant experience in the IR world and have more than a clue.

[disconnectedradical]

It may not be a differentiator in terms of USAF requirements, but considering that the exhaust trench of the YF-23 shields direct view of the exhaust at the bottom, I think it’s quite likely the YF-23 IR signature is lower than the YF-22 when viewed from below, although from the top it may not be much different. And even the YF-22 and F-22 flat nozzles help reduce IR signature of the exhaust by flattening the plume and cooling it with vortices compared to a normal round nozzle. So while IR reduction wasn’t part of USAF requirement, it may be something Northrop designed into the YF-23 anyways, and Lockheed did as well with the YF-22 flat nozzles though not to the same extent. Just like how TVC wasn’t a USAF requirement either but the YF-22 has it to improve maneuverability.

[disconnectedradical]

The story that I heard was USAF went to Lockheed (or vice versa) and said they needed to compromise on one of the following..

1.) Speed (super-cruise)
2.) Weight (or was it RCS?)
3.) Range

At that point, the decision was made it would be range. So they dropped/removed approximately 2,650lbs of the YF-22A's internal fuel (20,650lbs internal fuel in YF-22A, vs. 18,000 in the F-22A). I also recall hearing mention that the STOL requirement was dropped later in the program, which resulted in the YF-23A design team ditching the engine's thrust reversers. Since both used the same engine, I presume the YF-22A did as well.

This is one thing I've consistently heard on the forums, but have not found any documentation for, is that apparently in the mid-1990s, Lockheed told USAF that they can only pick 2 of the following 3, speed, range, or maneuverability. I've seen this stated several times on multiple forums but I haven't found any actual sources for this. Does anyone here know?

By the way, that 20,650 lbs of fuel number is from a USAF TO on the F-22 where they listed the volumes of all internal tanks, but I think the feed tank was listed in there and it shouldn't be counted towards fuel volume. Take that away and you'll get something closer to around 18,000 lbs.