Hello! I think I know the answer to this but I was curious if anyone here knew the answer. You often see references to these two engines in 90s publications. On is AL-37fu which is supposedly an updated thrust vectoring engine for the Su-37. Supposedly here is a picture and a description of its design
It allegedly uses technology from the AL-41f (much like the later Al-41f1). This seemingly goes against naming conventions and yet this is the alleged engine.
Next is AL-31fm (al-35f) alleged similar engine to the AL-31fm1 a decade later. Meant for SU-32, SU-27m, Su-30. I’ve seen nothing on this engine, but older publications refer to it as if it existed.
What’s the deal? We’re these paper projects, prototypes? Are the related to later AL-31f upgrade programs?
For me, the AL-37FU was just a proposal, which used a project designation (Su-37 -> AL-37FU: so it is a Lyulka engine, derivated from the AL-31F, got the designation of the Su-37 aircraft and FU, which is referring on the Forsazhniy, Upravlennie, so the Afterburner and Control).
So far, it is clear.
But what kind of quickly applicable design features were ready to use on the early summer of 1996, which were both came from the still not trully flight ready AL-41F, and enough simple to install and fit on the AL-31F and in the Su-27M airframe... is a good question.
I am afraid, the fancy new designation of AL-37FU was just covering a highly uprated good old AL-31F (izdelye 99) with the very first available iteration of the Viktor Chepkin-designed single pivoted TVC AN-100 nozzle and thats it.
The thrust could be higher, applied an RPT to improve the AB thrust up to 128kN was a quite common option, both for the early Sukhoi OKB demo airframes, such as the bort No 388, 389, or Kvochur's demo aircrafts.
And for further thrust uprate, there was the fuel line modification in the afterburner itself, where the fuel pump rated up and the fuel pipeline got a bigger diameter flow reductor. The fuel mixture of the AB going to be slightly more rich from the base setup, so as the heat load, but with this feature the thrust could reach the 135kN.
However, they still had to do something with the engine control, due to the fact, the pair of the "AL-37FU" had not just the TVC, but the asimmtrical thrust control as well.
And both of the two controls were fully integrated into the aircraft's own FbW.
It means, the engines had to have a kind of FADEC, which was not an option for a regular AL-31F back then.
Yes, the recent AL-31FM-1 (izdelye 42) also able to reach the 132-138kN, but with a completely different low pressure first stage.
So anything, what was called as an AL-37FU, could be a way closer relative of the recent AL-31FP (99FP) especially, because the time gap between the two engines was just 2 years, than the deeper modified AL-41F-1S (izd 117S).
However, after all of this, the question is still there: what was the correct engine designation of the No. 711 aircraft, after the retrofit from Su-37 into Su-35 in 2000?
As you know, the 711 was born as Su-35 originally (after the project type designation change in 1993) and turned to be Su-37 in the same year, technically on the manufacturing line.
Fun fact: the aircraft already had the later three-tone blue standard low vis paintscheme, when it was heavily modified to applied the entire TVC system. At this phase it get the famous "desert" camo.
However, in year 2000, this aircraft was turned back to Su-35 and its TVC was gone.
But only the TVC!
The FbW was still actively used the asimmetrical thrust control, mostly for the after stall supermaneuveting, but also to catch the departure attitude which was from the gyroscopic precession effect from the engine spools.
So this aircraft had a "regular" AL-31F again, but with a slight twist with its extended engine control, however, I assume, the also kept the higher thrust settings as well.
I don't know, how heavy was the 711 airframe, but the basic Su-35 dry weight was around 19 tonns, 2.5 tonns heavier than a regular Su-27. And the No. 711 still had the equal dynamic acceleration and impressive climb.
I know, from a video, it is misleading a bit, so as everything in a flight demonstartion is about the pilot skill and the clever fuel load, but I assume, those engines were not a typical AL-31Fs in the 711, during its last period (2000 - 2002 Dec 20)
