Very true, there are no requirements to have official aircraft status designations start at X and then Y before going to production; there were no official XF-22 aircraft released before the prototype was shown to the USAF.

There are two different meanings to 'X' in an aircraft designation:

• the basic mission can be experimental (such as the X-1, X-15, etc.)
• the status of an aircraft can be experimental (like the XF-11 and XF-89)

The X-35 has a basic mission of experimental (not fighter) ... it was an experimental aircraft (not a fighter with experimental status). If it were a fighter with experimental status then it would have been the XF-35. In that sense, there were no XF-35 and YF-35 aircraft made -- just a fully experimental aircraft that led to a production aircraft.

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~JetWhiz <8)

Sunday, October 04, 2009 -- 6:25:41 PM PDT

The X- designation can mean a number of things, it generally stands for experimental, however an aircraft with the X- designation can still become a production aircraft without officially having a YF-, YB-, etc designation.

actually there is a difference. X is actually pointing towards an experimental aircraft. not necessarily a combat aircraft (in fact i can only think of a few instances where that happened. that was the JSF) Y is actually used for Young (i think) Fighter. so you get Young Fighter 22. this is used when the aircraft is competing for a contract like with the YF-16 and YF-17. or in this case, the YF-22, and YF-23. as soon as whichever aircraft is decided the winner, the Y is dropped and you just get F-22.

no x means that

The 'Y' denotes that the aircraft has a Prototype status. You can see a list of all possible letter codes involved in the US Tri-Service system on our definitions page

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~JetWhiz <8) Wednesday, September 30, 2009 -- 5:41:08 AM PDT

A few of mine... F-16 Falcon F-15 Eagle F4U Corsair P-51 Mustang P-40 Warhawk P-47 Thunderbolt