Since this thread appears to be otherwise dead, I’ll dare to continue the variable cycle discussion.

Feel free to check. for Kaveri

“Kaveri engine has been specifically designed for Indian environment. The engine is a variable cycle-flat-rated engine in which the thrust drop due to high ambient, forward speed is well compensated by the increased turbine entry temperature at the spool Kabini altitude test speed. This concept has been already demonstrated with high temperature and pressure condition in DRDO’s High Mach Facility. Kaveri engine is controlled by Kaveri full authority digital control unit {KADECU), which has been developed and successfully demonstrated at DRDO’s test bed.”

https://www.drdo.gov.in/drdo/pub/tec…000/Kaveri.htm

As i’m no expert in engines and technical english is a bit hard to me, i’ll give you a link about M53. Feel free to explain me

http://www.institut-strategie.fr/Moteurs_10.htm

Well, let’s say the bypass ratio variation from the wider speed/altitude envelope is 1.5x greater on the M53 than the CFM56 – i.e. we only consider the altitude effect because it has variable inlets to take care of Mach number. In the CFM, we have a 12% BPR fluctuation, so a very crude estimate for the M53 (without accounting for the adjustable mixer) comes to 18%. A 0.32 to 0.4 difference is actually a 20% range, so the supposed variable cycle technology may well be responsible for a mere tenth of the bypass ratio variation. And that assumes the surge characteristics of the M53 fan even accommodate a mixer area schedule which optimizes fuel consumption. For all we know, its primary function of maintaining stable flow forces it to close down at operating conditions where for best efficiency it should really open up (or vice versa). BTW, a similar solution (rather blandly called the “Variable Area Nozzle”) was prepared by P&W for the bypass stream on PW1000G geared turbofan due to its low pressure ratio fan – it turned out to have adequate stability margins with a fixed bypass nozzle though.

As for the links you supplied, the French author is unequivocally wrong on the claim that the M53 is the first ever variable cycle engine to enter service (that honour belongs to the J58, as mentioned), so what makes you think his assertion on it being a VCE at all is any less hyperbolic? People make preposterous exaggerations occasionally – it’s a fact of life. In the case of Kaveri, the English used on that page is pretty tortuous and other technical terms are used incorrectly as well (for example “pressure Combustion Chamber Liner ratio”, whatever that’s supposed to mean). The author may be refering to something entirely different from the accepted sense of variable cycle, for example “dual mode” as in dry/reheated.

Another thought on variable cycle engines – the STOVL F135 can most certainly be thought of as one. In cruise mode its BPR is about 0.6, but in powered lift configuration with the shaft-driven fan engaged (where it essentially becomes a geared turbofan like the PW1000G) it will be well above that – not sure how high, but I’d guess comfortably more than 3.0. Unlike what may be the “conventional” idea of variable cycle it’s a binary thing here (there are two distinct modes without smooth variation), but the BPR range is bound to be extremely wide.