Quote:
Originally Posted by jab2
I'm a great enthusiast of the SR-71/Oxcart program and have on more than one occasion read that at normal cruise speed more than, I think it's about 70%, of the thrust is generated by the intake cone of the engine.
|
What that statement actually means is that, at the
SR-71’s design cruise speed of about mach 3.1, about 70% of its thrust is produced by afterburner combustion of fuel using air diverted around its J58 engines’ compressor sections. Another way of putting this would be to say that at mach 31., the SR-71 is about 70% a ramjet.
Since, along with its controllable bleed ducts, its movable intake spike is key to controlling how much air is diverted around the compressor section, it’s reasonable to say that 70% of its thrust is generated by the spike, though technically, the spike is source of drag, not thrust.
The primary purpose of the spike is to slow air to subsonic speed before it enters the compressor and compressor bypass. Note that even the bypass air in the J58 is subsonic – if it weren’t, it would technically be a
scramjet, like the
X-43’s.
The control system for all this is amazingly complicated, using a custom-built analog computer. All this was designed and built, in a hurry, from 1957 to 1963!
The J58 is IMHO better shown in pictures than described in words. From the linked wikipedia article:
----------------
Moderator: Computers and Technology; Medical Science; Science Projects and Homework; Philosophy of Science; Physics and Mathematics; Environmental Studies
