The YF-23 was one of the most stealthy aircraft of all time and had a range capability of 2,000 miles (that's more than some airliners can travel) but never entered service. The F-22, has high maneuverable, and is considered to be the second option compared the to YF-23 stealth and speed. So why did the YF-23 never enter service? Image source: NASA/DFRC
The YF-23 lost the Advanced Tactical Fighter program to the YF-22, however it has not been made public why. The ATF evaluation is still classified and details about the YF-23's performance are not easy to come by. They are both excellent aircraft, performed similarly, and there is much speculation why the YF-22 won.
According to the Air Force, factors in the selection for production of the F-22 were a better designed for maintainability, greater potential for future development, and slightly lower cost. Secretary of the Air Force Donald B. Rice stated that the choice was based on confidence in the ability of the Lockheed team and Pratt & Whitney to produce the aircraft and its engine at projected costs. Emphasizing the importance of the Lockheed team's management and production plans, he denied that either prototype was significantly more maneuverable or stealthy. A popular view is that the decision reflected a preference for maneuverability over stealth
Because the YF-23 lost the Advanced Tactical Fighter program to YF-22, from which F-22 was developed.
Actually, the YF-22 had thrust vectoring and was the more agile of the two.
The Advanced Tactical Fighter (ATF) competition was different than some of the other fighter competitions. The planes never squared off in any kind of mock combat. The pilots who flew the YF-22 never flew the YF-23 so there was no way to directly compare the 2 in that way. The competition focused on whether or not the planes met the requirements. Both aircraft met the requirements so the decision is said to have come down to assessments of the ability of the competing contractors to deliver the aircraft. Northrop was busy with the B-2 and the YF-22 was thought to be more fully developed and more ready to turn into the F-22. Some have claimed that Lockheed made a better sales pitch. It should be noted that the YF-23 could carry 4 AMRAAM internally while the YF-22 could carry 6, which may have factored into the Air Force decision.
The decision was non-technical
You can hear it from the test pilots themselves:
The rating was actually based on stop lights. Individual requirements (e.g. supercruise) could be rated red, yellow, or green. At the end of the test program, both planes rated green on all requirements. This was all Secretary of the Air Force Donald B. Rice had been given to decide. So the decision had to be made on a non-technical base.
Rice had more confidence in the project management of Lockheed (this is consistent with the Global Security quote in Schwern’s answer). He was probably strongly influenced by the fact that
- the YF-22 demonstrated missile launches and the YF-23 did not (even though it had not been asked to)
- there are photos of the YF-22 at 60° angle of attack even though the YF-23 “would do that exact same maneuver and stabilize at that exact same angle” (49:25).
I.e. Lockheed put a lot into showmanship.
The YF-22 was probably not more maneuverable
There was never a pilot to fly both planes, intentionally. YF-23 test pilot Paul Metz, however, switched to Lockheed after the end of the program to fly the first production F-22, so he’s probably the only person entitled to compare them at least to some degree.
In the above video he states that the YF-23 “would stand side-by-side with anything else and […] exceed the capabilities of anything else” (51:03). Here, anything else sounds like it’s pointed towards the YF-22.
Thrust vectoring had no influence on the decision
- At 52:06, Jim Sandberg says exactly that and repeats that the decision was made on non-technical issues because both planes were rated green on all requirements (which would include post-stall performance).
- He also mentions the YF-23’s tail surfaces being all-moving, huge (almost the size of an F-18 wing!) and driven by high-speed acuators.
- While thrust vectoring improves pitch and roll performance, the YF-23’s tail surfaces also provided great yaw/roll performance.
There is no proof that the YF-23 was faster
Top speed of the YF-23 is entirely speculative:
- The only declassified fact is: the YF-23 with the GE engines was faster than the YF-22 with the GE engines, but only marginally faster than the YF-22 with the P&W engines (46:10).
- The test pilots say that they “never tested them to their maximum speed” (51:51).
- Any estimations for top speed are still classified.
- The top speed of the production F-22 is rumored to be not limited by engine thrust but rather by heating of radar-absorbing materials and force on the canopy. The YF-23’s canopy cracked multiple times during the tests (some photos at 45:28) at transonic and low supersonic speeds. It doesn’t mean anything that this would be fixed with a production F-23, since we know from declassified plans that a production F-23 would also have been substantially heavier.
There is no proof that the YF-23 was more stealthy
There is a hearsay story that a general couldn’t believe the low RCS of the YF-23 mockup. Good luck finding a reliable source.
I recommend watching the above video, the explanations are pretty clear and the knowledge is first-hand.
Officially both aircraft met or exceeded the government requirements set by the ATF program office, but the Lockheed jet won out in the end of the ATF program.
The reasons why are a strange combination of Pentagon politics and little showmanship on the part of Lockheed.
At the time of the ATF program, Northrop was in the doghouse with the Pentagon due to program delays and cost overruns on the B-2 Stealth Bomber program, which made ATF program managers skeptical of Northrop’s proposed program timeline and budget numbers submitted with their ATF proposal.
Midway through the ATF flyoff, the Navy inexplicably added an additional requirement to the program that they wanted to evaluate the ATF prototypes to create a naval variant as a replacement for the F-14 airplane. This requirement was added after both ATF designs had passed CDR and parts were being cut for both aircraft. The Navy evaluated both designs and felt the F-23 would have been unsuitable for carrier operations.
In addition, USAF commanders were not totally convinced of the merits of stealth and BVR air warfare at the time of the ATF program. Many had been pilots who had flown in Vietnam and had to deal with the shortcomings of fighting small, maneuverable MiGs in big, powerful Phantoms with out a gun. The experiences had led to the development of airplanes like the F-15 and F-16 with suberb dogfighting capabilities. Leaders did not want to stray from this winning formula, particularly given just how successful it had been against modern Soviet hardware in Operation Desert Storm and were more skeptical of an aircraft which relied heavily on stealth for defense and attack. This is not a terribly fair perception; the YF-23 was a very agile airplane, particularly in the transonic and supersonic regimes of flight. But the Air Force was more interested in an advanced F-15 with stealth characteristics, which is what Lockheed perceived and delivered with their proposal.
Finally Lockheed laid in a little showmanship with it proposal which included sorties where their jet launched missiles, giving the fallacious impression that their design was much closer to combat ready than the Northrop proposal.