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Fantastic Video on the J58


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How does the YJ93 differ from the J58?

 

They're both single-spool turbojets of mid sixties vintage designed for sustained mach 3 cruise, but otherwise they're quite different.  YJ93 was designed by General Electric, the One True Jet Turbine Designer, while J58 was designed by the heathens at Pratt and Whitney (but they get a pass because anything that is attached to the blackbird automatically is holy).

 

YJ93 is, according to everything I have read, essentially an embiggened J79 (phantom's engine).  The J79 was unusual in that it reverted to a single spool just after double spools had become popular.  In order to have a high pressure ratio on a single spool, the J79 was the first jet engine to feature variable-incidence compressor stators.

 

single_spool.gif

 

In a single spool engine there is a single, central shaft taking power from the turbine blades to the compressor blades.

 

two_spool.gif

 

In a two-spool engine there are two concentric shafts; one that connects the high pressure portion of the turbine to the high pressure portion of the compressor (red in the diagram), and one that connects the two low pressure sections (green).  The advantage of this design is that the two portions don't need to rotate at the same speed, so blade geometry and velocity can be better tailored and optimized.  The disadvantage of this design is that you have goddamn concentric power shafts rotating at a billionty RPM, so the bearings had better be up to it.

 

In a few twin-spool designs like F119, the two shafts rotate in opposite directions.

 

There are a few airliner engines that are three spool, and additionally the engines in the tornado and the TU-160 are three spool designs as well.

 

three_spool.gif

 

How would the R-15 do the super-dooper shock cone thingie, though?

 

Same way an F-14 or F-15 or concorde does:

 

5mSmr.jpg

 

The inlet has variable geometry elements, but they're planar instead of radially symmetrical.  Different way to accomplish the same thing.

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