OldBUFFkeeper
The beginning of your text makes me want to scratch my old, grey, head in wonder, as I have heard it before, and many times. Given that the J-58 and the J-93 were roughly the size, to hear that the J-58 was an 80%(!!) "scale model" of the J-91, originally offered as a competitor to........... the J-93, as a B-70 powerplant, one must wonder just how much of a monster that engine (the J-91) must have been, and what was P&W thinking when they offered it as a J-93 alternative?
The J91 had a pressure-ratio of 7:1, and the J58 had a pressure-ratio (IIRC) of 8.8:1 so the J58 would get more thrust for it's size. I'm not sure if the J91 had a variable IGV or the airflow-controlled nozzle, but the J58 had both of these. The former may have been to keep the turbine inlet temperature in line at high mach-numbers; the latter, might have been to squeeze extra AB performance out of the engine.
I'd like to make note that I'm not sure if 80% scale meant 80% the weight, 80% the diameter, 80% the mass-flow.
Perhaps, there was a FOUR(!!)-engined version of the Valkyrie that no one, (certainly not I), has never seen! But then again, when one hears the thrust figures for the J-91, (approx. 41,500lbs w/AB) they're not that much greater than the most powerful versions of either the J58 or J-93, both of which "clocked in" at around 33,500/35,000lbs.
That's because of the lower pressure ratio. I actually didn't know the thrust was that high actually.
To add insult to injury, the weight, around four and a half TONS(!!!)
The J91 weighed 9,000 pounds?
Great info there, and now recall that the first two stages of the, by then defunct, J-91 became the fan for the turbofan version of the J-57/JT-3, i.e. the TF-33/JT-3D. Since the inlet diameter of the that engine was around 53 inches, your figure for the J-91 seems borne out.
I'm not sure if the two compressor stages were exactly the same or simply derived from the J91. Still there's a connection between the two.
am also still wondering how/why P&W managed to use the same designation, JT9, for what now seem to be TWO COMPLETELY SEPARATE(!!!) gas generators, since there is no way the core for the JT-9D turbofan could have been 50+ inches in diameter at the first stage after the fan?
Manufacturers have their own proclivities when it comes to designating their products. For example the JT3C was a J57 variant that powered the 707 and DC-8. When they made a turbofan; they called it the JT3D. After that point, virtually every turbofan they developed had a -D after it.
Upon measuring off a photograph of an operational version of the JT-11D-20, it became excrutiatingly self-evident that the total cross sectioal area, and, by definition, delivery capability, of the six bypass tubes coming off the compressor just after the fourth stage, was substantially less than the similarly tasked area available with a fully annular bypass duct in a classic turbofan.
Because it wasn't designed to use the fan to produce thrust like a propeller -- it was meant to dump excessive air around the engine as a way of lowering the pressure-ratio at high-mach as a means of lowering the turbine-inlet temperature.
The airflow was fed into the afterburner as a way of making use of that compressed air. It increased the pressure of the airflow in the afterburner inlet and also increased the air-percentages
(60-65% of the engine exhaust is air -- the bypass air is 100% oxygen)
Which leads to my question: does anyone know what the claimed "bypass ratio" of the JT-11"D" actually was?
Allegedly 65% of the airflow was routed around the engine, and fed into the afterburner. So the bypass was 2.86:1
When looking at the respective bypass ducts of F-100s, F-110s, and F-135s, measuring the available areas there, dividing by six, then PI, extracting the square root, and multiplying by two, i.e. the reverse figuring for the area of a circle, I came up with tube diameters more than TWICE(!!!) the diameter of those on the J-58, thus exposing the JT-11D as not much more than a "leaky" turbojet, and leaving me to wonder just how useful such an arrangement could ultimately be above mach-3 when ANY(!!!) rotating machinery in the way of ramjet/afterburner airflow is about as desirable as a drag chute?
The idea evidently was to basically operate as a turbojet
(which you need for takeoff and landing), and progressively relieve the excess pressure more and more as you went faster and faster and feed it into the afterburner which doesn't have the same limits as the turbo-compressor
(the core of the engine) -- plus I'm not 100% sure of this, even without turbine temperature limits, there might be a point of diminishing returns as to your ability to compress air and get propulsive efficiency out of it
(without cooling the air, which is used with the SABRE and Scimitar engine designs used for SKYLON and the Reaction Engines LAPCAT A2)
Regardless there's only a certain degree of efficiency you need to accomplish a task -- the rest is gravy.